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

You can't go home again

[Harmonious Botch]

...we fried it duing liftoff.

acceleration?

[OrangeTide]

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

Re:acceleration?

[scoot80]

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

Re:acceleration?

[ozmanjusri]

Would it be multi G-force worth, that might be impractical for humans.

Forget humans.

How much faster will my shark go with this thing bolted to it's head?

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:acceleration?

[Harmonious Botch]

About 1/2 G.

Re:acceleration?

[chis101]

Assuming this is a real calculation, does this include slowing down at Mars without killing the people on the spaceship, or is it just 1/2G to *get* to Mars in 1 week?

Re:acceleration?

[Harmonious Botch]

It includes turnaround at the halfway point.

Re:acceleration?

[Score Whore]

It seems likely that it would be quite a small amount of thrust, it's photons that you are "pushing" against. Even on the big engine.

The important thing is that it'll accelerate all the way there. With continuous acceleration it doesn't take much to get going really fast.

According to the article Mars is 100 Million km away and a big version of this will travel that in a week. We'll assume that you want to stop when you get there so just figure half the trip in half the time (since the second half will be braking):

50,000,000 Km = a * (302400 sec) ^ 2

a = .0005467722 Km/s^2

Acceleration due to gravity is 9.81 m/s^2, or 0.00981 Km/s^2. So he's talking about 1/18th G acceleration. Speed at turnover will be: .0005467722 Km/s^2 * 302400 sec = 165 Km/s.

Whee!

Of course it's more complicated than that since that low of an acceleration won't get you off the ground. So you'll be starting your trip in orbit. Which means you've got to take some time to get to a high enough orbit that you can accelerate away from the earth without having to do lots of high thrust maneuvers. Still, you can probably plan on Mars in a month.

Re:acceleration?

[Score Whore]

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?

[Hucko]

Do you currently find 1G uncomfortable?

Re:acceleration?

[scoot80]

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

Re:acceleration?

[iocat]

Getting to Mars is included. Stopping once you get there is an exercise left to the reader. Seriously though, TFA (or TFPressRelease) first had me skeptical, since it's Dr. Bae of the Bar Institute claiming to have done something no one's even done before (I got that cold fusion feeling). But it's getting published in a peer-reviewed journal, so... man, sounds kind of impressive.

Re:acceleration?

[E 99]

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:acceleration?

[Anonymous Coward]

Backwards.

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?

[pintpusher]

If you put another thruster at the other end of the ship, then you have to spend the rest of the trip unbolting all the tables and chairs from the new ceiling and rebolting them to the new floor. And taking all the sheets off the new bottoms of the mattresses and putting them on the new tops. And reworking all the plumbing so the water comes out of the old drains and somehow runs into the old faucets.

Since you've got to steer the thing at some point anyway, why not use whatever that mechanism is to just flip the thing around, Its way more fun and worse case, you'll have to mop up a few buckets of puke from the vertigo. Well, okay, worst case something breaks and you tumble out of control for eternity, but that's always a possibility whether you flip the thing or not.

Re:acceleration?

[demonlapin]

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?

[i_b_don]

actually there is another problem with this concept besides the extremely wasteful "building a second engine" part. Think about crew quarters... if you've got 1G acceleration you've got a floor and a ceiling. If you just reverse directions of the engines without spinning the craft you now swap what is your floor and what is your ceiling. Makes for some interesting redecorating, but not really vary practical. It makes MUCH more sense from an engineering point of view to spin the ship. It's easier and more efficient.

d

Re:acceleration?

[somersault]

Market the trip as a nice hot sauna vacation. Half of the ship is toasty and humid, the other half can have a nice cool pool. You could also separate the main drive from the living quarters of course?

Re:acceleration?

[TheRaven64]

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?

[Hucko]

Actually the funny part is, I was confused. I thought I had misunderstood my physics education.

Re:acceleration?

[Hal_Porter]

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?

[Sunburnt]

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?

