≡ Menu

Laser Bounce to the Stars

Via advanced nanotechnology, the news that the Solid State Heat Capacity Laser (SSHCL) has achieved 67 kilowatts of average output power in the laboratory. Six to eight months of additional work are needed, it is believed, to reach the 100 kW mark. Which sets Brian Wang to pondering a “…proof of concept photonic laser propulsion system using mirrors to bounce laser light and multiply the effectiveness of lasers generate 35 micronewtons of thrust using low wattage lasers and 3000 bounces.”

Wang then quotes from a paper on multi-bounce methods by Geoffrey Landis and Robert A. Metzger. A major problem in laser lightsail techniques is reducing the power requirement, which can be onerous:

It has been proposed that extremely small payloads (10 kg) could be delivered to Mars in only 10 days of travel time using laser-based lightsail craft (Meyer, 1984), but in order to do so, would require a 47 GW laser system.

And if we start thinking interstellar, the laser numbers go sharply up. We’re talking about lasers in the range of 65 GW to 7.2 TW, power levels approaching the total power generating capabilities of Earth. A limiting factor is the sheer inefficiency of momentum transfer from a photon to a lightsail. But bounce methods can dramatically alter power requirements.

The bounce method Landis and Metzger discuss seems straightforward. A laser beam sent to a lightsail is directed back to its source, from which it is reflected again to the lightsail. Landis and Metzger see the limitations on the number of bounces feasible being dictated by our ability to re-aim the reflected beam, the efficiency of the spacecraft (and the reflector at the laser site) in reflecting the beam, and the heating of the lightsail.

Can multi-bounce methods make the difference? Landis and Metzger’s conclusion: “The use of a multi-bounce approach radically reduces the power requirement of the laser system (by a factor of 1000) as compared to conventional single bounce laser sail schemes, making the possibilities of such multi-bounce lightsail craft feasible within the coming decades.”

So 67 kW for a laser in a laboratory setting is getting us into interesting territory. Wang goes on:

One thousand 100 kilowatt laser modules and 2000 bounces would be equal to a 200 Gigawatt laser. This would be 4 times the 10 kg system and could deliver 40kg payloads to Mars in ten days. Ten thousand modules would allow for 400 kg payloads to Mars in ten days.

All of which makes for fascinating reading. The Landis and Metzger paper is “Multi-bounce laser-based sails,” Space Technology and Applications International Forum 2001, in AIP Conference Proceedings, Vol. 552, with abstract here. Fortunately, the full text is also online. Interesting to study this one in connection with Young Bae’s work on laser bounce techniques as recently discussed in these pages.

Comments on this entry are closed.

  • Brian Wang March 1, 2007, 11:59

    I exchanged some info with Young Bae. He sounds confident about being able to scale up from the 10W system up to the high power lasers (a few years) and having made innovations to solve the problems that others have had implementing multi-pass photon propulsion.

    For relatively near-term interstellar usage (a whole lot/decades of engineering work) but the key would be to refine the lasers so that when you bounced them say 100,000 times between the source and end of the acceleration range (say 200,000km to 5 million km) the distance travelled after all those reflections is 20 billion km to 500 billion km). The mirrors have to also be perfected not just for reflections but for maintaining beam quality.

    Wild speculation:
    1GW arrays of lasers seem doable and if one were serious and purposely built a few dedicated nuclear reactors OR if one increased civilization power levels using interplanetary resource development over a few decades. Then some milestones for interstellar capabilities would be

    2000 bounces, 1 GW laser array 2TW equivalent, some 10% light speed small probe configurations

    10,000 bounces, 10 GW laser array 100TW, 20% of light speed, bigger probes and missions

    100,000 bounces, 500GW laser array 50PW, 50% of light speed, manned crew size vehicle. The vehicle laser material would be monster probably about 1000km. But it looks achievable with an expectation of technological progress in this century.

    A few of the first system (or one halfway to the second system) scattered around the solar system and people and things would be buzzing around all over the bouncing laser solar highway.

  • philw March 1, 2007, 13:17

    I, for one, don’t want to be standing there on Mars when that 400Kg payload arrives with velocity commensurate with its 10 day trajectory. Mars does NOT need any more craters!

  • Adam March 1, 2007, 13:39

    Nice point philw. Wow! I had no idea this system was even viable – I thought for sure the reflectivity and focus of the system would thermalise the beam in a real hurry. But Landis is the laser-sail guru and if he reckons it works, then the sky is the limit!

