THEMIS ELECTRIC FIELD INSTRUMENT (EFI) Dr. John Bonnell and the THEMIS EFI Team University of California-Berkeley University of Colorado-Boulder

Outline Personnel and Organization Summary of EFI Status at MPDR Requirements, Specifications, and Design Compliance Design Overview Top-Level Design Designs of Individual Elements Design Drivers and Compliance DC Error Budget AC Error Budget Schedule Design Long-Lead Procurement ETU EPR Results

Personnel and Organization Organizational Chart (all UCB unless noted): Prof. F. Mozer (EFI Co-I). Drs. J. Bonnell, G. Delory, A. Hull (Project Scientists) P. Turin (Lead ME) Dr. D. Pankow (Advising ME) B. Donakowski (EFI Lead ME, SPB) R. Duck (AXB ME) D. Schickele (Preamp, SPB ME) C. Smith (THEMIS Thermal Eng) S. Harris (BEB Lead EE) H. Richard (BEB EE) R. Abiad (BEB FPGA Eng) G. Dalton (EFI GSE Mechanical and General Mechanical) J. Lewis, F. Harvey (GSE) Technical Staff (H. Bersch, Y. Irwin, H. Yuan, et al.) R. Ergun (DFB Co-I; CU-Boulder) J. Westfall, A. Nammari, K. Stevens (DFB Eng; CU-Boulder) C. Cully (DFB GSR; CU-Boulder)

EFI Status at MPDR Design: Procurement: Personnel: The current EFI design meets Mission and Instrument requirements (exception: SPB mass estimate). The design will be ready for ETU fabrication on schedule. The critical paths on the design (SPB boom length, AXB deploy and stability,Preamp electro-mechanical and thermal, DFB FPGA definition and requirements) have been identified, and design elements are mature (exception: radial boom length (see EPR-Radial Booms)). Procurement: All long-lead items have been identified: EEE parts ordered; rad testing of required parts arranged. SPB and AXB mechanical items (custom wire cable, stacers, actuators, motors) have been ordered, with exception of SPB motors (see Schedule and Procurement)). Vendors for mechanical and electrical machining and fabrication identified at mission-wide level. Personnel: Team is essentially complete: All design engineering positions filled. Two remaining MT positions to be hired Nov-Dec ’03; on-board by ETU in Jan-Feb ’04.

Mission Requirements REQUIREMENT EFI DESIGN IN-1. The Instrument Payload shall be designed for at least a two-year lifetime. Compliance. Lifetime has been considered in all aspects of EFI and DFB design (parts, performance degradation, etc.). IN-2. The Instrument Payload shall be designed for a total dose environment of 33 krad/year (66 krad for 2 year mission, 5mm of Al, RDM 2) Compliance. Common Parts Buy for Instrument Payload. All parts screened for total dose. Radiation testing planned if TID is unknown. IN-3. The Instrument Payload shall be Single Event Effect (SEE) tolerant and immune to destructive latch-up. Compliance. Common Parts Buy for Instrument Payload. All parts screened for total dose. Radiation testing planned if LET is unknown. DFB design includes latchup mitigation circuits on ADCs, inclusion contingent upon results of LTC1604 radiation testing.

Mission Requirements REQUIREMENT EFI DESIGN IN-7. No component of the Instrument Payload shall exceed the allocated mass budget in THM-SYS-008 THEMIS System Mass Budget.xls Compliance. SPB: 1.88 kg Allocated; 1.92 kg CBE (CAD model). AXB: 2.30 kg Allocated; 2.00 kg CBE (CAD model). (Harness, BEB and DFB tracked with IDPU) IN-9. No component of the Instrument Payload shall exceed the power allocated in THM-SYS-009 THEMIS System Power Budget.xls Preamps: 0.09 W Allocated; 0.07 W CBE (BB). BEB: 1.76 W Allocated; 1.67 W CBE (BB). DFB: 1.00 W Allocated; 0.86 W CBE (modeling). IN-13. The Instrument Payload shall survive the temperature ranges provided in the ICDs Compliance. SPB/AXB ICDs signed off. Verification by Environmental Test planned. IN-14. The Instrument Payload shall perform as designed within the temperature ranges provided in the ICDs Compliance. SPB/AXB ICDs signed off. Verification by Environmental Test planned. Special thermal shock testing of preamp ETU planned.

