NASA-HDBK-4001: “Electrical Grounding Architecture for Unmanned Spacecraft”
I have long complained that the word “grounding” means too many things in electrical engineering. It can mean (1) A connection to Earth/dirt; (2) A current return path; or (3) A voltage/potential reference. At least in this publicly available NASA document (free to download here) we don’t have to worry about meaning #1–there’s no way we’re connecting a spacecraft to the dirt back on Earth. This guidance document from 1998 has useful information for anyone looking at implementing “grounding” (both in terms of (2) and (3)) on a mobile platform with largely conductive structure.
Although fairly concise at 29 pages, 4001 covers a lot of ground (pardon the pun). It acknowledges up front that there’s no single “correct” grounding approach, and it covers which design considerations are most important in designing a grounding architecture. It approaches grounding design from the systems perspective, largely looking at the connections between modules. I find the conceptual diagrams to be particularly helpful, such as the ones highlighting power distribution and signals below.
Topics addressed in NASA-HDBK-4001:
Ground isolation and ground loops
Different requirements for different frequencies of interest
Single point ground (SPG or “star” grounding) vs. multiple point ground
Bleed resistors
Bonding
Different requirements depending on platform size
Grounding for sensors, RF systems, pyro devices, etc.
Ground fault isolation
It also shows a fascinating example in the appendix drawn from the Cassini mission of what this kind of grounding architecture looks like on a large and complex spacecraft
TIP:
NASA-HDBK-4001 calls out MIL-B-5087B for bonding guidance, but today the recommendation would be to refer to NASA-HDBK-4003. The latter document had not yet been written in 1998 when 4001 was first published.
Designing in appropriate grounding for complex systems is such a large topic that it’s not captured in many other standards. While its main applicability is to a very specific set of hardware, NASA-HDBK-4001 is a good starting point for people outside of NASA and outside of aerospace who are having to make grounding-related design decisions.