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."

You can't go home again

...we fried it duing liftoff.

acceleration?

What sort of acceleration would that be? Would it be multi G-force worth, that might be impractical for humans.

Re:acceleration?

They didn't say you would get there alive. They just said you would get there in a week.

Re:acceleration?

About 1/2 G.

Re:acceleration?

Half a G will get you way further than Mars in a week. The greatest distance between Earth and Mars is 391 million Km. Assuming you're going to go constant acceleration half way and constant acceleration in the other direction the second half of the trip, 1/2 G acceleration will get you 897 million Km end to end in seven days.

If you don't mind going through the Sun, that 1/2 G will get you Earth to Jupiter, in the worst geometry possible, in seven days and one hour and thirty minutes.

Re:acceleration?

No, that only works if you're accelerating in the same direction at 1/2G the whole time. If you want to end up in the right place with zero speed, you need:

s = 0.5at^2

s = 0.5 * 4.9 * (3.5d * 24h/d * 3600s/hr)^2

= 224 042 112 000 m, a bit over 224 million km

Then double it, since you'll go just as far in the deceleration, and you get 448 million km, not 897.

Re:acceleration?

If you don't mind going through the Sun, that 1/2 G will get you Earth to Jupiter, in the worst geometry possible, in seven days and one hour and thirty minutes.

I'm not a rocket scientist, but isn't that kind of a deal-breaker?

Not if you go at night.

Re:acceleration?

It includes turnaround at the halfway point.

Re:acceleration?

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?

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?

Our chief scientist, Davros McDonald, has calculated the ultimate evolutionary form of the human race to be McNuggets. Why do you struggle against progress?

Re:acceleration?

The current space shuttle seems to deal with the heat from explosives fairly well in the atmosphere and in space. They use a model called "let's not put it next to the astronaut's faces".

Re:acceleration?

But then the living quarters would never leave earth orbit would they? ;D

Re:acceleration?

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?

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:acceleration?

Do you currently find 1G uncomfortable?

Re:acceleration?

That was funny, I'll give you that one. I am an idiot.

Re:acceleration?

Interesting moderation. You're currently at +5 insightful, for two statements:

• That the grandparent post was funny.
• That you are an idiot.

Both of these could reasonably considered informative, however the second is likely untrue, since in my experience idiots are quite likely to be the last to realise, and the moderation totals on the grandparent would have informed even the most humour deficient. Or are moderators now giving karma to people who admit their errors? If so, have I accidentally logged into some kind of bizarro-Slashdot, where everyone is polite and respectful? And is there a way of making sure I don't accidentally end up on the other one again?

Re:acceleration?

Both of these could reasonably considered informative, however the second is likely untrue, since in my experience idiots are quite likely to be the last to realise

Remember, there's a big gap between "likely untrue" and "always untrue." When someone can look at their own statement, realize what it implies about their capacities, and then confidently declare "I am an idiot," they are displaying insight that is well above average, and certainly deserving of mod points.

I, for one, welcome our new self-insight-possessing commenters.

have I accidentally logged into some kind of bizarro-Slashdot, where everyone is polite and respectful? And is there a way of making sure I don't accidentally end up on the other one again?

Staying out of the Politics and YRO threads may reduce your vitriol exposure by as much as 300%. Ask your doctor!

*Disclaimer: poster is a frequent and vitriolic contributor to Politics and YRO threads.

Re:acceleration?

Remember, there's a big gap between "likely untrue" and "always untrue." When someone can look at their own statement, realize what it implies about their capacities, and then confidently declare "I am an idiot," they are displaying insight that is well above average, and certainly deserving of mod points.

I, for one, welcome our new self-insight-possessing commenters.

I'm an idiot, too. ...can I have my +5 Insightfool karma boost?

Re:acceleration?

His demonstration thruster produces 35 micronewtons.

35 micronewtons / .0005467722 Km/s^2 = 64 milligrams, so if we were using this to power a marscraft with the mass of the acetominophen contained in a single extra strength tylenol tablet, it would be more than 10x too heavy. Of course they said it could be scaled up, but that's a heckuvalot of scaling.

I doubt the smallesst possible manned Mars vehicle could be less than 1,000kg. That's a scaling factor of 15.6 million. I can jump over 3 feet on the trampoline in my back yard, which translates to a maximum velocity of 4.23 m/s. If I scale that up by 15.6 million, I would be launching myself at 66,000,000 m/s, far exceeding escape velocity, and reaching Mars under my own power in under 30 minutes.

