NASA's Perseverance rover on course for Mars landing this week, to search for signs of past life
A week after two space probes from China and United Arab Emirates slipped into orbit around Mars, NASA's $2.4 billion Perseverance rover, by far the most complex and ambitious of the three, will plunge into the red planet's atmosphere Thursday for an automated white-knuckle landing.
If it survives the "seven minutes of terror" from atmospheric entry to its rocket-powered touchdown in Jezero Crater, the nuclear-powered Perseverance will proceed on its mission to search for evidence of past microbial life in deposits left over from a now-vanished lake.
"Perseverance is our robotic astrobiologist, and it will be the first rover NASA has sent to Mars with the explicit goal of searching for signs of ancient life," said Thomas Zurbuchen, NASA's director of science operations.
"It will build upon what we currently know from our previous rovers, orbiters and landers. And it will attempt to answer an age-old question that has eluded humanity for generations: whether life has ever existed elsewhere beyond our own planet, our Earth."
Promising rock and soil samples, extracted and collected by a drill at the end of a 7-foot-long robot arm, will be placed in a complex internal carousel mechanism designed to load them in airtight lipstick-size containers.
The samples will be left in caches on the surface for retrieval by another NASA rover later this decade. That rover will be shot into orbit atop a small rocket and then ferried back to Earth by a European spacecraft for laboratory analysis. It will be history's first round trip to another planet and back.
In another first, before Perseverance's exploration and sample collection commences, it will deploy a small, $80 million helicopter named Ingenuity to demonstrate the feasibility of powered flight in the ultra-thin atmosphere of Mars — what NASA has called a "Wright bothers' moment" on another world.
If the 4.5-pound helicopter and its 2,400 rpm counter-rotating blades work as expected, engineers likely will design more capable drones that could fly instruments and cameras to targets that might be inaccessible to rovers and astronauts, greatly extending the scientific reach of future missions.
Along those same lines, an instrument carried by Perseverance will attempt to extract oxygen from Mars' mostly carbon dioxide atmosphere, technology that one day could allow astronauts to partially "live off the land" by manufacturing their own air and rocket fuel.
Looking for signs of past life
The primary goal of Perseverance is to look for fossilized evidence of past life, and Jezero Crater offers one of the most promising places on Mars to look.
"Three-and-a-half billion years ago, Mars was very similar to Earth," said project scientist Ken Farley. "It had a substantial atmosphere. It had lakes and rivers on its surface, and it had habitable environments, places where organisms that we know about on Earth today could have thrived."
Between 3 and 4 billion years ago, Jezero Crater was filled with water that entered through a channel cutting through its rim, depositing sediments in a broad delta. The lake was hundreds of feet deep and remnants of microbial organisms, if present, would have settled out and possibly been preserved in the sediments Perseverance will examine.
Scientists are hopeful because at roughly the same point in Earth's history, single-cell organisms flourished in Earth's rivers, lakes and seas, some of which are preserved in clearly visible sedimentary formations known as stromatolites that can be seen today in western Australia.
"Such biosignatures are the oldest undisputed evidence of life on Earth," Farley said. "Life was abundant on Earth 3-and-a-half billion years ago." Stromatolites, he notes, "can be large enough to see with your eyes."
"We also have capabilities on the rover to study the rocks microscopically to look for structures at a much smaller scale that could have been produced by microbial life. And we have the ability to detect and map organic matter. And of course, organic matter is important because all life as we know it is made out of organic matter."
What is the likelihood Perseverance will find unambiguous evidence of past life on Mars?
"We don't know the answer to that," Farley said. "But I'd like to point out that those rocks that are 3-and-a-half billion years old on Earth, that have stromatolites in them, were deposited by microbes in the bottoms of shallow lakes and seas.
"The Perseverance rover is about to land in a former lake, 3-and-a-half billion years old. This is a tantalizing similarity."
Like the Curiosity rover before it, Perseverance will rely on a novel landing system designed to lower the heavier rover to the surface from a rocket-powered backpack — the sky crane.
Major improvements and upgrades have been built into Perseverance's entry, descent and landing system, enabling the vehicle's flight computer to identify hazards and to autonomously alter the flight path to reach a safe landing zone.
That new technology is needed to safely land in Jezero, where the rover must avoid the towering rim of the crater, high cliffs on the periphery of the rocky delta, sand dunes and smaller impact craters.
