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There is discussion of a gyrocompass in comments on the page How does Curiosity know how to point and move it's high gain antenna in real time? but so far I don't think there is a hard "Yes" or "No" supported by sources that states unequivocally if these rovers have gyrocompass capability, nor if they do if they use it.

A gyrocompass is a gyroscope that measures precession caused by the slow, steady rotation of the planet on which it sits. A rover would have to "sit still" during this measurement long enough for the precession vector to be calculated, allowing the planet's axis of rotation to be determined relative to the rover's coordinate system. If you know your latitude and longitude you can then determine (at least partially) your body attitude or orientation.

See also:

Of course if you have historical data, several images and an inclinometer or accelerometer, you can also get that information without a gyrocompass. See this answer:

We can assume that the Surface Attitude Position and Pointing (SAPP) is similar to the one used in the Mars Exploration Rover. Because of that, we can rely on a paper called "Mars Exploration Rover Engineering Cameras"

https://doi.org/10.1029/2003JE002077

It seems that the attitude information is collected from two main sources: an inertial measurement unit and the rover cameras. The IMU provides the rover's roll and pitch angles (Nadir vector) by measuring gravity acceleration. The NAV cameras are used to calculate the Sun position.

Section 3.1 (paragraph 27) from that paper says:

In addition to ground operators on Earth, there are a number of onboard users of the MER cameras. The autonomous navigation (NAV) software uses the cameras to detect hazards during a traverse, and the Surface Attitude Pointing and Positioning (SAPP) system uses the cameras to locate the sun and calculate the rover orientation. Both of these onboard modules can request an image at any time (typically during or immediately after a traverse) and have access to the same functionality as the ground commands, including the ability to send an image to the downlink system. If desired by the operations team, it is possible to downlink all (or a fraction) of the autonomously collected images through the setting of IMG parameters.

So while that answer suggests that these rovers use cameras, plus accelerometers as tiltmeters (nadir vector) I'd like to ask:

Question: Do Curiosity and Perseverance have gyrocompasses? Has any rover had one? If so, what kind and how do they work?

Are there any selfies of Curiosity or Perseverance with their high gain antenna deployed and "looking up"?

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  • $\begingroup$ What bearing do those linked camera questions have on this question, other than containing the string 'gyro'? What bearing does the linked question about the selfie have on this question? $\endgroup$ Nov 25, 2021 at 5:00
  • $\begingroup$ @OrganicMarble not everybody understands how sensitive a gyroscope sensor can be to determine the spin-axis of the Earth (or Mars) and that even a small MEMS-based "gyro" chip (as opposed to a rotating gyroscope) is so affected by the planet's rotation that it will blur a DSLR's image rather than stabilize it if your exposure is long enough. In fact the effect will be 16x worse on the ISS, so using image stabilization on those night photos of aurora and airglow could be really problematic; so much so that it deserves a new question! Anyway, goal is to add some background for future readers. $\endgroup$
    – uhoh
    Nov 25, 2021 at 5:18
  • $\begingroup$ My speculation is a gyrocompass would be a mass burden during launch and when on Mars it would be an energy burden, firstly as a mass that needs to be moved when the rover moves & secondly it would use electrical energy when being used to take measurements. Accelerometers, emphersises & humans controlling the system on Earth might be less taxing to a rover's electrical and overall energy systems. $\endgroup$
    – Fred
    Nov 28, 2021 at 6:56
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    $\begingroup$ Apparently the Apollo lunar rovers had gyroscopic compasses. See Section 5. Heading. "A circular moving scale, with the marker at the top indicating the heading of the lunar rover, in degrees. Essentially, a gyroscopic compass which was calibrated using the Sun Shadow Device". $\endgroup$
    – Fred
    Nov 28, 2021 at 7:40
  • $\begingroup$ @Fred I think that's a gyroscope but not necessarily a gyrocompass. A gyrocompass "finds North" by itself, it doesn't need to be calibrated with an initial heading. $\endgroup$
    – uhoh
    Nov 28, 2021 at 19:38

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