Mission Requirements REQUIREMENT EFI DESIGN IN-16 The Instrument Payload shall comply with the Magnetics Cleanliness standard described in the THEMIS Magnetics Control Plan Compliance. THM-SYS-002 Magnetics Control Plan. Budget for EFI Magnets (Boom Motors) is <0.75nT @ 2 meters. IN-17 The Instrument Payload shall comply with the THEMIS Electrostatic Cleanliness Plan Compliance. Design, fabrication, and testing in accordance with THM-SYS-003 Electrostatic Cleanliness Plan. IN-18 The Instrument Payload shall comply with the THEMIS Contamination Control Plan Compliance. Design and fabrication in accordance with THM-SYS-004 Contamination Control Plan. IN-19. All Instruments shall comply with all electrical specifications Compliance. Design in accordance with THM-IDPU-001 Backplane Specification (BEB, DFB). IN-20. The Instrument Payload shall be compatible per IDPU-Instrument ICDs Compliance. THM-SYS-103 DFB-to-IDPU ICD signed off. THM-SYS-104 BEB-to-IDPU ICD signed off. Verification Matrices to be completed. IN-21. The Instrument Payload shall be compatible per the IDPU-Probe Bus ICD. Compliance. Both THM-SYS-108 Probe-to-EFI Radial Booms ICD and THM-SYS-109 Probe-to-EFI Axial Booms ICD are signed off. Verification Matrices to be completed. IN-23 The Instrument Payload shall verify performance requirements are met per the THEMIS Verification Plan and Environmental Test Spec. Compliance. THM-SYS-005 Verification Plan and Environmental Test Specification preliminary draft. Verification matrix to be completed. IN-24 The Instrument Payload shall survive and function prior, during and after exposure to the environments described in the THEMIS Verification Plan and Environmental Test Specification

Science Requirements REQUIREMENT EFI DESIGN IN.EFI-1. The EFI shall determine the 2D spin plane electric field at the times of onset at 8-10 Re. Compliance. Via compliance with IN.EFI-5 and -13. IN.EFI-2. The EFI shall determine the dawn/dusk electric field at 18-30 Re. IN.EFI-3. The EFI shall measure the 3D wave electric field in the frequency range 1-600Hz at the times of onset at 8-10 Re. Compliance. Via compliance with IN.EFI-6, -8, -9, -10, and –11. IN.EFI-4. The EFI shall measure the waves at frequencies up to the electron cyclotron frequency that may be responsible for electron acceleration in the radiation belt.

Performance Requirements EFI DESIGN IN.EFI-5. The EFI shall measure the 2D spin plane DC E-field with a time resolution of 10 seconds. Compliance. On-board spin-fit of spin plane E-field at 3-s (one-spin) resolution. IN.EFI-6. The EFI shall measure the 3D AC E-field from 1 Hz to 4kHz. Compliance. 3-axis E-field measurement sampled at 8 ksamp/s. See AC Error Budget. Verified through Calibration. IN.EFI-7. The EFI shall measure the Spacecraft Potential with a time resolution better than the spin rate (3 seconds; from ESA to compute moments). Compliance. On-board spin-avg’d sphere potentials at 3-s (spin-rate) resolution; EFI data rate allocation includes single spheres at ¼-rate of E-field data. IN.EFI-8. The EFI DFT Spectra Range shall be 16Hz to 4kHz, with df/f~25%. Compliance. Spectral products from DFB cover 8 Hz to 8 kHz at 5%, 10%, or 20% BW (16, 32, or 64 bins) IN.EFI-9. The EFI shall measure DC-coupled signals of amplitude up to 300 mV/m with 16-bit resolution. Compliance. Analog gain and ADC resolution of DFB set accordingly. Verified through Calibration. IN.EFI-10. The EFI shall measure AC-coupled signals of amplitude up to 50 mV/m (TBR) with 16-bit resolution. Compliance. Analog gain and ADC resolution of DFB set accordingly. Verified through Calibration.

Performance Requirements EFI DESIGN IN.EFI-11. The EFI noise level shall be below 10-4 (mV/m)/Hz1/2. Compliance. Low-noise preamp chosen (OP-15); good analog design practices throughout preamp, BEB and DFB; CBE is 3x10-5 on AXB, 3x10-6 on SPB. Verified through ETU testing. IN.EFI-12. The EFI HF RMS (Log power) measurement shall cover 100-500 kHz with a minimum time resolution of the spin rate (on-board triggers). Compliance. CBE of EFI response has gain of 0.8 out to 1 MHz; DFB provides HF-RMS at 1/16 to 8 samp/s. IN.EFI-13. The EFI shall achieve an accuracy better than 10% or 1 mV/m in the SC XY E-field components during times of onset. Compliance. See DC Error Budget Discussion.

