Messenger now in orbit around Mercury
After a six-and-a-half-year fall into the inner solar system, NASA's compact Messenger probe fired its main engine for 15 tense minutes Thursday to break into a looping orbit around hellish Mercury, becoming the first spacecraft to take up long-term residence around the solar system's hard-to-reach, innermost planet.
Following pre-programmed instructions, Messenger's main engine ignited on time at 8:54 p.m. EDT (GMT-4), beginning the job of slowing the spacecraft enough for capture by Mercury's gravity. Engineers in the Messenger control center at Johns Hopkins University monitored subtle changes in a radio beacon from the spacecraft as the probe's velocity changed to track the progress of the rocket firing.
"The Messenger spacecraft went into orbit around Mercury tonight, we can confirm that through the Doppler signals we've seen," said Eric Finnegan, the systems engineer. "It is extremely exciting in the MOCC (Mission Operations Control Center, everybody was whooping and hollering, we were elated. We are in orbit! Now, there's a lot of work left to be done, but we are there."
Gallery: Messenger from Earth reaches Mercury orbit
Messenger probe closes in on Mercury
The rocket firing was designed to slow Messenger by about 1,930 mph to put it into an elliptical 12-hour orbit tilted 80 degrees to the planet's equator with a low-point of around 124 miles and a high point of 9,400 miles.
While a precise determination of the actual orbit will depend on analysis of telemetry from the spacecraft, Finnegan said "we hit the trajectory to within a half a sigma, for my engineering friends in the crowd; it was right on the money."
