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?

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.

Ahead of Schedule Despite Some Challenges

Odyssey’s lead navigator, Bob Mase, says the aerobraking effort has
"generally gone better than expected.

"The atmosphere did not behave exactly as we predicted, but we were able to
compensate for the weather patterns that we experienced. We are actually
finishing ahead of schedule, which is better than we anticipated."

Challenges along the way included occasional telecommunications outages
between Odyssey and NASA’ Deep Space Network, when bad weather or other
glitches cut off the two-way radio link with the spacecraft. And despite
daily reports, Mars’ weather created some hurdles, too, says Mase.

"We were surprised by the polar vortex that we observed in the atmosphere
near the north pole. The atmosphere was very turbulent in that region, but
very quiet near the pole. So although we had to slow down to get through the
edge of the vortex, we were able to make up time while we were in the quiet
polar region."

But no matter what problems were thrown at the team, he says, "we were
always able to work around them."

Odyssey navigator Darren Baird had volunteered for the graveyard shift
because of the lonely but challenging learning opportunity it offered. He’ll
miss the frequent 5 a.m. visits by Odyssey project manager Matt Landano,
who’d pop in for early morning updates on the mission’s progress. Little
perks also made the graveyard shift more easily manageable. "As stupid as
this may sound, you’re guaranteed a great parking spot" at the sprawling JPL
campus, Baird noted. Nonetheless, he looks forward to a return to the sunlit
working world so he can resume acquaintances with his girlfriend and family
and return to a life of normal sleep cycles.

For navigator Peter Antreasian, "the hardest part is going home exhausted at
9 a.m., wanting to sleep, but getting a wide-awake three-year-old jumping on
your stomach instead." He described the aerobraking phase as stressful, but
well worth the sacrifice. The successful results Odyssey’s aerobraking, he
says, "have led us to a standard for aerobraking that’s going to be pretty
commonplace on missions in the future."