Unconventional Spacecraft Interfaces to Reduce Mass and Accommodate Exceptional EMI Requirements

The Naval Research Laboratory (NRL) Compact Coronagraph (CCOR) instrument was a late addition to the National Aeronautics and Space Administration (NASA) Geostationary Operational Environmental Satellite (GOES-U) Spacecraft. Accommodating the baseline design of CCOR's power system electronics was not feasible due to physical constraints on the GOES-U spacecraft's Solar Pointing Platform (SPP). In addition, CCOR's baseline design was not able to meet the Electromagnetic Interference (EMI) requirements of GOES-U, which were unusually challenging due to the sensitivity of several other instruments on the spacecraft. GOES-U had rigid limitations on conducted emissions and several exceptionally stringent radiated emission notch limits in S-band frequencies. However, by utilizing an unconventional approach to the spacecraft power interface and supplementing Commercial off-the-shelf (COTS) EMI filters with additional front-end filtering, CCOR was able to significantly reduce the footprint of the power system electronics box as well as reduce the instrument emissions enough to meet mission requirements. This paper outlines the approach and strategies used by CCOR, which may be applicable to future instruments ridesharing on other spacecraft. The paper will discuss common circuitry used in spacecraft bus power interfaces that were omitted to reduce the size of the electronics and how the CCOR instrument was able to utilize highly dense COTS EMI filters in conjunction with custom discrete filter designs to achieve extremely low conducted emissions. Furthermore, it will identify measures taken by the CCOR team to mitigate the risks incurred by unconventional design approaches. The paper will also discuss practices used in the harness construction and mechanical design features that mitigated radiated emissions. Precise details of the NRL circuit designs and GOES-U requirements are omitted, but prudent high-level architecture and conceptual approaches are included as well as data collected regarding the performance of the CCOR instrument in formal EMI testing.