All posts by Ned Potter

No Sleep Till Jezero: Touchdown Time for Mars Perseverance Rover?

Post Syndicated from Ned Potter original

They used to call it “Seven Minutes of Terror”—a NASA probe would slice into the atmosphere of Mars at more than 20,000 kilometers per hour; slow itself with a heat shield, parachute, and rocket engines; and somehow land intact on the surface, just six or seven minutes later, while its makers waited helplessly on Earth. The computer-animated landing videos NASA produced before previous Mars missions—in 2004, 2008, and 2012—became online sensations. “If any one thing doesn’t work just right,” said NASA engineer Tom Rivellini in the last one, “it’s game over.”

NASA is now trying again, with the Perseverance rover and the tiny Ingenuity drone bolted to its undercarriage. NASA will be live-streaming the landing (across many video and social media platforms as well as in a Spanish language feed and in an immersive, 360-degree view) beginning at 11:15 a.m. PST/2:15 p.m. EST/19:15 UTC on Thursday, 18 February 2021. 

While this year’s animated landing video is as dramatic as ever, the tone has changed. “The models and simulations of landing at Jezero crater have assessed the probability of landing safely to be above 99 percent,” says Swati Mohan, the guidance, navigation and controls operations lead for the mission.

There isn’t a trace of arrogance in her voice as she says this. She’s been working on this mission for five years, has teammates who were around for NASA’s first Mars rover in 1997, and knows what they’re up against. Yes, they say, 99 percent reliability is realistic. 

The biggest advance over past missions is a system called Terrain Relative Navigation—TRN for short. In essence, it gives the spacecraft a way to know precisely where it’s headed, so it can steer clear of hazards on the very jagged landscapes that scientists most want to explore. If all goes as planned, Perseverance will image the Martian surface in rapid sequence as it plows toward its landing site, and compare what it sees to onboard maps of the ground below. The onboard database is primarily based on high-resolution images from NASA’s Mars Reconnaissance Orbiter, which has been mapping the planet from an altitude of 250 kilometers since 2006. Its images have a resolution of 30 cm per pixel. 

“This is kind of along the same lines as what the Apollo astronauts did with people in the loop, back in the day. Those guys looked out the window,” says Allen Chen, the mission’s entry, descent, and landing lead. “For the first time here on Mars, we’re automating that.”

There will still be plenty of anxious controllers at NASA’s Jet Propulsion Laboratory in California. After all, the spacecraft will be on its own, about 209 million kilometers from Earth, far enough away that its radio signals will take more than 11 minutes to reach home. The ship should reach the surface four minutes before engineers even know it has entered the Martian atmosphere. “Landing on Mars is hard enough,” says Thomas Zurbuchen, NASA’s associate administrator for science missions. “It is not guaranteed that we will be successful.” 

But the new navigation technology makes a very risky landing possible. Jezero crater, which was probably once a lake at the end of a river delta, has been on scientists’ shortlist since the 1990s as place to look for signs of past life on Mars. But engineers voted against it until this mission. Previous landers used radar, which Mohan likens to “closing your eyes and holding your hands out in front of you. You can use that to slow down and to stop. But with your eyes closed you can’t really control where you’re coming down.”

Everything happens fast as Perseverance comes in, following a long arcing path. Fewer than 90 seconds before scheduled touchdown, and about 2,100 meters above the Martian surface, the TRN system makes its calculations. Its rapid-fire imaging should by then have told it where it is relative to the ground below, and from that it can project its likely touchdown spot. If the ship is headed for a ridge, a crevice, or a dangerous outcropping of rock, the computer will send commands to eight downward-facing rocket engines to change the descent trajectory. 

In that final minute, as the spacecraft slows from 300 kilometers per hour to zero, the TRN system can shift the touchdown spot by up to 330 meters. The safe targets map in Perseverance’s memory is detailed enough, the team says, that the ship should be able to reach a suitable location for a safe landing. 

“It’s able to thread the needle of all these different hazards to land in the safe spots in between these hazards,” says Mohan, “and by landing amongst the hazards it’s also landing amongst the scientific features of interest.”

NASA’s Mars Perseverance Rover Should Leave Past Space Probes in the Dust

Post Syndicated from Ned Potter original

If you could stand next to NASA’s Perseverance rover on the Martian surface… well, you’d be standing on Mars. Which would be a pretty remarkable thing unto itself. But if you were waiting for the rover to go boldly exploring, your mind might soon wander. You’d be forgiven for thinking this is like watching paint dry. The Curiosity rover, which landed on Mars in 2012 and has the same chassis, often goes just 50 or 60 meters in a day. 

