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The other article has a nonzero information content, for a change: http://txchnologist.com/post/32463368168/channeling-star-trek-researchers-to-begin-fusion ht

by uvdiv 14y ago

The other article has a nonzero information content, for a change: http://txchnologist.com/post/32463368168/channeling-star-trek-researchers-to-begin-fusion http://txchnologist.com/post/32463368168/channeling-star-tre... Summary: it's nuclear pulse propulsion (riding the shock wave of a nuclear explosion). Small nuclear explosions in this concept: they hope to create small (~1 ton TNT eq.) pure-fusion explosions using nanosecond bursts of extremely powerful electric currents (plasma Z-pinch). Basically, it's the same problem as fusion power plants based on "inertial confinement" (euphemism for "explosion"). Lithium is a progenitor of tritium. This is common D+T fusion. This concept is not remotely close to practicality. Which is why the reported goal ("a mind-bending 62,600 mph") is bizarre; it's only a small factor better than chemical rockets. It's just as bad as e.g. nuclear thermal propulsion, which was designed and built 40 years ago. So I really don't see the point.

WiseWeasel 14y ago
The fuel has a much greater energy density than chemical rockets, making longer distances practical, and the process is safer than nuclear fission.
- 001sky 14y ago
  link to oldskool version > http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion
- uvdiv 14y ago
  That's my complaint, it doesn't have much greater energy density, or more precisely it's not usefully translated to momentum. The speed target in the article is extremely low ("62,600 mph") -- only a small factor higher then what chemical rockets achieve, and comparable (as I mentioned) to nuclear thermal rockets. (It looks like they edited their article to mention NTRs.) They have extremely energetic fuel, but they don't get any meaningful specific impulse out of it. Maybe they don't easily extract momentum from high-energy radiation. Or maybe they lose too much mass to radiation damage or vaporization ("ablative shield") -- their mass consumption could be dominated by shielding, not fuel. Their ultimate goal is to develop a nuclear fusion propulsion system by 2030 that can spirit spacecraft from Earth to Mars in around three months—about twice as fast as researchers think they could go with a nuclear fission engine, another scheme that is being investigated but has not yet been built.
  - WiseWeasel 14y ago
    The speed doesn't tell us the whole story. If a chemical rocket can only practically carry enough fuel to burn a couple times on a one-way trip to Mars, while this has fuel to burn for maneuvers and a return journey, then it is a big advancement. We weren't given enough info, so it's a bit early to discount it as worthless.

by uvdiv 14y ago

WiseWeasel 14y ago

The fuel has a much greater energy density than chemical rockets, making longer distances practical, and the process is safer than nuclear fission.

001sky 14y ago
link to oldskool version > http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion
uvdiv 14y ago
That's my complaint, it doesn't have much greater energy density, or more precisely it's not usefully translated to momentum. The speed target in the article is extremely low ("62,600 mph") -- only a small factor higher then what chemical rockets achieve, and comparable (as I mentioned) to nuclear thermal rockets. (It looks like they edited their article to mention NTRs.) They have extremely energetic fuel, but they don't get any meaningful specific impulse out of it. Maybe they don't easily extract momentum from high-energy radiation. Or maybe they lose too much mass to radiation damage or vaporization ("ablative shield") -- their mass consumption could be dominated by shielding, not fuel. Their ultimate goal is to develop a nuclear fusion propulsion system by 2030 that can spirit spacecraft from Earth to Mars in around three months—about twice as fast as researchers think they could go with a nuclear fission engine, another scheme that is being investigated but has not yet been built.
- WiseWeasel 14y ago
  The speed doesn't tell us the whole story. If a chemical rocket can only practically carry enough fuel to burn a couple times on a one-way trip to Mars, while this has fuel to burn for maneuvers and a return journey, then it is a big advancement. We weren't given enough info, so it's a bit early to discount it as worthless.