Quote from: Robotbeat on 03/01/2013 06:47 pmQuote from: JimO on 03/01/2013 06:45 pmIt's not too early to ask, but maybe in bad taste: what is the expected orbital lifetime of an inert 'Dragon' in its current orbit? If thrusters are not required, are we looking at an unguided random reentry? I'm not actually sure about the first question (don't know Dragon's altitude, though someone does), but Dragon isn't inert. With one thruster pod, you still can have partial attitude control.like a one armed man in a row boat
Quote from: JimO on 03/01/2013 06:45 pmIt's not too early to ask, but maybe in bad taste: what is the expected orbital lifetime of an inert 'Dragon' in its current orbit? If thrusters are not required, are we looking at an unguided random reentry? I'm not actually sure about the first question (don't know Dragon's altitude, though someone does), but Dragon isn't inert. With one thruster pod, you still can have partial attitude control.
It's not too early to ask, but maybe in bad taste: what is the expected orbital lifetime of an inert 'Dragon' in its current orbit? If thrusters are not required, are we looking at an unguided random reentry?
like a one armed man in a row boat
I hope everyone here understands that distance from ISS is not a critical factor - what IS critical is the orbital plane - every minute that Dragon is not at the same altitude as ISS, its orbital plane diverges from ISS, due to precession.At the current difference in altitude, Dragon's orbital plane will precess by some fraction of a degree each day, not counting the upcoming drop in altitude caused by drag (the drop in the altitude will result in even more precession).Someone here can probably calculate the actual precession rate, but its probably a matter of 5 or 6 days in this relative position before the precession makes later rendezvous very difficult. If it looks like the thrusters can be fixed, but it will take time, it might be worthwhile for SpaceX to attempt to raise orbital apogee a bit to buy some time, even with just one thruster.
lol, i choked down some coffee reading that. thanks jim.
Note that Robotbeat said "attitude". One armed rower can have quite good control of boat's heading. Moving forward is the difficult part.
Star trackers are used for attitude determination. This is useful not just for pointing for burns but also for power (solar arrays) and thermal pointing.
Quote from: mlindner on 03/01/2013 06:50 pmQuote from: Danderman on 03/01/2013 06:45 pmI hope everyone here understands that distance from ISS is not a critical factor - what IS critical is the orbital plane - every minute that Dragon is not at the same altitude as ISS, its orbital plane diverges from ISS, due to precession.At the current difference in altitude, Dragon's orbital plane will precess by some fraction of a degree each day, not counting the upcoming drop in altitude caused by drag (the drop in the altitude will result in even more precession).Someone here can probably calculate the actual precession rate, but its probably a matter of 5 or 6 days in this relative position before the precession makes later rendezvous very difficult. If it looks like the thrusters can be fixed, but it will take time, it might be worthwhile for SpaceX to attempt to raise orbital apogee a bit to buy some time, even with just one thruster.Thanks I was not aware of the precession issue. I always catch myself thinking in terms of orbital rendezvous in kerbal space program which has non-precessing orbits. Couldn't a burn at one of the crossing points of the precessed orbits correct for this, depending on fuel amounts?Yes, but as danderman noted the fuel amount required for the plane change will increase with time. 5-6 days is his SWAG but there is definitely a point beyond which rendezvous is no longer possible.
Quote from: Danderman on 03/01/2013 06:45 pmI hope everyone here understands that distance from ISS is not a critical factor - what IS critical is the orbital plane - every minute that Dragon is not at the same altitude as ISS, its orbital plane diverges from ISS, due to precession.At the current difference in altitude, Dragon's orbital plane will precess by some fraction of a degree each day, not counting the upcoming drop in altitude caused by drag (the drop in the altitude will result in even more precession).Someone here can probably calculate the actual precession rate, but its probably a matter of 5 or 6 days in this relative position before the precession makes later rendezvous very difficult. If it looks like the thrusters can be fixed, but it will take time, it might be worthwhile for SpaceX to attempt to raise orbital apogee a bit to buy some time, even with just one thruster.Thanks I was not aware of the precession issue. I always catch myself thinking in terms of orbital rendezvous in kerbal space program which has non-precessing orbits. Couldn't a burn at one of the crossing points of the precessed orbits correct for this, depending on fuel amounts?
Quote from: Jim on 03/01/2013 06:48 pmQuote from: Robotbeat on 03/01/2013 06:47 pmQuote from: JimO on 03/01/2013 06:45 pmIt's not too early to ask, but maybe in bad taste: what is the expected orbital lifetime of an inert 'Dragon' in its current orbit? If thrusters are not required, are we looking at an unguided random reentry? I'm not actually sure about the first question (don't know Dragon's altitude, though someone does), but Dragon isn't inert. With one thruster pod, you still can have partial attitude control.like a one armed man in a row boatNoone said that it would be particularly efficient or elegant
