Drill recovery issues go interplanetary
No sample from Perseverance drill hole; Earth geos can relate Metal Tech News – August 11, 2021
Last updated 8/17/2021 at 3:04pm
Many Earthbound mineral exploration geologists can relate to the disappointment that must have been felt by NASA scientists when they realized that the Perseverance rover did not recover a sample from the first hole drilled by the Martian explorer.
"When core drilling that is as highly anticipated as the Perseverance drilling recovers nothing, the deflation and disappointment felt by both driller and geologist is palpable," said Curt Freeman, a geologist with more than four decades experience at drilling mineral deposits on Earth, told Metal Tech News.
Perseverance uses a hollow coring bit and a percussive drill at the end of its seven-foot-long robotic arm to bore holes into rocks that have the potential to offer textbook writing information on the geology and potential ancient life on the Red Planet.
Data sent back to Earth indicates that Perseverance's first hole went according to plan, the drill and bit were engaged, a hole was clearly drilled into the selected rock in Jezero Crater, and the sample tube was processed as intended. Everything went exactly as planned, except for one small detail, the titanium sample tube meant to be sealed and cached for pickup and return to Earth by a future mission was empty.
"The sampling process is autonomous from beginning to end," said Jessica Samuels, the surface mission manager for Perseverance at NASA's Jet Propulsion Laboratory in Southern California. "One of the steps that occurs after placing a probe into the collection tube is to measure the volume of the sample. The probe did not encounter the expected resistance that would be there if a sample were inside the tube."
A peek inside the tube by Perseverance confirmed that no Martian regolith – dirt and rock – was collected from the first drill hole.
While not the proverbial "hole-in-one" (pun definitely intended) that the Perseverance team had hoped for, setbacks are not unexpected while carrying out a drilling operation 384 million miles away from Earth.
Surprising rock and regolith properties have challenged previous Mars missions.
In 2008, the Phoenix mission sampled soil that was "sticky" and difficult to move into onboard science instruments, resulting in multiple attempts before achieving success. Additionally, Curiosity drilled into rocks that turned out to be harder and more brittle than expected. And most recently, the heat probe on the InSight lander, known as the "mole," was unable to penetrate the Martian surface as planned.
"I have been on every Mars rover mission since the beginning, and this planet is always teaching us what we don't know about it," said Jennifer Trosper, project manager for Perseverance at JPL. "One thing I've found is, it's not unusual to have complications during complex, first-time activities."
When it comes to recovering drill core, complications are now an interplanetary issue that can arise even with an experienced crew working directly on a rig boring into Earth.
"This is a very common problem during core drilling in the mining sector when you are drilling highly altered, broken, or faulted rock. And it is often the case that the worst recovery comes from the most mineralized rocks," Freeman said. "Geos love this sort of rock; drillers hate it!"
A similar dynamic may be at play on Mars, where the best place to collect geological data at the bottom of a crater that was once a lake, may also be a tough locale for collecting samples.
The very name of the pale-colored stones that NASA scientists believe to be from the original floor of the Jezero Crater – Crater Floor Fractured Rough – indicates the potentially troublesome broken nature of the rock at Perseverance's first drill target on Mars.
The problem, however, could also be mechanical.
Freeman says that a weakness in a barrel spring that should allow core to pass upward into the sample tube and prevent it from sliding out, much like the toy Chinese handcuff finger puzzles, is a mechanical issue that causes sample collection issues on Earth.
Trosper believes the lack of core in the Perseverance sample tube is more likely due to the rock than hardware.
"The initial thinking is that the empty tube is more likely a result of the rock target not reacting the way we expected during coring, and less likely a hardware issue with the sampling and caching system," she said.
To determine whether the issue is geological, mechanical, or some combination of the two, Perseverance is taking close-up pictures of its initial hole with the WATSON (Wide Angle Topographic Sensor for Operations and Engineering) imager at the end of its robotic arm.
A response team assembled here on Earth will analyze the images and other data from the first drilling and sampling to better understand what happened ahead of scheduling the next sample collection attempt.
"The drilling issues now faced by Perseverance reminds me of the Winston Churchill statement 'Personally, I am always ready to learn, although I do not always enjoy being taught.' I am sure some of the NASA scientists are feeling this way at this very moment!" said Freeman.
Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate in Washington, believes the response team will live up to the rover's name in learning what went wrong and how to resolve it.
"I'm confident we have the right team working this, and we will persevere toward a solution to ensure future success," he said.
NASA has yet to say whether it plans to drill another hole at Crater Floor Fractured Rough or if the rover will travel to the nearby Séítah – meaning "amidst the sand" in the Navajo language – which also hosts Mars bedrock, along with ridges, layered rocks, and sand dunes.
Recently, the Perseverance science team began using color images from the Ingenuity Mars Helicopter to help scout for areas of potential scientific interest and to look for potential hazards. Perseverance's flying sidekick completed its 11th flight on Aug. 4, traveling about 1,250 feet downrange of its current location so that it could provide aerial reconnaissance of the southern Séítah area.
Perseverance's initial science foray, which will span hundreds of sols, or Martian days, will be completed when the rover has made a 1.6- to 3.1-mile trek that ends back at its landing site. With any luck, the robotic Mars geologist will have filled eight of the 43 drill sample tubes it has onboard.
On its second scientific endeavor, Perseverance will investigate Jezero Crater's delta – the fan-shaped remains of the confluence of an ancient river and lake within Jezero Crater. The region may be especially rich in carbonate minerals, which often preserve fossilized signs of prehistoric microscopic life here on Earth.
More information on Perseverance, its scientific instruments, and current mission can be read at Mars geologist preps for historic drilling in the August 4, 2021 edition of Metal Tech News.