|MARS POLAR LANDER|
December 2, 1999
JEFFREY KAYE: After an 11-month journey of 470 million miles, a U.S. spacecraft is expected to drop down tomorrow afternoon close to the South Pole of Mars. If successful, the Mars Polar Lander will be the fourth U.S. spacecraft to set down on Mars. A chief science goal of the mission is to help solve a puzzle. The Martian surface is covered with deep channels carved by water. There is some ice on the surface, but researchers are trying to figure out where the water went. Richard Zurek, of NASA's Jet Propulsion Laboratory, JPL, near Pasadena, California, is the project's chief scientist.
|On the lookout for Martian water|
RICHARD ZUREK, Jet Propulsion Laboratory Science: The question is, if you look at how much water was required to carve those channels, that's a lot more than what we see on the surface and in the atmosphere. Where's that water gone? We think it's gone into the subsurface. It's in the ground, frozen as ice. And the question is, how far into the ground do you have to go to find it?
JEFFREY KAYE: To try to answer that question, engineers packed the spacecraft with a laboratory of science equipment. Finding out about the water will not only offer clues to the possibility that forms of life existed or still exist on Mars; if water is found, engineers could use it to generate rocket fuel on Mars for future missions. Unlike the 1997 Pathfinder, this mission does not carry a Rover, the little vehicle that traversed the Martian surface. Scientists are working on a full-scale model of the Lander in a test bed at UCLA. Scientist David Paige of UCLA leads a team of researchers from Denmark, Finland, Germany, Russia and other U.S. science institutions. Paige says researchers outfitted the spacecraft to replicate the kind of gear human explorers would take.
DAVID PAIGE, NASA Research Team: We have our eyes, which are the surface stereo imager, and which are able to pop up and be able to look around in both directions. And we'll have color, stereo images, very much like you get with your eyes. We'll also have an arm, a robotic arm, which can reach out and scoop up soil or dig in it, or stick thermometers in it. We also have robotic arm cameras that can take a picture close-up of the soil, much like as if you scooped up a piece of soil and looked at it with a hand lens. We have a meteorology station that can tell how hot it is on Mars, how fast the wind is blowing, the pressure on the surface, as well as the humidity in the atmosphere.
JEFFREY KAYE: One device will heat up and analyze the scooped-up soil samples. A microphone will record sounds. Another instrument will aim laser beams upwards to measure how high the clouds are. The spacecraft itself was designed and built by Lockheed Martin, near Denver, Colorado.
ENGINEER: Typically, in cruise, we'd go to the uplink loss.
JEFFREY KAYE: Working with JPL in California, Lockheed Martin engineers are responsible for monitoring and controlling the spacecraft. Kenny Starnes heads the Lockheed Martin flight operations team.
KENNY STARNES: We are in the driver's seat. We're like the bus drivers. And we do the maintenance on it, too, to the extent that we can. Of course, it's many millions of miles away.
JEFFREY KAYE: And the folks at JPL, they're the back seat drivers?
KENNY STARNES: Yeah, pretty much. And they give us most of the direction on what we do. They tell us... or they direct us into what our mission plan is, and they help us work that out. They give us direction, as far as what the spacecraft must do at any particular point in time.
|Making the approach|
JEFFREY KAYE: As it approaches Mars, the spacecraft will be traveling at more than 15,000 miles an hour, but will slow down rapidly as it enters the atmosphere. A parachute fired from a small cannon will continue to slow the descent. A camera will take pictures as thruster engines fire to enable a soft landing.
DAVID PAIGE: At that point, we'll wait a little while for the dust to settle, and then the solar cells will be deployed. The Lander will start to gain energy back from the Sun; we'll then start taking pictures, deploy our various instruments like the antennas, the meteorology package, and the camera, and then point the Lander's radio dish at the Earth and phone home and say "hello, we're there. We're going to start the mission now."
JEFFREY KAYE: And how soon after it lands might you expect word that everything is a-okay?
DAVID PAIGE: The first transmission...if we get any transmission at all from the Lander, that means things are basically a-okay. And those first transmissions will also include the first images of the surface, which we'll hopefully put right on TV, right on the Web site, and have a press conference at JPL directly afterwards.
JEFFREY KAYE: As the Lander's instruments go to work, yet another experiment should be under way: Two probes that hitched a ride aboard the spacecraft should be collecting data from underground. Sarah Gavit of JPL is in charge of the probe experiment.
SARAH GAVIT, Mars Probe Project Manager: Just prior to atmospheric entry on Mars, the Mars Polar Lander will separate from its cruise ring. That'll initiate a sequence of events that will then end up separating the two probes from the cruise ring about 18 seconds later. And unlike most spacecraft before, these probes don't have rockets or parachutes to slow them down. Rather, they just crash into the planet at speeds of about 400 miles an hour.
JEFFREY KAYE: Scientists expect the probes will penetrate one to two feet, depending on the surface. And they hope that even after the crash-landings, a drill and computer encased in each probe will function.
SARAH GAVIT: After impact, we have a motor that drives this drill out the side of the probe about a half an inch. And in drilling out the side of the probe, it collects soil. And the tailings fall into a small cup inside the probe. And we seal off that cup, and we heat it up. We cook the soil sample.
