BOULDER, Colorado - Ground controllers are ready to perform a major maneuver today of NASA's Mars Reconnaissance Orbiter (MRO)--an "end game" tactic that puts the orbiting probe a step closer to scientific sensor sweeping of the red planet.

For months, the MRO has been aerobraking--using the friction of the planet's thin atmosphere to slow the craft. That technique saves on onboard propellant.

Spacecraft engineers and navigation experts are planning a burn today of MRO's Trajectory Correction Maneuver (TCM) thrusters, said Wayne Sidney, MRO Flight Engineering Team Lead for Lockheed Martin Space Systems, the firm that designed and built the spacecraft in neighboring Denver, Colorado.

"For regular burns up to this point...over the last six months...they last on the order of seconds. This one is going to last six minutes. It's a hefty burn," Sidney told "It's the biggest burn just with these TCM thrusters."

There's still more nudging to do with MRO over the next few months, fine-tuning tweaks that push the probe into a final, desired orbit. The mission's main science observations are scheduled to begin in November, after a period of intermittent communications while Mars passes nearly behind the Sun.

Rock-solid, well behaved

Overall, MRO is in excellent health, Sidney explained. However, one nagging item cropped up a few weeks ago. A radio frequency switch to flip between MRO's high and low-gain antennas is stuck. A tiger team of experts is investigating the issue, trying to ascertain the root, probable cause of the problem.

"If we don't get the switch unstuck we've lost some redundancy...but we still have the capability to communicate over the low and high-gain antennas using the other transmitter," Sidney explained. At this point in MRO's aerobraking campaign, "everything else has been really rock-solid, right on...and gone really well. It has been a remarkable spacecraft. Very well behaved," he added.

Dipping in and out of the martian atmosphere, MRO has seen very few surprises. A worry for aerobraking specialists is encountering dust storm activity that can mix things up in the atmosphere, playing havoc with the delicate, spacecraft-slowing maneuvers.

"The atmosphere has been very cold and clear the whole six months as we hoped it would be," Sidney said.

Science objectives

"We just made the decision to exit aerobraking today...on orbit 445," noted James Graf, MRO Project Manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "This burn gets us out of the atmosphere. We have two more maneuvers over the next two weeks before we are in the final orbit," he told

Launched in August 2005, MRO swung into an elongated orbit around Mars in March of this year.

The $750 million MRO mission is designed to contribute to several science objectives: Determine whether life ever arose on Mars; characterize the climate and geology of Mars; as well as prepare of eventual human exploration of the red planet.