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Aerographite: An Advance in Sail Materials with Deep Space Implications

Invented at the Technical University of Hamburg and developed with the aid of researchers at the University of Kiel, a new material called aerographite offers striking prospects for solar sail missions within the Solar System as well as interstellar precursor implications. Judging from the calculations in a just published paper in Astronomy & Astrophysics, aerographite conceivably enables a mission to Proxima Centauri with a flight time of less than two centuries. We are not talking about laser-driven missions here, but rather meter-scale craft that would be pushed to interstellar velocities by solar radiation; i.e., true solar sails.

But let’s focus near-term before going interstellar. I’ve been talking to René Heller (Max Planck Institute for Solar System Research, Göttingen) about the paper, along with co-authors Guillem Anglada-Escudé (Institut de Ciencies Espacials, Barcelona), Michael Hippke (Sonneberg Observatory, Germany) and Pierre Kervella (Observatoire de Paris). Just what are the prospects for aerographite, and what are its problems? The authors stress that aerographite for space applications implies a development path through laboratory work and near-term experimentation in space. “Before we run, we need to walk,” as Anglada-Escudé told me in an email that summarized how the idea grew.

Anglada-Escudé and Heller had been studying the conditions that would allow a sail pushed by solar radiation, as opposed to laser beaming, to leave the Solar System, developing calculations for the kind of material needed, and initially envisioning a sail made of graphene (about which more in a moment). As Hippke and Kervella joined the discussion, the connection with aerographite was made and the previous computations recalculated. Says Heller:

“Aerographite is both ultralight and opaque (= black) so that it effectively absorbs photons and overcomes the gravitational attraction from the Sun under certain circumstances. We find that a hollow sphere (or shell) with a diameter of a few meters and a shell thickness less than 1 mm would become unbound from the solar system if it were submitted to sunlight in interplanetary space. It could be brought into space as a piggyback mission to any interplanetary mission without adding significant amounts of mass to the payload (because aerographite is so ridiculously lightweight)”.

Adds Anglada-Escudé, on how a material might be ‘unbound’ from the Solar System:

It is known that small dust (mostly SiO2 [silicon dioxide] balls, which are quite dense) in the solar system are blown away at some 100 nanometer sizes, so any material lighter than that should work. Also, one does not need to be reflective. Absorbance is also OK (only a factor of 2 worse than a fully reflective material).

The reference to Starshot is useful because it sets up some technology comparisons I want to make, while also driving home the point that as a near-term goal, something as relatively “local” as a demonstrator released from the International Space Station could move the ball forward. So what I want to do in the course of the next several posts is to examine the Astronomy & Astrophysics paper and consider the uses of aerographite in a variety of mission concepts as we begin to explore how such a sail could be constructed and flown.

But we also need some context, and a nod to a slightly earlier and itself promising sail material gets the story in motion.

Image; This graphic shows a detail of the world’s lightest material: aerographite. Open carbon tubes form a fine mesh and offer a low density of 0.2 milligram per cubic centimetre. The picture was taken with a scanning electron microscope (SEM). Credit: TUHH.

Sails for Deep Space Missions

Sails have been considered for long-duration, conceivably interstellar missions since the days of Robert Forward, and Centauri Dreams readers will also be aware of such seminal works as Greg Matloff’s 1981 paper “Solar Sail Starships—The Clipper Ships of the Galaxy,” which ran in the Journal of the British Interplanetary Society. What we are after is a thin sail that is temperature tolerant and rugged enough to endure its passage through the interstellar medium. Such a sail is usually assumed to be highly reflective, though aerographite will put a new spin on this. A ‘sundiver’ maneuver, taking a shielded sail close to the Sun for deployment at perihelion, was seen as offering travel time to the Centauri stars of perhaps a thousand years. And travel times like that seemed the best we could do with solar sails.