Re:IMPULSE DRIVE

voila! sublight speed!

Big deal. I have sublight speed sitting at my desk.

-jcr

How "scaled up" is this?

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?

It only says it can get the spacecraft to Mars in a week. It does claim to be able to stop once it gets there.

Re:How "scaled up" is this?

Actually, it says that it can get the spacecraft to Mars in a week and can stop once it gets there. But it doesn't claim that anyone will survive the impact.

Re:How "scaled up" is this?

Survival isn't necessary. Just get your ass to Mars. G-G-Get your ass to Mars.

Re:How "scaled up" is this?

nasa knows how to stop things at mars, that's easy. (think: "feet, meters, same difference")

Re: Metric Joke

A harsh lesson that I have learned here...

If you're going to make a lame joke, at least include a cite so there's a chance of getting modded up as "informative."

The Mars Climate Orbiter:
http://en.wikipedia.org/wiki/Mars_Climate_Orbiter [wikipedia.org]

"The Mars Climate Orbiter was intended to enter orbit at an altitude of 140-150 km above Mars. However, a navigation error caused the spacecraft to reach as low as 57 km. The spacecraft was destroyed by atmospheric stresses and friction at this low altitude. The navigation error arose because a NASA subcontractor (Lockheed Martin) used Imperial units (pound-seconds) instead of the metric units (newton-seconds) as specified by NASA."

Re:How "scaled up" is this?

I would think that scaling wouldn't make the laser bigger but would instead use multiple lasers like they do with ion engines. Of course, IANARS (I am not a rocket scientist) so take what I say with a big grain of NaCl.

Power = Thrust * Exhaust Velocity

To send a ship to Mars in a week, Thrust should be roughly 10m/s^2 times the ship's weight, which we'll say is only ten metric tons. (Because we're getting there in a week, we can pack light... pack light, get it? I slay me.) That gives us 10^5 Newtons of thrust.

Exhaust Velocity is the speed of light, or about 3*10^8 m/s.

So our power consumption is 3*10^13 Watts.

By comparison, the USA is currently consuming less than 1*10^13 Watts on average.

In other words, if think you think it costs too much to refuel an RV now...

It's not completely implausible to use light to propel a spacecraft, but either that propulsion will be ridiculously slow (e.g. solar sails, laser sails, or the "precisely tweak your satellite's orbit a tiny bit" applications mentioned in the article), or it's going to require ridiculous "cheap antimatter" amounts of energy.

Minor correction

To get to Mars in a week, only about 5m/s^2 is necessary. ( Mars at 1G is about 3.5 days, so a week is 1/2 G, turnaround halfway )
So call it a mere 1.5*10^13 watts.

Re:How "scaled up" is this?

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:I guess I don't get...

No. The momentum gathered from sunlight points in one direction, the laser in another and you are going wherever the vector sum leads you.

Re:How "scaled up" is this?

You must have forgotten that nuclear power, by definition, harms the environment.
That's just how it works.
There's no environment to harm in space so nuclear power can't possibly work out there.

Re:How "scaled up" is this?

> Republicans, you mean.

Anybody who's read my posting history knows I'm a dyed-in-the-wool liberal, but I don't think we can singularly blame the GOP for this one. There's resistance to nuclear power coming from both extreme ends of the spectrum. Environmental activists who don't understand the science on the left, and oil industry lobbyists on the right.

I'm constantly frustrated with people who I know are well-intentioned and genuinely concerned, who are so afraid of nuclear power. I mean I agree, solar and wind power are great ideas, but right now we're generating power using f'ing COAL.

All a matter of scale...

And if scaled up, cockroaches run at 800mph and fleas could jump over a mile. However, the increase in mass and energy requirements would make it impossible.

Small scale thrusters using only lasers is a good start, but we'll have to see what else gets bigger with scale, other than just the thrust.

Re:All a matter of scale...

"we'll have to see what else gets bigger with scale, other than just the thrust."

