|Mission Timeline: Surface Operations
Surface science operations on Mars involve driving the Mars Exploration Rovers to selected rock and soil targets and examining these features with a suite of science instruments.
After the rover leaves the lander, it has a daily routine of carefully calculated scenarios that are designed to return as much science as possible.
A day (or sol) in the life of a rover
Each rover is a solar-powered machine. Its workday is from sunrise to sunset. A typical rover day begins with a morning wake-up that is triggered by an on-board alarm clock. Commands are received from Earth via the rover´s high-gain antenna. The commands are "uplinked" to the rover and become its master sequence for the day. These are tasks that it will complete during the current martian day (known as a "sol") as well as part of the next. This overlap is necessary so that the rover will know what to do in the hours between wake-up and uplink on each subsequent sol.
In the afternoon, the communication between Earth and the rover is reversed. Data that have been gathered are transferred to scientists and engineers via a "downlink" through the high-gain antenna. This information is used to determine the rover's condition and assess results of science experiments. The roveršs UHF antenna is also used for the return of science and engineering information via two orbiters the Mars Global Surveyor and the Mars Odyssey. Data are analyzed and the next solšs activities are planned. A sequence of commands is created to uplink to the rover the next morning.
Tasks that the rovers will be asked to do
Each sol may be designated to focus on different kind of task. One might involve a taking panoramic data with Pancam and Mini-TES that can be used by scientists to select targets for further study. Another might involve measurements with the science tools the rover carries on its arm (called the Instrument Deployment Device or IDD). Others might be to drive as great a distance as possible, or to approach a rock target that has been identified. The rover is commanded to travel from point A to point B and is intelligent enough to maneuver through a martian landscape littered with boulders and rocks. An approach sol is used to position the rover so that its multi-jointed arm can reach a selected target. Hazard avoidance cameras, or Hazcams located under the solar panel deck capture images of the work area to make sure it is clear. Only then is the arm deployed.
A typical scenario for using the science tools on the arm of the rover might be to deploy the Microscopic Imager to collect close-up views of a selected martian rock. The arm then rotates to bring the Rock Abrasion Tool (RAT) into position to grind into the target´s surface. The Microscopic Imager is repositioned to collect images of these freshly exposed layers. The Alpha-Particle-X-ray-Spectrometer (APXS) then may be used to gather information on the elemental make-up of the rock, or the Mössbauer Spectrometer may be brought into position so that scientists can learn the composition of the iron-bearing minerals in the selected target. The arm is then returned to its stowed position before another drive.
Each rover also carries three sets of magnetic targets that will collect airborne dust for analysis by the science instruments.
Challenges in accomplishing tasks and an eventual end of mission
The design of the Mars Exploration Rover surface operations must take into account several constraints. Each instrument has different energy needs and the position of the sun affects the availability of solar power. Various pieces of equipment have thermal requirements and the entire rover must be kept warm while it sleeps during the cold martian nights. In addition, the position of the Earth and the location of the two Mars orbiters affect telecommunication, and must be continuously known by the rovers.
Throughout the life of the mission, an increase in distance between Mars and the Sun coupled with a build-up of dust on the solar panels will slowly chip away at the rover´s ability to return science. It is estimated that each rover will be able to continue its work on the martian surface for about 90 sols.