Laser-beaming could conceivably change the equation, and the Breakthrough Starshot effort revolves around a massive, ground-based laser array that would drive small sails up to 20 percent of the speed of light for fast passage to Proxima Centauri or other stars. In any case, the question of materials figures prominently in sail literature. The most studied material to date has been beryllium, but in 2012 Greg Matloff revisited sails with graphene in mind. He described it as “a mono-molecular lattice of carbon atoms” and noted that materials experts and condensed matter physicists had graphene under intense investigation. Matloff saw prospects for graphene in terms of thin-film probes and much larger manned starships:

In its application to interstellar solar sailing, it seems that graphene can exceed the performance of beryllium with less extreme perihelion requirements, peak temperatures and maximum accelerations. Thousand-year transits to Alpha Centauri do not seem out of the question for probes and generation ships using this mode of acceleration and deceleration.

Matloff also noted the problems posed by graphene, pointing to the difficulty of large-scale preparation at high-purity levels and questions involving its performance during a close solar pass, a maneuver that colleague Roman Kezerashvili had analyzed for beryllium sails several years earlier. The question facing Heller, Anglada-Escudé, Hippke and Kervella was whether the newly discovered aerographite could significantly upgrade the performance of a graphene sail, allowing us to reduce travel times to something below that 1,000 year threshold.

Aerographite offered several clear advantages along with some properties that would need to be analyzed and accounted for. It is true that graphene’s extremely low mass per cross section ratio can theoretically enable high velocities. But graphene turns out to be all but transparent, with a reflectivity close to zero. And now we run into difficulties with creating a graphene sail that I want to illustrate by quoting the Heller et al. paper. In the passage that follows, sigma (σ) stands for the mass per cross section ratio, which for graphene is 7.6 × 10−7 kg m−2:

The absorptive and reflective properties of graphene can be greatly enhanced by doping graphene monolayers with alkali metals (Jung et al. 2011) or by sandwiching them between substrates (Yan et al. 2012). But this comes at the price of greatly increasing σ. The limited structural integrity of a graphene monolayer requires additional material thereby further increasing σ and complicating the experimental realization. All of this ultimately ruins the beautiful theory of a pure graphene sail.

To be sure, Matloff and others working on the graphene sail concept are well aware of these issues and various papers have investigated the prospects for surmounting them. But the prospect of an aerographite sail, a material with its own strengths and question marks, gives us a new entrant in the sail arena, now with initial calculations provided by Heller and team. Specifically, what the Astronomy & Astrophysics paper does is to examine a hollow sphere at meter-scale, one made out of aerographite, that can be launched into interplanetary space by conventional rocket and released, allowing solar photon pressure to go to work.

Missions within the Solar System assuming such a sphere with a shell thickness of roughly 0.5 mm could, according to these calculations, reach the orbit of Mars within 60 days, arriving at Pluto’s orbit in 4.3 years. If the material proved capable of withstanding a close solar pass, there are mission prospects for Proxima Centauri in the range of 185 years of travel time.

But a Proxima mission gets way ahead of the game. We need to look at aerographite in terms of what we can learn about it in the near-term, with missions within the Solar System of various complexity part of the learning curve. In the next post, I want to go into how an early aerographite sail could be made, and how deep space sails might be configured, and we’ll consider whether in the near-term, solar as opposed to laser sailing may be our path toward true interstellar precursors. And either tomorrow or in a third post, we need to examine how to overcome some problems raised by this material in terms of both navigation and monitoring / communications.

The paper is Heller, Anglada-Escudé, Hippke & Kervella, “Low-cost precursor of an interstellar mission,” Astronomy & Astrophysics 7 July 2020 (abstract / preprint). The discovery paper for aerographite is Mecklenburg et al., “Aerographite: Ultra Lightweight, Flexible Nanowall, Carbon Microtube Material with Outstanding Mechanical Performance,” Advanced Materials Vol. 24, Issue 26 (12 June 2012). Abstract. Matloff’s paper on graphene is “Graphene: The Ultimate Interstellar Solar Sail Material?” JBIS 65, pp. 378-381 (2012) (full text).