Which is why Rich Rieber and his teammates have been at work for five years, building a new driving system for Perseverance that they hope will set some land-speed records for Mars. 

“The reason we’re so concerned with speed is that if we’re driving, we’re not doing science,” he said. “If you’re on a road trip and you drive to Disneyland, you want to get to Disneyland. It’s not about driving, you want to be there.”

Rieber is the lead mobility systems engineer for the Perseverance mission. He ran the development of the drivetrain, suspension, engineering cameras, machine vision, and path-planning algorithms that should allow the rover to navigate the often-treacherous landscape around Perseverance’s destination, called Jezero crater. With luck, Perseverance will leave past rovers in the dust. 

“Perseverance is going to drive three times faster than any previous Mars rover,” said Matt Wallace, the deputy mission manager at NASA’s Jet Propulsion Lab. “We have added a lot of surface autonomy, a lot of new AI if you will, to this vehicle so that we can complete the mission on the surface.”

The rover, if everything works, will still have a maximum speed of only 4.4 cm per second, which is one-thirtieth as fast as human walking speed. It would travel the length of a football field in 45 minutes. But, says Rieber, “It is head and shoulders the fastest rover on Mars, and that’s not because we are driving the vehicle faster. It’s because we’re spending less time thinking about how.” 

Perseverance bases much of its navigational ability on an onboard map created from images taken by NASA’s Mars Reconnaissance Orbiter–detailed enough that it can show features less than 30 cm across. That helps tell the rover where it is. It then adds stereo imagery from two navigational cameras on its top mast and six hazard-detection cameras on its body. Each camera has a 20-megapixel color sensor. The so-called Navcams have a 90-degree field of view. They can pick out a golf ball-sized object 25 meters away.

These numbers add up: The technology should allow the rover to pick out obstacles as it goes—a ridge, an outcropping of rock, a risky-looking depression—and steer around many of them without help from Earth. Mission managers plan to send the rover its marching orders each morning, Martian time, and then wait for it to report its progress the next time it can communicate with Earth. 

Earlier rovers often had to image where they were and stop for the day to await new instructions from Earth. Curiosity, on days it’s been ordered to drive, only spends 13 percent of its time actually in motion. Perseverance may more than triple that. 

There are, however, still myriad complexities to driving on Mars. For instance, mission engineers can calculate how far Perseverance will go with each revolution of its six wheels. But what if the wheels on one side slip because they were driving through sand? How far behind or off its planned path might it be? The rover’s computers can figure that out, but their processing capacity is limited by the cosmic radiation that bombards spacecraft outside the Earth’s protective magnetosphere. “Our computer is like top of the line circa 1994,” said Rieber, “and that’s because of radiation. The closer [together] you have your transistors, the more susceptible they are.”

Matt Wallace, the deputy project manager, has been on previous missions when—sometimes only in hindsight—engineers realized they had barely escaped disaster. “There’s never a no-risk proposition here when you’re trying to do something new,” he said. 

But the payoff would come if the rover came across chemical signatures of life on Mars from billions of years ago. If Perseverance finds that, it could change our view of life on Earth.

Is there a spot somewhere at Jezero crater that could offer such an incredible scientific breakthrough? The first step is to drive to it.

The Long Arm of NASA: The OSIRIS-REx Spacecraft Gets Ready To Grab An Asteroid Sample

Post Syndicated from Ned Potter original

Just how do you bring home pieces of asteroid? Carefully, that’s how, with grudging respect for the curveballs the asteroid can throw you.

Sixteen years after NASA’s OSIRIS-REx mission was first proposed and two years after the robotic spacecraft went into orbit around asteroid 101955 Bennu, mission team members are now counting down to the moment when it will descend to the surface, grab a sample—and then get out of there before anything can go wrong.

The sampling is set for next Tuesday, Oct. 20. If it works, it will be a first for the United States. (A Japanese probe is currently returning to Earth with samples from asteroid 162173 Ryugu.)

