Slashdot Mirror
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."
About 1/2 G.
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...
Javascript + Nintendo DSi = DSiCade
It includes turnaround at the halfway point.
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."
This comment is fully compliant with RFC 527.
No. The momentum gathered from sunlight points in one direction, the laser in another and you are going wherever the vector sum leads you.
Baker's Law: Misery no longer loves company. Nowadays it insists on it
http://www.sigsegv.cx/
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.
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).
... it was a combination of quite a few political reasons:
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
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.
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..
So between 2½ days and a week to get to Mars. Not bad..
[ReidNews]
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).
Note to self: Stop putting jokes in my insightful comments so I can get something other than +1 Funny!
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.