Cellphones have become ubiquitous, and while their benefits are apparent, the risks are sometimes more hidden.

After experiencing two incidents of cellphone interference with sensitive hardware, Goddard Space Flight Center’s Safety and Mission Assurance (SMA) Chief Engineer Jesse Leitner raised the concern to the Goddard SMA Risk Advisory Board as a potential cross-center risk. Although the board identified interference from cellphones as low-risk, it found it to be one worth characterizing and mitigating to help ensure mission success.

The Backstory

Back in 2015, both Goddard and a vendor experienced cellphone interference with hardware. Cellphones frequently have functional uses for active projects, such as for photography and communication, but the susceptibility of the hardware to Electromagnetic Interference (EMI) needs to be taken into account. 

The first instance occurred during the integration and test of a sensitive detector system on a Goddard space flight project. Abnormal telemetry readings indicating a high frequency signal spike discovered during testing spurred an investigation. The primary contributor turned out to be a cellphone in close vicinity to the flight hardware that had data collection coinciding with messages coming in and out of the phone.

A second event occurred at a vendor site, in which hardware under vibration testing experienced an excessive, undesired acceleration. The subsequent investigation showed that text messages coming into the phone effectively caused a spurious command through an unprotected controller box in the loop for the vibration control system. Although vibration tables have various forms of limiters to prevent them from “going too crazy,” as Leitner put it, the interference affected the actual controller, overriding one of the protection mechanisms. According to Leitner, this type of over-testing could have caused 10s of millions of dollars of damage had a particular vibration level been achieved:

“It [the damage] would only have been constrained by how hard the table could shake the hardware,” explained Leitner.

Both incidents were repeatedly reproduced by having the cellphone in close vicinity to the hardware in question with incoming text messages submitted while the sensitive hardware was in operation, confirming the findings of both investigations.

Taking Action

Noting that there is a growing Radio Frequency (RF) environment across the center, going well beyond cellphones, and that such equipment is not always practical to ban outright, Leitner tasked Goddard’s EMI and Electromagnetic Compatibility group (in Code 565) with testing the effects of cellphones and other common RF devices to determine what types of restrictions were necessary and appropriate. The results were characterized in NA-GSFC-2017-01, released in July 2017.

In summary, the advisory notes that cellphones, notepads, wifi routers and other similar devices should be kept at least 1 meter from sensitive hardware, when such hardware is powered, and RF Identification devices should not be operated within 2.7 meters of any powered sensitive hardware.  

Leitner notes that banning cellphones outright is not enforceable — people forget they have them on them or have a need to use them. Simply put, it’s not practical.

“The two extremes don’t usually work,” explained Leitner. “And those extremes are to ban completely or let whatever happens happen. [We] found a happy medium.”

Questions can be directed to Leitner.