NASA Spacecraft Fine-Tunes Course for Mars Landing

PASADENA, Calif., April 10 /PRNewswire-USNewswire/ -- NASA engineers have
adjusted the flight path of the Phoenix Mars Lander, setting the spacecraft on
course for its May 25th landing on the Red Planet.

"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 NASA's Jet Propulsion Laboratory in Pasadena, Calif. The
mission's two prior trajectory maneuvers, made last August and October,
adjusted the flight path of Phoenix to intersect with Mars.

NASA has conditionally approved a landing site in a broad, flat valley
informally called "Green Valley." A final decision will be made after NASA's
Mars Reconnaissance Orbiter takes additional images of the area this month.

The orbiter's High Resolution Imaging Science Experiment 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 8 miles 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 12 miles. 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. 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 set
itself down safely onto the Martian surface.

"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.

Phoenix 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.

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

"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.

Today's 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 13,000 mph. The
spacecraft will release a parachute and then use pulse thrusters at
approximately 3,000 feet from the surface to slow to about 5 mph and land on
three legs.

"Landing on Mars is extremely challenging. In fact, not since the 1970's have
we had a successful powered landing on this unforgiving planet. There's no
guarantee of success, but we are doing everything we can to mitigate the
risks," said Doug McCuistion, director of NASA's Mars Exploration Program at
NASA Headquarters in Washington.

For more information about Phoenix, visit:

http://www.nasa.gov/phoenix

SOURCE NASA

Dwayne Brown of NASA Headquarters, Washington, +1-202-358-1726,
dwayne.c.brown@nasa.gov, or Guy Webster of NASA's Jet Propulsion Laboratory,
+1-818-354-6278, guy.webster@jpl.nasa.gov; or Sara Hammond of University of
Arizona, Tucson, +1-520-626-1974, shammond@lpl.arizona.edu