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{ 48 comments… add one }
  • Alex Tolley July 27, 2020, 15:20

    Absorbance is also OK (only a factor of 2 better than a fully reflective material).

    Did you mean: only a factor of 2 worse than a fully reflective material?

    • Paul Gilster July 27, 2020, 16:56

      I also think it’s a factor of 2 worse, Alex. Doubtless a typo, but am checking with the source.

      • Paul Gilster July 27, 2020, 17:42

        Confirmed — it was just a typo. I’ve fixed the text.

  • John walker July 27, 2020, 16:16

    Payload mass plus all structural and navigational aids would presumably need to represent only a very small percentage of total mass in order to retain the benefit of aerographites(or graphene aerogel) low density. A one meter sphere at 0.5mm wall thickness would have a mass of about 0.12g. Just for fun, some relative sphere sizes in theoretical use scenarios. Retaining density to 105% means a 1g starchip payload would at 0.5mm wall thickness need a modest 2.7 meter sphere. A 1000 ton generation ship would need a sphere at least 2.7km diameter given the same wall thickness.

    • Andrey July 27, 2020, 18:04

      1000 ton is way too small for a generation ship. It’s a little more than twice the ISS weight.

    • Guillem Anglada-Escudé July 27, 2020, 18:52

      > A 1000 ton generation ship would need a sphere at least 2.7km diameter given the same wall thickness.

      which would be entirely reasonable, wouldn’t it?

    • Alex Tolley July 27, 2020, 20:56

      According to the paper, the payload-to-sail ratio is many multiples. A 1g Breakthrough Starship chip would fit inside a small (<1 meter) hollow sphere. The paper has all teh needed calculations to test different options.

      What is not mentioned in the paper is the possibility of boosting the velocity with a low power laser. All the calculations assume the sun provides all the energy. It should be fairly easy to determine the laser power requirements to boost the sail velocity to allow for faster travel times, both in the solar system, and interstellar trips.

      However, if the science teams can tolerate the longer journey times to Proxima, the advantage over laser boosted sails is that the sail will slow down in the target system, allowing far longer data collection times.

  • Robin Datta July 27, 2020, 16:58

    Does this herald the dawn of a new era of sailing ships? Perhaps to precede more sophisticated propulsion systems?
    The equivalent of 8+ (present) human generations to the nearest star sans life extension or suspended animation would be a bit daunting, but volunteers will likely still be found.

  • Alex Tolley July 27, 2020, 17:47

    From the end of the paper:

    Three key challenges for such a mission remain to be addressed:
    (1) manufacturing a meter-sized sub-millimeter thick
    sphere of aerographite; (2) producing and installing gram-scale
    onboard equipment to enable communication with Earth; and (3)
    transporting the ultra thin aerographite sphere into interplanetary
    space while preserving its structural integrity.

    Interesting questions. I wonder if in-space manufacturing would be the best approach, using a dedicated 3D printer. The theoretical calculations are very impressive, and I like the hollow sphere model to produce a lightweight, structurally robust , meter-scale “sail” that could transport a very lightweight probe.

  • Alex Tolley July 27, 2020, 20:45
  • Eniac July 27, 2020, 20:46

    This sounds too good to be true. I noticed that the authors assume complete absorption of light at any thickness, which cannot be the case. Any material will transmit light if sufficiently thin. I could not find any data on aerographite that speaks to this, but if I am not mistaken the authors have not considered it. That turns me off, and I await clarification on this point before I get excited.

    • Paul Gilster July 27, 2020, 21:09

      A good question and one that, as I understand it, the authors are already considering. Aerographite is still new enough that a good deal of experimental work needs to be done, as they acknowledge.

      • Eniac July 29, 2020, 3:03

        You are right, Paul, the stuff is new. Still, simply cutting a thin slice and holding it up to the light could have illuminated the issue. The experimentalists apparently didn’t think of it, or didn’t consider it noteworthy, and the present authors likely didn’t have access to a sample.

    • Alex Tolley July 28, 2020, 0:48

      aerographite looks very opaque to me, although those 1 mm wall thicknesses might not be totally dark.

