Over the past few weeks, there was quite a bit of excitement in the air at the NASA Jet Propulsion Laboratory in Pasadena, California, where mission controllers were prepping the Perseverance rover to acquire its first sample from the Martian surface. This mission milestone would be the culmination of years of hard work by a team of over 90 dedicated scientists and engineers.
The commands to commence operations to take its first sample (from drill site Roubion) were sent to the rover on Sol 164 (Thurs, Aug. 5th). On the morning of Friday, Aug. 6th, the team gathered to witness the sampling data come in. Everything appeared to be fine until they were notified a few hours later that the sample tube was empty! Since then, the rover’s science and engineering teams have been investigating what could have become of the sample.
Perseverance‘s Sample Caching System (SCS) is a unique piece of hardware. Basically, it is the first system that allows for sample return missions without the need for boots on the ground – as was the case with the moon rocks brought back by the Apollo astronauts. It is composed of three robotic elements, which include the 2-meter (7 foot) and five-jointed robotic arm, which carries a large turret that includes a rotary percussive drill to collect core samples.
The second element is the bit carousel, which provides the drill bits and empty sample tubes and transfers sample-filled tubes into the rover chassis for assessment and processing. The third is the 0.5-meter (1.6-foot) sample handling arm (aka. the “T-Rex Arm”) that is located in the belly of the rover and is responsible for moving sample tubes between storage and documentation stations as well as the bit carousel.
Louise Jandura, the Chief Engineer for Sampling & Caching at NASA JPL, shared the story on NASA’s Perseverance website. As she explained, the team gathered together online at 02:00 AM PDT (05:00 AM EDT) to see the first data come in from the coring operation. The data verified that the Corer had drilled to the desired depth of 7 cm (inches). At the same time, one of the rover’s navigation cameras provided an image of the borehole surrounded by the cuttings pile.
“So far, so good we thought as we signed off to try and get a few more hours of sleep before the next set of data arrived about 6 hours later,” she said. However, as she went to describe, what they learned next sent them on a roller-coaster ride of emotions:
“Engineering telemetry and an image from the CacheCam inside the Adaptive Caching Assembly (ACA, the tube processing hardware) confirmed we had transferred the sample tube from the Corer to the ACA, sealed the sample tube, and successfully placed it in storage – a huge first-time success. The team was elated. Then the volume measurement and post-measurement image arrived indicating that the sample tube was empty.”
The team spent the next two days combing through the mission data to determine the cause of the issue. So far, they have managed to investigate three possible explanations. First, they examined data from the Corer to assess its performance during both the abrasion and coring activities, then compared it to the data provided by the Earth-based testing (where over 100 core samples were drilled in a simulated environment).
Second, they examined images of the Martian surface where the rover traveled during its post-coring activities. These revealed nothing out of the ordinary during the coring process, nor did they turn up an intact core or core pieces on the Martian surface. As a result, the team decided to take depth measurements of the borehole using images taken after the core sample was drilled.
This included the original coring image and merged images taken by the Wide Angle Topographic Sensor for Operations and eNgineering (WATSON) imager – which is part of the Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC) instrument. Based on these measurements, said Jandura, the team arrived at the following conclusion:
“[T]he coring activity in this unusual rock resulted only in powder/small fragments which were not retained due to their size and the lack of any significant chunk of a core. It appears that the rock was not robust enough to produce a core. Some material is visible in the bottom of the hole. The material from the desired core is likely either in the bottom of the hole, in the cuttings pile, or some combination of both. We are unable to distinguish further given the measurement uncertainties.
In short, they’ve concluded that the powdery core sample fell apart between the point where they removed it from the ground and attempted to put it into a tube and back in the SCS. Both the science and engineering teams believe that the nature of the rock was the main contributor to the difficulty they experienced and has since decided to carry on and wait for the rover to reach its next sample location.
This spot is in the region of the Jezero Crater known as South Seitah, which was photographed from the air as recently as Wednesday, Aug. 11th, by the Ingenuity Mars Helicopter. This will be the farthest Perseverance has traveled for this phase of its science operations. Based on images obtained by the rover and Ingenuity thus far, the rover team anticipates that they will likely encounter sedimentary rocks that will be easier to obtain a core sample from.
Barring any delays or developments, the teams anticipate that they will be extracting a core sample from this region by early September. This experience, where the hardware performed as expected but the environment did not cooperate, is a reminder of the nature of exploration, said Jandura:
“A specific result is never guaranteed no matter how much you prepare. Despite this result, science and engineering have progressed. We achieved the first complete autonomous sequence of our sampling system on Mars within the time constraints of a single Sol. This bodes well for the pace of our remaining science campaign.”
Further Reading: NASA