Detective work allows the Perseverance Mars rover team to revive the SHERLOC device

After six months of effort, the instrument that helps the Mars rover search for potential signs of ancient microbial life is back online.

The SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics and Chemicals) instrument aboard NASA’s Perseverance Mars rover used its spectrometer and camera to analyze a rocky target for the first time since it encountered the problem last January. The instrument plays a key role in the search for signs of ancient microbial life on Mars. Engineers at NASA’s Jet Propulsion Laboratory in Southern California confirmed on June 17 that the instrument had succeeded in collecting data.

“Six months of running diagnostics, testing, image and data analysis, troubleshooting and retesting could not have produced a better conclusion,” said SHERLOC Principal Investigator Kevin Hand of JPL.

Mounted on the rover’s robotic arm, SHERLOC uses two cameras and a laser spectrometer to search for organic compounds and minerals in rocks that have been altered in an aquatic environment and can reveal signs of past microbial life. On January 6, a movable lens hood designed to protect the instrument’s spectrometer and one of its cameras from dust froze in a position that prevented SHERLOC from collecting data.

The SHERLOC team’s analysis pointed to a failure of a small motor responsible for moving the lens hood as well as adjusting the focus for the spectrometer and the Autofocus and Context Imager (ACI) camera. Testing potential solutions on the SHERLOC duplicate at JPL, the team began a long and painstaking evaluation process to determine if and how the lens hood could be moved to the open position.

SHERLOC detection

Among many other steps, the team experimented with heating a small lens hood motor, commanding the rover’s robotic arm to rotate the SHERLOC instrument in various orientations using supporting Mastcam-Z images, rocking the mechanism back and forth to dislodge any debris that might block the lens. cover, and even engage the rover’s percussive drill to try to loosen it. On March 3, images returned from Perseverance showed that the ACI cover had opened more than 180 degrees, clearing the imager’s field of view and allowing the ACI to be positioned close to the target.

“With the shroud out of the way, line of sight was established for the spectrometer and the camera. We were halfway there,” said Kyle Uckert, deputy principal investigator of SHERLOC at JPL. “We still needed a way to focus the instrument on the target. Without focus, the SHERLOC images would be blurry and the spectral signal weak.”

Like any good ophthalmologist, the team set out to find a prescription for SHERLOC. Unable to adjust the focus of the instrument’s optics, they relied on the rover’s robotic arm to make small adjustments to the distance between SHERLOC and its target to achieve the best image resolution. SHERLOC was ordered to take images of its calibration target so the team could verify the effectiveness of this approach.

“The robotic arm of the rover is amazing. It can be controlled in small quarter-millimeter steps to help us evaluate the new focus position of SHERLOC, and it can place SHERLOC with high precision on target,” Uckert said. “After testing first on Earth and then on Mars, we found that the best distance to place the SHERLOC robotic arm is about 40 millimeters,” or 1.58 inches. “At that distance, the data we collect should be as good as ever.”

Confirmation of ACI’s correct location on the Martian rock target came on 20 May. Verification on June 17 that the spectrometer was also functional checked the team’s last box, confirming that SHERLOC was functional.

“Mars is hard, and bringing instruments back from the edge is even harder,” said JPL’s Perseverance Project Manager Art Thompson. “But the team never gave up. With SHERLOC back online, we continue to survey and collect samples with a full complement of scientific instruments.”

Perseverance is in the later stages of its fourth science campaign, looking for evidence of carbonate and olivine deposits in the “Margin Unit,” an area along the inner rim of Lake Crater. On Earth, carbonates typically form in the shallows of freshwater or alkaline lakes. It is thought that this could also be the case for the Margin unit, which formed more than 3 billion years ago.