August 2, 2021

Mars rover ready for riskiest part of $2.7 billion mission


If you would like to see more articles like this please support our coverage of the space program by becoming a Spaceflight Now Member. If everyone who enjoys our website helps fund it, we can expand and improve our coverage further.
Artist’s illustration of the Perseverance rover’s heat shield under the mission’s supersonic parachute. Credit: NASA/JPL-Caltech

NASA’s Perseverance rover is racing toward Mars for a daring high-speed plunge into the Red Planet’s atmosphere Thursday, ready to use a heat shield, a supersonic parachute, and braking rockets for a pinpoint touchdown on a dried-up river delta that may harbor clues about the potential for past life.

The nuclear-powered robot has one shot to make the landing. Ground teams at NASA’s Jet Propulsion Laboratory in Pasadena, California, will track the spacecraft’s arrival at Mars. Controllers expect to receive confirmation of Perseverance’s landing at 3:55 p.m. EST (2055 GMT) Thursday.

The $2.7 billion mission’s primary goals are to search for signs of ancient life on Mars and collect rock specimens for return to Earth by a future spacecraft. The 2,260-pound (1,025-kilogram) Mars 2020 Perseverance rover will become the most sophisticated vehicle to ever land on Mars, carrying seven science instruments, 25 cameras, the first microphones to fly to another planet, and a small rotorcraft to demonstrate a capability to fly through the Red Planet’s thin carbon dioxide atmosphere.

“Before we can get that surface mission going, we have to land safely on Mars, and that is always a challenging feat for us,” said Matt Wallace, the rover’s deputy project manager at JPL, in a press conference Wednesday. “This is one of the most difficult maneuvers we do in the space business. Almost 50% of the spacecraft that have been sent to the surface of Mars failed. So we know we have our work cut out for us tomorrow to get down to the surface safely at Jezero Crater.

“We’re going to ballistically approach the planet at about 12,000 miles an hour, and the trick we have to perform is to slow down to just a couple miles an hour so that we can gently touch the vehicle down on the surface,” Wallace said. “That all has to happen in about seven minutes, and it all has to happen autonomously. Perseverance really has to fight her way down to the surface on her own. It’s something like a controlled disassembly of the spacecraft.”

The seven-minute descent, sometimes known as the “seven minutes of terror,” will cap a journey of 293 million miles (471 million kilometers) from a launch pad at Cape Canaveral, where the rover blasted off July 30 aboard a ULA Atlas 5 rocket.

If the landing goes according to plan Wednesday, NASA will have successfully landed nine robotic missions on the Red Planet since the Viking probes reached Mars in 1976. Perseverance will use the same type of entry, descent, and landing system proven by the similarly-sized Curiosity rover, which arrived at Mars in August 2012 and continues exploring the planet today.

After braking from its blistering entry velocity with the help of a protective heat shield and parachute, Perseverance’s descent stage will fire retrorockets to slow down to a crawl. The rocket pack will lower the rover to the surface on a bridle, set the craft down on its six wheels, then cut the cord and fly a safe distance away before running out of fuel.

The landing of Perseverance is the riskiest part of the mission, said Allen Chen, entry, descent, and landing lead on the mission.

“We just can’t guarantee success,” Chen said.

“We’ve never really come up with a good way of calculating the probability of success,” Wallace said. “The systems are so complex, and they’re interacting with an undefined environment in many ways.”

Perseverance will try to achieve the most precise landing in the history of Mars exploration, aiming for a location where sediments deposited by a river billions of years ago may contain signatures of past life. To get there, the rover will employ new software developed since Curiosity’s landing in 2012, giving Perseverance a better sense of where it is heading as it dives through the atmosphere.

The upgraded navigation capability has been tested on Earth using helicopters and other simulations. But it’s the first time the technology has been used at Mars.

The Perseverance rover’s landing ellipse measures just 4 miles across. Credit: NASA/JPL-Caltech

“Mars still has things we don’t understand about it,” Wallace said. “This is still exploration.”

NASA engineers saw several surprises during Curiosity’s landing in 2012. The local gravity field at Curiosity’s landing site in Gale Crater affected the performance of Curiosity’s control system during descent, according to Wallace.

“You just also have to factor in the complexity of this system,” Wallace said. “We’ve got 2 million lines of software code running, hundreds of thousands of electronic parts, miles of copper conductors. We’ve got more than 70 pyrotechnic devices that all have to fire, closed loop guidance and navigation and control systems that really have to operate with sub-second precision for all this to work.

“There are no go backs. There are no retries,” Wallace said. “It’s a difficult and dangerous part of the mission … I don’t have a specific answer for you on the probability of success. I think we’ve done everything we can to make it successful, and we’ll see how it goes tomorrow.”

“If you don’t stay humble in this business, and especially if you’re going to Mars, you’re going to pay for it,” Chen said.

Perseverance’s landing will play out more than 11 minutes before radio signals from Mars will reach Earth. By the time engineers at JPL receive confirmation that the spacecraft and entered the Martian atmosphere, the rover will already be on the surface, one way or another.

That leaves no opportunity for human input once the descent begins.

