The New York TimesJul 29, 2020 17:31:24 IST
Send a robotic spacecraft to Mars, grab some rocks and dirt and bring those back to Earth.
How hard could that be?
It’s more like an interplanetary circus act than you might imagine, but NASA and the European Space Agency think that now is the time they can finally pull off this complex choreography, tossing the rocks from one spacecraft to another before the samples finally land on Earth in 2031.
“The science community, of course, has lusted after doing this for quite some time,” said James Watzin, the director of the Mars exploration program at NASA.
Over the last couple of decades, robotic explorers have revealed an increasingly complex picture of Mars, but planetary scientists are limited by the amount of science that can be packed in a spacecraft.
“You can only carry so much instrumentation into the field, robotically,” Watzin said. “To really get into some of the really intriguing questions at a detail level means we need to parse the evidence down on the molecular level and try to tease the information out of very, very old material. And that requires a whole suite of instrumentation that was clearly too large to shrink and send to another planet.”
With fresh Mars rocks on Earth, more scientists will be able to examine them, employing a wide array of the most sophisticated equipment in laboratories around the world.
The first step of this epic undertaking, known as Mars sample return, starts soon with Perseverance, the next NASA rover. It is scheduled to liftoff on July 30, headed for Jezero, a crater that was once a lake about 3.5 billion years ago, and is a promising place where signs of past life on Mars could be preserved.
One of the key tasks for Perseverance is to drill up to 39 rock cores, each a half-inch wide and 2.4 inches long, that look interesting enough to merit additional scrutiny on Earth. Each sample of rock and dirt, weighing about half an ounce, will be sealed in an ultraclean cigar-size metal tube.
But initially, NASA had no plans to bring those tubes back to Earth. Perseverance has no way of flinging the rocks off Mars.
Three years ago, a team of engineers at NASA’s Jet Propulsion Laboratory in California, began taking a closer look at when the return part of Mars sample return could be undertaken. They considered the possibility of launching the retrieval spacecraft in 2026 with the samples returning three years later.
That timeline, they found, was too ambitious.
But if the landing on Earth was pushed back to 2031, the schedule appeared to be feasible. “We actually feel like we could do this,” Watzin said.
The Trump administration’s budget request for NASA for fiscal year 2021 included $233 million to continue development, two years after the agency received $50 million for the initial studies. Last month, the 22 member nations of the European Space Agency gave the go-ahead on the collaboration with NASA.
The Perseverance science team has already begun preliminary geological analysis about what should be brought back to Earth.
“We became ever more focused on how to do that element of it right,” said Kenneth Farley, the project scientist for Perseverance. “We’ve kind of transitioned from a ‘yeah, someday these samples will get picked up’ to ‘yeah, they might get picked up pretty soon.’ It’s been an important evolution.”
Space agency officials have not yet announced a total price tag, but the cost is expected to run several billion dollars.
“We’re trying to keep this under a certain cost target,” said Brian K. Muirhead, who is leading the sample return design at the Jet Propulsion Laboratory. “We’re really coming up with the estimates — ‘This is what we think it’s going to take’ — and so far, NASA has said, ‘OK, keep going.’”
If everything goes to plan, two spacecraft will blast off to Mars in 2026. One will be a NASA-built lander that will be the heaviest vehicle ever put on the surface of Mars. It will be carrying a rover, built by the Europeans, to fetch the rock samples, and a small rocket that will launch the rocks to orbit around Mars.
The lander will take a roundabout trajectory to Mars, arriving in August 2028, the beginning of the Martian spring. The solar-powered fetch rover will then roll off the lander, make a dash to collect at least some of the rock samples and bring them back and transfer them to the lander. The samples, in turn, will be robotically moved to the top of the Mars ascent vehicle, the rocket that will launch the rocks off Mars.
The second spacecraft, the Earth Return Orbiter, will be built by the European Space Agency. It will take a quicker path to Mars, pulling into orbit before the lander’s arrival. That will allow the orbiter to serve as the relay for communications from the lander as it zooms to the surface.
The launch of the ascent vehicle will deposit a container, about the size of a soccer ball, with the rock samples circling around Mars about 200 miles above the surface. The orbiter then has to find this container, like a baseball outfielder chasing down a fly ball. The orbiter will be tracking the launch of the rocket, but for simplicity, the container itself does not possess any thrusters or a radio beacon. It is, however, white, which should make it easier to spot against the darkness of space.
“This is obviously one of the key issues: How do you find it?” Muirhead said. “Once you know where its orbit is, it’s very easy to match orbit.”
A door on the orbiter will open to capture the container. A 1,000-pound contraption within the orbiter then rotates and slides the container to the proper configuration within the spacecraft, taking care to seal off the possibility that anything from Mars could contaminate anything outside of the sample container.
The orbiter would then depart Mars. As it approached Earth, it would eject the samples, now mounted within what is called the Earth entry vehicle, on a collision course with the Utah desert.
Parachutes were another complication that engineers decided was unnecessary, so the entry vehicle, which resembles a large sombrero, is to hit the ground at a speed comparable to a highway car crash: 90 mph.
The scientific cargo — rocks and dirt, which are not fragile — will easily survive that impact.
Many of the details like where the lander will set down, remain undecided. If Perseverance is still in good working condition, it might head to a second site outside Jezero where there might have been geothermal hot springs, another environment where life could have thrived.
But these decisions do not have to be made for years, and the best answers may not become apparent until Perseverance gets a good look at Jezero.
If one piece breaks, the sample return mission does not necessarily fail. Perseverance will likely drop some of the sample tubes on the ground in case it suffers a malfunction later in the mission. If the fetch rover breaks, then Perseverance could bring samples to the lander instead.
Even if the orbiter fails, its soccer-ball-size container holding samples could remain circling Mars for years until another spacecraft could be sent to catch it.
“That’s been my job as the architect,” Muirhead said. “To think through the process from the concept of operations, develop the concepts that can achieve the objectives of the different phases and make sure there’s good margins built in everywhere. So that the design isn’t fragile.”
Kenneth Chang c.2020 The New York Times Company
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