The Dawn mission was put on standdown last October after going over budget and suffering several setbacks that included the rupture of two xenon fuel tanks during testing, forcing engineers to reduce the amount of xenon to be loaded in the tanks.
For background reading on the mission and its difficulties, I suggest the paper by C. T. Russell et al: Dawn Discovery Mission: Status Report (pdf). The report includes some useful insight into the typical problems with spacecraft development:
Dawn has not been immune from the difficulties generally encountered by spaceflight projects that have fixed, tight schedules. Manufacturers have fluctuations in their workloads when unexpected orders arrive. Small changes in process may be made without much concern or documentation, until the subsystem fails inspection or test. Advanced planning may be inadequate so that needed parts are not on hand on assembly day, etc. These lapses all lead to delays which must be overcome with the expenditure of schedule or cost reserves. Thus far Dawn has delayed its launch date only by three weeks, principally due to an early lapse in support for the project, rather than any of the many technical issues experienced in system development. It is the Dawn projectâ€™s self-assessment at the present time that it can continue to move on schedule to launch, barring a major technical problem outside the control of the project, such as the perennial problem of the possibility of a launch vehicle standdown. A potential issue of this nature does exist with the processes used to fabricate Dawnâ€™s xenon tank. However, we expect that Dawn will not be affected by the questions associated with the processes used to build the tank for the reasons outlined below.
Design, analysis, and test of the titanium tank for the xenon propellant are also discussed in the report:
The flight tank installed in Dawn has been tested to well above the pressures needed for ground and flight operations and it has been taken to theses high pressures repeatedly. However, when tanks similar to the flight tank have been ruptured by increasing the pressure on them until they cracked, the tanks ruptured at pressures above that needed by Dawn but below the theoretical estimates, necessitating a review of the construction processes, assumptions and the actualities of the as-built tanks. The root causes for the reduced pressure at rupture are now known and how to build stronger tanks understood. Thus there should not be problems with future tanks, but what to do with Dawnâ€™s tank now in the spacecraft?
This mission might make a nice case study in spacecraft design. In the words of Mario Salvadori’s mother-in-law, commenting on his book Why Buildings Stand Up:
This is nice, but I would be much more interested in reading why they fall down.
Spacecraft failures are interesting too, and I wrote about them in this 2003 conference paper:
When Spacecraft Won’t Point (pdf).