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Rocket Gyroscopes - Why so large?
by
Danderman
on 26 Aug, 2013 14:28
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#1
by
IRobot
on 26 Aug, 2013 14:41
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Your cellphone has no gyroscope, it has a 3D magnetometer and accelerometer.
Although the accelerometer works fine (and could be used on a rocket), the magnetometer can't.
First, it does not have enough accuracy. Second, it will only work near earth's surface, third, works really bad with metal and magnetic fields around.
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#2
by
Jim
on 26 Aug, 2013 15:24
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#3
by
IRobot
on 26 Aug, 2013 15:36
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Jim, the chip he has on his phone measures some 5x5mm by 2mm high, that is why he says gyros are large...
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#4
by
Patchouli
on 26 Aug, 2013 15:36
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#5
by
jongoff
on 26 Aug, 2013 19:39
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We did some work a few years ago for a company doing nanosat launch upper stages. You can make the GN&C work with a relatively "low-end" and small IMU + a good GPS w/ Real Time Kinetics + a good Kalman filter. We fit the whole GN&C avionics onto a system that was about the size of a 3x5 card, IIRC.
For bigger launchers that aren't so volume/mass constrained, a fancier IMU may provide some accuracy benefits. The IMU DC-X used wasn't much bigger than a 1U cubesat's volume for instance.
~Jon
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#6
by
IRobot
on 26 Aug, 2013 19:41
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Patchouli, thanks, I was unaware that there were solid state gyros on the market. I read the Iphone article and despite having the pads on the PCB, they did not solder the gyro, probably to cut down costs.
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#7
by
baldusi
on 26 Aug, 2013 22:46
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Do those giros have to give accurate integration at around a 5 burn/9hr mission in deep space?
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#8
by
Patchouli
on 27 Aug, 2013 02:01
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Patchouli, thanks, I was unaware that there were solid state gyros on the market. I read the Iphone article and despite having the pads on the PCB, they did not solder the gyro, probably to cut down costs.
Well it's in the iphone but they decided to leave it out of the ipad at the time which is really nothing more then a big iphone.
It might be because of cost or maybe in that platform because it being a larger device the accelerometer sees a larger movement then it does in a phone so they decided it doesn't need the gyro.
The PS move and Wii Motion plus also have MEMS gyros as well and would be a cheap source if you want one to experiment with.
http://www.techradar.com/us/news/gaming/sony-playstation-move-tear-down-report-717793http://en.wikipedia.org/wiki/Wii_MotionPlusDo those giros have to give accurate integration at around a 5 burn/9hr mission in deep space?
The one found in a phone probably not unless you did a lot of cleaning up of the signal and went through testing and characterizing a lot of parts etc.
Even then the accuracy probably would be a far cry from a good space rated gyro.
The one in Cassini does something a lot harder then that though it's not a MEMS but works on the same principal and is still very small.
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#9
by
Danderman
on 27 Aug, 2013 13:47
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Remembering that the gyros that caused the recent Proton crash were in the first stage, can anyone explain why the first stage requires more accuracy than can be obtained from a small solid state gyro as is found in cell phones?
I can understand why an upper stage flying 25,000 miles from the surface might need a more complex gyro than a cell phone system, but I would bet that the Briz gyros are a lot smaller than the first age gyros.
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#10
by
Jim
on 27 Aug, 2013 13:52
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Remembering that the gyros that caused the recent Proton crash were in the first stage, can anyone explain why the first stage requires more accuracy than can be obtained from a small solid state gyro as is found in cell phones?.
Can cell phone gyros provide fraction of a degree accuracy?
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#11
by
jongoff
on 27 Aug, 2013 14:10
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Remembering that the gyros that caused the recent Proton crash were in the first stage, can anyone explain why the first stage requires more accuracy than can be obtained from a small solid state gyro as is found in cell phones?.
Can cell phone gyros provide fraction of a degree accuracy?
Probably not cellphone ones per se, but the ones we used for the project I mentioned earlier were still pretty darned small (looks like 23x23x23mm), and had gyro performance that was creeping up on the low end of commercial IMUs (like the Crossbow we had used at Masten). For a big rocket that you're spending lots of money on, adding in a better IMU might make sense, but this one we picked for the nanosat launcher upper stage was good enough when combined in a Kalman filter with a good GPS board with RTK.
~Jon
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#12
by
kevin-rf
on 27 Aug, 2013 15:27
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Or you could go with occam's razor and say, legacy.
The best evidence of that was the Express-AM4 failure a few years ago. It was caused the Gyro being ICBM legacy and not able to go 360 degrees.
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#13
by
baldusi
on 27 Aug, 2013 17:28
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Or you could go with occam's razor and say, legacy.
The best evidence of that was the Express-AM4 failure a few years ago. It was caused the Gyro being ICBM legacy and not able to go 360 degrees.
That one was on the Briz-M and yes, was a big mechanical gyro that had, on one axis, a hard limit (270?). But I think that Proton-M modernization did included some new avionics. Still, on an 800tonnes and 53m rocket, I don't think that a few extra kg and liters of gyros would be so much of a problem. In fact, as of right now, I think it's the heaviest currently launching rocket.