Radiation Belt Storm Probe • Electric Field and Waves Instrument • (EFW) • Prof. John Wygant (PI, UMN)
Science and Measurement Objectives (1) • Science Objective: Measure electric fields associated with a variety of mechanisms causing particle energization, scattering and transport in the inner magnetosphere. • These mechanisms include: • Energization by the large-scale convection E-field. • Energization by substorm injection fronts propagating in from the tail. • Radial diffusion of energetic particles mediated by ULF MHD waves. • Transport and energization by intense magnetosonic waves generated by interplanetary shock impacts upon the magnetosphere. • Coherent and Stochastic acceleration and scattering of particles by small-scale, large-amplitude plasma structures, turbulence and waves (EM and ES ion cyclotron waves, kinetic Alfven waves, solitary waves, electron phase space holes, zero freq. turbulence)
Personnel (1) • Science Team: • University of Minnesota • John Wygant, P-I • Cindy Cattell, Data Analysis, • John Dombeck, Data Analysis, • SSL, Berkeley • John Bonnell Lead EFI Hardware • Forrest Mozer (Technical/Design Advisor) • Chris Chaston (Data Analysis, Theory, Simulations) • Stuart Bale (Data Analysis, Theory) • University of Colorado, Boulder • Bob Ergun, Lead Digital Signal Processing Board • Dan Baker Data Analysis • Xinlin Li Theory/Simulations • EFW Non-Hardware Co-I Institutions: • Mary Hudson, Dartmouth College - Data Analysis/Theory /Simulations • Jay Alpert, Don Brautigam, AFRL -Data Analysis Theory/Modeling • John Foster, Haystack Observatory/MIT Mid latitude Radar: Ionospheric E fields • Ian Mann, University of Alberta, Edmonton: Ground magnetometer arrays/ Mode
Why Measure E on RBSP? • The Dynamics of the Earth’s Radiation Belts are all about particle energization, scattering, and transport; in other words, particle acceleration. • In collisionless plasmas, such as the Earth’s Radiation Belt, the electromagnetic field is responsible for all the observed particle acceleration. • Particle acceleration occurs in the Radiation Belts at a variety of spatial and temporal scales: • … from the large-scale E-field associated with the global circulation of plasma in the magnetosphere, down to small-scale structures in plasma density. • … from the slow pumping of particles by ULF waves, to the scattering and energization by high-frequency whistlers. • While EMFASIS concentrates on higher-frequency mechanisms, EFW looks to the lower registers of the EM spectrum, where a rich variety of phenomena await…
E-Fields in the Active Radiation Belt CRRES measurements of the E-field during a pass through the inner magnetosphere: interplanetary shock induced electric field, large scale MHD waves, and enhancement in convection electric field: March 1991 Main Phase MHD waves: an important mechanism for radially diffusing and energizing particles. The shock induced magnetosonic wave created a 5 order of magnitude increase in 13 MeV electron fluxes in <100 seconds resulting in a new radiation belt that lasted two years The large scale electric field produced a ~70 kV potential drop between L=2 & L-4 and injected ring current plasma. dDst/dt= - 40 nT/hr
Science and Measurement Objectives (3) • Key Measurement Quantities: • Spin plane component of E at DC-12 Hz (0.05 mV/m accuracy). • Spin axis component of E at DC-12 Hz (~3 mV/m accuracy). • E- and B-field spectra for nearly-parallel and nearly-perpendicular to B components between 1 Hz and 12 kHz at 6-s cadence. • Spacecraft potential estimate covering cold plasma densities of 0.1 to ~100 cm-3 at 1-s cadence. • Burst recordings of high-frequency E- and B-field waveforms, as well as individual sensor potentials for interferometric analyses.
