January 03, 2004
Navigators for NASA's Spirit Mars Exploration Rover put the spacecraft so close to a bull's-eye with earlier maneuvers that mission managers chose to skip the final two optional maneuvers for adjusting course before arrival at Mars.
With less than four hours of flight time remaining, Spirit was on course to land within a targeted ellipse 62 kilometers long by 3 kilometers wide (39 miles by 2 miles) within Mars' Gusev Crater. A trajectory correction maneuver scheduled for four hours before landing was cancelled.
"The navigation status is truly excellent," said Dr. Lou D'Amario, the mission's navigation team chief at NASA's Jet Propulsion Laboratory, Pasadena, Calif. A slight trajectory adjustment on Dec. 26 was the fourth and final for the flight.
Preparations in the past two days for arrival at Mars have included an adjustment that will open Spirit's parachute about two seconds earlier than it would have been without the change, in order to compensate for recent weather on Mars. "A dust storm seen on the other side of the planet has caused global heating and thinning of the atmosphere at high altitudes" said JPL's Dr. Mark Adler, Spirit mission manager.
Also, engineers sent commands today to alter the timing when several pyro devices (explosive bolts) will be put into an enabled condition prior to firing. Enabling will begin 40 minutes earlier than it would have under previous commands. These pyro devices will be fired to carry out necessary steps of descent and landing, such as deploying the parachute and jettisoning the heat shield.
Mars is 170 million kilometers (106 million miles) away from Earth today, a distance that takes nearly 10 minutes for radio signals to cross at the speed of light. Counting that communication delay, Spirit will hit the top of Mars' atmosphere at about 04:29 Jan. 4, Universal Time (8:29 p.m. Jan. 3, Pacific Standard Time), and reach the surface six minutes later.
JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA's Office of Space Science, Washington, D.C. Additional information about the project is available at http://marsrovers.jpl.nasa.gov , http://www.nasa.gov and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu .
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