Interconnect Technology for Manned Space Flight

Interconnect Design for Radiation- Induced EMI/RFI Interference In the previous arcticle, we discussed how radiation—in the event it penetrates into satellite materials—can cause embrittlement and other forms of degradation, potentially impacting the mechanical, physical, and even electrical (impedance) properties of mission-critical equipment including electrical wire interconnect systems. Now, let’s turn to a second key issue of radiation in space: managing the surface charge build-up of electrons that can lead to EMI noise and signal degradation in electronic systems. As with mitigation efforts to reduce penetration damage from alpha, beta, and gamma radiation, design disciplines for EMI noise mitigation include laminate shielding of wiring, conducting unwanted interference to ground, and the use of filtering technologies at box I/O interfaces to attenuate high-frequency interference. The many benefits of good shielding Traditional interconnect and wire harnessing products have a strong design emphasis on electromagnetic shielding to prevent unwanted interferences. This can of course be the case on spacecraft as well, many electronic systems must interact and not interfere with each other while fulfilling their missions. In addition, the metallic shields on spacecraft will protect the layers below from radiation. They will further bleed off unwanted charge accumulations on various areas of the craft. Finally, in the event of a discharge, they provide a safe place for the current to go.

Space-grade materials and plating choices for EMI/RFI mitigation As mentioned in the previous article, the most abundant element in Low Earth Orbit is atomic oxygen, which is in a highly reactive state and can produce serious corrosion of surfaces through oxidation. Critical electrical junctions must therefore be protected from corrosion with surface platings, typically either electroless nickel or gold in order to maintain the ground path and shielding characteristics necessary in the management of EMI. Glenair plating codes M and Z2 are appropriate for all aluminum shell connectors. The XM plating code is for Glenair composite thermoplastic connectors and backshell accessories. Plating code GME is reserved for ESCC-compliant backshells only. All of these plating codes are qualified for use in LEO applications. Space-Grade Finish Options Finish Code Description Specification M Electroless Nickel SAE-AMS-26074 Class 3 XM Electroless Nickel (Composite Only) SAE-AMS-26074 Class 3 Z2 Gold Plated ASTM B488 GME Gold over Electroless Nickel ESCC No. 3401 087 Para. 4.4.1

Ground plane connectors reduce both electrical equipment emissions and susceptibility to EMI The use of a conductive metallic ground plane as a packaging option for shielded contacts and optical fiber links can effectively reduce the size of the penetration in the equipment enclosure Faraday cage. Metallic ground planes in connectors are typically made of aluminum, and the thickness is on par with the wall strength of the connector shell itself. Ground planes are always grounded to chassis.