≡ Menu

Holographic Sails for Project Starshot? — Homage to Bob Forward

One of the reasons I described Greg Matloff as the ‘renaissance man of interstellar studies’ in my Centauri Dreams book is the continuing stream of ingenious ideas that he develops and delivers through papers and conference presentations. I found the holographic sail concept below fascinating, and would have referenced Bob Forward myself if Greg hadn’t already done it in the text. These two must have been great to hear in conversation! Read on to learn how Greg, a physicist at New York City College of Technology (CUNY) came up with the idea, a process that deftly blended science and art and may provide solutions to some of the more intractable problems posed by Breakthrough Starshot. The author of The Starflight Handbook among many other books (volumes whose pages have often been graced by the artwork of the gifted C Bangs), Greg has been inspiring this writer since 1989.

By Greg Matloff

It was perhaps inevitable that I would be asked to serve on the Advisor’s Board of Yuri Milner’s Breakthrough Starshot, because of my long experience in the analysis of interstellar travel techniques. According to Phil Lubin’s paper on this technology development project, a 50-70 GW laser array mounted atop a southern hemisphere mountain would generate a beam that would be projected against an Earth orbiting ~1 m photon sail for a period of minutes [1]. The sail would be a major component of a ~1 gram wafer-scale spacecraft with a ~0.1-gram payload that would exit the beam after experiencing average accelerations of ~5,000 g. The planned interstellar cruise velocity of the tiny spacecraft is ~0.2c and the voyage time to the Proxima/Alpha Centauri system is approximately two decades.

Image: Gregory Matloff (left) being inducted into the International Academy of Astronautics by JPL’s Ed Stone.

So I attended the first Starshot Advisors Meeting in August 2016 and left with a non-optimistic attitude. Yes, it is possible to design very-high efficiency optical reflectors at the laser wavelength (about 1 micron) to tolerate the enormous thermal load while maximizing acceleration [1]. But these devices tend to be physically thick and massive.

A major problem turned out to be beam-riding sail stability. The sail must be configured to remain in the beam, with its source located on the moving Earth and its terminus directed towards the Centauri system, for a period of minutes. Analysis discussed during the August 2016 meeting and later published revealed that a spherical sail curvature was the best approach to address the beam-riding stability issue [2]. But how would the sail maintain its required spherical curvature during the minutes-duration high-acceleration run?

Finally, rare ~1-micron interstellar dust grains impacting a sail moving through the interstellar medium at ~0.2c pack quite a wallop [3]. So if the spherical sail somehow survived acceleration, it would be a good idea to straighten it post-acceleration to a flat sheet and reorient the spacecraft edge-on to the direction of travel.

Initially, I could think of no way to satisfy all of these requirements. So I encouraged theoretical physicists associated with CUNY to think about ways of increasing graphene reflectivity in response to an expected Request for Proposals (RFP) from the Starshot management team. Because such a development is not impossible, I delivered several papers on the utility of reflective graphene in interstellar solar-photon sailing. In collaboration with other researchers, I also considered toned-down space applications of wafer-scale spacecraft and less intense collimated power beams. Even if the Starshot goal could not be met, I hoped that some major technological advances might come from the decade-duration, $100 million research effort.

But the goals of robotically exploring the planetary systems of our nearest stellar neighbors on voyages requiring a few decades seemed too enticing to simply abandon. So when my partner, artist C Bangs, suggested that I reconsider holographic photon sail coatings, a concept we had collaborated on in 2000-2001, I agreed.

Bob Forward and Holographic Photon Sails

Long before C and I married, we were collaborators. She has generated chapter frontispiece art for most of my books, including The Starflight Handbook. During the summer of 2000, my second year as a NASA Faculty Fellow at Marshall Spaceflight Center in Huntsville Alabama, we attended an International Academy of Astronautics symposium organized by Giancarlo Genta of Politechnico di Torino in Aosta, an Italian alpine city. My participation was concerned with extrasolar and interstellar solar-photon sailing, since NASA had funded my research in the Heliopause Sail Technology Project, under the direction of Les Johnson. C’s role was to curate and hang an art show, “Messages from Earth”, in a medieval Aosta chapel. About 30 international artists contributed work presenting their conceptual message plaques that could be mounted on a solar-photon sail bound for the stars.

During the reception associated with the art show, C was approached by the late Robert Forward. As many Centauri-Dreams readers will remember, Bob pioneered numerous approaches to interstellar travel during the last few decades of the twentieth century. When Bob reached into his wallet and withdrew a credit card, on-lookers expected that he might be making a purchase. Instead, he asked C how she would affix a message plaque to the sail. She responded that a physical plaque (as was done in Pioneer 10/11), a long-playing phonographic record (as was done in Voyager 1/2) or a computer chip were possible approaches. Bob drew her attention to the white-light hologram on the credit card and expressed the opinion that a low-mass, thin-film holographic plaque could contain a huge amount of information.

After the symposium, C returned to Brooklyn and I rejoined the Marshall sail team. A few weeks later, while C was coincidentally visiting me in Huntsville, we were invited to a lecture by Bob. When Les Johnson introduced him, Bob pointed to C and said: “Fund that woman to do a prototype holographic interstellar message plaque”.

So my small NASA University Challenge Grant through Pace University, where I taught at the time, was reconfigured to support the creation of the hologram. I received no salary from this grant so that the project could be financed. We contacted the Center for Holographic Arts (then located in Long Island City) and the rainbow hologram was completed at that facility with two sculpted figures and four line drawings by C with a transparency of the Apollo 17 image of Earth from deep space that is always visible and supports the holographic images.

We delivered one of the three resulting holograms to NASA Marshall in mid-2001. Another was later purchased by a collector and donated to New York City College of Technology. We use the third for display purposes.

There are seven 2D and 3D monochromatic images on this hologram, representing our solar system, probe trajectory and the human form in a similar manner to the Pioneer plaque. During the summer of 2001, we showed it to many NASA and contractor employees. As part of the research effort associated with the plaque, we participated in simulated space-radiation tests of holographic wrapping paper samples. Holograms are apparently immune to image degradation caused by intense solar flares [4-6].

Image: A view of the Rainbow Hologram created by C Bangs. The hologram contains six images. As the viewer moves from left to right the images transition from one frame to the next. On the extreme left side is a line drawing that places our home solar system on the edge of the Milky Way Galaxy and our planet, third from our sun. The second frame is a line drawing of the female figure holding the payload of the solar sail to demonstrate her size relative to it. The third frame is the sculpted female figure. The fourth frame is the sculpted male figure with his hand raised in what is believed to be a universal greeting. The fifth frame is a line drawing of the male figure. The last frame contains equations that describe the acceleration of the solar sail that the hologram would hypothetically be traveling on. In front of all the images is an photograph of the full Earth visually demonstrating the beauty of our home planet. Credit: C Bangs.

It became apparent to the team that Bob Forward was interested in other applications of holographic solar sail applications than message plaques. As discussed in Ref. 5, it is possible to change the reflectivity of a white-light hologram with a slight rotation. It is therefore conceptually possible to accelerate a solar photon sail from Low Earth Orbit by rotating the sail to reflect sunlight when the Sun is behind the spacecraft and transmit sunlight when the sail faces the Sun.

Current Technology Holography and Project Starshot

During 2017, C and I had several meetings with Dr. Martina Mrongovius, Creative Director of the NYC HoloCenter. The HoloCenter is the outgrowth of the Center for Holographic Arts.

The art and science of holography has advanced at a rapid pace during the past few decades. Holograms as thin as 25 nm have been produced by an Australian-Chinese team [7]. Highly efficient wavelength-selective holographic filters and reflectors have been produced and evaluated [8-10].

Color of contemporary holograms displayed at the HoloCenter seems true to life. If the observer slowly changes position to view an experimental 3D holographic movie, action seems continuous with no breaks. Clearly, a vast amount of information can be stored on a single thin-film hologram. According to the Wikipedia article on holography, thousands of images can be produced and stored per second. Martina reports in a YouTube video that some modern holograms contain 10,000 holographic layers.

It no longer seems impossible to me that the Project Starshot goals can be achieved. One would use a holographic film and expose the image of a filter or mirror that is highly reflective in the laser’s wavelength range. My colleague at Citytech, Lufeng Leng teaches optics. She is quite sure that a hologram of a spherical surface will behave optically like a spherical surface. So the filter or mirror should ideally have a convex spherical shape, from the point of view of the observer (or laser).

If the holographic filter or mirror sail is sufficiently reflective to laser light, the thermal issue should be resolvable. Since the hologram is a flat sheet, it should be tolerant to high accelerations. If the spherical filter/mirror 3D image behaves as discussed in Ref. 2, the sail should self-correct its position and remain in the moving laser beam. If a pair of tiny thrusters are mounted on the anti-laser face of the sail, it should be possible to rotate the flat sail by 90 degrees after acceleration terminates to minimize damage by the interstellar medium.

Image: An artist’s conception of a laser-beamed sail. Credit: Adrian Mann.

The April 2018 Breakthrough Committee Meeting

On April 11, the Starshot advisors met at a Breakthrough facility in the NASA Ames Space Flight Center. While C displayed the prototype holographic message plaque, I presented the case for a holographic sail. We learned that Harry Atwater of the California Institute of Technology and his team are investigating technologies that combine aspects of engineered metamaterials and holography. Most participants agreed that the idea of a holographic sail is promising. Some, including Avi Loeb of Harvard, suggested that experimental validation is required.

