If you really want to de-orbit after direct-to-GEO, it would be much more efficient to include xenon thrusters. At an ISP of 3000-4000, it would only take 250 kg of xenon to give a 4.5t second stage -1500 m/s to drive it into the atmosphere.Since time is not critical here, a very simple system might suffice. Perhaps fixed solar panels covering the payload adapter, then simply use whatever power is available and that determines the pace. Just thrust near apogee for efficiency, again since speed is not a main concern.For Deep Space One, the thruster, power control, tank, and wiring massed about 50 kg.. Body mounted solar cells at about 50 w/kg would mass 20 kg for a 1kw array that might fit on the payload adaptor.So a total mass of 350 kg should be enough to de-orbit a 4.5t stage. This would make a great public service project for NASA, ESA, or other space agency. A 350 kg kit, all engineered, for de-orbiting GEO payloads. You could even imagine that at some point, something like this would be required for GEO payloads themselves.
Quote from: LouScheffer on 02/15/2018 02:16 pmIf you really want to de-orbit after direct-to-GEO, it would be much more efficient to include xenon thrusters. At an ISP of 3000-4000, it would only take 250 kg of xenon to give a 4.5t second stage -1500 m/s to drive it into the atmosphere.Since time is not critical here, a very simple system might suffice. Perhaps fixed solar panels covering the payload adapter, then simply use whatever power is available and that determines the pace. Just thrust near apogee for efficiency, again since speed is not a main concern.For Deep Space One, the thruster, power control, tank, and wiring massed about 50 kg.. Body mounted solar cells at about 50 w/kg would mass 20 kg for a 1kw array that might fit on the payload adaptor.So a total mass of 350 kg should be enough to de-orbit a 4.5t stage. This would make a great public service project for NASA, ESA, or other space agency. A 350 kg kit, all engineered, for de-orbiting GEO payloads. You could even imagine that at some point, something like this would be required for GEO payloads themselves.Not really, it would have to managed, tracked and controlled for weeks or months. You forgot attitude control gas and more power to control the valves. Also, a redesigned GNC architecture and receiver to accept commands. Need to add GPS or star trackers to keep INS updated.
If you really want to de-orbit after direct-to-GEO, it would be much more efficient to include xenon thrusters.
Dead stages in a graveyard orbit, or worse yet debris, need to be tracked forever,
It's not obvious you need a command receiver - all existing stages de-orbit based strictly on pre-programmed instructions.
Quote from: LouScheffer on 02/15/2018 02:16 pmIf you really want to de-orbit after direct-to-GEO, it would be much more efficient to include xenon thrusters.It would also be notably cheaper than the direct burn to smack it into an encounter with the moon, scattering it into an orbit it will rapidly escape to solar.To fly past L1, you need only about 900m/s, half that of decircularising a GEO orbit.1.2 ton fuel use needed, not the 3 or so for decircularising.