EFI Board Requirements EFI DESIGN DFB FUNCTIONAL REQUIREMENTS IN.DPU-36. The IDPU DFB shall provide an FFT solution for determining the parallel and perpendicular components of E and B in both fast survey and burst modes and produce spectra for each quantity separately. Compliance. DFB design includes FPGA-based projection (E dot B, E cross B) and FFT solutions. Verified through Test and Calibration of ETU. IN.DPU-37. The IDPU DFB shall integrate FGM digital data and EFI data to produce E·B Compliance. DFB design includes FPGA-based projection ( E dot B, E cross B) solutions. Verified through Test and Calibration of ETU.

EFI Board Requirements EFI DESIGN BEB FUNCTIONAL REQUIREMENTS IN.DPU-38. The IDPU BEB shall provide sensor biasing circuitry, stub and guard voltage control, and boom deployment for the EFI. Compliance. The BEB design provides 3 independent bias channels per sensor (BIAS,GUARD,USHER) and one shared bias channel for the SPB sensors (BRAID). Boom deployment is provided through the IDPU/PCB and DCB. IN.DPU-39. The IDPU BEB shall distribute a floating ground power supply to the EFI sensors. Compliance. The BEB design provides 6 independent floating grounds to the LVPS, and distributes the derived +/-10-V analog supplies to the six EFI sensors. IN.DPU-40. The IDPU BEB shall generate six independent BIAS, GUARD and USHER voltages with an accuracy of 0.1% for distribution to the EFI sensors. Compliance. The BEB design includes matched gain-setting components, along with >12-bit DAC, allowing accuracy of better than 0.1%; Verified through Test and Calibration of ETU.

EFI Boom Requirements REQUIREMENT EFI DESIGN IN.BOOM-5a. Deployed EFI Axials shall be repeatable and stable to Dq = 1 degree and DL/L = 1%. Compliance. Adequate stiffness and angular alignment of AXB stacers and deploy system included in design; verified by testing of ETU. IN.BOOM-5b. Deployed EFI Radials shall be repeatable and stable to Dq = 1 degree and DL/L = 1%. Compliance. Proper SPB cable design (stiffness, tempco) along with std. Cable winding procedures included in design; verified by testing of ETU. IN.BOOM-6. EFI Axial Booms shall be designed to be deployed between 2 and 25 RPM about the Probe's positive Z axis. Compliance. Adequate stiffness and angular alignment of AXB stacers included in design; verified by testing of ETU. IN.BOOM-7. EFI Radial Booms shall be designed to be deployed between 2 and 25 RPM. Compliance. Adequate strength margins on cable included in design; verified by proof-loading of cable and testing of ETU. IN.BOOM-8. EFI Axial Booms deployed stiffness shall be greater than 0.75 Hz (1st mode). Compliance. Part of AXB stacer spec; verified by Testing of ETU. IN.BOOM-12. All deployed booms shall include TBD inhibits to prevent inadvertent release. Compliance. Test/Enable plugs included in design. Red tag door (SPB) and tube (AXB) covers.

A High-Input Impedance Low-Noise Voltmeter in Space EFI Block Diagram A High-Input Impedance Low-Noise Voltmeter in Space sheath sensor preamp Floating ground generation BIAS USHER Bias channels GUARD BRAID VBraid VBraidCtrl Vref

Diagram of THEMIS EFI Elements Top-Level Design (1) Diagram of THEMIS EFI Elements

Description of THEMIS EFI Elements Top-Level Design (2) Description of THEMIS EFI Elements Three-axis E-field measurement, drawing on 30 years of mechanical and electrical design heritage at UCBSSL. Closest living relatives are Cluster, Polar and FAST, with parts heritage from CRRES (mechanical systems, BEB designs, preamp designs).

Description of THEMIS EFI Elements Radial Booms Description of THEMIS EFI Elements Radial booms: 20.8 to 27.8 m long. 8-cm dia., DAG-213 or Ti-N-coated spherical sensor. 3-m fine wire to preamp enclosure. USHER and GUARD bias surfaces integral to preamp enclosure. BRAID bias surface of 3 to 6-m length prior to preamp (common between all 4 radial booms). Sensor is grounded through 10 Mohm (TBR) resistance when stowed, providing ESD protection and allowing for internal DC and AC functional tests. External test/safe plug (motor,door actuator,turns click, ACTEST) to allow for deploy testing/enabling and external signal injection.

Description of THEMIS EFI Elements Axial Booms Description of THEMIS EFI Elements Axial booms: 4-m stacer with ~1-m DAG-213-coated whip stacer sensor. Preamp mounted in-line, between stacer and sensor. USHER and GUARD bias surfaces integral to preamp enclosure. No BRAID bias surface. Sensor is grounded through TBD Mohm resistance when stowed, providing ESD protection and allowing for internal DC and AC functional tests. External test/safe plug (deploy actuator, ACTEST) to allow for deploy testing/safing and external signal injection.

