Learning how to assemble a basic electronic circuit is something every burgeoning electrical engineer will learn. Some of the concepts driven home the hardest include component polarity, reviewing test procedures, and protecting against electrostatic discharge. At least once in the academic career of an electrical engineer, a mistake will happen—at least once—with one of these core lessons while assembling a test circuit on a project board.
At least we're in good company. NASA keeps a repository online in what they call the "Lessons Learned Program". There, for all to see, is a collection of entries that detail problems arising from mistakes like backwards capacitors and electrostatic discharge. Such trivial problems can lead to catastrophic failures that cost huge amounts of money and derail tight schedules.
Here’s a look at a few electrical engineering mishaps from NASA’s Lessons Learned files.
Reverse Capacitor Polarity on the CALIPSO Avalanche Photodiode Detector Assembly
The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite is a joint project between NASA and CNES (France’s national space agency). It's equipped to take measurements and collect data on Earth’s climate. In particular, CALIPSO monitors cloud and aerosols in the atmosphere, helping scientists determine what roles they play in the overall regulation of weather and climate on Earth.
This entry in NASA’s Lessons Learned repository comes from July 30th, 2006. Something as simple as reversed capacitors resulted in the failure of CALIPSO’s Avalanche Photodiode Detector Assembly during thermal/vacuum testing. The error was traced back to design drawings which indicated the wrong polarity for the tantalum capacitor.
A tantulum capacitor is an electrolytic capacitor which is dependent on polarity for proper performance. Image courtesy of capacitorguide.com.
The error resulted in the disassembly of the payload, removal of the APD detector, and the repair of some damage that resulted from the disintegration. When the payload was re-integrated and calibrated, some of the qualification testing was skipped to help minimize impacts on schedule and cost.
In the Lessons Learned notes, it is recommended that polarized capacitors should only be used in certain situations because the lifetime of the components are reduced when reverse biased incorrectly. All components with polarity should be catalogued to help with quality assurance tracking and inspection.
Reverse Voltage Polarity on the Magellan Power Control Unit
The Magellan spacecraft was launched by NASA in 1989 as a probe to map Venus's surface and measure its gravitational field.
Before the spacecraft’s completion, an entry in NASA’s Lessons Learned archive details an engineer performing tests on the Magellan Power Control Unit after-hours and without proper testing protocols. Without quality assurance overview or testing procedures, a mistake was made and a reverse voltage was applied to the unit.
Magellan's deployment. Image courtesy of NASA.
The power control unit is a critical component in many spacecraft systems, and the mistake resulted in blown fuses and damaged circuitry. Ultimately, the repairs were made without any impact on the launch schedule for the spacecraft.
In the Lessons Learned notes, there's a comment that adequate personnel should be in attendance during the testing of all flight hardware with proper test procedures outlined and quality assurance overview at hand.
Electrostatic Discharge: A Threat to Hardware
In this entry from NASA’s Lessons Learned archive, a general recommendation is made on considering the threat and mitigation of electrostatic discharge damage to hardware in NASA’s Reliability Preferred Practices for Design and Test document. The entry lists various examples in which failure to prevent ESD resulted in, or could have lead to, damage of hardware.
In one case, a ground strap being dragged across a floor came into contact with a power outlet, creating sparks and melting the straps and power connectors during testing of the Mars Exploration Rover. The lesson was to request that vendors use proper ESD handling procedures.
Electrostatic discharge damage magnified. Image courtesy of JPL.
In another entry, ESD was pinpointed as the cause of a discrete capacitor building up a residual charge. This resulted in damage to an integrated circuit and, ultimately, in failure. The recommended lesson to learn was that testing procedures should include checking components for residual charges and shorting capacitors from storage to installation to help mitigate this issue.
So, you see, rookie mistakes aren't reserved just for rookies. Sometimes it's the basic lessons that slip through the cracks and cause big problems. Cruise through NASA's Lessons Learned files to see how the pros learn from their mistakes.
Featured image used courtesy of NASA.