From: NASA MESSENGER
Posted: Wednesday, January 21, 2015
24 October 2014: MESSENGER mission controllers at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., conducted the third of four maneuvers today to raise the spacecraft's minimum altitude sufficiently to extend orbital operations and delay the probe's inevitable impact onto Mercury's surface until early next spring.
The first of the four maneuvers, completed on June 17, raised MESSENGER's altitude at closest approach from 115 kilometers (71.4 miles) to 156.4 kilometers (97.2 miles) above the planet's surface. The second of the four maneuvers, completed on September 12, raised MESSENGER's altitude at closest approach from 25.2 kilometers (15.7 miles) to 93.7 kilometers (58.2 miles) above the planet's surface. Because of progressive changes to the orbit over time, the spacecraft's minimum altitude has continued to decrease since September.
At the time of this most recent maneuver, MESSENGER was in an orbit with an altitude at closest approach of 26 kilometers (16.1 miles) above the surface of Mercury. With a velocity change of 19.37 meters per second (43.33 miles per hour), the spacecraft's four largest monopropellant thrusters (with a small contribution from four of the 12 smallest monopropellant thrusters) nudged the spacecraft to an orbit with a closest approach altitude of 185.2 kilometers (115.1 miles). This maneuver also increased the spacecraft's speed relative to Mercury at the maximum distance from Mercury, adding about 7.4 minutes to the spacecraft's eight-hour, five-minute orbit period.
This view shows MESSENGER's orientation shortly after the start of the maneuver.
MESSENGER was 116.9 million kilometers (72.64 million miles) from Earth when the 2 minute, 29 second maneuver began at 2:58 p.m. EDT. Mission controllers at APL verified the start of the maneuver 6.5 minutes later, after the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network tracking station outside of Goldstone, California.
One more maneuver, on January 21, 2015, will again raise the spacecraft's minimum altitude, allowing the MESSENGER science team to continue to collect images and other data from the spacecraft's instruments.
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