[AR] Re: Cold Gas Hydrogen Thruster (Re: Roll control...)
- From: Nels Anderson <nels.anderson@xxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Thu, 7 Jun 2018 11:16:50 -0400
On 2018-06-07 10:42 AM, Craig Fink wrote:
On Thu, Jun 7, 2018 at 9:30 AM Henry Vanderbilt
<hvanderbilt@xxxxxxxxxxxxxx <mailto:hvanderbilt@xxxxxxxxxxxxxx>> wrote:
Laser diodes (in fact any directional light emitter) produce
ridiculously small amounts of thrust, but at ridiculously high Isp.
But, they would easily extend themselves to a dual mode thruster if
you point the lasers down center-line of a Hydrogen Thruster. Low
thrust ISP in the millions, High thrust ISP in the thousands. So, you
would have to pick the right frequency for the laser diode to excite
the Hydrogen.
I wish they had put one of those one the New Horizons probe, low
thrust mid-course corrections, hi thrust planetary burns. Sounds like
it was made for planetary probes.
With Isp's like that, the propellant mass would be low and, hence, would
cease to be a very relevant criterion. The question is, what's the mass
of the system, including the power supply needed to run it at high thrust?
But I have another worry every time the idea of heating hydrogen gas
with IR LEDs comes up: what's the opacity of cold H2 gas? Despite the
fact that hydrogen is by far the most abundant element in the Universe,
astronomers very rarely observe H2. That's because its symmetry means
that it has no electric dipole moment. When it is observed in the IR,
it's through electric quadrupole transitions. So I'm not sure how much
of that IR will be absorbed by the H2 over a path length measured in
centimeters (maybe you can get that up to meters by relying on the
tank's reflectiveness). Maybe it would be better to heat the H2
resistively, though that is not nearly so sexy. And one cannot help
noting that resistojet's appeal is limited to a few special situations.
Other related posts:
