Phil Christensen

An Interview With...

Phil Christensen

Planetary Scientist/Principal Investigator
TES, THEMIS and Mini-TES
Arizona State University
Arizona, USA

What would you consider your greatest technological accomplishment?

I would say just designing and building and getting the TES [Thermal Emission Spectrometer] instrument to Mars. And it really is a team activity. There are sixty people who were involved with that. So, I am not a technologist by training, I'm a scientist, but the opportunity of working with that team of people and getting that instrument built ... It didn't exist before we started and now we have sort of created something.

How did the "Mars Observer" become lost, and did you recover any information from that mission?

We think it was lost by an explosion in the fuel system, just prior to when the rocket engines would have fired to slow it down and put it in orbit around Mars. It is a complex system of two chemicals that mix together. They are supposed to mix together in the rocket engine and that's what they burn and they cause the rocket to fire. It looked as though those two chemicals mixed in one of the fuel lines and something the size of a straw blew a hole in it the size of a pea and that was it. All the fuel came out. A tiny little mishap can destroy a whole mission.

It was a very discouraging time for everybody involved. At that point, we had no idea that we would get an opportunity to do it again. It turns out that NASA said this was a very important mission, they were very important instruments, so out of that failure came Mars Global Surveyor. Actually, it turned out to be a good thing because NASA said, instead of an extremely expensive mission, a billion dollar mission once every ten years, which is how we had been exploring Mars, they said, let's send less expensive missions so if we lose them it is not as catastrophic a failure. Let's send a $200,000,000 mission every two years. The cost is the same but now you are sending a lot more spacecraft to Mars. That's the program we have now. Every two years, something goes to Mars. So it actually turned out to be a good thing. Painful, but a good thing.

What was the motivation behind building the TES, and what did you hope for it to accomplish?

I had worked on a previous instrument with Hugh Kieffer who was the principal investigator. It had made the first infrared measurements of Mars, but they were very simple measurements. I had worked on that instrument as a grad student and from what I’d learned, was able to say: if we could take this concept, or this idea, and extend it, make it better, make it more complicated and measure more information in the infrared, that would be the next logical thing to do. That's what TES is. We just simply said, hey this looks like it will work, let's make it better. So that was the motivation behind it. As for as what we hoped to accomplish, we really wanted to map the planet, find out what rocks were there. I think it turned out to have been wildly successful. It's worked better than I thought it would, found more interesting things than I thought. So it’s really exceeded our goals.

What are some factors you had to take into consideration when designing the TES?

That's a great question. The main factors are weight: the spacecraft can only carry so much to Mars. So, the instruments we send must be extremely light weight. TES weighs about 25 pounds. But that's ... not much. The next one is power, how much power these things use. We have to have solar panels which use solar energy to make electricity. TES runs on 12 watts of power. The entire spacecraft runs on the equivalent of like two light bulbs. So that's huge. The next one is reliability. These instruments have to run for years and years. And the final one is cost. Trying to make things small and miniature costs. So it is a trade off between those four.

Beyond that, you say: here is what I want it to do, and you turn a group of engineers loose and you let them design to the best they can. That's where I get involved a lot. They come back and say, well we can do this but we can't do that. Or, if we had a little bit more money we could make it better here. Or, if we had a little more mass we could do this. Or, we could save some mass if we didn't do quite as well in this area that you'd like. Is that ok?

So there is this constant trade off between the engineers and the scientists. We want to make it as good as we can and they want to make it work. So, that's why I work with them daily, helping design these things.

Have you ever released information about the spectroscopy to the public, and later found it to be false?

Yes we have. And that is just a natural part of science. If we waited until we were absolutely sure about our conclusions than it would be five or ten years. People would have forgotten that this mission even existed. So, we try very hard. There is the original data which we release. Then we process the data to turn it into a spectrum and there are steps in that process which there can be problems with and we try really hard to get that right. And then there is the analysis, where we say, we think we have discovered this mineral or this whatever and there can be problems all along the way. That is just the way things work. You think you have discovered something and later it turns out to be wrong. That is just the way science works.

Early on, we had looked at some of the spectra and we thought we had identified a particular mineral. It turns out, it was a mineral that is found in volcanic rocks, which we have since discovered really is there, but it turned out in the spectra that we were interpreting, this was me, it looked like the shape of the spectrum from this one mineral but it wasn't.

