MESSENGER probe's altimeter helps keep mission going

The instrument is being employed to keep careful track of the spacecraft's position relative to the surface of Mercury.
By Andrew McDonald | Apr 14, 2015
According to a NASA statement, the MESSENGER probe orbiting Mercury is nearing the end of its mission. However, the probe's Mercury Laser Altimeter, which measures the distance between the probe and the surface, is helping mission managers prolong MESSENGER's study of Mercury.

Earlier in its mission, MESSENGER orbited between 124 and 311 miles from the surface at periapsis, the closest approach. Now, the probe's elliptical orbit brings it to a periapsis altitude of just 3.7 to 24.2 miles from the surface. The mission team has planned a series of orbital maneuvers to adjust the probe's course and keep it functioning as long as is feasible.

The altimeter has been used to map Mercury's surface, its data having been used to determine the locations and topographic relief of craters, mountains, and other surface structures. These data have been used to assemble a digital elevation model, a map of Mercury's surface.

Now the altimeter is being used to monitor MESSENGER's position above the surface. The data are transmitted to Earth every day, and a computer model is then used to determine MESSENGER's position in three dimensions. This allows the mission team to compare the probe's actual course with the predicted orbit and determine whether they need to make any adjustments.

"It's a special case to use this science instrument to help with navigation," said Dan O'Shaughnessy, MESSENGER's Mission Systems Engineer at the Johns Hopkins University Applied Physics Laboratory. "But now that we are getting very close to the planet, it's new territory."

"The bottom line is that the altimeter data give the navigation team added confidence that their orbit prediction is solid," said Greg Neumann, a member of the altimeter team at Goddard Space Flight Center. "We're helping them make sure that the plan they put in place is still the right one to follow."


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