NASA - National Aeronautics and Space Administration

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Narrator: A countdown to a touchdown on Mars. I'm Jane Platt with JPL -- NASA's Jet Propulsion Laboratory in Pasadena, California. It's really hard to successfully land a spacecraft on Mars. But if all goes as planned, that's exactly what will happen on May 25. Joining us is Barry Goldstein of JPL, project manager for Mars Phoenix Lander. Barry, first off, why don't you tell me where exactly Phoenix is headed and why it's going there?

Goldstein: Well, Phoenix is going to be the first mission to hopefully successfully land north of the arctic circle on Mars. And the reason we're going there is consistent with the Mars program theme of following the water. We're actually going to dig and anaylze the recently discovered near-surface water, ice water in the northern plains of Mars.

Narrator: And how does this mission fit in with the science goals of NASA's Mars program overall?

Goldstein: One of the obvious themes of the Mars program has been to follow the water, and the reason the theme was to follow the water is we know on Earth that wherever there is water, regardless of other environmental extremes, whether it's at the volcanic trenches in the ocean or even up in the Arctic, no matter how cold or hot, where there's water there's always been various signs of life. And while Phoenix is not a life detection mission, what we are trying to do is determine the biological potential, the potential for life being in a region on Mars and where better to go than where the water is.

Narrator: OK, and the Phoenix lander is going there, and has actually inherited some old technology. Tell me about that

Goldstein: Yes, what we've done on Phoenix, and its name is somewhat apropos, is we've taken the concepts and designs of the payload from the Mars Polar Lander, and we've taken the hardware that was actually in development for the Mars '01 lander, which was postponed after the MPL, Mars Polar Lander failure. And we've basically resurrected them in a mission, and we've spent an enormous time over the past five years testing, analyzing and simulating all the capabilities of the '01 lander to make sure it's a success.

Narrator: Can you explain a little bit about how you took the existing technology and you tested it and tested it and tested it again?

Goldstein: Absolutely. What we had proposed when we first put together our mission concept was that we would spend the first portion of the mission actually going through the analysis that was done and looking at the pedigree of the hardware and making sure that it would be compatible with the mission we've designed. So the first part of the mission, what we call Phase B, we went and we re-did and re-looked at all the analyses and re-verified the capabilities of the system performing the way we wanted it to. We made several changes based on that, and then we went into the next phase, which is looking at the system design and seeing how it performed analytically. There is where the focus on EDL really took hold, and we found several issues that we've corrected relative to the architecture it was designed or defined, I should say. And entry, descent and landing, which is our most difficult phase. And we did a significant amount of testing, and we identified several problems that were not known before with the architecture, and we've mitigated all of them.

Narrator: So your comfort level is …

Goldstein: (chuckles) My comfort level -- apprehensive, I'm very optimistic and very confident that we've done the best job that can be done. I'm apprehensive because we're at the whim of lots of things. The environment is one of the things we're susceptible to. We've done everything we could in the design to put margins in based on anything we could possibly think of in this environment, as well as all the data that we've collected in terms of our landing site, to be very confident that we won't be at the whim of rocks. But the bottom line is we have a lot of things going on in the span of the last 14 minutes before touchdown, we have 26 events, pyrotechnic events, separations and deployments that have to go right. And for all those things to happen autonomously in that quick period of time outside of our control, we can't react to those problems from Earth, obviously. There's a lot that has to go right in a short period of time, so it makes people nervous.

Narrator: And that's the scary entry descent and landing, or EDL.

Goldstein: Yes, entry descent and landing, no matter what system you used, no matter how often it's worked in the past, by its very nature, because its happening autonomously, its happening outside of your control, and all the hardware, all the long hours, all the sleepless nights of worrying about problems, all comes down to that final period of time.

Narrator: A lot of people are familiar, especially our younger listeners, with the two rovers that have been on Mars for four years working great, Mars Spirit and Opportunity. Those landed with airbags, as did Pathfinder back in '97. But this one, Phoenix, is landing a different way. Explain briefly about that.

Goldstein: That's correct, we're using what we call pulsed thrusters, for what we call terminal descent phase, the last phase of slowing down the vehicle before it touches down on the Mars surface. And the reason we went away from airbags is airbags have a limitation, or I should say a shortfall, in that it's very mass inefficient. By that what I mean is the amount of mass that you have to put into an airbag system to deliver another amount of mass that actually does the science on the surface is very high. With thrusters, we actually have a much greater ratio of the amount of mass that we can deliver to do the science relative to the amount of mass we use for the terminal descent phase of entry, descent and landing.

Narrator: OK, so basically a smaller rover, lander you can use airbags, but Phoenix is bigger and you can't.

Goldstein: Phoenix is bigger and it becomes very mass expensive to do so. Saying can't is probably a little bit too extreme, but we believe and we know, I should say, that the amount of mass we'd have to put into a lander of this size down on the surface would be prohibitive.

Narrator: The reality is that Mars has not been a very kind place to spacecraft coming to visit it.

Goldstein: Well that's absolutely right, and more to the point, for landers its been particularly harsh. Fifty-five percent of all the landers that have been attempted to Mars have been failures. Obviously not a good statistic. U.S.-built landers have done a little better than that. We've landed five out of six successfully -- the two Viking missions, the two MER missions and Pathfinder have all been successful. However, its been a while since we've used thruster descent as our terminal descent phase, and hopefully we can get that track record rolling in the right direction on May 25th.

Narrator: As we count down the days and hours to landing, how do you control your stress factor?

Goldstein: You're under the misconception that I' m controlling it. (laughter) No, the best thing you can do is just realize, and I do this all the time, I've been doing it for five years, that I've got the best team in the world working on this. And so I know I've got the, there is no better organization to work on Mars landers than the teams that are working out of the various organizations on Phoenix, between the team here at JPL, the Lockheed Martin team, the U of A team, all of our partners at Langley and everywhere else.

Narrator: And landing time on May 25 is a very civilized time actually, some of ours land in the middle of the night.

Goldstein: Well, it wasn't very civilized when we launched, since we launched a little bit before 5:30 in the morning East Coast time on August 4th. We actually land Pacific time at 4:53 p.m. on May 25th. That is when I should say we have detection of landing, because the landing actually occurs a little bit more than 15 minutes earlier than that, but it takes light that amount of time to travel, and I should say in this case it's the radio signal, that amount of time to travel to Earth for us to detect landing.

Narrator: Well, let's hope we have a good day and everybody will be excited and happy and we'll have some good science coming back.

Goldstein: That is what we're hoping for.

Narrator: Thank you very much for your time, I appreciate it.

Goldstein: Thank you very much.

Narrator: For a lot more information on Phoenix, including animations, you can check out www.nasa.gov/phoenix. And you can watch the landing live on Sunday, May 25th, from a link on that Web site and also on NASA TV. Thanks for joining us for this podcast from NASA's Jet Propulsion Laboratory.

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