Her detractors said she really didn’t know her science well, but she made her lack of expertise into an asset because she had no scientific agenda, nothing to prove. She was content to bang heads together cheerfully and say, “Look, guys, now we are going to do it this way.” To the increasing number of women coming out of graduate school to work for NASA, she became a symbol. These younger women liked to tell a story about the time Donna Shirley attended a launch party at Cape Canaveral. As usual in those days, she was the only woman present. A guitarist singing a bawdy song, accompanying himself on the guitar, stopped dead when he saw her. She took his guitar and completed the song herself, delighting everyone. That was great, as far things went, but she didn’t realize there was a tradition at these launch parties that a woman – a hooker, basically – was paid to show up and pull a stunt like that. One of the men assumed Donna had been hired for the occasion, maneuvered her into an alcove, and grabbed her. “I didn’t exactly deck him,” she said, “I just hit him on the nose.”
Working on Pathfinder, she saw her team of engineers and scientists as a large family, her family. To her credit, she encouraged everyone to talk to everyone else, if only in self-defense, and she always smiled and radiated optimism. Most found it impossible to bear a grudge for long in the face of such cheerfulness; it was too exhausting to oppose her. Still, she wanted her radio-controlled rover for Pathfinder, and Tony Spear, the project manager, did not. “In his position, I wouldn’t either,” she said, “because he had the impossible job of landing on Mars for a fraction of what it cost the last time we landed. He had no idea how to do it, and here’s this parasite coming along, giving him nothing but trouble. What I did was to convince the scientists that we really could do useful work with the rover. That was number one. Number two was to convince Tony that we really could fly without damaging his mission.” When Donna presented her case to NASA’s review board, one member, Jim Martin, the former Viking project manager, insisted a Mars landing could not cost less than Viking had. As for the rover, “he thought it was terrible.” Donna and the rover team persisted, building better iterations of the rover and demonstrating they worked as advertised. “It became a very powerful selling tool,” she realized, and eventually, to everyone’s surprise, it turned into the mission’s raison d’être.
If Pathfinder’s engineering was, ultimately, carefully weighed, the mission’s science component tended to be rushed, improvised, an afterthought. Plenty of scientists were eager to participate in the new Mars mission, but they needed time and money to formulate, conduct, and analyze experiments. Pathfinder didn’t work that way. At the last minute, for instance NASA stuck a couple of stereographic cameras on the lander and another camera on the rover. These weren’t your standard television cameras; they used a technology known as a Charge Couple Device. The CCD reproduces light very accurately and is especially useful for spectroscopy, which reveals more than the naked eye can see by measuring which wavelengths of light are absorbed, and which reflected, from an object. They were useful, but they were not capable of sending back the sparkling, gorgeous images returned by Viking twenty years earlier. Pathfinder also carried an Alpha Proton X-ray spectrometer to detect the composition of Martian rocks, and a weather mast to measure the Martian temperature and atmospheric conditions. Every so often, Pathfinder would collect the weather mast’s data and return it to Earth, so for the first time it would be possible to obtain accurate weather reports from the surface of Mars. Everyone agreed the weather mast would be a terrific experiment, if it worked. It looked like Pathfinder had a chance to become a real mission, after all.
Manning’s team conducted early Pathfinder landing tests at a NASA facility in Cleveland, Ohio, which featured a large vacuum chamber. Within, girders, lava rocks, and wood simulated the Martian surface. They dropped Pathfinder in its protective bubble onto the sharp objects and observed the result.
R-r-r-r-r-r-rip!
“The first time we did it, we had a tear the size of a human being,” Manning said. They took it back to the lab, fixed it up, and dropped it again.
R-r-r-r-r-r-rip!
They tweaked it and tried again. R-r-r-r-r-r-rip! … R-r-r-r-r-r-rip! … R-r-r-r-r-r-rip!
The trials went on like that for months; they were “total disasters,” said Manning, and NASA nearly canceled the mission. Late in 1995, the Pathfinder team redoubled its efforts. The engineers adjusted the spacecraft’s small guidance rockets. They modified the shape of the sphere contained inside the protective beach ball. They had been imitating the Russian model, which was spherical and consequently difficult to manufacture; now they adopted a tetrahedron, which was easier to manufacture. They toyed with the air bags protecting the tetrahedron, trying one deflation strategy after another, getting incremental improvements. Gradually, they came to feel more confident about Pathfinder. They did have one advantage: because the gravity of Mars is less than half of Earth’s, the spacecraft would endure less wear and tear. “We always worked in terms of the mass, and the mass kept getting bigger and bigger,” Donna said. “That meant the mechanical parts had to be heavier because they were supporting all of this additional structure. The mission design people came to the rescue. They said, ‘Okay, if we’re going to fly into the atmosphere of Mars, there’s a corridor we have to hit. If we go in too shallow, we’ll just skip out of the atmosphere and keep on going. If we go in too deep, we’ll burn up on entry, or we won’t have enough atmosphere to slow down before we hit the surface.’ So there’s a narrow range of angles at which you can enter the atmosphere, and that takes some really accurate shooting by the navigators. So the navigators heard this and said, ‘Okay, if we can shoot more accurately and give up some of our margin for error, we can let the spacecraft have more mass.’” Now the engineers were able to add small thrusters that would slow Pathfinder during its descent to the surface.
The mission was still alive, but the development of a decent, affordable rover still posed engineering problems. JPL had to devise a nimble mechanical creature that could scale small barriers and climb over rocks, like a little tank. To complicate matters, it would take twelve or fifteen minutes for a radio signal to travel from the Earth to Mars, which eliminated spontaneous, real time commands. “If you’re looking through the rover’s eyes, and you see a cliff coming, and you say, ‘Stop!’ it’s too late – it will be over the cliff, so it has to be smart enough to stay out of trouble,” Shirley said. In addition to negotiating the Martian terrain, which was in many details unknown, the rover had to keep its solar panels in position to receive sunlight, or it would lose power and die.
Attempting to meet these requirements, JPL devised variations on a theme. They built a rover the size of a small truck, and they built one just eight inches long, nicknamed “Tooth.” They built a mid-sized rover called Rocky, which, when tested in the desert, actually did things required on Mars, such as scooping up soil. Rocky went through various iterations until it weighed just fifteen pounds, yet negotiated the kind of obstacles and terrain that geologists expected to find on the surface of Mars. It could perform simple experiments, and it appeared sturdy enough to withstand the rigors of landing on the Martian surface and bouncing around inside a beach ball.
The development of Pathfinder’s components took place in a knowledge vacuum, because the engineers and scientists didn’t know exactly where they were going on Mars or what to expect when they got there. From a spacecraft’s point of view, Mars presents a landscape of treachery. The team expected to receive finely detailed studies of the surface from Mars Observer, the billion-dollar spacecraft launched on September 25, 1992. It was supposed to reach Mars the following August, when its cameras would send back pictures of the Martian surface with much higher resolution than Viking had captured in the seventies, and those pictures were supposed to give JPL a well-informed notion of where to land their bouncing beach ball.