Fail of the Week: NASA Edition

There’s a reason we often use the phrase “It ain’t Rocket Science”. Because real rocket science IS difficult. It is dangerous and complicated, and a lot of things can and do go wrong, often with disastrous consequences. It is imperative that the lessons learned from past failures must be documented and disseminated to prevent future mishaps. This is much easier said than done. There’s a large number of agencies and laboratories working on multiple projects over long periods of time. Which is why NASA has set up NASA Lessons Learned — a central, online database of issues documented by contributors from within NASA as well as other organizations.

The system is managed by a steering committee consisting of members from all NASA centers. Public access is limited to a summary of the original driving event, lessons learned and recommendations. But even this information can be quite useful for common folks. For example, this lesson on Guidance for NASA Selection & Application of DC-DC Converters contains several bits of useful wisdom. Or this one about IC’s being damaged due to capacitor residual discharge during assembly. If you ever need to add a conformal coating to your hardware, check how Glass Cased Components Fractured as a Result of Shrinkage in Coating/Bonding Materials Applied in Excessive Amounts. Finally, something we have all experienced when working with polarized components — Reverse Polarity Concerns With Tantalum Capacitors. Here is a more specific Technical Note on polarized capacitors (pdf): Preventing Incorrect Installation of Polarized Capacitors.

Unfortunately, all of this body of past knowledge is sometimes still not enough to prevent problems. Case in point is a recently discovered issue on the ISS — a completely avoidable power supply mistake. Science payloads attach to the ISS via holders called the ExPRESS logistics carriers. These provide mechanical anchoring, electrical power and data links. Inside the carriers, the power supply meant to supply 28V to the payloads was found to have a few capacitors mounted the other way around. This has forced the payloads to use the 120V supply instead, requiring them to have an additional 120V to 28V converter retrofit. This means modifying the existing hardware and factoring in additional weight, volume, heat, cost and other issues when adding the extra converter. If you’d like to dig into the details, check out this article about NASA’s power supply fail.

Thanks to [Jarek] for tipping us about this.

Retrotechtacular: DC to DC Conversion by Vibrator

Electricity comes in two basic forms: Alternating Current (AC) and Direct Current (DC). DC is handy to use and is easy to analyze. However, AC has some useful properties too. In particular, AC current can operate a transformer which can step it up or down easily. Power is conserved, of course (well, actually, you get less power because of losses in the transformer).

You can’t do that trick with pure DC. You can reduce a voltage, although that typically wastes power in heat (for example, a voltage divider or linear regulator). You can’t readily increase a DC voltage unless you convert it into some sort of AC first.

This was a particularly bad problem in the era of tubes–especially tubes in car radios. The car’s voltage was probably 12V but the tube’s plates might take hundreds of volts. What do you do? Some old car radios used what is called a dynamotor. This is just a motor and a generator in one box. You could spin the motor with 12V and have the generator produce a different voltage (even a DC voltage).

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