Below are the questions asked during the live event, along with their respective answers.
RTH = Robert Houle
JCM = John McCloskey
Q: Do you perform PCB card-level testing if you do not have a defined subsystem? How do you qualify conducted and radiated tests and to what standards?
RTH: Our testing lab is designed more for box level and higher up systems. The center in some codes however does have the capability to test for cross talk emissions at the PCB level. The testing is conducted typically to GEVS which is a consortium of tests from MIL-STD-461C and G. We also support many ISS payloads and some commercial vendors. Since most of these vendors dock with the ISS, then they use the same test methods. SSP 30237/8 are ISS-related.
JCM: I believe we discussed this during the session, but..we do encourage designers to perform early diagnostic testing at the card level whenever practical. Such testing is limited to conducted testing; radiated testing on an exposed card without shielding provided by a metal enclosure would give an unrealistic assessment that would not be meaningful.
Q: Would love to hear technical details about some specific EMC challenges faced, along with some details about the application systems at hand.
RTH: I have far too many to list just here. My biggest challenge at the moment is supporting 21st century spacecraft using a facility designed in the infancy of the space age. The facility works for smaller payloads but the larger ones cause some very unique challenges.
JCM: I have plenty of “war” stories and not enough time to write them all down. I will just say that the technical challenges, while not always very easy, really are the easy part. The bigger challenge is convincing your management that you do indeed have a problem that requires their attention. The first reaction is almost always, “Can we live with it?” rather than “How do we fix the problem properly so that it truly goes away and does not bite us during the mission?” This is probably the biggest problem I face during just about every test campaign, and it will never go away. All I can say is that you just have to stick to your principles and, stay the course.
You also have to be mindful about where and when to fall on your sword. You don’t want to end up being known as the EMC engineer who cried “wolf”. Sometimes the impacts of a given interference may not be terribly severe, and they may be accepted without putting the mission at undue risk. In these cases, it may be best to accept it, get on with things, and save falling on your sword for another occasion when it’s more needed (and don’t worry; you won’t have to wait very long for another opportunity).
This judgment comes only from experience. So buckle up and enjoy the ride.
Q: Where does the MIL-STD-tailored AIAA-S-121A fit in to NASA standards?
JCM: I can only speak for GSFC and GEVS in particular. I have incorporated a number of tailoring guidelines from AIAA-S-121A into GEVS.
Q: What are the main differences of what you do nowadays compared to 5-10 years ago technology-wise regarding guidelines and standards, revisions due to technology available?
RTH: With regards to emissions testing, the development and integration of FFT receivers has been a game-changer. Not only has it sped up testing but it has also brought the ability to capture the spurious signals.
JCM: The biggest difference probably is the availability of Fast Fourier Transform (FFT) technology for EMI receivers/spectrum analyzers. It allows emissions sweeps to be completed in a very small fraction of the time it used to take with traditional frequency-swept receivers. It has allowed us to make much more efficient use of test time.
Q: Do space systems encounter interface issues from other satellites and spacecraft?
JCM: Interference between satellites is generally not a significant concern, mainly because of physical separation and frequency management. The greatest threat of interference is almost always equipment in close proximity, i.e. on the satellite itself.
Q: What are the EMC standards used for spacecraft?
RTH: There are numerous standards for spacecraft but at GSFC we primarily test to GEVS, which is MIL-STD-461C/G based.
JCM: Our starting point is MIL-STD-461G, which is a general military standard applied to a wide variety of platforms. We further tailor it into a standard we use at NASA/Goddard called the General Environmental Verification Standard (GEVS).
Q: Why are Flexible Printed Circuits (FPCs) more commonly used in space vs Flat Flat Cable (FFCs)?
JCM: I don’t know that they are. We use standard printed circuit boards, flexible printed circuits, and flex cables as determined by the needs of any given program.
Q: Is there any EMI/EMC training provided by NASA engineers?
RTH: John and I typically work on getting EMC training in the center every couple of years through various commercial and government means. Our test staff are all iNARTE certified and when we bring on new personnel, it’s a requirement that they have to become certified within a certain time frame. With the help of folks like Mike Violette, there are more options than ever to train our EMC engineers. Outside of that, it’s being paired up with a senior EMC member and just lots of lab time.
JCM: Sure. I have provided some myself for engineers at GSFC. Several excellent courses are provided by Mike Violette’s company, Washington Labs. Contact Mike at mikev@wll.com for details.
Q: Is that EMI/EMC framed artwork hanging behind Robert specifically for this webinar or always up?
RTH: We had a project that had a not-so-pleasant time the first time through EMI. One of their personnel is also a graphic artist and they drew up their image of EMI gremlins and brought it into the lab for good luck. Thankfully they were kind enough to print me another copy and I have it hanging up at home. At the very bottom of the picture they actually had a log to keep track of their testing progress.
Q: How do you simulate the Space EM field in the testing here?
RTH: Box/sub-system level testing we recreate the spacecraft RF environment using MIL-STD-461G test methods. When we get to higher stages of testing before delivery then we’ll perform self-compatibility testing with onboard systems.
JCM: We define our test limits to provide upper bounds for the environments we expect to see during the mission.
Q: Will you observe in space the electric and magnetic field?
RTH: Depending on the unique environment the spacecraft will be interacting with, yes. Pablo Nevarez from JPL did an outstanding presentation on the shielding of instruments on the JUNO spacecraft. I’d strongly take the time to watch it on YouTube as it covers both magnetic and electric shielding of components.
JCM: Certainly. We observe both electric and magnetic fields in space; we will always have both wherever voltage and currents exist.
Q: Which frequency range is in your focus?
RTH: I oversee both magnetic and EMI testing for GSFC so I typically cover DC to 40 GHz in all its forms.
JCM: We generally perform conducted testing from 30 Hz up to 50 MHz. We generally perform radiated testing up to 18 GHz by default. We will test at higher frequencies if a given project specifically requests it, but the 18 GHz upper limit is sufficient in the large majority of cases.
Q: RF or EMC Engineering? What’s the best choice for young Engineers looking for a challenging and fulfilling future? I know it is a preference question but interested in hearing what you think.
RTH: Wow, that’s an interesting question. I personally like problem-solving so I would lean more towards EMC versus RF. You’re going to face many challenges in both areas but typically with EMC, you’re working with RF, power, system personnel, and more to work towards the final goal of delivering a product.
JCM: Tough question with no easy answer. If you like math and enjoy a healthy mix of theory/analysis and practical application that gives you the opportunity to play with cool test equipment, either RF or EMC is a good fit. Personally, I like EMC because it allows me to sink my teeth into EVERYTHING. We deal with grounding issues down to DC, we perform conducted tests on power systems down to low frequencies, and we go all the way up to RF and play with antennas.
Q: RF or EMC Engineering? What’s the best choice for young Engineers looking for a challenging and fulfilling future? I know it is a preference question but interested in hearing what you think.
RTH: Wow, that’s an interesting question. I personally like problem-solving so I would lean more towards EMC versus RF. You’re going to face many challenges in both areas but typically with EMC, you’re working with RF, power, system personnel, and more to work towards the final goal of delivering a product.
JCM: Tough question with no easy answer. If you like math and enjoy a healthy mix of theory/analysis and practical application that gives you the opportunity to play with cool test equipment, either RF or EMC is a good fit. Personally, I like EMC because it allows me to sink my teeth into EVERYTHING. We deal with grounding issues down to DC, we perform conducted tests on power systems down to low frequencies, and we go all the way up to RF and play with antennas.