Experimental Results for Laser Pushed Propulsion

Philip Lubin and his team are continuing to make progress toward laser pushed sails. This is a way to achieve significant fractions of the speed of light for interstellar missions and a way to beam power for movement within the solar system at high speeds.

One of the key aspects to this work is phase locking an array of lasers. There is experimental progress towards phase-locking arrays of lasers.

There have been test for phase locking a handful of lasers in the lab and there were tests to phase lock at distances up to 22 kilometers.

By 2030, the hope is to use a 1.3 megawatt system to propel a cubesat.

500 megawatt systems could be used to send human missions to Mars within 30 days.

Lubin’s preliminary calculations indicate that a 100-GW phased laser array 10 km on a side could accelerate each Starchip spacecraft to 0.2c (20 percent of the speed of light) by firing for roughly three minutes. There are other teams working on the ultralight sail.

34 thoughts on “Experimental Results for Laser Pushed Propulsion”

  1. I remember the Forgettomori story called “Laser stars laser planets.” There, it is suggested that asteroids be dropped into the sun will cause a powerful laser. The sun gets hit with comets all the time.

    Just be in the right spot to catch the photon wave

  2. I assume you'd have to have a power beamer at the other end, too.

    One nice thing about solar power satellites is that you can throw ion thrusters on them, and move them to anyplace in the solar system. So, assuming your laser array is in orbit, rather than on the ground, it's almost as easy to place one at Mars as at this end of the trip.

  3. This is a question by someone unfamiliar with the physics of laser propulsion. How do you determine the optimum frequency of lasers, and the optimum power imparted to a target laser sail? I get the "optimum reflective efficiency" the sail is composed of dictates its reflectiveness, hence efficiency. But how do you "tweak" the combination of laser frequencies, and Gwatts (or more) that let you push that sail as fast and quick as possible, as opposed to vaporizing it?

  4. Laser output has been growing exponentially for the last decade or so. I think 100GW is doable if you have the money.

  5. Capital cost of the laser source has always been the issue. For a few ships, chemical engines are good enough to go to Mars. And if you need to get there faster then nuclear engine or a nuclear reactor and some kind of electric engine is OK.

  6. Another idea: the hive mind wasn't necessarily AI based. Probably it was made of affluent human beings/transhumans merged with AIs, with the Machiavellian human brains running the show assisted with super-human AI abilities.

    AIs in that world were too rational and nice (always looking to serve and to have human contact ) to plan it themselves.

  7. Sometimes it is better to work either in arcseconds or nanoradians.  
    Somehow the tiny numbers seem less daunting. 

    I believe that the idea is similar to the 'artificial coherence star' used in very modern large astronomical telescopes having deformable wavefront correction optics… adaptive optics.  Nowadays, sodium wavelength lasers are focussed onto the ionosphere in the imaging field (actually 4 to 6 of them!); when the tight beam passes into the ionized sodium gap, it causes Na fluorescence. Down here on planet Dirt, it looks almost like a distant star.  Sodium's very specific emission wavelength allows dichroic mirrors to filter it out at high efficiency. 

    Astronomers are happy. 
    All's cool in the Observatory. 

    Thing is, if the receding interplanetary ship is reflecting a bit of the beam back to Dirt's laser orbits, the wavefront is definitely both coherent and convergent. Nice gimme, kind of for free. Now, whether all the itsy-bitsy lasers can use the µW of that back-beam to cohere in a phase locked manner, well … that's a really interesting problem. 

    Interesting 'cuz Doppler reddening will stretch things, which lasers don't like.  

    If one's transmitting laser is variable wavelength, of course it can track. But if it increases the wavelength, the reflected beam a few seconds later will also be further red-shifted. Seems like a Catch–22.

    ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  8. Oh, I don't know what to say. 

    Maybe I should pitch into all the DrPat'n'Kith bits regarding photons, and EM drives, and Wiggard-Snorkel theory or subspace monkeys.  


