≡ Menu

Going Interstellar with a Laser-Powered Rocket

As far back as the 1960s, aerospace engineer John Bloomer published on the idea of using an external laser as the energy source for a rocket, using the incoming beam to fire up an onboard electrical propulsion system. And it was in a 1971 speech that Arthur Kantrowitz, looking toward the technologies that would succeed chemical rockets, suggested using lasers to heat a propellant within a rocket. This is laser-thermal propulsion, in which hydrogen (the assumed propellant) is heated to produce an exhaust stream. The hybrid method would be studied extensively in the 1970s.

So when Al Jackson and Daniel Whitmire took up the idea in a 1978 paper, they were in tune with an area that had already provoked some research interest. But Jackson and Whitmire had ideas that would refine the ramjet design introduced by Robert Bussard. They were pondering ways to power a starship, one that would carry its own reaction mass. Uneasy about the core Bussard design, the duo had, the year before, published on the idea of using a laser to augment the ramjet. Bussard sought to ignite fusion in reaction mass gathered by a magnetic ramscoop, gathering its own fuel as it roamed the galaxy. It was a dazzling idea, but problems had soon become apparent.

Image: Al Jackson, whose laser-powered ramjet and laser-powered interstellar rocket concepts, developed with Daniel Whitmire, refined the Bussard ramjet design and illustrated its shortcomings.

For the Bussard design, as we’ve seen not long ago in Peter Schattschneider work with Jackson (see John Ford Fishback and the Leonara Christine), runs into serious problems, including igniting the proton/proton fusion reaction Bussard advocated. We would go on to learn that the vast magnetic ramscoop of the ramjet generates far too much drag to be practical.

So Jackson and Whitmire proceeded first to come up with a laser-augmented ramjet that applied beamed energy from a transmitting installation in the Solar System, one that would interact with hydrogen collected by the starship ramscoop. They then turned their attention to beaming energy to a craft that operated using its own reaction mass rather than mass drawn from the interstellar medium.

It’s that latter idea that has the most resonance. Robert Forward in this period had been talking about beaming laser energy to space sails. Now the laser idea goes into the service of a hybrid propulsion concept that loses at least one Bussard showstopper. I’ve described Jackson and Whitmire’s idea in the past as ‘rocketry on a beam of light.’ It’s an ingenious solution, even if it does not permit us to leave the propellant behind.

Image: Daniel Whitmire, collaborator with Al Jackson on the laser-powered interstellar ramjet and rocket concepts, and author of important work on Carbon Nitrogen Oxygen cycle (CNO) fusion possibilities for the ramjet. Credit: University of Louisiana at Lafayette.

And it’s this ‘laser-powered rocket,’ as opposed to a ramjet, that should get more attention in the community than it has, given that subsequent studies of the interstellar medium have cast doubt on how even the most efficient ramscoop could collect enough reaction mass given variations in the distribution of hydrogen in the galaxy. In other words, you might have to get up to relativistic speeds in the first place just to ignite a ramjet, if indeed it could be ignited, and you would have to reckon with varying supplies of interstellar material along the way. Poul Anderson’s wonderful take on the interstellar ramjet in Tau Zero (1970) becomes highly problematic!

The laser-powered interstellar rocket contains the added advantage of being able to accelerate not only away from the laser beam but towards it, for the beam is conceived purely as an energy source, not a source of momentum. This has immediate benefits in mission planning. One of the great challenges of interstellar flight is that once you’ve managed to get your craft up to relativistic speeds, you’d like to do more upon arrival at destination than simply blitz through a planetary system at 20 percent of c. The laser-powered interstellar rocket, however, operates efficiently in both acceleration and deceleration phases. No need for Robert Forward’s ‘staged sails’ when using this take on a starship, or for the deployment of a magnetic sail as a brake.

Image: Laser-thermal propelled spacecraft in Earth orbit awaiting its departure. Credit: Creative Commons Attribution 4.0 International License.

The history of interstellar studies has involved conceiving of ideas that do not break physics and then probing them to find out whether they work. Like the original Bussard ramjet and so many of Robert Forward’s ideas, Jackson and Whitmire’s concept is highly futuristic, but I love what Al said in a reminiscence on the matter in these pages: “The importance is in showing that the physics allows an opening for the engineering physics. There is no exotic physics here, only – so to speak – exotic technology.”

