NEW YORK — Scientists are welcoming the return of NASA’s Mars Reconnaissance Orbiter (MRO) to full operations after a year during which the powerful probe experienced a series of mysterious technical glitches that interrupted its observations.

The troubles, dating back to February 2009, led mission managers in August to put the spacecraft into a protective “safe mode,” which typically entails shutting down all but the most essential life-support functions. The spacecraft was resurrected in December and has since resumed science operations, much to the delight of Mars scientists, who have waited patiently for the orbiter to return to duty.

“It’s good to have the instruments back on,” said MRO Mission Manager Dan Johnston of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif. “This has been a long stand-down. Now we’re ready to resume our science and relay mission.”

MRO’s troubles began Feb. 23, 2009, when the orbiter underwent a quick reset. That was followed by an event June 4 that “was virtually identical to the first one,” said Jim Erickson, the spacecraft’s project manager at JPL.

Engineers still do not know exactly what caused those rapid resets.

In August, a different type of reset occurred and the spacecraft temporarily switched over to its backup computer. Whether or not all the resets are related still is not known.

With the repeated events, mission managers wanted to take precautions against the unlikely but potentially mission-ending event of having two resets happen within a minute of each other. On Nov. 30, they beamed up a software upgrade to the orbiter’s nonvolatile memory, where information is preserved even if another reset interrupts its power.

“Above all else, we have to make sure the spacecraft is safe,” Erickson said in an interview.

Engineers ran a few more checks and eventually brought MRO out of its safe mode Dec. 8. On Dec. 16, mission managers announced that the orbiter was back in business and ready to resume science operations, though engineers will be watching for any more resets.

Erickson said that during the safe mode interlude, scientists were champing at the bit to get the valuable orbiter back. MRO has taken the most detailed images yet of the martian surface from on orbit and has made key findings that add to the understanding of the geology and history of water on Mars.

The timing for MRO’s return is fortuitous for its continued observations as well.

“It is northern spring in the northern hemisphere on Mars, and we are eager to take advantage of the good visibility provided by the relatively dust-free atmosphere present at this season,” said JPL’s Rich Zurek, MRO project scientist. “A major goal of the mission is to look at changes on Mars. For example, the instruments will observe the changing polar caps, examining the extent and composition of the retreating north polar frosts and the growth of the south polar cap during this period.”

MRO is also important for its relay capabilities with other martian spacecraft, particularly NASA’s twin rovers, Spirit and Opportunity. Those functions have also resumed, NASA said.

MRO’s mission, which began after it reached Mars in 2006, is extended through 2010. Mission controllers will send in proposals for further extensions in January, and those will be decided in February, Erickson said.

Erickson is confident that MRO’s capabilities will be in demand for quite some time — especially with new missions, such as the flagship-class Mars Science Laboratory, coming up — and mission engineers plan to do everything they can to keep it safe and running.