      However, they have the equations set up so that you could plug in the 0<Krad<=1 value to determine wall thickness. The breakeven for Krad = 1, was a thickness 1/4 the radius of the sphere. That gives you plenty of thickness to work with, and allows for tailoring the thickness based on absorption.

      I don't think this would be a showstopper.

      • Eniac July 29, 2020, 2:52

        The whole geometry part is a distraction. The best sail is always flat and as thin as possible. Aerographite is just a seriously crumpled version of graphene and has to be less efficient than flat graphene. I suspect that if transparency is taken into account for both, graphene wins by a multiple. Yes, it is nearly transparent, but also incredibly thin. 50 layers of graphene would be opaque, but, absent structural considerations, the highest specific impulse is still achieved with the single layer. Doping could potentially help, with both materials.

      • Eniac July 29, 2020, 3:18

        The hollow sphere geometry is particularly silly, because more than half of it is unilluminated dead weight.

  • Jurov July 28, 2020, 2:15

    With the sail material being pitch black fluff ball which seems will be rolling unpredictably, I wonder how is the active part (electronics chip) going to shed heat?

  • AlexTru July 28, 2020, 2:37

    If it is black – it will efficiently collect heat, i.e. such object will effectively heat up and with same efficiency will radiate heat…
    Let.eave aside the possible thermal damage, but there is the second important thing – Yarkovsky effect.
    When it is applied to asteroids it has more significant influence to the body trajectory, than photonics pressure.
    And here Yarkovsky is somehow ignored by authors.

    • Alex Tolley July 28, 2020, 12:57

      As they are talking about a potential stating point at 0.04 AU from the sun, thermal damage is unlikely at greater distances from the sun.

      Doesn’t the Yarkovsky effect effect require a slow rotation of the body? If the sphere is stable, then this is not an issue, is it?

      • charlie July 28, 2020, 17:50

        “If the sphere is stable, then this is not an issue, is it?”
        What about tidal grav. effects , esp. pronounced near the sun?

      • AlexTru July 29, 2020, 2:03

        I suppose we can accept by default that this sphere will rotate (everything in our solar system has rotation moment) , opposite, the stabilization of body orientation will require more energy than movement.
        Again astronomic observations detects much more significant influence of Yarkovsky effect on the space body trajectory , than trajectory affected by photon pressure.
        Accounting color of discussed sphere, I am sure that Kinetic moment caused by Yarkovsky effect will be more actual than kinetic moment transferred by photon pressure (by the way body heating is caused by energy of the the same photons)…

  • Adam Crowl July 28, 2020, 3:34

    Hi Paul

    The team released it on ArXiv here: Low-cost precursor of an interstellar mission

    Interesting – if it performs as hoped. There are other options for ultra-low areal mass density carbon allotropes, even so.

  • Michael Fidler July 28, 2020, 3:44

    What about putting the sphere close enough to the Sun to be catapulted by the magnetic reconnection of a solarflare. If done at solar maximum sunspot and flares would be occurring certain latitudes at a much higher rate. To increase the odds several hundred spheres could be launched and maybe one to ten percent would catch a ride on a flare. These could reach Proxima Centauri at a much faster speed and scout out the system. Possibly the same could be done when reaching Proxima as the red dwarf flares almost continually and may slow the sphere enough to bring it into orbit. The questions is the magnetic and electric properties of the sphere?

    • Paul Gilster July 28, 2020, 5:11

      More on that question in the next two articles. It’s a big one.

      • Michael Fidler July 28, 2020, 7:48

        This article came out today and is perfectly timed!

        CfA Scientists and Team Take a Look Inside the Central Engine of a Solar Flare for the First Time.

        https://www.cfa.harvard.edu/news/2020-15

        Researchers offer unprecedented look into ‘central engine’ powering a solar flare.