"Jezero Crater is a great place, a magnificent place for science," said Allen Chen, the engineer in charge of the rover's entry, descent and landing. "But when I look at it from a landing perspective, I see danger. It's a formidable challenge.
"The site is replete with steep cliff sides that we're having to run right through the middle of the landing site. There's sand, there're boulders, there're impact craters, all these would be a bad day if we touched down on them."
When NASA's Curiosity rover landed in Gale Crater in 2012, the predicted landing footprint — an ellipse reflecting the uncertainty in where the spacecraft might end up — measured 15.5 miles by 12.4 miles. Perseverance's more advanced landing system is aiming for a footprint three times smaller, 4.8 miles by 4.1 miles.
Chen is optimistic Perseverance will stick the landing, but there are no guarantees.
"Entry, descent and landing is the most critical and most dangerous part of the mission," he said. "Success is never assured, and that's especially true when we're trying to land the biggest, heaviest and most complicated rover we've ever built (at) the most dangerous site we've ever attempted to land on."
Bracing for "seven minutes of terror"
Unlike UAE's Hope spacecraft and China's Tianwen-1, which braked into Mars orbit February 9 and 10, respectively, Perseverance will plunge straight into the atmosphere Thursday and descend directly to the floor of Jezero Crater.
Because of the 117-million-mile distance between Earth and Mars on landing day, radio signals will take more than 11 minutes to cross between the planets.
As a result, flight controllers cannot provide any real-time control during the descent. Perseverance must carry out the complex entry, descent and landing on its own.
"We're really throwing our vehicle up in front of Mars and letting Mars run into us," Chen said. "From that position on, really, the spacecraft's on her own to fly out where we're trying to go."
The entire procedure — only half jokingly referred to as seven minutes of terror — will either succeed or fail before radio signals, or lack thereof, are able to convey the outcome back to Earth.
"There's really nothing we can do," said Matt Wallace, the deputy project manager. "We call it 'do EDL' ... we literally send a command to the spacecraft that says that, and then the spacecraft on its own has to get from outside the (atmosphere), moving at 12,000 miles an hour, all the way down safely to the surface without any human interaction.
"It's basically a controlled disassembly the whole way. It's by far the highest risk phase of the mission."
Slamming into the atmosphere at some 12,100 mph, Perseverance's heat shield will endure temperatures as high as 2,370 degrees as atmospheric friction slows the craft to just under 1,000 mph in four minutes. At that point, at an altitude of about seven miles and a velocity of around 940 mph, a 70.5-foot-wide parachute will unfurl.
The timing will depend on a new technology known as "range trigger" that will allow the flight computer to choose the best time to deploy the parachute based on its actual position and the distance remaining to the landing zone.
The heat shield will fall away 20 seconds after parachute deploy, exposing Perseverance to the elements. Shortly after, its radar system and cameras will begin actively measuring altitude and velocity while mapping the surface below and comparing the view to orbital maps stored in on-board memory.
The "terrain relative navigation" system, being used for the first time, will enable Perseverance to select the best possible landing site in the targeted footprint, moving the touchdown point by up to 2,000 feet as required to avoid large boulders, steep slopes or sand dunes that might otherwise cause problems.
"It matches up landmarks that it sees with its camera, with its eye, with those onboard maps to figure out where she is," Chen said. "That helps us get our uncertainty and where we're at down to a couple tens of meters. ... If it wasn't for range trigger and terrain relative navigation, we just could not go to Jezero."
Five minutes and 50 seconds after atmospheric entry, at an altitude of about 1.3 miles, Perseverance will be released from its backshell and parachute, falling freely at a velocity of about 190 mph. Seconds later, the rover's sky crane jet pack will fire up to begin the final phase of the rocket-powered descent.
Up until this point, Perseverance will have been sending X-band radio signals directly back to Earth, using 256 tones to signify various entry events. Actual telemetry from the rover, uplinked via UHF signals, will be relayed to Earth by NASA's Mars Reconnaissance Orbiter as it passes over the landing site.
But Earth will drop below the horizon of Mars about a minute before touchdown, cutting off the direct X-band tones. For the final moments of landing, flight controllers will have to rely on the MRO spacecraft to confirm a successful landing.
In any case, by the time it reaches an altitude of just 70 feet or so, Perseverance will be descending at a sedate 1.7 mph.
At that point, the sky crane jet pack, using eight rocket motors to maintain orientation, will slowly lower Perseverance to the surface on a tether, cutting the cable when the flight computer detects "weight on wheels" about six minutes and 50 seconds after entry. The no-longer-needed sky crane then will fly away, crashing to the surface a safe distance away.