JEFFREY KAYE: Inside here?
SARAH GAVIT: Inside of the cylinder.
JEFFREY KAYE: Inside the cylinder, right.
SARAH GAVIT: Right. And if there's water in the soil, it will come out of the soil. And what we do is, we shine a laser through the vapor. And if there's water present, then the intensity of the laser will decrease, and we'll know we've detected water.
|Recovering from failure|
|JEFFREY KAYE: Each probe is designed to send computer signals
to the small ground station above it, which in turn should transmit the
data from its antenna to Earth. Communications between the Mars Polar
Lander and Earth have been complicated by the loss of another spacecraft,
the Mars Climate Orbiter. In September, the Orbiter, which was supposed
to have served as a communications relay between the Lander and Earth,
was lost in space. Flight controllers at Lockheed Martin gave the wrong
data to navigators at JPL. Engineers learned a very hard lesson, says
Lockheed Martin's program manager for development of the two spacecraft,
EDWARD EULER, Lockheed Martin: The mistake was that we had to give the Jet Propulsion Lab some data that is used to compute very, very small little thrust pulses onboard the spacecraft. And we did give them the data in the wrong units... and in English units, and it should have been in metric. And they used the data as if it were metric, and underestimated the magnitude of these small, little pulses that come out of the jets of the Orbiter by about a factor of five. And that in turn made it very difficult to get the proper navigation, or determine the position and velocity of the spacecraft, which eventually led to the failure.
JEFFREY KAYE: After the failure, NASA investigated operations at both Lockheed Martin and JPL, and issued a critical report blasting both agencies.
The failure prompted Mars Lander engineers to hold virtually nonstop meetings to review and double-check calculations. Team members say the pressure to succeed has been intense. But more significantly, the loss of the Orbiter means compromises in the mission. Engineers say 10 to 20 percent less data than originally planned will come back from the Lander. It will now have to transmit directly to giant receivers on Earth.
RICHARD ZUREK: It takes more power to operate the direct-to-Earth link. You have to push those bits all the way from Mars back to Earth instead of to an orbiter that's just overhead, and that takes more power. That's power that's diverted from what we would have used for further observations with the science payload.
JEFFREY KAYE: May there be fewer images, or fewer high-resolution images?
RICHARD ZUREK: Right. The biggest impact is on data-intensive things. And interestingly enough, that's sort of two areas. One of those is just visual images of the landscape itself. And what that really will mean is that we'll still get a panorama of the whole landscape, but we won't be able to look at it as repeatedly during our landed mission as we might like.
JEFFREY KAYE: The other area of compromise caused by the loss of the orbiter will be the operations of the digging scoop attached to the 6.5-foot arm. Jeffrey Slostad heads a JPL team that's been working on the robotic arm for four years.
JEFFREY SLOSTAD, Robotic Arm Engineer: We won't be able to dig as much. The power it takes to run the antenna all day long-- or for four hours, or whatever-- that basically means instead of having a six-hour day for just digging, we'll now have maybe a two-and-a-half-, three-, maybe four-hour day, if we're really lucky. And things get a lot more difficult, particularly if we have a big hole to dig.
JEFFREY KAYE: Slostad and his colleagues have made elaborate preparations for the mission. They practiced digging in Antarctica, where the surface approximates that of the Martian South Pole. More recently, they tested their computer commands in the sandbox at UCLA. The challenge was a problem familiar to any kid who's ever gone to the beach with a shovel.
JEFFREY SLOSTAD: If the soil is very soft, it's easy to dig, and it's easy to fill the scoop, but you have to take many, many scoops to dig a hole, because the trench keeps caving in on itself. It's kind of a Goldilocks sort of thing, though. If it's just right-- if it's not too hard, not too soft-- if the walls have enough strength to them that they don't cave in, yet it's soft enough that we can dig through easily, then we're very happy, and you'll see us smiling a lot, and we'll get some sleep from time to time.
JEFFREY KAYE: Much of the knowledge gained on this trip will be used for planning future missions. In five or six years, scientists on earth are hoping to be able to study bits and pieces of Mars in their own labs.
EDWARD EULER: What you're looking at here is a mockup of the Lander that's going to fly in 2003 to return samples from Mars.
JEFFREY KAYE: The 2003 Mars Surveyor will be equipped with a rock-collecting Rover.
EDWARD EULER: There will be a drill, and also the Rover will acquire soil and rock samples, put them in a container into the nose cone of this rocket.
JEFFREY KAYE: Right.
EDWARD EULER: And the rocket will launch off the deck of the Lander, and launch the samples, in a container, into Mars's orbit.
JEFFREY KAYE: Martian orbit.
EDWARD EULER: That's correct.
JEFFREY KAYE: To be picked up when?
EDWARD EULER: They will be picked up in the 2005-2006 time frame, by an orbiter which is actually being built by the French. So this will be an international mission, as well.
JEFFREY KAYE: As for the current mission scientists hope the solar-powered Lander will operate on the surface for about three months. It should run out of energy and stop working as the Martian summer ends, and the Sun gets lower.