1. THEMIS program: an Overview
Vassilis Angelopoulos
THEMIS Principal Investigator

2. 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:

3. MAGNETOSPHERE EQUATORIAL PLANE SOLAR WIND
Auroral eruptions and substorms
Auroral eruptions…
…are a manifestation of magnetospheric substorms
SOLAR WIND
Aurora
MAGNETOSPHERE
EQUATORIAL PLANE

4. 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”

5. 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

6. Events occuring during a substorm
Current Disruption
Reconnection
Auroral Eruption

7. 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 WhenWhere
… 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

8. 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

9. 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 .

10. 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

11. Synergy with Cluster and MMS
Ideal overlap of objectives and orbits
With MMS (2008)
With Cluster/DoubleStar (2006)

12. 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

13. 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