I sometimes forget how venerable some of these ideas are, for even while Jackson and Whitmire were doing their work on laser beaming variants to adapt the Bussard design, George Marx had already published a paper in Nature in 1966 with the provocative title “Interstellar Vehicle Propelled by Terrestrial Laser Beam.” Laser lightsails were under active discussion, and now there was a laser rocket. We have had half a century to ponder these ideas, and I see that another variant on beaming power to a spacecraft with onboard fuel has just emerged. While it’s a system advocated for fast transit to Mars, it plays upon motifs that can turn interstellar.

In a paper appearing in Acta Astronautica, lead author Emmanuel Duplay (McGill University, Montreal) and colleagues take a near-term look at what such methods can achieve. But they also give a nod to interstellar prospects, pointing out that trends like the emergence of inexpensive fiber-optic laser amplifiers and the possibility of phase-locking large arrays of such amplifiers to operate as a single element are now under active study. Moreover, adaptive optics methods can smooth beam distortions if moving through the atmosphere, allowing such an array to beam energy to a spacecraft from the surface of the Earth. Long-term, a space-based array offers huge advantages, but deep space missions do not depend on this.

Indeed, the new work responds to a recent NASA solicitation looking for propulsion concepts for rapid interplanetary missions capable of making the Earth-Mars crossing in no more than 45 days, and reaching a distance of 5 AU in no more than a year, or 40 AU (in the realm of Pluto/Charon) in no more than five years. As Mars is a feasible target for human crews in the not distant future, such a capability would mitigate the risk to astronauts of exposure to galactic cosmic rays and dangerous solar activity.

I’m intrigued by the idea that beamed propulsion can become a major factor in creating a system-wide infrastructure, one that will along the way develop the needed technologies for missions to another star. So in the next two posts, I want to turn things over to Andrew Higgins (McGill University), who is at the heart of the work in Montreal. Rapid transport to Mars is the baseline design here, but it’s a metric that not only allows us to compare competing propulsion methods but also look ahead to the deep space missions it enables.

The Jackson and Whitmire paper is “Laser Powered Interstellar Rocket,” Journal of the British Interplanetary Society, Vol. 31 (1978), pp.335-337. The Bloomer paper is “The Alpha Centauri Probe,” in Proceedings of the 17th International Astronautical Congress (Propulsion and Re-entry), Gordon and Breach. Philadelphia (1967), pp. 225-232. The paper we’ll look at next is Duplay et al, “Design of a rapid transit to Mars mission using laser-thermal propulsion,” Acta Astronautica Volume 192 (March 2022), pp. 143-156 (abstract / preprint).


Comments on this entry are closed.

  • James Franklin February 15, 2022, 12:05

    Interesting reading, and interesting engineering. Personally, I am unsure how efficient or practical many of these ideas are, but unless we do the hard part and think about them, and maybe build a few prototypes, we will never truly know, Lightsail is a prime example.

    For interplanetary mission, at present, we need to change our entire thought process. Elon Musk has it woefully wrong with Starship, we need to be building interplanetary craft in orbit that simply do the Journey too and from. By constructing in orbit they can be heavier than anything launched from the surface, they can have real shielding to protect the crew and there propulsion systems can be significantly bigger as a result.

    Then we need to develop a reusable way to get from Orbit to surface and back again – a nut we have cracked, just needs adapting and modernising.

    Before we consider Inter-stellar, we need to seriously crack the interplanetary nut, some of the technology will clearly bleed over from one to the other, and sending out unmanned probes with innovative prototype propulsion systems is a good call, but humanity needs to come together, this is not a national issue, it should be a humanity issue. Long gone are the days when the notion of a national space agency made both financial and engineering sense, we need an International Agency that can pool finances, pool both human and materials resources and work together to take us truly forward – because the piecemeal approach will simply not do the job.

    • Alex Tolley February 16, 2022, 13:40

      Elon Musk has it woefully wrong with Starship, we need to be building interplanetary craft in orbit that simply do the Journey to and from. By constructing in orbit they can be heavier than anything launched from the surface, they can have real shielding to protect the crew and their propulsion systems can be significantly bigger as a result.

      I tend to agree that the operational model for spaceships should be oceangoing ships. Very large, only suited to operating in their environment. Using shuttles and other means to embark and disembark. SpaceX seems to be thinking more of the passenger aircraft model, one that seems to have been accepted by the countless SciFi movies and stories. Heinlein and Bradbury’s rocketships are his model, but with 2 stages for Earth to Orbit, and refueling in LEO for interplanetary flight (to Mars).

