1. TIME HISTORY OF EVENTS AND MACROSCALE INTERACTIONS DURING SUBSTORMS (THEMIS)
SCIENCE GOALS:
Primary:
“How do substorms operate?”
One of the oldest and most important questions in Geophysics
A turning point in our understanding of the dynamic magnetosphere
First bonus science:
“What accelerates storm-time ‘killer’ electrons?”
A significant contribution to space weather science
Second bonus science:
“What controls efficiency of solar wind – magnetosphere coupling?”
Provides global context of Solar Wind – Magnetosphere interaction
RESOLVING THE PHYSICS OF ONSET AND EVOLUTION OF SUBSTORMS
Principal Investigator
Vassilis Angelopoulos, UCB
EPO Lead
Nahide Craig, UCB
Program Manager
Peter Harvey, UCB
Industrial Partner
SWALES Aerospace

2. Science Overview
THEMIS determines where and how substorms are triggered.
Substorms are…
…important to NASA:
Fundamental mode of magnetospheric circulation
Important for geo-storms have societal implications.
Rich in new types of basic space plasma physics.
SEC Roadmap: “Understand energy, mass and flux transport in Geospace”
SEC Roadmap: “How does solar variability affect society?”
NRC, National Academy: A strategic question in space physics (1995).
Auroral eruptions are recurrent (~3-6hrs)
Magnetospheric substorms are responsible for auroral eruptions.

3. Current Disruption Model
Events occuring during a substorm
Current Disruption
Reconnection
Auroral Eruption P2 P1 P3 P5 P4
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

4. Mission elements
Probe conjunctions along Sun-Earth line recur once per 4 days over North America.
Ground based observatories completely cover North American sector; can determine auroral breakup within 1-5s …
… while THEMIS’s space-based probes determine onset of Current Disruption and Reconnection each within <10s.
: Ground Based Observatory

5. Science Objectives
THEMIS HAS FOCUSED MINIMUM (TO BASELINE) OBJECTIVES:
Time History of Events…
Auroral breakup (on the ground)
Current Disruption [CD] (2 probes at ~10RE)
Reconnection [Rx] (2 probes at ~20-30RE)
… and Macroscale Interactions during >5 (>10) Substorms (Primary):
Current Disruption and Reconnection coupling
Outward motion (1600km/s) of rarefaction wave
Inward motion of flows (1000km/s) and Poynting flux.
Ionospheric coupling
Cross-tail current reduction (P5u/P4) vs flows
Field aligned current generation by flow vorticity, pressure gradients (dP/dz, dP/dx).
Cross-scale coupling to local modes
Field line resonances (10RE, 5 min)
Ballooning modes, KH waves (1RE, 1min)
Weibel instability, cross-field current instability, kinetic Alfven waves (0.1RE, 60Hz)
Production of storm time MeV electrons (Secondary)
Control of solar wind-magnetosphere coupling by the bow-shock, magnetosheath and magnetopause (Tertiary)

6. Probe conjunctions well understood
BASELINE: >10 substorms achieved w/ 5 probes in 2 yrs & 50% margin.
MINIMUM: >5 substorms achieved in 1yr w/ 4 probes (margin factor of 3).
computations include lunar, solar, drag, J2 terms
dYP1/2/3/4/5<±2RE; dZP3,4,5/NS<±2RE; dZP1,2/NS<±5RE
Ascent design is optimal for science
maximizes conjunctions, minimizes shadows
… immune to launch insertion errors
small, piece-wise DVs increase placement fidelity
… and immune to probe insertion errors.
Can withstand insertion error of dV=80cm/s on any probe
Actual conjunction times in 1st year

7. 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 SST: Super-thermal plasma FGM: Low frequency B-field SCM: High frequency B-field
EFI: Low and high frequency E-field
Instrument I&T
UCB
Ground

