Laser propulsion.

[kunkmiester]

How would microwaves work instead of laser light? You can tune them straight to water, too. IIRC, they're absorbed by the atmosphere less, so you'll be able to use it farther up. I can't see why they wouldn't be absorbed fast enough by the water "fuel" to provide decent thrust.

[MSimon]

How would microwaves work instead of laser light? You can tune them straight to water, too. IIRC, they're absorbed by the atmosphere less, so you'll be able to use it farther up. I can't see why they wouldn't be absorbed fast enough by the water "fuel" to provide decent thrust.

With microwaves the size of the wave "catcher" would need to be much larger due to differences in wavelength.

[D Tibbets]

Dan,

If the engine melts the thrust goes to zero. That would be most unfortunate.

The flame temperature of hydrogen and Oxygen is 3200 C.

Stainless melts at 2,781 F roughly 1,550 C.

H being lower mass will give the highest ISP at temperatures the engine can reasonably attain (about 2,400 C for the shuttle IIRC).

Yes, hydrogen would allow the highest ISP per exaust unreacted particle, but it does so by lowering the temperature overall. Considering the low density of liquid hydrogen (larger and heavier tanks) the less efficient use of the propellents, decreases the advantages of the lightweight hydrogen. I don't know the details or where the spacecraft weight -vs- engine efficiency balance point would be, but this would eat into the advantages hydrogen has over other fuels like methane that burn at cooler temperstures (and have larger average weight exaust particles (molecules)), but can be burned more completly and require smaller tanks, etc. It makes me more sympathetic for advocates of liquid methane-LOX powered rockets.

Dan Tibbets