    Now another reason to build SPS – powering all the laser-sail shuttles around the Solar System!

  • Administrator March 1, 2007, 13:51

    Great point, Phil. We haven’t worked out the braking yet…

  • Brian Wang March 1, 2007, 14:29

    The breaking is done with a receiving laser bounce system on Mars OR you would need to carry a good superconducting magnetic sail to slow you down OR you have to bring along a drive system to slow you down OR you do not go faster than you can brake (aerobraking, whatever drive you have for braking etc…)

    I would say that you first send over the robotic parts and gear on slower trips. Bigger, slower payloads with aerobraking and whatever else you have for braking. Maybe an early package would be the nuclear gas reactors (still to be made but on the drawing board) and laser, mirror systems. Send those multi-ton packages over on 96 day or 6 month trips. Whatever you can brake safely from. Then the receiving lasers have power. Then you can do a better job of slowing in bound shipments. Then you can start sending things over faster. Go twice as slow send 4 times as much stuff. Go ten times slower and send 100 times as much stuff. The laser/mirror system is still very efficient in terms of the cost of consumables (mainly just electricity).

  • Brian Wang March 1, 2007, 14:41

    Here is an article that I just put up on braking, expanding the above comment slightly and added some more links

  • Stephen March 1, 2007, 15:36

    My telescope mirror reflects 95% of the incoming light. Do these mirrors do an awful lot better to get 3000 bounces? Perhaps my telescope needs to reflect a range of frequencies, and these mirrors only need to reflect one…

  • Administrator March 1, 2007, 16:00

    Yes, we’re talking about remarkably efficient reflectors here. A bit from the Landis and Metzger paper on this: “Very high reflectivity thin film technologies now exist which can produce reflectivities, R, for a specific wavelenth in excess of 99.9%. High reflectivity Bragg Reflectors constructed of alternating layers of thin materials, including both semiconductors and insulators (1-100 nm) with different dielectric constants can be tailored to produce nearly ideal reflectors. Such composite thin films with reflectivities of 99.95% would enable at least 1000 bounces before the power in the beam was greatly reduced due to absorption of the laser beam in the reflector or lightsail. Under these conditions, the effective power which the lightsail experiences is NxP where N is the number of bounces the laser makes from the sail. For purposes of this example, we will assume that N can have a value of 1000. This increases the effective power that the lightsail experiences by a factor of 1000.”

  • Jonathan Burns March 1, 2007, 22:45

    25 kW CW (continuous-wave) was Jordin Kare’s threshold scale for the
    lasers in his modular ground-based beam launch architecture.

    4,000 of those would make up a 100 MW array, required to orbit a
    100 kg (capsule+payload) heat-exchanger rocket.

    Fewer and more powerful lasers could be hard to build, and the array
    would be more vulnerable to unit failures; more and less powerful
    would require a major drop in the price of astronomy-grade mirrors.

    That’s according to this paper (presently offline?):

    A Comparison of Laser and Microwave Approaches to CW Beamed Energy Launch
    Jordin T. Kare and Kevin L. G. Parkin

    However, in the talk referenced below, Kare is considering 10 kW CW lasers,
    in clusters of 6 per telescope:

    Modular Laser Launch Architecture:. Analysis and Beam Module Design.
    NIAC Phase I Fellows Meeting. 24 March 2004.
    Jordin T. Kare. Kare Technical Consulting …

    So, I’ve been waiting for the 25 kW diode laser threshold for a couple
    of years, and now it seems we’ve crossed it. Now, Kare’s rough cost
    estimate for the 100 MW system was about $2 billion, and I don’t
    expect that to be budgeted any time soon; nor the US armed forces
    to turn a novel technological advantage to civilian purposes. But in
    principle, if these 67 kW lasers could be developed for long duty
    cycles, and if they could be combined with high-power heat exchanger
    experience from “5th generation” nuclear reactor research, then we
    could be on our way.

    What I haven’t seen from Kare or anyone else, though, is a plausible
    fault-tolerant space architecture, orchestrated for thousands of 100 kg
    vessels. That’s an outstanding challenge for the beam launch concept.

  • Eric James March 2, 2007, 1:13

    Whatever happened to the Magbeam concept? Is it stilll viable?

