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NASA Relies on Thrusters to Steer Station
Craig Fink wrote:
Your right there are a lot of ways to get attitude without the traditional gyroscopes. As you said fiber optic gyros, or couple of star trackers. When the Hubble is pointed at a star, pitch and yaw can come from the target image. All that is needed are a couple of cameras perpendicular to get roll. I wouldn't think there is anything more accurate than using the stars. The problem isn't getting a measurement of the attitude, stars work just fine for that. The problem is maintaining that reference as the craft changes attitude, and measuring the rates of change and motion, which is pretty hard to do with star sensors. Two different functions, which only a gyroscope or similar technology can provide in a single system. D. -- The STS-107 Columbia Loss FAQ can be found at the following URLs: Text-Only Version: http://www.io.com/~o_m/columbia_loss_faq.html Enhanced HTML Version: http://www.io.com/~o_m/columbia_loss_faq_x.html Corrections, comments, and additions should be e-mailed to , as well as posted to sci.space.history and sci.space.shuttle for discussion. |
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Space Station attitude control downmode ( NASA Relies on Thrusters to Steer Station)
Bjørn Ove Isaksen wrote:
Rusty B wrote: NASA Relies on Thrusters to Steer Station Last time I saw the numbers for required upmass it was pretty tight conserning especialy water. Without gyros and back to RCS the station would spend a lot more fuel (IIRC it was a new feature of Mir). Is there someone here that has an idea of the problems this might lead to? Sincerely Bjørn Ove If they only have two CMGs, then they can use only two and still maintain attitude control without using any fuel. They might have to slightly modify the software, but it should be doable. Treat the sum of the torques on the Station as a controller in place of the broken CMG. Leave the remaining two CMGs perpendicular to each other, but not perpendicular (45 degrees might be best) to the sum of the torques. Allow the two remaining CMGs to fight the sum of the torques. When a CMG become saturated, flip over changing the sign on the sum of the torques to desaturate the CMG. The two remaining CMGs and sum of the torques would be able to perform the flip maneuver. I would think that it would give an almost full range (only slightly degraded) of attitude control away from the stable attitude. Essentially, allow the sum of the torques to act as a controller in place of the third CMG and pick an attitude where the sum of the torques is never close to being perpendicular to the other two CMGs. Of course, maybe they already have this downmode capability built into the software and have downmoded to thrusters because they aren't concerned about fuel usage. Things get a little tougher with only one CMG, but it could still be used to minimize fuel usage. Craig Fink |
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NASA Relies on Thrusters to Steer Station
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Space Station attitude control downmode ( NASA Relies on Thrusters to Steer Station)
Craig Fink wrote in
ink.net: If they only have two CMGs, then they can use only two and still maintain attitude control without using any fuel. They might have to slightly modify the software, but it should be doable. Correct. ISS uses two-axis CMGs, so two CMGs gives you three-axis control with one redundant axis. No software changes needed. And in fact, that is what they are doing right now. Several of the stories in the media appear to be incomplete (surprise!) ISS is currently using CMGs for attitude hold, thrusters only for maneuvering from one attitude to another. Or at least that was the case last I checked. -- JRF Reply-to address spam-proofed - to reply by E-mail, check "Organization" (I am not assimilated) and think one step ahead of IBM. |
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Space Station attitude control downmode ( NASA Relies on Thrusters to Steer Station)
Jorge R. Frank wrote:
Several of the stories in the media appear to be incomplete (surprise!) ISS is currently using CMGs for attitude hold, thrusters only for maneuvering from one attitude to another. Or at least that was the case last I checked. Thanx for clearing that up. The only diffrence is as I understand it that only attitude manuvering is now done by thrusters, instead of CMG's. Attitude hold is still done by CMG's. This should'nt have a big impact on fuel usage as it is'nt preformed all the time. Sincerely Bjørn Ove |
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Space Station attitude control downmode ( NASA Relies on Thrusters to Steer Station)
Craig Fink wrote in message link.net...
If they only have two CMGs, then they can use only two and still maintain attitude control without using any fuel. They might have to slightly modify the software, but it should be doable. It's already in the software. Two can be used (and have been used). Of course, maybe they already have this downmode capability built into the software and have downmoded to thrusters because they aren't concerned about fuel usage. There were some inaccuracies in the reports that came out. The use of thrusters only was for attitude *maneuvers*, not attitude control during normal bore-hole-in-the-sky operations. Maneuvers are relatively uncommon events, maybe once every few weeks. During steady-state ops, control is still going to be maintained on CMGs and that's where all the propellant savings comes from. The reason there isn't much concern on prop usage for maneuvers on thrusters is because, frankly, they really aren't much less efficient than using CMGs with thruster assist. Maneuvers were utilized with CMGs in control more for operational convenience than anything else (no control handover to the Russian Segment required). Things get a little tougher with only one CMG, but it could still be used to minimize fuel usage. Interesting point. Someone who worked on Skylab told me IBM was developing one-CMG control software when they started to have problems with a second CMG after the first one failed (Skylab only had three). I've not seen any evidence of how far that got. |
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NASA Relies on Thrusters to Steer Station
On 06 Dec 2003 11:24:54 -0500, Jim Kingdon wrote:
Apparently somewhere in between the size that will pass through a Progress docking port and that which will pass through a Shuttle docking port. I don't actually know whether it is size or mass which prevents use of Progress (possibly both). The CMG itself is over 220 kg and the following article also refers "to the weight and volume of equipment needed to carry the CMG into orbit": http://www.space.com/missionlaunches...te_020608.html That's because a CMG package - the gyro and necessary sub-assemblies - weighs some 1,100 pounds [500 kg] at launch and must be mounted on a special carrier beam in the shuttle's cargo bay. http://spaceflightnow.com/station/sts111/020608cmg/ Thank you. I must confess that I didn't realize just how massive they are (and obviously need to be). Dale |
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Space Station attitude control downmode ( NASA Relies on Thrusters to Steer Station)
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NASA Relies on Thrusters to Steer Station
Assuming that the girodines can be placed in any reasonably sized
module, I would assume that sooner or later they will be sent to ISS aboard some sort of module. Can the girodines operate successfully with the CMGs? capbrit wrote in message . .. On 7 Dec 2003 08:04:21 -0800, (Explorer8939) wrote: Do the Russians have any plans to include gyrodines in any of the future modules? There are half a dozen RS gyrodynes sitting in a building outside Moscow waiting for a home. Originally the gyrodynes were to be housed in the SPP (Science Power Platform) but it got downsized. Then they were to be in the UDM (Universal Docking Module). Ditto. |
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