

Microwave-Powered Rocket Ascends without Fuel  - cwan
http://www.technologyreview.com/blog/mimssbits/25701/

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Groxx
They're covering this like it's a new thing... At least at the end they
mention this:

> _The rocket traveled 1.2 meters into the air - the world record for such a
> craft is 72 meters and 12.7 seconds of flight, accomplished in 2001._

ie, 9 years since a massively more successful demonstration. Slow science news
day?

edit: the ones I've seen before were essentially two cones, one upside down
and inside the other. It was spun, and lasers / masers were shot at the
bottom, creating a bit of plasma near the joint of the two cones.

    
    
          /\
         /  \
        /    \
       / \  / \
        ^ \/ ^
        │    │
        └────┴── plasma

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JoeAltmaier
I'm confused - I thought the idea was to use "light pressure" to propel
rockets from the ground - not gas expansion. Light pressure would work all the
way to space - in fact could propel a Mars mission from a stationary/orbital
laser.

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mikemol
Not only no on-board fuel, but no on-board propellant, either. There goes
everything I learned about rockets from Heinlein. Slick!

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tocomment
Why don't we investigate this more? It sounds very promising. What are the
primary obstacles?

~~~
Das_Bruce
Some would include that it super heats the air to gain thrust, as you get
higher the air gets thinner meaning less thrust. Also there are limits to how
narrow you can keep a laser beam through air and atmospheric absorption and
diffusion.

All these things combine to make it more difficult to get energy to the craft
as it get's further away.

~~~
tocomment
Would adaptive optics help? and/or Could the rocket carry its own propellant
but get power from the beam? E.g., carry its own air.

~~~
Das_Bruce
I don't know what you mean when you say adaptive optics sorry, but yes it
could carry it's own air, I'm not sure of the practicalities but it's
possible.

Also there are hard physical limits on how finely you can converge a point of
light, MinimumDiameter = (2.44 _wavelength_ frequency)/LenseDiameter This is
called the minimum spot size.

~~~
tocomment
Adaptive optics lets telescopes compensate for atmospheric distortions to get
similar performance to telescopes in space. It's also used for lasers. I don't
know how it works but it sounds like it would be applicable here.

Your minimum diameter formula doesn't sound too restrictive.