A number of experiments should be possible. Some of these could be addressed in response to the Starshot Sail RFP, which is scheduled for release in the near future. Jason Wentworth, a frequent contributor to Centauri Dreams, has informed me that projectiles fired by large naval guns routinely survive very high accelerations. A small thin-film hologram mounted on or in a suitable projectile might demonstrate whether a hologram can survive the requisite ~5,000 g acceleration.

It is not possible today to test a holographic filter’s reflectance and survival in a continuous ~50 GW laser beam. But according to Wikipedia, the inertial-fusion confinement lasers at the National Ignition Facility located at Lawrence Livermore can deliver 500 terawatts for a few picoseconds. Perhaps a test of a holographic sail could be performed at that facility.

If a prototype thin-film holographic spherical filter or mirror is engineered to reflect in the microwave region rather than at the laser wavelength, another test is possible using existing facilities. Beam-riding stability could be demonstrated using the equipment applied by Jim Benford, Greg Benford and colleagues to examine beam-riding stability of a number of sail shapes during 2001 [11].

In any event, the situation is hopeful. Both C and I felt that we were channeling Bob Forward during our presentation. It’s nice to imagine that his shade is smiling and cheering on the efforts of the Project Starshot team.


1. P. Lubin, “A Roadmap to Interstellar Flight”, JBIS, 69, 40-72 (2016).

2. Z. Manchester and A. Loeb, “Stability of a Light Sail Riding on a Laser Beam”, arXiv:submit/1680014 [astro-ph.IM] 29 Sep 2016.

3. T. Hoang, A. Lazarian, B. Burkhart, and A. Loeb, “The Interaction of Relativistic Spacecrafts with the Interstellar Medium”, arX1v: 1608.05284v1 [astro-ph.GA] a8 Aug 2016.

4. G. L. Matloff, G. Vulpetti, C Bangs and R. Haggerty, “The Interstellar Probe (ISP). Pre-Perihelion Trajectories and Application of Holography”, NASA/CR-2002-211730, NASA Marshall Space Flight Center, Huntsville, AL (June, 2002).

5. R. Haggerty and T. Stanaland, “Applications of Holographic Films in Solar Sails”, presented at STAIF-2002 Conference, University of New Mexico, Albuquerque NM (January, 2002).

6. G. L. Matloff, Deep Space Probes: To the Outer Solar System and Beyond, 2nd. ed. Springer-Praxis, Chichester, UK (2005).

7. M. Irving, “World’s Thinnest Holograms Could Lead to Thin-Film 3C displays”, New Atlas (May 18, 2017).

8. W. Wang, “Reflection and Transmission Properties of Holographic Mirrors and Holographic Fabry-Perot Filters. 1. Holographic Mirrors with Monochromatic Light”, Applied Optics, 1994, May 1;33:2560-6. doi: 10.1364/AO.33.002560.

9. P. Sharlandjiev and Ts Mateeva, “Normal incidence Holographic Mirrors by the Characteristic Matrix Method”, Journal of Optics, 16, 185-190 (1985).

10. D. W. Diehl, “Holographic Interference Filters”, Ph.D. Thesis, Institute of Optics, Schoolof Engineering and Applied Science, University of Rochester, Rochester, NY (2003).

11. James Benford, Gregory Benford, Olga Gornostaeva, Eusebio Garate, Michael Anderson, Alan Prichard, and Henry Harris, “Experimental Tests of Beam-Riding Sail Dynamics”, Proc. Space Technology and Applications International Forum (STAIF-2002), Space Exploration Technology Conf, AIP Conf. Proc. 608, ISBN 0-7354-0052-0, pg. 457, (2002).


Comments on this entry are closed.

  • Andrei April 20, 2018, 11:46

    Thank you for the interesting summary and ideas presented here.

    It seem that the idea make progress, for the sail itself, and it would really need to fly with a side, else it would be shredded before arrival.

    The main problem is if that holographic film can make the sail reflective to 99.9999999…%

    To also send information back, the sail should also be able to be a reflector for the transmitter, perhaps also that can be another layer of that hologram.

    The big problem is to build the instruments so small that they only weight grams, to measure magnetic field around a planet might be possible if one sail of a fleet come close to one world.
    Also spectra, but what lens is needed to get even a small image of a planet that show interesting details?

    We seem to be close to get spectra of more worlds from instruments on Earth and coming space observatories.

    So even though I say congratulations to the proposed solutions that have been identified here, I remain skeptical that a starshot sail will be much more than a holographic postcard.

    • Greg Matloff April 20, 2018, 17:32

      Dear Andrei

      Nice comment. I took wonder about the ultimate reflectivity that can be achieved. Only experiments will reveal this. It is too early in this process to estimate ultimate performance and how closely it will approximate project goals. Other teams are examining laser issues, payload integration, communication with Earth, etc.


      • Andrei April 25, 2018, 4:31

        Hello Greag and thank you too for your article.

        I don’t know if my reply were altogether nice. :)
        I do believe that it is possible to push a sail with a laser beam to the stars – since basic physics can predict that.
        But I am skeptical that it will be able to accomplish much science, and instruments in orbit and on Earth might get the capacity to study the nearest stars in quite some detail in the same time period the sail would need to fly.
        If progress will remain as fast as it have in late decades the development of new telescopes could get wonderful results in the next 50 years – said if the sail would fly today.
        But keep up the good work, I do think laser powered sail will do important work with larger instrument packages and in the solar system.

    • Brett Bellmore April 23, 2018, 6:14

      “The main problem is if that holographic film can make the sail reflective to 99.9999999…%”

      Not gonna happen. The hologram depends on different areas of the film having different optical properties. Which means whatever the best possible properties are, the whole film can’t have them.

      Holographic mirrors are always going to have lower reluctance than regular mirrors.

      • Andrei April 25, 2018, 4:38

        Yes that is what I thought but not certain about the facts, thank you for confirming that.
        That mean a holographic mirror sail would turn into vapor or even plasma instantly when it is hit by that gigawatt laser beam.

      • Greg Matloff April 25, 2018, 7:56

        Dear Brett

        I am not sure that anything can get 99.9999999…% reflectance. But if you check my cited references, holographic filters and mirrors do pretty well. Only experiments will determine the limits. And these limits may constrain Starshot goals.


        • Andrei April 27, 2018, 10:52

          That such incredible reflectance is impossible is my point here.
          While I do think the idea with a sail could be made to work.

          If I understand the ideas right, there would be many laser units in a battery, why not have them fire in succession instead of at a single time.
          Spreading out that Terajoule level of energy that can compared to a small nuclear blast – then any of the composite coatings we already know could be used.
          There’s some various values stated for such materials, I did see some quote of 99.999% reflectance for a narrow wavelength – then it would be some engineering to get the lasers to match that.
          With lasers firing in succession – I do agree the holographic mirror is interesting and should be studied. :)

          • Michael April 29, 2018, 2:11

            You don’t need 99.9999% reflectance or 99% just have fairly high reflectivity and low absorption materials and the rest goes straight through with no heating. We have the materials already we just need to put them together and test the concept.

  • Gary Wilson April 20, 2018, 13:44

    What material is the holographic film actually made of? Is it possible to estimate the density of 1 micron dust grains in the volume of space the probe would travel through? The sail and payload would both travel edge on for most of the voyage presumably? Then they have to be re-oriented near the target. Is it likely we will see a test scale effort made with a less powerful laser and possibly a larger payload and sail before the 100 M dollar investment is completely spent? Is any funding project underway to try to add money to the project. I’m sure many would contribute.

    • Greg Matloff April 20, 2018, 17:37

      Dear Gary

      Not being an expert on holograms, I assume that the film is similar to photographic emulsion film. In the local interstellar medium, there is something like one dust grain per cubic kilometer. Reorientation of sail/payload at the target is also essential. I agree that many experimental tests must be performed before building a gigantic laser array. I have outlined a few of them. The 100 M dollar is for the 10-year research effort.Constructing the laser array will likely cost a lot more. I am not aware of any current effort by the project managers to raise outside money. This might be necessary when/if the construction phase begins.


  • Alex Tolley April 20, 2018, 14:42

    I holographic images act like optical components, can’t we make concentrating mirrors, objective lenses and diffraction lenses too?

    Super-diameter, lightweight telescopes would be possible with flat, spinning holographic sheets as the collecting mirror.

    Is this really possible?

    While holography is usually associated with light, the principle should apply to other wavelengths, eg IR, UV, microwaves, using the appropriate way to represent the interference patterns.

    • Greg Matloff April 20, 2018, 17:42

      Dear Alex

      Yes. A number of teams are considering holographic optics for varying applications. I think that light collimation is the necessary requirement and that various wavelengths can be used to prepare holograms. But there might be limits that I am not aware of.


      • J. Jason Wentworth April 22, 2018, 16:19

        Hello Greg,

        Thank you for including my reference to Gerald Bull’s 16″ space gun Martlet projectiles. The M712 Copperhead guided 155 mm gun projectile’s electronics withstand even higher firing accelerations of over 9,000 g, and other such projectiles (see: http://en.wikipedia.org/wiki/Cannon-launched_guided_projectile ) are also available. Some of them carry sub-munitions, and the dispenser(s) could carry test sails. Also:

        You mentioned microwave holographic sails in your article; could these perhaps make Bob Forward’s Starwisp microwave-pushed interstellar sail possible? (While laser-pushed sails would be preferable for starprobes, microwave-pushed sails could be useful for inexpensive interplanetary probe missions, and they should be helpful for basic R & D test flights before trying laser-pushed holographic sails.) In addition, the following passage in your article grabbed my attention (and raises a question):

        “It became apparent to the team that Bob Forward was interested in other applications of holographic solar sail applications than message plaques. As discussed in Ref. 5, it is possible to change the reflectivity of a white-light hologram with a slight rotation. It is therefore conceptually possible to accelerate a solar photon sail from Low Earth Orbit by rotating the sail to reflect sunlight when the Sun is behind the spacecraft and transmit sunlight when the sail faces the Sun.”

