GOLDEN, Colo. – Sent to the moon more than two years ago, NASA’s Cislunar Autonomous Positioning System Technology Navigation and Operations Experiment (CAPSTONE) is busier than ever, testing techniques to improve spacecraft operations in cislunar space.
Launched on June 28, 2022 aboard a Rocket Lab Electron booster from New Zealand, CAPSTONE, a microwave-sized cubesat weighing just 25 kilograms, is on a mission and operational in near-rectilinear halo orbit (NRHO) around the Moon.
NRHO is the planned orbit for NASA’s cislunar Gateway space station, which is intended to serve as an outpost for long-term human exploration of the Moon and beyond. It will also provide crews with access to the lunar south pole, a priority area for the space agency’s Artemis program.
Overcoming the early problems
CAPSTONE’s mission has not been an easy one. Early in its mission, a recalcitrant thruster caused the probe to switch to rapid fall mode. It also overcame a thruster jam, among other problems.
Having overcome these technical challenges, the spacecraft is now scheduled for cislunar operations for several more months, said Thomas Gardner, chief engineer of Advanced Space of Westminster, Colo., which owns and will operate CAPSTONE throughout its mission.
“Advanced Space is working with other potential customers within NASA and other government agencies, such as the Air Force Research Laboratory, to provide testing opportunities for their experiments,” Gardner said. Space News.
These experiments are primarily focused on autonomous navigation and precision timing, Gardner said, as well as other operations in the cislunar domain, including communications relay services as well as rendezvous, proximity operations and spacecraft docking. NASA says the mission will cost about $30 million, which includes the purchase of a $10 million launch vehicle from Rocket Lab. The spacecraft was built by Terran Orbital (formerly Tyvak Nano-Satellite Systems) under a commercial subcontract with Advanced Space.
Software testing platform
CAPSTONE relies on the Cislunar Autonomous Positioning System (CAPS), a real-time system for estimating the absolute position and velocity of spacecraft operating in the cislunar environment.
The Cubesat is equipped with an onboard atomic clock provided by JPL to accurately determine the spacecraft’s coordinates in space and time. Gardner explained that Advanced Space successfully demonstrated CAPS autonomous navigation technology using both two-way telemetry with NASA’s Lunar Reconnaissance Orbiter orbiting the moon and one-way uplink telemetry with JPL’s Deep Space Network.
In addition to testing the CAPS navigation system software, Gardner said efforts are underway to evaluate a wide range of software features, which involves the use of an additional computer aboard CAPSTONE. This computer allows ground controllers to run software without interfering with spacecraft operations.
“It’s essentially the only software testing platform in cislunar space,” Gardner said.
Deep Space Maneuvers
Among the software tested, Gardner said, is Neural Networks for Enhanced Planning software, which calculates optimal maneuvers for autonomous stationkeeping — keeping an active spacecraft in the same orbit as another vehicle — and also validates safe and predictable maneuvers for satellites that use electric or chemical propulsion.
There is also SigmaZero software that identifies anomalies in a spacecraft’s behavior, determines the cause of the error, and classifies the anomaly data so operators can make informed decisions to correct course.
Additionally, a flight dynamics system evaluates the ability to provide rapid navigation and maneuver planning for deep space and cislunar missions.
“We test each software system independently and then as a whole to see how the spacecraft responds,” Gardner said.
The combined capabilities of these three algorithms will form an integrated suite called Autopilot, Gardner said.
“By testing maneuver planning, instrument panel operations and cislunar autonomy,” Gardner added, “we will eventually have a spacecraft that knows where it is, what time it is, how to maneuver properly and how to validate maneuvers with integrity.”
Lessons from Lunar Orbit
Meanwhile, NASA’s Gateway team is receiving briefings on lessons learned from NRHO operations from Advanced Space.
According to Gardner, there are several key points to consider for small spacecraft operating in deep space. First, suppliers must ensure they understand the system requirements before the preliminary design review.
“Commercial-off-the-shelf products are often not developed as advertised,” Gardner advised. “You have to understand how your system will interact with terrestrial systems, such as the Deep Space Network. Connecting to that is not as simple as it’s made out to be,” he said.
Another lesson learned is to allow extra time to obtain the appropriate regulatory approvals, Gardner said, which often require much more time and resources than anticipated.
Obtaining other authorizations can also impact spacecraft operations, such as authorization to use certain radio frequencies or managing planetary protection and orbital debris issues. Then there are range safety requirements for launch and export controls if a payload is sent into space by a foreign provider.
Finally, “read your telemetry carefully to determine what is happening based on the data you are receiving,” Gardner said.
Ultimately, Gardner said, the CAPSTONE and ground support teams look forward to continuing to use the spacecraft to support and demonstrate various tasks in the unique cislunar environment for the remainder of its mission.