Adam Steltzner: 'I could not imagine the Curiosity landing working'

The leader of a group of Nasa engineers tells how his team on Earth guided a one tonne rover to land safely on Mars
Adam Steltzner (R) celebrates successful Mars landing
Adam Steltzner, right, and team celebrate a successful landing at Nasa's laboratory in Pasadena, California, on 5 August. Photograph: Brian van der Brug/epa/Corbis

On the evening of 6 August 2012 Adam Steltzner and his team of Nasa engineers pulled off the most daring landing on another planet in the history of space exploration when they safely delivered the one tonne Curiosity rover to the surface of Mars.

After an eight-month voyage, the rocket stage carrying the rover tore into the Martian atmosphere at 6 km a second. Moments later, explosive charges blasted free two tungsten blocks, to shift the balance of the probe so it could fly itself to a prearranged landing spot.

The spacecraft steered great s-curves in the Martian sky as it closed on its target, released a parachute to slow its descent and jettisoned its heat shield, which took the brunt of the 2,000C generated by its terrific speed through the atmosphere. Then came the tricky part.

A mile above the ground, the spacecraft cut loose its parachute and began to plummet, until eight retrorockets fired up to stabilise the fall. Then, as the ground rose up, the remaining stage, called the sky crane, lowered the rover down on nylon ropes. The moment it touched soil, the sky crane blasted out of harms way and crashed a safe distance away.

Steltzner's team had come up with the hair-raising landing strategy in a brainstorming session after it became clear that the standard means of getting down on Mars, the parachutes, air bags, and retrorockets, of previous missions were not going to work for Nasa's largest rover. Although it looked crazy, and sounded crazy, the approach was less risky than it seemed. At least that's what Steltzner's team thought.

"Some wonderfully intoxicating brew of naivety and arrogance led us to feel that of course everybody would agree with us, but in fact that was not the case. We had to convince a lot of people, not least Mike Griffin, the head of Nasa at the time," says Steltzner.

Griffin summoned Steltzner to Washington, where he was asked to justify the radical idea at a meeting with delegates from all of Nasa centres. "At the end of the day, Griffin addressed the room again and reminded the room he thought it was crazy, but that now that he'd heard us out, he thought it just might be the right sort of crazy."

Steltzner wasn't bound to be a Nasa engineer. At High School he was focused on the arts and theatre and played bass in a rock band. At some point in his 20s, Steltzner decided to focus on his studies. He found he had an aptitude for engineering, quit the band and wound up with a PhD in engineering physics. He completed his studies while working at Nasa's Jet Propulsion Laboratory, operated by Caltech in Pasadena, California.

The night Curiosity was due to reach Mars, Steltzner gathered his team together and thanked them for the years of work they had put into the project. "It was anxiety provoking to be any of us that day. It's an incredible team of very, very talented people who were incredibly invested in this. We all had the better part of a decade on the line. But by that time we were bystanders. What ever was going to happen was going to happen," he says.

It takes a radio signal 20 minutes to get from Earth to Mars, so the spacecraft had to pull off every manoeuvre perfectly and without human intervention. The team had been over every detail, but still the sheer audacity of the landing was enough to play on the mind.

"I personally could not imagine it working. I had spent so much time thinking about the ways in which it couldn't work, or wouldn't work, that the idea of feeling that it would work, of relaxing and trusting that it would work, felt like a dereliction of duty to me. I was rationally confident, because when I'd go through all the risks we knew, I was satisfied, but I was emotionally terrified, because I was forever concerned about that one risk that we didn't know about," he says.

Things looked bad the moment the spacecraft slammed into the Martian atmosphere. Instruments on the heat shield flashed up error messages. One read: "Data out of bounds: Catastrophic." It meant the probe was hurtling towards Mars at the wrong inclination. "It got the blood flowing," says Steltzner.

The readings turned out to be wrong, a glitch caused by a calibration problem on the spacecraft. Within a second or two, the spacecraft was beaming back less heart-stopping signals. The descent was not dubbed – by Nasa's own engineers – the "seven minutes of terror" for nothing.

The information beamed back to Nasa showed the spacecraft performed exquisitely well. But even in the final stages of descent there was plenty that could go wrong. The team ran triple checks before announcing they were down safely. The first green light came when the rover sent news that it had landed slowly enough to be in one piece.

Next, it reported that it was not moving or being dragged around on the surface. Final confirmation came when Curiosity beamed signals back after the sky crane had flown away and ditched a safe distance away. It meant it hadn't come crashing down on top of the rover.

"Only once those three things were checked did we announce that we had touched down. I felt strangely numb, exhilarated, and slightly in disbelief. You work so many years of your life, so hard, on something that seems crazy even to us at times, it looks risky in a very visceral way, and then to have it just work out. You're just, wow. We just did that. To be honest I'm still a little in shock that it worked," he says

Once the rover was down and checked out, the entry, descent and landing team had essentially finished their job. Since then, Steltzner and his team have been poring over the data sent back from the spacecraft to recreate the landing. The work, which lasts several months, will make clear whether everything went as smoothly as it seemed, or it they were closer to disaster than they realised. "That takes us to June. And then we all better have other jobs to do or we'll be on the unemployment line," he says.

Nasa has announced a 2020 mission to the surface of Mars, using an identical rover, and Steltzner is keen for one of his team to take the helm for the entry, landing and descent.

He's hoping to work on another part of the mission, but has his eye on more ambitious landings in the future. "I'd really love to put a lander on the surface of Europa, the moon of Jupiter, that we feel is a place in the solar system most likely to have life. So there are challenges out there, and I am looking," he says.

The Curiosity rover landed in a feature on Mars called the Gale Crater, a vast basin with a 5km mountain rising from the centre. Its mission is not to look for life, but for signs that the planet was once habitable for organisms in the distant past.

So far, instruments aboard the rover have measured water, oxygen, and carbon dioxide, and even a whiff of organics, which might be from meteorites, or the result of contamination from Earth. They might be interesting for the question of life on Mars, as organics are the building blocks of life as we know it.

For Steltzner, the mission is greater than the science. "When we explore, when we are operating at the edges of our capability, we are fundamentally wondering about who we are as humans," he says.

"That process brings up the question how grand are we? How great is our reach? What questions might we dare ask and attempt to answer? When we do this, I think we become, all of us, a little tiny bit better. And that is the greatest gift for me, to be able to be part of such a process."

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