        Although I can’t find the online reference to it (or even recall its full name–it’s called a “di-[something]” sail), I recently read that a sail concept that is being pursued–although rather forlornly, because its realization has seemed far off–would allow light (and other EM radiation) to pass through it in one direction, but would reflect light in the other direction, rather like the “one-way mirror” window film, and:

        It ^sounds^ like holographic sails could do essentially this, and if so, could they–if oriented correctly–continue to accelerate away from the Sun (even utilizing starlight from that direction)? If so, they might be able to reach high interstellar transit speeds over time, after initial high acceleration utilizing a laser boost, a close solar flyby, or a Jupiter-Sun or Saturn-Jupiter-Sun gravity assist (with an initial laser boost).

        • Greg Matloff April 23, 2018, 8:43

          Dear Jason
          Thanks again for your info on naval gun acceleration. Certainly a holographic optical filter could be designed in any wavelength range. But most of the very-high reflectance filters only work at specific wavelengths, so relativistic holographic solar sailing seems difficult. Unpowered gravity swing-bye don’t work too well at very high velocities.
          Regards, Greg

          • J. Jason Wentworth April 23, 2018, 20:13

            You’re welcome, Greg. I was referring to using a lower-powered laser (an ordinary rocket boost should also work) if the multi-terawatt laser array wasn’t available for a long time, for any reason; the boost would only be enough to inject the sail into the giant planet/solar gravity assist trajectory. Velocities of up to 0.1 c or so are usually considered non-relativistic (the effects do occur, of course, but are too slight to really matter at such speeds). If a close Earth flyby was arranged to occur after the gravity assists (or all of them except the final, solar leg), a laser could be used to further boost the sail velocity, and:

            For outer planet and ultraplanetary missions (including out to the Sun’s gravitational focus)–especially if no propulsive laser array was yet available–holographic solar sails should be particularly useful for “Sun-diver” missions (as close to the Sun as the hologram substrate could stand), with optional Jupiter or Saturn-Jupiter flybys (before the solar flybys) for additional velocity, if necessary. Also:

            Since holographic sails apparently have the same “cross-body” reflective properties as the “real” sails whose 3D images are contained within them, holograms of conical or spherical-section sails should be strongly self-stabilizing (producing strong restorative forces to keep them pointing into the sunlight, that is), especially if they were spun.

    • Andrew Palfreyman April 21, 2018, 13:46

      Yes; the article leaves one with the impression that an image made of light somehow interacts with incident light as if that image were made of solid stuff. This is clearly not going to happen.

      • Greg Matloff April 22, 2018, 7:15

        Dear Andrew
        Please check the references I list on holographic mirrors and filters. It seems a bit magical to me as well, but apparently holographic images of optical components seem to behave like their “real” counterparts. But the test will be in the experiments.

        • J. Jason Wentworth April 22, 2018, 16:47

          I had wondered about this, too. My guess is that a flat hologram of a 3D curved sail in the shape of, say, a portion of a sphere (an object shaped like the Arecibo dish’s spherical-section reflector, presented “convex-side-forward” to the laser, to serve as a self-stabilizing sail in the laser beam) would function like many of the various flat, planar array radio antennas, and:

          Numerous planar array antennas, which have multiple elements that operate in phase with each other, can produce the same antenna pattern as a parabolic dish antenna (one main, narrow-beam lobe with–unless they’re suppressed–much smaller side lobes). Also:

          The spherical-section sail (a paraboloid, hyperboloid, or even ellipsoidal shape, “turned around backwards” to form a negative [divergent] mirror, would also work as a self-stabilizing, laser beam-riding sail) is just a spherical-section mirror facing backwards toward the laser beam, and the layers in a flat hologram of such a sail would–I *think*–reflect the incident light across the image in the same way that the 3D, physical spherical-section sail would reflect the light that was incident across its curved surface. The layers of the flat hologram would preserve the “reflection phase angles” of the physical curved sail.

      • Alex Tolley April 22, 2018, 20:20

        the article leaves one with the impression that an image made of light somehow interacts with incident light as if that image were made of solid stuff. This is clearly not going to happen.

        That was the first impression I had until I looked into it further. The reality is that the holographic pattern creates the same effect of a curved mirror or lens. Because holograms create 3D images, there might be the impression that the projected object is capable of being interacted with, even though this is not the case. Therefore the holographic medium must be highly reflective or it will vaporize under the lasers.

        This might mean that while this approach cannot be used for the Breakthrough Starshot, it may still be quite viable for other, lower power, beamed sail missions.

        • Greg Matloff April 24, 2018, 6:14

          Dear Alex

          I agree that there must be limitations to holographic photon sailing. The characteristics of the medium will be significant. A lot of experimental work must be done. Thanks foe the comment.


  • Scott Guerin April 20, 2018, 15:25

    Greg and C,

    Great article and can we assume that imagery and information would be imprinted into the sail in case it would be discovered?


    • Greg Matloff April 20, 2018, 17:39

      Hello Scott

      C is continuing her work with holograms. It is not impossible that a message plaque can be combined with a holographic sail.

      Regards to all,

  • Gary Wilson April 20, 2018, 17:31

    Amazing idea. It certainly needs serious attention. Has any thought been given to a gradual increase in laser power over the beginning of the time (something on the order of a few seconds)required to reach 0.2 c? Surely just immediately hitting the sail with full power is not likely to succeed? I hope to learn more about holographic films for solar sail use now.

    • Greg Matloff April 21, 2018, 7:53

      Dear Gary

      In the latest scenario, the laser power delivered to the sail is varied during the acceleration run. So your input is on target.


  • Brett Bellmore April 20, 2018, 18:37

    These passive stabilization concepts are going to induce transverse stresses in the sail. How do they compare to the sail’s tensile strength? Are they exclusively tensile?

    • Greg Matloff April 21, 2018, 7:55

      Dear Brett

      I think that the only solution to this issue is to maintain the physical sail normal to the beam throughout acceleration. Hopefully, the spherical hologram sail can account for stability. But experiments are, of course, necessary.


      • Brett Bellmore April 21, 2018, 13:33

        Even if you maintain the physical sail normal to the beam, you’re getting your centering by having the beam reflected off normal by the hologram, which is going to produce transverse stresses in the sail. If it didn’t, there’d be no restoring force.

        And normal reflection vs angled reflection is going to produce different normal thrust on the sail from place to place. So, the center of the sail might be accelerating at 5,000 Gs, and the edge at 4,750 Gs. Going to take some structural strength to have them not go their separate ways.

        • Greg Matloff April 22, 2018, 7:20

          Dear Brett

          Experiment must be performed on any suggested Starshot sail material to determine whether reflection is diffuse or specular. No one knows at this time what the limitations are. But thanks for your response.


          • Brett Bellmore April 23, 2018, 19:59

            I suppose I shouldn’t suggest a problem without venturing a solution.

            First, assume the beam is stronger towards the center. This is not unreasonable, while it’s possible to set up a beam with a central low energy area, it won’t stay that way for long. “Bessel beams” can’t be maintained for the same range as an ordinary beam, given the same size optics. Eventually they turn into normal beams.

            Thus, clearly in order to have a restoring force, the edges of the sail must reflect light angled towards the center, causing a force away from the center of the sail, which becomes weaker on whatever edge of the sail approaches the beam edge, thus being overcome by the opposite force from the other edge of the sail.

            Thus the sail must be in tension. Forget buckling stresses.

            The tensile stresses needn’t be designed to be high, assuming the sail starts out reasonably centered. This just leaves the difference in acceleration from the center to the edge of the sail, due to the normal reflection at the center being more efficient at producing thrust than the angled reflection near the edges.

            This could be countered by making the sail slightly transparent in the center, just enough to equalize the efficiency across the sail. I don’t think the whole sail would be holograph, just a band around the outside.

  • Alex Tolley April 20, 2018, 18:50

    Apparently it really does work.

    Holographic lens printing method could allow printing of telescope lenses in space

    Quite extraordinary. While there are no doubt tradeoffs compared to real lenses and mirrors, this “good enough” approach might open up all sorts of useful applications for sensing, especially if it is lighter and has higher performance than those stamped, flat plastic lenses that were once so popular back in the last century (I think I still have one from Edmonds’ Scientific).

    • Greg Matloff April 21, 2018, 7:57

      Dear Alex

      I believe that I had come across something like this in my literature search. But thanks for alerting Blog readers to it.


    • J. Jason Wentworth April 22, 2018, 18:01

      In addition to those holographic printed flat lenses being useful for optical instruments aboard probes–and for solar concentrators for solar electric propulsion systems–I wonder if they might make Bob Forward’s laser-pushed Starlite (a 1-tonne, 3.6 km diameter lightsail starprobe) and Starlite Special (his famous 1,000 km diameter, three-stage Epsilon Eridani round-trip laser lightsail starship, with an equally huge Fresnel laser-focusing lens in the outer solar system) more practical…or at least, somewhat less impractical?

    • Robert April 24, 2018, 12:51

      I wonder if a holographic lens could be used to collimate sunlight? By that I mean straighten out the divergence due to the finite size of the sun which is about 0.5 degrees.

      • Greg Matloff April 25, 2018, 7:59

        Dear Robert

        From my much earlier work, I don’t think that any lens system can collimate light from an extended source such as the Sun. But I really hope that I am proven wrong!


