How Bad Cabling Cost a Spanish Engineering Team 200 Million EurosNovember 20, 2020 by Jake Hertz
This past week, Spain’s attempted launch of its first optical imaging satellite ended in tragic failure—and the reason was frustratingly avoidable.
In 2007, Spain launched a program to develop Ingenio, the country’s first-ever optical imaging satellite. Fast forward 13 years, 200 million euros, and immeasurable work by engineers and the project was finally ready to be launched as of last week. Unfortunately, this project didn’t reap success as project participants had hoped.
Ingenio: the 200 million Euro project that failed. Image from El País
About eight minutes after launch, the control center noticed that the satellite was moving away from its established path. Then, the satellite lost control altogether, eventually failing and crash landing in a remote area of the Arctic. After analyzing the telemetry data, the team determined the cause of failure— and it was something out of an engineer's worst nightmare.
The Culprit? Erroneously-Assembled Cabling
The cables connected to the engines that controlled the trajectory of the rocket were plugged in backward. Not a design flaw, but an assembly error.
While numerous testing procedures should have caught the error, one simple way to have avoided the situation was to use cables with unique connectors on both ends of the cable. Assuming that constant impedances could be maintained with two connector types and that the insertion losses were kept to a minimum, this solution would’ve made it impossible to install the cables in the wrong direction.
This image depicts a small, cheaply-designed transformer In the early 20th century. EEs used to design the windings and choose the type of wire that worked best for a design. Now, we use thinner wires because they're cheaper—but motors burn them out faster. Today, EEs are less familiar with the ins and outs of wiring. Image used courtesy of the Edison Tech Center
This incident speaks to the necessity for engineers to not only be experts at the more complex aspects of circuit design but also to attune an eye for detail with seemingly prosaic skills, like cable assembly and connectorization.
The news can teach us another valuable lesson as well. In general, how does cabling affect design?
Cabling Impacts Design
Engineers are faced with a number of considerations when selecting cables for electrical designs: What type of wire should I use (for example, braided, stranded, or solid)? What material wire should I opt for—aluminum, copper, or gold? How is the wire insulated?
For the sake of this article, however, we’ll only explore two fundamental reasons that cable selection can impact design: EMC and transmission line effects.
Cabling and EMC
With respect to EMC, one thing to keep in mind when selecting cables is the fact that all cables are antennas. By the laws of physics, all conductors create electric and magnetic fields from the charge and current through them. For this reason, cables can be the principal means by which signals cause radiated emissions and external fields contaminate signals (susceptibility and immunity).
Conductor length vs. antenna efficiency. Image from Keith Armstrong
Cabling and Transmission Line Effects
Transmission line effects occur when interconnect lengths become greater than wavelengths of the transmitted signal. Since physical cables tend to be the longest interconnects in electrical designs, they are most prone to transmission line effects.
An important consideration in this regard is the characteristic impedance (Z0 = √L/C ) of a line. These impedances are unavoidable, so to mitigate their effects we have to choose cables that either have Z0 kept constant over the entire length of the interconnect or match the load and source to the characteristic impedance of the line.
This is why RF and all EMC test equipment use controlled-impedance 50-ohm transmission line cables and connectors.
Attention to Detail Matters
Although cable selection and assembly are often overlooked aspects of design, these details can have huge impacts on a system's operation. Yes, the satellite incident in Spain was an extreme illustration of this concept, but it can serve as a valuable reminder to engineers to reexamine less "glamorous" skillsets and commit to greater attention to detail.
Sometimes, the most consequential design failures come down to simple errors. Have you ever heard of such a mistake? What takeaways can the EE community internalize from such incidences? Share your thoughts in the comments below.