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WORKING CRUISE

When Spirit and Opportunity left Earth, they entered the "cruise" phase of the mission. For seven months, these spacecraft will sail through the interplanetary void on a trajectory for Mars. You may think this is a time when engineers and scientists can kick back, relax, take vacations, catch up on some reading. Not so. The Mars Exploration Rover mission is still in high gear and its focus is not only on the health and navigation of the spacecraft. Here on Earth, the cruise phase of the mission is an intense time of training for the people who will operate the rovers on Mars.

Like athletes who must prepare for the main event, the MER team has a training schedule. Scientists and engineers will immerse themselves in several tests that simulate the situations they will face during landed operations. These are not tests that take hours. These are tests that last for days, sometimes weeks. The rovers are complex machines. It takes practice, practice and more practice to learn how to command them. Software has to be learned and example scenarios played out. Scientists have to learn how to make decisions collaboratively since there is a limited amount of time to complete individual experiments on Mars.

The first big test for the science team was the Science Process test. The entire team walked through the procedures they will use to do science on Mars. This included a simulation of the uplink and/or downlink process. Uplink is when instructions are sent to the rovers from Earth. Downlink is when data are received from the rovers. A rehearsal of the science process gives the team a chance to correct potential problems and smooth out rough spots before they face the real thing on the Red Planet.

Following the Science Process test is a seven-month schedule packed with SORTs — Surface Operations Readiness Tests. Scientists and engineers use a bank of computers at the Jet Propulsion Lab to send commands to a full-scale rover located in a large chamber with a simulated martian surface. They do not see the test rover. The commands are sent blindly, just as they will be when the rovers are on Mars. Computer software offers a simulated 3-D view of the rovers and their martian landing sites. Only after the test is complete is the MER team allowed to view the actual rover model and how it responded to their instructions.

Groups of instructions that tell the rovers where to go and which tasks to complete are called "sequences." Throughout the seven months of cruise, scientists and engineers are designing and building sequences that will be tested in a SORT. There are nominal sequences that cover routine tasks, and there are contingency sequences that act as back-up should the rovers be unable to complete their original duties.

Each SORT focuses on a different aspect of landed operations. An "impact to egress" SORT covers the critical time from touch down through egress — when the rovers leave their landers. There is a lot to do. After the long journey to Mars and the impact of landing, the health of the rovers and their science payload must be checked. The first MER-view images of Mars are acquired and sent back to Earth. Pancam and Mini-TES take their first panoramas. These are 360-degree surveys of the terrain. From these images, scientists select interesting targets for further study and a drive direction for the rovers. Egress from the lander is a risky maneuver that must be carried out very carefully. Then, after the rovers are on solid martian ground (or, in this case, simulated martian ground in the test chamber), images are taken to assess the safety of the drive off the landers.

Other SORTs include "surface approach," which helps the team understand how to approach a target rock and position the rover arm when it deploys, and "anomalies" SORTs that serve up a week's worth of difficult situations.

Another Earth-based activity during the cruise phase of the mission is similar to a SORT, but is not a blind test. A full-scale model of the rover is transported to a Mars-like location here on Earth and is sent a string of commands. MER scientists and engineers watch the rover as it responds to the commands. The more that is learned about the way the rover and its science instruments move, the easier it will be to understand how to build sequences for the rovers.

As Spirit and Opportunity speed toward Mars, more than three hundred scientists and engineers here on Earth will learn how to act in unison to master the art of commanding two very complex robots to do science on another world.

Web content editor/writer: Pamela R. Smith

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