  • David April 20, 2018, 22:06

    Have the other teams run into or overcome major obstacles?Communication had been my biggest worry.The other issues seemed to be more about cost as long as the sail would hold and we could communicate. I am just thinking flybys of course.Thanks G and C.

  • Greg Matloff April 21, 2018, 7:58

    Dear David

    Last I talked with one of the laser people, they too are feeling a bit more optimistic. I don’t know the latest from the Com folks.


    • David April 22, 2018, 0:37

      Thanks so much. I first read Bob Forwards books as a kid loved them. He was the only engineer really looking at interstellar travel. I am excited we are here to fulfill his vision maybe sooner than he would have expected

  • Harold Shaw April 21, 2018, 11:11

    If holography could be applied to other wavelengths, could it also be used to increase the strength of radio communications from possible Starshot probes?

    • Greg Matloff April 22, 2018, 7:17

      Dear Harold

      At least one researcher is working on this. But he/she has requested that I stay mum.


  • Michael April 21, 2018, 14:25

    A fibre optic quality glass backing and hollowed out silicon lattice ridges of the right pitch will give near 99%+ reflectance and very, very low absorbance (HCG mirror). Optical quality glass is very flexible and has very good qualities for manufacture. I would also choose 1.55 micron as not only is it used in the communication industry but it is eye safe.


    • Greg Matloff April 22, 2018, 7:23

      Dear Michael

      Thanks for the response. Your idea sounds very nice. Perhaps you should consider responding to the RFP when it is issued. The selection of the ~1 micron waveband in Phil Lubin’s paper is due to an atmospheric window.

      Regards, Greg

      • Michael April 23, 2018, 9:06

        Thanks Greg,

        The RFP, is there a formal process and do you have a link to the location and a date when they usually ask?

  • djlactin April 21, 2018, 14:28

    I doubt that the first of these probes will be aimed at Proxima Cen. To iron out the wrinkles, they will be sent to local objects like Uranus or Planet X. These missions would not need 0.2c speed as would not require the power levels that you fear.

    • Greg Matloff April 22, 2018, 7:28

      Dear djlactin

      Lots of intermediate targets in or near the outer solar system are under consideration by various researchers on the Starshot team. I have been requested not to “fear” the enormous required power levels but instead to acknowledge that they are “very challenging”.

      Regards, Greg

  • Gary Wilson April 21, 2018, 19:31

    What size prototype lasers and sails are people envisioning? Finding the correct mountaintop sight for both the prototype laser and the full scale laser would be well worthwhile.

    • Michael April 22, 2018, 2:39

      I would like the minimum to be around 10 megawatts laser output, this could get a 4 gram probe out to the solar gravilens line in around 5 years ! Chile offers good high and dry locations.

    • Greg Matloff April 22, 2018, 7:25

      Dear Gary

      Laser people are now experimenting with very small arrays of solid-state lasers. Hopefully, these can be scaled up. The current site under consideration for the array is a high volcano in Chile.


  • J. Jason Wentworth April 22, 2018, 18:42

    Regarding structural reinforcement of the holographic sails, that and communication (via radio) might be two birds that could be killed with one stone, as follows:

    If memory serves, Yuri Artsutanov was inspired (at least partly) to invent the space elevator after reading about iron whiskers that had tremendous tensile strength per square centimeter. A spherical, inflated lightsail made as a super-pressure balloon (or even a flat, spin-rigidized sail) could have such metal whiskers–perhaps titanium ones–incorporated into the holographic sail material, and:

    In the case of a flat, spin-rigidized sail (although a spherical one could also be flattened after laser acceleration, by deflating it and spinning it using micro-thrusters), the metal tension whiskers could also serve as long wire (many wavelengths long) radio antennas. The longer a wire antenna (or a doublet antenna [a length of wire fed in its middle by the two-conductor transmission line]) is, the more the signal is fired off the end(s) of the antenna in a narrow beam or beams, like a parabolic dish antenna (the receive and transmit antenna patterns are identical). Since the sail would be spinning to keep itself flat, the multiple tension whiskers–which would look like the wires of a “wagon wheel”-type E-sail (Electric sail)–could be electronically selected via a solid-state commutator, so that each whisker antenna that pointed at the Earth would be selected in turn (several of the U.S. Air Force’s spin-stabilized Lincoln Experimental Satellites successfully used such “electronically de-spun” antennas, as they are called).

  • Alex Tolley April 22, 2018, 20:27

    One of the advantages of white light holograms is that the image can change as the viewer changes viewpoint. This offers something much more than a static image like that with the Pioneer plaque. Also, unlike the Voyager record, no special technology is required to operate it. I heartily endorse such an approach to communicating with any aliens (or our descendants).

    • ljk April 24, 2018, 10:08

      The only “special” technology needed to play the Voyager Interstellar Record is a needle and a stylus, plus something to turn the record on. The first two items were included with each of the space probes, along with pictorial instructions on the record cover.

      Even if the recipients were only able to place a needle into the record groove, they could still receive just about everything on the record except the images, and most of the record consists of music, sounds, and languages.

      • Alex Tolley April 24, 2018, 14:45

        Degradation of any equipment, especially with moving parts is a problem. I doubt that a record player with mere thousands of years antiquity would work well enough to convey very much. That is a problem with any system that uses encoding and decoding. A record player needs a good pickup needle, with the associated kit to translate the signals into sounds or images. In another millennium, could an archaeologist recover music from a found audio record, or images and video from a laserdisc? Look at how difficult it was to recover video of the Apollo moon landings from the tapes.
        Apollo 11 missing tapes

        One other advantage of holograms over even 2D pictures is that local damage just reduces the quality of the image, rather than erasing parts of the image. Theoretically, this should increase longevity and maintain content fidelity as long as the medium is robust too.

        • J. Jason Wentworth April 25, 2018, 2:19

          The Voyager Interstellar Record on each probe comes with a phonograph cartridge and needle, along with binary instructions and at least one diagram for how to play the record, and at the correct speed (if the recipients are advanced enough to detect and recover the long-silent spacecraft in interstellar space, they’ll be smart enough to build a phonograph to play the record on, using the cartridge and needle). Also:

          In the 1950s, light-beam phonographs were made for a while; they played regular phonograph records via a light source and a photocell pickup in the tone arm (a low-power laser would work even better). They worked just fine, but they never caught on enough to reach critical mass in the market, probably because diamond-needle cartridges were perceived as being better, and:

          If interstellar probes (including Bracewell probes) with enough mass allowance for similar messages are one day launched (Soviet engineers and CETI specialists presented papers at the 1973 CETI conference to the effect that 5% of c, Earth orbit-launched ion-drive interstellar probes [about the size of a Saturn rocket] were feasible with then-current technology), a Voyager-type phonograph record with encoded sounds and pictures (including color ones, as on the Voyager records) would be ideal, as the metal record would last far longer than a plastic CD. It could be played on a phonograph with a light beam/photocell pickup (the “optical cartridge,” or even the entire phonograph, could be included). In addition:

          If non-solid-state electronic devices would better survive the radiation and the sheer time, the phonograph’s electronic components (including the tone arm’s light source and optical pickup) could be–or be packaged inside–sub-miniature tubes, which are durable and draw little current. (The first pocket radios and walkie-talkies used sub-miniature tubes, and ran off ordinary dry-cell batteries [the recipients would surely have variac transformer power supplies, and the phonograph’s input voltage and amperage could be explained in the binary language].)

      • Greg Matloff April 25, 2018, 8:01

        Dear ijk

        Yes, but the long-playing record technology became obsolete on Earth shortly after Voyager was launched.


        • J. Jason Wentworth April 26, 2018, 12:11

          Hello Greg,

          You really need to get out more. :-) Not only is the phonograph/records combination *not* a dead technology, but is is undergoing a renaissance, so it is ready and waiting to be pressed (no pun intended :-) ) into service again for conveying durable audio and pictorial content (perhaps including moving pictures, in small quantities) to the stars aboard spacecraft, and:

          Phonographs and records–especially LP records (Long-Playing records)–never went away completely, and they have come back (a surprising number of young artists now release their music on LP records as well as on MP3s and CDs) for three main reasons:

          [1] *Sound quality* The analog LP records offer sound quality that digital records can’t quite match. David Crosby (of Crosby, Stills, Nash, and Young) described the difference when he first heard a digitally re-mastered CD of one of their classic albums: “The sound washed over me like a wave of ice cubes!” (he also said that their analog recordings had a warm, rich sound that simply wasn’t there in the digital versions). AM radio audio also has this kind of warm, rich sound (in contrast to FM audio, which has a “dry,” over-crisp sound, which makes crumpling paper sound like the crackling flame of a burning match);

          [2] *”Scratching”* Hip-hop artists and live DJs (Disc Jockeys) found that phonographs and records–especially LPs–are excellent for “scratching,” which doesn’t mean actually scratching the records. They manually move the turntable quickly forward and backward (or vice-versa), so that the ‘brief samples’ of the music that are played serve as a type of sound effect. They also often quickly manually play sung lyrics off the records (while this “lyric sampling” can also be done electronically via a computer, the manual phonograph method is cheaper, quicker to use in music production, and more easily enables each artist or DJ to play in his or her own distinctive style, and:

          [3] *Cover art (and album inserts, pictures, etc)* When CDs came out, it wasn’t long before bands and solo artists–for whom the album cover art is a major draw to sales (as are record sleeve-printed lyrics, included 8″ x 10″ photographs, catalogs of other albums in their discographies, etc.)–noticed that CDs, being much smaller, greatly limit these possibilities or prevent them altogether. Gradually, established artists and bands, and then new ones, began offering LP albums again (along with CDs and MP3 recordings of their works), and this became so common that consumer electronics firms that had made phonographs (Teac and Electrohome are just two of these [I don’t think Teac ever stopped entirely]) began making and selling phonographs–including high end ones–again. Just Google “phonograph,” “record player,” “LP record,” and “Teac” and “Electrohome” (and other phonograph manufacturer names), and you’ll see new-production ones available. I’m not trying to “show you up”; rather, I’m just spreading the news that this old and serviceable technology for conveying interstellar messages is alive, well, and growing!