Performance Specification EFI radial sensor baseline will be 41.6 m, tip-to-tip. EFI axial sensor baseline will be ~10 m, tip-to-tip. 16-bit resolution. Spacecraft potential: +/- 60 V, 1.8 mV resolution, better than 46 uV/m resolution (allows ground reconstruction of E from spacecraft potential to better than 0.1 mV/m resolution). DC-coupled E-field: +/- 300 mV/m, 9 uV/m resolution. AC-coupled E-field: +/- 50 mV/m, 1.5 uV/m resolution. AKR log(Power) channel: <= 70 uV/m amplitude, 100-500 kHz bandwidth.

DFB Functional Block Diagram

DFB Data Flow Block Diagram

EFI Data Rates Data Rates Slow Survey Fast Survey Particle Burst Spin-fit radial and axial E-fields; SC potential (via ptcls). Filter Banks. Fast Survey 3 E-field at 32 samp/spin; 2-3 sphere potentials at 8 samp/spin. Filter Banks and FFT spectra. Particle Burst 3 E-field at 128 samp/s; 2-3 sphere potentials at 32 samp/s. Wave Burst 3 E-field at 1024 or 4096 samp/s; 2-3 sphere potentials at 256 or 1024 samp/s. Diagnostic Mode (TBR) E-field and sphere potentials at >= 32 samp/s. Bias control levels at >= 1 samp/s.

Individual Design Elements Radial Boom Unit (Spin-Plane Boom, or SPB) Boom Motor Driver Board (BMD) Axial Boom Unit (AXB) AXB and SPB Thermal Modeling Preamp (Mechanical and Electrical) Boom Electronics Board (BEB) Digital Fields Board (DFB; see Top-Level Design) GSE (Mechanical and Electrical)

SPB Design Overview Sphere and Preamp Main Wire Spool Meter Wheel Base (Magnesium) Release Doors (Spring Preloaded) Brushless Gearmotor With Bevel Gears 4 x Attach Legs with G10 Spacers for Thermal Isolation Exit Tube

Customization of Design for THEMIS Use Wire Length Increased to 18 m; capability of 25 m. Packaging for mounting to THEMIS Probe Structure Attachment Magnesium replaced 6061 Al for weight savings Sphere Coating Titanium Nitride may replace DAG 213 DC Gearmotor Same Motor Manufacturer (Globe Motors) Similar Performance (300 ounce-inches Torque) Brushless Unit Selected over Brushed Brushless better design in vacuum Better Thermal Characteristics Less Stray Magnetic Field Higher Performance in smaller package New Electronics Drive Package Required (BMD) Designed in-house Prototype up-and-running 5 weeks without problems

Theory of Operation Integration and Launch Deployment Science Ops Stowed and Unpowered Wire Wound about Spool, constrained by pinch wheels Release Doors Closed Sphere/Pre-Amp Constrained by Release Doors Deployment Release Doors Opened via SMA Pin-Puller Spin of S/C puts outward force on Sphere and Preamp Motor Acts as brake to prevent motion; coaxial wire in tension Motor powers rotation of Meter Wheel Sphere and Preamp is payed out Release Doors Close Back Around Wire As Centrifugal Force exceeds 2G at Sphere, Sphere Key Reel Spring force is overcome and Sphere moves away from Preamp Monitoring Limit Switch on Shaft counting Rotations Tension Sensor to sense High Tensile Force Science Ops Deployed Booms Configuration Unchanged

Theory of Operation Meter Wheel Preamp Pinch Rollers Motor Sphere Release Doors Motor Drive Electronics Main Wire Spool

Materials and Construction Standard UCB Construction Most Components Machined Aluminum 6061 T6 and 7075 T73 Alodined and Anodized Machined Plastics PEEK Machined Magnesium Alloy AZ31B Chosen for Weight Relief in Structure Not MSFC-SPEC-522 High Resistance to SCC Table II ‘Moderate Resistance’ Requires MUA for use Thermal Treatments Surfaces covered with VDA tape or blankets No Heaters Required Common manufacturing techniques used No Unusually Tight Tolerances No Difficult Fabrications

BMD Requirements: SPB Boom Motor Driver (BMD) Brushless DC Motor driver Sense rotor position with Hall Effect devices Drive stator coils based on commutation logic Supply voltage: 28 ± 6 Volts Load current: ~300 mA Higher radiation environment than IDPU (100-kRad) Short term exposure (6 months)

BMD Block Diagram Motor Driver Board Brushless Gearmotor

Axial Boom (AXB) Overview AXB are integral part of THEMIS probe Primary probe structure provided by Swales Aerospace AXB located along center axis of probe AXB deployment through top and bottom decks of probe. Antennae Mount (TBD by Swales) AXB Assembly Composite Tube Upper AXB THEMIS Probe Upper Deck Mount Test & Safe Plug Lower Deck Mount Lower AXB AXB relative to THEMIS Probe AXB Housing Internal View

