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MER-B Webcast - MER-A and MER-B How Are They Different?
Question and Answer Board

Luke from Comox
What does MER-A do? What does MER-B do?
Both MER-A and MER-B have the same set of science objectives, Tiffany. They are meant to serve as robot geologists on Mars. They are looking for evidence that has been preserved in the soil and rock record of past water on Mars to give an indication whether the habitat on Mars might have been conducive to life. As it turns out, they are going to two different places on Mars. The first rover, the one, Spirit, that launched on June 10, is going to Gustav Crater. That is a crater lake on Mars that looks like a place where water flowed in and may have stood in a lake for a long period of time. The second one, the one Opportunity that is going to launch in a couple of days, that is going to a place on Mars where there are minerals that on Earth usually form in the presence of water. So although the rovers are identical and they have the same set of mission objectives and the same payload, they are going to two different places to look for basically different kinds of evidence of past water on Mars.
Jennifer from Edmonton, Canada
The Mars Pathfinder Rover was only intended to have a mission of 30 days, however, it kept sending information for several months. Is the mission duration of 90 days for the MER Rovers an adjusted length as a result of Pathfinder's extended mission, or is it due to improved battery power systems? If so, what do you expect the "real" mission length to be?
Those are very good questions. The duration of the mission is driven solely by the power available to the rover and to the mission needs, power needs that are going to be placed upon it. The power basically comes from the solar array that you seen on top of the rover, in the many pictures that you've seen, and it is the size of the solar ray that determines how much power that we have. Over a period of time that power will get less and less because dust from the Martian atmosphere will deposit itself on the solar panels, just like dust in your house accumulates on your dining room table. And it will get a little bit colder and the sun will move to the north, away from us, during the mission. Now the scene that sets the demand for the power is the operation of the instruments, the operation of the payload, and the mobility system, the motors that allow us to drive around on Mars. When we run out of power and we can't run the rover anymore, that's when the mission happens to end. Right now the rovers are sized for 90 days -- that is what we designed into the system from the very beginning. But we have gotten slightly better solar panels than we thought we would get, the insulation on the rover to keep us warm is a little bit better, and some of the electronics don't use quite as much power as we thought they would. So we really expect that it will last maybe 115, 120, maybe even as much as 130 days.
Jennifer from Edmonton, Canada
Other than geographical location, what are the differences in terrain between Gusev Crater (Spirit) and Terra Meridiani (Opportunity)? Will any differences in terrain affect the battery life of the rovers, or has this been considered when building the rovers? For example, if one terrain is more 'hilly' the rover will use more power navigating that terrain than the other rover.
There are some significant terrain differences between the two landing sites. Meridiani is extremely flat; if there are hills there, they will probably be very low and modest. And it has what's called a low rock abundance that means the number of rocks that you see sitting on the surface is not going to be as much as you saw on the Pathfinder photographs. That means it will be easier to travel long distances, so the power use of the rover will probably do more, longer traverses at Meridiani than it will do at the other site. Gustav, as I mentioned before, is a crater lake. It tends to be a little bit more hilly; it has a little bit more rocks. There will probably be places closer to the rover that will want to spend a lot of time looking. So it will be much more, I think, a stop and go mission. The power is really not sized according to whether one's going to a hillier terrain or one's not going to a hillier terrain. Basically it's a budget that the scientist are allowed to use everyday to best satisfy their objectives. Whether they want to use it to send data to Earth, or they want to drive more, or they want to use their instruments more.
Jaclyn from Rockaway
Why does the Opportunity (MER-1) need to launch on a Delta II Heavy when the Spirit (MER-2) launched on the Delta II since they both are identical?
That's a really, really good question, I like that question, and I heard it a lot. If you recall from the discussion about going to Mars, is we can only go to Mars once every 26 months because that's when the planets are in the right alignment to go from one to another. What that means is that if you are right at the right place, you can give it the least amount of extra energy and you will arrive at Mars. That was the place where we launched Spirit. Opportunity is launching almost a month later; in fact the launch periods are about 25 days apart. Which means we need to give Opportunity more energy, more velocity, to go to Mars because it's not right in the right place in the relationship between Mars and Earth. Because of that, we have to use the Delta II Heavy to give us more velocity and more energy to get to Mars.

Host: Well, it kind of sounds like the name Opportunity is quite appropriate then, because it needs more opportunity to get to where its destination is.

I don't think we thought of that one, a name for a name, but that's a good point.
Peter from Basel, Switzerland
Can the rovers, Spirit and Opportunity, after landing on Mars go to the Viking Landers from the year 1975?
The short answer is no. And the long answer is, it gets into how far apart they really are. Both the Viking Landers landing in the northern part of Mars, and that had to do with the time of year they were arriving and their mission objectives. They are thousands of kilometers away from the two landing sites for Spirit and Opportunity. They are in the equatorial regions of Mars, very close to the equator. And they are there because that happens to be where the sunlight is, and that's what we need to power the solar-powered rover.
Junichi from Niihama City
What is the difference between MER-1 and MER-2? Do they have much different mission?
They are actually identical; they were built to be identical. There are small differences like the radio frequencies, and the transmitter frequencies, so that we can talk to one or talk to the other and we can make sure we don't get confused or they don't get confused. They are different in terms of where they are going, as I've mentioned, one going to the Gustav and the other going to Meridiani. But they have the same suite of science objectives. I think when we get there, we will discover that they probably develop a little bit of their own personalities, and we'll find one will operate a little bit better in certain ways than the other. Certainly, we have two separate teams to operate the rovers; they will develop their own personality, that's for sure.
Junichi from Niihama City
Why don't you take bacteria on Earth and observe how it reacts on Mars?
I don't know that people have thought about that directly. There are a couple things that control our ability to do that. One has to do with what we are called Planetary Protection Rules. There is a set of international treaties and agreements that regulate the ability of us to take bacteria or organic material or spores to Mars in order to avoid contaminating Mars for future scientific investigations. The Mars Exploration Rover project is what is called a Class B. We're not involved in the search for life and so we have a level of cleanliness that we did when we put the rovers together. If you were a Class A mission looking more directly for life, the requirements would be much more stringent. You would actually have to sterilize the equipment, almost like an operating room, in order to be able to satisfy these agreements. It would depend on those agreements and how they interacted with what you wanted to do, whether or not you could take bacteria to Mars to see how it would live there.
Wim from Antwerp, Belgium
Can MER-A and MER-B communicate with each other in anyway?
No, they really can't. Their transmitters and receiver frequencies are designed to talk to Earth, through the Deep Space Network, and they are designed to talk through Odyssey and Mars Global Surveyor, two spacecraft that are in orbit around Mars that have UHF relay capability. But they are not at the same frequency that allows them to talk to each other. It's not like the intercoms that so many of us use, or the cell phones that so many of us carry.