With a 30-minute blast from its main rocket engine, NASA's Messenger spacecraft slipped into orbit around the planet Mercury Thursday evening, becoming the first craft from Earth ever to circle the closest planet to the sun.
At 9:10 p.m., when early telemetry indicated that the rocket burn had finished and the probe had been captured by Mercury's gravity, a round of applause went up from the mission control room at the Johns Hopkins University's Applied Physics Lab near Laurel.
Grinning scientists and engineers stood, clapped each other on the shoulders and shook hands until they were asked to return to their seats and get back to work, tracking the spacecraft and monitoring its systems.
"This is going to be a long night; they've got a lot of data to look at. But so far, it's been a great night," said Michael Paul, a mission engineer providing color commentary from a nearby auditorium where APL personnel were following the critical phase of the mission.
About 40 minutes later, mission lead engineer Eric Finnegan announced that the spacecraft was in a near-perfect orbit. "Right down the alley," he said. "We hit the trajectory to within half a sigma, for my engineer friends in the crowd. It was right on the money."
Edward J. Weiler, NASA's associate administrator for science, noted that Mercury is now the fifth planet NASA's spacecraft have orbited, a singular moment in history.
"You only go into orbit for the first time at Mercury once in human history," he said. "We're going to learn more at Mercury than we ever dreamed of, and the most exciting stuff will be the stuff we weren't expecting."
Over the ensuing hours and days, personnel at APL will be poring over data from the spacecraft, checking the health of its systems and switching on its science instruments. They'll also need to be sure it's in the 12-hour orbit around Mercury they wanted and, if not, send commands for further orbit corrections.
NASA's Messenger spacecraft was on auto-pilot for most of the day Thursday as it raced toward Mercury.
While scientists and engineers watched from their mission operations center in Maryland, Messenger's onboard computer ran through a series of programmed commands to put it into the right orientation for the 30-minute rocket burn at 8:53 p.m. EDT that would slip it into orbit.
"We're really excited. This is an event," said Eric Finnegan, the mission's lead engineer.
Thousands of miles away, the big dish antennas of NASA's Deep Space Network, in California, Spain and Australia turned toward the spacecraft, ready to track its progress and download the radio signals that will tell engineers whether the craft had arrived safely in Mercury orbit.
By all accounts, Messenger was performing well in the final hours before its arrival, with no problems that threatened to spoil scientists' hopes to achieve orbit and spend at least a year in close-up study of Mercury.
"There's probably a little bit of tension in the building. There always is with these things," said Ralph McNutt, Messenger project scientist.
Messenger's planned orbit would take it within 120 miles of Mercury's cratered surface once every 12 hours. For the next several days mission managers expected to be busy ensuring that the probe is in the proper orbit, confirming the health of its systems, and turning on and testing its seven scientific instruments.
Messenger was designed and built by scientists and engineers at the Johns Hopkins University Applied Physics Lab near Laurel. And its flight is being controlled from a room on the APL campus.
"People who have been working on the program for a long time are excited; others are really nervous," Finnegan said from the control room Thursday before the spacecraft began orbiting Mercury.
The spacecraft was launched on its $446 million mission in 2004. Since then it has flown by Earth and Venus (twice) on a circuitous 4.9 billion-mile journey. It made three high-speed flybys of Mercury in 2008 and 2009 and sent back a lode of scientific data and more than a few surprises for planetary scientists.
If all goes well, they should have at least a year of photography, mapping and cataloging of Mercury's composition ahead. They hope to find clues to Mercury's formation and evolution, and to learn more about its tenuous atmosphere and the space environment it inhabits near the sun.