THEMIS Mission Networks Expansion - Adding the Deep Space Network for the ARTEMIS Lunar Mission Phase

Abstract

THEMIS is a five-spacecraft constellation launched in 2007 to study magnetospheric phenomena leading to the aurora borealis. During the primary mission phase, completed in the fall of 2009, all five spacecraft collected science data in synchronized, highly elliptical Earth orbits. For an ambitious mission extension, the Project proposed to split the constellation into two parts - THEMIS-Low and ARTEMIS. THEMIS-Low includes the three spacecraft on the inner orbits with approximately one-day periods, continuing their study of the magnetosphere in a tighter formation. ARTEMIS involves transferring the outer two spacecraft from their Earth orbits with two and four-day periods into lunar orbits to conduct measurements of the interaction of the Moon with the solar wind and of crustal magnetic fields. This transfer was initiated on July 21, 2009 and follows low-energy trajectories with Earth and lunar gravity assists. The THEMIS mission is controlled from the highly automated multi-mission operations center at the University of California, Berkeley and was originally designed to be supported by 11-m class ground stations and NASA's Space Network. To increase the telemetry bandwidth for science data return at lunar distances, the mission network was expanded to also include the 34-m subnet of NASA's Deep Space Network (DSN). This paper discusses all aspects of the process to seamlessly integrate the new DSN interfaces into the THEMIS/ARTEMIS mission control network, and describes challenges and lessons learned with the implementation of real-time telemetry and command data transfer using the CCSDS Space Link Extension protocol. It also includes on-orbit characterization of the transponder ranging channels, orbit determination results using two-way Doppler and range data from a combination of conventional ground stations and DSN stations, as well as pass scheduling via the DSN Resource Allocation Planning Service and via automated, electronic data exchanges. All of these tasks were accomplished within a compressed schedule of one year, with very limited staffing resources, and on a tight budget.