    And, tho' I also wasn't in the mood to cross check 'the work', I did, there is validity in the 25-to–40 day (Earth → Mars) transit idea. With reaction mass, tossed out an ion thruster, at an ISP of around 5,000, a photovoltaic efficiency of 30%, ion efficiency of 80%, a reaction-mass fraction of 80%, (75 : 25, accel, decel), 500 MW and a 25 metric ton 'payload'. The physics works out quite nicely.  Of course, all those ISP / fuel fraction / payload, megawatts are pulled directly from between my bûtt-cheeks. 

    But hey… SO ARE Lubin's. 

    Using reaction mass, as stultifying as that seems compared to pure photons, is about 3,500 times more energy-to-force efficient than using photons alone with really, really good reflective sails. The PV 'sail' collector needs to be at least 250 m in diameter; it still heats up to well over 500° K

    Ultimately, said 'rocket ship' attains about 47 km/s or 37 day per AU.
    Not bad.  

    And only 115 GWh of laser output is needed!
    Not so sure at the terminus how it slows down for an orbit insertion. 

    Oh well.
    ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  9. Part of the challenge here is the "if everything in reality is". QM purists would say that QM is an accurate measurement system, that does not say anything about the "reality" of the phenomena being measured.

    Seems like an aspect of the challenge is that "reality" is sufficiently complex that it can only be described using multiple reference frames (wave vs particle) that do not appear to be consistent with each other. However, if we see them as "just descriptions in limited reference frames" then the inconsistencies can be dismissed. Not at all satisfying, however, judging from the general results, the overall system of the universe does not seem to be optimized for producing satisfied human beings.

    And…oddly coincidental references to AI in the comments for this
    post, Wtrmute…if they ARE coincidences…

  10. The books are still very good but a bit dated in some areas, including their lack of foresight in some of them (e.g a USENET-like text based net in the first book), their over-optimism over some other technologies (dry nanotech), specially in the prequels. But Moving Mars isn't placed in the near future, but several centuries hence, so you can buy it.

    Nevertheless the widespread availability of "dry" nanotech and AI makes the lack of a faster propulsion methods unlikely.

    With those abilities, they could have built huge space lasers, fed with the Sun's light and push ships between planets at constant acceleration and arrive in days or weeks tops. Pretty much as Brian has mentioned as feasible here before. And we don't have the novel's technological miracles yet, if ever (the idea of dry nanotech is a bit passé).

    In our case, as space industrialization and settlement develop and multiply their size, we will come up with better methods for space travel due to them becoming affordable and necessary. Be it laser pushing of light sails, thermonuclear rockets or legit fusion, or several at once.

    I suspect the age where Mars trips take several months and happen every two years only will be relatively short lived in historical terms, eventually seen as a 21th century thing.

  11. Exactly, if everything in reality is standing waves in quantum fields, what does "impact" even mean? I do not think that this question can be meaningfully answered, but here are some considerations:

    1. Momentum can be (and usually is) treated as a rather primary concept, so the mere momentum conservation argument can simply be invoked: the photon had a momentum p going one way, and now has a momentum of -p going the opposite way. Because momentum must be conserved, the 2p which is required to settle this sum must have gone somewhere, and the only reasonable suspect is the sail.
    2. When talking about fermions, the Pauli exclusion principle explains why they cannot occupy the same space at the same time (while having the same quantum numbers). So the mechanisms which enforce this principle are the ones which generate the pressures (which are related to forces, which are momentum transfers) which are responsible for material object collisions. When talking about bosons, however, the concept breaks down because the exclusion principle does not apply to them. However, the same underlying mechanism may be responsible for momentum transfer of bosons during absorption and reemission.
  12. Good point. I didn't catch the AI basis of the hive mind, but indeed hive mind it was, with a strong AI assist. And the contrast to individual human beings was definitely part of the story and conflict. There was a fractal echo of that in the challenge of unifying the Martian planetary government, versus the independence of the BLMs. And then again in the relationship between Casseia and Charles, where Casseia wanted to maintain her independence and Charles wanted to merge. And that whole story line of Casseia taking on the brain implant to keep up with Charles, and Charles going two levels beyond that in merging with the Quantum Logic Thinker. Hmm. Greg Bear. Him deep!

