If you're trying to speed your program up by writing source code to compile optimally, one of two things is happening: 1) you're at the bleeding edge, writing some inner loop that's gonna run 1E14 times on a Cray, or 2) you're wasting your time. I've always found that when my program is too slow, it's because I'm not using clever enough high-level algorithms.
Which satellite is that, I wonder? Looks like you're near Boston so I'm assuming CXO? Our satellite (FUSE) has never had detector background problems that could be strongly associated with solar flares. However, we're in safemode for other reasons right now, so I don't know what the most recent flare would have done to our detectors.:)
Other universities do control satellites as well. UC Berkeley ran EUVE (reentered at the end of January), as well a spacecraft called FAST and the newly launched HESSI
There may be others but I don't know.
Re:The remaining wheels are still used
on
Hack in Space
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· Score: 3, Informative
You're right, the two remaining wheels are still used.
What they probably managed to do is to use the two remaining wheels to do the fine pointing but the satellite will tend to slowly spin ?of course? lacking the two other wheels to compensate. By bringing the torquers into the loop they cancel the spin and attain the fine pointing.
Actually, not quite. The roll and "skew" wheels are the ones that still work fine. The new design allows the torquer bars to correct an axis that is basically perpendicular to the roll and skew directions, which is sort of diagonal across the science apertures.
It turns out that although the torquer bars are not designed for fine control (their control bandwidth is 15 times lower than the reaction wheels), the satellite is also heavy compared to the MTB's torque. So, the pointing stability is in fact quite good, and the jitter is not much worse than what we had before... as long as the satellite is not pointed in a part of the sky where gravity gradient disturbances are strong.
Re:magnets .... (I wish it were that simple!)
on
Hack in Space
·
· Score: 1
Ok then... I'll give you some code for a high fidelity magnetic field model and an orbit propagator. If I just tell you the dipole moments of the three torquer bars and the spacecraft's inertia tensor, you should be able to come up with a simple control algorithm in fairly short order.
By the way, we can't accept any more than 1/4000 degree in attitude jitter.
Oh yes, your solution has to run on a 386 and not crash for the next 3 years or more, by the way.:b
Kidding of course!
I used to work on EUVE as a planner, it'll be sad to see it go.
Contrary to what a lot of people are guessing, EUVE had no onboard thrusters or fuel of any kind, so there is no way to control re-entry. The re-entry has nothing to do with the decomissioning, and everything to do with the fact that atmospheric drag is finally bringing it down. EUVE would have lasted longer in a higher orbit, but those are much more expensive, and it just wasn't practical. This is the case for the vast majority of low earth orbitting satellites (and especially inexpensive astronomy statellites that aren't out to make a profit).
Satellites like EUVE can change their pointing by spinning reaction wheels -- that's how the telescope was pointed at different targets all over the sky -- but merely rotating the satellite around does nothing to affect when it's going to re-enter.
All I can say now is, "There will be fireworks!" --Anon
Slashdot Mirror
If you're trying to speed your program up by writing source code to compile optimally, one of two things is happening: 1) you're at the bleeding edge, writing some inner loop that's gonna run 1E14 times on a Cray, or 2) you're wasting your time. I've always found that when my program is too slow, it's because I'm not using clever enough high-level algorithms.
Which satellite is that, I wonder? Looks like you're near Boston so I'm assuming CXO? Our satellite (FUSE) has never had detector background problems that could be strongly associated with solar flares. However, we're in safemode for other reasons right now, so I don't know what the most recent flare would have done to our detectors. :)
'ten HUT! There's a flight software guy on deck! :>
Other universities do control satellites as well. UC Berkeley ran EUVE (reentered at the end of January), as well a spacecraft called FAST and the newly launched HESSI
There may be others but I don't know.
What they probably managed to do is to use the two remaining wheels to do the fine pointing but the satellite will tend to slowly spin ?of course? lacking the two other wheels to compensate. By bringing the torquers into the loop they cancel the spin and attain the fine pointing.
Actually, not quite. The roll and "skew" wheels are the ones that still work fine. The new design allows the torquer bars to correct an axis that is basically perpendicular to the roll and skew directions, which is sort of diagonal across the science apertures.
It turns out that although the torquer bars are not designed for fine control (their control bandwidth is 15 times lower than the reaction wheels), the satellite is also heavy compared to the MTB's torque. So, the pointing stability is in fact quite good, and the jitter is not much worse than what we had before... as long as the satellite is not pointed in a part of the sky where gravity gradient disturbances are strong.
Ok then... I'll give you some code for a high fidelity magnetic field model and an orbit propagator. If I just tell you the dipole moments of the three torquer bars and the spacecraft's inertia tensor, you should be able to come up with a simple control algorithm in fairly short order. By the way, we can't accept any more than 1/4000 degree in attitude jitter. Oh yes, your solution has to run on a 386 and not crash for the next 3 years or more, by the way. :b
Kidding of course!
Contrary to what a lot of people are guessing, EUVE had no onboard thrusters or fuel of any kind, so there is no way to control re-entry. The re-entry has nothing to do with the decomissioning, and everything to do with the fact that atmospheric drag is finally bringing it down. EUVE would have lasted longer in a higher orbit, but those are much more expensive, and it just wasn't practical. This is the case for the vast majority of low earth orbitting satellites (and especially inexpensive astronomy statellites that aren't out to make a profit).
Satellites like EUVE can change their pointing by spinning reaction wheels -- that's how the telescope was pointed at different targets all over the sky -- but merely rotating the satellite around does nothing to affect when it's going to re-enter.
All I can say now is,
"There will be fireworks!" --Anon