Ohio researchers play role in mission

1/6/2004

Talk about your tense moments. As the Mars Exploration Rover Spirit bounced across the planet s surface, the people in charge of ensuring its safe landing held their breath.

For a mile it rolled and caromed, taking at least six big bounces. Would the airbag cocoon that shielded the rover do its job? The team at NASA Glenn Plum Brook Station in Sandusky waited quietly for the rover s tone, its signal of a safe landing. It was a long five minutes.

“It was extremely exciting. It is kind of hard to describe because we just spent the last three years working on this thing,” said Jerry Carek, facility manager at Plum Brook.

Across the country, Ron Li of Ohio State University cheered with the crowd at the rover s command center, the Jet Propulsion Laboratory in Pasadena, Calif., when Spirit sent its signal.

Now he can t settle down. It s too exciting, watching the images come in, and turning them into navigational maps.

“I haven t gotten much sleep. After the landing, I got back to my room and I couldn t sleep. I tried for three hours.” He gave up and headed back to JPL.

For the airbag team at NASA Glenn, the landing was a triumph they hope to repeat later this month with the landing of the twin rover, Opportunity, but for Dr. Li there s still plenty to do on Spirit.

The Plum Brook team proved they can be trusted to carry the eggs.

They tested a system of airbags that would protect the rover when it hit the Mars surface at 60 mph.

They started with the same bags used to protect the Pathfinder during its 1997 landing. But the Pathfinder was lightweight compared to the new Spirit rover. The rover, with its lander and support system, weighs 1,000 pounds, about 50 percent more than the Pathfinder and its lander.

The researchers wrapped a model lander, along with enough metal to match the rover s weight, in airbags. The complete cocoon looked like a fat cluster of giant grapes. Then they dropped it 110 feet in the world s biggest space simulation chamber.

The drop “just tore the airbags to shreds, Mr. Carek said.

Major changes followed. ILC Dover, Inc., of Delaware, which makes blimps and spacesuits, selected a stronger version of the Kevlar-like fabric called Vectran. The Plum Brook group tested and tested again, helping to find the right airbag arrangement and eliminate fabrics of the wrong grade, thickness, and weave, without increasing airbag weight or size.

Although the 110-foot Plum Brook simulation chamber is big, it wasn t tall enough to create the 25,000 pounds of force in a Mars landing. To attain that, they rigged an elaborate system of bungees to pull the airbag cocoon, adding another 4,000 pounds of force to the plunge. Moments before the airbags hit the surface, the bungees released, for a true free-fall experience.

The cocoon struck a terrain as rocky as any it might find on Mars, filled with skin-slicing lava rocks and coffee-table size boulders. To complete the simulation, researchers maintained the chamber at the low-pressure of the Martian atmosphere. The bags also were tested at a very Mars-like chill of minus 110 degrees.

“We did over 50 tests. Once we got to maybe test No. 30, we pretty much had the design down, Mr. Carek said.

With the successful landing Saturday night, exploration can begin, and that s where Dr. Li s work comes in. Any great explorer creates great maps, and it s the software from Dr. Li and a team from OSU performing the cartography.

While the images Spirit sends hint at lots of information, they don t allow measurement or direction. Scale is impossible to determine.

But by matching the images from the rover with satellite views of the planet surface, the mapping software begins to triangulate the rover s precise location.

“We use the orbital images to identify the big landmarks, and then the ground images give you detailed information, Dr. Li said.

Dr. Li s role at JPL is to select the best image for the mapping. He sends the image to OSU, where a group led by Kaichang Di processes the results and returns them to JPL.

“We ve been waiting for this moment since 1998, Dr. Li said. “It s a long time, and it s paying off. I m just too excited.”