[ultranova]

Or are moderators now giving karma to people who admit their errors?

Well, since this is a science article, let us use the awesome power of experimental empirical experiments to research the issue:

I'm an idiot, so mod me up !

BTW. Isn't "photonic laser" a bit redundant - the "l" in laser stands for "light", after all ?

Re:acceleration?

[pablochacin]

claiming to have done something no one's even done before Isn't it what innovation is all about?

Re:acceleration?

[TuringTest]

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?

[aliquis]

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

Re:acceleration?

[Zaatxe]

Half a G will get you way further than Mars in a week. The greatest distance between Earth and Mars is 391 million Km.

You are taking in consideration that the ship wouldn't go from Earth to Mars in a straight line, right?
Oopsy Daisy!

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?

[mykdavies]

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? Strangely enough, the answer to this could be lasers as well - have a search for Laser Cooling

Re:acceleration?

[SunTzuWarmaster]

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?

[SleptThroughClass]

"If you don't mind going through the Sun..." OK, you've just toppled the people worried about heat from the drive.

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.

Re:acceleration?

[The Fun Guy]

"The only way to dissipate the heat would be through radiation, and that's slow compared to convection."

It's only slow if there is a small temperature differential between your source and your sink. Pointing the radiating fins out toward dark space would let them dissipate it pretty quickly.

Re:acceleration?

[Clith]

Although his math was a bit off, the grandparent's point remains valid.

At closest approach, Mars is about 56 million km away.Iif we switch the d=½at^2/ equation around, we get t=sqrt(2d/a). 'd' would be ½ the 56 million km distance, to allow for turnover, giving t/2, so..

t/2 = sqrt( 2 * 28*10^9 / 4.9 )
t = 59.4 hours =~ 2½ days

So between 2½ days and a week to get to Mars. Not bad..

Re:acceleration?

[tehcyder]

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?

Re:acceleration?

[suggsjc]

You must be new here...

Re:acceleration?

[HarvardAce]

Why wouldn't you go in a straight line from Earth to where Mars would be when you got there? Well, there's a few issues.
1) If you're talking about the point when Mars is farthest from Earth, it's presumably on the other side of the sun. Going in a straight line would lead you through the sun, which probably would cause a few issues.
2) There's this thing called gravity...while you could, for the most part, ignore the gravity of the planets, the sun is another issue. It's going to cause you to travel in an arc, unless you're moving directly to/from the sun (which incidentally you would be doing in the first case).

Re:acceleration?

[morcego]

I think we are missing something here.

If the ship is heating, then it is absorbing energy. The point of this (if I understood correctly) is for it NOT to absorb the energy, so it can move.

Yes, it can't be 100% efficient, so there will always be heat absorption. But I wonder if it will be enough to be a problem.

And yes, I don't have any idea what I'm talking about. This is just gut feeling.

Re:acceleration?

[Homr Zodyssey]

I am Nugget Sec. Together with Nugget Thay, Nugget Jast and Nugget Caan, we make up the Cult of Mayo. All of Humanity will kneel before the might of the New Nugget Empire. You will comply! Exterminate! EXTERMINATE!

Re:acceleration?

[tarkas]

Generally, radiatiative cooling will be limited by the Stefan Boltzman law, j (watts/m^2) = (stefan-boltzman constant) * T^4 (kelvins), http://en.wikipedia.org/wiki/Black_body

where = 5.670 400(40)×108 Wm-2K-4. http://en.wikipedia.org/wiki/Stefan-Boltzmann_constant So, the hotter your radiator, it increases output by a power of 4 and since space is very near absolute zero, for emissivity and absorption considerations, it's really dumping energy. You'd be surprised at how fast a simple radiation cooling scheme will operate.

I had to run a themo-vacc qualification test for some ISS hardware (on the mobile transporter). In a chanber with a very hard vaccum, even under a shroud made from a 1/8" skin aluminum box, painted with high emmissivity paint, we had good performance using a cooler lining the chamber, chilled with LN2, aprox -375F IIRC. I forget the cooling rate, but it wasn't bad. We had to modulate the cooler to get our cooling/heating profile, so we could have gone faster.