RBSP-EFW Elements (1) Schematic Diagram of EFW
RBSP-EFW Elements (2) Resource Summary
RBSP-EFW: IDPU • Mass: 4.7 kg. • Dimensions: 9.75H x 4.7W x 7.95D inches (add 2-inch keepout for connectors to depth). • Power: 7.5 W (primary side, CBE). • Elements and Function: • Chassis – provides structural integrity and radiation shielding (7-mm Al equiv.). • Backplane – signal and power distribution. • Low-Voltage Power Supply (LVPS) and Power Controller Board (PCB) – power conversion, regulation, and switching. • Data Processing Unit (DPU) and Memory (SSR) – instrument control; data storage, routing, and compression. • Boom Electronics Board (BEB) – sensor and bias surface control. • Digital Signal Processing Board (DSP) – analog signal conditioning, ADC, digital waveform filtering, on-board spectral product calculation. • UIowa (EMFASIS) Interface Board (UII) – buffering of E-field signals to EMFASIS; buffering of B-field signals from EMFASIS; burst coordination signals; etc. (may be part of DSP or BEB).
RBSP-EFW: Response Model • Sheath impedance is Rs || Cs, and connects to SPHERE. • Output load is Cc || (Rc + RL), connected to Vout.
RBSP-EFW: SPB Example of SPB, Cable, Preamp, Fine Wire and Sphere (THEMIS Flight Model) • Mass: 2.2 kg/unit (4 total). • Footprint: 4.4H x 8.1W x 9.1D inches. • Deployed Length: 80/100 m tip-to-tip. • 47 m cable + 3 m fine wire in each SPB. • Deploy Rate: 0.5-1.0 cm/s. • Cable Mass Rate: ~3 g/m. • Fine Wire Mass Rate: < 1 g/m. • Preamp Mass: 48 g (up to 150 g w/up-shield and cable driver). • Sphere/Keyreel Mass: 100 g. • Deployed spin MOI: 600 or 360 kg-m2/boom (100-g preamp); 1920 kg-m2 total. • Power: 2.6 W/unit (typ., deploy motor only). • Actuators: Doors are spring-loaded, SMA or FrangiBolt-released; Cable deploy is motor-driven; no pyros required for actuation. RBSP-EFW: SPB Packaging Concept
RBSP-EFW: AXB Examples of AXB, Tube, and Preamp/Whip (THEMIS Flight Models): • Mass: 4 kg total (2 booms + tube). • Footprint: 41H x 5 to 6 OD inches. • Deployed Length: • 12 to 13 m tip-to-tip. • 1-m whip sensor stacer. • Power: 35 W max for 1-2 s, per boom (deploy only). • Actuators: deploy is spring-driven, Frangibolt-released; no pyros required for deploy.
RBSP-EFW: IDPU • Mass: 7.45 kg. • Dimensions: XXX cm. • Power: 7.5 W (primary side). • Elements and Function: • Chassis – provides structural integrity and radiation shielding (7-mm Al equiv.). • Backplane – signal and power distribution. • Low-Voltage Power Supply (LVPS) and Power Controller Board (PCB) – power conversion, regulation, and switching. • Data Processing Unit (DPU) and Memory (SSR) – instrument control; data storage, routing, and compression. • Boom Electronics Board (BEB) – sensor and bias surface control. • Digital Signal Processing Board (DSP) – analog signal conditioning, ADC, digital waveform filtering, on-board spectral product calculation. • UIowa (EMFASIS) Interface Board (UII) – buffering of E-field signals to EMFASIS; buffering of B-field signals from EMFASIS; burst coordination signals; etc. (may be part of DSP or BEB). IDPU Block Diagram
RBSP-EFW: DSP(2) • The DSP board provides analog conditioning of the signals from the E- and B-field sensors on RBSP, analog-to-digital conversion of those signals at 16-bit resolution, digital waveform filtering, and on-board FFT-based spectral product computations (auto- and cross-spectra). • All analog signals (V1-V6, E12, E34, E56 (both DC- and AC-coupled) and SCM1-3) are sampled at a constant 32-ksamp/s rate through the analog mulitplexer and switch system, and the three 256-ksamp/s ADCs. • The 3 ADCs can be reconfigured so as to maintain sampling at lower base rates if one or two fail during the mission. • Independent Survey and Burst digital filter chains provide anti-aliased and down-sampled waveform data at power-of-two intervals from 32 ksamp/s to 1 samp/s. • Broadband power-of-two Filter Bank channels are derived directly from the digital filter chain outputs for use in on-board triggering or Survey science output. • DC B-field data (EMFASIS fluxgate) used to rotate AC E- and B-Field into field-aligned coordinate system for input to on-board FFT-based spectral processing. • On-Board FFT-based spectral processing of AC E- and B-Field data used to produce auto- and cross-spectral data products.
