Continuous Global Birkeland Currents from the Active Magnetosphere and Planetary Electrodynamics Response Experiment Brian J Anderson, The Johns Hopkins University Applied Physics Laboratory
Partners Sponsor National Science Foundation Data provider Boeing Service Company Data source Iridium Satellite LLC PI Institution, Science Data Center The Johns Hopkins University Applied Physics Laboratory
Iridium Capabilities • Magnetometer on every satellite – Part of attitude control system – 30 n. T resolution: S/N ~ 10 • >70 satellites, 6 orbit planes, ~11 satellites/plane • Six orbit planes provide 12 cuts in local time • 9 minute spacing: re-sampling cadence • 780 km altitude, circular, nearpolar orbits (86° inclination) • Polar orbits guarantee coverage of auroral zone • Global currents never expand equatorward of system
Science • Objective: To understand the global-scale coupled electrodynamic response of the ionosphere and magnetosphere to solar wind forcing. • Capability: Provide the first global continuous observations of the Birkeland currents with sufficient time resolution/re-sampling cadence to chart the system’s dynamics.
Telemetry Solution SC health telemetry packet MAG samples (0. 1% of total) • Existing system: – Magnetometer data embedded in satellite engineering data packet – Enormous quantity of engineering data: voltages, currents, temperatures, other attitude sensors, RF system (rec’d intensities), power system (arrays/batteries), computer/memory monitors … • Modification: – Use alternate path: event message. Designed for satellite to report ‘event’ of interest to operators – New software to query magnetic field from attitude system processor – Pack set of magnetic samples (~10 to 100) in an event message. – Event messages delivered in continuously, sequentially (SV 001, 002 …) using satellite network to ground station in true real-time
Development Effort • Space software upgrade and installation • Ground data system to extract and archive data at Iridium operations center • AMPERE Science Data Center: capability to ingest real-time (100 x more than current), 24/7 data acquisition and product generation Flight Software Ground Architecture Real-time stream Supplementary Product Generation TLM files Real-time Extractor & Processor Data Accounting Database TLM files Store & dump Store-dump Extractor & Processor Data Transmission Constellation JHU/APL AMPERE Science
Processing & Data • • ΔB map via spherical harmonic fit to horizontal perturbations j|| from curl(ΔB): arbitrary geometry & conductances Data: 24/7, ~15 min latency to j||; definitive products ~ weekly 9 min cadence for Birkeland currents: set by inter-spacecraft spacing Cross-track DB Spherical harmonic fit: DB Downward J|| j|| = curl DB Upward J|| 00 UP Iridium: 22 Apr 2001 0800 -1000 UT
Magnetosphere Flow Ionosphere Convection Field lines convey potential Momentum Finite conductance - current Currents convey stress Energy dynamo Dissipation - drag EM Energy Flux
Operations Plan • Nominal operation – 20 s sampling on every satellite – Sufficient to resolve large-scale features – 9 minute cadence • Enhanced rate operations – 2 s on all satellites (normally ~20 s) – Promotion either via alarm (automated) or scheduled (campaign) – 36 -hour promotion span – 16 per year budgeted – Effected in ~1 hour
Relation to RBSP • Magnetosphere-ionosphere specification – Reflect expansion/relaxation in latitude of current source regions – Constrain distribution of ring current – Assimilation for inner magnetosphere models: empirical (TSclass) & physical (RCM and CRCM) – Boundary condition for MHD simulations: validation • Dynamics resolvable with 9 -min time cadence – Storm phases main & recovery: hours – Sub-storm growth and recovery, sawtooth events: ~10 s of minutes – Magnetosphere reconfiguration: ~ 10 s of minutes • Supplemental product – Upset counters: multiple on-board processors continuously scrub RAM and monitor memory bit upsets. – Reported from all SVs in nominal engineering TLM (200 s) – To be explored for usefulness during development
Development Timeline First ‘light’ Testing and validation Real-time development ‘Burst’ promotion Completion Dec 2009 CY 2010 CY 2011 CY 2012 May 2013 • Release of products will occur during development as they are ready
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