Steven Stolper
Flight Software Engineer
Jet Propulsion Laboratory, Pasadena, California

What I Do

Robotic spacecraft, like Mars Pathfinder, are controlled by computers. The computer onboard Mars Pathfinder controls thrusters, a sun sensor, a star scanner, a radar altimeter, explosive charges, a parachute and much, much more. Almost every activity performed by the spacecraft is controlled by a central computer. The computer that controls our spacecraft is just like the personal computers found in schools and in people's homes.

Like all computers, the computer controlling Mars Pathfinder follows a set of instructions called a program. It is my job, along with several others, to write the program that allows the computer to control the spacecraft. This is very challenging because the computer must fly the spacecraft during the seven-month cruise to Mars as well as control the atmospheric entry, descent and landing on the surface of the planet.

I have worked at the Jet Propulsion Laboratory (JPL) for seven years and have written flight control software for several planetary spacecraft. The last spacecraft that I worked on was the Galileo Orbiter, which placed a probe into the atmosphere of Jupiter in December 1995.

The programs that control spacecraft, or anything else that operates in the "real world," are called real-time systems. The programs that control the anti-lock brakes for a car, a microwave oven, or a jet airplane are examples of real-time systems. These systems are especially exciting to me because they have to operate in the "real world" where the amount of time it takes the program to perform a task is very important. It is also critical that these systems operate correctly, even when something goes wrong.

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