8. Instruments required to achieve Primary Mission Objective
Selected instruments built en masse before
Identical instrumentation provides high science margins and fault tolerance
Instrument redundancy:
SST-ESA energy overlap
FGM-SCM frequency overlap
P1/P2 redundant instrumentation (only directional flux needed in one of two).
Each probe has:
1FGM
1ESA (i/e)
2SSTh (2heads, i/e)
1SCM
4EFIs (4spin plane)
2EFIa (2axials)
Instruments required to achieve Primary Mission Objective
Measurement goals P1 P2 P3 P4 P5
Time History of Events
P3,4&5 monitor CD P1,2 bracket Rx tres<30s, dY<±2RE
FGM
1SSTh
2EFIs
ESA
2SSTh
Macroscale Interactions
Track rarefaction wave, inward flows, Poynting with dB<1nT, dV/V~10%
Radial/cross-sheet pressure, velocity and current gradients require dP/P~ dV/V ~ dB/B ~10%, non-MHD
Cross-tail pairs measure FLRs, KH, ballooning on B, V, 10s and fast modes on Bxyz and 60 Hz
FGM ESA SCM
FGM ESA
SCM 4EFIs 2EFIa
ESA 2EFIs
TOTAL
Minumum mission (Red)
Baseline add-ons (green)
SCM 2EFIs

9. Mission profile is robust
Pre-Launch
(6hrs)
Launch
(25min)
Check-out & ascend
(60days)
Science ops
(2yrs)
Re-entry
Checkout
Countdown
2nd stage burn
Spin-up
3rd stage burn
Spin-down
Probe dispense
Bus check-out
Dply mags/check instr.
Orbit place. Total of:
- 6 side thrustings
- 6 reor/fire/reor sequences
Deploy EFI
Minor ctrl ops (all):
22 side-thrustings
2 inclination changes
- 8 side-thrustings
Passive re-entry thereafter (1-10yrs)
Minor ctrl ops (Side-thrusts, finish by EOM+9mo)
Fuel consumption, maneuvers and contacts during ascend: validated with GMAN.

10. First bonus: What produces storm-time “killer” MeV electrons?
Affect satellites and humans in space
ANIK telecommunication satellites lost for days to weeks during space storm
Source:
Radially inward diffusion?
Wave acceleration at radiation belt?
THEMIS:
Tracks radial motion of electrons
Measures source and diffusion
Frequent crossings
Measures E, B waves locally

11. Important for solar wind energy transfer in Geospace
Second bonus: What controls efficiency of solar wind – magnetosphere coupling?
Important for solar wind energy transfer in Geospace
Need to determine how:
Localized pristine solar wind features…
…interact with magnetosphere
THEMIS:
Alignments track evolution of solar wind
Inner probes determine entry type/size

12. Mission design meets requirements
Mission profile
Two year mission design easily met in this high Earth orbit
Launch: D2925 from CCAS (40min window any day) permits 32% lift margin
Simple probe carrier (3rd stage fixture) w/ release built by an experienced team
Science & routine ops and multi-object tracking has ample heritage at UCB
Simple RCS, heritage sfw & ground-cmd and GSFC/GNCD support benefits MOC
Probe design
Simple, passive thermal design w/ thermostatically controlled heaters
Survival at all attitudes under worst shadow conditions
Simple data flow / automated routine science ops minimize cost and risk
Store/Forward 375Mbit/orbit (256Mbyte capability permits multi-orbit storage)
Orbit control & knowledge exceed placement rqmts by factor of 10
Early EMC/ESC mitigation as per heritage practices (e.g. FAST, POLAR)

13. Active trade studies constantly reduce risk
An integrated team of scientists and engineers constantly optimize mission design and resources, reducing risk.
Phase A main trade studies:
Direct inject with passive PCA on larger LV reduces schedule and ops risks
PCA dispense simplified: improves clearances, reduces risk
Increased fuel tank capacity to take full advantage of mass to orbit capability, yet at lower cost
Added solar panels at bottom face
ACS solution simplified with micro-gyros replacing accelerometers
Connected RCS propulsion pods
Phase B main trade studies:
Exercised alternate path for SST instrument
Tuned Phase A orbit design to reduce differential precession; enhanced 2nd year science products
Changed BAU processor to reduce software complexity motivated by GSFC experience
Increased thruster size to reduce finite arc inefficiency and Msn Ops complexity
Repackaged SST and SCM electronics along with IDPU
Removed ESA attenuator (simplified instrument) with minimal effect on bonus science
Included redundant actuators and surge protection in instrument designs

