CPOD Satellites

Demonstrate proximity operations and docking between CubeSats.

Demonstrate proximity operations from various distances, approach scenarios, and lighting conditions: nominal operating distances: 50 m to 2 km, full range of distances: 0.5 m to 25 km. Demonstrate docking between two vehicles. Safely approach and make contact between test vehicles.

A combination of radio frequency licensing obstacles, propulsion system issues discovered and subsequently reworked by the manufacturer (VACCO Industries), and rideshare launch vehicle delays, the vehicles ultimately launched in May 2022. As such, despite the recent launch date, the vehicles feature previous-generation hardware, missing out on seven years of hardware upgrades and refinements. On the other hand, the vehicles could accept software upgrades with comparative ease, and thus flew Terran’s state of the art GNC software. CPOD ultimately achieved rendezvous and passively safe formation flying. Docking was not exercised due to fuel depletion brought about by challenges associated with the outdated hardware. Operations concluded in May 2023 and the vehicles were decommissioned in June 2023.

CPOD ultimately achieved rendezvous and passively safe formation flying. Docking was not exercised due to fuel depletion brought about by challenges associated with the outdated hardware. Operations concluded in May 2023 and the vehicles were decommissioned in June 2023.

Key Accomplishments

• 5 major experiments yielding rendezvous and passively safe formations
• 3 guidance algorithms validated on-orbit for autonomous RPO
• Exceptional robustness to disturbance forces

Key Lesson Learned

• Primary performance bottleneck: propulsion system reliability
• Dynamic modeling will improve performance with existing hardware
• Improved hardware will further increase performance and flexibility

Reduced Solar Power Generation

• Both vehicles lost 5-10 W of generation capacity
• Likely due to an inaccurate integrated circuit spec
• Risk known before launch; redesigned MPPT rolled out to other vehicles, but did not fit in 3U CPOD bus

Disturbances from Cold Gas Prop System

• Rebuilds by system vendor reduced total Δv
• 2 thrusters stuck open on one vehicle
• Plenum pressure varied widely (up to 75% error)⟹ Thrust force likely varied widely

The CPOD mission ultimately achieved autonomous rendezvous of a 3U CubeSat to an RSO using its RPO architecture. On-orbit experiments specifically validated an SCP algorithm for exceptionally fuel efficient semi-autonomous rendezvous from long distances, a nonlinear MPC algorithm for fully autonomous rendezvous, and a linear MPC algorithm for ingress to a passively safe flying formation.

The limiting factors in on-orbit experiments stemmed largely from hardware systems that were obsolete at launch due to many years of logistical launch delay. The experience of confronting these challenges in the years preceding CPOD launch generated insights into pain points that have improved subsequent missions. Additionally, while the on-orbit hardware challenges limited the scope of experiments, they also stress-tested the robustness of the RPO architecture and revealed its strong disturbance rejection capabilities.

Marked as Failure in the NASA SmallSat/CubeSat Fleet Missions Database.

• PLATFORM - Tyvak