From TFA, it wasn't clear how they were pumping the photon source, I assume it'll be electric. So it's either batteries(Ha!) or some sort of nuke plant - thermionic orf some sort of (sterling ?) heat engine, either of which will be rejecting a bunch of heat, to generate - what, someone said like 370MWatt? So ya, big radiators of some sort. Plus, the photon source might also be generating it's own heat, aside from the photons, depending on the efficiency.

This'll basically be a big flashlight, just don't stand behind it or you're looking at one heck of sunburn, at least until you're vaporized. But the really cool thing is you don't need to schlep along tons of reaction mass, the photons do it for you, as they have a (very small) momentum. You just need a nice compact high power energy source.

Re:acceleration?

[nanotrends]

How to scale up.
The original demo was from 10 watt lasers and 3,000 reflections (it is good to actually research original papers to know what is being discussed.)
It is theoretically possible to achieve 100,000 reflections (you may have to go outside the atmosphere to ensure less losses of energy (ie like from a lunar launch system
We will soon be making 100 Kilowatt solid state lasers. (US military made 67 kw earlier this year and will have 100 kw system done later this year or early next year.
We can use arrays of lasers
(ie more than one). Power is provided in electrical form to the lasers. Say from nuclear power (3.2 GW twin reactors, and can have more reactors) or hydro power (Three gorges dam generates 18 GW). So wattage can go up say 100 million times to 1GW. (reduced the nuclear plant power by inefficiencies for the lasers.
the reflections can increase by 33 times.
Therefore, 3.3 billion times more power.

Thus you can send several ton vehicle to Mars at high speed
http://advancednano.blogspot.com/2007/02/use-67-kilowatt-solid-state-lasers-for.html

Re:acceleration?

[Blain]

3) There's this other thing called momentum, which anything leaving Earth orbit has to account for. The vehicle doesn't start out at the edge of Earth orbit stationary compared to anything -- it starts out orbiting the Sun at the same speed as the Earth. The most efficient path won't be to try to kill that momentum and then push in a straight line at Mars. IANARS, but my guess is that the most efficient path would be a curve between the orbits.

Re:acceleration?

[tkw954]

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.

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?

[Mothinator]

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?

[dethl]

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.

Re:How "scaled up" is this?

[Dachannien]

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?

[Lloyd_Bryant]

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. If you RTFA, you'll note that the quote about reaching Mars in a week doesn't mention anything about a manned mission.

The real question: how the hell are they going to power this laser? For micro-thrusts for satellites, solar panels are fine, but for an interplanetary trip you'd need something like a nuclear reactor (unless that "interplanetary vessel" consisted of a mass of solar panels and a payload about the mass of a postage stamp).

I'd classify this one as just more hype about a technology with an, at present, very limited usefulness. Maybe at some point in the future the human race may use something like this on a large scale. But for now, don't hold your breath.

Re:How "scaled up" is this?

[azenpunk]

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

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?

[dwywit]

Moties, here we come!

Re:How "scaled up" is this?

[kocsonya]

> ... I have to wonder just how powerful the laser has to be.

Well, you can do a back-of-the-envelope calc easily. The mass of the ship is, let's say, about 10 tons or 1E4 kg. You want a 1g acceleration, or about 10 m/s^2 all the way. Assuming a laser with 500nm wavelength a photon leaving will give you an impulse of h/lambda, that is, 6.6E-34 / 5E-7 ~ 1E-27 kg*m/s. Your craft needs to get 1E5 kg*m/s impulse per second to maintain its acceleration, which is then roughly 1E32 photons per second. An 500nm photon has the energy of h * c / lambda, 6.6E-34 * 3E8 / 5E-7 that is ~ 4E-19 J. Thus, all together you need about 4E13 Watts of power, if you have a 100% efficient laser. Now that's about 40TW. Considering that the US produces 4TWh electricity in a year and that a year is about 8760 hours long, you need a power source that is approximately 90 thousand times as powerful as all the power stations of the US put together and it has to fit snugly in your 10 ton rocket, including the fuel. The latter is not as bad as it sounds: if you generate the power by 100% efficient matter-antimatter annihilation the required 40TW power output only needs about a quarter of a gram of each per second, so for a 1-week trip, which is roughly 600,000 seconds, you can get away with about 150kg of each.