Unique Requirements • SC Charging and Electrostatic Cleanliness (ESC) • SC potential symmetrization, in addition to charging control. • All exposed surfaces sufficiently conducting and tied together electrically. • See THEMIS ESC Specification for example of implementation and verification plan. • Spin Axis Pointing • RBSP spin axis shall point at least TBD degrees (CBE is >15 degrees) from Sun in order to ensure equal illumination of the two EFW axial sensors. • RBSP spin axis shall point at least TBD degrees (CBE is 3 deg) from Ecliptic Normal in order to ensure limited shadowing of the four EFW spin plane sensors. • Velocity and B-Field Accuracy • Determination of spacecraft vector velocity and local vector B-field must be such that the -VxB E-field estimate is accurate to 0.1 mV/m above 2 (TBR) Re altitude.
Technical Readiness • Boom Deployment Systems • TRL 9, based on ISEE, CRRES, Polar, FAST, Cluster-II, and THEMIS heritage. • Changes will include thinner cable, different accommodating SC. • Sensor Electronics (Preamp and BEB) • TRL 8, based on Polar, Cluster-II, and THEMIS heritage. • Changes will include thinner cable, possible cable driver. • IDPU Power, DSP, DPU, and Burst Memory • TRL 7-8, based on Polar, FAST and THEMIS heritage. • Changes will include interfaces to other instruments and SC, adjustments to filter frequencies and ADC rates, flight software changes.
System-Level Issues (1) • Radiation Environment • Mission-level consensus on radiation environment model. • Impact (cost, schedule) of comensurate parts plan. • Spin-Axis Pointing • Impact of different illumination on DC and AC systematic errors (EFW and EMFASIS). • Impact of pointing requirement (eg. Sun vs. Ecliptic Normal) on mission lifetime in nominal SC attitude. • Axial Boom Accommodation and SC Stability • Dual Axial booms to be accommodated along central axis of RBSP SC. • Potential for solar array shadowing issues in Sun-pointed attitudes. • Well-known and understood issues of dynamic stability (spin/transverse MOI requirements).
Phase A Activities • Develop Management Plan (Organization, Cost, Schedule, etc.). • Participate in Requirements definition and flow-down efforts. • Participate in Spin Axis Pointing trade study. • Participate in Spacecraft Accommodation Studies, including: • On-axis booms • SC charging and ESC specification. • C&DH system interface • Boom mounting and dynamics • Thermal interface • Perform EFW Design Trade Studies, including: • Choose custom Gore cable for SPBs (mass vs. electrical response). • Define EFW frequency response and noise level requirements (joint with EMFASIS). • Choose processor for DPU (8085 or FPGA-based). • Choose preamp floating supply range (100 vs. 250 volts). • Define capabilities of on-board Burst and Spectral Product systems. • Define EFW-EMFASIS interface.
Integration and Test Plan (1) • Instrument Level I&T (occurs at UCB): • Preamp Thermal Qualification and Acceptance Test: • Performed informally on previous missions (Polar, Cluster, FAST), and formally as part of parts qualification on THEMIS. • Preamps generate little internal heat, and are either isolated from SC heat sources (SPB), or attached to efficient radiators (AXB). • Thus, preamp enclosure and PWB exposed to relatively extreme temperature swings during eclipse: • THEMIS Tmin of -135 C for 3-hour eclipse. • 1 C/min rate of cooling. • Batch of complete ETUs (8 on THEMIS) run through TBD hot-cold cycles to verify design meets or exceeds performance requirements. • Each Flight Preamp run through TBD hot-cold cycles to verify that the unit meets or exceeds performance requirements.
Integration and Test Plan (2) • Instrument Level I&T, con’t (occurs at UCB): • Boom Unit (SPB, AXB) Vibe, Functional and TVAC Testing: • Vibe tests as per GEVS requirements: • Levels as per launch vehicle environment and SC modeling. • Tests performed in Bay Area (Quanta Labs, for example). • Performance Tests (Science and Engineering). • Performed at Ambient; Hot and Cold TVAC. • Limited DC and AC Functional Tests (gain, offset, phase at DC and selected frequencies). • Mechanical and actuator performance: • Motor, SMA, or frangiBolt current at min, max, and nominal supply voltages. • Deployed length measurement and length indicator calibration. • Run-out (straightness) and 1st-mode estimation (AXB only).
