WASHINGTON — NASA’s Perseverance Mars rover will soon begin depositing a cache of samples it has collected since landing last year as part of efforts to return those samples to Earth.
In an online briefing held Dec. 16 during the fall meeting of the American Geophysical Union (AGU), project officials said the rover is scheduled to place the first of 10 sample tubes on the surface as early as December 19. Confirmation that the tube was successfully placed on the surface would come in images returned the next day.
Perseverance is depositing the tubes to create a reservoir that could be retrieved by subsequent missions in the Global Mars Sample Return (MSR) campaign. It will serve as a backup to Perseverance itself, which will hold other tubes and return them to a future Sample Retrieval Lander.
This landing will carry two helicopters, based on the Ingenuity helicopter included in the Perseverance missions, which will fly from the landing to the cache, picking up one tube at a time and returning them to the lander. This approach, as described in a revised Mars sample return strategy published in July, eliminates a rover that would collect samples, reducing the overall cost of the mission.
The cache is located in a region called Three Forks that will also serve as a landing site for the future Sample Retrieval Lander. “One would be hard-pressed to imagine a more benign place,” said Michael Meyer, principal scientist for the Mars Exploration Program at NASA Headquarters. The terrain is flat with few rocks or other obstacles. “The surface is like a pool table, very boring.”
The pipes will not be dropped in one place, but will be spread over tens of meters. “There are a lot of different requirements on how far apart the tubes can be to allow recovery,” said Justin Maki, a Mars 2020 imaging scientist at the Jet Propulsion Laboratory. One of the biggest is to place them far enough apart that the helicopters can pick them up without disturbing the rest of the cache.
The result is a complex pattern with the 10 tubes placed between 5 and 15 meters from each other. Depositing them requires carrying out a “highly choreographed and strategically coordinated” plan, said Katie Stack Morgan, JPL’s assistant project scientist. This process will take between one and two months, he estimated.
Once the deposit is complete, Perseverance will continue its science mission, exiting the Jezero crater floor and into the upper part of the delta created by the ancient river that flowed into the crater. The rover will continue to the rim of the crater and perhaps beyond, collecting additional samples along the way.
The creation of the repository will also mark a change in Perseverance’s sampling strategy. “During this primary mission, the sampling approach adopted by Mars 2020 has been to collect paired samples,” said Meenakshi Wadhwa, MSR principal scientist at Arizona State University. One tube of each pair will be placed in the cache and the other will be kept in the rover.
After the cache is complete, Perseverance will switch to a “single sample strategy,” Stack Morgan said, collecting only one sample at a time. “We can think of more places and more types of rocks that we can test.” Perseverance has so far filled 21 of its 43 tubes.
Perseverance will deposit ten sample tubes in a complex pattern to avoid any interference problems when the helicopters come to retrieve them. Credit: NASA/JPL-Caltech
Development of helicopters
As Perseverance deposits sample tubes as a deposit, engineers are working on designing the helicopters that would pick them up.
That effort began in earnest about six months ago, when MSR executives asked the Ingenuity team if a helicopter based on this design could be used to collect sample tubes, said Teddy Tzanetos, manager of Sample Recovery Helicopter at JPL, during another AGU fall meeting. report of December 12. There had been previous studies, he said, looking at the feasibility of using an Ingenuity-based helicopter to transport sample tubes.
The new helicopter is similar to Ingenuity, with the biggest differences being the addition of a robotic arm to collect tubes and sample wheels on each of its four landing legs. It weighs 2.3 kilograms, about half a kilogram more than Ingenuity, and can carry a 150-gram sample tube. Other characteristics, such as its maximum speed, range and flight time, are the same as the Ingenuity.
“We want, where we can, to rely on heritage and, where appropriate, deviate from that heritage to build this new capability,” he said. “But we’re taking great advantage of all the incredible lessons we’ve learned, and will continue to learn, from Ingenuity over the past year and a half.”
Retrieving a sample will take four suns, or Martian days. On the first sun, the helicopter will fly from the Sample Retrieval Lander to a landing site a few meters from the tube. On the second sun, the helicopter will roll up to the tube and grab it. On the third sun, the helicopter will fly back to land, and on the fourth sun, it will rotate into position so the lander’s robotic arm can pick up the tube.
“Now we’re really a fusion of a little rover that can fly, or you can think of it as a little helicopter that can drive,” Tzanetos said.
He said the new helicopter can take advantage of Ingenuity’s design because of the conservative margins in Ingenuity’s design, so the new helicopter can be heavier without any major changes. “We’ll continue to test it to see how far we can push our old heritage design. We’ll make some decisions in the months ahead about how much of our heritage we want to keep versus how much we want to change.”
Meanwhile, Ingenuity continues to operate on Mars, far exceeding original plans of no more than five flights. At the AGU briefing on December 12, Håvard Grip, Ingenuity’s chief pilot, noted that before the first flight the project created a logbook to record the flights. “A book with only five pages would look too silly, so we put a bunch of extra pages in here, to make it look like a real book.”
Ingenuity made its 36th flight on December 10, traveling 110 meters in one minute. “Guess what?” Grip said. “We’ve run out of pages.”