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A.J.S. RaylJanuary 3, 2004

NASA Begins Countdown to Spirit's Arrival on Mars

Team Ready for "Six Minutes From Hell"

Spirit – the first of NASA's two robot geologists en route to the red Planet -- is “in “excellent” health, NASA and JPL scientists reported at a news briefing at JPL this afternoon, and the countdown to touch down on the Red Planet has begun.

After a journey of some 300 million miles over the past seven months, Spirit is currently scheduled to land on time at 8:35 p.m. Pacific Standard Time (PST) [4:35 a.m. Greenwich Mean Time (GMT)] in an area in Gusev Crater, described in this morning's press conference as “the distance from Pasadena to Malibu, California,” about 50 miles.

At about 7:04 p.m. Pacific Standard Time (PST) Spirit will rotate to turn its heat-shield forward for final approach. As it hits the Martian atmosphere around 8:30 p.m. Pacific Standard Time, it will appear, from Mars, much like a bright meteor streaking across the sky.

“It is the riskiest step in the process and the one everyone is concerned about,” MER Project Manager Pete Theisinger told the throng of reporters assembled at JPL's Von Karman Auditorium, and the countless thousands tuning in from distant parts via the Internet. Nevertheless, the MER team is anticipating no untoward events and is generally confident about tonight's events.

If all goes as planned, Spirit will enter the Martian atmosphere, the cruise stage will come off, the parachute will open up, the heat-shield will come off, and the spacecraft will speed like a spinning bullet, until its rockets are fired to slow it down from 180 mph to 0. The bridle will be cut before it touches down and the protective airbags will deploy to soften its landing. Then, Spirit will hit the ground, bouncing as high as a four-story building, and it will continue bouncing, hopefully, as many as 30 times, before it comes to a stop.

“This rover has performed very well over the cruise, the spacecraft has performed well,” offered Mark Adler, MER mission manager for cruise, entry, descent, and landing. “We had a small solar storm that we weathered successfully and now we're on our way to ED&L entry. Our cruise has ended now with the TCM 4 [the fourth trajectory correction maneuver]. We completed [that] trajectory correction maneuver last Friday . . . a very small maneuver to give a little nudge to the spacecraft to arrive about 13 seconds later.” That maneuver was so successful, he said, they have just cancelled two other planned maneuvers – the 5th and 6th trajectory correction maneuvers.

The team has set the EDL parameters, Adler continued. “We had to adjust the EDL parameters just yesterday to compensate for a dust storm that we saw on the other side of the planet.” That storm, he said, could “change the density a little bit over the Gusev site,” even if there was no dust over Gusev. Basically, he said, the storm has been heating up the atmosphere and making it thinner over Gusev, so the team decided to adjust the parameters to deploy the landing parachute a little bit higher.

Other than that, basically everything has been proceeding by the book and all systems are operating as designed. “We have good attitude, and good power cruise solar panels, and good communications at 120 its per second and the spacecraft is in EDL mode,” Adler said. “It is prepared to run the EDL software when it encounters the atmosphere, and is also prepared to turn on inertial measuring units and gas generators to prepare for the entry event. So the spacecraft is ready.”

There remains, however, some concern about wind gusts. “The reality is we don't know what the winds will be at the time we land,” Adler admitted. Therefore, they and the software are prepared to make any needed additional trajectory corrections.

Mars is, as so many scientists and NASA officials have stated, a harsh environment, where nearly 2 out of every 3 attempted missions fails. Despite the harshness and the rigors of entry, descent, and landing, “this is a vehicle that's designed to [withstand] this,” said Rob Manning, entry, descent and landing design development manager. “We think about this as a harsh environment from human perspective. . . but this is what this vehicle is designed to do, like an athlete tuned to perform at the Olympics This vehicle wants to do this. From a human perspective, it's very terrifying we designed it for it not to be terrifying. It is exciting. No question it's a nail-biter, but it's something in which we've got a lot of confidence in that we have done all the things we can to make things go right.”

The lander could survive even if one of its protective airbags tears, because the design features so many “layers” of protection, added Manning. So even should an airbag tear, just like a bulletproof vest, it is designed to hold up better than one might initially think. At the same time, this lander is designed to handle 50 Gs at impact, according to Manning. Pathfinder saw 18-19 Gs from impact load.] “It's easy to build robots that do this and we did.”

The EDL sequence has often been called “six minutes from hell.” But, noted Adler: “It isn't the entry that gets you it's the sudden stop at the end.” Right now, though confidence levels are high, fingers are crossed that the landing won't be so sudden, but bouncy and light.

Although Ed Weiler, associate administrator for space science at NASA Headquarters, has often reiterated in recent weeks that he and others call Mars the “death planet,” and that it is “all up to Mars now,” the Mars Exploration Team at JPL is exuding confidence about landing tonight. “I think today is a great day to land on Mars,” Adler told reporters this morning.

Both MER Project Manager Pete Theisinger and Cornell University's Steve Squyres, the principal investigator on the science package aboard both Spirit and Opportunity, agreed. “At this stage of the game, how you feel really comes down to what you believe,” Squyres told The Planetary Society earlier. “I believe in our rovers, and I believe in our team. The team that built these vehicles is the best I've ever seen JPL assemble and I've got faith in these vehicles.”

Added Theisinger: “I am confident. There are two things that can get you: the things you know; the things you don't know. We understand the things we know and we understand what the risks are with the environment and the rocks and all that stuff. There's nothing in the back of my mind saying, ‘Oh I should have done this or that.' It's the unknowns you worry about, so I am also anxious. Here's my analogy: we've got a really strong team and we should win this game and on paper it's easy. But we've got to play the game. We'll be anxious until we do and find out how it goes. That's where we are.”

If all goes as planned, the first images from Spirit could come as early as 11:30 p.m. tonight.

Read more: Spirit, mission status, Mars Exploration Rovers, Mars

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Salley Rayl
A.J.S. Rayl

Contributing Editor for The Planetary Society
Read more articles by A.J.S. Rayl

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