Axial Boom General Assembly Design Modifications Stacer Length Double Deploy Assist Device SMA Frangibolt Actuation Whip Sensor Whip Canister (Whip Sensor Inside) Preamp DDAD Doors Roller Nozzles Whip Doors Whip Posts Stacer Canister (Stacer inside) Double Deploy Assist Device (“DDAD”) Tube Mounting Brackets Frangibolt Actuator (inside) Cable Bobbin STACER INDIVIDUAL BOOM IN STOWED CONFIGURATION

AXB Theory of Operation Integration & Loading Whip Sensor is loaded into whip canister Whip canister is locked to the preamp by the whip clamp Stacer is loaded into stacer canister, DDAD doors hold the DDAD, and whip doors hold the whip canister Removable stacer pin is inserted through stacer tip piece, which locks the stacer, DDAD, and Whip canister to the boom assembly Cable is spooled around the cable bobbin Stacer actuation bolt is threaded into Stacer tip piece and Frangibolt actuator is slid over bolt and screwed tight with nut. Stacer pin and whip clamp are removed Boom is loaded into housing Deployment SMA Frangibolt is actuated and actuation bolt is broken. Stacer tip piece is released DDAD extends and initiates stacer deployment DDAD separation opens whip doors, initiating whip sensor deployment Science Ops Deployed boom configuration unchanged

Theory of Operation Deployed Properties Whip sensor deployed length: 40 inches Stacer deployed length: 150 inches Roller Nozzle Whip Canister Whip Sensor 4” Whip Doors DDAD 4” DDAD Doors Stacer Canister Stacer Tip Piece Stacer Cable Bobbin with Cable Frangibolt Actuator Deployed Boom Stowed Boom Deployed DDAD 150” 40” Deployed Whip Sensor

AXB Assembly & Materials Standard Flight Materials AL 6061 T6, SST 440, Eligiloy, PEEK, M55J Graphite Composite. Standard Flight Coatings DAG-213, DAG-154, Type 3 Hard Anodize. Long Lead Items (see Schedule and Procurement) Stacers, Multi-conductor wire, FrangiBolts.

SPB and AXB Thermal (1) Heat Transfer Monitoring and Control 80 mW dissipated at preamp irrelevant to bus temperatures. Essentially inert hunks of metal after deployment Long eclipse temperatures: Top deck, -93 C. Bottom deck, -36 C. Preamp, -170 C. AXB and SPB are heat leaks for bottom deck, and are isolated with 1/8-th inch G10 spacers. All surfaces covered with low e VDA tape or blankets. External snout of SPB dominates its heat leak; black-body open end of AXB tube dominates its heat leak. Monitoring and Control Probe bus monitors near one SPB; no monitoring on AXB. No thermistors in preamp. No operational heaters required. No survival heaters needed after deploy. Unlikely to need deploy heaters.

SPB and AXB Thermal (2) AXB/SPB Limits (°C) Predictions (°C) Margin Cold Hot Deployment 30 8/-17 35/36 -5/-6 Pre-Amp 52 -130 Steady state prediction based on deck temperature from Swales Cold prediction from cold orbit, not long eclipse. Hot prediction from hottest orbit and attitude. Will not deploy in extreme hot or cold cases. Better predictions await more complete instrument thermal models.

Preamp and Sensor Geometry Evolution of CLUSTER-II sphere/”puck” design Simple design, flight-proven components 3m Preamp Housing, d ~2.3 cm 3m thin wire, d ~10 mil sphere, d ~8 cm 1 m Preamp Housing, d ~2.3 cm

DC: Coupling impedances up to 10,000 M. Preamp Requirements DC - 500 kHz DC: Coupling impedances up to 10,000 M. AC: Minimize capacitive voltage division (low input capacitance) Radial Ccoupling ~13 pF, Axial Ccoupling ~6.5 pF Wide temperature range (+100-370º K) Survive high radiation exposure (~750 kRad/year behind 1 mm of Al)

Preamplifier Mechanical Design Goal: Minimize preamp-sphere interference (shadowing, photoelectrons, potential geometry…)

Sphere Preamplifier Sensor Electronics Design ±40 V

Preamplifier IC Op-Amp: OP-15AJ MIL-STD 883, CRRES Heritage Rin ~1012 ohms, Cin ~3 pF Low Power Dissipation (<80 mW) Internally compensated, unity-gain stable Capability to drive capacitive loads (>4000 pF) 40 kRADs with little performance degradation (satisfied behind ~7 mm Al over two years)

Functional Requirements BEB Requirements Functional Requirements Spin Plane Booms, for each provide: Floating Ground Driver “Bias”, “Stub”, “Usher” programmable potentials “Braid” programmable, switchable potential AC test signal source Axial Booms, for each provide:

BEB Requirements (con’t)

BEB Analog Electronics

BEB Block Diagram

BEB Braid Bias

Mechanical GSE Requirements Functional Requirements Provide for simulation of actuators and motors during functional tests, FSW testing, etc. Connect through test/enable plugs on SPBs and AXB pair.

