[meteorite-list] Phoenix Fine Tunes Course for Mars Landing

[Ron Baalke]

April 10, 2008

Dwayne Brown 
Headquarters, Washington
202-358-1726
dwayne.c.brown at nasa.gov

Guy Webster 
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster at jpl.nasa.gov

Sara Hammond
University of Arizona, Tucson
520-626-1974
shammond at lpl.arizona.edu

RELEASE: 08-100

NASA SPACECRAFT FINE TUNES COURSE FOR MARS LANDING

PASADENA, Calif. -- 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

	
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