Though the mission plan has so far been executed almost flawlessly, an outsider might be forgiven for thinking there’s something a bit…well, counterintuitive about it. The spacecraft has no landing legs, because it will never actually land. Instead, the OSIRIS-REx spacecraft vaguely resembles an insect with a long snout—a honeybee, perhaps, hovering over a flower to pollinate it. The “snout” is actually an articulated arm with a 30.5 cm round collection chamber at the end. It’s called TAGSAM – short for Touch-And-Go Sample Acquisition Mechanism. You’ve doubtless heard the old expression, “I wouldn’t touch that with a 10-foot pole.” The TAGSAM arm is an 11-foot pole.

The TAGSAM collector will gently bump the surface—and then try to kick up some rock and dust with a blast of nitrogen gas from a small pressurized canister. If all goes well, at least 60 grams of dirt will be caught in the collection chamber in the 5 to 10 seconds before the spacecraft pulls away.

The mission was conceived in 2004 at the Lunar and Planetary Laboratory at the University of Arizona. It was rejected twice by NASA before it won approval in 2011. The spacecraft was launched in 2016, reached Bennu in 2018, and has surveyed it for two years. If Tuesday’s sample pickup is successful (if not, there are two backup nitrogen canisters), the ship will bring its cargo back in a sealed re-entry capsule for a parachute landing in the Utah desert on Sept. 24, 2023.

Think about that: nearly 20 years of work, seven years in space, US$800 million spent, and the moment of truth—actually touching the asteroid—will not even last a minute.

And all for just 60 grams? “That’s like a few sugar packets that you use for your coffee,” says Michael C. Moreau, the deputy project manager at NASA’s Goddard Space Flight Center in Maryland. But for scientists involved in the mission, that’s enough to conduct their experiments and put some aside for future research. Bennu, and other near-Earth asteroids like it, are interesting because they are rich in carbon, probably dating back 4.5 billion years to the formation of the solar system. Might they tell us about the origins of life on Earth? “We are now optimistic that we will collect and return a sample with organic material—a central goal of the OSIRIS-REx mission,” said Dante Lauretta, the OSIRIS-REx principal investigator at the University of Arizona, who has been on the mission team from the start.

Bennu is not a friendly place for a spacecraft, especially a robotic probe operating on its own 334 million km from Earth, far enough away that commands from mission managers take 18 minutes to reach it. The asteroid is a rough, rocky spheroid, about 500 meters in diameter, and it spins fairly rapidly: a “day” on Bennu is about 4.3 hours long. It’s probably not solid. Scientists call it a rubble pile, a cluster of dirt and rock held together by gravity and natural cohesion. And when Moreau says Bennu threw them “a bunch of curveballs,” some of them were literal—pieces of debris being flung out into space from the surface, though not enough to endanger OSIRIS-REx.

An asteroid the size of Bennu has almost no gravity to speak of: an object on the surface would weigh 8 one-millionths of what it would on Earth. That means staying in orbit around it is very delicate business. OSIRIS-REx’s orbital velocity has been on the order of 0.2 km/hr, which means a tortoise could outrun it. More important, it can easily be thrown off course by solar wind, or heating on the sunlit side of the spacecraft, or other miniscule forces. “Wow, a[n extra] millimeter per second three days later changes the position by hundreds of meters,” says Moreau.

Which is an error they can’t afford. Scientists thought Bennu would have a fine-grained surface, but were surprised when the spacecraft’s images showed a rugged, craggy place with house-sized boulders. They had hoped to pick a touchdown spot 50 m across. But the best they could find was a depression they nicknamed Nightingale, all of 8.2 m wide, with a jagged rock nearby that they call Mount Doom. OSIRIS-REx has a hazard map on board; if it appears off-target it will automatically abort at an altitude of 5 meters.

So there will be some nail-biting on Tuesday, but after 16 years on the project, Dante Lauretta said they’re as ready as they can be. “It’s transcendental,” he said, “when you reach a moment that you’ve devoted most of your career to.”

Airbus Plans Hydrogen-Powered Carbon-Neutral Planes by 2035. Can They Work?

Post Syndicated from Ned Potter original

Imagine that it is December 2035 – about 15 years from now – and you are taking an international flight in order to be at home with family for the holidays. Airports and planes have not changed much since your childhood: Your flight is late as usual. But the Airbus jet at your gate is different. It is a giant V-shaped blended-wing aircraft, vaguely reminiscent of a boomerang. The taper of the wings is so gentle that one cannot really say where the fuselage ends and the wings begin. The plane is a big lifting body, with room for you and 200 fellow passengers.

