Formation Flying of a Telescope/Occulter System with Large Separations in an L2 Libration Orbit
- Paper number
IAC-08.C1.6.2
- Author
Mr. David C. Folta, National Aeronautics and Space Administration (NASA)/Goddard space Flight Center, United States
- Coauthor
Mr. Jonathan Lowe, Analytical Graphics, Inc., United States
- Year
2008
- Abstract
Flying an occulter in formation with a telescope in a sun-Earth L2 co-linear libration orbit requires an understanding of the interactions between the dynamics of the three-body restricted system and formation control methods. When the separation distances become a large fraction of the telescope’s libration orbit amplitude, linear approximations break down and formation control becomes problematic, requiring high-fidelity modeling and specific targeting methods. Recently NASA began a study of such a system of spacecraft for the New Worlds Observer (NWO) mission. The study was performed to investigate control methods and to determine their mission implementation cost. System control is further complicated by the requirement to achieve deterministic occulter positions relative to the telescope in a timed sequence for science observations. These positions align the system to observe selected stars as they become visible in the field of regard. The occulter is constrained to a large separation distance from the telescope that approaches 25 percent of its libration orbit x-axis amplitude, yielding uncharacteristic restricted three-body motion. This paper considers control approaches and determines delta-v requirements to re-align the telescope-occulter system and to maintain the viewing geometry during an observation sequence. Implemented in a full-ephemeris model with numerical propagation and targeting, control cost (delta-v and fuel mass) are derived for impulsive and finite maneuvers. The impulsive approach implements the customary two-maneuver concept at the boundary conditions determined only by position and time constraints. The finite maneuver implementation uses low-thrust with multiple combinations of boundary conditions derived from position, velocity, and time. A differential correction process is used in both applications and is compared to an optimization process to determine any improvements. Total mission delta-v cost and impacts from various observations sequences are discussed. An approach to permit extended separation formations is found.
- Abstract document
- Manuscript document
IAC-08.C1.6.2.pdf (🔒 authorized access only).
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