  • Adam March 2, 2007, 1:27

    Hi Eric

    Mag-beam’s viability hasn’t changed any. This new work expands the potential for in-space laser launchers, which may or may not compete with Mag-beam as a rapid interplanetary transit system.

    One problem I’ve yet to analyse is the effect of distance on the bounce rate – for constant power beaming that’s got to bring the thrust down. I’m not sure how to tackle it mathematically just yet.

  • Eric James March 3, 2007, 23:21


    Good luck with that math thing. Just thinking about a few of the variable factors boggles me. How would you even determine the acceleration rate accurately? This alone relies on the reflectivity of the mirrors and how much energy they can handle. You’d have to talk to a materials scientist just to begin a rough scratch. Incorporating a cooling system could expand the energy handling potential. How much though?

    I know that the Magbeam creator (Dr. Robert Winglee) proposed a similar reflective arrangement. I was wondering how this might work. Wouldn’t the charged particles repel each other and scatter?

  • James M. Essig December 20, 2007, 1:49

    Hi Folks;

    In the near term, certain forms of superconducting carbon nanotubes might permit huge numbers of microwave beam or perhaps even infrared laser beam bounces. In the limit that a material becomes superconducting, for certain longer wavelength frequencies of light, it becomes effectively perfectly reflective with zero skin depth. I can imagine appropriately superconducting grid like thin film materials wherein the grid spacing is much smaller than the impinging wavelength that would allow near perfect reflection of IR as long as the IR radiation is not so intense that non-linear absortive effects occur which lead to a breakdown in reflectivity. Thus, very large laser beam collection areas might be provided to collect subsequent bounces using very high mass specific reflectance power output sails.

    Suppose we were to scale the heck out of the laser bounce concept and allow for a 10 EXP 15 Watt array with one million bounces for an equivalent of 10 EXP 21 Watts or suppose we were to scale up further to 10 EXP 21 watt array with 400,000 bounces or 4 x 10 EXP 26 Watts equivalent which is the integrated solar output.

    Perhaps having a mirror coated with a very very thin-one nuetron thick layer of superconducting neutronium or an even thinner layer of quarkonium- could survive the intense radiation to allow very rapid accelleration to almost C.

    The space craft could have g-force cancellation mechanisms such as hydrostatic pressure vessels to contain the crew, magnetic fields to induce dipole moments within the ships contents, and/or nanotechnologically applied electric charge and electric fields to cancel the forces of accelleration.

    Let’s push this farther, how about after thousands or 10s of thousands of years of technical development, an 10 EXP 23 Watt array and 1 million bounces for an apparent power output of 10 EXP 29 Watts with a thicker neutronium shield if necessary.

    Let me not stop here, how about after millions of years of technological development, an 10 EXP 30 Watt array powered perhaps by some how drawing in energy from depoloarized vacuum energy fields or through the fusion of a whole lot of Oort cloud cometary hydrogen or helium and a million bounces.

    Now these examples are sucessively more extreme but, in theory, this is what this technology is capable of with the said requisite advances in materials sciences. Folks, this is awesome technology with awesome possibility of propelling mankind ever more closely to C! This is true even when considering the dopplar based losses of craft with very relativistic recessional velocities.

    If the theory of doubly special relativity or simmilar theories have any truth to them, then the higher the frequency of a photon, the greater its velocity in a vacuum. The difference in velocity for everyday observed photons from radiowaves through ordinary gamma rays would not, accordingly, be readilly detectable, however as the photon energies appraoched the Planck Energy, the associated values of C would become significantly greater than 2.998 x 10 EXP 8 meters/sec. Such an associated photon beam would not experience much loss even as the craft closed in on C due to dopplar redshifting. Moreover, the beam could experience many more bounces as the speed would be much greater than 2.998 x 10 EXP 8 meters/sec.. According to some versions of this theory, the limiting value of C as photon energy appraoches for all practical purposes, infinity, is infinite. Now finding a material to reflect even Planck Energy photons is going to be difficult but may be surmountable given billions if not trillion of years of technical development.

    Another option to power light sails is to bounce tachyons if they exist back and forth between the mirrors which would have to be tachyon reflecting. One could recieve many bounces even for small differential time elements wherein the mirrors would be lightyears apart. Note that some theories of tachyons hold that their speed can even surpass a billion times the speed of light. If the tachyon beam were activated while the mirrors where located a good distance apart in space, the tachyon beam according to some models of superluminal inertial travel through space would travel back in time as it bounced between the mirrors thereby inducing some temporally backwardly oriented temporally based casual effects on the energy gain of the reflectors and space craft possibly harnessable to increase the velocity of the space craft even further.

