Scientists Brace for Pathfinder’s Encounter
The Pathfinder spacecraft, poised for its historic descent to the Martian surface today, got close enough to the Red Planet to begin to feel its gravitational attraction at 4 a.m. Thursday. “I think it’s safe to say we’re all [feeling the pull of Mars],” flight system manager Brian Muirhead said.
At 11 a.m. Thursday, the heaters turned on to inflate the air bags that will protect the craft when it hits the surface. By 7:45 p.m., the spacecraft was as close to Mars as the moon is to Earth.
But while mission specialists at the Jet Propulsion Laboratory in Pasadena were losing sleep over today’s precarious landing, NASA chief Dan Goldin declared the mission a success--”no matter what happens.”
Mars program manager Donna Shirley said she was as anxious as a child on Christmas Eve waiting to open presents and slept only four hours Wednesday night. “I can’t wait,” she said. “I want it to be now.”
Goldin stressed that Pathfinder is one of a series of high-risk, low-cost spacecraft planned for Mars--and should Pathfinder crash, it won’t be “the last ship out of the port.”
Speaking at a press briefing next to a model of the red, white and blue Pathfinder and a painted, rose-colored Martian landscape, Goldin admitted that it was odd for the boss to congratulate the troops before the mission was over, but said “we want to encourage people to take risks.”
Still encased in a series of protective shells like Russian dolls, the 1-foot-high, six-wheeled dune buggy Sojourner still had a series of high-wire acts to endure before it could begin its science mission on the Martian surface. One concern, said chief flight engineer Rob Manning, is that “we don’t know exactly where Mars is.”
Since both the Pathfinder and the Red Planet are moving targets, the “landing” is actually more of a rendezvous, where both objects have to be at the same place at the same time, like circus performers meeting in the air between flying trapezes.
And keeping track of Mars is no trivial matter: The best optical and radar sources can pin it down only within a couple of miles, said Manning. Yet Pathfinder’s aim has to be practically perfect. Manning compared the spacecraft’s shot at Mars to a golf ball hit from a tee in Houston that has to land in a 4-inch hole in Los Angeles. To make matters worse, the golf course (the landing site on Mars) keeps moving.
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If Pathfinder’s aim is not true, it won’t just get stuck--it will either skip off into outer space or crash and burn on the Martian surface.
Now that Pathfinder has been snared in Mars’ gravitational sphere of influence, said Manning, it is being tugged toward the planet--increasing its speed from 12,000 mph to more than 16,000 mph at arrival.
Half an hour before sinking into the Martian atmosphere--at precisely 9:32 a.m. Pacific time today--Pathfinder is due to throw off the flight pack that’s been helping it get to Mars. Thirty-five minutes later, at 10:07, it should pop its parachute, fire its rockets and bounce to the ground on giant air bags, rolling and skidding to a halt.
At that point, the craft is expected to cease communications with Earth for about four hours--waiting for the sun to rise on Mars and power up the lander’s solar batteries. Scientists anticipate a tense period until they hear the first scheduled signal at 2:07 p.m. telling them whether Pathfinder has landed.
While the super-strength air bags could absorb a bounce as long as a football field, these acrobatics won’t be filmed, and engineers said they wouldn’t even know exactly how far the air bag-encased Pathfinder bounced and skidded until they reconstruct the landing from data a week or so from now.
However, by 2:07 p.m., they should at least know whether the spacecraft made a safe landing. By 4:30, there might be some preliminary snapshots that will look at the air bags to see if they’re draped over one of Pathfinder’s solar panels, blocking power, and might have to be moved.
Between 6 and 7 p.m., if all goes well, Pathfinder will send back the first panoramic color pictures of Mars since the Viking landing 21 years ago. Then, the first Mars rover will stretch up from its crouched traveling position to its full height, roll down the ramp and get to work doing a geological survey of Martian soil and rocks.
As Goldin pointed out, however, success is anything but assured. Out of 20 attempted missions to Mars by the United States and Russia, only six have been successful.
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So far, things look good for Pathfinder, however. According to weather forecasts from the Kitt Peak Observatory in Arizona, the weather at the Martian landing site is clear and cold. Even if there were a surprise dust storm, “We expect the atmosphere on Mars to be no worse than the atmosphere in L.A. [with the Azusa fire’s smoke],” said Pathfinder project scientist Matthew Golombek.
And the spacecraft is closing in on its target landing site, an ancient flood plain called Ares Vallis. While the size of the target has been narrowed somewhat since earlier this week, its position has shifted to the east. This is because engineers had slightly miscalculated how the solar wind would blow the tiny spacecraft off course, said Manning.
Still, Pathfinder did not seem to be heading for any of the obvious obstacles that surround the landing site, including some rough-looking terrain to the east and some teardrop-shaped land forms surrounding hills of uncertain height. “It’s the kind of terrain you’d just as soon not have your rover in,” said Golombek.
NASA officials stressed that Pathfinder is just the beginning of a series of planned missions to Mars. “We’re back, and we’re back to stay this time,” said NASA space science administrator Wesley Huntress.
Practical considerations aside, the trip to Mars is clearly a sentimental journey for all involved, said Goldin. Mars is a small planet, with one-tenth the mass of Earth. “Yet it has an unbelievable pull on the American people,” he said.
An additional pull for Shirley is a “secret” she said is traveling on the rover. Thinking about it, she says, still brings tears to her eyes.
During the time when JPL engineer Greg Hickey was building the electronics box for Sojourner, his wife, Denise, died. In her memory, Hickey wrote the name of their son, Patrick, into Sojourner’s belly.