Low-resolution thumbnail images from cameras on the front and back of the rover are expected to be sent back to Earth within a few minutes of touchdown. Higher-resolution imagery will be sent back over the next several days as engineers begin a 90-day checkout operation.
Perseverance is carrying a record 23 cameras, with two more on the Ingenuity helicopter. During descent, cameras will record the release and inflation of the parachute, they will show the ground rushing up, the backshell pulling away, the rover dropping away from the sky crane and a view looking up from the rover to the jetpack.
Those never-before-seen images will be sent back over several days, giving engineers their first looks at the sky crane technology in action.
A robot geologist on Mars
Perseverance, launched from Cape Canaveral on July 30, was aimed at a point in space just ahead of where Mars was predicted to be this week. It has taken seven months to complete the trip, covering 293 million miles. It is the 22nd spacecraft sent to Mars by the United States at a total cost of roughly $25 billion.
Perseverance is the largest lander ever sent to Mars, tipping the scales at 2,260 pounds. It is roughly 10 feet long, 9 feet wide and 7 feet tall. It is equipped with a multi-joint robot arm, stretching 7 feet when fully extended, that carries a rotating 99-pound turret at its far end housing a camera, a rock drill and chemical analyzers.
The rover's body is mounted on six ribbed wheels arranged in a "rocker-bogie" design that evenly distributes the weight and allows it to easily roll over low-lying rocks.
Power is provided by a multi-mission radioisotope thermoelectric generator, or MMRTG, that produces heat from the decay of 10.6 pounds of radioactive plutonium 238 dioxide. That heat produces 110 watts of power to operate Perseverance and charge two lithium-ion batteries to meet higher demands during science operations.
Excess heat from the MMRTG also is used to keeps the rover's sensitive electronics warm in Mars' sub-freezing temperatures.
Perseverance is equipped with 23 cameras, 13 computers and seven science instruments:
- Mastcam-Z: Two zoomable cameras at the top of the rover's remote sensing mast capable of high-definition video, stereo imagery and 3D panoramas
- MEDA (Mars Environmental Dynamics Analyzer): A suite of weather and meteorology sensors and instruments
- MOXIE (Mars Oxygen ISRU Experiment): An experimental instrument designed to test the feasibility of extracting oxygen from Mars' thin, mostly carbon dioxide atmosphere; such technology might one day help astronauts produce air, water and rocket fuel
- PIXL (Planetary Instrument for X-ray Lithochemistry): Mounted on the rover's robot arm, PIXL fires high-energy X-ray beams at targeted rocks to map out their elemental chemistry
- RIMFAX (Radar Imager for Mars' Subsurface Experiment): A ground-penetrating radar
- SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals): An ultraviolet laser on the robot arm that is designed to look for organic compounds
- SuperCam: A camera-and-laser instrument designed to zap rocks and soil to probe their chemistry
Also on board: three silicon chips carrying the names of 10.9 million people from around the world who signed up to tag along in spirit and a small plate honoring coronavirus medical responders around the world
Before beginning its exploration of Jezero Crater and the search for biosignatures, Perseverance will be commanded to release the solar-powered Ingenuity helicopter from an attachment fixture on the rover's belly. (Both Perseverance and Ingenuity got their names from students in a nationwide contest.)
The rover then will drive a safe distance away and aim its cameras at the helicopter as it carries out a series of up to five test flights, the longest lasting about 90 seconds. Maximum altitude will be about 15 feet during flights carrying Ingenuity up to 160 feet downrange.
The drone carries no science instruments. Its purpose is simply to demonstrate the feasibility of flight in the thin martian atmosphere. Two pairs of 4-foot-long counter-rotating blades will spin at about 2,400 rpm to achieve liftoff.
And in what is sure to be riveting video, cameras aboard Perseverance will attempt to document the helicopter's short flights while two cameras aboard Ingenuity image the surrounding terrain and the rover.
"This is really something that's cutting edge, something that's never been attempted before," said Wallace. "The atmosphere of Mars is only 1% the density that we have here on the Earth, and trying to control a system like this under those conditions is not easy. ... This is something that we're taking with us so that we can learn how to do this for future missions."
With Ingenuity's testing complete, Perseverance will finally be ready to begin its search for evidence of past life across the rocky floor of Jezero Crater.
