Talk-Polywell.org

Early this year, scientists in Japan successfully "launched" a tiny metal rocket using an unusual source of thrust - microwaves. The test was the latest a proof of principle for a kind of propulsion that has never been the beneficiary of the levels of investment poured into traditional chemical rockets, but which its proponents say could some day be a superior way to get spacecraft into orbit.

http://www.technologyreview.com/blog/mimssbits/25701/

... 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.

This is an equivocation. They're saying there's no fuel but there is certainly propellant. The air inside the rocket tube is used as propellant.

GIThruster wrote:The air inside the rocket tube is used as propellant.

Which would simply make it useless as a launchcraft up to orbit. You're still going to need to carry propellant for the part up where there's no air. This is more like a pulse jet than it's a rocket.

Interesting, albeit impractical.

Well, on the bright side, you would surely have hot tea for the brief and exciting flight.

Puns, a national pass-time...

Using microwave power transmission to heat a working fluid carried by a rocket could work. How well depends on what kind of engine performance you get. If the microwave collector is small and light enough for the power collected you might get SSTO performance or better. Count on a fair portion of the transmitted microwaves being lost, and needing a POWERFUL transmitter.

The engineering to get such a launch system is non-trivial.

what percentage of the velocity you want is done in atmosphere though? IIRC the big arguments with the polywell powered SSTO were whether the air breathing engine outweighed the fuel that would be used instead.

This seems to be a bit simpler--less mechinery to worry about. I found some of the off topic comments on the page amusing. Odd what people come up with.

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.

Ladies and Gentlemen,

We have been arguing laser array-powered launch over in:

The Next Generation of Human Spaceflight

viewtopic.php?t=2590

this is basically the same thing Myrabo has been doing for over 10 years already...

Diogenes wrote: http://www.technologyreview.com/blog/mimssbits/25701/

Lightcraft with microwaves.

http://www.lightcrafttechnologies.com/

AcesHigh wrote:this is basically the same thing Myrabo has been doing for over 10 years already...

Great minds...

And IIRC, Myrabo's been at it 20+ years.