NASA's Spirit rover spacecraft fired its thrusters for 3.4 seconds on
Friday, Dec. 26, to make a slight and possibly final correction in its
flight path about one week before landing on Mars.
Radio tracking of the spacecraft during the 24 hours after the
maneuver showed it to be right on course for its landing inside Mars'
Gusev Crater at 04:35 Jan. 4, 2004, Universal Time (8:35 p.m. Jan. 3,
Pacific Standard Time.) Spirit's twin, Opportunity, will reach Mars
three weeks later.
"The maneuver went flawlessly," said Dr. Mark Adler, Spirit mission
manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
This was Spirit's fourth trajectory correction maneuver since launch
on June 10. Two more are on the schedule for the flight's final three
days, if needed. Adler said, "It seems unlikely we'll have to do a
fifth trajectory correction maneuver, but we'll make the final call
Thursday morning after we have a few more days of tracking data.
Right now, it looks as though we hit the bull's-eye."
The adjustment was a quick nudge approximately perpendicular to the
spacecraft's spin axis, said JPL's Chris Potts, deputy navigation team
chief for the NASA Mars Exploration Rover project. "It moved the
arrival time later by 2 seconds and moved the landing point on the
surface northeast by about 54 kilometers" (33 miles), Potts said. The
engine firing changed the velocity of the spacecraft by only 25
millimeters per second (about one-twentieth of one mile per hour).
For both NASA rovers approaching Mars, the most daunting challenges
will be descending through Mars' atmosphere, landing on the surface,
and opening up properly from the enclosed and folded configuration in
which the rovers arrive. Most previous Mars landing attempts, by
various nations, have failed.
Each rover, if it arrives successfully, will then spend more than a
week in a careful sequence of steps before rolling off its lander
platform. The rovers' mission is to examine their landing areas for
geological evidence about past environmental conditions. In
particular, they will seek evidence about the local history of liquid
water, which is key information for assessing whether the sites ever
could have been hospitable to life. Opportunity will land halfway
around Mars from Spirit.
As of 13:00 Universal Time (6 a.m. PST) on New Year's Day, Spirit will
have traveled 481.9 million kilometers (299.4 million miles) since
launch and have will have 5.1 million kilometers (3.2 million miles)
left to go. Opportunity will have traveled 411 million kilometers
(255 million miles) since its July 7 launch and will have 45 million
kilometers (27.9 million miles) to go, with three remaining scheduled
opportunities for trajectory correction maneuvers.
JPL, a division of the California Institute of Technology, manages the
Mars Exploration Rover project for NASA's Office of Space Science,
Washington. Additional information about the project is available from
JPL at
http://marsrovers.jpl.nasa.gov/home/index.html
and from Cornell University, Ithaca, N.Y., at
http://athena.cornell.edu/ .