Block Diagram of EFI/BEB GSE Electrical GSE Block Diagram of EFI/BEB GSE

Electrical GSE Requirements (1) Power/Thermal/Mechanical Provide regulated voltages. Facilitate current measurements. 6U VME support (w/out Wedgelocks) for BEB. Portable and rugged for transport. Open rack for access while under test. Connectors acceptable for Flight interconnection Electrical Interface Backplane interface per IDPU backplane specification. 1 MUX’d analog housekeeping output (ANA HSK). GSE interface circuitry must be flight-grade.

Electrical GSE Requirements (2) Command and Telemetry Handling GSE sends 24-bit CDI commands per ICD specification. Command format is compatible with IDPU and MOC GSE (TBD). Before DFB and DCB, data is from GSE’s IEEE-1394 ADC. Afterwards data is extracted from telemetry. Test Support Equipment GSE controls GPIB function generator and +/- 100-V supplies. “Faraday cage”-type test fixture (pairs for SPB and AXB). Compatibility with Next Level of Integration Uses ITOS, Matlab (or equiv), C. PC standards. Easy accessibility to data for offline processing (FTP, HTTP, etc.).

Electrical GSE Requirements (3) Data Manipulation and Display Plot any of 16 channels over user-specified timespan. Calculate 2N-point FFT on user-specified channels. Compute and display power spectra and transfer functions of user-specified channels. Display control values for GPIB and GSE interface equipment. Support hardcopy output. Raw and derived data, as well as configuration information stored in tabular ASCII format file. Data manipulation and display scriptable to allow for automation of test and cal procedures.

DC Error Budget (1) The estimated electric field along the direction between the two probes is E=(v1-v2)/2L. Errors arise from and are mitigated by: Errors in baseline (L). Errors in v1 and v2; eg. (v1-v2) or each individually.

DC Error Budget (2) Errors in baseline (L). Fly as long of booms as possible, given resources (41.6-m baseline, ~55-m possible w/in mass resources). Control boom length to 1%. Trim deploy length to 4-cm accuracy to allow for electrical center offsets (AXB in particular). Increase fine wire length to reduce boom shorting effect (observed up to 20% on Cluster; predicted 5% on THEMIS (better Lf/L)). Fly dual-length system to allow for differentiation between geophysical and SC fields.

DC Error Budget (3) Errors in v1 and v2; eg. (v1-v2) or each individually. Use TI-N or DAG-213 coating on sensors for uniform photoemission. Keep all sensors clean pre-launch. Use high-impedance preamp (1012 ohm) to reduce DC attenuation. Current-bias sensor to reduce sheath impedance and susceptibility to photoemission asymmetries (20-100 Mohm typ.; 0.2-0.5 mV/m SPB systematic). Mount sensor on fine wire and reduce emission area of preamp to reduce magnitude and effect of asymmetric photoemission (3-10 times smaller than Cluster; < 0.5 mV/m SPB systematic). Use USHER and GUARD surfaces to control photocurrents to sensor (>= 20-V bias range, well above bulk of photoelectron energies). Use fine wire and BRAID bias surface to reduce ES wake effects (scale with D/L or 1/L; roughly equivalent to Cluster). Fly dual-length SPB system to detect ES wake effects. Enforce 1.0-V electrostatic cleanliness specification on THEMIS to reduce SC potential asymmetry effects to < 0.1 mV/m on SPB; 0.1-V goal reduces AXB effects to this level as well.

EFI Spectral Coverage and System Noise Estimates AC Error Budget EFI Spectral Coverage and System Noise Estimates Maximum Spectra (DC-Coupled) 1/f3 1/f flat CDI BBF AKR band 1-LSB Spectra (DC-Coupled) Preamp and Rbias Current Noise Preamp Voltage Noise axial radial Spin frequency 10-Hz Ac-coupled roll-in 4-kHz Anti-aliasing roll-off

Design (Definition and BB) Schedule (1) Design (Definition and BB) Preamp Mechanical (Aug-Oct ’03; complete). Preamp Electrical (Aug-Oct ’03; complete). BEB (Jul-Oct ’03; complete). BMD (Sep ’03; complete). SPB (Aug ’03 – Nov ‘03; freezing design Nov 21). AXB (Jun ’03 – Dec ’03; freezing design Nov 14). DFB (Aug ’03- Dec ’03; 50%).