      Although Starship looks large by comparison to Apollo and Soyuz era craft, it will look positively small and frail compared to the spaceships of the future, like 15th-century sailing ships compared to ocean liners and cruise ships. Clarke’s description of Galaxy and Universe in 2063: Odyssey 3 are a direct descendant from the atomic pure-space ships that the BIS envisaged and Clarke popularized from his earliest non-fiction books in the early 1950s (e.g. Interplanetary Flight (pub. 1950)).

      However, spaceliners will need infrastructure at each end of the journey, possibly space stations, certainly ground-to-orbit shuttles, and most likely refueling facilities. That is a lot to put in place early on. It may well be that the aircraft operational model is more suited to the early era of spaceflight. Think DC3s operating anywhere there is a flat area that can be used as an airstrip.

      I would also point out that the convenience and speed of air travel have pretty much obsoleted oceangoing passenger liners. Today cruise ships are their legacy, with container ships as the dominant large ocean-going vessels.

      (One can only imagine if air travel had remained dominated by airships how a mature system would have evolved – jetways to the gondolas once moored?)

      Lastly, the requirement of the separation of shuttles and spacegoing liners is a feature of our current propulsion technologies. If spaceships were able to land and take off as gently as soap bubbles, avoiding the need for shuttles, then the operational model would again look more like civil airliners (and previously airships). I don’t anticipate such a technology, but only to illustrate that our ideas tend to be anchored to available technology. At the moment, it appears that spaceliners will be built in spacedocks and likely use some form of nuclear propulsion with Newton’s 3rd law as the mode of propulsion. It is possible that the energy to power these ships will be beamed rather than having the power onboard except as backup for maneuvers and emergencies, although I expect that really long flights to the outer system will require the ship to be self-contained. [Back when solar power satellites were a big thing, I recall seeing ideas for aircraft to be powered by microwaves beamed from space, and able to use the air as the working fluid for propulsion. Such aircraft could, in principle, stay aloft indefinitely, and require no fuel. Obviously, that idea went nowhere, but I do wonder if it might be revived with laser beaming technologies when it becomes cheap and widely deployed. It would overcome the battery range problem for carbon-free flight.]

    • Parker February 16, 2022, 17:42

      What you were talking is a mature space industry, get resources from entities without deep gravity well, build spacecraft never visiting the planet surface. It’s all great and beautiful.

      And Starship is the ONLY means IN SIGHT to jump start that.

      • Deanna Shaw February 17, 2022, 2:04

        I agree with Parker. Plus the Space X Falcon Super Heavy can hurl, what …..93? ….. tons into LEO per launch.

        So if we want a 1000 ton interstellar ocean liner assembled in LEO? Contract out the Super Heavy for a dozen launches.

        • Alex Tolley February 17, 2022, 11:12

          One needs to put 1000 tons lliner into perspective. It is the size of a Corvette class ship. Granted it is made of thick steel, and a spaceship could have a lighter construction. The Hindenberg airship was about 220 MT, and a Boeing 747 190 MT. (Both are largely made of aluminum alloys. By contrast, real ocean liners like the QE II are about 70,000 mT. Even paring that down with lightweight construction suggests a vessel of far greater mass than 1000 tons.

          For fictional spacecraft, a fan site suggests the Discovery from 2001: ASO is about 5400 MT, although no indication if that is dry or wet mass.

  • Alex Tolley February 15, 2022, 15:01

    Interstellar rockets, or whatever power source, still are subject to the rocket equation. So a vessel that reaches some fraction of lightspeed will need exhaust velocities comparable to some fraction of c itself. Solar thermal won’t cut it, even at the relatively high Isp of 3000s that the Duplay paper hopes may be possible for the Mars trip – the exhaust velocity is 3 orders of magnitude too low. Some form of electro-magnetic acceleration is needed, but on the scale of a small accelerator – a “table top” LHC if you will. Are there any designs that might fit the bill, given the energy supply?

    The second issue is that the laser light will be far more diffuse at the target star. All the beam phasing will not prevent this from happening. Either the collector will have to be much larger, or the beam intensity increased to compensate, or…

    What caught my eye in the Duplay paper was the note that the mirror collector may be less effective than other types of collector to convert the light to electricity and use that to heat the propellant. The mirror struck me as rather fragile and sensitive to orientation, while a collector that converts the light to electrical energy is going to be less sensitive, and the energy can also be stored and used intermittantly if required.

