Moving Along
The CAPSTONE spacecraft recently set a mission record of 112 days of spacecraft uptime. This is a testament to the resilience of the system, the team, and its ongoing performance. The 112 days were interrupted by a system reset caused by a ground station being unavailable as scheduled. On the positive side, this brief reset meant that the spacecraft operated as designed when it didn't hear from us.

Keeping in Touch
To navigate, the Cislunar Autonomous Positioning System (CAPS) software initiates radio crosslinks with the Lunar Reconnaissance Orbiter (LRO) to help the CAPSTONE spacecraft obtain measurements that will allow CAPS to determine the absolute position of both spacecraft in their orbits at the Moon. The longer the two spacecraft stay in touch, the more tracking data can be obtained and the more they can share their position information.

The most recent pass between CAPSTONE and LRO on January 7 was the longest CAPS crosslink tracking arc to date, with a total of 66 minutes of tracking data and 200 crosslink measurements, taking advantage of almost the entire window when LRO was not blocked by the Moon.

The tracking pass occurred after a lot of payload team work to refine the radio's setup on-orbit and to maximize the effectiveness of the CAPS crosslink measurements. This was the third successful CAPS crosslink demonstration. Having three successful passes helped the payload team analyze the results from each pass with more context. We are still processing data, but this is a big deal for the mission. The more data we collect, the better we can validate and improve our crosslink approach and can quantify data noise and overall performance.

We also updated the firmware used to control the spacecraft's Iris X-band radio and are now collecting one-way uplink measurements on every single pass from every station of NASA's Deep Space Network (DSN), including the site at Morehead State University. These measurements, developed in collaboration with NASA's Jet Propulsion Laboratory in Southern California, are providing tremendous amounts of data to evaluate and mature one-way uplink data processing for onboard navigation. In connection with these measurements, we also conducted several experiments related to when and how we capture this data to understand and isolate effects such as thermal transients on the stability and performance of the onboard chip-scale atomic clock (CSAC).

Software Scalability and Automation in Orbit
The ability of CAPSTONE's unique communication subsystem (custom-built radio) to crosslink enables it to expand its network by adding more users. This expandable network makes navigation solutions near the Moon more resilient and more accurate. With access to the CAPS software and a network of other cislunar vehicles, spacecraft using CAPS can determine its position and navigation state autonomously.

Operating at the Moon, CAPSTONE can serve as a test bed for further automation beyond navigation. With a separate computer onboard just to handle test software, CAPSTONE can upload and demonstrate other Advanced Space technologies.

For example, Neural Networks for Easy Planning (NNEP) uses neural networks to design maneuvers onboard while another Advanced Space machine learning tool we uploaded can filter data outliers and identify navigation anomalies. Both software tools are to be demonstrated on CAPSTONE by end of Q1 2024.

Lessons Learned
Because the CAPSTONE spacecraft achieved many "firsts," from being the first commercial satellite to operate at the Moon to the first spacecraft to fly in a Near-Rectilinear Halo Orbit (NRHO), we have learned a lot of lessons.

First, systems normally designed to fly in Earth orbit must be customized to fly in cislunar space. This includes activities such as launch targeting, propulsion, radios, concepts of operations, and fault detection, isolation, and recovery.

Next, we learned lessons about our ground segment regarding congestion and operating requirements. Our spacecraft arrived at the Moon 3 days before Artemis 1 and its secondary payloads launched. During this critical time for several different missions, the DSN team worked heroically to deconflict schedules and support all the missions. This congestion, however, is a likely example of what is to come in the future.

With expanded operations at the Moon, CAPSTONE clearly demonstrates the important work we are performing to reduce congestion on exquisite ground segment assets through automation and onboard navigation applications. Controlling the CAPSTONE spacecraft was not just about having access to large-aperture antennas. We also needed low data noise in our navigation measurements, clock stability at the ground stations for measurement precision, and the global distribution of DSN's antennas, all of which DSN delivered, and all of which are different from standard ground segments used for spacecraft operating in lower orbits.

When it came to flight operations, NRHO presented its own special challenges, including unique flight dynamics (which is dominated by the Earth for part of the orbit and by the Moon for part of the orbit - behaving similar to a lunar fly-by every orbit). Given these challenges, any functions we automated on the spacecraft had a high return on investment because they were used frequently. By automating more of our systems, we demonstrated a method for reducing the DSN's workload in the future.

What the Future Might Bring
With real flight data and experience, Advanced Space can build scalable, secure, and resilient cislunar communications relay and navigation systems in the future. Given the nature of CAPSTONE's onboard hardware and significant fuel margin, we can perform extended operations with the spacecraft and flight processor after completing our enhanced mission in May 2024.

The CAPSTONE vehicle with on-board processing to demonstrate applications like autonomous Dynamic Space Operations (DSO) and Precision Navigation and Timing (PNT) demonstrations is an ideal on-orbit test bed to demonstrate these capabilities. With a software defined radio (SDR) on board, CAPSTONE also could be used to test other ground segments. Currently, CAPSTONE is using the NASA DSN ground architecture, but other ground segments could be demonstrated.

Our work is not done, and we are proud that CAPSTONE will be forever remembered as a pathfinder that led us back to the Moon-this time to stay!

Related Links
Advanced Space
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