J. E. EICHSTEDT ET AL. STEREO Mission Operations John E. Eichstedt, Daniel A. Ossing, George Chiu, Paul N. Boie, Timothy O. Krueger, Alan S. Faber, Timothy A. Coulter, Owen E. Dudley, and David A. Myers olar TErrestrial RElations Observatory (STEREO) mission opera- tions team is tasked with maintaining the health of the two STEREO spacecraft, Ahead and Behind, and ensuring the flow of science data from the spacecraft to the science community. The STEREO ground system includes a STEREO data server for distribution of all of the data and products required for operation of the STEREO observatories, as well as two hardware-in-the-loop simula- tors for verification of commanding and analysis of anomalies. The STEREO ground system is uniquely divided between the two spacecraft such that communications with the two spacecraft can be simultaneous while minimizing the risk of confusion. This division has been consistent through all phases of STEREO operations: plan- ning, real-time operations, and assessment. Particular consideration was given to the Sarea of command and memory management, where differences between the two spacecraft must be maintained. Since the STEREO launch in October 2006, the mission operations team has completed the phasing orbits/early operations check- out phase of the mission, transitioned to the heliocentric orbit/prime science mission, and completed a move to automated/unattended real-time operations, all the while focusing on the science data return and maintaining the health and safety of each of the spacecraft while operating with a minimal operations team size. INTRODUCTION The Solar TErrestrial RElations Observatory Delta II 7925-10L rocket on 26 October 2006 at 0052 (STEREO) spacecraft successfully launched from Cape UTC. One launch vehicle was used to launch the Canaveral Air Force Station, Florida, with a Boeing stacked STEREO observatories; STEREO A (Ahead) 126 JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 28, NUMBER 2 (2009) STEREO MISSION OPERATIONS was mounted on top of the STEREO B (Behind) obser- continuous coverage for the first week, 24 h of coverage vatory. At 0117 UTC, the Delta third stage completed for each ∆V maneuver, and a daily 3-h track otherwise. the injection of the STEREO stack into its highly ellipti- After the lunar swingbys, the prime science mis- cal orbit, and the two observatories separated from each sion commenced on 22 January 2007, when the Behind other by the separation springs. Two minutes later, more spacecraft entered heliocentric orbit and both spacecraft separation springs separated STEREO A and STEREO were moving away from the Earth at a rate of 22°/year. B, and at 0120 UTC, all three objects emerged from the The track schedule shifted to one daily 4-h track for Earth’s shadow into sunlight. By using the trajectory each spacecraft with the primary objective to play back determined from the early Deep Space Network (DSN) the solid-state recorder (SSR) data. The STEREO data tracking data, the launch injection itself was extremely return requirement, deliver 5 Gbits of data per day aver- accurate, with an estimated spacecraft stack underburn aged over a year, was designed to maximize science data of 0.393 m/s, only about 0.1 s. return at a reasonable cost to the mission. Therefore, The STEREO mission design used four phasing orbits, there is typically only one daily opportunity to down- which lasted 2 months, to target three lunar swingbys, link any particular data, because the instruments con- one for Ahead and two for Behind, to place each obser- tinuously generate data and most SSR partitions are set vatory in its correct heliocentric orbit (see Fig. 1). During to overwrite. this time, the spacecraft subsystems were checked out, STEREO mission operations were designed around and most instrument commissioning objectives were this data return requirement, and although loss of some completed. Although the potential for a ∆V maneuver data was deemed acceptable, maximizing data return existed at each apogee and perigee, a possible total of 9 was kept a priority. After 6 months in heliocentric orbit, maneuvers for Ahead and 11 for Behind, only 4 maneu- STEREO returned a daily average of 7.0 Gbits of data vers for Ahead and 6 maneuvers for Behind were neces- from the Ahead spacecraft and 7.7 Gbits of data from sary because of the very accurate launch injection. DSN the Behind spacecraft. STEREO employs decoupled track coverage during the phasing orbits consisted of spacecraft bus/instrument operations modeled after = Planned V HGA Cals A5 Maneuver Key #2, 3, & 4 76 = TCM V Event ID (STA) Mission Day Engineering Ahead Burn #2 = G&C Maneuvers IMPACT PLASTIC IMPACT S1+ Boom LV on A2 MAG Cal 63 Deployment A1 22 Maneuver HGA Cal #1 Open 8 COR Cal COR 1/2, A3 (STA & Rolls (STA) HGA Cals STB) EUVI & 36 HI Doors #2, 3, & 4 A4 (STB) 47 S2 MAG, S1 57 SIT/SEP 97 SEP, Covers Open IDPU on STE (STB) Behind and SWEA & SIT Cover Open SIT/SEP Engineering Covers Open COR Cal Burn #1 (STA) Rolls (STB) HGA IMPACT commissioning Deployment A3+ P4 PLASTIC commissioning TIP P2 40 