14. Descope list and science-related risk mitigation factors
Re-positioning allows recovery from failure of critical instruments on some probes
Graceful degradation results from partial or even full instrument failures
Instrument frequency and energy range overlaps
Complete backup option for EFI radials (need 2 in most probes but have 4)
Relaxed measurement requirements (1nT absolute is not permitted to drive team, but rather a nicety)
Substorms come in wide variety; can still see large ones with degraded instruments
Minimum mission can be accomplished with a reduced set of spacecraft requirements
EMC and ESC requirements important for baseline but less severe for minimum mission
Observation strategy can be tuned to power loss (turn-on/off) and thermal constraints (tip-over/back)
Fuel and mass margins for 1st year (minimum) are 30% larger than for a two year (baseline) mission

15. Minimum mission provides definitive answer to the substorm question.
Simultaneous observations in the key regions
Ideal geometries for tens of substorms
Data rates / time resolution exceed requirements
Analysis tools available from Cluster, ISTP, FAST
Experienced co-Is are leaders on both sides of substorm controversy
5-probe build affords high reliability (Ps=0.93) for minimum mission (4/5) even with single string design
Minimum mission achieved within 8 mo. from nominal launch date (~1yr regardless of launch date) P5 P4 P3 P2 P1

16. BACKUP SLIDES

17. Baseline L1 Requirements
S-1 Substorm Onset Time
Determine substorm onset time and substorm meridian magnetic local time (MLT) using ground ASIs (one per MLT hr) and MAGs (two per MLT hr) with t_res<30s and dMLT<1 degree respectively, in an 8hr geographic local time sector including the US. (M-11, GB-1)
S-2 Current Disruption (CD) Onset Time
Determine CD onset time with t_res<30s, using two near-equatorial (within 2Re of magnetic equator) probes, near the anticipated current disruption site (~8-10 Re). CD onset is determined by remote sensing the expansion of the heated plasma via superthermal ion flux measurements at probes within +/-2Re of the measured substorm meridian and the anticipated altitude of the CD. (M-9, IN.SST-1, IN.SST-4, IN.FGM-1)
S-3 Reconnection (Rx) Onset Time
Determine Rx onset time with t_res<30s, using two near-equatorial (< 5Re from magnetic equator) probes, bracketing the anticipated Rx site (20-25Re). Rx onset is determined by measuring the time of arrival of superthermal ions and electrons from the Rx site, within dY=+/-2Re of the substorm meridian and within <10Re from the Rx altitude. ….. (M-9, IN.EFI-2, IN.ESA-1, IN.SST-2, IN.SST-3, IN.SST-4, IN.FGM-1)
S-4 Simultaneous Observations
Obtain simultaneous observations of: substorm onset and meridian (ground), CD onset and Rx onset for >10 substorms in the prime observation season (September-April). Given an average 3.75hr substorm recurrence in the target tail season, a 2Re width of the substorm meridian, a 1Re requirement on probe proximity to the substorm meridian (of width 2Re) and a 20Re width of the tail in which substorms can occur, this translates to a yield of 1 useful substorm event per 18.75hrs of probe alignments, i.e, a requirement of >188hrs of four-probe alignments within dY=+/-2Re. (M-1, M-12, IN.FGM-1)