Artist’s concept of the Perseverance rover’s descent engines firing just before landing. Credit: NASA/JPL-Caltech

Around 10 minutes before reaching the upper edge of the Red Planet’s atmosphere, the spacecraft will shed the cruise stage that will have guided the rover toward Mars since its launch. NASA expects to receive signals verifying the cruise station separation at 3:38 p.m. EST (2038 GMT).

The rover’s 14.8-foot-diameter (4.5-meter) heat shield will take the brunt of the energy during the craft’s plunge into the atmosphere of Mars beginning at 3:48 p.m. EST (2048 GMT). While temperatures outside the heat shield reach more than 2,000 degrees Fahrenheit, small thrusters will adjust the angle of the vehicle’s trajectory, allowing it to control lift and begin navigating toward its landing site.

Around four minutes after entering the atmosphere, the spacecraft will unfurl a 70.5-foot-diameter (21.5-meter) supersonic parachute at an altitude of about 7 miles, or 11 kilometers. Perseverance’s parachute is stronger than the one used on Curiosity, and the Mars 2020 mission will employ a new technique to deploy the chute based on the craft’s position relative to the target landing site, rather than time it to occur a predetermined velocity.

That will result in a higher-precision landing, NASA says.

“It’s a very big parachute that’s the size of a Little League infield,” Chen said. “It snaps open in about 0.6 seconds while going almost Mach 2. So there’s a lot of risk concentrated there.”

Roughly 20 seconds after deploying the parachute, the heat shield at the bottom of the spacecraft will drop away, allowing a downward-facing guidance radar and cameras to start seeing the Martian surface.

The atmosphere of Mars is much thinner than Earth’s, so a parachute by itself is unable to slow the spacecraft enough for a safe landing. The rover’s descent stage will release the backshell and parachute around 1.3 miles (2.1 kilometers) above Mars. Eight throttleable thrusters will further slow the rover’s descent from about 190 mph (306 kilometers per hour) to a speed of near zero just 66 feet (20 meters) above the surface.

During this time, advanced guidance software loaded into the rover’s flight computer will begin searching for a smooth place to set down. The new capability, named terrain relative navigation, was developed since Curiosity’s landing in 2012 and will be used on Mars for the first time with Perseverance.

It works by comparing imagery taken in real-time during descent with a map of steep slopes, boulders and other hazards pre-loaded into the computer using pictures captured from Mars orbiters. If the rover sees it is heading for dangerous terrain, it will adjust its path to reach a smoother area.

Artist’s concept of the Perseverance rover suspended under its descent stage. Credit: NASA/JPL-Caltech

Finally, a bridle will lower the one-ton Perseverance rover to the surface of Mars using a technique called the sky crane, which engineers invented and demonstrated on the Curiosity rover’s landing in 2012. Once the rover’s six wheels touch Mars — NASA expects confirmation at 3:55 p.m. EST — the bridle will be cut and the descent stage will fly away to crash a safe distance away.

The Perseverance rover will target a landing inside the 28-mile-wide (45-kilometer) Jezero Crater on Mars, home to an ancient river delta and lake that scientists believe filled the crater some 3.5 billion to 3.9 billion years ago. Scientists hope to find signatures of ancient life in the rocks and sediments deposited in the dried-up delta.

Perseverance is designed to land as close to the delta deposits as possible, but avoid nearby cliffs standing hundreds of feet tall.

The rover will send beacon tones directly to Earth up until the final phase of the landing, giving JPL engineers insight into the spacecraft’s status as it ticks off milestones on the way to the surface. NASA’s Mars Reconnaissance Orbiter will be flying over the landing site to relay data from Perseverance back to Earth during landing, and could send home the first images from the rover’s hazard cameras after touchdown.

Additional data could come down from Perseverance Thursday night, including the first glimpses of imagery captured by the spacecraft’s descent cameras, which will record the rover’s arrival at the Red Planet.

Then Perseverance will begin its work on Mars, heading off on a mission expected to last at least two years. If Curiosity’s performance is any guide, NASA’s new Mars rover could last much longer.

Ken Farley, the mission’s project scientist at JPL, said the rover could drive up to 10 miles, or 16 kilometers, in its first two years. One of its first tasks will be to release the 4-pound (1.8-kilogram) Ingenuity helicopter, a small drone developed at JPL that will attempt to become the first rotorcraft to fly at another planet.

Ingenuity’s technology demonstration is an add-on to the Perseverance mission, and could prove out new methods of aerial interplanetary exploration.

“The potential for aerial reconnaissance and exploration in the future, using this type of technology, is terrific, not just on Mars but other places as well,” Wallace said.

The rover could be ready to use its drill for the first time by the middle of the year, according to Farley.

Perseverance will use the drill in concert with a complicated internal sorting mechanism to collect more than 30 samples of rock powder and soil for return to Earth by a future mission being designed by NASA and the European Space Agency.

Email the author.

Follow Stephen Clark on Twitter: @StephenClark1.


If you would like to see more articles like this please support our coverage of the space program by becoming a Spaceflight Now Member. If everyone who enjoys our website helps fund it, we can expand and improve our coverage further.
Spaceflight Now