          • J. Jason Wentworth April 26, 2018, 13:12

            Speaking of phonograph records as interstellar messages, there are now *laser turntables* for playing standard phonograph records–including LP records (Long-Playing records)–*without* touching them (see: http://en.wikipedia.org/wiki/Phonograph_record and http://en.wikipedia.org/wiki/Laser_turntable ), and:

            The Voyager Interstellar Record (one of which is aboard each probe) contains audio (music, spoken greetings, a Humpback Whale’s song, etc.) and audio-encoded photographs, including color ones (these have red, blue, and green versions, which when combined produce proper color pictures). Future Solar System-escaping spacecraft could also carry such etched metal records, along with a laser turntable “cartridge,” or even a complete laser phonograph aboard each probe, for playing the records. Also:

            Such spacecraft (particularly smaller ones) could, if desired or needed, carry a “Compact Double” 33-1/3 RPM LP record (this is a small, 45 RPM “single” [single song per side]-size LP record with the standard small spindle hole, like the old 78 RPM records and the large standard LP 33-1/3 RPM records, see: http://en.wikipedia.org/wiki/Phonograph_record ). It could be used for recording shorter, more abbreviated audio and/or pictorial messages. As well:

            Like the regular (large, full-size 33-1/3 RPM LP records) that the Voyagers are carrying, Compact Double LP records could be sent along with either a standard cartridge & needle, or with a laser phonograph “cartridge” for playing the audio and/or audio-encoded images in the record grooves. The Compact Double LP record can store a surprisingly large quantity of audio, considering its physical small size. When he was in medical school, my brother-in-law Kip Amazon (the family’s original surname was Frankenstein) listened to some lectures that were distributed on Compact Double LP records. I recall one, on anesthesiology, that was about 1 hour and 20 minutes long (both sides, in total)! A 45 RPM single record, which is the same size, can hold maybe (if memory serves) 10 – 20 minutes’ worth of audio in total. A laser turntable/etched-metal LP record—either Compact Double or full-size—sounds ideal for interstellar probes.

  • Curious April 22, 2018, 22:13

    I havent followed the details so apologies on my ignorance. But on the matter of the sail getting too hot – have you already looked into coating the receiving side with a suitable ablator? This would provide protection from the heat pulse and as it ablates it should contribute thrust against the sail. Eventually it completely burns off thus lowering the mass of the sail craft.

    • Greg Matloff April 23, 2018, 8:46

      Dear Curious

      An ablator or deserter is a nice idea except in adds mass to spacecraft and reduces acceleration and final velocity. Such concepts work best with solar sailing.

      Regards, Greg

      • Brett Bellmore April 23, 2018, 20:08

        IIRC, the laser levitated graphite sails were tested recently, and a good deal of the thrust derived from adsorbed gasses being driven off. An ablative surface, if consistent with the mirror remaining high quality after being burned off, could provide an initial high thrust at lower power, until the sail was far enough away for the whole laser array to be brought to bear.

        Think of it as a first stage.

      • J. Jason Wentworth April 23, 2018, 20:43

        Curious’ question suggests another:

        If the PROCSIMA team’s “long-focus-hold” laser (whose composite beam also includes a neutral particle beam) works as advertised, would an ablator-coated sail then perhaps be advantageous? The PROCSIMA laser beam (see: https://www.centauri-dreams.org/2018/04/05/tightening-the-beam-correspondence-on-procsima/ [I realize that it will require R & D work, of course]) could, it appears, remain tight over at least “near-interstellar” distances, giving a long ‘acceleration runway’ for sail probes (they envision a 0.1 c velocity probe), and:

        The ablator might be a metal-containing coating that would boil away while remaining reflective, absorbing much of the laser beam’s heat so that it would boil away (perhaps something rather like pewter, although with a higher melting point). Being able to employ an ablator-coated sail might–if a holographic sail is rather temperature-sensitive–enable high beam power to be used for a significant portion of the acceleration run without damaging the hologram.

    • Greg Matloff April 24, 2018, 6:17

      I meant “desorpter”, not “deserter”.


  • AlexT April 24, 2018, 4:24

    This idea sounds fine.
    But I have the question about image content :
    Why human (male and female) figures are looking so ugly and not realistic, it looks like sculptures from stone ages? I can accept the point that artist see our world this way, but do you think that message sent to ETI should carry so distorted information about message creators?
    May be it will be better not to send any image and save some funds for other parts of the project.

    • ljk April 24, 2018, 9:18

      Perhaps the holographic image could be redesigned to include multiple racial and gender representations which appear and change depending on how you look at it.

      In the event this may be confusing to the recipients – for we should not assume they will know what humans look like, or resemble us, or even that they may assume the images represent the beings who built and sent the vessel, as “logical” as that may seem to us – we should have more detailed information about us included somewhere in the interstellar probe for clarification.

      When artist Linda Salzman designed the Pioneer Plaque, she endeavored to include the facial characteristics of at least three different races on the human representation diagrams. Of course what happened is that some people complained they saw everyone BUT their own race in the faces of the man and woman on the plaque. Sigh.


      Let us also hope there will not be similar issues with showing nude humans aboard our future interstellar explorers as there were with the Pioneer Plaque, with NASA actually being accused of sending “smut” into space. While the male genitalia was depicted, the female counterpart was left out, which some worried would only confuse the presumably ETI recipients. See here to learn how one fellow came up with a “solution” to explaining the human reproductive process to our galactic neighbors:


      Some may find this all amusing or worse, but the Final Frontier contains vast and countless unknowns for our little species, which has barely gotten out of its cradle/nest. At the very least we need to make real efforts to present ourselves properly to who or whatever is out there, lest we create situations for which we are not prepared for – which often turns out to be a lot.

      • AlexT April 24, 2018, 14:25

        I understand that there is lot of limitations related to human culture, religion, ideology, philosophic etc. We also do not know what will be ETI’s reaction to discovery of our existence.
        So may be it will be beter to concentrate our resources and efforts to laser sailes development and not overload engeneers by non needed and problematic tasks like fine looking (to some human artist) hologram.
        On my opinion, this “hologram story” looks like – the people began to spend Milner’s funds for the things that does not have any connection to space exploration.

        • Greg Matloff April 25, 2018, 8:03

          Dear Alex T

          I refer you to the NASA report I cite that includes the work on holograms. It is not wise to be too critical of Bob Forward’s insights in this field. If he thought that holographic sail coatings had relevance, this should not be ignored.


        • ljk April 25, 2018, 9:54

          The New Horizons team made the same “argument” about putting so much as even a Pioneer Plaque style message on their space probe, when they could have easily asked a group of volunteers to create an information package that would not have interfered with their main work. After all, that is how the Voyager Interstellar Records came to be.

          Ironic, though, that they had the time and resources to spare to put Clyde Tombaugh’s ashes on NH. I mean no disrespect to the man and understand why they would do this, but I know NASA well enough that this must have involved a fair deal of red tape and time, some of which could have been spent making an information package for any probe finders too.

          Here are the details on what they put on New Horizons:


          I have argued this before here in this blog and will so again: If we are going to send probes roaming aimlessly into the wider Milky way galaxy after their missions as we have done so far with every vessel leaving the Sol system (plus their final booster stages), then we need to have some way to identify them as non-threatening to anyone who may find them some day, even if it is an imperfect gesture.

          • J. Jason Wentworth April 26, 2018, 11:18

            ** GOLF CLAP ** (with rodeo/country music festival “Yahoos!!!” of assent) Not only should all outward-bound, Solar System-escaping probes and their final stages carry *at least* suitably-modified (to fit the vehicles’ or stages’ configurations) Pioneer plaques, but:

            Interstellar flyby probes (like Daedalus, Icarus, StarShot, or designs derived from them) will–if their velocities are 537 km/s or more, which seems likely (see: http://www.newscientist.com/article/dn24249-stars-escape-velocity-shows-how-to-exit-the-milky-way/ )–also eventually escape from the Milky Way. This would make a galactic origin map advisable as well, particularly since the Milky Way has two close–by galactic standards–satellite galaxies, Nubecula Minor and Nubecula Major (the Small and Large Magellanic Clouds). Plus, even such stellar system fly-through probes that weren’t aimed in those satellite galaxies’ directions could easily–after longer intervals–happen to pass through (and maybe even be captured into) other galaxies of the Local Group.

            • ljk April 27, 2018, 9:32

              Good point on the galactic origin information aboard our deep space vessels. The Voyager Record contains an image of the Andromeda galaxy which was used to help recipients gain some measure of how long ago the probe had been launched – though now I am concerned it may cause some origin confusion. :^)

              Regarding New Horizons, the irony is that they could have essentially reproduced the Pioneer Plaque with little modification if any to bolt onto that probe. The basic diagram of the Pioneer probe resembles New Horizons and Pluto is part of the Sol system diagram across the bottom of the plaque.

