NASA’s twin Grail spacecraft, which settled into lunar orbit over the New Year’s weekend, have been given new names as they prepare to map the Moon’s gravity in unprecedented detail.

“So far these spacecraft have operated nearly flawlessly,” Maria Zuber, Grail principal investigator at the Massachusetts Institute of Technology in Cambridge, Mass., said in a press conference Jan. 17. “I’ve said that I know now what it’s like for people who raise twins, but they’re very well behaved twins.”

Zuber spoke during a NASA event to unveil the new names of the twin Grail spacecraft, which were originally dubbed Grail A and Grail B. NASA held a nationwide student contest to find new names, ultimately picking the monikers “Ebb” and “Flow.”

The names were selected from an essay contest that more than 11,000 students from 900 schools participated in. The winning names were suggested by a class of 28 fourth-grade students at Emily Dickinson Elementary School in Bozeman, Mont.

Currently, both spacecraft are operating independently, but after a series of engine maneuvers, the two probes will be placed in a tandem orbit just 55 kilometers above the Moon’s surface. Then, the Grail probes will be ready to begin collecting data in early March, Zuber said. The data-gathering phase of the mission will last 90 days.