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When a spacecraft is built and prepared for a future launch, its parts and the whole spacecraft usually goes through a lot of testing - for example, the James Webb telescope has already been through the Cryogenic Testing under extreme cold temperatures, the Acoustic Vibration tests in a special acoustic test chamber etc.

All of these tests put a lot of "pressure", load and stress on a spacecraft and its hardware.

Does all of this come at some cost? Is not by applying stress and checking how would it perform in extreme conditions we are reducing the durability and fault tolerance of a spacecraft?

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    $\begingroup$ I don't know about spacecraft--they're obviously very expensive so they can't necessarily build a lot of extras, but when we test our hardware, we don't ship the same units we've stress/load tested to customers. $\endgroup$ – c32hedge Dec 18 '17 at 15:05
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    $\begingroup$ The stress of the planned testing is included along with the stress of the mission in the design of the spacecraft. The spacecraft is simply designed to take it. $\endgroup$ – Mark Adler Dec 22 '17 at 13:31
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The simple answer to "Does stress-testing a spacecraft affect its durability?" is Yes, it does, in the classical western view of test programmes.

I can't answer for the James Webb Telescope specifics but a common approach is to divide a test programme conceptually into design verification and workmanship verification. As an aside, the design verification tests are called the "qualification" tests where as the workmanship verification tests are also known as "acceptance" tests.

Qualification tests are aimed at showing that the system works at some given range of environment and can survive at some greater range. These will all be the expected mission environment (temperature, radiation, vibration plus some margin, all for some given length of time). Acceptance tests are similar but with lower margins. The usual philosophy is that a flight model can not be subjected to qualification levels and so a special qualification model has to be built for the qual tests. This fits the usual serial production well, the qual model is tested hard but never flies, the flight models only see acceptance testing.

In the James Webb case the production is just one satellite and there may not be a qualification model at satellite level. In this case sometimes the mission management agree with their customer that the flight model will be tested to qualification levels of temperature and vibration stress but only for durations consistent with acceptance testing. This is called "proto-flight" testing and it explicitly recognises that testing affects durability.

As an aside I often think that protoflight testing is a bit of a fudge that both undertests for qualification purposes and over tests for acceptance (workmanship purposes), but that's just my tuppence.

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  • $\begingroup$ That clears up a lot of questions I had, now I am going to interpret the spacecraft testing events I read about quite differently. Thanks so much for the answer! $\endgroup$ – alecxe Dec 26 '17 at 0:16
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    $\begingroup$ Glad to hear it. I live in Europe and grew up on national standards for satellite AIT but the European (i.e. ESA) standards and US commercial practices are very similar to one another, by which it seems likely that NASA and DoD are probably also similar in philosophical terms. These big procurement organisations have publically available standards (for ESA look up ECSS) though it can be a bit of a labyrinth to start with. $\endgroup$ – Puffin Dec 26 '17 at 22:53
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Each part of a space craft has a life span of x number of hours. Parts are changed out on space craft long before the x number of hour life span, long before failure, due to prevent any malfunction.

Thermal Stress testing on proto-flight hardware over the temperature range of +75°C/-20°C is done for 24 hours at the cold end and 144 to 288 hours at the hot end but the hardware has many hours of life left after stress testing.

Thermal stress tests, coupled with rigorous design practices, provides ahigh confidence that the hardware design is not marginal during its intended long life, high reliability mission.

Some of the tests performed by NASA can be viewed at http://www.klabs.org/DEI/References/design_guidelines/nasa_reliability_preferred_practices.htm#1404

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    $\begingroup$ Some of the tests performed by NASA are non destructive tests, they don't stress flight hardware. Other destructive tests are done with parts from the same batch, but not with parts used for flight. Tests reducing reliability or life span should also be done with parts from the same batch. $\endgroup$ – Uwe Dec 21 '17 at 19:03
  • $\begingroup$ @Uwe this is exactly what was always puzzling me - on one hand, we cannot directly stress-test everything that goes then into space, but then "same batch" idea does not guarantee that a part from the same batch would perform as an another in the batch. I guess that puts some serious responsibility on the vendors of these batches..I hope you can see my motivation for this question here. Thanks. $\endgroup$ – alecxe Dec 22 '17 at 0:51
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    $\begingroup$ @alecxe: I expect that there are other kinds of engineering tests to determine how consistent a given production process is within a batch. You wouldn't do stress testing the way Uwe described unless you had reason to expect the parts from a single batch are all reasonably consistent with each other. If they're not, you'd either do the stress testing differently or demand more consistency from the part supplier. $\endgroup$ – Blckknght Dec 25 '17 at 0:41

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