As explained in @karthikeyan's answer the InSight lander will rely upon its landing system to orient the lander properly, so that once on the ground instruments such as the RISE antennas will be pointing in the proper direction, in this case roughly East and West, more specifically, towards Earth when InSight is near the edge of the planet's disk as seen from Earth.

From this short conference paper:

For RISE, Doppler measurements will be made at times when the Earth is at low elevation, when the Doppler signature due to the rotation of Mars is largest. Two fixed medium-gain antennas, one pointed to the east and one pointed to the west, will be used to provide adequate gain for RISE.

While InSight is still moving horizontally with high velocity during its entry, it has its velocity vector (from whence it comes) as a reference with respect to the terrain. But very near the end of its seven minutes of terror, in the final hover and drop, what reference will it use for lateral orientation (rotation about the vertical)?

There's no useful planetary magnetic field for direction-finding. Is it known what cues the landing system will actually use to orient InSight correctly?

  • 1
    $\begingroup$ I am going to taste a guess before looking up for references. I feel that surface features might be compared with the database of images from MRO, which might help in identifying the cardinal direction. Usually, the remote landing employs a camera to look directly below the probe, right from a altitude of few kilometers $\endgroup$ Nov 24 '18 at 2:44
  • 1
    $\begingroup$ @karthikeyan I have a hunch that you have good taste in guesses ;-) I think there are some other answers here about terrain-based navigation on Mars in general, that may have helpful resources. $\endgroup$
    – uhoh
    Nov 24 '18 at 2:59
  • $\begingroup$ haha! It was a typo. I meant "I am going to TAKE a guess..". Anyways, thanks for the suggestions to look into. I'll start my hunt $\endgroup$ Nov 24 '18 at 3:11
  • 1
    $\begingroup$ there seems to be a lack of attitude related information! And I consider my camera backed answer as the resolutions from MRO and lander might be different. $\endgroup$ Nov 24 '18 at 5:43
  • 1
    $\begingroup$ Another possibility is to land while the Sun is at a low inclination close to the horizon and use this as a reference for direction. $\endgroup$
    – asdfex
    Nov 24 '18 at 14:16

By integrating inertial measurements, initialized from the final star tracking about 20 or 30 minutes earlier.

Also, from Spaceflight 101:

With the separation of the Cruise Stage seven minutes before re-entry, the InSight spacecraft solely relies on its MIMU for attitude propagation, rate measurement and the deceleration trigger for the critical parachute deployment event. Two redundant MIMUs reside on opposite sides of the lander, each comprising three QFLEX accelerometers for linear acceleration measurements along the three body axes and three Honeywell ring-laser gyros for angular rotation measurement.

The MIMU outputs data at 200 Hz including the accumulated linear velocity change and the accumulated angle change in three Cartesian axes. After digitization of the raw data, the MIMU achieves a delta-v resolution of 2.7 mm/sec at a noise level of under 0.08 mm/sec and angular data is delivered with a resolution of 0.011 deg/sec.

enter image description here

Honeywell MIMU – Credit: Honeywell Source

  • 1
    $\begingroup$ Life would be so much easier if we had two, dissimilar Suns. $\endgroup$
    – uhoh
    Nov 24 '18 at 4:18
  • $\begingroup$ okay then: Why are InSight's two RISE horns pointed slightly south of east, and north of west? $\endgroup$
    – uhoh
    Nov 24 '18 at 4:35
  • 4
    $\begingroup$ @karthikeyan No. It's a tactical-grade IMU. $\endgroup$
    – Mark Adler
    Nov 24 '18 at 7:38
  • 1
    $\begingroup$ @karthikeyan I've added a bit more information on the two IMUs. $\endgroup$
    – uhoh
    Nov 25 '18 at 6:09
  • 2
    $\begingroup$ Very nice. @uhoh should get the credit for this answer. $\endgroup$
    – Mark Adler
    Nov 27 '18 at 5:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.