So, unless I did a gross miscalculation (entirely plausible) the 1-week Mars flight seems to be a bit out of the realm of reality yet.

Re:How "scaled up" is this?

[MrNaz]

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

Re:How "scaled up" is this?

[Smight]

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?

[Rhinobird]

I'd say that was funny, except I swear that's how some people actually think.

Re:How "scaled up" is this?

[FauxPasIII]

> 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.

Re:How "scaled up" is this?

[Lloyd_Bryant]

I'm pretty sure we managed nuclear technology at some point. Actually, we came pretty close to having a working nuclear rocket engine more than 30 years ago (google for "NERVA" and ignore the Roman emperor links).

The reason we *don't* have such technology today is a result of combining short-sighted congresscritters with techno-illiterate anti-nuclear groups.

To be fair, there *were* some reasonable concerns about the radioactivity of the exhaust (at least while it was near Earth, and there was something in the vicinity to pollute). Using a nuclear reactor to power these new thrusters would alleviate this.

But regardless of this, I suspect that the exact same forces would kill any new attempt at creating a nuclear powered spacecraft. The anti-nuke groups would still be going "Oh Noes - it's nucular, so it's bad". And the congresscritters would still insist on pork from the project for their districts, or else.

So combining these thrusters with a nuclear power source might be *technically* possible, I expect it to remain a political impossibility for the foreseeable future.

Re:How "scaled up" is this?

[StressedEd]

but right now we're generating power using f'ing COAL.

It's worse, much worse. Burning coal releases copious quantities of radioactive isotopes into the air.

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.

All a matter of scale...

[Microlith]

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...

[iamhassi]

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

That's what she said ;)

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:I smell bullshit

[s4m7]

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

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).

Re:I smell bullshit

[Rie Beam]

His website doesn't exactly inspire confidence, either

Bae Institute is a unique institute dedicated to creating revolutionary technologies for the next generation space and medical endeavors, yet aiming at facilitating their rapid implementation and commercialization. For that reason, we specialize in applying highly focused proven technologies to innovative solutions, thereby reducing development time while improving the viability of practical applications. An important goal of the Bae Institute is the commercialization of our innovative and revolutionary technologies. By licensing our unique intellectual properties, launching commercially viable companies, or by partnering with existing companies - we hope to quickly bring proven solutions to market.

Re:I smell bullshit

[suv4x4]

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.

On the other hand even the current institutions started as someone creating them at some point.
And quite a lot of scientists were ridiculed by the establishment at a time they made a revolutionary discovery.

What worries me more is his unsubstantiated "if we just scale it up" argument. That doesn't stand basic math/logic/physics.

Re:I smell bullshit

[Rie Beam]

Bae also does Acupuncture research, if that reflects on him in any way. NASA saw him fit enough to give him a grant, however.

I don't know what to make of this guy. He doesn't seem like a quack, but I really don't know enough about the subjects to know if what he's spewing is genius or something else entirely.

Re:I smell bullshit

[dbIII]

MIT also has a website for a materials science group promoting the idea of ridiculous superhero underwear (ridiculous because being able to spread the energy of impacts is how bullet proof stuff is made so nanometre thick stuff is not going to solve the problem on it's own) that none of their students would believe past first year. Loud Lysenkoism is how things are done these days even if the people actually doing the stuff are legit. We really need work on the K-12 education system because that is all our decision makers are really going to get, and currently snakeoil scams are attracting a lot of serious attention from poeple that we would hope would know better.