Schedule (2) Long-Lead Parts AXB stacers (ordered Sep ’03; delivery by 26 Dec ’03 (12-wk lead time)) SPB wire cable (final RFQ issued 7 Nov; final order expected by 17 Nov; delivery by 15 Jan ’04) FrangiBolt actuators (final RFQ issued 7 Nov; final order expected by 17 Nov; early delivery of 3 units late Dec; remainder in late Jan ’04). SPB motors: Original vendor on brushless motors (Avnet/Globe) returned with 21-week, rather than 12-week lead time. This would push EFI F1 delivery back 3 months, leaving no schedule slack for delivery to II&T. Exploring two options: New brushless vendor (MicroMo) with space-qualified pedigree. 12-wk lead time (pushes F1 delivery back 1 month to 16 Jul ’04. Example ordered for validation Nov 17-21; order to follow if passes validation. Brush motors from Avnet/Globe. Original SPB design. 8-wk lead time (no schedule impact). Additional magnetic impact.

Schedule (3) EM/ETU SPB AXB Preamp (Mechanical and Electrical) BEB BMD Mach, Dec ’03; Assy, Dec ’03 – Jan ’04; Test, Feb ’04. AXB Mach, Dec ’03 – Jan ’04; Assy, Feb ’04; Test, Feb ’04. Preamp (Mechanical and Electrical) Layout/Fab/Assy, Oct-Nov ’03; Test, Dec ’03. BEB Layout/Fab, Nov-Dec ’03; Build, Dec ’03; Test, Dec ’03. BMD DFB Layout/Fab, Jan-Mar ’04; Build, Mar ‘04; Test, Apr ‘04.

Summary of EPR Findings Radial Boom design (1,2,3,9; Draft findings, 3 Nov 2003): Dynamic stability issues (spin/trans MOI ratio) (Bus EPR) Dual-length/longer-length designs Axial Boom design (6,10): Deploy force margin Length vs. noise margin, whip vs. sphere sensors. Attitude information and jitter requirements (14). Miscellaneous mechanical findings (15,18,5): Deploy sequence modeling. Boom deployment temperature. SPB miter gear life testing. Hot parts and thermal stresses Gain and Filter Specifications of EFI and SCM on DFB (4,8,12). BEB FPGA specification and programming (20). Preamp electro-mechanical design (11). Electrostatic Cleanliness Specification (RFA UCB-8)(7,17). EMI/EMC Specification (RFA UCB-9)(13). Detailed I&T plan development (RFA UCB-10)(19).

EPR Findings—Radial Booms Dynamic stability issues: Bus and Instrument team analysis of dynamic stability not in accord; question is proper spin/transverse MOI ratio for non-rigid boom systems on THEMIS. Swales analysis indicates shorter AXB (60%) or longer SPB required to achieve stable configuration (Bus EPR finding). Longer-length/Dual-length designs (science-driven): 56-m (2x(25+3)m system) tip-to-tip SPB possible with current mechanical design. Direct improvement in DC error budget (30%). Allows for dual-length (21/28 m) system that would allow the detection of ES wake effects (not mission critical, however). Mass hit (56 g/SPB) for 7-m cable addition; fuel hit (~60%, 452 g increase) for final spin up. Resolution: Must be resolved by Jan ’04 (EFI F1 Cable Assy); Cable Assy schedule margin allows push back to Apr ’04, if necessary. Dynamic stability analysis is ongoing at Swales and UCB.

EPR Findings—Axial Booms Deploy force margin and AXB length repeatability: AXB design may not have enough deploy force margin to ensure dL/L = 1% repeatability of deploy length. Resolution: AXB ETU testing (Feb ’04). Length vs. Noise Margin; whip vs. sphere sensor response Current AXB length (~9-m effective, 10-m tip-to-tip) allows only factor of 3 S/N margin at 4 kHz (CBE of system noise level). SC perturbations will strongly affect DC E-field in AXB (several mV/m, dependent upon SC potential (plasma conditions). AXB whip sensor may have different response para/perp to B than SPB sphere+wire sensor. Resolution: AXB length can not be reduced significantly without compromising 3D AC measurement. AXB lengths will be trimmed based on simulation results to reduce DC offset due to SC potential (final length Feb ’04 (AXB F1 Mach)). Literature on antenna response to be investigated to determine significance of whip vs. sphere effect (no mitigation planned; different capacitance of SPB and AXB sensors already known, and part of electrical Calibration plan).

