Stoney3K wrote:... and how are they going to propel that once it hits thin atmosphere?
In situations close to the ground, this will probably work, using the atmosphere as a working fluid and heating it through inductive heating of the rocket, or heating up the water vapor in the atmosphere.
However, once you're clear of the bulk of the air, what are you going to propel through your rocket? Worst case it means you *still* need to carry your propellant (like a lot of water) resulting in the same mass penalty.
It's not something I have looked at in a very long time, but it is my understanding that the bulk of fuel is expended just getting off the ground and punching through the atmosphere. As the energy to produce the thrust is provided from the ground, such a rocket would only have to carry the reaction mass. Not needing a reactive fuel or oxidizer would save a lot of money and weight all by itself.
In addition to this, using microwave propulsion, it might be possible to produce thrust at greater pressures and velocities than it would be with a turbo pump powered rocket engine.
In the book "
The millennial project", the author suggests using an electromagnetic accelerator system up the side of Mount Kilimanjaro with a group of laser power boosting stations at the peak to vaporize Ice (reaction mass) attached to the bottom of the ascent vehicle.
I don't see any obvious reason why such a system shouldn't work if the necessary laser (or microwave) power levels and focusing on a moving target can be achieved.
