There has been some excitement in the air over the past few weeks at NASA’s Jet Propulsion Laboratory in Pasadena, California, where mission controllers were preparing the Perseverance rover to collect its first sample from the surface of Mars. This mission milestone would be the culmination of years of hard work by a team of over 90 dedicated scientists and engineers.
The orders to start the first sampling (from the Roubion drilling site) were sent to the rover on Sol 164 (Thursday, August 5th). On the morning of Friday, August 6th, the team gathered to see the sample data come in. Everything seemed fine until a few hours later they were notified that the sample tube was empty! Since then, the rover’s science and engineering teams have been studying 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 enables test return missions without boots on the ground – as was the case with the lunar rocks brought by the Apollo astronauts. It consists of three robotic elements, including the 2 meter (7 foot) long, five-jointed robotic arm that supports a large tower that contains a rotating percussion drill for collecting core samples.
The second element is the chisel carousel, which provides the drill with the drill bits and empty sample tubes and transfers tubes filled with samples to the rover chassis for assessment and processing. The third is the 0.5 meter (1.6 foot) long sample handling arm (also known as the “T-Rex arm”), which is located in the belly of the rover and is also responsible for moving sample tubes between storage and documentation stations as a bit carousel.
Louise Jandura, Chief Engineer for Sampling & Caching at NASA JPL, shared the story on NASA’s Perseverance website. The team met online at 2:00 a.m. PDT (5:00 a.m. EDT) to see the first data from the core drilling, she explained. The data confirmed that the corer had drilled to the desired depth of 7 cm (inches) while one of the rover’s navigation cameras provided an image of the borehole surrounded by the cuttings.
“So far, so good, we thought when we checked out to get a few more hours of sleep before the next data came in about 6 hours later,” she said. What they learned next, however, as she began to describe, sent them on a roller coaster ride of emotions:
“Technical telemetry and a picture from the CacheCam in the Adaptive Caching Assembly (ACA, the tube processing hardware) confirmed that we had transferred the sample tube from the corer to the ACA, sealed the sample tube, and successfully stored it – a huge first-time success. The team was thrilled. Then the volume measurement and the image after the measurement came and indicated that the sample tube was empty. “
The borehole from Perseverance’s first sampling attempt can be seen in the left image along with the rover’s shadow, which was captured by one of the rover’s navigation cameras. The image on the right is a composite image of the first Perseverance borehole on Mars, created with multiple images from the rover’s WATSON imager. Credits: NASA / JPL-Caltech / MSSS
The team spent the next two days searching the mission data to determine the source of the problem. So far they have succeeded in examining three possible explanations. They first examined the core drill’s data to assess its performance during both the Abrasian and core drilling activities, and then compared it to the data from the earth-based tests (where over 100 core samples were drilled in a simulated environment).
Second, they examined images of the Martian surface that the rover was traveling on during its post-core drilling activities. These did not reveal anything noticeable during the core process, and there were also no intact cores or core pieces on the Martian surface. As a result, the completed team decided to take depth measurements of the borehole using images taken after the core sample was drilled.
This included the original coring image as well as merged images captured with the Wide Angle Topographic Sensor for Operations and eNgineering (WATSON) Imager – which is part of the Scanning Habitable Environment with Raman & Luminescence for Organics & Chemicals (SHERLOC) instruments . Based on these measurements, Jandura said the team came to the following conclusion:
“[T]The core activity in this unusual rock resulted in only powders / small fragments that were not retained due to their size and lack of any significant core. It seems that the rock wasn’t tough enough to produce a core. Some material is visible in the bottom of the hole. The material of the desired core is likely to be either in the bottom of the borehole, in the clippings, or a combination of both. A further differentiation is not possible due to the measurement uncertainties.
Image of the South Seitah region, taken with the Ingenuity Helicopter (the shadow of which is visible at the bottom of the image). Photo credit: NASA / JPL-Caltech
In short, they concluded that the powdered core sample disintegrated between the point they removed it from the ground and tried to put it in a tube and back into the SCS. Both the science and engineering teams believe the nature of the rock was the main factor behind the difficulty encountered and have since decided to go ahead and wait for the rover to reach its next sampling location.
This location is in the region of the Jezero crater known as South Seitah, which was only photographed from the air by the Ingenuinity Mars Helicopter on Wednesday, August 11th. This will be the furthest distance Perseverance has traveled for this phase of its scientific operations, and based on the images the rover and Ingenuity have received so far, the rover team believes they will likely encounter sedimentary rocks from which a core sample is easier to take.
Aside from delays or developments, the teams expect to collect a core sample from this region by early September. That experience, with the hardware working as expected but the environment not working together, is reminiscent of the nature of exploration, Jandura said:
“No matter how much you prepare, a certain result is never guaranteed. Despite this finding, science and technology have advanced. We have achieved the first fully autonomous sequence of our sampling system on Mars within the time constraints of a single sol. This is a good sign of the pace of our remaining science campaign. “
Further reading: NASA