TPF-I SWG Report - Exoplanet Exploration Program - NASA

F ORMATION F LYING A L G O R I T H M D E V E L O P M E N T
Appendix C
Formation-Flying Algorithm
Development
Formation Flying Control Architecture
Key requirement for the formation flying control architecture is to be scalable to more telescopes, yet
robust while encompassing the traditional single spacecraft control functions and capabilities. This
appendix describes details of the Formation and Attitude Control System (FACS) and the Formation
Algorithms and Simulation Testbed (FAST).
The overall formation-flying control architecture, regardless of the specific implementation, retains the
traditional single-spacecraft attitude estimation, attitude guidance, and attitude control functions within
each spacecraft to allow for “standalone” mode, while providing a centralized “formation” guidance
function on any of the selected spacecraft in formation, designated the formation “leader”.
The leader/follower control architecture was selected for TPF-I since it is effective for smaller formations
(~2–10 s/c) and its stability properties are well-understood. In the leader/follower architecture, the
centralized “formation” guidance functions ensure resource-efficient, collision-free, and coordinated
formation maneuvering across all spacecraft within the formation via leader (combiner) generated
commands, which are communicated over the inter-spacecraft communication (ISC) links to all the
follower spacecraft (collectors). During formation experiments, the centralized formation-guidance
commands, once received over the inter-s/c communication links, are implemented locally on each
spacecraft through a local six-DOF control function. In the event of ISC dropouts or failure, each
spacecraft within the formation reverts back to local “standalone” on-board attitude control mode to
maintain power-positive Sun-pointing, while still being capable of performance ground-commanded linear
delta-V maneuvers. The overview of the formation-flying control architecture is shown in Fig. C-1 within
context of the s/c uplink/downlink and the ISC. Key features of the FACS architecture are summarized
below:
1. Hybrid Control Architecture
a. Centralized translation guidance
b. Decentralized attitude guidance
c. Decentralized translation control
d. Decentralized attitude control
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