              • J. Jason Wentworth April 29, 2018, 3:20

                I’d forgotten about that. While the M31 (Andromeda galaxy) picture would help to date the Voyager spacecraft (shifts in the positions of M31’s two satellite dwarf elliptical galaxies [the more distant one from M31, as we view them, is M32; the other one is officially “part” of M31] would help date the launches), it is just possible, although unlikely, that any recipients might conclude that “their” Voyager probe came from M31 or M32 [the picture being from another probe], but reached them–elsewhere in the Milky Way–via a wormhole or some other odd effect (maybe something like the fictional Hasslein Curve).

              • J. Jason Wentworth April 29, 2018, 3:41

                “Regarding New Horizons, the irony is that they could have essentially reproduced the Pioneer Plaque with little modification if any to bolt onto that probe. The basic diagram of the Pioneer probe resembles New Horizons and Pluto is part of the Sol system diagram across the bottom of the plaque.”

                I have no quarrel with some of Clyde Tombaugh’s ashes being aboard New Horizons (the state quarters and the piece of SpaceShipOne seem less relevant), but I couldn’t agree more. At the very least, a “template plaque” of the same format as the Pioneer 10/11 plaque should be affixed to every extrasolar spacecraft and final stage, with the Solar System course and the spacecraft outline (behind the human figures) being changed as needed to match the course and outline of the extrasolar object in question. In the case of final stages, the plaque might show the trajectories of the stage and its spacecraft, and the plaque could be a metallic “decal” applied to the stage casing, while the “standard” 6″ x 9″ etched metal plaques would be bolted to the spacecraft. Also:

                In Paul Davies’ book “The Eerie Silence” (which is about SETI’s lack of success after decades of listening), I was stunned to read his criticism of including the human figures on the Pioneer plaques, in which he said that no one cares what ET beings look like. (My reaction is, “Speak for yourself, Paul! Besides addressing most people’s curiosity, a similar etched image of them would answer many biological and cultural questions about them.”)

                • ljk April 30, 2018, 9:52

                  Paul Davies is entitled to his opinion, but he is wrong. :^) This reminds me of the early NASA rocket engineers who initially did not want to include any windows on the Mercury spacecraft because they didn’t think the astronauts would want to look outside while in orbit!

                  How is it that the same people who can envision and create vessels that explore the stars suddenly lack vision when it comes to such things as considering a way to communicate with any ETI recipients of their creations in deep space? The Pioneer Plaques and Voyager Records encountered such thinking before, during, and after their development.

                  Have you seen the 2017 documentary The Farthest about the Voyager probes and their Golden Records? More than once the engineers lamented the existence of those records, or said how others felt they were scientifically useless and got more attention than the actual planetary missions themselves.

                  Such lack of foresight from the very people who made missions into deep space possible is just head-shaking to me. This is why these information packages had to be developed by outside groups and why New Horizon’s lack in this regard is going to be a loss for all of us down the interstellar road.

                  • ljk April 30, 2018, 9:54

                    As Ellie Arroway said in Contact, they should have sent a poet!

                    • J. Jason Wentworth May 1, 2018, 11:15

                      When we send Bracewell interstellar messenger probes (large, cumbersome, and expensive–but workable–ion-drive ones could be launched today), they will be, among other things, interstellar “wandering poets and storytellers.” Several CETI astronomers, including Ronald Bracewell himself, even advocated transmitting poetry and music (particularly Bach) once we knew where to send direct interstellar signals where they would be received (and expected).

                  • J. Jason Wentworth May 1, 2018, 11:03

                    Davies’ lack of imagination in this area astonishes me. Even a Pioneer plaque-type line drawing of ETIs on an alien starprobe would provide hints about the beings’ chemistry and planetary environment, their star’s type, and even their diet and psychology. Also:

                    That might have been the “official excuse,” but the Mercury engineers did fear a blowout of the large pilot window that the astronauts wanted (due to pressure changes; the smaller porthole windows didn’t arouse such fears)–but Corning Glass developed a rugged pilot window for the capsules. John Glenn took his orbital pictures using a Leica 35 mm camera and film that he bought at a Cocoa Beach drugstore, because NASA didn’t think such pictures were important (!), and:

                    Skylab almost didn’t get a window, either, and that was long after the scientific value of pictures (Mariner 9 almost flew sans TV cameras, which soon proved their scientific worth) had been well-demonstrated. The Skylab crews–and Wernher von Braun–insisted on a window, and several multi-spectral cameras used the window (that was in addition to the EREP–Earth Resources Experiment Package–on one end of the Orbital Workshop). NASA objected to the window for cost reasons, because they wanted Skylab’s converted S-IVB stage to be as un-modified as possible, with only add-ons rather than structural modifications and their associated engineering work (which incorporating the window made necessary), and:

                    No, I haven’t seen the 2017 Voyager documentary (I stopped watching TV in 2009, although I watch YouTube videos and, perhaps once a year, a DVD on my computer). But the engineers’ complaints sounds familiar, as I read that the thermal design engineers resented having to account for the Voyager records’ heat transfer effects. Also:

                    I can understand–although I disagree with–those who thought the plaques and records were scientifically useless and over-shadowed the scientific goals of the missions, because their odds of being found (by aliens) are small, and the scientific objectives weren’t just “chopped liver.” But such “PR efforts” help missions like these get funded (even Mariner 3 and 4 each have a “Great Seal of the United States” stamped metal “facet” on one side of their octagonal spaceframes, and Mariner 1 and 2 had/have American flags that were sneaked aboard the space probes). As well:

                    When I read about New Horizons’ artifacts, the mission personnel who were responsible for selecting and installing them seemed annoyed when others suggested that Pioneer 10/11-type or Voyager 1/2-type items should have been placed aboard it. (Even the man who installed the Voyagers’ RTGs took the opportunity to write a message [which he declined to describe] to possible ETI finders of the probes inside their casings, white the New Horizons crew seemed bereft of any imagination, wonder, or even impishness.)

      • Alex Tolley April 24, 2018, 14:51

        We have enough trouble understanding our own history and artifacts and constantly misinterpret even our closest cousins. Alien ETI might be even more clueless despite our best efforts to communicate with images and symbols.

        We should be wary of what we do, although I don’t think that should make us timid either.

        • ljk April 25, 2018, 9:59

          Either we step out into the Universe or don’t bother at all. In any event with 7.6 billion humans present, some of them are going to make the attempt to leave the nest on a grand scale regardless. Better that we make an effort to deal with the potential consequences than ignore the issue.

      • J. Jason Wentworth April 25, 2018, 1:37

        Carl Sagan (Linda Salzman Sagan’s husband at that time) wrote that most people, regardless of their race, thought that the human beings depicted on the Pioneer plaque looked like *their* race. He and the plaque design team were pleased by this, because he wrote that they had deliberately intended to make the human figures pan-racial.

        • ljk April 25, 2018, 9:32

          I could have sworn it was the opposite, but I will take your positive comments instead, thank you. Perhaps I was influenced not only by an old memory filtered through space and time but the prominence of all the negative reactions to the Pioneer Plaque then and now, especially how people reacted to the fact that the two human representatives were – gasp – not wearing clothing!

          • J. Jason Wentworth April 26, 2018, 10:32

            While I’m certain of what Sagan wrote, that doesn’t mean that your memory is faulty. He wrote that–if I recall the timing correctly–a little while after Pioneer 10 and 11 were launched (but still in the mid-1970s, I think), *but*:

            News outlets, whose credo is “If it bleeds, it leads” (or the closest thing to that, if no one died or was injured in any given story), would have been more drawn to report the controversial, negative reactions to the Pioneer plaque that you recall, than the majority of non-controversial, positive reactions that Carl Sagan reported somewhat later. (I recall an extremely negative one in which NASA was accused of “spreading filth beyond our Solar System,” and a funny counterpoint to that, showing an unaltered copy of the plaque with the caption: “Hello. We’re from Orange County.” [For Americans or non-Americans who may be unfamiliar with that reference, Orange County was–and may still be–an unusually old-fashioned area of California, very culturally distinctive from the rest of the state, which was/is much more “hippy-like,” or at least “hippie-friendly,” including regarding nudism].)

            • ljk April 27, 2018, 9:22

              Carl Sagan’s 1973 book, The Cosmic Connection, has an entire chapter devoted to the development of the Pioneer Plaque and the various reactions to it – good, bad, and just plain WTF.

              The chapter includes a very funny bit from an old British satire magazine called Punch imagining what various ETI would think and say if they found the plaque. One in particular imagined that the recipients looked like the pulsar map, which sadly was positioned in a way that was considered an incredibly rude gesture in their culture.

              If you have not seen this already, you will also enjoy this short SF story from the April, 1980 issue of Omni magazine by Ian Stewart. It has Voyager 1 encountering a black hole and being split into seven copies sent into seven alternate universes and the reactions from a wide range of the ETI who find it.

              The story is reproduced online in full here:


              • J. Jason Wentworth April 29, 2018, 3:04

                I’m glad that I was not, ironically (as the beginning and ending of that account made reference to) *eating* (or drinking) anything in front of my computer’s screen when I read that story! :-) I’d forgotten which of Sagan’s books covered the Pioneer plaque story–thank you (I’ve ordered a copy of “The Cosmic Connection” from an AbeBooks vendor).

    • J. Jason Wentworth April 25, 2018, 2:47

      I’m not 100% sure, but I think the people shown in the “sample sail pictures” are just reused sample images from Greg’s and C’s 2015 book “Starlight, Starbright: Are Stars Conscious?” (see: http://www.amazon.com/Starlight-Starbright-Are-Stars-Conscious/dp/0993400213 ; they look like pictures of early humans from that book), with the holographic sail pictures being a provisional example of how such a visual message *might* be constituted. I understand what you mean regarding the aesthetics, as I prefer the appearance of Arabian and Shire mares (whose brawn doesn’t detract from their feminine grace) to that of Przewalski’s Horse mares, who look more (in human terms) “peasant-like.”