    • Brett Bellmore February 15, 2022, 20:27

      It seems unlikely, though, that enough energy could be locally stored to matter in the context of interstellar propulsion. Batteries probably aren’t going to be any more energetically dense than rocket propellants, or they’d be used AS rocket propellants, after all. Maybe energy could be stored in nuclear isomer transitions, there are two or three known that can store amounts of energy more on a nuclear than chemical scale for significant periods of time, but we have no known way of reversibly and efficiently storing energy in this form.

      And any energy storage mechanism would compromise your mass ratio.

      The proposal for a combined EM and particle beam, with each component focusing the other, and the difference in velocities between the two suppressing instabilities and aiming jitter, seems promising. It suggests that we might be able to provide a beam that would not diverge, and which supplies both energy AND reaction mass.

      It might even be possible to use traveling wave accelerator technology to use the beam to provide thrust in both directions, without having to terminate the beam, allowing one beam to propel multiple ships.

    • Andrei February 16, 2022, 19:15

      Having a LINAC for propulsion of one interstellar craft have been among my favourite ideas for a very long time. Not because it currently seem doable. The way we currently manufacture such magnets make those very heavy, and such a drive system end up with a mass in the mass of hundreds or even thousands of tons. Which completely offsets the incredible (potential) ISP such a drive might have.
      So the accelerator need to be built in lightweight materials, and with super conductors, and the spacecraft will have the look of some of those fancy illustrations extremely stretched out. One advantage could be that the nuclear reactor that power the thing could be placed in the furthest end of that structure and so at least save a bit of shielding on that part.
      So it’s one idea I like, but only have mentioned in a few verbal discussions, this since while it got a fantastic potential, there’s remain a number of obstacles that is unsolved.

      • Brett Bellmore February 16, 2022, 21:39

        I was thinking more of a traveling wave tube accelerator. As I understand it they don’t actually require much in the way of magnets if they’re straight, just a bit of axial field to keep the particles centered.


        The notion was that if beamed power was used, it could be directly coupled into the tube without any conversion, saving a huge amount of weight.

      • Randy Chung February 17, 2022, 13:35

        Take a look at US patent 10,772,185.

  • Geoffrey Hillend February 15, 2022, 17:14

    It isn’t just the specific impulse that is the problem, for it is also the type of engine. If it is only a liquid propellant, which is heated and sent through a combustion chamber like a nuclear rocket engine, then we need to have to carry too much propellant with the ship. The VASIMR uses radio waves to heat and ionize gas and get a high specific impulse. Using a laser to heat up gas and have a magnetic field for a nozzle would be like a copy of VASIMR.

    I wouldn’t know how to fix that problem, but a laser beam rocket propulsion might work if it is strong enough and you could keep the thing firing for a long time.

    • Alex Tolley February 16, 2022, 0:42

      The VASIMR engine is claimed to have an optimal Isp of 5000s. However, the “39 days to Mars” vehicle supposedly requires a 200MW nuclear reactor. If so, it is impractical without a very high power/mass ratio. Even beamed power might have a problem reaching the needed power/mass ratios.

      What I find interesting is that this STR design has a far higher Isp that is traditionally assumed for such designs. usually using mirrors to focus sunlight, somewhat in the range of 10x those earlier design ideas. The energy comes from the focused 10MW laser and the rocker chamber that is designed to handle the needed heat and pressures.

      • Geoffrey Hillend February 16, 2022, 18:08

        I thought it was 400MW. A strong thrust still requires the need to carry a lot of propellant especially if one is using a conventional rocket. Using a laser to heat fuel and push it through a combustion chamber is similar to a nuclear thermal rocket. The problem with these is the although there is more thrust than a VASIMR, there is not enough to launch it off the ground. The same would be true of a laser heated rocket. There is a lot more thrust when fuel is burned with an oxidizer or liquid oxygen which is why Saturn V had so much thrust or even just a single stage Atlas which sent John Glenn into orbit. Having to use an oxidizer of course means twice as much propellant is needed. Other technology like solar sails and laser beam acceleration avoids the problem of having to carry a lot of propellant mass, but not slowing down to stop at the destination.

        • Geoffrey Hillend February 17, 2022, 17:34

          Pardon me for the mistake. VASIMR needs a 10 to 20MW of power to get the highest ISP.

