Computer screenshot of aerobraking-related data

It's 7:30 a.m., and Brian Kennedy's about to clock out, having successfully driven his spacecraft around Mars four times in the last eight hours.

"I just delivered four orbits," he says matter-of-factly. "That's a record for me."

Kennedy is one of 11 navigators at JPL who are responsible for the 'round-the-clock guidance of NASA's Mars Odyssey spacecraft through the mission's aerobraking phase - repeatedly flying Odyssey through the top of the martian atmosphere, using friction to lower and circularize the spacecraft's orbit.

As Odyssey gets closer to achieving the orbital geometry required for the mission, the end of the delicate, three-month-long aerobraking phase is nearing an end. And Kennedy and his colleagues are looking forward to getting off the graveyard shift: "I'm not going to miss it," he says, having polished off a thermos of coffee and a one-liter bottle of soda to help stay awake, now looking forward to a four-hour nap before eating dinner at noon.

Legacy of Aerobraking Expertise

With the successful completion of the aerobraking effort, the Odyssey navigation team is leaving a legacy of well-honed interdisciplinary tools and techniques certain to be used on future missions using aerobraking.

Aerobraking represents a huge cost savings to space exploration. Instead of using a large amount of propellant to deliver a spacecraft into its final orbit around Mars, aerobraking uses well-controlled "drag passes" through the upper atmosphere to slowly shrink and adjust the altitude of the spacecraft. By not having to carry hundreds of extra kilograms of propellant, the spacecraft is lighter. And a less massive spacecraft can use a smaller, less expensive launch rocket.

How Low Can You Go?

Simulated aerobraking passes

The hardest part is determining where to send the spacecraft on each pass. Too low an altitude, and the denser atmosphere could cause parts of the spacecraft to overheat. Too high, and there may not be enough atmosphere there to provide the desired resistance for effective aerobraking. Adding drama to the process, the martian atmosphere is constantly changing in altitude and density. The design of each aerobraking pass is based upon daily weather assessments provided by Odyssey's scientific atmospheric advisory group, which watches Mars weather through Odyssey and another NASA spacecraft - Mars Global Surveyor.

Kennedy and his colleagues recall the early days of aerobraking shortly after Odyssey first entered orbit around Mars Oct. 23, 2001. "It was very calm. There would be several hours between drag passes, and we would accumulate several hours of data and deliver it to the operations team at Lockheed Martin in Denver," he recalls. But as the orbit tightened around Mars and the spacecraft has rounded the planet more frequently, the pace has quickened. As time progresses, there has been less time to assemble the results of each drag pass before the next one starts. "It's been getting more interesting," says Kennedy.