One other important thing you notice before you board: The plane is venting vapor, a lot of it, even on a crisp morning. That, you know, is because the plane is fueled by liquid hydrogen, cooled to -253 degrees C, which boils off despite the plane’s extensive insulation. This is part of the vision Airbus, the French-based aviation giant, presents as part of its effort against global climate change.

Airbus is now betting heavily on hydrogen as a fuel of the future. It has just unveiled early plans for three “ZEROe” airliners, each using liquid hydrogen to take the place of today’s hydrocarbon-based jet-fuel compounds.

“It is really our intent in 15 years to have an entry into service of a hydrogen-powered airliner,” says Amanda Simpson, vice president for research and technology at Airbus Americas. Hydrogen, she says, “has the most energy per unit mass of…well, anything. And because it burns with oxygen to [yield] water, it is entirely environmentally friendly.”

But is a hydrogen future realistic for commercial aviation? Is it practical from an engineering, environmental, or economic standpoint? Certainly, people at Airbus say they need to decarbonize, and research on battery technology for electric planes has been disappointing. Meanwhile, China, currently the world’s largest producer of carbon dioxide, pledged last month to become carbon neutral by 2060. And 175 countries have signed on to the 2015 Paris agreement to fight global warming.

According to the European Commission, aviation alone accounts for between 2 and 3 percent of the world’s greenhouse gas emissions – about as much as entire countries like Japan or Germany.

Two of the planes Airbus has shown in artist renditions would barely get a second glance at today’s airports. One—with a capacity of 120-200 passengers, a cruising speed of about 830 kilometers per hour (kph), and a range of more than 3,500 km—looks like a conventional twin-engine jet. The second looks like almost any other turboprop you’ve ever seen; it’s a short-haul plane that can carry up to 100 passengers with a range of at least 1,800 km and a cruising speed of 612 kph. Each plane would get electric power from fuel cells. The company said it won’t have most other specifications for several years; it said to think of the images as “concepts,” meant to generate ideas for future planes.

The third rendering, an illustration of that blended-wing aircraft, showed some of the potential—and potential challenges—of hydrogen as a fuel. Airbus said the plane might have a cruising speed of 830 kph and a range of 3,500 km, without releasing carbon into the air. Liquid hydrogen contains about three times as much energy in each kilogram as today’s jet fuel. On the other hand, a kilogram of liquid hydrogen takes up three times the space. So, a plane would need either to give up cabin space or have more inside volume. A blended wing, with its bulbous shape, Airbus says, may solve the problem. And as a bonus, blended wings have shown they can be 20 percent more fuel-efficient than today’s tube-and-wing aircraft.

“My first reaction is: Let’s do it. Let’s make it happen,” says Daniel Esposito, a chemical engineer at Columbia University whose research covers hydrogen production. He says hydrogen can be handled safely and has a minimal carbon footprint if it’s made by electrolysis (splitting water into hydrogen and oxygen) using renewable electricity. Most industrial hydrogen today is extracted from natural gas, which negates some of the carbon benefit, but the International Energy Agency says that with renewable electricity capacity quickly growing (it passed coal as a power source in 2019), the cost of carbon-free hydrogen could drop.

“It can be done,” he says. “It’s just a matter of the political will and the will of companies like Airbus and Boeing to take the lead on this.”

Others have their doubts. “A lot of these things, you can; the question is, should you?” says Richard Pat Anderson, a professor of aerospace engineering at Embry-Riddle Aeronautical University. “When we say, ‘Should you?’ and you get into economics, then it becomes a much more difficult conversation.” Anderson says battery-powered aircraft are likely to become practical later in this century, and it is a dubious proposition to build the massive – and costly – infrastructure for hydrogen power in the meantime.

But in a warming world, Airbus says, the aviation sector needs to get going. McKinsey & Company, the consulting firm, surveyed airline customers last year and found 62 percent of younger fliers (under age 35) “really worried about climate change” and agreed that “aviation should definitely become carbon neutral.”

So, you’re on that jetway 15 years from now, on the way home. What will power the plane you’re boarding?

“Hydrogen is coming,” says Simpson at Airbus. “It’s already here.”

NASA’s Next Mars Rover Will Carry a Tiny Helicopter

Post Syndicated from Ned Potter original

If ever there was life on Mars, NASA’s Perseverance rover should be able to find signs of it. The rover, scheduled to launch from Kennedy Space Center, in Florida, in late July or early August, is designed to drill through rocks in an ancient lake bed and examine them for biosignatures, extract oxygen from the atmosphere, and collect soil samples that might someday be returned to Earth.