Re:I smell bullshit

[Ruie]

I smell bullshit

I have my doubts as well. There is a picture there of Dr.Bae standing next to an experimental setup which consists of precision scales, a mirror sitting on these scales, another mirror above it and some sort of laser medium in between.

From this I figure that his thruster uses Fabry-Perot cavity to amplify amount of light circulating between mirrors - not exactly a new trick. However the press release says something about importance of putting laser medium inside the cavity so, hopefully, he is doing something more involved (though not described).

Also, this thrust could only be used to push two mirrors apart - so it is hard to see how one can use this for docking - but undocking would work fine..

Lasers are better with Photons...

[fahrbot-bot]

Photonic Laser Thruster

Muuuuch better than using those LASERS without Photons.

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

Re:Lasers are better with Photons...

[markov_chain]

Guys, stop making light of this invention! I'm sure Dr. Bae is a perfectly bright young man.

Re:Lasers are better with Photons...

[Anonymous Coward]

Of course don't forget to hang a mirror off the back of the laser rocket for those photons to reflect off of or it's not going anywhere...

Newton's Third Law of Motion would like to have a word with you.

Re:Lasers are better with Photons...

[jollyreaper]

Guys, stop making light of this invention! I'm sure Dr. Bae is a perfectly bright young man. Yes, but how coherent is he?

Energy source?

[StefanJ]

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?

[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.

Re:Energy source?

[Yazeran]

Well that is not a big problem. At least a couple of Mars probes have used atmospheric breaking to enter Mars orbit (called 'areocapture' i believe). While it is a tricky maneuver to get right, it can slow the spacecraft enough to enter a stationary orbit (do it wrong and you either burn up or 'skip' off the atmosphere and continue off into interplanetary space...) Fortunately Mars atmosphere is thin and has a higher 'scale height' than Earths atmosphere making the maneuver slightly easier on Mars, but still..

Yours Yazeran

Plan: To go to Mars one day with a hammer.

Re:Energy source?

[Arabani]

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 (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.

Power = Thrust * Exhaust Velocity

[roystgnr]

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.

Re:Power = Thrust * Exhaust Velocity

[Beryllium Sphere(tm)]

Thrust is the derivative of momentum with respect to time, and momentum is conserved, so in an open-loop drive F=dp/dt=d/dt(E/c)=(1/c)dE/dt, so power (dE/dt) is force times C.

But here's where the novel part comes in. Every photon is bounced back and forth thousands of times between the spacecraft and a mirror. The mirror experiences the same force as the spacecraft but in the opposite direction. The spacecraft's momentum comes from "pushing against" the mirror, rather than "pushing against" the exhaust photons.

For every photon with momentum E/c, the spacecraft gets a momentum kick of E/c when it emits the photon, 2E/c when the photon bounces off it again after a round trip to the mirror, 2E/c again on the next round trip, and so on until the limits of the optics lose the photon out into space. If the drive could really deliver the thousands of photon reuses Dr. Bae talks about, then the power requirements drop to more like 1E10 watts.

OK, fitting that into ten metric tons means we still need antimatter.

Scaling up is fun

[suv4x4]

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.

Re:Star Trek anyone?

[Short Circuit]

I don't believe it was mentioned in TOS. However, 1970s scifi books used it. (Notably The Mote in God's Eye).

Re:Solar system escape velocity!

[tftp]

Presumably the speed at the mid-point would be even higher.

Twice the average speed if you want constant acceleration.

Re:Solar system escape velocity!

[Howzer]

Twice the average speed if you want constant acceleration.

Bingo! 160 km/s somewhere between Earth and Mars absolutely qualifies as solar system escape velocity! I'm a little rusty, but isn't it 400 km/s from the surface of the sun, and around 15 km/s out past Pluto? Voyager II was doing 16 km/s when it left the building...