        Shocking Measurements
        “The team’s measurements and matching simulation results revealed that the flare’s current sheet features an electric field that produces a shocking 4,000 volts per meter. Such a strong electric field is present over a 40,000-kilometer region, greater than the length of three Earths placed together side by side.
        The analysis also showed a huge amount of magnetic energy being pumped into the current sheet at an estimated rate of 10-100 billion trillion (1022-1023) joules per second — that is, the amount of energy being processed at the flare’s engine, within each second, is equivalent to the total energy released by the explosion of about a hundred thousand of the most powerful hydrogen bombs (50-megaton-class) at the same time.”

        https://phys.org/news/2020-07-unprecedented-central-powering-solar-flare.html

        Measurement of magnetic field and relativistic electrons along a solar flare current sheet.

        https://export.arxiv.org/abs/2005.12757

        Reading the Mecklenburg paper on aerographite electrical properties as a supercapacitor the possibility that the sphere would be similar to a giant electron. This with the magnetic re-connection in the solar flare could boost electrons to relativistic energies where they can be accelerated to nearly the speed of light.

        German Scientists Develop Aerographite – The World’s Lightest Material.

        https://inhabitat.com/german-scientists-develop-aerographite-claim-it-as-the-lightest-material-in-the-world/

        • Andrew Higgins July 28, 2020, 10:59

          The idea of riding a magnetic reconnection event is intriguing, but not clear if it can be applied to macroscopic objects. The fundamental issue is charge-to-mass ratio:
          Electrons have a charge-to-mass ratio of 10^11 C/kg. For any macroscopic object—even a micron-sized grain of dust—obtaining a charge-to-mass ratio of 1 C/kg is difficult: Coulomb repulsion quickly exceeds the material’s strength and will rip itself apart. This is discussed in my JBIS paper (see Table 1 at the end): https://arxiv.org/ftp/arxiv/papers/1806/1806.07501.pdf

          Also, when looking at supercapacitors, there is a common mistake—I had this misconception myself—that they store charge and the charge-to-mass ratios can be enormous. However, the more proper statement is that dielectrics *separate* charge while keeping overall charge zero. There are devices that store charge called electrets, but again, obtaining a charge-to-mass ratio beyond 1 C/kg with electrets is very difficult.

          • Michael Fidler July 28, 2020, 23:03

            In “Low-cost precursor of an interstellar mission,” paper they do bring up the subject of the sphere becoming electrically charged in section 5.3:
            “5.3. Other physical effects on the sail trajectory.
            Quickly after submission to the solar radiation, an aerographite photon sail could become electrically charged by the solar UV radiation or possibly by the solar wind.”

            Electrolytic capacitor do become polarized. My own personnel experience on beer bottles capacitors for my Tesla coil, which ended up breaking most of the bottles when I had left them charged!
            This is the big question on how the magnetic and electrical properties would effect a Aerographite sphere. Could they be modified by doping with a minute amount of an element that could improve these properties? They also mention use of a small super capacitor to power the chip and transmitter but what if the sphere itself could be used as such capacitor?
            Travelling thru space for long periods and when encountering Proxima Centauri may charge the sphere from charge particles and UV radiation.
            There are still many effects on these spheres that need to be looked into. Modifications to its properties may be easily done by doping the graphene’s network of tubular carbon. What needs to be done now is to launch some of them and have minute instruments on board to measure the changing electric and magnetic properties under real conditions. (solar UV radiation and charged particles)
            One point that has not been mentioned in the comments is the ability to compress Aerographite to 20 to 30 times its original size and it will return to its original shape with no damage. What size would an almost empty one meter sphere be when compressed to this level? Could several thousand be put in a piggy back package???

  • Ron S. July 28, 2020, 8:09

    I certainly do hope the follow on articles answer some of the big questions. I got about 2 pages into the pre-print before growing quite frustrated at the critical issues they blithely cast aside.

    No matter whether the properties of the graphene sphere are in some fashion perfect for the application it is still quite useless. Without an *effective* payload it is worthless. If all we want is to send inert matter to Proxima knock the envelope off a junk CRT and point the electron gun in that direction. A payload free graphene ball is no better.