          • Alex Tolley February 17, 2022, 21:26

            Multi-megawatt nuclear reactors are well out of the range of any development for space applications. What is needed is a space version of the small nuclear reactors that generate 10-100 MW of electrical energy. So much less massive, but with radiators to dump the excess heat. The Russians talk about such power plants, but until one is demonstrated…

  • Michael February 15, 2022, 18:02

    Perhaps instead of using hydrogen to thermalise we use a large number of mirors or metastable particles stored on the craft. The external laser light is bounced between each mirror or group of particles which provides the acceleration.

  • Andrew Higgins February 15, 2022, 19:09

    Alex: The issue with a collector that converts laser light to electricity is that photovoltaics are temperature sensitive, and lose efficiency quickly as they heat up. Current photovoltaics are limited to about 10 suns, beyond which they cannot generate electricity.

    A photovoltaic must absorb the laser photons and—at best—convert ~50% of them to electricity; the rest go to heat. The inflatable mirror collector, on the other hand, either reflects the laser photons or is transparent to them.

    The 10-m diameter inflatable mirror collector should be able to tolerate 100 MW, which is about 100 suns of average flux. (See Section 3.3 of our Duplay et al. paper for detailed calculations of how much flux the inflatable mirror collector can tolerate.) This greater flux directly translates into greater thrust.

    • Alex Tolley February 16, 2022, 1:04

      You are quite right that PV arrays are temperature sensitive. However, there are solutions:

      1. Use very lightweight PV arrays that have a much larger collection area and a beam that is less focussed, so that the energy is distributed over a wider area. A 30 m diameter PV array reduces the laser energy to 10 suns. Whether that is achievable with the needed mass and conversion efficiency, IDK. Probably not with today’s technology.

      2. Use a different beam type, e.g. microwaves, and a rectenna – but again that needs to be lightweight. The power/mass ratios are of the same order as PVs from the limited research I have been able to do in the past, but I am always open to new information and surprises.

      I do like that your paper is looking at beaming energy for propulsion. Even if the design proves too difficult, we know that the phased laser arrays have different uses, as Lubin always points out (and some he avoids mentioning).

      Lastly, the design uses a very conventional inflatable mirror (I think I have seen that design shown at Glenn). However, there are other possibilities that allow for flat surfaces to be used:

      1. Fresnel lenses to focus the beam.
      2. metamaterials to reflect/refract light
      3. Holographic mirrors (Idk if they work or are just fanciful ideas)

      • Michael February 17, 2022, 12:37

        Would it not be better off to use the laser light directly and take advantage of photon bouncing rather than heavy PV cell and engine luggage. The reaction mass is the mirrors which can be made to what ever size they need to be, a 100 MW laser bounced several times between the ejected mirror would generate a very high specific impulse.

        • Alex Tolley February 17, 2022, 14:29

          I think you are describing a photonic drive where one mirror is fixed at the base where the laser is beamed, and the other on the ship. The laser light is then bounced back and forth between the 2 mirrors pushing the ship with multiple times the laser force.

          The issue with this is that the mirror on the ship must stay exactly aligned with the base and not move. Any tracking loses the prior light bounces. Easy to show in a lab, but much harder to do (if even possible) in a ship moving in a curved orbit (elliptical or hyperbolic).

          Are we talking about the same concept, or have you something else in mind? [Did you suggest this as a way to store laser light energy on the ship by trapping the light between 2 mirrors in some way, on another thread?]

          • Michael February 17, 2022, 17:17

            The laser light is shone from the ground and is reflected onto a mirror which is on the main craft. The craft mirror reflects the laser light onto very thin mirrors that are ejected from the back of the craft. The ejected mirrors allow light to be reflected back and forth negating the need to go back to the earth as they are pushed away. This closeness of the ejected mirrors to the craft allows very high bounce rates and these very thin mirrors can handle 100 of thousands to millions of g’s. Kare wrote a article about micro sails a while back, I will need to find it again.

            • Alex Tolley February 17, 2022, 21:19

              I get it now. So the propulsion is photonic, but the reflecting mirrors are close by. I suppose alternatively the force on a mirror could be allowed to increase and that mirror released as a “propellant” providing thrust.

              If you have the Kare link or even a rough title, that would be interesting to read.

