Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
2002-06-03
2004-01-06
Dinh, Tien (Department: 3644)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
Reexamination Certificate
active
06672542
ABSTRACT:
BACKGROUND OF THE INVENTION
Several constellations currently inhabit the LEO environment (OrbComm, Iridium, GlobalStar) and more are in the deployment stages or are planned for the future (Teledesic, etc.). Some of these constellations take advantage of orbital dynamics to maintain the same perigee location in inertial space with a non-varying value of the eccentricity. These are called “frozen” orbits; the optimal eccentricity of a frozen orbit is called the “frozen eccentricity”. Frozen orbits can assist in the operational aspects of a constellation by providing easier and more consistent satellite-to-satellite linkage as well as reducing the residence times of satellite failures.
The problem, however, lies in the initial deployment of the vehicle or subsequent errors in the maneuvering. For near-circular orbits, the frozen eccentricity is difficult to achieve during deployment and the only currently known way to drive the eccentricity to the frozen value once a vehicle has been deployed is to either conduct radially directed burns or transfer Hohmann burns in pairs. But radial burns often interfere with operational constraints and pairs of Hohmann burns require extra fuel. Thus, the frozen quality of the orbit is difficult to achieve, and the effectiveness of using the frozen orbit within the constellation is therefore diminished. Under current stationkeeping algorithms, changing the eccentricity in near-circular orbits is either costly or can only be accomplished by burning in the radial direction. Operational constraints often prohibit burning in these ways. Accordingly, it would be desirable to be able to move the eccentricity to the frozen value without interfering with mission operations, or without requiring extra fuel beyond that which is expended through typical drag-compensation burns in the along-track direction when the satellites occupy a regime low enough that drag is the dominant non-conservative force.
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Dinh Tien
Henricks Slavin & Holmes LLP
The Aerospace Corporation
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