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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."
I don't believe it was mentioned in TOS. However, 1970s scifi books used it. (Notably The Mote in God's Eye).
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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...
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It includes turnaround at the halfway point.
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.
.0005467722 Km/s^2
.0005467722 Km/s^2 * 302400 sec = 165 Km/s.
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 =
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:
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.
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."
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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
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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.
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?
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?
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.
Actually the funny part is, I was confused. I thought I had misunderstood my physics education.
Semi-automatic amateur armchair Australian philosopher; conjecture ready at any moment...
It's worse, much worse. Burning coal releases copious quantities of radioactive isotopes into the air.
Be nice to people on the way up. You will meet them again on your way down!
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.
The world has changed and we all have become metal men.
"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.
The man who does not read good books has no advantage over the man who cannot read them. - Mark Twain
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.
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
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.