    An effective payload includes instruments and communications as the minimum. Even if we are wildly optimistic about its size and weight that alone dwarfs the graphene sphere and renders it superfluous.

    I am not optimistic about the material at this first glance.

    • Alex Tolley July 28, 2020, 12:55

      You could make the exact same argument about the Breakthrough Starship approach too. The challenges are daunting, maybe impossible – if you need huge laser arrays to power the vehicle, which is where most of the cost is sunk. The point of the aerographite hollow sail is that it is powered by sunlight, so in principle, if you can manufacture a large enough sphere, you can propel any sized instrument package. As the abstract states, a 5m hollow spjere with 100um thickness has a payload potential of 55g. As both force and mass (with a constant shell thickness) are dependent on the square of the radius, the scaling is simple. A 55kg payload needs a 158m radius sphere. If the wall thickness has to be increased for stiffness, say to 1mm, then the payload reduces to 5.5kg.

      It would look like a very large black soap bubble, best observed in the IR against the black of space. For stability, I would think the payload should be suspended inside the sphere behind the CG. With 3D printing, I see no need to use a constant thickness shell, but rather one with variable thickness to give it more strength, e.g. a geodesic structure with thicker ribs, but enough thickness of the skin to keep the light absorption close to 1.

      Unlike the Breakthrough Starship approach, this solar sail approach can slow down, and hence even potentially return to the solar system after many centuries. This obviates the need for a long distance communication platform if there is none available. Maybe we will really need the patience of cathedral builders for such a mission. ;)

      The questions about manufacture and real-world performance at various starting points from the sun are probably more interesting than the theoretical calculations.

      • AlexTru July 31, 2020, 2:08

        Breakthrough Starship concept also very problematic and I can bet – it will never bring promised result. So your note is correct, both approaches that do not take in account scientifically important payload are very speculative and unrealistic.

  • ljk July 28, 2020, 12:36
  • Ron S. July 28, 2020, 15:57

    “You could make the exact same argument about the Breakthrough Starship approach too.”

    I could and I did.

    “The challenges are daunting, maybe impossible”

    Indeed. That’s the point. I am not being a naysayer by saying that the paper’s authors very neatly cast aside those challenges. I look at it and I see many. Structural integrity, stability while in motion, ablation (ISM and solar wind, etc.), extreme size, effective payload size and weight, among others.

    Focusing on one critical issue is interesting but insufficient. Hopefully in the Paul’s planned follow on articles one or more of these challenges will be addressed.

    • John walker July 29, 2020, 14:48

      I agree that the article would have been more satisfying with a concrete list of basic obstacles and challenges. Two more being electrostatic charging and destructive(particularly to payload) penetrating radiation and thermals at proposed close perihelion. But, these will perhaps be elucidated in Paul’s upcoming continuation on this interesting topic.

  • charlie July 28, 2020, 16:43

    I confess that I’m totally mystified by the idea that you should put your sail in the form of a sphere to make the voyage to another star system. According to what I understand, this entire idea is you would place the object that would do the scanning and evaluate the new star system into the center of the sphere as it was going on it’s passing voyage to get accelerated by the sun.
    Is that my understanding of this particular idea?
    And how would a sensor that is supposedly in the center of the sphere be able to do its readings of the new star system to actually function? Finely as a last question what would prevent the arrival of the so called sphere to actually be deaccelerated at the new star system using the same graphite sphere as your deacceleration system?

    • Paul Gilster July 28, 2020, 20:12

      To some extent I’ll be working on both those questions in the third post in the series. That should run on Thursday. I’ll have the second one up tomorrow (Wednesday) morning.

    • Eniac July 31, 2020, 22:44

      You are right. A hollow sphere is obviously silly, because half of it is not illuminated, thus dead weight. The right geometry is a flat sail, producing more than three (Pi, actually) times the amount of thrust compared with a sphere.

      The sail should be as thin as possible, with embedded carbon fiber strings as structural reinforcement. Like a parachute, but flat. It would be rotating to keep it spread out, and the payload would sit at the center.