    There was a very brief description of the ship to Earth having a fusion drive. The interplanetary transport time bothered me during my FOURTH reread of the book (hey, people listen to music albums over and over, don't they?), but on the latest read I just told myself, ok, in THAT universe, they somehow did not develop a decent continuous thrust engine for "zipping around the solar system like hornets". (Well, until they found a way to blow up planets.) And the travel speed was important in maintaining, as you pointed out, the cultural separation.

    My only problem with the book now is the number of places I've had to use Scotch tape to keep it together…

    Hopefully the high powered lasers in the current post will not require such ad hoc maintenance methods (attempt at getting back on topic…)

  13. Mostly option 2
    When your hand touches a table how is the force transferred to the nuclei? It is via electromagnetic actions with the electrons in the orbitals around the nuclei. Light hitting a mirror is reflected by interactions with the electrons in the mirror which in turn interact with the nuclei of the atoms.

  14. Pretty cool if they would be able to phase lock multiple lasers. It may open up to really powerful laser beams for weapons systems. Killing is bad, but if you really have to do it, why not do it in high tech manner?

    Though, I have a hard time seeing how this could be used to minimize the beam divergence meaningfully when considering the distances here. Comparing the phase control required for power beaming that requires about 0,01 degrees of phase control over a distance of 12000 km, you would need about 1500 lower beam divergence to power the sail for 1 minute only. I.e. about 0,000007 degrees of phase accuracy.

    I am not sure that is even possible of optical sources. Furthermore, the phase noise has to be less or equal to to this value. Again unsure if this is possible…

  15. Earth's populace was gradually and pleasantly falling into the grip of hive-mind sentient AIs, fostering in the background a mindset favorable towards shared minds, to erase relevant dissension and have a single shared view for all the consciousnesses in the solar system. Remember the friendly girl fully wired into the net on her head and the Gaia worship game Casseia participated in. Those games and ways of life were made possible by the AIs and brain-nanotech interfaces, and Earthlings were very much into it.

    These puppet master AIs suspected some big physics breakthrough was overdue, and wanted to make sure all of humanity was under control before it happened.

    Mars was a thorn in their paw, because they were fiercely independent and well, settlers, rejecting things like the Earthling's trust on brain-AI fusion technologies, and the outward niceness of Earth's culture made them pretend they didn't want to control Mars. Until they dropped the pretense and attacked.

    Cultural separation is a good way to define it, but it was an inhuman hive mind in the making vs mostly human beings.

  16. Curiously the slowness and hassle of interplanetary travel are featured prominently in that book, with the protagonist's trip to Earth taking a few chapters, one onboard the ship.

    They had top notch sentient AIs, nanotech and self healing ship hulls, but it took them several months to go from one planet to another. I don't recall if the propulsion was fusion, maybe it was. But it was slow.

    That was a quaint addition to an otherwise hyper-advanced future, but I didn't mind because it made believable that Mars was still a bit outside of Earth's grip, by being just a small peripheral place compared to the Earth-Moon metropolis.

    Funnily, a prequel has humanity receiving news from a probe sent to Alpha Cen by the late 2040s, launched in the 2020s… now that's over-optimistic.

  17. Cool! They will lose me on the math, however it seems to be speaking to the same area of phenomena. The key word may be "ponderomotive". When I search on "ponderomotive photon momentum" the topics seems to be heading in the right direction. I'll dig into it more tomorrow. Grazie!