EPR Findings—Attitude Attitude knowledge and jitter requirements are modest, and achievable by Bus and Instrument designs. 5.6 degree (10%) knowledge required; better than 1 degree (0.5%) achieved via post-processing of FGM and EFI data. Better than 3-degree accuracy and jitter in spin phase required for accurate on-board spin fits of E-field data; current IDPU design provides much better than 0.1 degrees. Alignment requirements more stringent, driven by DC error budget of SPB. Opposing pairs of SPB booms must align within 1 degree to bring systematic error due to differential photoemission below 1 mV/m for nominal biasing scheme and sphere sheath impedances.

EPR Findings—Misc. Mech. UCB should initiate kinematic and dynamic modeling of the boom deploy sequences. Resolution: Kinematic model of boom deploy already exists (Th_booms3d.xls; D. Pankow) at UCB as tool for understanding timing, spin-up requirements, mechanical loads, boom/SC modes, coriolis displacements, etc. Resolution: Algor product will be taken under advisement as part of on-going resolution of dynamic stability question (see Radial Booms; Jan ‘04). Boom deployment temperature range should be defined. Resolution: Boom deployment temperature range will be defined as part of I&T test flow (Dec. ’03-Jan. ‘04). SPB miter gear life testing under worst-case load required. Resolution: Such testing will be included in SPB I&T test plan (Dec ’03 – Jan ’04).

EPR Findings—Hot Parts High-dissipation (> 100 mW) parts should be identified, and junction temperature coefficients tabulated. Resolution: Data will be provided to thermal analysis as required.

EPR Findings—Gain/Filter DC/AC-coupled dynamic range and solitary waves Large-amplitude (>=100 mV/m) solitary waves have been observed at frequencies from 1-1000 Hz on Polar and Cluster in the THEMIS observation region. Such waves will saturate the AC-coupled (10 Hz-6 kHz) E-field channels with a dynamic range of +/- 50 mV/m. Resolution: Other channels can handle the large-amplitude events, although not simultaneously. DC-coupled (0-4 kHz) channels have a dynamic range of +/- 300 mV/m. Dc-coupled sphere/whip voltages have +/-60-V range (3 V/m on SPB, ~13 V/m on AXB). AC-coupled gain may be reduced to allow higher rate sampling of large-amplitude signals (TBR, Nov-Dec ’03, DFB ETU design). Filter specifications SCM channels use Butterworth, EFI uses Bessel. Difference means non-trivial phase differences and time-domain responses over entire 0-4 kHz range, maximizing between 1-4 kHz, preventing direct comparison of time-domain signals. Resolution: Trade between filter types underway; component value issue; active filter topology doesn’t change (TBR, Nov-Dec ’03, DFB ETU design).

EPR Findings—BEB FPGA BEB FPGA specification and programming Resolution: BEB FPGA requirements are modest and now well-defined (CDI interface, DAC control, Analog housekeeping), and common to most IDPU boards, allowing FPGA programmer (R. Abiad, UCB) to work on design and programming within BEB ETU schedule (Build/Test, Dec ’03).

EPR Findings—Preamp Bootstrapping and guarding of preamp inputs Bootstrapping and guarding of preamp electronics in the current electromechanical design should be reviewed. Potentials of all conductors need to be defined (can, shields, etc.). Resolution: Current design does not include input guard, based on estimated input capacitance of preamp enclosure. Preamp ETU Assy and Test begins early Dec ’03 to characterize input capacity, and allow for changes and re-evaluation before FLT fabrication begins (Jan ’04).

EPR Findings—ESC Electrostatic Cleanliness Specification and Enforcement Resolution: Rev. B of THM-SYS-003 Electrostatic Cleanliness Plan has been posted for review and will be signed off in Nov ’03. It includes a complete specification of electrostatic cleanliness requirements as well as verification procedures. The specification sets a 1-V potential uniformity requirement under an 8 nA/cm2 current density, with 0.1-V potential uniformity as a goal (see DC Error Budget for discussion).

EPR Findings—EMI/EMC Electromagnetic Interference/Cleanliness Specification Resolution: A Draft of the THEMIS EMI/EMC Specification has been posted for review and will be signed off in TBD. This specification is modeled on that for the FAST mission, adapted to the instrument properties on THEMIS (SCM/EFI system noise levels and expected wave amplitudes). Testing and verification of compliance with EMI/EMC TBD, and requires some work, due to low frequencies of interest (0-4 kHz).

EPR Findings—I&T Plan I&T test flow needs to be defined to include development, ETU, qualification and acceptance testing. Resolution: An EFI I&T plan will be developed in Dec ’03 to support qualification and acceptance testing of the EFI ETU in Jan-Mar ’04.