THEMIS FGM CDR Peer ReviewBerlin, April 6, UCB/Swales should identify an individual that will assume responsibility for magnetic cleanliness on the project. UCB magnetic czar designee (Michael Ludlam) responsible for tracking issues, developing plans, filtering guidelines and budgeting requirements to the instruments and bus The MSE (Ellen Taylor) acts as the single point of contact for all communications UCLA is charged with an advisory role to the program, and the responsibility to conduct parts testing, modeling and training as needed. Bi-weekly magnetic telecons of the Magnetics Control Board are conducted between UCB, UCLA and Swales. 2. a) Review the magnetic cleanliness requirement; Magnetics Control Board has reviewed the magnetic requirements as originally stated during the SRR and in Revision A of the MRD (thm_sys_001a_MRD). As a result, the DC magnetic noise requirement (M-31a) was relaxed from 1nT as stated at the SRR to 5nT with the understanding that the offset can be measured on the ground and on- orbit in the solar wind. The 5nT level is commensurate with ACS requirements (1deg at 300nT provides a good orbit arc for modeling) and, if measured, meets the Level 1 science req. In addition to the absolute DC offset, THEMIS mission objectives are also concerned with DC drifts (from Level 1 requirements, 1nT absolute knowledge and stability of 0.2nT over 12 hours is required). Therefore, a DC stability requirement was added. FGM PDR Peer Review RFA #1

THEMIS FGM CDR Peer ReviewBerlin, April 6, b) Develop a magnetic cleanliness plan to meet the requirements set by the project; A Magnetics Contamination Control Plan has been developed and reviewed (thm_sys_002c_Magnetics Cleanliness). 2. c) Obtain concurrence of the relevant flight hardware developers on the plan; The Magnetics Contamination Control Plan is a controlling, signed document between UCB and Swales Requirements and guidelines detailed in the Plan have been used to develop the magnetic field emission requirements detailed in Probe Bus flight hardware specs. 2. d) Reviewed spacecraft systems level design for traditional sources of stray fields (solar array, current loops, grounding, latch valves, batteries, etc.); Specific aspects of the system design, including traditional sources of stray fields such as solar array layout and battery cell layout are reviewed and discussed during the bi-weekly mag telecons with the Magnetic Control Board. When adherence to requirements is threatened (e.g., loop current strength) or guidelines are violated by standard practices (e.g., small magnetic components within subsystems), the Magnetic Control Board provides evaluation, technical workaround, or exemption if deemed appropriate. In the case of exemption the offender is recorded and tracked to ensure proper mitigation (e.g., offending loop not operational during science, or magnetic component degaussing and characterization). FGM PDR Peer Review RFA #1

THEMIS FGM CDR Peer ReviewBerlin, April 6, e) Maintain grassroots magnetics budget verified by some benchtop measurements; and UCB is maintaining the THEMIS magnetics budget. This budget is currently in spreadsheet form to track main offenders, materials, component testing and results. It is in the process of being ported to a DC tracking tool from JPL that UCLA is familiar with. 2. f) Verify that magnetic cleanliness requirements are met. THEMIS’s test and verification philosophy is commensurate with: early guidelines dissemination and training of personnel, main offenders recognition and risk mitigation, clear requirements specification and understanding across the program, specifications of magnetically clean parts and subsystems across the entire system. 3. At least one spacecraft should undergo magnetic mapping at a large coil facility where any stray fields can be characterized (spacecraft on/off, perm/de-perm) to establish compliance with +/- 1nT specification and provide basis for dealing with any non- compliance. Based on recommendations from this Peer Review, the THEMIS team is planning on testing P1 during environmental testing at GSFC. This test will ensure that the magnetic cleanliness contamination specifications have been met at a system-level, validating the analysis and component testing performed throughout the program. FGM PDR Peer Review RFA #1