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THEMIS program: an Overview
Vassilis Angelopoulos THEMIS Principal Investigator
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THEMIS was selected on March 20, 2003
as the next NASA/MIDEX mission (#5) to study the: Onset and evolution of magnetospheric substorms Addresses a 30yr old question (the holy grail) in magnetospheric physics A 5 spacecraft (probe) mission Single launch vehicle (Delta 2925) Launch in August of 2006 In Tail (midnight) on February 21, 2007/2008 Two year nominal duration Extended phase of 2 years possible (overlap with Cluster and MMS) Details at:
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MAGNETOSPHERE EQUATORIAL PLANE SOLAR WIND
Auroral eruptions and substorms Auroral eruptions… …are a manifestation of magnetospheric substorms SOLAR WIND Aurora MAGNETOSPHERE EQUATORIAL PLANE
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Compelling science driver
Substorms are: Fundamental processes… …and important for space science …for understanding magnetospheric transport … for basic physics … for space weather and society Sun-Earth-Connections Objective #1: “Understand the changing flow of energy and matter through … planetary magnetospheres” US National Academy of Sciences: “A strategic question in space physics” SEC Objective#2: Explore fundamental physical processes of plasma systems SEC Objective #3: “Define origins and societal impacts of variability in SEC”
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Most important science result and its science impact
Answers how substorms operate Explains how magnetospheres process solar wind energy Explains how auroras erupt ASTROSPHERE GALACTIC CONFINEMENT SUBSTORM RECURRENCE: MERCURY: 10 min EARTH: 3.75 hrs JUPITER: days
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Events occuring during a substorm
Current Disruption Reconnection Auroral Eruption
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Primary Objectives, Goals and Means Onset and evolution of substorms
Distinguishes among competing models: impartially answers a well-posed question… Primary Objectives, Goals and Means Onset and evolution of substorms Time History of Events (Onset)… Delineate cause and effect Measure WhenWhere … and Macroscale Interactions during Substorms (Evolution) Coupling in the magnetosphere Measure plasma flows and waves Coupling to the ionosphere Measure currents and structures ? Rarefaction wave ? Current Disruption Model time Event 0 sec Current Disruption 30 sec Auroral Eruption 60 sec Reconnection ? Reconnection Model time Event 0 sec Reconnection 90 sec Current Disruption 120 sec Auroral Eruption GBO P5 P4 P3 P2 P1 …as implied by Themis, goddess of impartial justice Flows
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Mission elements Probe conjunctions along Sun-Earth line recur once per 4 days over North America. Ground based observatories completely cover North American sector; determine auroral breakup within 1-3s … … while THEMIS’s space-based probes determine onset of Current Disruption and Reconnection each within <10s. : Ground Based Observatory
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Extensive orbit study shows high event yield
THEMIS’s goal is to study >10 substorms w/ 4- or 5–probe alignments along X [limit case]. Met w/ >50% margin by a fault-tolerant orbit strategy. Need 188hrs; have 300hrs/yr (>50% margin) computation includes lunar, solar, drag, J2 terms Conditions: dYP1,2,3,4,5<±2RE; dZP2,3,4/NS<±2RE Ascent: minimizes shadows and post-L&EO ops maximizes science (conjunction durations) Mission immune to probe insertion errors RCS capability of dV<8cm/s exceeds rqmt dV<80cm/s … 3rd stage insertion errors long duration piece-wise major DVs with ground contact .
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Mission overview: Fault-tolerant design has constellation and instrument redundancy
SST ESA EFIa EFIs FGM SCM Tspin=3s BGS CCAS Operations UCB Encapsulation & launch Mission I&T Swales Probe instruments: ESA: Thermal plasma (UCB) SST: Super-thermal plasma (UCB) FGM: Low frequency magnetic field (TUBS/IWF) SCM: High frequency magnetic field (CETP) EFI: Electric field (UCB, LASP) Instrument I&T UCB Ground
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Synergy with Cluster and MMS
Ideal overlap of objectives and orbits With MMS (2008) With Cluster/DoubleStar (2006)
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Inspires young minds and excites public
“Student-operated instruments detect space storms affecting satellites and humans in space” EPO ground magnetometers at K-12 schools: Promote inquiry-based and theme-based instruction Allow hands-on student participation Captures public imagination: Auroral eruption trigger identified in space Substorms, key to predicting space weather Expands on existing partnerships and resources: Space Grant Consortium Science museums International collaborations SFUSD Teachers ‘01 RHESSI Solar Camp ‘00 Total eclipse ’98, SF Exploratorium
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Summary Fully answers a compelling science question Ushers a new era in magnetospheric physics Benefits international space science program Unique Timely: Science and technology pathfinder
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