The near-rectilinear halo orbit sounds like something invented by a science fiction writer who wanted to sound technical. It is, in fact, a real trajectory — a specific family of halo orbits around the Earth-Moon L2 Lagrange point that trace an elongated path swinging close to the lunar south pole on each pass and retreating to roughly 70,000 kilometers from the Moon at maximum distance. The orbit requires almost no station-keeping fuel because it is dynamically balanced between Earth and Moon gravity, making it efficient for a long-duration station. It provides continuous communication with both Earth and the lunar surface. Its geometry allows access to the polar regions of the Moon, which is where Artemis astronauts will land. The NRHO is, in short, exactly where NASA wants Gateway — and before Gateway goes there, NASA wanted to know that the NRHO works as advertised.
CAPSTONE — the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment — was a 25-kilogram, 12-unit cubesat built by Advanced Space and Tyvak Nano-Satellite Systems. Launched in June 2022 on a Rocket Lab Electron, it took a ballistic lunar transfer trajectory to the Moon, arriving in NRHO in November 2022 after a four-month cruise. Ballistic lunar transfer exploits the gravitational dynamics of the Sun-Earth-Moon system to minimize fuel use for the transfer, at the cost of a longer journey time. For a technology demonstration with no time-critical science objectives, the tradeoff was acceptable.
Navigation autonomy
CAPSTONE's primary technology objective was to demonstrate spacecraft-to-spacecraft navigation in the NRHO — measuring its own position relative to the Lunar Reconnaissance Orbiter without ground station involvement. The technique, called crosslink navigation, has CAPSTONE exchange radio signals with LRO and use the measured range and range rate to compute a position fix autonomously. This capability matters for Gateway because the station will spend significant time with its crew conducting extravehicular activities or operating in regions of limited communication with Earth; autonomous navigation reduces dependence on ground teams during those periods.
CAPSTONE experienced a serious anomaly shortly after launch in July 2022 when its primary flight computer failed to boot correctly, causing the spacecraft to spin and lose attitude control. The recovery took several days of intensive ground operations, during which the team commanded the spacecraft to use its sensors to measure the spin rate and gradually apply thrusters to stabilize. The recovery demonstrated both the spacecraft's fault tolerance and the team's ability to operate it in degraded conditions — experience that has direct relevance to Gateway operations in a similarly remote environment.
What Gateway inherits
CAPSTONE's operations data validated the NRHO's stability, fuel requirements, and communication geometry over a multi-month period. The results matched predictions from dynamical models closely enough to increase confidence in the Gateway planning assumptions. The spacecraft also demonstrated that small commercial cubesats can navigate and operate in cislunar space — a regime that previously had been accessible only to large flagship missions. The NRHO validation, along with the crosslink navigation demonstration, gave Gateway's program managers two key unknowns in their risk register a more definitive answer: the orbit exists as predicted, and autonomous navigation in it is achievable with current technology.
Gateway itself, consisting initially of the Power and Propulsion Element and the Habitation and Logistics Outpost module, is planned to begin assembly in the late 2020s. CAPSTONE's year in the NRHO was the trail marker for a much larger structure that will follow it into the same trajectory — and eventually, if plans hold, serve as the transfer point from which astronauts board landing vehicles headed for the lunar south pole. The real legacy of CAPSTONE may be less about Gateway specifically than about what it demonstrated for commercial spaceflight more broadly: a 25-kilogram spacecraft, built by a small company, successfully operated in deep cislunar space for over a year and validated orbital dynamics that large flagship missions had previously handled only in simulation. The techniques it demonstrated — ballistic lunar transfer, autonomous crosslink navigation, NRHO station-keeping — are now proven engineering practices that the next generation of cislunar missions can inherit rather than reinvent.
