Station Keeping Highly Inclined Eccentric Orbits (HEO) Using Low Thrust Plasma Propulsion

Paper number

IAC-07-B2.4.07

Author

Mr. Christopher Croom, Sirius Satellite Radio, United States

Year

2007

Abstract

Over seven years ago, a Satellite Digital Audio Radio Services (SDARS) system was established to provide broadcast service to mobile and fixed subscribers throughout North America.  The system has been operating with extremely high availability providing over 65 commercial free music channels, over 70 voice channels (i.e., news, sports, comedy, traffic, ethnic languages, weather, etc.) and a few television channels to more than 6 million subscribers.

     The system employs three satellites forming an orbital constellation.  The satellites are in inclined, elliptical geosynchronous orbits whose planes are separated from each other by 120°.  The constellation provides high elevation angles to all subscribers, providing a distinct advantage in particular for the northern half of the United States where elevation angles from geostationary (GEO) satellites would be low.
SIRIUS is now considering options for the replacement follow-on constellation.  One geostationary satellite is already on contract and will be added to the SIRIUS fleet, creating a hybrid GEO-HEO constellation.  Following that, additional satellites will be added to replace the aging HEO satellites.  The new satellites, both GEO and HEO, will likely be equipped with plasma / electric propulsion subsystems, providing higher payload mass-on-orbit capability.  Although low thrust station keeping methods for GEO platforms are well understood, electric propulsion station keeping for HEO is relatively immature.

     The most immediate complication to HEO station keeping is the requirement of sun-nadir steering.  Due to the high inclination of the satellite, the sun does not in general lie near the orbital plane.  In order to maintain acceptable power levels, the satellite must perform sun-nadir steering throughout the orbit.  Specifically, the satellite must continually rotate about the nadir axis so that the solar arrays can be oriented directly to the sun line of sight.  Although this is favorable to the power subsystem, this motion adds significant complexity to maneuver planning, especially given that low thrust maneuvers can require hours to execute.
  
     The paper will describe several system design options including a comparison to the heritage chemical propulsion system.  The options addressed include the location, orientation, and count of the electric propulsion thrusters.  For all of the options, the paper will outline mission delta-v requirements, design risk considerations, and complications to operational complexity.

Abstract document

IAC-07-B2.4.07.pdf

Manuscript document

IAC-07-B2.4.07.pdf (🔒 authorized access only).

To get the manuscript, please contact IAF Secretariat.