      Metal nanofoil would be better than aerographite in all respects, especially Beryllium.

      • Ron S. August 1, 2020, 10:16

        Perhaps not entirely silly since inevitable instabilities in a sphere are less destructive thus giving more opportunity to safely correct during flight. The dead weight is an issue but that makes it no different from the payload itself. It’s the total mass and propulsion parameters that must be considered, that and the structure’s integrity. I have yet to see how aerographite’s beneficial properties as a sail can be effectively exploited because of its structural deficiencies.

      • Alex Tolley August 1, 2020, 12:56

        A hollow sphere has a mass 4x a flat circle, but with the same area impinged by the solar flux. So the effective acceleration of a flat circle is 4x that of the sphere.

        We should have some data based on current solar sails of the boom mass compared to the sail material. The only data I have is an estimate for components of a flat disk sail in Wright’s Solar Sailing. It looks like the non-sail material is about 28% of the mass of the sail material. If this holds for the aerographite sail, then a flat sail would be preferable to a hollow sphere sail asit is a small fraction of the extra mass of a hollow sphere.

        • Eniac August 1, 2020, 20:32

          Thanks, Alex, for pointing out my mistake with the cross section. I guess it is 4, not Pi!

          I don’t think an optimally thin sail would allow much of a boom in the mass budget. A rotating sail stretched by centrifugal force seems the best design. I see no reason at all to make it spherical.

          The trick will be to make the structural mesh strong enough to resist tearing, but sparse and lightweight enough to add only a small fraction to the sails areal mass density. That suggest carbon fiber as the right material. So, the best sail would be Beryllium nanofoil draped over a very sparse mesh made of carbon fibers, rotating very slowly to keep it spread out, but minimize tension otherwise.

  • charlie July 28, 2020, 17:01

    “Missions within the Solar System assuming such a sphere with a shell thickness of roughly 0.5 mm could, according to these calculations, reach the orbit of Mars within 60 days, arriving at Pluto’s orbit in 4.3 years. ”

    Are these missions within the Solar System to be accomplished without a close solar pass?

    • Paul Gilster July 28, 2020, 20:12

      Yes. No solar pass on these. The sundiver calculations were for a Proxima Centauri mission.

  • ljk July 28, 2020, 17:28

    Imagine the materials needed to operate a rover on Venus…

    https://www.space.com/steampunk-venus-robot-lander-nasa-jpl.html

  • Mike Serfas July 28, 2020, 17:38

    On interstellar missions one hopes not to crash, but … well, these crashes could involve a micrometer thick shell released from near Earth with density 0.18 g/L, moving at over 1000 km/s. By comparison, Hayabusa2 shot a projectile of 5 g at 300 m/s. With a velocity ratio over 30000, squared, it should take about 0.45 micrograms to get a similar kinetic energy at impact, i.e. 2 microliters of the micrometer-thick shell, or 20 square centimeters if all went well just now with my math. Hayabusa2 blasted a crater at least 10m wide and 2m deep. While the system might have some potential as a space weapon, it would be more respectable to use it as an adjunct to existing and planned research missions. What might Juno be able to detect if you could direct several of these impacts at locations of your choice during its present mission?

  • Neil Stahl July 28, 2020, 19:49

    I leave the computations to others but presumably a generation ship inside a hollowed-out asteroid inside a Behemoth black sphere would work. The outside material would need to resist whatever it might encounter on the way. Intuitively both thrust and resistance would be proportional to cross-sectional area so a giant one might be as good or bad as a chip-sized one. And an asteroid might provide what a crew would need to patch one en-route.

    If this all gets worked out we might want to set our computer astronomers to be watching for stars whose light curves suddenly dim or blink out once then come back and stay on. There could be a lot of these things out there already.

  • Alex Tolley July 29, 2020, 14:42

    Nit:

    The image caption: “scanning electron microscope (TEM)”

    should be : “scanning electron microscope (SEM)”

    • Paul Gilster July 29, 2020, 14:59

      Good catch! I’ll make the change.

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