NASA is examining beamed energy propulsion for space launches.

[bananas]

http://www.space.com/10658-laser-rocket-propulsion-technology.html

Laser Propulsion Could Beam Rockets into Space
Prachi Patel, Astrobiology Magazine
Date: 21 January 2011

<snip>

NASA is now conducting a study to examine the possibility of using beamed energy propulsion for space launches. The study is expected to conclude by March 2011.

<snip>

Thermal propulsion vehicles would be safer than chemical rockets since they can't explode and don't drop off pieces as they fly. They are also smaller and lighter because most of the complexity is on the ground, which makes them easier and cheaper to launch.

<snip>

Parkin developed the idea of microwave thermal propulsion in 2001 and described a laboratory prototype in his 2006 Ph.D. thesis. A practical real-world system should be possible to build now because microwave sources called gyrotrons have transformed in the last five decades, he says. One megawatt devices are now on the market for about a million U.S. dollars.

<snip>

Sending a spacecraft to a moon of Jupiter, for instance, would require a laser that gives billions of watts of power. "You'd have to have another couple generations of space-based telescopes to do something like that," Kare says. "You can in fact launch an interstellar probe that way but now you're talking about lasers that might be hundreds of billions of Watts of power." Laser technology could reach those levels in another 50 years, he says.

[HereSince1628]

1. Seems to have DARPA written all over it.

Not so much for space vehicles, but for those hundreds of billions of Watts of laser power.

[PetrusMonsFormicarum]

2. If we want the solar system

we're going to have to find a way to do it as inexpensively as possible. Propulsion methods that effectively "fire" spacecraft like bullets or missiles leave the propulsion technology at the launchpad, making more room for air, water, and the rest of our primate junk. Such facilities on the far end of the trip would be absolutely necessary for any economically feasible harvesting or colonizing.

Railguns are another great possibility where the vast amounts of energy needed to make space trips worthwhile are contained in a stationary launch facility.

[Thor_MN]

3. I don't like the idea of my primate junk sitting on a billion watt laser beam...

cringe worthy. Using that to get the bulk of equipment up to speed wouldn't be bad.

[txlibdem]

9. Don't worry, it's not a laser --it's a billion watts of microwaves

eom

[Posteritatis]

12. Is it really any less cringeworthy than sitting on several hundred tons of explosives? (nt)

[krispos42]

6. I don't think railguns or coilguns will work as a propellsion device

Orbiting the Earth in low orbit requires moving at about 17,000 miles per hour, or about Mach 23. To enter orbit with a final speed of "only" Mach 23, your launch speed would have to be incredibly high to punch through the thickest part of the atmosphere and gain over a hundred miles of altitude. Mach 35? Mach 40? More?

And of course, punching through the atmosphere at, say, Mach 35 or Mach 40 would vaporize you pretty damn quick. Not to mention the time to build up to those speeds.

Accelerating at 6 g's would requires something on the order of 225 seconds to reach maximum velocity, during which time the distance travelled would be over a thousand miles.




Not going to happen, unfortunately. Now if we were on the Moon...



What we could do, though is build a space elevator. Haul the low-orbit satellites way up so they gain lots of kinetic and potential energy, then let'em go. If you do it right, they should drop down in an orbit that will let them skim the atmosphere to lose speed and assume a low, circular orbit.

Or something. Maybe a cheap SRB would do it instead.

[bananas]

7. NASA is looking at a 2-mile railgun to launch hypersonic scramjets

which then launch their payload to orbit.
See the third link in this post: http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=228x74533

[muriel_volestrangler]

8. Bad reporting by 'PopSci'; a linear motor is not a 'railgun'

The linear motor will accelerate the vehicle at about 3g ; a railgun is, well, a gun, that accelerates things far faster than that, in which the rails and a sled for the projectile form the circuit:

http://en.wikipedia.org/wiki/Railgun

Yeah, Wikipedia is more reliable than 'Popular Science'.

Anyway, the point is that the initial stage, on the rails of a few miles, just accelerates to about Mach 1.5 ('just'; this still breaks the land speed record by a long way, and supersonic travel at that speed right by the ground may be interesting). Then a turbojet has to take over for speeds up to about Mach 4 (presumably along the lines of the Blackbird's jets); then a scramjet takes over, and accelerates it up to Mach 10 (which is about 7000 mph at 200,000 ft); then the rocket separates, and accelerates up from 7000 mph to orbital velocity of 17,500 mph. The first 3 forms of propulsion only get the speed up to less than half of what is required.

[TheMadMonk]

10. VASIMR can do it with a couple of megawatts dragged along.

And we don't have to build another fooking great lazer to turn around and come home.

It's not quite intersellar, but the Kupier belt is about a year away for a nuclear powered VASIMR drive, and a robotic mission to the inner reaches of the Oort cloud is not out of the question if we're willing to be patient. And it would certainly be useful if whatever we sent to go look on our behalf, had the means to "call home" at a speed at least a little better than that of a hunt and peck typist.

And a kilowatt zapper on site, that can cut a hair thin line, seems more useful than one back home that can resurface Enceladus when not blinding that side of the galaxy.

[DetlefK]

4. An exemplary calculation...

Assumptions: a height-independent gravity well

Getting a fully-loaded Space Shuttle (109 tons) to a 50km-orbit takes 109,000 kg * 9.81 m/s² * 50,000 m = 53.5 GJ
So you would need 5 megawatt-devices firing for 10 seconds at maximum output.

Problems:
- You would need a gigantic perfectly shaped aluminum-prism to focus the beams into one beam.
- Imagine the surface of the launched projectile is not perfectly flat, just a small ditch: The death-ray would not be reflected back to the launch pad, but a part of it would be reflected in a different angle. The result: Stray death-rays. No thanks.
- If the reflection angle at the bottom of the projectile is not perfectly controlled, for example if the craft is slightly tilted by strong winds in the upper atmosphere, then the projectile will slowly skid out of the beam:
1. The reflected beam would hit some other place than the launch pad.
2. If that happens before it's high enough to fly the rest of the distance by some conventional engines, your craft will drop like a dead bird.

[muriel_volestrangler]

5. Your calculation leaves out too much to be useful; but the article and Wikipedia have figures

(a) 50km is too low for an orbit - there's still significant drag at that altitude. The Space Shuttle orbits at an altitude of about 300 to 500km. So PE = mgh = 400 GJ, say.
(b) There's also the kinetic energy of the orbiter; a low earth orbit is about 8000 m/s, so KE = 0.5*m*v*V = 3500 GJ
(c) That's the energy imparted to the orbiter. More is given to the high speed exhaust - much more, by the time the fuel has been first accelerated along with the rocket in one direction, and then suddenly thrust out the back at high speed.

But, anyway, the wikipedia article for beam powered propulsion says a rule of thumb is 1 megawatt of beamed power per kg put into orbit (and that is in the ballpark of the OP article that says an array of a hundred 1 megawatt devices could put a satellite into orbit - something weighing 100kg, say). Something shuttle-sized would need 100,000 MW for the few minutes it takes to achieve orbit.

[LongTomH]

11. This has been discussed for a long time..............

The late Arthur Kantrowitz studied the concept in 1972. NASA and DARPA funded some small scale studies; but, NASA didn't want to spend money on anything that would compete with the shuttle.

The time may have come to revive the idea, now that there is renewed interest in Solar Power Satellite.

Edited to add: see this thread: http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=228x75517