But to succeed at a Mars mission, you always need a little ingenuity; that’s literally what Perseverance is carrying. Bolted to the rover’s undercarriage is a small autonomous helicopter called Ingenuity. If all goes as planned, it will become the first aircraft to make a powered flight on another planet.

Flying a drone on Mars sounds simple, but it has been remarkably difficult to design a workable machine. Ingenuity’s worst enemy is the planet’s atmosphere, which is less than 1 percent as dense as Earth’s and can drop to –100 °C at night at the landing site.

“Imagine a breeze on Earth,” says Theodore Tzanetos, flight test conductor for the project at NASA’s Jet Propulsion Laboratory, in Pasadena, Calif. “Now imagine having 1 percent of that to bite into or grab onto for lift and control.” No earthly helicopter has ever flown in air that thin.

Perseverance and Ingenuity are set to land in a crater called Jezero on 18 February 2021 and then head off to explore. About 60 Martian days later, the rover should lower the drone to the ground, move about 100 meters away, and watch it take off.

While the car-size Perseverance has a mass of 1,025 kilograms, the drone is just 1.8 kg with a fuselage the size of a box of tissues. Ingenuity’s twin carbon-fiber rotors sit on top of one another and spin in opposite directions at about 2,400 rpm, five times as fast as most helicopter rotors on Earth. If they went any slower, the vehicle couldn’t get off the ground. Much faster and the outer edges of the rotors would approach supersonic speed, possibly causing shock waves and turbulence that would make the drone all but impossible to stabilize.

Ingenuity is intended as a technology demonstration. Mission managers say they hope to make up to five flights over a 30-day period. No flight is planned to last more than 90 seconds, reach altitudes of more than 10 meters, or span more than 300 meters from takeoff to landing.

“It may be a bit less maneuverable than a drone on Earth,” says Josh Ravich, the project’s mechanical engineering lead at JPL, “but it has to survive the rocket launch from Earth, the flight from Earth to Mars, entry, descent, and landing on the Martian surface, and the cold nights there.”

That’s why engineers struggled through years of design work, trying to meet competing needs for power, durability, maneuverability, and weight. Most of the drone’s power, supplied by a small solar panel above the rotors and stored in lithium-ion batteries, will be spent not on flying but on keeping the radio and guidance systems warm overnight. They considered insulating the electronics with aerogel, a super-lightweight foam, but decided even that would add too much weight. Modeling showed that the Martian atmosphere, which is mainly carbon dioxide, would supply some thermal buffering.

The team calculated that the best time of day for the first flight will be late in the Martian morning. By then, the light is strong enough to charge the batteries for brief hops. But if they wait longer, the sun’s warmth would also cause air to rise, thinning it at the surface and making it even more difficult to generate lift.

To see if the drone would fly at all, they put a test model in a three-story chamber filled with a simulated Martian atmosphere. A wire rig pulled up on it to simulate Mars’s 0.38-g gravity. It flew, but, says Ravich, the real test will be on Mars.

If Ingenuity succeeds, future missions could use drones as scouts to help rovers—and perhaps astronauts—explore hard-to-reach cliff sides and volcanoes. “We’ve only seen Mars from the surface or from orbit,” says Ravich. “In a 90-second flight, we can see hundreds of meters ahead.” 

This article appears in the July 2020 print issue as “A Mars Helicopter Preps for Launch.”

Can Astronauts Use GPS to Navigate on the Moon? NASA Scientists Say Yes

Post Syndicated from Ned Potter original

If astronauts reach the moon as planned under NASA’s Project Artemis, they’ll have work to do. A major objective will be to mine deposits of ice in craters near the lunar south pole—useful not only for water but because it can be broken down into hydrogen and oxygen. But they’ll need guidance to navigate precisely to the spots where robotic spacecraft have pointed to the ice on the lunar map. They’ll also need to rendezvous with equipment sent on ahead of them such as landing ships, lunar rovers, drilling equipment, and supply vehicles. There can be no guessing. They will need to know exactly where they are in real time, whether they’re in lunar orbit or on the moon’s very alien surface.

