Online NewsHour: Mars Mission -- December 3, 1999



	MARS MISSION

December 3, 1999

Ray Suarez has the Mars story.

RAY SUAREZ: Another opportunity to find a signal from the surface of Mars passed a short time ago, with no success in locating the polar Lander. This was one of several windows this evening. For the latest, we're joined by NASA's associate administrator for space science, Edward Weiler. Well, Mr. Weiler, when was the last time the JPL had some contact with the craft to know that it was intact and heading where it was supposed to be heading?

EDWARD WEILER: The last contact we had with the Mars polar Lander was about half an hour before it actually landed. At that point in time, the last radio contact we measured its position, basically, its trajectory and everything was looking absolutely perfect. It looked like we were going to hit the spot we wanted to hit on Mars, a very smooth spot with little rocks or anything like that. So we're very confident we landed successfully. It is a matter of getting the antenna on the Mars polar Lander pointed at the earth.

RAY SUAREZ: As I understand it there were a series of steps that had to be taken by the craft in these initial phases once it reached Mars. Tell us about those and how you can figure out whether those actually happened or not.

EDWARD WEILER: I think even though we were hoping that we'd hear the first signal at about 12:39 this afternoon California time, we all knew that an awful lot of things had to happen just perfectly for that to occur. For instance, as the spacecraft settled down and touched down, it was going to... it had to find its orientation in latitude or... longitude, or azimuth, if you wish, and it does that with a gyro system. As it was touching down, it does that. If after it touched down it started to sink a little bit or settle even a few millimeters, it would throw off the calculation. That's critical because that azimuth calculation, that longitude calculation then is used to tell the high gain antenna where to point toward the Earth. Right now the best guess is that we're probably not looking that... that antenna is not looking right at the earth. But at 8:00 tonight California time, that antenna will start being commanded; it will actually start moving around in the sky. We'll be listening here in California. And when we hear it, we can then tell the craft on the ground stop there. That's the right spot. From that point, it could be a nominal mission.

RAY SUAREZ: There are so many variables that you obviously can't control for. I'm wondering if the craft itself can respond. For instance if one leg sinks deep into the surface or indeed if the whole craft is on its side, can it make the necessary adjustments to still get you some data?

EDWARD WEILER: Well, the craft has the capability of moving its antenna in quite a wide range, like 60 degrees in azimuth and 30 degrees in longitude. If it's on a slope, it can take that problem into account. There is another solution, and that is it has a so-called low gain antenna or omni directional antenna. On Sunday if we still haven't heard from the craft, what we'll do is get signals sent up from the craft up to the Mars global surveyor which is a Mars satellite in orbit around Mars right now, and that satellite will relay the signal from the landed craft to the earth. So that's actually another back-up system we have in place.

RAY SUAREZ: Right now you are still looking for this signal. And we're told by the Jet Propulsion Laboratory that windows open and close. Why does that happen? Does it have to do with the position of the earth and Mars? Is it a power question?

EDWARD WEILER: No, it's actually what you said at first. The position of Earth and Mars. Mars of course is rotating around its axis. So for half of a Martian day, 24 hours roughly, the spacecraft is pointed toward Earth. Our antennas on Earth, which are in Australia, Spain, and California, are also rotating. It's a complicated set of trigonometry when the windows of opportunity occur.

RAY SUAREZ: Can you gradually eliminate places in space where the signal might be or eliminate patches of Mars and sort of narrow down your search as you look for this signal or do you just have to keep listening until you hear it?

EDWARD WEILER: Well, actually, starting at around 6:30 tonight California time, we will command from Earth -- we'll send a command from the Earth to the Mars Lander and tell it to start rastering its antenna. What I mean by that, you can almost think of it as taking your digital antenna outside and trying to find the communication satellite up in the sky. It will move the antenna a little bit, and send a signal; move it a little bit more and send a signal. We're listening. If we see the signal, we'll know what to tell the Mars Lander as to what is the sweet spot in the sky to stay pointed at.

RAY SUAREZ: There have been missions that haven't gone well in the past in our efforts to reach Mars. At what point do you start to speculate on things having happened to the craft, start to rule out the possibility of a error-free landing?

EDWARD WEILER: I think right now we're not even, you know, speculating that far because we have several opportunities tonight. We have more opportunities on Saturday and Sunday. Again, you know, one of the best opportunities is when we actually use the Mars global surveyor satellite as a communication link, so to speak. Then there are several opportunities Monday, Tuesday and Wednesday. So I'd say over the next week -- we still have a lot of reason for hope.

RAY SUAREZ: There's a second piece of equipment that went pounding into the surface of Mars. Do you need the main Lander to be working and sending you data in order to get the things that that second craft is picking up?

EDWARD WEILER: That's an excellent point. I'm glad you brought it up. There are three spacecraft on Mars right now as we speak. We know these things came down. In addition to the polar Lander, there are two basketball-sized probes which also landed on Mars although landed is a strange term because they crash landed on purpose. They came in at ballistic velocity 400 miles per hour. And they hit the ground at about 50,000 G's. But they were designed to do that. As they hit, a probe goes down about 30 inches or 36 inches or so. Those are two separate probes. They have two separate communication systems. And we expect to... the earliest we can hear from them is 7:30 tonight, again Pacific Time. So there are really three different probes on Mars at this point in time.

RAY SUAREZ: So to be clear, the wonderful things they could be finding out about water, about the make-up of gases in the Martian soil, we can still get that even if you don't get your pictures from your main frame?

EDWARD WEILER: Excellent point. The two so-called deep space probes are independent from the Lander. They do not depend on the Lander whatsoever. Their communications are with the Mars global surveyor, which is a currently operating spacecraft around Mars.

RAY SUAREZ: So does everybody go into sort of overdrive at this point? Are you handing on duties to Spain and to Australia that you didn't have to expect to have to do because you just haven't heard from the craft yet?

EDWARD WEILER: No, right now, actually long before launch, we had a very well laid out plan for contingencies. All these radio contact times were already set up with Madrid and Spain and Goldstone in California. It has been preplanned. Nobody is changing anything. Everything is proceeding in a very ordinarily fashion.

RAY SUAREZ: NASA's Associate Administrator for Space Science, Edward Weiler, thanks for being with us,

EDWARD WEILER: Thank you.

Program
Support
From: