Capstone
HOUSTON—As the six-month primary mission of the NASA-funded Cislunar Autonomous Positioning System Technology Operations and Navigation’s (Capstone) satellite demonstration nears its conclusion in late May, the Advanced Space-led operations team is planning a 12-month enhanced mission phase and perhaps an even longer extension if systems remain operational.
Launched on June 28, 2022, the Capstone small satellite on Nov. 13 became the first spacecraft to enter a Near Rectilinear Halo Orbit (NRHO), a fuel-efficient, necklace-shaped trajectory around the Moon that is to be home to the NASA-led, human-tended Gateway outpost.
The enhancement/extension plan is part of a Capstone mission update issued by Advanced Space on April 17. Based in Westminster, Colorado, Advanced Space received a $13.7 million contract from NASA in September 2019 to develop and operate Capstone to assess the communications and navigations characteristics of the NRHO, which varies from 1,000 mi. to 43,500 mi. above the lunar surface over a weeklong orbital period.
A critical element of NASA’s commercial and internationally partnered Artemis program, Gateway is to receive astronauts launching to the Moon aboard Space Launch System rockets and Orion crew capsules. Once docked to Gateway, lunar explorers are to transfer to a docked commercial Human Landing System for transport to and from the lunar south pole. Assembly of the multi-module Gateway is planned to begin no earlier than November 2024.
Among Capstone’s mission objectives is the demonstration of spacecraft-to-spacecraft navigation and communications systems capabilities working with NASA’s Lunar Reconnaissance Orbiter (LRO), which was launched in 2009 to accurately determine the separation distance between the two spacecraft. The technology is intended to provide a means for Capstone, and eventually Gateway, to determine their position in space without relying on Earth-based tracking.
On April 7, the Advanced Mission team that includes Terran Optical and Stellar Exploration carried out what appears to have been a successful Capstone/LRO crosslink demonstration, though the telemetry is under assessment. That followed less successful attempts at longer separation distances in January and March that prompted subsequent software updates and patches, while providing lessons learned.
“This demonstration significantly improves on the observed performance from prior attempts,” the Advanced Space update says. “Coordinating this crosslink demonstration has provided significant lessons learned related to interdependent operations between spacecraft during phases of flight with high relative dynamics between two spacecraft at the Moon. As Capstone traverses its closest approach to the Moon, and thus its closest approach to LRO, the limitations of antenna slew rates prevent some crosslink opportunities from being attempted. These design and operational lessons learned are being captured to support future crosslink activities at the Moon.”
Advanced Space also forecasts an upcoming Capstone software update to initiate the demonstration of a Chip Scale Atomic Clock to enable ranging using one-way radio communications data from NASA’s Jet Propulsion Laboratory-managed Deep Space Network (DSN) to further enhance the spacecraft’s Cislunar Autonomous Positioning System, a capability intended to provide future NRHO missions with increased operational autonomy.
As of the update, Capstone has logged 23 NRHO circuits of the Moon, while relying on ground-based navigation and tracking data from the DSN to carry out operations, including orbital maintenance maneuvers, though not without some challenges.
Capstone managed to remain on course but it was unable to receive ground commands between Jan. 26 and Feb. 6, though still able to transmit telemetry to Earth. An automatic command-loss timer rebooted the spacecraft, restoring two-way communications.
On Sept. 8, Capstone began to spin beyond the control of its reaction wheels to counter following a trajectory correction maneuver on its course to the Moon. The source was traced to a propellant valve in one of the spacecraft’s eight thrusters that was stuck open. Ground commands restored control and stopped the spin on Oct. 7.
But the spacecraft has been commanded to conduct six orbital maintenance maneuvers since entering NRHO, fewer than the once per orbit but each with greater propulsion than originally planned.
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