Continuous Global Birkeland Currents from the Active Magnetosphere and Planetary Electrodynamics Response Experiment Brian J Anderson, The Johns Hopkins University Applied Physics Laboratory

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 Partners

Iridium Capabilities Magnetometer on every satellite –Part of attitude control system –30 nT 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, near- polar 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 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 (SV001, 002 …) using satellite network to ground station in true real-time SC health telemetry packet MAG samples (0.1% of total)

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 (100x more than current), 24/7 data acquisition and product generation Data Accounting TLM files Real-time Extractor & Processor Store-dump Extractor & Processor Database TLM files Constellation Store & dump Real-time stream JHU/APL AMPERE Science Data Transmission Supplementary Product Generation Flight SoftwareGround Architecture

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 Iridium: 22 Apr UT Spherical harmonic fit:  B Cross-track  B j || = curl  B 00 UP Upward J || Downward J ||

MagnetosphereIonosphere Flow Convection Field lines convey potential Currents convey stress MomentumFinite conductance - current Dissipation - dragEnergy dynamo 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 (TS- class) & 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: ~10s of minutes –Magnetosphere reconfiguration: ~ 10s 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 (200s) –To be explored for usefulness during development

Development Timeline First ‘light’ Dec 2009 Testing and validation CY 2010 Real-time development CY 2011 ‘Burst’ promotion CY 2012 CompletionMay 2013 Release of products will occur during development as they are ready