[AR] Re: CubeSat V2
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sun, 4 Aug 2019 14:31:43 -0400 (EDT)
On Sat, 3 Aug 2019, adam paul wrote:
It could even be as simple as using the same form factor for both, the
only difference is one eventually separates from the satellite and one
never deploys. If you had integrated payloads that finished their
experiments in different time frames you could even eject dead
experiments to improve station-keeping propellant efficiency...
That last might seem appealing but it doesn't actually help much. To a
rough first approximation, the stationkeeping requirement is that the
thrust from the propulsion system, averaged over the time between
reboosts, must equal the air drag (averaged over the same time). The mass
of the spacecraft is entirely irrelevant -- a heavier spacecraft needs
reboosting less often, but needs more fuel for each reboost. Only if
ejecting dead experiments reduced *surface area*, and therefore air drag,
would it help significantly.
(To a second approximation, you can gain a little by jettisoning surplus
mass just before a reboost -- hang onto it until then so it slows orbit
decay, then dump it so the reboost burn doesn't have to push it.)
Henry
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