18. … continued: Baseline L1 Requirements
S-5 Earthward Flows
Track between probes the earthward ion flows (400km/s) from the Rx site and the tailward moving rarefaction wave in the magnetic field, and ion plasma pressure (motion at 1600km/s) with sufficient precision (dV/V=10% or V within 50km/s whichever is larger, dB/B=10%, or B within 1nT whichever is larger, dP/P=10%, or P within 0.1nPa whichever is larger) to ascertain macroscale coupling between current disruption and reconnection site during >10 substorm onsets (>188hrs of four-probes aligned within dY of +-2Re). (IN.ESA-1, IN.SST-3, IN.FGM-1)
S-6 Pressure Gradients
Determine the radial and cross-current-sheet pressure gradients (anticipated dP/dR, dP/dZ ~0.1nPa/Re) and ion flow vorticity/deceleration with probe measurement accuracy of 50km/s/Re, over typical inter-probe conjunctions in dR and dZ of 1Re, each during >10 onsets. The convective component of the ion flow is determined at 8-10Re by measurements of the 2D electric field (spin-plane to within +-30degrees of ecliptic, with dE/E=10% or 1mV/m accuracy whichever is larger) assuming the plasma approximation at t_res<30s. (IN.EFI-1, IN.ESA-1, IN.ESA-2, IN.SST-3, IN.FGM-1)
S-7 Cross-Current Sheet changes
Determine the cross-current-sheet current change near the current disruption region (+/-2Re of meridian, +-2Re of measured current disruption region) at substorm onset from a pair of Z-separated probes using the planar current sheet approximation with relative (interprobe) resolution and interorbit (~12hrs) stability of 0.2nT. (IN.FGM-1, PB-42, PB-43, PB-44)
S-8 non-MHD plasma
Obtain measurements of the Magneto-Hydrodynamic (MHD) and non-MHD parts of the plasma flow through comparisons of ion flow from the ESA detector and ExB flow from the electric field instrument, at the probes near the current disruption region, with t_res<10s. (IN.EFI-1, IN.ESA-1, IN.SST-3, IN.FGM-1)

19. … continued: Baseline L1 Requirements
S-9 Cross-Tail Pairs
Determine the presence, amplitude, and wavelength of field-line resonances, Kelvin-Helmholz waves and ballooning waves on cross-tail pairs (dY=0.5-10Re) with t_res<10s measurements of B, P and V for >10 substorm onsets. (IN.ESA-1, IN.SST-3)
S-10 Cross-Field Current Instabilities
Determine the presence of cross-field current instabilities (1-60Hz), whistlers and other high frequency modes (up to 600Hz) in 3D electric and magnetic field data on two individual probes near the current disruption region for >10 substorm events. (IN.EFI-3, IN.ESA-3, IN.SCM-1)
S-11 Dayside Science
Determine the nature, extent and cause of magnetopause transient events (on dayside). (IN.ESA-4, IN.SST-6)

20. Minimum L1 Requirements (from L1’s)
Substorm Onset Time
Determine substorm onset time and substorm meridian magnetic local time (MLT) using ground MAGs (at least one per MLT hr) with t_res<30s and dMLT<6 degrees respectively, in a 6hr geographic local time sector including the US.
Current Disruption (CD) Onset Time
Determine CD onset time with t_res<30s, using two near-equatorial (within 2Re of magnetic equator) probes, near the anticipated CD site (~8-10 Re). …(same as baseline)
Reconnection (Rx) Onset Time
Determine Rx onset time with t_res<30s, using two near-equatorial (<5Re of magnetic equator) probes, bracketing the anticipated Rx site (20-25Re). … (same as baseline)
Simultaneous Observations
Obtain simultaneous observations of: substorm onset and meridian (ground), CD onset and reconnection onset for >5 substorms in the prime observation season (September-April). Substorm statistics discussed in S-4 point to a requirement of >94hrs of four probe alignments.
Energetic ion and electron fluxes
SST to measure near the ecliptic plane (+/-30o) superthermal i+ and e- fluxes (30-100keV) at t_res<30s.
Earthward Flows
Track between probes the earthward ion flows (400km/s) from the reconnection site and the tailward moving rarefaction wave in the magnetic field, and ion plasma pressure (motion at 1600km/s) with sufficient precision precision (dV/V=10% or V within 50km/s whichever is larger, dB/B=10%, or B within 1nT whichever is larger, dP/P=10%, or P within 0.1nPa whichever is larger) to ascertain macroscale coupling between current disruption and reconnection site during >5 substorm onsets.