That's what she said ;)

The Warriors

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

I smell bullshit

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:I smell bullshit

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.

http://www.photonics.com/content/news/2007/September/7/88894.aspx [photonics.com]

Bae founded the institute to develop space technologies and has pursued concepts such as photon, antimatter and fusion propulsion for more than 20 years at SRI International, Brookhaven National Lab and the Air Force Research Lab. He has a PhD in atomic and nuclear physics from UC Berkeley. Several aerospace organizations have expressed interest in collaborating with the institute to further develop and integrate PLT into civilian, military and commercial space systems, Bae said, and he has recently been invited to present his work by NASA, JPL, DARPA and the Air Force Research Laboratory (AFRL).

Lasers are better with Photons...

Photonic Laser Thruster

Muuuuch better than using those LASERS without Photons.

[I hear that adding the photons also makes them lighter...]

Energy source?

Where is the energy coming from to create those photons?

Since you're dealing with a photon drive, the reaction mass usage (as determined by the classic rocket equation) is going to be negligible for the speeds required for interplanetary travel.

In fact, I'm not sure what the reaction mass would be in this case.

But in any case, you're going to need a lot of energy to create that photon thrust. Great phrigging big reactors, which means great, great, phrigging big radiators since you don't have the luxury of a river to carry away your waste heat.

Antimatter might be a compact way to store the required energy, but converting the gamma rays from matter/antimatter reactions to electricity is going to require heat exchangers and great big radiators as well.

Well, anyway, scaling this up is going to involve several bears of a problem.

Also, please note that this "article" is a press release from the guy who made the invention.

Re:Energy source?

I did quite a bit of reading on spacecraft propulsion recently (specifically Nuclear pulse propulsion [wikipedia.org] 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?

The concept of external (i.e. explosions are not contained within the ship's structure) nuclear pulse propulsion was actually studied in the late 50s, early 60s as Project Orion [wikipedia.org] (internal NPP, which is like your car analogy but with nuclear explosions instead of fuel-air explosions, places too great of a stress on the ship's structure to be feasible).

They never did get enough funding for a test with a nuke, but they did build 1-meter scale models powered by RDX charges. Powered by I believe 6 explosive charges, one of these reached 100 meters in a controlled test flight, proving that the concept worked (at least with lower energy pulses). As for whether or not it would work with nukes, their numerical modeling strongly indicated that it would.

You mentioned that the blast wave might be moving too fast to be useful, but actually that's the whole point - the impulse of the blast wave impacting against and then rebounding off the back of the spaceship is what provides thrust, so the faster the blast wave is moving, the greater the impulse and thrust.

Of course, the spaceship would have to be stupidly large to survive the instantaneous acceleration, but that was why it was so attractive. A ship around 10000 tons could've made it to Pluto and back within a year. Plus, it had a very high thrust-weight ratio, which meant that the fraction of the weight that was useful payload was stupidly high as well.

So then if NPP is so good, why was the project killed? It wasn't because it didn't work ... it was a combination of quite a few political reasons:
1) NASA had thrown its support behind the competing NERVA rocket.
2) Fallout was problematic.
3) There was no mandate from Congress for missions that would require such performance, and NASA had no desire to dictate policy.
4) Partial Test Ban Treaty of 1963 banned all above-ground nuclear testing.

Re:Energy source?

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.

Scaling up is fun

I wonder why we don't just scale up a bridge right to Mars and drive to there with a drag racer car. If the latter is too slow, I suppose no problem, we can scale it up as necessary.

Incredible!

Senior Aerospace Engineer at AFRL, Dr. Franklin Mead, "Dr. Bae's PLT demonstration and measurement of photon thrust (is) pretty incredible. I don't think anyone has done this before. It has generated a lot of interest."

Perhaps the demonstration would generate even more interest if it were credible.

Scale.

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...

With all due respect to James Doohan...

Scaled up, a similar engine could speed a spacecraft to Mars in less than a week.

Aye. And if my grandmother had wheels, she'd be a wagon.

"Scaled up"

Because as we all know, it's just that easy! Nothing that worked at one scale ever proved impractical or impossible to do at another!

Re:Solar system escape velocity!

So anyone riding the spacecraft better hope that there isn't a malfunction of the "slowing down" laser at the other end, as depending on the angle, that might be enough to exit the solar system altogether!

The article calls this a "Photon Thruster". What that means is that the device would be mounted on the vehicle as a thruster rather than the vehicle "riding" a laser-beam like in Beam-powered propulsion [wikipedia.org]. So as long as the laser restarts after you flip the ship, you're good to go.

Note that this is a separate issue from powering a laser cluster large enough to reach Mars in a week...