  18. Good point. The conflict in Bear's book was hinged on cultural separation, which was hinged on transportation time. On the other hand, "people" don't go to war so much as their power-maddened leaders drag them into wars. Of course, no reason we could not end up with power-maddened leaders on Mars…

  19. Actually looked into this when I was trying to figure out whether Shayer's explanation for the EmDrive made sense. (http://www.emdrive.com/theorypaper9-4.pdf)
    I've never found anyone to refute his theory, in HIS terms, but his theory depends on:
    1) believing the math (which has references), and then
    2) believing that the math actually applies in his gadget.
    How ever you look at it though, it involves photons smacking into things.

    And looking into that, I could not find any obvious papers on the subject on the InterWeb. Looked pretty hard.

    I'm sure someone has figured it out. It's probably just buried in some obscure paper somewhere, and most people say "who cares: p=hλ."

  20. the whole idea of Mars becoming so isolated from Earth that they would fall into conflict falls apart

    I haven't read the book, but that line doesn't make sense to me. People fall into conflicts with countries that are one footstep away all the time. Indeed they are probably the most common place to go to war against.
    The only rival being a civil war, where the enemy is even closer.

  21. There's a kind of quasi-anthropomorphic principle at work here, where the author has to construct a universe in which the humans and the aliens are relatively evenly matched, all within feasible technologies. Niven and Pournelle did that particularly well in "Footfall". I like Greg Bear's "Moving Mars", however the plot depends on the fact that even though Earthlings have developed utterly mind-boggling advances in nano, bio, neuro and cyber technology, it still takes eight months to get between Earth and Mars. With "fusion drives" or the like, the whole idea of Mars becoming so isolated from Earth that they would come to open conflict falls apart. Robinson handled that in his Mars Trilogy because the technology was not that far advanced, and the transport time still made sense. However, I thought Bear's universe in that story was incongruent on the space travel issue.

    Of course this is completely relevant, since after all we are talking about interplanetary space travel, and there's this guy who seems to be sneaking right up on it in the near future…

  22. I'm not the person to ask, but I'd start by looking at the magnetic and electric field fluctuations that a photon actual consists of, and how those fluctuating fields would apply forces to a charged particle.

  23. Annoying question: exactly how is force/momentum transferred from a photo to the material in a light sail? And I'm NOT asking for the formula that MEASURES the transfer of momentum, that is p=hλ.

    Something has to make the atoms in the sail move the hadrons in the nuclei have to gain momentum from the impact of the photons.

    Two options that I can see:
    1) Photons impact the hadrons in the nuclei directly. No clue about that possible physics. What energy levels would be required?
    2) Photons interact with the electrons in the electron shells. The photons somehoe distort the electron orbitals, which then push on the protons in the nuclei.

    Can anyone "shed light" on this?

  24. Don't think we are going to see a 100-GW laser anytime soon. That's anti-ballistic missile tech..

  25. Not my favorite depiction. Made the Moties look foolish. Admittedly, the one doing it was crazy, but attacking the aliens wasn't the best contingency plan. A few explosives to destroy itself would have done a better job for revealing less.

    IRL big lasers for interstellar ships would be like beacons making a star suddenly more luminous in a narrow angle of the sky. Same for serious fusion and antimatter torches, being visible for several light years.

    Launch several starships in a cosmic quest of knowledge, and you'll put under warning a lot of places. Better launch something smaller and more discrete to make a survey of the target system and send data back through the solar gravity lens.

    Earth itself is pretty visible, and it has been reflecting the Sun's light with life's signatures for several billion years. If we haven't been visited yet, it's probably because there's no one interested in a good radius.

    But hey, probably the ancient astronauts theorists have a point and we have been visited. They just left after lingering for a while.

  26. Well, the Moties got to the New Scotland system with that technology. Didn't do them a lot of good because they didn't have an effective plan for dealing with a technologically advanced civilization on arrival.

  27. I'd be interested to know what's going on with folded beam momentum exchange for orbital vehicles.

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