Dynamics Of Reconfigurable Multibody Space Systems Connected By Magnetic Flux Pinning

Many future space systems, from solar power collection satellites to sparseaperture telescopes, will involve large-scale space structures which must be launched in a modular fashion. Currently, assembling modular structures in orbit is a challenging problem in multi-vehicle control or human-vehicle interaction. Some novel approaches to assembling modular space structures or formation-flying space systems involve augmenting the system dynamics with non-contacting force fields such as electromagnetic interactions. However, familiar divergenceless forces are subject to Earnshaw's Theorem and require active control in 6 DOF for stability. This study proposes an approach to modular spacecraft assembly based on the passively stable physics of magnetic flux pinning, an interaction between superconductors and magnetic fields which is not limited by Earnshaw's Theorem. Spacecraft modules linked by flux pinning passively fall into stable, many-degree-of-freedom basins of attraction in which flux pinning holds the modules together with stiffness and damping but no mechanical contact. This dissertation reports several system identification experiments that characterize the physical properties of flux pinning for spacecraft applications and identify avenues for design of flux-pinning space hardware. Once assembled in orbit, altering a spacecraft to effect repairs or adapt to new missions presents significant control challenges as well. Flux-pinning technology also offers exciting possibilities for new spacecraft-reconfiguration techniques, in which a spacecraft changes structure and function at the system level. Flux-pinned modular spacecraft can reconfigure in such a way that the passive physics of flux pinning and the space environment govern the low-level dynamics of a reconfiguration maneuver, instead of full-state feedback control. These reconfiguration maneuvers take the form of sequences of passively stable evolutions to equilibrium states, with joint kinematics between modules preventing collisions. This dissertation develops a theory for multibody spacecraft reconfiguration controllers that take a high-level, hybrid-systems approach in which a pre-computed graph structure stores all the reachable configurations that meet certain design-specified criteria. Edges of the graph carry mission-related weights so that a space system can optimize power consumption, robustness measures, or other performance metrics during a maneuver. These technologies and control strategies may provide opportunities for versatile space systems that can accomplish a wide variety of future missions

Janus and Lunar Trailblazer: Lockheed Martin Deep Space SmallSats for NASA SIMPLEx Missions

NASA’s Small Innovative Missions for Planetary Exploration (SIMPLEx) program is a principal investigator-led planetary science program focusing on small spacecraft. In the SIMPLEx-2 opportunity, the cost cap for SIMPLEx missions is approximately 1/10th the cost of the next larger class of planetary exploration missions, the Discovery Program. Unlike Discovery missions, SIMPLEx missions launch as rideshare payloads with other NASA primary missions. Lockheed Martin has developed a science-capable deep space small spacecraft architecture to support two missions selected for the SIMPLEx-2 opportunity: Janus and Lunar Trailblazer. Janus is a two-spacecraft mission to fly by two different binary Near Earth Asteroids, partnered with Dr. Dan Scheeres at the University of Colorado Boulder. Lunar Trailblazer is a lunar orbiter led by Dr. Bethany Ehlmann at Caltech which will map water on the Moon; both have passed PDR and are confirmed for flight. Janus will launch first, in August 2022. A scalable suite of hardware subsystems enables the same low-cost spacecraft architecture to support both missions with a high degree of commonality, despite their disparate mission designs, environments, physical configuration, and science operations. As both missions move through project implementation, the management and engineering teams have learned valuable lessons for developing deep space-capable small spacecraft, adapting from both Earth-orbiting SmallSats and traditional larger planetary exploration missions in the Discovery and New Frontiers program classes. Key lessons learned include the value of early and close coordination between interested science teams and spacecraft providers, the need to tailor the complexity of science investigations to SmallSat spacecraft capabilities, the importance of evaluating component lifetimes against the deep space mission environment, and the challenge of planetary mission design to a rideshare launch. Rideshare missions on planetary launches must meet schedules determined by primary spacecraft with inexorable planetary launch windows and must provide enough propulsion to reach their own destinations which may include planetary orbit insertion or targeting a completely different solar system destination than the primary spacecraft

Janus: Launch of a NASA SmallSat Mission to Near-Earth Binary Asteroids

Janus is a two-spacecraft SmallSat mission to fly by two different pairs of binary near Earth asteroids, (175706) 1996 FG3 and (35107) 1991 VH. The two identical Janus spacecraft are scheduled to launch during a launch period opening 1 August 2022 as secondary payloads with the NASA Psyche mission, on a SpaceX Falcon Heavy launch vehicle. Janus is led by principal investigator Dr. Dan Scheeres at the University of Colorado Boulder and managed, built, and operated by Lockheed Martin. These planetary SmallSats share many deep space challenges similar to larger missions: Janus must execute deep space maneuvers to achieve hundreds of meters per second ΔV to reach its destinations, close a telecommunication link at ranges up to 2.4 AU, autonomously manage a several-month-long telecommunications blackout during solar conjunction, operate at a maximum Sun range of 1.62 AU, and survive for approximately four years in interplanetary space before encountering their target asteroids. During the encounters, the spacecraft will return high resolution visible and infra-red images of the asteroids. In getting Janus to the pad, the implementation team successfully managed an aggressive mission schedule despite COVID-19 related supply chain impacts and work environments, all while remaining on target for the SIMPLEx-2 cost cap. Janus is a pathfinder for achievable and affordable SmallSat science missions and demonstrates the valuable partnership between an experienced deep space mission engineering team, the SmallSat commercial component industry, and a forward- looking NASA model for Class-D science missions