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

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.

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

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

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)

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

Mission overview: Fault-tolerant design has constellation and instrument redundancy SST ESA EFIa EFIs FGM SCM Tspin=3s BGS D2925-10 @ 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

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, P @ 10s and fast modes on Bxyz and Exy @ 60 Hz FGM ESA SCM FGM ESA SCM 4EFIs 2EFIa ESA 2EFIs TOTAL Minumum mission (Red) Baseline add-ons (green) SCM 2EFIs

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.

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

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

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)

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

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

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

BACKUP SLIDES

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)

… 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)

… 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)

Minimum L1 Requirements (from L1’s) 4.1.2.1 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. 4.1.2.2 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 CD site (~8-10 Re). …(same as baseline) 4.1.2.3 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) 4.1.2.4 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. 4.1.2.5 Energetic ion and electron fluxes SST to measure near the ecliptic plane (+/-30o) superthermal i+ and e- fluxes (30-100keV) at t_res<30s. 4.1.2.6 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.