EMI brings down Virgin Galactic SpaceShipTwo: Don’t Let it Happen to You

The importance of dealing with electromagnetic interference (EMI, also called radio frequency interference or RFI) in electronic systems was once again brought home to me as I read through the transcript of Virgin Galactic’s recent earnings call which included the statement: “During the December test flight, the rocket motor halted as it was starting the ignition sequence because the onboard rocket motor computer lost connection . . . we’ve identified and isolated the issue to be a reboot of the computer likely caused by electromagnetic interference.” According to the transcript, a new flight-control computer system had been installed and was one of the components being tested.

The transcript continued, “EMI is a relatively common challenge in aerospace. And in January, we proceeded with modifications that were designed to lower the EMI levels and better protect certain systems . . . Our estimate to complete this work is eight to nine weeks, which suggests our next test flight will be in May [it was originally scheduled for February.]”

Figure 1: Virgin Galactic’s SpaceShipTwo, also called VSS Unity, glides back to earth after a supersonic test flight in 2019. (Image source: Virgin Galactic)

Troubleshooting issues related to EMI can be tricky. While a reboot of the new control computer system that triggered the abort was determined to have been caused by EMI, without more data it’s hard to know how they determined EMI to be the actual source and how exactly it affected the system. Regardless, it clearly shows the importance of good EMI detection and mitigation practices upfront in a design. Still, it’s hard to preempt all instances of EMI, so the next step is to mitigate it upon detection.

Filtering out EMI

Fortunately, designers have multiple options for dealing with EMI, including filters on signal and data lines, power entry filters for EMI emissions control, and kits of common EMI filtering components for designing custom RF filtering solutions. Let’s review three: one each from Bourns, TE Connectivity Corcom Filters, and TDK.

EMI network filters: Designers of computers, telecommunications equipment, audio and video equipment, and industrial systems can use Bourns’ EMI T network filters that provide ten different 25 decibel (dB) attenuation ranges (Figure 2).

Figure 2: EMI T network filters provide designers with ten different 25 dB choices of attenuation ranges and excellent noise filtering at high frequencies. (Image source: Bourns Inc.)

These T network filters are offered with attenuation frequency ranges from 800 to 1000 megahertz (MHz) for the EMI220T-RC, and down to 15 to 200 MHz for the EMI103T-RC. If a circuit board or subcircuit is susceptible to a specific range of EMI frequencies, the addition of one of these compact filters could mitigate the problem.

Power entry filters: Switching power converters can be a significant source of EMI. Standard power entry filters can be used to provide enhanced filtering and can offer various levels of EMI mitigation. It’s possible that exchanging an existing filter for one with higher performance could eliminate harmful emissions.

The X, Y, Z series from TE Connectivity Corcom Filters offer three levels of performance designed to bring most digital equipment (including those with switching power supplies) into compliance with specific EMI emissions limits. Specifically:

  • The X series is designed for compliance with FCC Part 15J, Class B conducted emission limits.
  • The Y Series is designed for compliance with EN55022, Level A and FCC Part 15J, Class B conducted emission limits.
  • The Z series is designed for compliance with EN55022, Level B and FCC Part 15J, Class B conducted emission limits.

The filters come in through-hole board mount or external mount configurations (Figure 3).

Figure 3: The X, Y, Z series of power entry filters from TE Connectivity Corcom are available in board mount (left) and external mount (right) styles. (Image source: TE Connectivity Corcom Filters)

For example, the 3EXP (left) is a 3 ampere (A), low-leakage (<0.5 milliamperes (mA)), 250 volt AC single-phase line filter configured for through-hole mounting.

Kit for custom RF filter designs

Of course, the EMI problem may be a result of increased susceptibility of a new computer system to emissions from other adjacent subsystems, such as an RF section. While I have often been able to use standard filters to address power supply EMI, in the case of RF sections, custom filter designs are often needed. To assist designers in this, TDK Corp. offers the RF-KIT, an RF filter components kit for systems operating at 900 MHz and 2.4 gigahertz (GHz). The kit comprises 290 pieces; 29 values each of 10 different surface mount filter components, including baluns, multiplexers, and RF filters.

Figure 4: TDK Corp. simplifies custom filter design for the 900 MHz and 2.4 GHz bands with a 290 piece RF filter design kit. (Image source: TDK Corp.)


EMI issues can be tricky to identify and resolve, and they can be crippling to system performance. As shown from the experience of SpaceShipTwo, it is important to thoroughly test and identify EMI problems as early in the design process as possible. EMI issues that pop up later in the design cycle can result in serious delays. Fortunately, designers have multiple avenues available to mitigate both EMI susceptibility and emissions.

About this author

Image of Jeff Shepard

Jeff has been writing about power electronics, electronic components, and other technology topics for over 30 years. He started writing about power electronics as a Senior Editor at EETimes. He subsequently founded Powertechniques, a power electronics design magazine, and later founded Darnell Group, a global power electronics research and publishing firm. Among its activities, Darnell Group published, which provided daily news for the global power electronics engineering community. He is the author of a switch-mode power supply text book, titled “Power Supplies,” published by the Reston division of Prentice Hall.

Jeff also co-founded Jeta Power Systems, a maker of high-wattage switching power supplies, which was acquired by Computer Products. Jeff is also an inventor, having his name is on 17 U.S. patents in the fields of thermal energy harvesting and optical metamaterials and is an industry source and frequent speaker on global trends in power electronics. He has a Masters Degree in Quantitative Methods and Mathematics from the University of California.

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