13
$\begingroup$

I'm curious if curiosity has started to drive backwards, at least occasionally, as part of an effort to reduce the rate of damage to the wheels.

This has come up after writing this answer to the question Does the Curiosity rover really have a chance of driving to the top of Mt. Sharp?

Emily Lakdawalla's 2014 blogpost Curiosity wheel damage: The problem and solutions says in part (it's very long and very thoughtful post):

4. How can they prolong the life of the wheels?

They can't go to Mars and switch out the wheels. Fortunately, they have identified several ways to reduce the rate at which the wheels accumulate damage.

Driving more judiciously.

Rover drivers are avoiding every pointy rock they can steer around. This only helps in the first 10 or 20 meters of a drive, where they can see smaller potentially hazardous rocks. On hazardous terrain, performing shorter drives allows them to avoid many potentially wheel-damaging rocks.

Driving backwards.

When they turn the rover around, the rover's middle and front wheels are dragged behind their supporting arms rather than being shoved forward. And the angle of the bogie arm that holds the rover's rear wheel is such that it does not experience the same kind of downward forces that the front and middle wheels do when the rover is driving forwards. Heverly showed a video, taken in the JPL Mars Yard, of a test wheel being driven over the sharpened metal spike with the rover driving backwards, and the wheel was only dented, not punctured.

There is a cost to driving backwards. At the end of each drive, they have to face forwards in order to acquire images of the path ahead for planning. They can't take those images while facing backwards, because the RTG and antennas on the rover's rear deck obscure the view from the cameras on the mast. So to drive backwards, they have to turn in place, then drive, then turn in place again. Each turn in place puts about 6 meters on the rover's wheels, or 12 meters for the drive. For short drives (which is what they do in bad terrain), this can swiftly add up. The drivers have to weigh the cost of increasing drive distance against the potential savings to the wheels of driving backwards. Driving backwards therefore is most valuable on long "blind" drives where the drivers aren't steering around smaller rocks.

$\endgroup$
  • 1
    $\begingroup$ Emily Lakdawalla's article was worth reading and your question got me more interested in Curiosity and its activities ! $\endgroup$ – Conelisinspace Oct 17 at 7:42
  • 1
    $\begingroup$ @Conelisinspace That's great to hear, and Emily Lakdawalla rocks! $\endgroup$ – uhoh Oct 17 at 7:45
12
$\begingroup$

From the msl mission updates:

February 19, 2014

Testing on Earth has shown that driving backward should reduce wear on the front and middle wheels so the Sol 547 drive was the first long, 100 meters, backward drive. It went very well, and the terrain ahead looks good, so another long drive is planned for Sol 548, again mostly backward.

February 20, 2014

The rover drove over 100 meters on Sol 548, so it is time for another full set of wheel images to monitor wear.

April 27, 2018

One of the advantages of driving backward is that rocks the rover has driven over end up in view of the remote sensing instruments.

The updates above were the only ones talking about driving backward in all those mission updates, so it seems that it happened so regularly after February 19, 2014 that it even was not worth mentioning !

Note: Sometimes forwards or backward driving can be detected with raw images.
The distances below are estimated with this source and this map.

For some drives backward 12 m. has to be substracted because of the 2 turns that have to be made after a drive. (see the question above.)

On sol 549 (February 20, 2014), Curiosity drove 7 meters forwards.
On sol 550 (February 21, 2014), Curiosity drove 17 meters forwards.
On sol 552 (February 23, 2014), Curiosity drove 81 meters backward.
On sol 553 (February 24, 2014), Curiosity drove 57 meters backward.
On sol 555 (Feb. 24, 2014), Curiosity drove first 42 meters backward and then 10 m. forwards.
On sol 563 (March 7, 2014), Curiosity drove > 15 m. backward.
On sol 565 (March 9, 2014), Curiosity drove 35 m. backward.
On sol 569 (March 13, 2014), Curiosity drove 107 m. backward.
On sol 572 (March 16, 2014), Curiosity drove 94 m. backward.

On sol 743 (September 8, 2014), Curiosity drove 92.6 m. forward.

$\endgroup$
  • $\begingroup$ This is great research, thank you! $\endgroup$ – uhoh Oct 12 at 1:30
  • $\begingroup$ Year one 1.8 km, two 7.2 km, three 2.4 km, four 3.1 km, five 4 km, six 3 km, seven 1.6 km. $\endgroup$ – Conelisinspace Oct 19 at 15:23
  • $\begingroup$ 7th year 105 drives, 8th year 65 drives. $\endgroup$ – Conelisinspace Oct 19 at 17:30
1
$\begingroup$

From the article Relating geologic units and mobility system kinematics contributing to Curiosity wheel damage at Gale rater, Mars:
DOI: https://doi.org/10.1016/j.jterra.2017.03.001
From 6. Traverse planning and accumulated wheel damage

In addition, -X direction drives were implemented more frequently (Fig. 19) to minimize additional damage to L1,L2,R1, and R2, until it was theorized that the wheel wear caused by the required post-drive turns in place to position the rover for end of drive imaging and telecommunications outweighted the benefits of -X direction driving. This led to the decision to return to +X direction drives as a baseline. The turns in place were thought to cause additional wheel damage, particularly to the middle wheels because they sweep the smallest radius arc during these maneuvers, creating elevated loads when engaging obstacles.

..............................................Figure 19...........................................................

-X and +X drives

$\endgroup$

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.