Which got some scientists thinking. Here on Earth, our lives have been transformed by the Global Positioning System, fleets of satellites operated by the United States and other countries that are used in myriad ways to help people navigate. Down here, GPS is capable of pinpointing locations with accuracy measured in centimeters. Could it help astronauts on lunar voyages?

Kar-Ming Cheung and Charles Lee of NASA’s Jet Propulsion Laboratory in California did the math, and concluded that the answer is yes: Signals from existing global navigation satellites near the Earth could be used to guide astronauts in lunar orbit, 385,000 km away. The researchers presented their newest findings at the IEEE Aerospace Conference in Montana this month.

“We are trying to get it working, especially with the big flood of missions in the next few years,” said Cheung. “We have to have the infrastructure to do the positioning of those vehicles.”

Cheung and Lee plotted the orbits of navigation satellites from the United States’s Global Positioning System and two of its counterparts, Europe’s Galileo and Russia’s GLONASS system—81 satellites in all. Most of them have directional antennas transmitting toward Earth’s surface, but their signals also radiate into space. Those signals, say the researchers, are strong enough to be read by spacecraft with fairly compact receivers near the moon. Cheung, Lee and their team calculated that a spacecraft in lunar orbit would be able to “see” between five and 13 satellites’ signals at any given time—enough to accurately determine its position in space to within 200 to 300 meters. In computer simulations, they were able to implement various methods for improving the accuracy substantially from there.

Helping astronauts navigate after landing on the moon’s surface would be more complicated, mainly because in polar regions, the Earth would be low on the horizon. Signals could easily be blocked by hills or crater rims.

But the JPL team and colleagues at the Goddard Space Flight Center in Maryland anticipated that. To help astronauts, the team suggested using a transmitter located much closer to them as a reference point. Perhaps, the scientists wrote, they could use two satellites in lunar orbit—a new relay satellite in high lunar orbit to act as a locator beacon, combined with NASA’s Lunar Reconnaissance Orbiter, which has been surveying the moon since 2009.

This mini-network need not be terribly expensive by space-program standards. The relay satellite could be very small, take design cues from existing satellite designs, and ride piggyback on a rocket launching other payloads toward the moon ahead of astronauts.

The plans for Artemis have been in flux, slowed by debates over funding and mission architecture. NASA managers have been banking on a planned lunar-orbiting base station, known as the Gateway, to make future missions more practical. But if they are going to put astronauts on the surface of the moon by 2024, as the White House has ordered, they say the Gateway may have to wait until later in the decade. Still, scientists say early plans for lunar navigation will be useful, no matter how lunar landings play out.

“This can be done,” said Cheung. “It’s just a matter of money.”

Boeing Sponsors $1 Million GoFly Prize for Best Personal Flying Machines

Post Syndicated from Ned Potter original

What would it take to be as free as a bird—flying above the treetops with the wind in your face and the world far beneath your feet?

For Mariah Cain and Jeff Elkins, the team behind DragonAir Aviation of Panama City Beach, Fla., the answer is a personal flying machine that makes the pilot look like a skier grasping two poles, standing atop an oversized hobby drone. For Stephen Tibbitts, who built the Zero-emissions Electric Vehicle Aircraft (ZEVA) ZERO in Tacoma, Wash., it was a bulbous eight-foot disc in which a pilot lies prone, sped across the sky by eight propellers.  

Maybe you’d design something different—like a tiny helicopter, open to the breeze? Or a lounge chair surrounded by a ring of rotors? How about a gondola with two sets of blades at its base? Or your machine might resemble a flying motorcycle, with rotors clustered in front and back.

Those are just some of the machines, many of them conceived by startups, built for a competition started by GoFly, a New York-based tech incubator. It plans to offer a US $1 million grand prize to the winners of a fly-off at NASA’s Ames Research Center in California from 27 to 29 February.

Aerospace Companies Compete to Build Lunar Landers for NASA’s Project Artemis

Post Syndicated from Ned Potter original

After 50 years of lamenting that America had abandoned the moon, astronauts are in a rush again, trying to go back within five—and NASA has asked aerospace companies to design the lunar landers that will get them there. The project is called Artemis, and the agency is now reviewing proposals to build what it calls the Human Landing System, or HLS. In January, it says, it will probably select finalists.

NASA had said a landing was possible by 2028. Then, the White House said to do it by 2024.

“Urgency must be our watchword,” said U.S. Vice President Mike Pence when he announced the new deadline in March 2019. “Now, let’s get to work.”