Integration and Test Plan (3) • Instrument Level I&T, con’t. (occurs at UCB): • Sensor and BEB Calibration (Science Cal, or SciCal). • Detailed calibration of Sensor and BEB operation and verification of required performance. • Instrument transfer function vs. frequency (gain, phase, offset). • Bias current and voltage frequency response and offset control calibration. • Noise levels. • IDPU Functional, Vibe and TVAC Testing: • Electrical Performance Tests. • Commanding and Instrument Modes Tests. • UII Testing. • Boom Deploy Testing (Simulated and Actual). • Power control and consumption. • Software control of SPB boom deploy.
Integration and Test Plan (4) • Suite and SC level I&T: • Fields Phasing and Timing Test: • Establishes relative phase and/or time delay between EFW and EMFASIS fields channels. • Electrostatic Cleanliness verification: • All instruments and spacecraft subsystems. • Functional Tests: • Commanding: • Instrument Modes (Survey, Burst, Common Burst, etc.). • Instrument Commissioning and Boom Deploy. • TM Playback. • Compatibility: • conducted and radiated EMI/EMC. • commanding and functionality (“playing well with other instruments and the spacecraft”). • Note that significant “self-test” capability exists in current design; ie. Minimal GSE required for performance testing at Suite and SC level.
Parts • Grade 2 parts program per Geospace MAR and EEE-INST-002 • Baseline is THEMIS parts list (Grade 2/3) • Some parts will need to be qualified and/or rescreened • Qulaification/screening program needs to start early to minimize schedule risk • Possibility of a common buy should be considered to save $ • RBSP Radiation dose similar to what we qualified THEMIS parts to (25-50krad) behind 7mm equivalent Aluminum shielding • We are carrying mass for this level of shielding • Most parts meet these levels; a few parts may have issues: • Commercial 16-bit ADC • OP15 in preamp (at the end of the boom), requires tantalum shield like THEMIS. Some tests indicate we may have parametric problems at RBSP radiation levels. • Other Radiation issues to be addressed as needed: • ELDR effects, SEL, SEU, Displacement Damage
Bonus Content • (Backup Slides)
CRRES Extreme SC Charging Event Spacecraft Charging on CRRES During an Injection Event near Geosynchronous Orbit (E-field and LEPA Particle data) • One orbit (10 Hrs) of CRRES data from perigee to apogee and back to perigee) • Top panel:from Electric field instrument: Negative of probe-spacecraft potential in Volts vs day of the year in 1991 indicating several hour intervals when SC potential was less than - 90 V. • Low Energy Plasma Analyzer Data (courtesy D. Brautigam, AFRL) showing simultaneous evidence for spacecraft charging in 90 deg. electrons (top color panel) on same scale. The electrons are repelled from spacecraft and produce a low counts (black)at energies below that of the spacecraft potential • Ions (perp) on an inverted scale show enhancement of flux at SC potential (second color panel |Perigee |Apogee | Perigee
AXIAL BOOMS • Main Boom Properties • Same Stacer Geometry as Themis, but Longer (5.0m vs 2.2m) • Formed from 0.005” x 5” Elgiloy Strip Material (0.70”f tip ; 1.20”f base) • Equivalent Tube Flexural Stiffness ≈ 62000 lb in2 • Projected Cantilever Resonance ≈ 0.5 Hz (30 RPM) • Bending (Buckling) Limit ≈ 300 lb in (at 2m deflection) • Stub Boom Properties • Same Stacer Geometry as Polar Stubs, but Longer (1.0m vs 0.6m) • Formed from 0.002” x 2” Elgiloy Strip Material (0.25”f tip ; 0.38”f base) • Equivalent Tube Flexural Stiffness ≈ 1000 lb in2 • Projected Cantilever Resonance ≈ 4 Hz (240 RPM) • Bending (Buckling) Limit ≈ 27 lb-in (at 0.3m deflection)