1. S. Frey, UCB, THEMIS 1 25th ISSFD, Munich, Germany, Oct.19-23, 2015 ARTEMIS THEMIS ARTEMIS The Revised Concept of the THEMIS and MMS Coordination Sabine Frey 1, Vassilis Angelopoulos 2, Manfred Bester 1 1 University of California – Berkeley 2 University of California – Los Angeles Time History of Events and Macroscale Interactions during Substorms

2. S. Frey, UCB, THEMIS 2 25th ISSFD, Munich, Germany, Oct.19-23, 2015 ARTEMIS THEMIS ARTEMIS Overview Motivation Revised THEMIS – MMS Alignment THEMIS – MMS Coordination THEMIS Orbit Redesign 2015 – 2020 Synchronizing Apogee Passes in 2015 and 2016 Summary http://themis.ssl.berkeley.edu http://www.nasa.gov/themis

3. S. Frey, UCB, THEMIS 3 25th ISSFD, Munich, Germany, Oct.19-23, 2015 ARTEMIS THEMIS ARTEMIS Motivation Goals: Improve understanding of coupling mechanisms across the entire magnetospheric system Quantify the effect of global processes on local phenomena Predict space weather Achieved by: Prolonged simultaneous observations at key regions: Reconnection sites at magnetopause (1), In the tail (2) Inner magnetosphere (3), Polar regions (4) Utilized by: Synchronized Orbits of THEMIS and MMS Coordinated space and ground assets of the Heliophysics Observatory Neutral Sheet 1 2 4 4 3

4. S. Frey, UCB, THEMIS 4 25th ISSFD, Munich, Germany, Oct.19-23, 2015 ARTEMIS THEMIS ARTEMIS Revised THEMIS – MMS Alignment  Originally nested tetrahedron of 7 S/C to study reconnection  Revised concept: Opposing apogees on day and night sides Apogee passes synchronized with GBOs and HSO space and ground systems to study coupling of day and night sides across polar regions Orbits shown sun referenced in ecliptic plane looking from north, sun to the left Dayside Nightside Dec. 2015 Jun. 2016 Jul. 2017 Jan., Sep. 2020 MMS THM THEMIS Ground Based Observatories in North America A ground asset of the Heliophysics System Observatory ARTEMIS @55R E MMS phase 1 MMS phase 1 MMS phase 2 MMS phase 2

5. S. Frey, UCB, THEMIS 5 25th ISSFD, Munich, Germany, Oct.19-23, 2015 ARTEMIS THEMIS ARTEMIS THEMIS – MMS Coordination Challenges of the multi-mission coordination despite similar science goals: Resolved by planning process that started long before MMS launch:  Long term planning to address alignment of lines of apsides by differential precession  Short term planning to address synchronization of apogee pass times in coordination with HSO assets THEMIS 8 years in orbit Nominal mission accomplished Limited fuel reserves Apogee pass times constrained by GBO conjunctions Fuel efficiency relies on long term planning MMS Launch uncertainties Fuel committed to ensure nominal science No time constraints on apogee pass times Probe separations are frequently reassessed based on recent observations

6. S. Frey, UCB, THEMIS 6 25th ISSFD, Munich, Germany, Oct.19-23, 2015 ARTEMIS THEMIS ARTEMIS THEMIS Orbit Redesign 2015 - 2020 Main Design Driver Primary science of extended mission phases Resonant orbits with MMS and HSO conjunctions Re-entry commitment Fuel efficiency Systems safety Main Orbit Design Component Apogee altitudes 11.5 – 16 Re, clustered in 2015, string-of-pearls in 2020 Discrete periods resonant with MMS and GBOs : T S, 8/7∙T S, 1/2∙T MMS, 4/3∙T S Minimize de-orbit maneuver Maneuver strategy Perigee altitude above 650 km T S sidereal period, T MMS MMS period P3 P4, P4 P5 Remaining Fuel After de-orbit maneuver Perigee Altitude No reduction before 2020 2017 2018 2019 2020 Apogee Altitude Final 13.2 Re defined by P5 MMS phase 1 MMS phase 2

7. S. Frey, UCB, THEMIS 7 25th ISSFD, Munich, Germany, Oct.19-23, 2015 ARTEMIS THEMIS ARTEMIS Synchronizing Apogee Passes in 2015 and 2016 P5 T7 P5 D7 drp=50km P3,P4 T7,D7 drp=0km P5 T8 drp=80km P4 T8 drp=90km P3 T8 drp=90km Perigee Raises May 2015 June 2015 Dec 2015 1 st Set period to drift per month 15 deg longitude, -1h UT at apogee 2 nd Set sidereal period to stop drift target Dayside season 7 100 0 -100 100 0 -100 Geographic Longitude of Apogee Passes [deg [deg] Days since 2016-Feb-16 -50 0 50 100 200 300 Dayside season 8 P3 110 days drift to target P4 80 days drift to target GBO MMS on dayside, phase 1 THEMIS on nightside, tail 8 Centered in December 2015 THEMIS planning had to start prior to MMS launch and account for launch delay and dispersion Two sequences of small maneuvers in spring 2015 to: Cluster all three probes by summer Synchronize apogee with MMS Raise perigee altitudes above 650 km MMS on nightside, phase 1 THEMIS on dayside, day 8 Centered in June 2016 Conjunction with South Pole ground observatories and MMS requires different UT targets for THEMIS probes; Set of small maneuvers includes perigee raises

8. S. Frey, UCB, THEMIS 8 25th ISSFD, Munich, Germany, Oct.19-23, 2015 ARTEMIS THEMIS ARTEMIS Predicted alignment for 2015-12-11 at 9.5 UT Summary Cluster THEMIS (night), MMS (day), Van Allen Probes, ARTEMIS at lunar distances THEMIS is committed to align with current and future HSO missions for a system-wide approach to study the dynamic interaction of the Earth’s magnetosphere with its space environment. THEMIS is progressively utilizing its fuel reserves towards the coordinated multi-mission constellation The revised alignment of THEMIS-MMS will provide prolonged simultaneous observations on the day and nightside. Coordinated observations with HSO space assets will deliver the global context. Synchronized observations with HSO ground systems will link processes across the magnetosphere. Challenges due to MMS launch delays and dispersion have been overcome. The first year of coordinated observations is underway. Many thanks to all supporters of this multi-mission endeavor, the MMS team, and the THEMIS operations and flight dynamics teams