ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/04 Probe and Probe Carrier Harness Dave Manges (301)

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/042 Harness Requirements  The Probe Bus harness shall provide power and data connections between the Probe Bus subsystems and the IDPU  GSFC 311-INST-001 Grade 3 parts shall be used with selective up- screening to Grade 2 for key items in critical sub-systems  Parts shall be derated to GSFC PPL-21 and MIL-STD-975  THEMIS workmanship standards shall be compliant with the Performance Assurance and Implementation Plan (PAIP) –Cable, Harness and Wiring Interconnects - NASA STD –Conformal Coating and Staking - NASA STD –Solder - NASA STD  The THEMIS Project shall meet the requirements of EWR 127-1

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/043 Harness Design Approach  General Guidelines –All Wiring Is Consistent With MIL-STD-975 Derating Guidelines –Power and Signal Interfaces Are Kept Separate, where possible –Wire Selection Guidelines High Power22 Awg < 1A24 Awg Signal26 Awg –Routing Determined by physical obstructions Shortest route between points A-B Temperature considerations Ease of mating/demating connectors Magnetic considerations EMI noise - separate noisy and quiet signals Minimize ground loops – Magnetics Pair and Twist power lines Minimize current loops Select components with low permeability

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/044 Probe Harness

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/045 Probe Carrier Harness

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/04 Harness Wiring  Signal Harness –Includes Data, Command, Analog Telemetry and Temperature –Twisted Shielded Pair for Differential Data and Clock Signals –Shield Wires Are Grounded to Chassis at driver end of the Interface for low speed signals and at both ends for high speed signals  Power Harness –Regulated DC Power (  5VDC) and Returns –Unregulated +28 VDC Power and Returns All Power and Return Wires Twisted Together –Coupling of Power Bus Noise Between Components Is Minimized by Having Dedicated Power and Return Wires to Each Component from the Power Subsystem –Double Insulation is Used in Cases Where Power Bus Conductors May be Exposed (Battery and Battery Relay Terminals, for Example)  Pyro Harness –Pyro Fire Lines Use Twisted Shielded Pairs Additional overall bundle shielding required –Handling is determined by Mil-STD-1576 –Electro-explosive Subsystem Safety Requirements and Test Methods for Space Systems

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/047 Shielding  Cable shields are grounded to chassis at one end for low speed signals and both ends for high speed signals  Shields are not used as signal returns  Selected harnesses will be double shielded by addition of a bundle shield –BAU to IDPU High Speed interface –Pyro firing signals  Bundle shielding is comprised of composite aluminum foil spiral wrapped with an aluminum mesh overwrap for connector close out  Bundle shields are electrically grounded at both ends to the connector backshells  Coaxial Cable shields are grounded to chassis at each end of the cable

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/048 Harness Material  Connectors –S xxxSubminiature D, High Density –S xxxSubminiature D –M83513xxxMicrominiature D –40M38298Miniature Circular –Mil-C-38999Subminiature Circular –SMAsRF  Wire –MIL-W-22759/11Teflon Hook up –MIL-W-27500RCxxSingle shield –MIL-W-27500CxxRCDouble shield –GORE Type 41RF Cable

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/049 Harness Flow

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/04 Grounding

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/04 Spacecraft Grounding Diagram

ITAR Restricted Data THEMIS Power Subsystem CDR Peer Review 6/14/04 Grounding  A Single Point Grounding (SPG) scheme is used –All circuit grounds are referenced to a common point –No current flows in the structure –Small size of the S/C results in relatively short wires, so high frequency effects are not a major concern  Primary Power (+28V Unregulated Power) is referenced to Chassis at a Single Point in the BAU Power Module defining Single Point Ground –The BAU Single Point Ground, located on the BAU Chassis, is connected directly to the Probe Separation Ring  At Each Component, the Primary Power and Power Returns are Isolated from Chassis and Secondary Power  All component chassis ground connections are routed to the Probe Separation ring