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.

ARTEMIS operations - Experiences and lessons learned

“…The DSN was integrated into the mission network to allow for deep space communications, two-way Doppler tracking, and ranging support during the transfer trajectory and libration point orbit phases, and for increased science data recovery from lunar distances. [6] Initial tracking and ranging tests with the DSN 34-m subnet stations began in December 2008, and were able to prove that the DSN sequential ranging scheme was compatible with the probe transponders. The fact that ranging data could be available in addition to two-way Doppler tracking data was a critical piece of information.…”

“…With the 34-m DSN stations, the telemetry data rate of 4.096 kbps provided adequate link margin. [6] Lunar Libration Point Orbits…”

“…Capabilities to perform pass automation with lights-out operations during off-hours were retained, but had be expanded to also include the significantly more complex ground network telemetry and telecommand data flows with DSN, involving the CCSDS Space Link Extension (SLE) protocol. [3,6,11,12] …”

Lunar magnetic field measurements with a cubesat

“…For the ARTEMIS mission extension, the required ranges for communications increased from 200,000 km up to 1,600,000 km for some of the trajectory regimes. Therefore, the 34-m subnet of NASA's Deep Space Network (DSN) was brought online and certified 30 to support telemetry reception, command transmission, as well as two-way Doppler tracking and ranging.…”

Multi-Mission Flight Operations at UC Berkeley - Experiences and Lessons Learned

“…Telemetry and command flows need to be established with several different networks, including NASA's Ground Network (GN), Space Network (SN) and Deep Space Network (DSN), and allowing passes to occur simultaneously with any of the five probes (THEMIS A-E) while involving different protocols for telemetry and command transfer. 12,13 The overall network topology is shown in Fig. 4.…”