Photonic Laser Thruster Promises Earth to Mars in a Week

serutan writes "Using lasers to drive spaceships has been a subject of interest for many years, but making a photonic engine powerful enough for practical use has been elusive. Dr. Young Bae, a California physicist, has built a demonstration photonic laser thruster that produces enough thrust to micro-maneuver a satellite. This would be useful in high-precision formation flying, such as using a fleet of satellites to form a space telescope with a large virtual aperture. Scaled up, a similar engine could speed a spacecraft to Mars in less than a week."

Comments

How "scaled up" is this?

[jandrese]

Are we talking about "accidentally cut Venus in half" scaled up? Typically the downside of photonic thrust has been the low power to weight ratio, so for a laser powerful enough to propel a ship to Mars (don't forget that it has to both accelerate and decelerate) that fast I have to wonder just how powerful the laser has to be.

Re:How "scaled up" is this?

[Nefarious Wheel]

You could make a laser out of water ice in orbit to any size using fusion purification and rotation of the billet, doping with chromium or rare earths as you go. Thermal mass should keep it solid enough to pipe light through, and if it's long enough you could add energy slowly enough to pump it to some pretty fantastic numbers of photons before the coherent beam left the less-reflective mirror. Fifty metre aperture? Kilometer in length? Mine the ice from the rings of one of the gas giants and use shaped solar reflectors. You could use silicon too, I imagine, but I like ice because it's cool. Plentiful, too, once we evolve past the point of STS and SFS (Space Food Sticks).

Re:How "scaled up" is this?

[hey!]

(1) You build your reactor to tolerate running somewhat hot; granted there will be some tradeoffs that might make your 1 week outward leg a bit longer.

(2) When you reach Mars, you ditch your reactor on Phobos, which has a gravity of about 1/1000 g -- just enough to be reasonably convenient.

(3) You let it sit there using Phobos as a heat sink, then pick it up for your return journey when your mission is done.

(4) You insert yourself into lunar orbit, where you ditch your reactor for good.

(5) You take the slow boat home from the Moon.

The Warriors

[PresidentEnder]

At least now we'll have a way to beat the Kzinti when we make first contact.

I smell bullshit

[Rix]

The Bae Institute was founded in 2002 by Dr. Young K. Bae In other words, no existing institution would accept the good doctor, so he made his own, and issued a press release written in false third person.

Re:acceleration?

[AKAImBatman]

As I recall, the computations for reaching Mars in a week were predicated on One-G acceleration. i.e. Earth normal gravity for a ship in transit. To slow down, you simply spin the ship at the halfway point and accelerate in the opposite direction.

If (and I stress *if*) this invention is not so much hyperbole, it could change the face of space travel forever. We could build interplanetary starships (in this context, ships that never land on a planet) that would be limited only by their power-generation capabilities and not by their reactive fuel. Which means that we could build a ship with a large nuclear powerplant on board, and it could cruise the solar system for as long as its Uranium/Plutonium fuel held out.

Of course, we still need to solve the problem of high cost of launch, but that little issue would be easier to solve if we actually had somewhere to go once we got in orbit. Scaling up the number of launches would almost certainly bring the price per launch down. In fact, the reason why the Space Shuttle never reached its promised price-per-kilo is because it was predicated on regular launches that never materialized. Starships could change all that. Especially if the cost of moving personnel and equipment was marginalized by carrying more of them per trip.

For example, I always figured that a special module could be fitted to the Shuttle's cargo bay to carry as many as 60 people to the ISS. Given that the Shuttle has to be man-rated for flight, carrying people makes a lot more sense than hauling around equipment that's better served by a Delta or Atlas rocket.

How exciting! And probably too good to be true.

Re:Energy source?

[Arabani]

I did quite a bit of reading on spacecraft propulsion recently (specifically Nuclear pulse propulsion and basically what I got out of it is that if you have a massive energy source (say, antimatter) you're better off just blowing it up and riding the blast wave. You can get extremely high thrust AND specific impulse that way, which is not possible with almost any other engine technology (either high thrust and low specific impulse like chemical rockets, or low thrust and high specific impulse like ion engines). NPP (and its derivatives) is basically the best way we know of right now to get high enough performance for interplanetary, or even interstellar, missions.

NPP originally started with using nuclear explosions, but more recent research has focused on inertial confinement fusion and even antimatter-catalyzed fusion. The obvious extreme is using antimatter-matter detonations and riding the blast wave, which I'm fairly certain would be more efficient and yield better performance than taking that energy and pumping it into a laser.

Re:Energy source?

[zippthorne]

Since you're using photon pressure, the reaction mass is zero. With sufficient energy, you could travel anywhere in the universe. But unfortunately, Thrust = Power / speed of light.

Even a 1 Newton thruster requires 300 MW at 100% efficiency.

You've gotta scale up the power plant to get more thrust, and it's already going to be pretty massive (I believe that puts it on the order of a medium sized commercial nuke plant.) so I just don't see you reaching Mars in a week. Proxima Centauri in a lifetime, perhaps, but no way on the mars thing.

Of course, since he's talking about a laser, it's possible he means to have the equipment on the ground (or moon, or earth orbit) and propel a much smaller craft. With sufficiently focused optics, you could propel a small probe the whole way to mars (in a week? My envelope just ran out of space...), though it would require some pretty heat-resistant mirrors. Fortunately, the energy requirements for that Newton drop by half when you factor reflection into the equation.

Scale.

[Rie Beam]

The problem with all of this is scale, right? The energy required to send larger and larger objects would be impractical.

So, what's the smallest thing we can send, then? How small can we make a satellite that can send some information back?

It may not be useful for transporting people to the other end of the universe in a practical amount of time, but I'm sure sending a probe that can check up on Mars every week or so would be of some sort of slight interest to researchers...

Of course, there's the issue of the touchdown...

Re:acceleration?

[h4rm0ny]

But what about the heat? It's quite difficult to cool off lump of metal in a vacuum without discarding hot material to do so. Even if you could feasibly power a craft to Mars with this, how would you stop yourself from arriving as Astronaut McNuggets?

Re:acceleration?

[ZOmegaZ]

If .5G could get you to your turnaround point in 3.5 days, that would mean you'd be going about 1500 km/s when you get there. That's equivalent to 1e6 MJ/kg, or 3.6 MW/kg. Sayth the Wiki that a nuclear fission plant can provide that kind of energy density, and to spare. Not sure about the power density, though, nor about the shielding requirements for human habitation. But from my inexpert viewpoint, the energy requirements look like they'd scale.

Re:acceleration?

[Randolpho]

I think the problem is that in order to create the propulsion, the laser has to *hit* the craft, not be directed away from it. If I read this correctly, the heat questioned in the grandparent post comes not from powering the laser but from the laser beam smacking against the drive plate.

And given the lack of atmosphere, a heat sink wouldn't help much. The only way to dissipate the heat would be through radiation, and that's slow compared to convection.

The question is, of course, is this really an issue? How much heat is generated from the laser blasting against the drive plate? How quickly will the heat be dissipated?

Re:acceleration?

[fmobus]

highly insulating structure? what about vacuum? the engine section does all the work and pushes the living section forward using magnetic repulsion.