Mars sample return: Testing the last meter of rendezvous and sample capture

One of the key challenges of a future Mars sample return mission is the autonomous capture of an orbiting sample canister, previously lofted from the Martian surface, by an Earth Return Vehicle. To accomplish the capture, the latter spacecraft rendezvous with the sample canister and captures it using a capture cone. Understanding the capture dynamics between the sample canister and capture cone in the zero gravity environment is paramount to designing an effective capture mechanism. Moreover, testing and validating the sample capture event in a zero gravity environment is a crucial, though challenging, element to ensure mission success. Although ground-based simulations and flat-floor facilities are cost-effective, they are lacking the required fidelity. On the other hand, space-based testing opportunities provide a true zero gravity environment, but are prohibitive because of their costs. This paper presents a novel, efficient, and cost-effective way to test and validate the "last-meter" rendezvous and capture event. The testing strategy exploits the zero gravity periods provided by NASA's C-9 parabolic aircraft and a novel free-floating test setup that allows the exploration of various capture conditions in a controlled manner. The testing methodology and test hardware are described, and the results and lessons learned from a weeklong flight test campaign are discussed. The methodology and the conclusions described herein can serve as a pathfinder for the test and validation of other zero gravity capture events including those envisioned for future planetary sample return missions.