A tiny NASA spacecraft launches to test a new orbit around the moon

Earlier today, a small microwave-sized NASA spacecraft began a four-month journey to the moon, where it will eventually slot into a unique, elongated lunar orbit that no NASA mission has visited before. The spacecraft’s goal is simple: test this particular orbit and see how it is. That’s because it’s the same orbit that moon-bound astronauts could use in the coming decade.

This characteristic orbit is called “near rectilinear halo orbit” or NRHO for short. It’s a special seven-day path spacecraft can take around the moon, taking vehicles relatively close to the lunar surface for one day before traveling far from the moon for the other six.

NASA is considering using this orbit for its Artemis program — the agency’s effort to send the first woman and first person of color to the lunar surface. Over the next decade, NASA plans to build a new space station around the moon called Gateway, a site that will serve as a training platform and living quarters for future astronauts flying to the lunar surface. And the space agency wants to park the gateway on that twisted orbit around the moon.

Because NASA has never sent a spacecraft to this orbit, the agency has no experience of what it’s like to operate a vehicle there. This mission, called CAPSTONE, is intended to serve as a trailblazer. It can also be seen as the first mission in the entire Artemis program, ushering in an intricately planned timeline that may culminate with humans returning to the moon after more than half a century. “We consider the CAPSTONE mission as a whole to be a valuable precursor,” Nujoud Merancy, chief of the Exploration Missions Planning Office at NASA’s Johnson Space Center, said during a news conference.

When astronauts flew to the moon during Apollo, their path to the moon was a more or less straight shot on a massive rocket called the Saturn V. When they arrived, they eventually placed themselves in a relatively circular orbit around the moon, one such put them within 62 miles to the surface. This would allow them to get to the ground and back into lunar orbit relatively quickly.

This approach got them to the moon quickly, but required a lot of resources. “Unfortunately, one of the things to be aware of when taking spacecraft and equipment to the moon using this typical approach is the significant amount of fuel that is required,” Elwood Agasid, deputy program manager for NASA’s Small Spacecraft Technology Program Ames Research Center, narrated The edge.

An infographic comparing the different types of orbits that spacecraft could take around the moon
Image: NASA

With Artemis, NASA wants to try some new approaches to exploring the moon. By parking the Gateway at NRHO, the future lunar space station will come within 1,000 miles of the moon’s south pole and swing out up to 43,500 miles from the other pole each week. This narrow pass is a much greater distance than the Apollo astronauts had to travel to reach the ground. But NRHO offers other important benefits. Spacecraft in NRHO have constant line of sight to Earth, allowing for continuous communications. The Apollo astronauts didn’t have that; Once in lunar orbit, they passed the far side of the moon and blocked their signals with Earth for nearly an hour during each lap.

Perhaps the biggest benefit is that being in NRHO doesn’t require as much fuel as it would in a circular orbit around the moon. That’s because this type of orbit is known as a three-body orbit; Spacecraft on this route are affected by the gravitational pull of the Earth, Sun, and Moon. As a result of this balancing act, spacecraft are relatively stable along this path, and they don’t have to burn a lot of fuel to stay behind or get to the surface.

“It has the advantage that there is little energy to get in and little energy to get out,” Chris Baker, the program manager for NASA’s small spacecraft technology program, said during a news conference. Baker describes spacecraft in this orbit as “Driving on that balance point between the gravity of the earth and the gravity of the moon.”

Finding that balance is crucial, and NASA wants to verify when Earth’s orbital pull will increase and when the Moon will intervene. CAPSTONE will give the mission team real-time experience of what type of maneuvers are required and when fuel is needed to be burned to properly keep a spacecraft on that path.

a graphic, developed by Advanced Space which CAPSTONE produced and shows the lunar ballistic transfer path that the spacecraft will take to the moon
Image: Extended Space

With CAPSTONE, NASA is also testing a fairly long way to the moon. Because the vehicle is so small, it doesn’t have much room for fuel, although it’s filled to the brim with what it can hold. “It’s a pretty dense package, mostly because the propulsion system takes up a lot of the spacecraft’s mass, space, and volume,” says Agasid. “It’s packed. It’s a technological marvel.” The spacecraft also launched from New Zealand on a relatively small rocket called the Electron, manufactured and operated by US aerospace company Rocket Lab. While Rocket Lab adds an extra boost with an extra booster called Photon, it still doesn’t have a lot of fuel to burn compared to, say, a massive rocket like the Saturn V.

So, over the next four months, CAPSTONE will reach the moon via a route known as lunar ballistic transfer, or BLT. Using the Sun’s gravitational effects, CAPSTONE will grind far out of the Earth and Moon systems, spiraling out ever further until it reaches the point where it can blend into NRHO. It requires far less fuel but far more time to complete.

CAPSTONE is scheduled to reach NRHO on November 13th. Once in orbit, it will remain in orbit for at least six months, allowing NASA to collect vital data about that lunar orbit. The agency also plans to test a new navigation feature where the spacecraft will attempt to determine its own position and speed in space. In this way, the vehicle requires less input from humans on the ground, a capability that could prove useful for future interplanetary exploration.

When its mission is complete, NASA will send CAPSTONE on a crash course with the moon, its historic task complete. But for now, the mission team will have to wait for the tiny satellites to come into lunar orbit. “The advantages of NRHO are clear, and we are pleased that CAPSTONE is testing and validating this orbit for the first time,” said Merancy.