It turned out it was a combination of dust in the atmosphere and water/ice clouds which was mimicking or copying the structure of this mineral. It turned out it wasn't that hard to realize it was really things in the atmosphere instead of the ground but, you know, there are things like that.

We try really hard, because if you release data and it's wrong and you release data and it's wrong, and especially the more spectacular the conclusion, the more careful you have to be. I mean we don't want to say: hey, we think we have found life on Mars, and then have to retract that.

Like this hematite discovery and [the possibility of past] liquid water and lakes on Mars: we worked really hard to make sure we were right, because it makes us all look bad if we are retracting things like that.

Is there any new technology being developed that will help speed up the process of the analysis of the spectroscopy?

The main new technology is just faster and faster computers. Even in the ten years since we started back in the Mars Observer days, computers have just improved incredibly. For example, when we planned TES, we thought we would get seven gigabytes of data. In 1990, it cost $500,000 to store 7 gigabytes of data. So, we couldn't keep all of the data on our computers. We had to store it off on tape. If we wanted that part of the data we had to bring it back from tape and that would have taken forever. Today, you can buy 7 gigabytes of disk space for $500. So it is easy to keep all the TES data on line all the time. So, it's mostly computers that's really helping us a lot. The computers are faster and they do more.

Do you personally see Americans going to Mars anytime in the near future?

Absolutely. The question is, what is the near future? I'm 47 and I expect to live to see Americans, or humans, go to Mars. I expect that it will be an international program just because of the costs. And because it is a way for nations to get together and to do something positive and constructive and therefore justify the cost. Not just for the science but also for humans to work together from different countries. So yeah, I think within the next 20 or 30 years. I would be very surprised if 100 years from now, humans had never gone to Mars.

Do you think we should go back to the moon first?

Personally, no. Because that is also very expensive and very complicated and I am just concerned that if we do that it will add 20 years to when we actually get to Mars.

There are definitely things we have to learn how to do. We have a space station that is really very nicely suited for learning those things. How to live in space, how to grow food, how to recycle water and oxygen, how to survive a six month trip to Mars. But you can do that on the space station, which is kind of what it was meant to do ... but either way, if we set up a colony on the moon, that would be a very good first step and from there it would be easier to get to Mars, but I would rather just go straight there.

What new technologies need to be developed in order for this to become a reality?

I think it's mostly a couple of things. We really, truly have to learn how to recycle oxygen, water, waste materials, grow food ... A spacecraft that goes to Mars, it can't carry all the oxygen and food and water that you would need for a three year journey for seven people. You have to grow food and have plants make oxygen. You have got to get really good at that. You don't want to get half way there and have all your plants die. Then what do you do?

I keep salt water fish and just keeping them alive is a struggle. So, if I am on my way to Mars and they say, well yeah, there's the corn and the wheat and the chickens and the pigs and we hope they don't get diseases and all die... <laughter> Hey, let's make sure they don't!

The other main issue is humans surviving in space. We know that your bones deteriorate and your muscles deteriorate if you are not in gravity. I think there is probably quite a bit of research that needs to be done there.

As far as the technology, we know how to build rockets, we know how to build space stations. The equipment, the machinery we need, is pretty much there. We know how to land on Mars. The trick is making all of that stuff really reliable so that a team of humans is willing to get inside this spaceship and say this will get me there safely and back again. We know how to do it, we just need to make it more reliable.

I think we also need to know how to fix things, so that if something breaks, you can fix it. Some thought has to go into that, but that's more planning, not so much technology. It's just really having a good plan. It's like the guys who go out for six months in a nuclear submarine and they are under water for six months. They would probably look at a mission to Mars and say: yeah, we can do that. If our submarine breaks, we fix it. We have to bring food. We have to bring water. We have to bring air. We can do it. It just takes some planning.

Did you ever expect Mars Global Surveyor to do as much as it has accomplished?

No, I really didn't. You know, you sort of sit down and list the things you'd like it to do. It has exceeded my greatest expectations. Just in terms of the breadth of what we have learned: the topography, the incredible pictures of gullies and layers that we've taken, the polar caps, what goes on in the winter time at the poles, the minerals we've discovered. It's amazing. We could stop now and collect no more data about Mars and still be discovering new things 20 years from now from the data Mars Surveyor has sent back.

Read Phil's New Interview (25 May 2003)

- 3 March 2001

Last Updated:
25 March 2002