    Another possibility in the far distant future is to use miniature solid elastic balls of some sort of “God know what” exotic form of matter. If the collsions where perfectly elastic, then the only energy losses would be those associated with the decreasing relative velocity between the balls and the ships as the system tended towards equilibrium. If faster than light elastic balls could be used and manufactured, we could have a field day in terms of kinetic energy powered spacecraft development wherein the space craft could essentially approach C.

    That’s all for now.


  • george scaglione December 20, 2007, 14:43

    jim,real good ideas scaling up the power of the lasers could indeed only help and using exotic matter sounds pretty cool too…know why?! because my friend the more we know or can use exotic matter the better.isn’t that the stuff that we would need to hold open the throat of those traversable wormholes we’d all so dearly love to build!! can’t get over it…those worm holes and “warp drive” would just be the best possible (in my opinion) space drives we could have! lol could you call wormholes a drive!? well yes i suppose in the sense that they are a way to get from here to there REALLY fast! ideas on that anyone? your friend george

  • forrest noble December 20, 2007, 22:49

    Adam, Phil, and Paul, The best laser focus that I have ever heard of is about 2X per every 4 million kilometers. That’s the key factor in how well this system works; to Mars it would be about 2.7 million kilometers half way. That’s an effective rate of 1/10 efficiency per bounce. We could only have a couple of bounces. Clue me if there are technologies beyond this.

    Crowlspace– the same problem. It’s the dissipation of the beam. To decrease this dissipation we need a really long barrel, maybe a mile long. Like a gun, the longer the barrel and the better the focus– even with several re-focusing devisees in the middle, beaming to Mars with today’s technologies would not be efficient. Am I wrong?

    Joanthan, you are right about that — we can all dream about the future possibilities that won’t occur in our lifetime limited by our funding but maybe some of the ideas being presented here will be garnered by future generations to facilitate these ideas.

    Ike, with today’s technology, as far as I know only a couple of bounces is possible, as far as Mars is concerned, but the possibilities are out there for a series of bounces as Wang and others have suggested.

    To improve the efficiency of laser bouncing will be the key to whether lasers well be used in the first place—It seemingly is an economically feasible idea in our time, I think- we’ll find out in the next 30 years.

    OK my good buddy Jim, Carbon nanotube systems might be a good base for strength of such systems, but bounce efficiency will be the key. I also haven’t heard of the kind of efficiencies for Martian distances being discussed.

    As far as tachyons are concerned, it would be nice if they existed. It would make possibilities far different than I perceive them to be now–as for my theories, as you know everything is extremely simple, 1+1=2; maybe a little more complicated than that but not much more.

    George, I absolutely love the transversable wormhole idea– exotic matter, isn’t that the stuff that we would need to hold open the throat of those traversable wormholes. If there is any possibility to get out there, there would be a million or more volunteers like me to jump in.

    your good friend forrest, All for now!

  • george scaglione December 21, 2007, 10:37

    forrest,yes this is indeed an interesting topic and the traversable wormholes are a great idea i think kip thorne came up with them! and yes the exotic matter is what we need to build them,lol,maybe one or two other things as well! hope i hear from everybody soon your friend george

  • ljk June 6, 2008, 9:13

    Using a laser beam from a Katrina memorial to power a solar sail mission

    Research affiliate envisions towering Katrina memorial

    Anne Trafton, MIT News Office

    June 4, 2008

    After Hurricane Katrina left its trail of destruction along the Gulf coast, MIT research affiliate Joe Davis decided to do something to memorialize the hurricane victims and inspire the survivors.

    His idea? Build a tower that will capture electricity from lightning, using it to power a laser beam that throws energy back into the sky.

    The 106-foot tower would be similar to a lightning rod but would differ in several important ways.

    When lightning strikes the tower, its three vertical aluminum masts will form the electrodes of a resonant cavity that would electrically break down nitrogen in the air and trigger an ultraviolet laser discharge that sends beams back into the sky.

    According to Davis, these beams may in turn trigger powerful secondary lightning discharges; as a consequence, enormously powerful secondary laser discharges will also be produced. Davis points out that solar sail researchers await such powerful lasers to propel solar sails beyond the inner solar system.

    Full article here: