Microwave-Powered Rocket Ascends without Fuel | Hacker News Reader

Microwave-Powered Rocket Ascends without Fuel

technologyreview.com

16 pointscwan10 comments

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

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.

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

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

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.

Gentlemen, I think I've solved our problem of air thinness at high altitudes. We use a RAM jet like shape for the rocket to funnel the air and compress it.

The rocket could like this:

  thin air
  
  \   /
   | |
   ||
  
  compressed air
  
  laser 
    |
  _____

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.

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 = (2.44wavelengthfrequency)/LenseDiameter This is called the minimum spot size.

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.

'Adaptive optics' generally means lenses and the like whose shape (and possibly other properties) varies during operation to meet current operational requirements.

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