WASHINGTON – NASA mission managers said they have tweaked the flight path of the Mars Science Laboratory spacecraft during a three-hour series of thruster-engine firings about 81 million miles from Earth.
The “trajectory correction maneuver” was designed to ensure that the spacecraft encounters Mars at precisely the right time and place in August. The result of the maneuver was to place the spacecraft’s trajectory 25,000 miles (about 40,000 kilometers) closer to its encounter with Mars scheduled for Aug. 5, 2012, mission managers at the Jet Propulsion Laboratory (JPL) said. The firing of the spacecraft's eight thrusters also advanced the time of its encounter by 14 hours.
The Mars Science Laboratory mission will attempt to land an SUV-size rover dubbed Curiosity using a new, risky sky crane technique. The landing site is Gale Crater, an area of the Martian highlands thought to contain evidence of water flows and organic compounds. "The timing of the encounter is important for arriving at Mars just when the planet's rotation puts Gale Crater in the right place," said JPL's Tomas Martin-Mur, chief navigator for the mission.
The target: Gale Crater Source: NASA
Despite a nearly flawless launch to orbit and engine firing to Mars last November, mission planners knew in advance that slight changes in probe’s trajectory would be required during its 352 million mile (567 million kilometer) flight to Mars. One reason is that the spacecraft’s initial trajectory was intentionally offset to prevent the upper stage of the launch vehicle from hitting Mars. JPL said the upper stage could not be cleaned the way the spacecraft was to protect Mars from Earth’s microbes.
During its nine-month voyage to Mars, the spacecraft rotates at about two revolutions a minute to control thermal conditions. The maneuver earlier this month included a 19-minute thruster firing to change velocity in the direction of the axis of spacecraft rotation. Then, a series of 5-second bursts repeated more than 200 times over a period of about two hours change the probe’s velocity in a direction perpendicular to the axis of rotation.
The result of the maneuver was a net change in velocity of about 12.3 miles per hour (5.5 meter per second) or what mission planners described as “combining a slight increase in speed with a small change in direction of travel.”
“We're not aiming for Mars,” a JPL official explained, “we're aiming for Mars to a point where Mars will be in its orbit on August 5 so that Mars will be there when we get there.”
The launch of the Mars Science Laboratory was timed to coincide with the
closest distance between Mars and Earth.
Mission planners said they expect to conduct several more trajectory corrections as the spacecraft approaches Mars. The spacecraft is “doing everything we need it to do,” the JPL official added. “It's measuring the temperature, it’s controlling the thermal conditions of the vehicle. The computer is working fine, everything is working just as we expect. Its whole job is basically to get us to Mars so we can land this rover.”