What are some common design guidelines/practices to combat the electrical effects of spacecraft charging(e.g. ESD, ground plane shift). Is it to focus on more resilient parts, and reduce resistance/impedence in the ground path, or are there other design guidelines/strategies?
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3 Answers
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Regarding grounding on the ISS,
The space station solar arrays operate at 160 VDC. When the arrays are producing power, the station structure will also tend to float to a voltage close to the array voltage. Under these conditions, the space station could be subjected to problems like arcing from its surface to the surrounding environment, or arcing to an astronaut. To avoid these problems, the structure has been grounded with a Plasma Contactor Unit (PCU). To protect the astronauts from shock hazards, the PCU is operated during all spacewalks.
The PCU acts as an electrical ground rod to connect the space station structure to the local environment and harmlessly dissipate the structure charges. Glenn [NASA Glenn Research Centre - ed.] engineers designed, manufactured, tested and installed the hollow cathode assembly, which is the critical component of the PCU. The Hollow Cathode Assembly performs this function by converting a small supply of gas into ions and electrons and discharging this stream to space. The stream carries with it the excess electrons that created the surface charge.
From NASA Factsheet PS-00537-0811, "Powering the Future".
My guess is that it would also be operated during docking procedures as well, to minimise ESD and ground potential difference between the ISS and the docking spacecraft.
Also have a look at "Principles of Space Instrument Design", Cruise, A.M et al., Cambridge Uni Press, ISBN 0521451647. There is a chapter on electronics. (I haven't read it yet - only just ordered it today.)
Within manned spacecraft atmospheres, ESD mitigation would most probably be a function of environmental control via humidifiers.
UPDATE 31 Jan 2016:
See Chapter 3, specifically section 3.2 Design Guidelines, of the definitive NASA JPL Space Science & Technology Series book: Guide to Mitigating Spacecraft Charging Effects, Henry B. Garrett, Albert C. Whittlesey, June 2011, 244pp.
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1$\begingroup$ Don't hold your breath on Cruise et al. ESD is mentioned there once or twice only. $\endgroup$ Commented Jul 31, 2015 at 13:30
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$\begingroup$ @DeerHunter, sounds like I done my money, but I couldn't find much on the market that was affordable, at least. $\endgroup$ Commented Jul 31, 2015 at 13:52
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1$\begingroup$ 's okay. It's a well-rounded book. $\endgroup$ Commented Jul 31, 2015 at 13:54
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$\begingroup$ I look forward to devouring it when it gets delivered in 3-4 weeks time. $\endgroup$ Commented Jul 31, 2015 at 14:01
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This document describes NASA's best practices for electrical grounding and ESD handling in rockets.
NASA also studied electrostatic effects on board the Apollo spacecraft, its final design included several measures to reduce static charging, e.g:
- inserting a metal mesh in the couches to prevent a static charge from building up as astronauts moved around,
- adding discharge resistors to biomedical sensors
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The precautions you take will vary according to the application/orbit etc. It would be prudent to spend some time looking into this; its a big topic and a cause of plenty of modern day failures. Don't rely on advice from this forum! That disclaimer made, here's some ideas to get you started.
Read up about the environment and agency standards for mitigation. Really, you, or someone in your organisation, should be on top of this, its worth asking around. Try this for a list of documents.
As a very rough guide the body of a satellite is usually considered to provide some shielding. Thus it takes high energy electrons to get inside - termed "internal charging" whilst low energy electrons still cause surface charging.
Three very broad failure modes come to mind:
Charging of dielectric material This can occur from surface charging or internal charging. This is hard to do in practice, its everywhere in the harness, though having a slightly leaky insulator can help.
Charging of floating metal Effects can be larger and more damaging discharges than from a build-up in dielectric though again it can be from surface or internal charging. Real world examples of design features that present a sufficient risk of ESD trigger (in GEO) that they would each warrant a grounding connection:
each layer of aluminised kapton in a blanket
metallic badge on an IC package (or removal of the badge)
unused connector pins
Three phase In locations where there is a high voltage between two conductors a small discharge from a nearby dielectric can produce a brief puff of plasma and thus trigger a sustained discharge between the power rails. Known to cause plenty of damage. I believe its more often associated with surface charging.
