MESSENGER Tweaks Its Route to Mercury
15 Sep 2006
(Source: Johns Hopkins University Applied Physics Laboratory)
The MESSENGER trajectory correction maneuver 11 (TCM 11) on September 12 lasted just under four minutes and adjusted the spacecraft's velocity by about 1.68 meters per second (5.5 feet per second). The short-duration maneuver kept MESSENGER on track for next month's Venus flyby. Tuesday's maneuver started at 7 p.m. EDT; mission controllers at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., verified the start of the maneuver about 12 minutes later, when the first signals indicating thruster activity reached NASA's Deep Space Network tracking station outside Canberra, Australia.
While MESSENGER has used all 17 of its thrusters in completing several successful maneuvers, TCM 11 was the first course correction to require two sets of primary thrusters. Part A of the maneuver began at 7 p.m. EDT and lasted 23 seconds; Part B began at 7:10 p.m. and lasted 202 seconds. Operators moved MESSENGER in two perpendicular movements during the maneuver - instead of on a straight path - to protect the spacecraft's heat-sensitive electronics from direct sunlight. The movements kept the sunshade in position to block the blinding sunlight, which warms the spacecraft nearly three times faster now than if MESSENGER were orbiting Earth.
The next TCM - the last chance for mission controllers to tweak the spacecraft's route prior to the Venus flyby - will take place no later than October 12. For graphics of MESSENGER's orientation during the maneuver, visit the "Trajectory Correction Maneuvers" section of the mission Web site at http://messenger.jhuapl.edu/the_mission/mission_design.html.