Author Topic: Electric/chemical Energy to kinetic energy conversion  (Read 135769 times)

Offline Bob B.

  • Global Moderator
  • Moonwalker
  • *****
  • Posts: 1438
  • Gender: Male
    • Rocket & Space Technology
Re: Electric/chemical Energy to kinetic energy conversion
« Reply #45 on: June 21, 2006, 12:57:50 PM »
Is meta-helium something real?
I never heard of it until ijuin mentioned it yesterday so I'm in the dark as much as you, Don.

EDITED TO ADD:

This web page has a little information about meta-helium:

Meta-helium He*: SPIN-POLARIZED TRIPLET HELIUM. Three helium atoms are aligned in a metastable state. When it reverts to normal state it releases 0.48 gigjoules per kilogram. The trouble is that it tends to decay spontaneously, with a lifetime of a mere 2.3 hours.

Meta-helium He IV-A: DIATOMIC METASTABLE HELIUM. One normal and one excited helium atom are paired to form a stable solid.

Exhaust Velocity:
Metahelium He*:  43,000 m/s
Metahelium He IV-A:  21,600 m/s

« Last Edit: June 21, 2006, 02:14:44 PM by Bob B. »

Offline Bob B.

  • Global Moderator
  • Moonwalker
  • *****
  • Posts: 1438
  • Gender: Male
    • Rocket & Space Technology
Re: Electric/chemical Energy to kinetic energy conversion
« Reply #46 on: June 21, 2006, 01:44:13 PM »
Yes the argument is about how to define efficiency. 

Is efficiency measured in mass of propellant required to move a given mass to a given delta-v?  If so we should try to set our exhaust velocity as close to the speed of light as possible.

Is efficiency measured in energy expended to move a given mass to a given delta-v?  If so we should try to set our exhaust velocity to the current cumulative delta-v.

Is efficiency measured in dollars to move a given mass to a given delta-v?  If so we may look at endless factors that effect the cost of design, construction, operating expenses and time to mission accomplishment.

Good, I think we’re reaching an understanding.  Let me add that for common chemical propellants, mass efficiency and cost efficiency are virtually indistinguishable.  If we optimize mass we’ve almost certainly optimized cost as well.

I was under the impression when we started this discussion that you were arguing the rocket designer should always try to optimize energy because it is always most efficient.  Of course I now realized your argument was not that simple.

Offline DonPMitchell

  • The Right Stuff
  • Moonwalker
  • ****
  • Posts: 1200
  • Gender: Male
    • Mental Landscape
Re: Electric/chemical Energy to kinetic energy conversion
« Reply #47 on: June 21, 2006, 06:10:19 PM »
I can't find any scientific reference to meta-helium.  It appears to be a science-fiction device used in some novels by Robert Forward.
Never send a human to do a machine's job.
  - Agent Smith

Offline jdbenner

  • The Right Stuff
  • Apollo CMP
  • ****
  • Posts: 381
  • Gender: Male
Re: Electric/chemical Energy to kinetic energy conversion
« Reply #48 on: June 21, 2006, 07:22:25 PM »
The science fiction device theory may be correct.  But another class of exotic theoretical propellants with similar performance has been investigated.  Using free radicals as propellant would allow high specific impulse, except that they are unstable.  It is highly unlikely that we will have propellant tanks filled with the likes of monatomic hydrogen,ever.  but it sure looks good on paper.
Joshua D. Benner Associate in Arts and Sciences in General Science

Offline Nik

  • Gemini Pilot
  • ***
  • Posts: 103
Electric/chemical Energy to kinetic energy conversion
« Reply #49 on: October 23, 2006, 11:37:56 AM »
Regret bump: I'd lost access to this site for several months...

D'uh, there is much discussion about that tapered wave-guide notion...

Problem is how you do the math: If it provides thrust, we'll all learn to do the math to suit. This is known, IIRC, as paradigm change...

If, per 'standard' version, it does NOT provide thrust, we'll toast the Old Math and drown our accelerated interplanetary dreams with same tankard of terrestial plonk...