NASA's proposed Capstone mission could enter lunar orbit in late 2020.

An artist's impression of Capstone.
Tyvak Nano-satellite Systems

A future CubeSat pathfinder is set to explore a unique orbital path that will be used later by humans exploring the Moon.

Last week, NASA awarded a $13.7 million contract to Advanced Space, based in Boulder, Colorado, to develop the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (Capstone). The mission consists of a 12U CubeSat the size of a microwave oven, and it could launch in late 2020.

NASA plans to return to the Moon with its Artemis program, sister to the Apollo program of the 1960s and 1970s. As part of this program, NASA is building a Lunar Gateway outpost, which will be  placed in a near-rectilinear halo orbit around the Moon.From this unique vantagepoint, the Lunar Gateway will eventually be dispatching crewed missions on expeditions to the lunar polar regions. Capstone will test the viability of this unique orbit.

The near-rectilinear halo orbit is extremely elliptical, which presents unique challenges. Capstone, and eventually the Lunar Gateway, will travel from a perilune of 1,600 kilometers (1,000 miles) to a distant apolune of 70,000 kilometers from the Moon's surface. Capstone will serve as a rapid lunar flight demonstrator, showing how to transition into and operate from this orbit. This knowledge is necessary not only for the Gateway's construction but also for the later logistics of transferring crew and supplies.

A near-rectilinear halo orbit around the Moon.
Advanced Space

“This is an exciting opportunity for NASA to aggressively push forward towards the Moon in partnership with several American small businesses as a vanguard to Artemis,” says Jim Reuter (NASA's Space Technology Mission Directorate) in a recent press release. “This mission is highly ambitious in both cost and schedule—and taking that deliberate risk is part of the objective of this mission.”

Communicating with Capstone

Capstone will come equipped with its own communications and propulsion system. Once in lunar orbit, Capstone will communicate with the Lunar Reconnaissance Orbiter, which has been circling the Moon since 2009, to measure its position. This is a technology demonstration for the Gateway, which could then determine its position without relying on Earth-based tracking.

Lunar comm
Lunar communications: past, present and future.
Advanced Space

Capstone will be only the third CubeSat to operate beyond Earth orbit, after the Marco-A and Marco-B missions that hitched a ride with Mars InSight last year,

The mission will launch either as part of a lunar rideshare mission or as the prime payload on a smaller launcher. The Space Launch System (SLS) rocket will also be carrying several CubeSats to the Moon as part of the first Artemis mission, but as Clare Skelly (NASA Goddard Space Flight Center) notes, Capstone has been developed so quickly, it did not exist yet when those payloads were determined. "NASA has requested information from U.S. industry on commercial launch options for the Capstone CubeSat," Skelly adds.

This year has been a busy year for lunar exploration, with the first ever soft-landing on the farside of the Moon by China's Chang'e 4 mission, two soft landing attempts by SpaceIL's Beresheet and India's Vikram landers, and India's Chandrayaan 2 entering lunar orbit. And more activity is afoot: The core module for the Lunar Gateway is currently set to launch as early as 2022.

If Capstone is successful, it will help guide the way for humans to visit lunar orbit.


Image of Anthony Barreiro

Anthony Barreiro

September 18, 2019 at 5:33 pm

I was curious about the rational for the near-rectilinear halo orbit. This article explains it well:

And this more technical video images the orbital path in an Earth-centered inertial frame, an Earth-Moon rotating frame, and a Moon-centered inertial frame:

The comments on this video are enlightening.

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Image of Anthony Barreiro

Anthony Barreiro

September 18, 2019 at 5:35 pm

"rational" should be "rationale". That's what happens when your misspelling is also a word in the spellcheck dictionary!

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