      • Greg Matloff April 25, 2018, 8:07

        Dear Jason

        These are originally from the NASA funded hologram. We paid a professional photographer to work with the hologram. C created a digital collage with the images. We have both used them in a number of places.

        Regards, Greg

        • J. Jason Wentworth April 26, 2018, 10:38

          Hello Greg,

          Thank you for confirming that. Ruminating more on them, they do look much like pre-Classical Greco-Roman “proto-Aphrodite/Venus” mother goddess figurines and illustrations that have been found by archaeologists.

      • ljk April 25, 2018, 9:43

        Aesthetics – now there is a subjective subject if ever was one.

        Of course evolution – both biological and technological – dictates that we may look so different from whoever finds the sail holograms that our tastes will probably be irrelevant. As I said above in this thread, let us try to use the technology to show a wide range of human types among other information about humanity and our world.

        FYI, here are the links to the two Centauri Dream articles on stellar consciousness by Greg Matloff:



        • J. Jason Wentworth April 26, 2018, 10:55

          I agree; the aesthetics likely would be irrelevant to any alien finders of the interstellar messages. But since such missions’ messages will, with certainty, be seen and/or heard by billions of human beings (including those who paid for the missions and messages [even if they are crowd-funded someday]), the aesthetics–not only of the human subjects, but also of the forms of the messages (their general appearance and layouts)–are important, because they are like brands or logos, and:

          I’ve always seen the Pioneer plaque and the Voyager Interstellar Record (including its “intro cover” with the pulsar map, radiological dating patch, and playing instructions) as being distinctive, attractive, and cool. So have–and do–many others, judging by the popularity of Pioneer plaque replicas. (I have a full-size etched metal one, and I’ve even seen miniature Pioneer plaque key chains–I got one for a friend, just in case, as I joking told him, “You ever get abducted by aliens and have to find your way back home.” :-) )

          • ljk April 27, 2018, 9:11

            This is true in that everyone, including Carl Sagan, said the plaques and records are as much a message to humanity as they are to any ETI. I am particularly pleased to see how many artists have discovered the Voyager Records and incorporating/paying tributes to their contents, especially on their fortieth anniversary.

  • Robert April 24, 2018, 12:47

    “Finally, rare ~1-micron interstellar dust grains impacting a sail moving through the interstellar medium at ~0.2c pack quite a wallop.”

    I suspect it would just leave a 1-micron hole like a bullet through tissue paper. If hit edge on however, the damage would be through the whole sail.

    • Greg Matloff April 25, 2018, 8:10

      Dear Robert

      There is debate about how much damage a dust particle would do on a broadside hit. But one estimate is that 20-30% of the sail would be eroded by end of mission. Since sail thickness is less than 1 micron, odds of an edge-on impact are a lot less.


  • ljk April 26, 2018, 9:36

    Jason Davis • April 25, 2018

    Pew pew! Lasers will help determine where LightSail 2 is:


  • ljk April 27, 2018, 10:29

    10,000-Year Nuclear Waste Site Marker

    Astro-artist Jon Lomberg, a longtime friend and colleague of Carl Sagan, on protecting future humans from America’s atomic past.

    Samuel Gilbert

    April 26 2018, 11:00 am

    At first, Jon Lomberg thought it was a joke. When the late Carl Sagan, his friend and mentor, told him about a US Department of Energy plan to future-proof an atomic waste site for 10,000 years, he wasn’t sure it could be real. But a few years later, in 1990, Lomberg signed on to help design the warning marker of this tomb of the Cold War.

    He had received a letter from Sandia National Laboratories in Albuquerque, New Mexico, with the unusual proposal. Sandia needed help developing a marking system to deter humans from entering America’s only active nuclear waste repository, the Waste Isolation Pilot Plant (WIPP) for the next 10,000 years. It would represent humanity’s longest attempt at consciously communicating through time. As someone long invested in “unique communication problems,” Lomberg was intrigued.

    Full article here:


    To quote:

    Prior to the WIPP assignment, Lomberg worked under Sagan, who chaired the NASA committee behind the Voyager Golden Record, a time capsule meant to impart the story of our world to aliens. Launched aboard NASA’s Voyager probes in 1977, the double record would become the first human-made object to ever leave our solar system. It contained everything from scientific diagrams, to music from across cultures and time periods, to the images and sounds of humans and animals that Lomberg helped create and select.

    Lomberg was also project director for the Planetary Society’s Vision of Mars, a message launched in August 2007 from Earth to prospective human inhabitants of the Red Planet. Delivered via the Phoenix lander in May 2008, the “vision” took the form of a silica glass mini-DVD embedded with literature, art, and personal messages about Mars from space visionaries, including Sagan. “When we colonize Mars,” Lomberg says, “I will be part of their prehistory.”

  • JimU April 27, 2018, 13:15

    Speaking of graphene, there is the anomalous propulsion result reported in:


    • J. Jason Wentworth April 28, 2018, 17:38

      JimU, this macro-scale, laser light-stimulated directional electron emission property deserves further study–and coverage. It might be useful for main propulsion and/or for attitude control (and very precise attitude control, at that) for spacecraft. If the ejected electrons were replaced by electrons “pumped into” the graphene via electrodes, from an electricity source, then a reactor or even an RTG could more-or-less directly propel a spacecraft (including powering the laser, although a ground-based laser might be useful for starting the vehicle going) via the electricity it produced, and:

      Last night I was surprised to come across another photonic propulsion concept that I had never heard of before (in aerospace writer Walter B. Hendrickson’s 1975 book, “Manned Spacecraft to Mars and Venus: How They Work”). He mentioned a fusion-powered (*not* matter/anti-matter-powered) photon rocket concept that Dr. Eugen Sänger and his wife, Dr. Irene Sänger-Bredt, had developed; this propulsion system, they calculated, could produce 1 g acceleration, enabling flights to Mars and Venus taking only hours each way (including braking into orbit around either planet), and near-c interstellar velocities.

      • Alex Tolley April 29, 2018, 14:19

        He mentioned a fusion-powered (*not* matter/anti-matter-powered) photon rocket concept that Dr. Eugen Sänger and his wife, Dr. Irene Sänger-Bredt, had developed; this propulsion system, they calculated, could produce 1 g acceleration


        • J. Jason Wentworth May 1, 2018, 10:00

          Bae’s PLT (Photonic Laser Thruster), which excited me at first, doesn’t seem to be–at least with current knowledge–as useful as it first did, partly due to Doppler shift effects as the movable mirror dashes away from the stationary laser (it looks practical for precision formation-flying satellites, though), but:

          Dr. Eugen Sänger’s and Dr. Irene Sänger-Bredt’s fusion photon rocket wouldn’t be subject to the Doppler shift problem, because the fusion reactor would be aboard the spacecraft. Even today, a “non-self-sustaining” fusion reactor (similar to the “fission-assisted fusion reactor” of the Project Longshot interstellar probe) could be used to power such a photon rocket, and the cryogenic fusion fuel (deuterium and/or tritium) could be used to regeneratively-cool the photon thrusting optics before being injected into the fusion reactor.

  • AlexT April 29, 2018, 4:23

    1. If your target to send hologram to the space – use laser beam only, without any Sail , in this case your message will travel with the speed of light.
    2. If your target to make space exploration – use laser Sail, you do not need hologram.
    I suppose it is biggest fault to make connetion between two totally different tasks, so I realy cannot , so huge respect to this idea in this community, sorry.
    There was many nice projects that ended by nothing , when they entered to the “positive feedback” of endless “improvements”.

    • Paul Gilster April 29, 2018, 18:07

      AlexT, you may want to re-read the original article Greg wrote. Let me quote from it:

      “It no longer seems impossible to me that the Project Starshot goals can be achieved. One would use a holographic film and expose the image of a filter or mirror that is highly reflective in the laser’s wavelength range. My colleague at Citytech, Lufeng Leng teaches optics. She is quite sure that a hologram of a spherical surface will behave optically like a spherical surface. So the filter or mirror should ideally have a convex spherical shape, from the point of view of the observer (or laser).”

      In other words, using a holographic film may well solve a key physics problem with the Starshot sail. Thus the hologram *may* be an enabling technology. Greg is calling for more work on the matter, particularly lab work in the kind of sail test facility that Starshot so desperately needs to build. The key here: a holograph of a spherical surface can behave as a spherical surface, while the actual sail can be of an entirely different shape, and thus can be turned to avoid interstellar dust during cruise. It’s a concept well worth consideration.

      • AlexT April 30, 2018, 1:58

        There is a key phrase in your answer that make huge difference between “hologram” that Lufeng Leng means and hologram (with stone ages sculpur) that you show in you article.
        Lufeng Leng means holograph of SPHERICAL surface… and I agree with this point 100% – exactly this way are built today big phased antenna arrays on Radio frequencies (i.e. much longer that light wavelenght).
        There is basic physical laws that dictate you which form should have hologram that is optimised to get maximal acceleration in desired direction and the fact it is not the fine image that was published here.
        I beleive published image can make fine job as advertisement and may be can help to draw some fund from investors, but it is not science.

        • Paul Gilster April 30, 2018, 7:59

          AlexT, Greg is not talking about using the hologram presented in the article’s image as the laser sail hologram — it’s there as background on how his interest in holograms grew, and as an example of a hologram that he has had experience with via his association with Bob Forward. He describes what he would use in laser work as “a hologram of a spherical surface [that] will behave optically like a spherical surface. So the filter or mirror should ideally have a convex spherical shape, from the point of view of the observer (or laser).” No one is talking about using the published image as the hologram for a laser sail. It’s just there as an illustration of a hologram, and one with an interesting history.

