Mars Science Lab fine-tunes path for rover landing
BY JUSTIN RAY
Posted: July 29, 2012
Firing its thrusters for a mere six seconds early Sunday, NASA's Mars-bound Curiosity rover added more precision to its flight path for a high-stakes entry, descent and landing next Monday morning.
Curiosity is headed a landing zone inside Gale Crater near the base of Mount Sharp where the rover will explore for two years (a full Martian year) to determine if the site was once habitable for life.
Touchdown is scheduled for 1:31 a.m. EDT (0531 GMT) next Monday, Earth-receive time.
Sunday's maneuver featured two brief firings at about 1 a.m. EDT to tweak the craft's planned atmospheric entry point by about 13 miles. Navigation tracking had indicated that without the burn MSL would have hit the top of the Martian atmosphere about 13 miles east of the target spot.
"The first look at telemetry and tracking data afterwards indicates the maneuver succeeded as planned," said Tomas Martin-Mur of NASA's Jet Propulsion Laboratory, chief of the mission's navigation team.
The accuracy is remarkable considering Curiosity will have traveled about 352 million miles on its 8-month interplanetary trek from Earth to Mars.
The thruster firings changed the 8,463-pound spacecraft's velocity by about one-fortieth of one mile per hour (one centimeter per second).
"I will not be surprised if this was our last trajectory correction maneuver," Martin Mur said of Sunday's burns. "We will be monitoring the trajectory using the antennas of the Deep Space Network to be sure Curiosity is staying on the right path for a successful entry, descent and landing."
Curiosity, packed within its protective descent pod, will enter Mars' atmosphere at a speed of about 13,200 mph (5,900 meters per second) and touch down on the red planet's surface at just 1.7 mph only seven minutes later. The heat shield, parachute and novel rocket-powered "sky crane" will work in sequence to slow the car-sized rover enough to set its wheels directly onto the ground at landing.
The mission's first two flight path corrections occurred on Jan. 11 and March 26 to put the spacecraft on a course to intercept Mars. They erased the deliberate, launch-induced miss of the planet by 25,000 miles so that the spent Centaur rocket body following Curiosity won't hit Mars.
The initial operation used 59 minutes of thruster firings, changing the craft's speed by 12.3 mph. The follow-up maneuver lasted 9 minutes and altered the velocity by 2 mph.
Another burn June 26 lasted 40 seconds to tweak the spacecraft's entry point by 125 miles and advanced that descent timing by 70 seconds, putting the vehicle on a course to hit the planet at the right place, angle and time.
In recent days, the flight batteries were topped to 100 percent via the cruise stage's solar arrays and engineers performed a final check of the descent sensor for tracking velocity and altitude during landing.
At the time of touchdown, Mars will be 154 million miles from Earth and the one-way communications time will be 13.8 minutes.
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