The first Cubesat to fly and operate on the Moon has successfully arrived

After a journey of nearly five months, taking it far beyond the Moon and back, the tiny CAPSTONE spacecraft has successfully entered lunar orbit.

“We’ve received confirmation that CAPSTONE has arrived in a nearly rectilinear halo orbit, and that’s a huge, huge step for the agency,” NASA’s Exploration Systems Development Manager Jim Freeh said Sunday night. “He just finished his first insertion a few minutes ago. And over the next few days, they will continue to refine its orbit and be the first cubesat to fly and operate on the Moon.”

It’s an important orbit for NASA and special because it’s really stable, requiring very little fuel to hold position. At its closest point to the Moon, this approximately one-week orbit passes within 3,000 km of the lunar surface, and at other points it is 70,000 km. NASA plans to build a small space station here, called Lunar Gateway, later this decade.

But before that, the agency is starting small. CAPSTONE is a modest commercial mission that was funded in part by a $13.7 million grant from NASA. Developed by a Colorado-based company called Advanced Space with help from Terran Orbital, the spacecraft itself is modest in size, just a 12U cubic satellite weighing about 25 kg. It can fit comfortably in a mini-fridge.

The spacecraft launched in late June on an Electron rocket from New Zealand. Electron is the smallest rocket to launch a payload to the Moon, and its manufacturer, Rocket Lab, has maximized the capabilities of the booster and its Photon upper stage to send CAPSTONE on its long journey to the Moon. It was Rocket Lab’s first deep space mission.

After separating from its rocket, the spacecraft spent nearly five months traveling to the Moon following what is known as a ballistic lunar transfer, which uses the Sun’s gravity to follow an expansive trajectory. Along the way, air traffic controllers managed to solve a rotation problem which could otherwise result in the loss of the spacecraft. It was a detour that brought the spacecraft more than three times the distance between the Earth and the Moon before turning back, but required relatively little fuel to reach its destination.

For example, the burn performed by CAPSTONE on Sunday evening to enter a nearly rectilinear halo orbit was extremely small. According to Advanced Spacethe vehicle burned its thruster in 16 minutes at about 0.44 newtons, equivalent to the weight of about nine pieces of standard printer paper.

CAPSTONE will not only serve as a guide to this new orbit—verifying theoretical properties modeled by NASA engineers—it will also demonstrate a new system for autonomous navigation around and near the Moon. This cislunar autonomous positioning system, or CAPS, is important because there is a lack of fixed tracking assets near the Moon, especially as the cislunar environment becomes more crowded over the next decade.

The mission is planned to operate for at least six months in this orbit.