[AR] Re: FW: drag brakes (was Re: Cubesats orbital grenades ?)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 16 Dec 2017 19:34:41 -0500 (EST)
On Sun, 17 Dec 2017, John Dom wrote:
I'd vote for bottled nitrogen expansion RCS type propulsion design (not
a gas gun!). Only requires only a solenoid valve plus actuator
electronics...
Unfortunately, thruster performance is poor and the high-pressure tank is
very heavy. GN2 at room temperature has a theoretical Isp of about 80s
with infinite expansion, which is probably going to be 65-70s with a real
nozzle and real losses. For a mere 100m/s deorbit, your spacecraft mass
has to be about 17% GN2 at the start of deorbit... which isn't too bad by
itself, *BUT* the tank will typically weigh rather more than its contents.
There is a high payoff for higher Isp (e.g., a resistojet rather than cold
gas) and a propellant that liquefies under pressure for storage (Freon,
CO2, N2O, maybe ammonia if you've got a really good negotiator).
Henry
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