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MER-A Webcast - Mission Overview
Question and Answer Board

Juan Rodríguez from Gijón (Spain)
Hello! Can you pick another landing site or make some trajectory correction maneuvers while the space probe is traveling from Earth to Mars? Thank you!
Yes, it turns out if we have a problem with the MER-B launch, the vehicle that we launched today at the trajectory correction maneuver number two about 50 to 60 days after launch, could be re-adjusted to go to the back-up site Meridiani in the event that we need to re-target we can do that as late as five months after the launch and go to Elysium which is a second back-up site.
Mike from Peoria
How do you know the MERs are entering Mars atmosphere correctly? (Not too steep and not too shallow?) And how would you know if it didn't enter correctly?
Well, the spacecraft transmits a signal and X-band and it is received here on the ground and our navigators can look at that signal along with other signals on the spacecraft and determine the location of the spacecraft as it approaches Mars. About 45 days out we enter the approach phase of the mission and we have three maneuvers that can be taken to pinpoint the spacecraft into the location that we want to land on the surface in a pre-defined spot. We can also tell using those same signals whether we entered too steeply or too shallow and skipped off the atmosphere of Mars and did not enter the atmosphere as we anticipated.
Danica from Reseda
What is the temperature that is outside the space vehicle when it lands on Mars?
Mark from Greensburg, Pennsylvania
What temperature is it on MARS?
The temperature on Mars varies from a high during the daytime of plus 10 Celsius or 50 degrees Fahrenheit to as cold as minus 100 degrees Celsius or approximately minus 150 degrees Fahrenheit. That cold temperature requires us to power things down and just have heaters on so we can survive the cold Martian night.
Richard from Arcadia, Florida
The height of Pathfinder was 42.694", is this lander the same height? I did the machining on Pathfinder as I worked for JPL at that time!
Yes it is to within about two inches. It turns out one of the design constraints that we had was to stay within the Mars Pathfinder system architecture that would allow us to use a direct entry and use the airbags system, so that forced us to have the landing petals and landing system pretty much the same as what was designed on the pathfinder.
James from Sacramento
What is the expected battery life of the two rovers? What percentage of on-board power is derived from solar collectors? How far will the rovers roam from accompanying base units (i.e., Carl Sagan Station)?
The battery life is not really a design constraint for us, it can survive several hundred cycles, discharge and charge, so that is not a constraint for the power sub-system or the length of the mission.

All the power is collected through the solar panels, what we use the batteries for is to store that energy overnight. So during the daytime we get the energy from the sun and store that so at night we can power the heaters and other things that require during that time frame. But that points out one thing of interest that were landing in this mission towards the end of the Martian summer, and therefore we are moving away from the sun and therefore the energy from the sun is diminishing as the mission moves along and therefore there is less energy towards the end of the mission and less power to run the systems on the spacecraft.

The rovers can move from the lander approximately 500-600 meters. So what we will do is depending on the science, traverse that distance or a portion of that distance.
Brian from Melbourne, Florida
What is the data transmission rate of the high gain antenna, and its transmitting power?
Okay, the direct to Earth transmission over the X-band transmitter is 15-watts at a data rate of 11 and half thousand bits per second.
Antti from Espoo, Finland
How are you prepared for possible communications problems with the rovers?
We have a couple of paths. We have in addition to the high-band antenna path over the X-band direct to Earth, we have a low gain antenna that allows us emergency communications and allows us to receive with more margin a signal from the Earth from both a command and telemetry sense. We also have a UHF transmitter and two orbiting assets, the Mars Global Surveyor and the Mars Odyssey. We can use that tele-communication path to both command and to provide telemetry. In fact most of the science is through the UHF link.
Arnold from Los Angeles
Can the two rovers talk to each other and can one help the other if there is a problem?
It turns out that the two missions are about a half a planet apart and therefore they do not have the capability to directly communicate with each other and the orbiting assets are not set-up to allow communication between the two rovers.
Joy from Los Angeles
Approximately how long will this expedition take, and is the mission to further explore whether humans can live on Mars or simply wanting to know more about Martian geology?
The mission's minimum length of time is 90 sols or 90 Martian days. The length of the mission is really driven by the ability of the power system to provide enough power for the instruments and the engineering systems to do the job that they are designed to do. That's somewhat driven by what I indicated previously with the sun moving away from Mars, the amount of solar energy available through the solar panels and therefore to the batteries diminishes. Also, with the wind on Mars dust can be picked up and deposited on the solar panels and change the efficiency and would minimum reduce the amount of energy. So we are expecting that the mission length time will be somewhere between the 90 sols and 120 days. The MER mission is a follow on “follow the water” aspect of the Mars Exploration Program. So we are geological rover and looking for the presence of water in the Martian path by looking at the elemental composition of the rocks that we encounter on the surface.
Peter from Basel
What is the speed of the rover on Mars?
Brian from Melbourne
What is the surface range on the MER-1 Surface Crawler and its average speed?
The rovers can traverse during the day if you were in parking lot -- a flat surface with no rocks about 100 meters but with the Martian surfaces we seen it before from Viking and Mars Pathfinder have a number of obstacles that will inhibit the progress of the rovers. So, with the use of the hazard cameras that are on board the rovers we can program the rovers to move around those obstacles or if required stop and have the ground intervene and that will reduce the travel from the 100 meters to about 20 to 40 meters within a given Martian day.
GeoBurn from Litchfield Park
Will images that the MERs take be available on a daily basis and how many images should we expect to see and study?
Just like with Mars Pathfinder the pictures from the surface of Mars will be put on the Internet. We expect approximately 50 images to be put on the Internet a day.
Richard, we received a number of questions from another question board about the CD-rom that is being carried to Mars. Unfortunately, we didn't get to respond to these questions during last Saturday's webcast -- could you tell us what that is all about.
Both rovers have identical DVDs and are located on the Lander's petals so they will not be with rovers when they traverse.