Artemis Satellite - Non-Geostationary Orbit
This may be a bit long, but I had a tiny part in it's subsequent success.
Nearly 20 years ago I worked for a company that was part of a consortium to produce the Artemis satellite. One of the innovations was an ion propulsion engine that used xenon to keep the orbiter at the correct inclination.
This engine was quite small, not much more than a meter in length and had a series of small diameter tubes around 12mm in diameter, made from small sections of stainless steel (SS) pipe welded together, in order to transport the xenon from the tank to the engine. These pipes were welded using an automated autogenous welding machine.
The manufacture of the satellite had suffered numerous set backs and it was touch and go as to whether it would be completed due to budget over-runs and delay. The propulsion lab encountered a number of problems associated with the welding quite far into the production of the unit and the materials lab (on site) were asked to investigate.
Subsequent analysis from supplied welded coupon samples showed that some of the pipes were made from the wrong SS alloy (not connected with the welding problems). In order for SS to be welded and remain corrosion resistant then you have to use an alloy that contains titanium (or niobium), which preferentially forms titanium carbide rather than chromium carbide when welded, because you want the chromium to remain in solution which is what provides the corrosion resistance. If chromium carbide precipitates then the percentage of chromium in solution drops thus reducing the corrosion resistance and potentially lead to cracking. This is known as "weld decay".
For some reason 316 stainless pipe had been supplied rather 316L (niobium or titanium stabilised). When the project manager for the ion propulsion engine came into the lab and was informed of the error, he went green and had to be sat down with a nice cup of tea! It looked like this screw up would put the kibosh on the whole project. Millions wasted.
We had to find out the extent of the problem, so a tiny scraping of each pipe section that had already been welded and manufactured was taken (dozens of them) and then examined in the scanning electron microscope (SEM) to identify if the section was 316 OR 316L. It took 2 weeks and the diagnosis was not good. There was a mix-match of the two alloys across every transport tube.
In the mean time we asked the propulsion lab to produce enough welded sections from the two alloys so we could perform a complete re-qualification process in order to provide all the data for the engineers to say whether the ion propulsion engine was fit to be stored and then fly. The previous qualification process had taken 6 months. We did the new one in 4 weeks!
Some of us were sleeping at work (I bagged the labs photographic dark room!) and we would order in a takeaway each night followed by "a full english" in the morning from the canteen! (all on expenses of course)
Subsequently the ion propulsion engine was qualified to fly.
When the satellite was launched a failure of the launcher meant that the satellite was put into the wrong orbit. The only way to finally get the thing into the right orbit was to use the ion propulsion engine. It worked! The engine was so good that it was operating greater than the designed efficiency so was able to not only 'boost' it to the correct orbit but also provide a good lifespan.
It was a simple mislabelling of the bar stock at one supplier that led to the whole fracas.
https://en.wikipedia.org/wiki/Artemis_%28satellite%29
http://www.aerospace-technology.com/projects/artemis/
