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I am surprised that no one has yet mentioned the Gyrocompass: https://en.wikipedia.org/wiki/Gyrocompass https://en.wikipedia.org/wiki/Gyrocompass The post ment

I am surprised that no one has yet mentioned the Gyrocompass: https://en.wikipedia.org/wiki/Gyrocompass https://en.wikipedia.org/wiki/Gyrocompass The post mentions manually-set directional gyroscopes, but gyrocompasses are a step ahead of that; on any sufficiently-quickly-rotating planet, a gyrocompass will point you towards the geographic poles by noting the axis of precession of a gyroscope with arbitrary orientation. That's even better than a magnetic compass on Earth, since the magnetic poles do not line up exactly with the geographic poles, and the magnetic is non-uniform anyway (which is why navigational charts include notations of the magnetic deviation in different areas).

creshal 11y ago
How maintenance intensive are they, though? Moving parts in or near vacuum tend to be a bit iffy (e.g. lubrication), especially for multi-year (or multi-decade) robotic missions.
- davewasthere 11y ago
  There are non-moving part designs that utilise fibre-optics or laser rings. I've only seen either the physical or laser ring gyros. Not sure about which ones they'd use in space though.
  - avian 11y ago
    Grandparent is talking about gyrocompasses, not ordinary gryoscopes though. I haven't heard of a laser-ring gyrocompass. Not sure it if that is even possible.
    - rprospero 11y ago
      The laser gyroscopes do exist. They use lasers, plus the Sagnac effect, to measure rotations around on axis by interferometry. https://en.wikipedia.org/wiki/Sagnac_effect https://en.wikipedia.org/wiki/Sagnac_effect
    - darkmighty 11y ago
      The gyrocompass orientation should, in principle, be obtainable by properly integrating gyroscope readings (and accelerometer? not sure if required).
      - hamiltonkibbe 11y ago
        You still need a way of determining the initial position/pose
        darkmighty 11y ago
        I don't think so. The gyrocompass relies on gyroscopic precession. The precession itself can be obtained by integration, which gives orientation. Of course, the precision of this process may well be very low or unusable.
        hamiltonkibbe 11y ago
        you don't need an initial heading measurement but you still need to know where you are
        darkmighty 11y ago
        It would suffice to know the radius of the planet and it's rate of rotation.
        hamiltonkibbe 11y ago
        Using only a compass and the knowledge that you were somewhere on the planet earth, could you determine the shortest route from your locations to Chicago?
        darkmighty 11y ago
        Ah I thought you were referring to the gyrocompass functionality. Yes, for general navigation you need an initial position to determine your position from inertial measurement alone (as I said, you can determine orientation and latitude, but not longitude).
- comboy 11y ago
  I would assume that once you establish direction you can just put some 3 beacons and have a local navigation system based on that.
kefka 11y ago
Maybe you would know, but are MEMS gyroscopes of accurate quality to output true north data? Specifically referring to Invensense 9150 9dof (3 accel, 3 magnetometer, 3 gyro)
- planteen 11y ago
  Not for very long at decent accuracy. My of the hip guess is minutes. The zero rate output is +/-20 deg/s for the part you listed with RMS noise of 0.02 deg/s.
  - kefka 11y ago
    Hmm. A group of us at our local hackerspace is building an autonomous robot. We already have that 9DoF sensor as well as a GPS and barometer. I'm able to accurately calculate where North(magnetic) is, as well as down, and roughly what altitude I am, and synchronize them to sporadic GPS locks. Depending how useful, this could be good at providing North(true). I'll see if any sort of calibration would be useful (considering I know my lat/lon and can calculate the expected rotational vector). I'm investigating using ORB-SLAM with ROS to also provide accurate locations of the localization. The whole idea is that I can use this as yet another piece in a probability-location detection as well as map other things quickly and accurately.
    - planteen 11y ago
      Yeah using a compass and a magnetic field model using GPS position should let you estimate the bias from the gyro.

creshal 11y ago

How maintenance intensive are they, though? Moving parts in or near vacuum tend to be a bit iffy (e.g. lubrication), especially for multi-year (or multi-decade) robotic missions.

davewasthere 11y ago
There are non-moving part designs that utilise fibre-optics or laser rings. I've only seen either the physical or laser ring gyros. Not sure about which ones they'd use in space though.
- avian 11y ago
  Grandparent is talking about gyrocompasses, not ordinary gryoscopes though. I haven't heard of a laser-ring gyrocompass. Not sure it if that is even possible.
  - rprospero 11y ago
    The laser gyroscopes do exist. They use lasers, plus the Sagnac effect, to measure rotations around on axis by interferometry. https://en.wikipedia.org/wiki/Sagnac_effect https://en.wikipedia.org/wiki/Sagnac_effect
  - darkmighty 11y ago
    The gyrocompass orientation should, in principle, be obtainable by properly integrating gyroscope readings (and accelerometer? not sure if required).
    - hamiltonkibbe 11y ago
      You still need a way of determining the initial position/pose
      - darkmighty 11y ago
        I don't think so. The gyrocompass relies on gyroscopic precession. The precession itself can be obtained by integration, which gives orientation. Of course, the precision of this process may well be very low or unusable.
        hamiltonkibbe 11y ago
        you don't need an initial heading measurement but you still need to know where you are
        darkmighty 11y ago
        It would suffice to know the radius of the planet and it's rate of rotation.
        hamiltonkibbe 11y ago
        Using only a compass and the knowledge that you were somewhere on the planet earth, could you determine the shortest route from your locations to Chicago?
        darkmighty 11y ago
        Ah I thought you were referring to the gyrocompass functionality. Yes, for general navigation you need an initial position to determine your position from inertial measurement alone (as I said, you can determine orientation and latitude, but not longitude).
comboy 11y ago
I would assume that once you establish direction you can just put some 3 beacons and have a local navigation system based on that.

kefka 11y ago

Maybe you would know, but are MEMS gyroscopes of accurate quality to output true north data? Specifically referring to Invensense 9150 9dof (3 accel, 3 magnetometer, 3 gyro)

planteen 11y ago
Not for very long at decent accuracy. My of the hip guess is minutes. The zero rate output is +/-20 deg/s for the part you listed with RMS noise of 0.02 deg/s.
- kefka 11y ago
  Hmm. A group of us at our local hackerspace is building an autonomous robot. We already have that 9DoF sensor as well as a GPS and barometer. I'm able to accurately calculate where North(magnetic) is, as well as down, and roughly what altitude I am, and synchronize them to sporadic GPS locks. Depending how useful, this could be good at providing North(true). I'll see if any sort of calibration would be useful (considering I know my lat/lon and can calculate the expected rotational vector). I'm investigating using ORB-SLAM with ROS to also provide accurate locations of the localization. The whole idea is that I can use this as yet another piece in a probability-location detection as well as map other things quickly and accurately.
  - planteen 11y ago
    Yeah using a compass and a magnetic field model using GPS position should let you estimate the bias from the gyro.