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Mission controllers have lost contact with a small spacecraft called CAPSTONE that's on its way to the moon. NASA is funding CAPSTONE as part of its own plans to put people back on the lunar surface. NPR's Joe Palca has more.

JOE PALCA, BYLINE: CAPSTONE is what's known as a CubeSat. These are small spacecraft no larger than a microwave oven that are relatively inexpensive to build and send into space.

(SOUNDBITE OF ARCHIVED RECORDING)

UNIDENTIFIED PERSON: Three, two...

(SOUNDBITE OF ROCKET LAUNCHING)

UNIDENTIFIED PERSON: ...One.

PALCA: CAPSTONE left Earth on June 27 aboard a rocket made by a company called Rocket Lab. After several adjustments while in Earth orbit, the rocket fired its engines for a final time on July 4, sending CAPSTONE toward the moon. Everything appeared to be going smoothly, and then - nothing. The spacecraft went silent.

The probe was going to orbit the moon in a way that's never been tried before. It allows a spacecraft to save fuel while in orbit. NASA is planning to use the same orbit for a home for astronauts around the moon. It's a space station called Gateway. Diane Davis is mission design lead for the Gateway program. She says CAPSTONE was going to be helpful, but...

DIANE DAVIS: It's not a required component of the Gateway program in that, you know, it is a CubeSat.

PALCA: Davis says people who build and launch small CubeSats have a very different mindset from the engineers who design missions with astronauts on board.

DAVIS: So they accept a higher risk than what you would accept with a crewed spacecraft.

PALCA: Davis says mathematical models have convinced Gateway mission managers that this new kind of orbit will work as expected.

DAVIS: So even if CAPSTONE is not a complete success, we're still going to be very confident in our Gateway plans.

PALCA: NASA says CAPSTONE mission managers are still trying to reestablish contact with the tiny probe. Joe Palca, NPR News. Transcript provided by NPR, Copyright NPR.