Mars Orbiters Prepare to Watch Phoenix Landing

Three robotic paparazzi orbiting the planet Mars are adjusting their flight paths to track an incoming NASA probe due to land on the red planet in late May.

The plan marks the first time that three orbiters will follow a landing on Mars and is expected to return an unprecedented level of coverage throughout the entry, descent, and landing of NASA?s Phoenix Mars Lander on May 25.

"We will have diagnostic information from the top of the atmosphere to the ground that will give us insight into the landing sequence," said David Spencer, deputy project manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.? Such information would help deal with landing problems, and lead to improved designs for future landers.

Launched on Aug. 4, 2007, Phoenix is aiming for a site farther north than any previous mission to Mars. There, the lander will use its robotic arm to sample the surface for soil and ice, as well as scan for conditions that could support microbial life.

The three orbiters - NASA?s Mars Odyssey, Mars Reconnaissance Orbiter (MRO) and Europe?s Mars Express - are maneuvering to be in the right place at the right time when Phoenix enters the Martian atmosphere at more than 12,750 miles per hour (20,519 kph).

"We have been precisely managing the trajectory to position Odyssey overhead when Phoenix arrives, to ensure we are ready for communications," said Bob Mase, the mission?s manager at JPL. "Without those adjustments, we would be almost exactly on the opposite side of the planet when Phoenix arrives."

NASA?s MRO spacecraft will make bigger adjustments, with one firing of thrusters on Feb. 6 and at least one more course correction planned in April. The European Space Agency's Mars Express orbiter, meanwhile, has also positioned itself to record transmissions from Phoenix during the landing.

Even NASA rovers Spirit and Opportunity, currently exploring the martian surface, have helped out by simulating transmissions from Phoenix to rehearse the orbiters? operations for the big day.

On that day, Odyssey will turn its robotic eyes from the heavens to point an ultrahigh- frequency antenna towards the descending Phoenix. A high-gain antenna will stream information back to Earth as Odyssey watches Phoenix slow itself through heat-shield friction, a parachute, and then firing descent rockets. That allows the lander to hit the Martian surface on three legs at just 5.4 miles per hour (2.4 m/s).

MRO and Mars Express will start recording Phoenix transmissions as backup data "about 10 minutes before landing," according to Ben Jai, mission manager at JPL for MRO.

Until then, all three orbiters are scoping out Mars for a suitable landing site.

• VIDEO: NASA's Phoenix: Rising to the Red Planet
• VIDEO: Looking for Life in All the Right Places
• Top 10 Amazing Discoveries by NASA's Mars Rovers