          • ljk April 30, 2018, 11:21

            I think putting a hologram on the laser sail itself so that any advanced enough ETI monitoring the unknown probe heading in their direction could see the images far ahead of encountering the vessel directly to get some idea of who and what they are dealing with.

            Yes, I know, it could be considered a trap to lull them into a false sense of security. However, an alien vessel entering a star system with no indications as to its intentions would be far more concerning. Besides, if a species were going to take out another species via interstellar travel, they would hardly announce their presence ahead of time if they were being strategic.

            • AlexT April 30, 2018, 16:14

              I do not think it is good idea to discover our location, but If you want to send message to ETI , it is more clever to use laser beam without any sail, it will require laser with significantly lower power and will propagate with speed of light…
              May be we can even organize laser light show pointing laser beam to the atmosphere of some distant planet (Trappist K) :-)

              • ljk May 1, 2018, 8:49

                We do not have to tell them where we are from but can still relay other information about ourselves and our world.

                • ljk May 1, 2018, 10:40

                  Though considering astronomers were able to make some good guesses on where Oumuamua came from without any informational help from ETI at all means that the recipients of our future star probes will likely be more advanced than us and therefore smart enough to figure out where their alien visitor came from whether we tell them or not on the vessel itself.

                  • J. Jason Wentworth May 1, 2018, 23:25

                    I agree. Also, if we want to find and/or contact other civilizations, we can never do so (unless we’re very lucky and happen to “overhear” radio or laser messages not meant for us) unless, at some point, we accept some level of risk, and:

                    Some people oppose METI radio and laser transmissions. But all Solar System-escaping probes such as Pioneer 10/11, Voyager 1/2, and New Horizons (and even their final stages [except Pioneer 11’s, which didn’t escape from the Sun])–and future starprobes–are (and will be) “physical METI” messages, even if they didn’t/don’t carry messages aboard them. Also:

                    Their mere existence and artificial nature will tell any alien recipients that ^someone^ made the probes and spent stages. They will also be able to figure out the direction from which “their” Terran artifact came, and they will be able to determine (based on the amount of interstellar particle erosion and the artifact’s velocity) which stars in that direction it could have come from. Unless the “finders” were on the other side of the Milky Way, their list of “candidate artifact origin stars” probably wouldn’t be very large, and they could beam radio or laser messages in our direction, in answer to our “message in a bottle.”

                    • AlexT May 2, 2018, 11:49

                      “They will also be able to figure out the direction from which “their” Terran artifact came” – I suppose you very optimistic too, if you think that after some significant time the probe movement vector will be pointing to the our solar system :-) And ETI can calculate departure point of the probe, they even will not know how many time probe will be traveling in the space, Wishful thinking, same case as Oumuamua.

                  • AlexT May 2, 2018, 3:24

                    I suppose you are very optimistic in when using phrase “astronomers were able to make some good guesses on where Oumuamua came from”, I suppose in reality astronomers cannot even give us expected order of error they have in this “where came from” calculations, in any case none can check those numbers – real science begins when you can repeat and recheck results of measurements, Oumuamua “where came from” it is populism…

                    • ljk May 2, 2018, 17:05

                      That is why I used the word “guess.”

                      That we had some idea at all rather than just any random point in the sky says to me that a more advanced species encountering an actual artificial vessel will have an even better chance of finding out where it came from even if its makers did not supply any kind of map or directions.

          • AlexT April 30, 2018, 15:58

            Thanks for clarification.
            But there is some connection in Greg’s article between those two totally different things , that use common definition – hologram.
            By the way even if it will be possible to put hologram on the sail (to form desired beam/acceleration vector) , the sail surface still should have perfect predefined physical (non virtual) shape.

      • AlexT April 30, 2018, 2:35

        I forgot to add that ideal reflector shape (for maximal sail acceleration) should be not spheric , but parabolic or hyperbolic.
        I suppose that word “spheric” was used by Lufeng Leng intentionally for simplification / popularisation.

        • Paul Gilster April 30, 2018, 12:14

          Although Avi Loeb and Zac Manchester have recently been pointing to serious advantages for a spherical sail:


          One problem with the concept is that a spherical sail cannot be turned ‘edge on’ to minimize dust impact damage during cruise. But if a ‘spherical’ sail can be established as a hologram on a flat sail, this problem disappears. Exactly what shape the Breakthrough Starshot sail should be is a continuing subject of debate, another reason why a dedicated test facility is under discussion. The sail’s shape has to be such that it maintains stability under the beam — much work ahead.

          • AlexT April 30, 2018, 16:04

            Yes, I remember this article, but using spherical surface you loose some efficiency and as sequence it require extra power for laser beam for the same acceleration.

  • ljk May 8, 2018, 9:29

    The material science of building a light sail to take us to Alpha Centauri

    We’re unsure about the best material and don’t have the measurements to know.

    John Timmer – 5/7/2018, 4:15 PM

    It has been about two years since Yuri Milner announced his most audacious piece of science-focused philanthropy: Breakthrough Starshot, an attempt to send hardware to Alpha Centauri by mid-century. Although the technology involved is a reasonable extrapolation of things we already know how to make, being able to create materials and technology that create that extrapolation is a serious challenge. So much of Breakthrough Starshot’s early funding has gone to figuring out what improvements on current technology are needed.

    Perhaps the least well-understood developments we need come in the form of the light sail that will be needed to accelerate the starshots to 20 percent of the speed of light. We’ve only put two examples of light-driven sails into space, and they aren’t anything close to what is necessary for Breakthrough Starshot. So, in this week’s edition of Nature Materials, a team of Caltech scientists looks at what we’d need to do to go from those examples to something capable of interstellar travel.


  • ljk May 9, 2018, 13:29

    Issues still to be addressed for Breakthrough Starshot project

    May 8, 2018 by Bob Yirka, Phys.org report

    A team of researchers at the California Institute of Technology has taken a hard look at the challenges facing efforts to carry out the Breakthrough Starshot project. In their Perspective piece published in the journal Nature Materials, the researchers outline the obstacles still facing project engineers and possible solutions.


    Had we stuck with Orion, which began in the 1950s, we might have been to Alpha Centauri by now, or at least certainly well underway.


  • ljk May 15, 2018, 12:54

    Pros and Cons of Various Methods of Interstellar Travel

    Article written: 14 May 2018

    by Matt Williams

    It’s a staple of science fiction, and something many people have fantasized about at one time or another: the idea of sending out spaceships with colonists and transplanting the seed of humanity among the stars. Between discovering new worlds, becoming an interstellar species, and maybe even finding extra-terrestrial civilizations, the dream of spreading beyond the Solar System is one that can’t become reality soon enough!

    For decades, scientists have contemplated how humanity might one-day reach achieve this lofty goal. And the range of concepts they have come up with present a whole lot of pros and cons. These pros and cons were raised in a recent study by Martin Braddock, a member of the Mansfield and Sutton Astronomical Society, a Fellow of the Royal Society of Biology, and a Fellow of the Royal Astronomical Society.

    The study, titled “Concepts for Deep Space Travel: From Warp Drives and Hibernation to World Ships and Cryogenics“, recently appeared in the scientific journal Current Trends in Biomedical Engineering and Biosciences (a Juniper Journals publication). As Braddock indicates in his study, the question of how human beings could explore neighboring star systems has become more relevant in recent years thanks to exoplanet discoveries.


  • ljk May 16, 2018, 10:12

    LightSail 2 launch slips to Fall

    Jason Davis • May 11, 2018

    The second flight of SpaceX’s Falcon Heavy rocket is now scheduled for no earlier than October 30, 2018.


  • ljk May 23, 2018, 12:14

    A very interesting interview with Avi Loeb. You just have to stomach the questions and comments of the interviewer, who is clearly out of his depth:


    To quote:

    Benyamin: Okay, so let’s set the stage here. You’re of the opinion that Earth will not be around forever, whether it’s because of climate change or an asteroid hitting our planet, it behooves us as a species to look for a new planet to call home. You, as a philosopher, slash, astronomer, are actively looking for a new planet for us to move to. That’s a pretty audacious goal. What would you say to someone who says that that’s just a pretty far out idea?

    Avi: Well, the point is that we will eventually get to that bridge and we will have to cross it. I’m just saying that this bridge exists. People may prefer to ignore it. You could ignore any danger in the future, but eventually it will come to haunt you because nature does not care about what we think and what we ignore. The reality will come to haunt us. There will be an asteroid that will impact the Earth, potentially. If we don’t deflect it, there will be a major solar storm that could affect conditions dramatically. There could be a nuclear war, there could be a climate change.

    Eventually, we’ll start contemplating how to move away from the Earth. It’s without a doubt that this will happen, the question is on what time scale? Whether it will be a hundred years, a thousand years, a million years or a billion years. For the billion years time scale, it’s a definite future that we will have to move away from the Earth, because all the oceans will be evaporated by the Sun warming up. Now, what can we do about it? We need to develop the technology to move away from the Earth. The first step would be to send a probe …

  • Dmitry Novoseltsev October 5, 2018, 11:12

    What opinions do you have about the durability of holographic images on the sails?
    Can they be used for long-term, up to billions of years, data storage on the sails of “keepers” probes on the peripheries of emerging exoplanetary systems , which I wrote about earlier?
    Is Professor Matloff’s opinion on this matter known?