P3 P1 42 54 SECCHI commissioning 16 31 S/WAVES commissioning PLASTIC Space Weather S/WAVES MCPs to Ops Antenna EA Mode PLASTIC Deployment Test ESA on Figure 1. STEREO phasing orbits and significant early operations. Ax, apogee x; Cal, calibration; COR1 and -2, coronagraphs 1 and 2; EA, Earth acquisition; ESA, electrostatic analyzer; EUVI, extreme ultraviolet imager; G&C, guidance and control; HGA, high-gain antenna; HI, heliospheric imager; IDPU, instrument data processing unit; IMPACT, In situ Measurements of PArticles and Coronal mass ejection Transients; LV, low voltage; MAG, magnetometer; MCPs, microchannel plates; Px; perigee x; PLASTIC, PLAsma and SupraThermal Ion Com- position Investigation; Sx, lunar swingby x; SECCHI, Sun–Earth Connection Coronal and Heliospheric Investigation; SEP, solar energetic particles package; SEPT, solar electron and proton telescope; SIT, suprathermal ion telescope; STA, STEREO A; STB, STEREO B; STE, supra- thermal electron telescope; S/WAVES, STEREO/WAVES; SWEA, solar wind electron analyzer; TCM, trajectory correction maneuver; TIP, target interface point. JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 28, NUMBER 2 (2009) 127­­­­ J. E. EICHSTEDT ET AL. the Thermosphere, Ionosphere, Mesosphere Energetics such that for most MOC functions, there are separate and Dynamics (TIMED) program. Operating only the hardware/software components for each spacecraft. This spacecraft bus and engaging a highly automated system, approach minimizes the risk of confusion among opera- STEREO mission operations are able to use a small team tors and other personnel, and it allows for the simultane- to safely operate two spacecraft simultaneously. The ous operation of both spacecraft. The STEREO ground STEREO ground system was developed to support this system architecture is shown in Fig. 2 and described in concept of highly automated operations from the APL the following paragraphs. Mission Operations Center (MOC) and multiple Payload The STEREO ground system is segmented into sev- Operations Centers (POCs). In addition, the STEREO eral distinct network “zones.” This design ensures the ground system includes a STEREO data server (SDS) for integrity of the STEREO spacecraft as well as STEREO distribution of all of the data and products required for and APL network resources. All real-time command operation of the STEREO observatories, as well as two and control of the STEREO spacecraft originates in the hardware-in-the-loop (HIL) simulators for verification STEREO ground system Restricted IONet (Internet Pro- of commanding and analysis of anomalies. This paper tocol Operational Network). The Restricted IONet is a will discuss the STEREO ground system used by mission secure NASA network that places secure controls on the operations as well as the processes and tools used by mis- users and facilities. Each spacecraft has a primary and a sion operations for planning, real-time operations, and backup command workstation in the Restricted IONet. assessment of spacecraft performance. These processes Dedicated Memory Allocation Examiner (or “MAX”) and tools allow for the safe operation of two spacecraft workstations for each spacecraft are also located on this by a minimum number of staff while maintaining a high network. Additionally, each spacecraft has a third com- rate of science data return. mand workstation, one that is remotely located in a sep- arate building on the APL campus. These workstations GROUND DATA SYSTEM/NETWORK ARCHITECTURE would be used to ensure spacecraft health and safety The STEREO ground system was developed with in the event that the entire STEREO MOC becomes the intention that the two spacecraft could be oper- inaccessible. ated simultaneously and independently of each other. The STEREO firewall isolates the Restricted IONet To achieve this goal, the ground system architecture is from the remaining components of the STEREO MOC APL APL MOC Multimission MOC A A B B Disaster STEREO Data Server/ Second- Recovery Command/Telemetry Database/ POC Command Level Workstations Workstations File Server Telemetry Archive/ Server Archive Data Servers Restricted Restricted IONet Ops DMZ IONet STEREO A A B B Firewall Backup Workstations Printers MAX Workstations Data XTerms Assessment StateSim Plotter/ HIL Workstations (6) Scheduler Simulator Ground APL JPL/DSMS Stations Connection via Internet Firewall APL Intranet STEREO STEREO Flight Science SECCHI STEREO Dynamics POC Center Archive Facility S/WAVES POC PLASTIC POC IMPACT Testbeds Spacecraft POC Visualizer Figure 2. STEREO ground system architecture. 128 JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 28, NUMBER 2 (2009) STEREO MISSION OPERATIONS ground system, which reside in the operations “demili- instrument has primary POCs located at their home tarized zone” (Ops DMZ) network (which has fewer institutions, which also have access to the STEREO restrictions and is a less secure network). Among the instrument command and telemetry servers, as well as equipment in the Ops DMZ are six STEREO assess- the SDS, via an Internet connection.