              • Michael February 18, 2022, 9:28

                That is how it will work, the ejected mirrors are the propellant or reaction mass and the laser provides the energy for ejection.

            • Michael February 18, 2022, 3:35
              • Alex Tolley February 18, 2022, 11:25

                The sail beam is not photonic propulsion as I visualized from your comment, but rather more akin to a “particle beam” composed of micro-sails ~ 1 mm in diameter and accelerated by laser so that they impact on the vessel to transfer momentum. A far easier solution to develop than a photonic drive where the laser light bounces back and forth between 2 mirrors increasing the separation force between them.

                • Michael February 18, 2022, 18:29

                  Much easier than you think.


                  • Alex Tolley February 19, 2022, 11:37

                    As I have said before, easy to demonstrate the principle in the lab where the mirrors can be kept perfectly aligned, but it is very different when in space when the mirrors are not so constrained. Had the lab demo been done on a tabletop allowing 2 dimensions of travel, rather than one, would it still have worked, or would small asymmetries in beam incidence have quickly stopped it from working?

                    I had read Bae’s paper on photonic propulsion:

                    Prospective of Photon Propulsion for Interstellar Flight
                    DOI: 10.1016/j.phpro.2012.08.026
                    Young Bae

                    • Michael Million February 20, 2022, 2:23

                      Alex with an acceleration of say 32 million g’s the distance between main mirror and ejected mirror is tens of meters and milliseconds. Remaining on stream can be more easily done with retroflective ejected mirrors or diffraction grated design to stabilise them.

                    • Alex Tolley February 21, 2022, 11:36

                      Where did you get the figure “32 million g” from? Is that a reference in a paper of a realistic system? Intuitively, that high figure suggests that even the slightest asymmetry of light over the surface will break either/both the “propellant” or main spacecraft mirror.

            • Michael February 18, 2022, 13:54

              I see where I went wrong

              ‘The laser light is shone from the ground and is reflected —onto—(should be by) a mirror which is on the main craft. The craft mirror reflects the laser light onto very thin…’

  • Michael Fidler February 15, 2022, 21:26

    I have heard so many ideas on how to get someplace quickly in space but none have ever been tested in space. We need to develop a contest to see who can reach the moon the quickest, like the air races before WWII. If someone gets in trouble not to difficult to rescue them and all the kinks and problems could be worked out in earth orbit. Unmanned first then manned mission contests. This would keep cost low and any type of propulsion could be used and would be open to world wide compatition. Keep it simple, with the spacecraft just desinged to swing around the moon then back to earth. The public would love it!

    • Deanna Shaw February 17, 2022, 2:28

      That’s a great idea, Michael…. let’s get Space X and Project Break Through to cosponsor. Launch about a dozen all at once into LEO with a Falcon Heavy. Have them take off for Luna all at once, maybe the Fed’s will ante up a $10 million prize to the winner.

  • Robin Datta February 16, 2022, 3:51

    All the ideas to throw energy at a vehicle to make it move might seem to an advanced scientific-technological civilization as makeshift arrangements. The real breakthrough would be the design of an effective containment vessel for the fusion reaction. The only effective artificial containment so far has been the force of a fission explosion.

    Nature does the trick with gravity of a sufficient magnitude in stellar reactors; gravity augmented with fission and fusion energy cooks up elements heavier than iron (and also makes neutron stars) in nova and supernova type of explosions. The containment vessels are force fields: shaping them to an effective but manageable scale is such a big problem because our know-how in manipulating force fields is not up to par with the requirements.

    • Michael Fidler February 16, 2022, 10:12

      Well, any advance civilazation is going to be jumping in and out of five dimensional space were all the dark energy exist. They understand the yin/yang of the electron/positron and the curvature of the wormhole thru spacetime. Our firecrackers are just that; a childs play thing.

  • Jeff Wright February 16, 2022, 4:35

    Perhaps pre-positioning ice units for the laser to pulse against as your clean Medusa sails by?

  • Taylor February 16, 2022, 17:43

    How would this be more efficient than say a nuclear thermal engine? It just seems like a nuclear engine with a lot of extra steps and it seems unclear how it’s more advantageous.

    • Alex Tolley February 17, 2022, 0:26

      The mass penalty of the nuclear engine plus shield is higher than the mirror. NTRs have an isp of ~ 1000s. The paper indicates that gas core nuclear engines have an Isp around 3000s. The claim is that the LTR might have a similar Isp to the gas core engine, which would reduce the propellant mass by 2/3rd compared to an NTR. But the engineering devil is in the details. As the paper notes, their reference design makes it very hard to thrust in a direction away from the beam direction. The design needs more optical components to handle this, which is handwaved away until more detailed designs can be made.

