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That's a cynical perspective. though. In each of the above cases, the mission end date was extended because the hardware was capable of doing more science (or

That's a cynical perspective. though. In each of the above cases, the mission end date was extended because the hardware was capable of doing more science (or for more time) than it was designed for (and budgeted for). Like JWST, some of the procedures required for a successful mission had never been done before, and could not be tested fully on Earth. Many of those procedures have implications on mission longevity. Very smart and dedicated people make their most educated guesses, build in what they know, try to handle the unknowns, and hope and pray -- and more often than not, are proven correct. That's pretty close to my personal definition of "impressive engineering". There's a political angle too, of course. We don't know what NASA's "estimate fudge factor" is. I'd be amazed to learn that it is 5x, 24x, or 56x.

wolverine876 5y ago
> the mission end date was extended because the hardware was capable of doing more science (or for more time) than it was designed for (and budgeted for) That is circular, it assumes that the announced end date isn't just underpromising what they know will be a later date. Neither of us is there when these dates are chosen, so we don't know what they are thinking. Arguably, NASA should be better able to estimate project lifetimes by now. NASA is doing amazing things; I'm not so cynical.
- frosted-flakes 5y ago
  The announced end date is the goal. It just so happens that making the system reliable enough to last x days means it also has a high, but not sure, chance that it will last 10x days.
  - wolverine876 5y ago
    That is a possible description of their thinking, but what is it based on?
  - loonster 5y ago
    Easier to just say it's NASA's high percentage confidence interval. Maybe it's the 95% mark. They are 95% certain it will last 5 years. They likely also have lower confidence intervals with longer times. (If anyone knows what percentage the confidence interval actually is, I would be curious to know)

wolverine876 5y ago

> the mission end date was extended because the hardware was capable of doing more science (or for more time) than it was designed for (and budgeted for) That is circular, it assumes that the announced end date isn't just underpromising what they know will be a later date. Neither of us is there when these dates are chosen, so we don't know what they are thinking. Arguably, NASA should be better able to estimate project lifetimes by now. NASA is doing amazing things; I'm not so cynical.

frosted-flakes 5y ago
The announced end date is the goal. It just so happens that making the system reliable enough to last x days means it also has a high, but not sure, chance that it will last 10x days.
- wolverine876 5y ago
  That is a possible description of their thinking, but what is it based on?
- loonster 5y ago
  Easier to just say it's NASA's high percentage confidence interval. Maybe it's the 95% mark. They are 95% certain it will last 5 years. They likely also have lower confidence intervals with longer times. (If anyone knows what percentage the confidence interval actually is, I would be curious to know)