Minor correction

[Harmonious Botch]

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: Minor correction

[Alaria Phrozen]

He didn't. Worst case distance, to get to Mars at 1G constant acceleration takes 3.5 days. What is there to confuse? The calculations are all throughout people's comments. RTF Cs?

Re:Solar system escape velocity!

[AKAImBatman]

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. 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...

Incredible!

[Riktov]

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.

Re: Metric Joke

[Telephone Sanitizer]

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

"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:I guess I don't get...

[arivanov]

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

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:Scale.

[Admiral Justin]

Not really, NASA has perfected slamming things into Mars. We're quite good at it.

IMPULSE DRIVE

[Anonymous Coward]

Hooray! They've finally discovered how to make an Impulse Drive engine. Now all they have to do is tie in a fusion reactor and voila! sublight speed! I'm just kidding. I didn't RTFA.

Re:IMPULSE DRIVE

[jcr]

voila! sublight speed!

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

-jcr

The BAE Institute

[Rie Beam]

His institute seems to have a lot of promising ideas, but no real substance. It has three major projects, one of which relies on the photon thruster and some kevlar straps to toss around satellites, and some sort of undeveloped nano-microscrope.

http://www.baeinstitute.com/

Bullshit, I indeed smell.

With all due respect to James Doohan...

[Spasmodeus]

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"

[Tim C]

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!

Call me when it's 1:1 thrust:weight

[The Master Control P]

Because until then, you're still paying $10000 per kilogram to low orbit where you can engage the photon drive, which means that no meaningful exploration is gonna happen.

Did I mention that 45 years ago the USAF tested a nuclear thruster that almost reached 1:1? And how fifty-five years ago they drew up plans for an 8 million ton nuclear-driven starship as part of Project Orion?

What's in a name?

[R3d Jack]

Isn't "photonic laser" redundant?

Now that fits well

[sircastor]

Photonic Laser Thruster... perfect. Sounds like it came right out of a pulp Sci-Fi Serial. "Sir!" "What is it Smith?" "The Photonic Thruster, it's out of power! We're dead in the water!"

Buckaroo?

[Mark_in_Brazil]

Am I the only one getting Buckaroo Banzai vibes from this?

Dr. Bae of the Bae Institute? Seriously?

I went to the Bae Institute's site and found that it is "an independent space and medical research center."

Physics and space science: check.
Institute named after its physicist founder: check.
Medical stuff: check. Dr. Banzai, of course, in addition to being a great physicist, is also a top neurosurgeon. At the Bae Institute site, it says the Institute's medical technologies can be used, among other things, for treating "brain and spinal cord surgeries."

If Dr. Bae is also the leader of a rock band and says things like "wherever you go, there you are," I'll be surprised if we don't see a wave of stories submitted very soon, all by people named named John, saying that Dr. Bae's research cannot be trusted. I expect these submissions to cite the work of another physicist, Dr. Emilio Lizardo.

Laffa while you can, Monkey Boy!

I just showed my age in a way a low Slashdot UID never could.

Accelerando

[VoidEngineer]

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.

I highly recommend the book Accelerando by Charles Stross, which has an extended story arc which deals with exactly this idea. They're trying to get a coke-can sized space shuttle with a solar sail to a brown start about three light years away (which has an intergalatic router nearby), and they power the shuttle with a laser beam powered by a cable dragged through the jupiter atmosphere/magnetic field. I highly recommend the book. Amazing concepts throughout.

Why *Photonic* Laser?

[smithmc]

Aren't all lasers "photonic" by definition? Was this thing named by the Redundant Department of Redundancy Department?

Just turning around does not work.

[nanotrends]

Just turning around does not work. You are being pushed by a laser from a remote source.
You either have to first deploy the receiving laser array and power system.
Or bring an alternative drive for breaking.

Here is my desciption of how to perform this in more detail
http://advancednano.blogspot.com/2007/03/putting-brakes-on-laser-mirror-systems.html