Playing with fusion-rockets
Apr. 29th, 2005 11:29 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
james_davis_nicollSpecifically with the table top fusion device.
Assume a probe has to be at least 5 tonnes to be interesting and that mass
ratios as high as e^3 are acceptable. Assume (since this thing doesn't produce
power) that we can dedicate a 10 gigawatt beam to powering this, of such a
wavelength that distance between the power plant and the probe isn't an insurmountable problem. In that case, I get an acceleration somewhere between
1/15 m/s/s and 1.33 m/s/s, with a final delta vee of around (obviously) 9,000 km/s. Does that look right?
If we are lazy, and I am, and we just use the 1/15 m/s/s value, then it takes
about 1560 days for the reaction mass to run out at which point the probe will be around 4000 AU out, moving at 3% the speed of light. Hmmm. 4000 AU suggests a short wavelength for the beam....
OK, it still takes so long to reach Alpha C that if such a probe were arriving now, it would have had to have been launched during the American Civil War. The probe does reach one light year in about a career's time, though.
Assume a probe has to be at least 5 tonnes to be interesting and that mass
ratios as high as e^3 are acceptable. Assume (since this thing doesn't produce
power) that we can dedicate a 10 gigawatt beam to powering this, of such a
wavelength that distance between the power plant and the probe isn't an insurmountable problem. In that case, I get an acceleration somewhere between
1/15 m/s/s and 1.33 m/s/s, with a final delta vee of around (obviously) 9,000 km/s. Does that look right?
If we are lazy, and I am, and we just use the 1/15 m/s/s value, then it takes
about 1560 days for the reaction mass to run out at which point the probe will be around 4000 AU out, moving at 3% the speed of light. Hmmm. 4000 AU suggests a short wavelength for the beam....
OK, it still takes so long to reach Alpha C that if such a probe were arriving now, it would have had to have been launched during the American Civil War. The probe does reach one light year in about a career's time, though.
no subject
Date: 2005-04-29 05:09 pm (UTC)Carlos
no subject
Date: 2005-04-29 05:19 pm (UTC)no subject
Date: 2005-04-29 05:26 pm (UTC)Carlos
no subject
Date: 2005-04-29 05:35 pm (UTC)I think that the Nature article must either have misquoted him or he doesn't understand rockets very well or I am misunderstanding something. To quote the article:
"Putterman also thinks that rocket propulsion could benefit. Space probes such as the European Space Agency's SMART-1, which recently arrived at the Moon, already use ion engines that eject a stream of charged xenon gas to produce a gentle forward thrust. The pyroelectric accelerator could produce a similar beam of ions moving at much greater speed, which would increase the thrust considerably, says Putterman."
No, it wouldn't. It would increase specific impluse. For a given power input, thrust would drop as ISP increases.
no subject
Date: 2005-04-30 03:01 pm (UTC)