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The Phoenix Lander is heading for northern arctic Mars.

By Lori Stiles, University Communications
April 10, 2008

Engineers adjusted the flight path of NASA's Phoenix Mars Lander today, putting the spacecraft on course for its May 25 landing on the Red Planet.

This is the first trajectory maneuver targeting a specific location in the northern polar region of Mars, Phoenix navigation team leader Brian Portock at NASA's Jet Propulsion Laboratory said. Two previous trajectory maneuvers, last August and October, adjusted the flight path to intersect with Mars.

The University of Arizona leads the Phoenix Mission on behalf of NASA, with project management by NASA's Jet Propulsion Laboratory, located in Pasadena, Calif. The spacecraft, which was developed by Lockheed Martin Space Systems, was launched Aug. 4.

The Phoenix spacecraft is to land on Mars on a Sunday afternoon Arizona time, May 25. After landing, an international team of scientists led by the UA's Peter Smith will run the robotic mission from the Lunar and Planetary Laboratory's Phoenix Science Operations Center in Tucson. The mission will be the first to dig into arctic Martian terrain in a search for clues on the history of water on Mars and for environment habitable for life.

Flying the Phoenix spacecraft 420 million miles, then landing it within a 62-mile-long, 12-mile-wide target is like shooting an arrow from Los Angeles' Dodger Stadium and hitting home plate at Wrigley Field in Chicago, Jet Propulsion Lab navigators say.

Trajectory correction maneuvers keep the spacecraft on course as it cruises through space at more than 44,500 mph.

The High Resolution Imaging Science Experiment, or HiRISE, camera on NASA's Mars Reconnaissance Orbiter has taken about 200 images of potential Phoenix spacecraft landing sites, HiRISE principal investigator Alfred McEwen of UA's Lunar and Planetary Laboratory said.

NASA conditionally approved a landing site in a broad, flat valley informally called "Green Valley" last August based on HiRISE imaging.

After analyzing more than three dozen images of this area, the Phoenix team shifted the center of the landing target eight miles (13 kilometers) southeastward, away from slightly rockier patches to the northwest. Navigators used that new center for planning today's maneuver.

The landing area is an ellipse about 62 miles by about 12 miles (100 kilometers by 20 kilometers). Researchers have mapped more than five million individual rocks in and around the landing region, each big enough to end the mission if hit by the spacecraft during landing. Knowing where to avoid the rockier areas, the team has selected a scientifically exciting target that also offers the best chances for the spacecraft to land safely.

"Our landing area has the largest concentration of ice on Mars outside of the polar caps," Smith said. "If you want to search for a habitable zone in the arctic permafrost, then this is the place to go."

"We have never before had so much information about a Mars site prior to landing," Ray Arvidson of Washington University in St. Louis said. Arvidson, who has worked on Mars landings since the first successful Viking landers in 1976, chairs the landing-site working group for Phoenix.

NASA will make a final landing site decision after studying more images the HiRISE camera will take this month.

Today's trajectory adjustment began by pivoting the spacecraft 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 13,000 miles per hour, or 21,000 kilometers per hour. The spacecraft will release a parachute and then pulse thrusters at approximately 3,000 feet, or 914 meters, from the surface to slow to about 5 mph, or 8 kilometers per hour, and land on three legs.

International contributors to the Phoenix mission are the Canadian Space Agency; the University of Neuchatel, Switzerland; the universities of Copenhagen and Aarhus, Denmark; the Max Planck Institute, Germany; and the Finnish Meteorological Institute.