      The other issue with an NTR is that if anything goes wrong, the crew cannot go near the engine. It is permanently off-limits. That makes reusability problematic. The engines may need to consume the nuclear fuel and then the whole engine is disposed of and a new one replaces it. The LTR theoretically allows for engine maintenance. The LTR shouldn’t have any environmental issues with the launch, unlike the care an NTR requires to be safely launched.

  • Keith Hali February 16, 2022, 20:43

    I’m very much a layman, but ISTM that this earth-based 100MW launch system with adaptive optics could do some rather nasty work on objects much closer by than Mars.
    I’d be surprised if DoD or DARPA weren’t working on something like this.

    • Alex Tolley February 17, 2022, 11:24

      They are. Lubin’s phased laser arrays are pitched to the DoD for planetary defense against asteroids. Pushing light sails is just another use that appeals to the space community. I have no doubt that the military has plenty of uses for very high-power laser arrays, although if they are in a fixed location, very vulnerable to attack by a range of weapons. The US “Star Wars” program in the 1980s included ideas for space-based lasers although these were never developed AFAIK.

    • Mike Serfas February 19, 2022, 10:48

      I’m afraid the situation is comparable to Project Azorian ( https://www.npr.org/sections/parallels/2017/09/18/549535352/how-the-cia-found-a-soviet-sub-without-the-soviets-knowing ), in which Howard Hughes and others feigned an interest in mining manganese nodules. There are still exploratory projects for such mining to this day, but the only practical thing that came out of it was a Soviet submarine.

      I’m reminded of Dyson telling a student to work on surveillance drones. In twenty years, there might be a few interstellar exploration projects … but around the world, hikers in the wilderness who might want to pee behind a bush will have a surveillance drone ready to put them on a sex offender list for life for exposing themselves to it. Where will the ambitious students make their careers?

      • Alex Tolley February 19, 2022, 12:56

        I think seabed mining for metal nodules has gone beyond exploratory.

        Race to the bottom: the disastrous, blindfolded rush to mine the deep sea

        Surveillance is a very 2-edged sword. From proponents like “Mr. Transparency” David Brin to the dystopia of 1984. Bob Shaw’s “The Light of Other Days” about “slow glass” was extended, IIRC, to where the world was covered in microscopic slow glass beads that would “record” everything happening on the planet, the ultimate panopticon. I am glad to see that there is legal pushback against surveillance, from the use of [flawed] facial recognition to malware on phones. However, I fear it is unstoppable, simply because it is too cheap and easy (e.g. cloud storage of Ring doorbell events and other similar products, that can be accessed by US law enforcement w/o a warrant) and the cameras are getting ever smaller and unobtrusive.

        • Mike Serfas February 21, 2022, 9:32

          The message I take from that article is that no such mining has occurred, and regulators want two years to decide if it is allowed before it is even contemplated. The histrionic tone of the article grates on me – it’s not that I think mining would occur without harm, but I don’t believe their concern about keeping one of the planet’s largest biomes entirely unspoiled while miners on the surface compete directly against protected reserves and ecological treasures. I suspect the real fear is not of ecological damage but of competition, or perhaps merely of giving more entities an excuse to deploy restricted technologies for viewing or manipulating objects deep in the ocean.

          The issue with surveillance is more than merely the availability of the technology. The practice has in theory a brother, sousveillance, in which those with less power observe those with more power. But sousveillance faces altogether a different reception! For example, if someone makes a device that can use terahertz to image inside objects, bodies, and clothes, it is widely deployed (indeed, the basis of ubiquitous 5G) so long as the right people see the signal – but for ordinary people to obtain scanners that would let them see others naked or in any other way to observe the hidden goings-on around them would be altogether a different matter! The technology may be widely available, but it is just as widely unavailable.

          • Alex Tolley February 21, 2022, 15:06

            A less “histrionic” academic review article on seabed mining.

