Phoenix Spacecraft Maneuvers for Mars Landing

by Nancy Atkinson on April 11, 2008

Looking towards a May 25 landing for the Phoenix Mars Lander, the navigation team for mission adjusted the flight path for the spacecraft on April 10. “This is our first trajectory maneuver targeting a specific location in the northern polar region of Mars,” said Brian Portock, chief of the Phoenix navigation team at the Jet Propulsion Laboratory. The mission’s two prior trajectory maneuvers, made last August and October, put the spacecraft on target to just intersect with Mars. But this recent maneuver put it on course to land at a site called “Green Valley,” a broad, flat valley in Mars north polar region. NASA announced they have “conditionally” approved this site, but a final decision has yet to be made. And why, you ask, hasn’t a final decision been made on a landing site at this late date?

Phoenix mission managers are still looking for a safe, yet exciting place to land. The proposed landing area is an ellipse about 62 miles by about 12 miles (100 kilometers by 20 kilometers). In looking at high resolution images of this area, researchers have mapped more than five million rocks in and around that ellipse, each big enough to end the mission if hit by the spacecraft during landing. “The environmental risks at landing — rocks and slopes — represent the most significant threat to a successful mission. There’s always a chance that we’ll roll snake eyes, but we have identified an area that is very flat and relatively free of large boulders,” said JPL’s David Spencer, Phoenix deputy project manager and co-chair of the landing site working group.

MRO’s High Resolution Imaging Science Experiment (HiRISE) camera has taken more than three dozen images of the area. Analysis of those images prompted the Phoenix team to shift the center of the landing target 13 kilometers (8 miles) southeastward, away from slightly rockier patches to the northwest. Navigators used that new center for planning the recent trajectory correction maneuver.

“Our landing area has the largest concentration of ice on Mars outside of the polar caps. If you want to search for a habitable zone in the arctic permafrost, then this is the place to go,” said Peter Smith, principal investigator for the mission, at the University of Arizona , Tucson .

When Phoenix lands, it will dig to an ice-rich layer expected to lie within arm’s reach of the surface. It will analyze the water and soil for evidence about climate cycles and investigate whether the environment there has been favorable for microbial life.

The April 10 trajectory adjustment began by pivoting Phoenix 145 degrees to orient and then fire spacecraft thrusters for about 35 seconds, then pivoting Phoenix back to point its main antenna toward Earth. The mission has three more planned opportunities for maneuvers before May 25 to further refine the trajectory for a safe landing at the desired location.

In the final seven minutes of its flight on May 25, Phoenix must perform a challenging series of actions to safely decelerate from nearly 21,000 kilometers per hour (13,000 mph). The spacecraft will release a parachute and then use pulse thrusters at approximately 914 meters (3,000 feet) from the surface to slow to about 8 kilometers per hour (5 mph) and land on three legs.

For more information about Phoenix , visit NASA’s site, and ASU’s site


Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

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