            An Overview of Seabed Mining Including the Current State of Development, Environmental Impacts, and Knowledge Gaps

            I would argue that this development will prove as destructive to the abyssal benthic ecosystems as commercial fishing has at other depths. The history of overexploitation, destruction of habitat, regulation, and then illegal fishing just repeats itself endlessly. It is a case of “If it can be exploited to destruction, it will be”. Extractive industries tend to operate similarly. I would bet money that the proposed seabed mining will not be stopped, even in the face of international restrictions. We are seeing the groundwork laid for the exploitation of space resources that are currently not allowed but are to be changed in the face of changed circumstances – i.e. there are now profits to be made.

            As for surveillance and sousveillance, I agree with you. Cost and regulations are always maintaining a favorable balance for the state. But as devices get cheaper, they inevitably get wider use. The recent concern that stalkers and others were using Apple’s Air-Tag devices is an example. I am surprised that I haven’t heard that criminals are planting them in police cars and other law enforcement equipment to alert them about proximity. (Maybe they already are?)

            • Mike Serfas February 22, 2022, 9:30

              That article is more scholarly, but I’m still struck by their concern for noise of ships and even the disorientation of sea birds by lighting on ships… specifically within the context of deep mining. Surely such impacts would be best handled in an across-the-board manner, without regard to the specific purpose responsible for them? I certainly don’t mean to cheerlead for the mining industry nor to suggest abolishing all sensible regulation, but I’m disturbed by what seems like a special emphasis on keeping frontiers closed – whether in the deep sea, Antarctica, the Arctic, or space. Isn’t it conceivable to expand in reasoned, sensible and fair ways?

              • Alex Tolley February 22, 2022, 13:54

                Isn’t it conceivable to expand in reasoned, sensible and fair ways?

                The oceans are treated as near lawless frontiers. Show examples where reasoned, sensible and fair has worked. Whaling still exists. Illegal fishing continues. Marine reserves to ensure breeding are invaded by the unscrupulous. New oil and gas reserves are still being exploited, even in sensitive areas like the Arctic. This isn’t new. The East India company was notorious for its abuses and control of the British government. The 19th-century railway and oil barons were the US version. Big business => big money => bribed legislators => weak laws => underfunded law enforcement. This MO applies across the poorest nations to the wealthiest. If reasoned, sensible, and fair was always applied, we wouldn’t have the various serious problems we have today. One can watch the current “water wars” playing out in California today and connect the dots.

                Is it human nature or culture? I think there are enough historical examples to indicate that it is the culture that is the main problem.

  • Andrei February 18, 2022, 10:34

    The hydrogen fluoride laser of the star wars program could have been very powerful but required a large tank for the chemicals used. But would be a first hit target for any military opponent. Regular military units rely on armour to some degree, but that’s not only expensive for space applications. Kinetic pellets sent in the the opposite direction in orbit would wreck everything but the smallest and most agile targets. Such would be cost effective also. War of the microsatellites.

    • Mike Serfas February 28, 2022, 9:05

      I can’t picture anyone putting large lasers in space. There’s nothing easier to send to orbit than light! I assume the laser arrays will end up in deep underground bunkers, with narrow boreholes to send the light to reflector satellites in orbit, using adaptive optics similar to those from astronomy to keep the beam on target. The satellites need be little more than shards of high quality mirror with a well-measured tumbling pattern (though attitude jets would be needed if you actually had a propulsion mission, or needed to bounce off a second mirror to reach sites on the far side of the world). They would need enough present in the same orbit that one of the boreholes can always line up. A basic use of the mirror system might be to send laser pulses to set wildfires in every square kilometer of a target country (reigniting them anywhere firefighters manage to put them out) before moving on to inhabited structures.

  • Andy Prada February 19, 2022, 6:38

    “I’m intrigued by the idea that beamed propulsion can become a major factor in creating a system-wide infrastructure, one that will along the way develop the needed technologies for missions to another star.”

    Certainly intriguing but how likely? Either we are alone in the galaxy (or our part of it at least) or we should be seeing at least some evidence of laser activity through our telescopes. As we aren’t i suspect it’s not a technology that was found sustainable in the long run.

    • Paul Gilster February 19, 2022, 7:18

      I’ll have to disagree. Power-beaming around other stars would only show up in our detectors as the (very) occasional inexplicable transient (of which we have many in the data). Unless a craft were headed straight for us under a power-beam, we wouldn’t see a consistent signal (shades of Pournelle and Niven’s Mote in God’s Eye, where exactly this scenario happens).

  • Michael February 21, 2022, 13:51

    Alex it is on page 7 of Kares article.