Ulysses Spacecraft on its Last Legs

doconnor writes "JPL announced that Ulysses' mission will be ending after 17 years. The power generated by the decay of a radioactive isotope has been slowly decreasing. To conserve power its main transmitter was shut off. Unfortunately due to a fault in its power supply it cannot be turned back on. The team plans to continue operating the spacecraft in its reduced capacity, using the alternate S-band transmitter, for as long as they can over the next few weeks." Congratulations to all the geniuses involved in this one.

Comments

Geniuses

[outlander78]

I'm not sure if the congratulatory statement was sarcastic or sincere, but I hope it was sincere. From the article:

"The joint NASA and European Space Agency Ulysses mission to study the sun and its influence on surrounding space is likely to cease operations in the next few months. The venerable spacecraft, which has lasted more than 17 years or almost four times its expected mission lifetime, is succumbing to the harsh environment of space."

Further on the article states that the lifetime was expected to be five years, so three times, not four, but still, a spacecraft tripling its expected useful life is a strong testament to the skill of its engineers.

Re:Geniuses

[Vellmont]

This kinda makes me wonder if NASA and other space agencies purposely over-estimate the useful lives of their spacecraft.


There's a hidden premise here. The premise is we can know the expected lifetime of something that:

• We never fully get to test each probe in the environment it experiences.
• We've only made (I'm guessing) less than 100 of these probes ever, each of which is very different and experiences very different environments.
• We don't even know exactly the environment each probe is going to experience.
• The technology itself is constantly changing over the last 40-50 years of sending out robotic probes.

Which do you think is more likely?

The engineers all know how long the thing is going to last, but lie about it to make themselves and NASA look good.

or

They really don't know how long it's going to last, but make some very conservative estimates about the above unknowns, to make sure it'll last at least as long as the time frame it's supposed to. Sometimes those guesses turn out to make the thing last a lot longer than it needed to be.

Re:D'oh

[sjames]

4 times the usefulness" is a bit of NASA doublespeak.

However, in this case, it really is on the tail end of the extended mission. The reason they wanted to shut the xband transmitter off was that the isotope generator is winding down. The output of the isotope generator is quite predictable. That is, they KNEW it would be out of energy by now. Had they been able to toggle the xband transmitter and divert energy as planned, it would have bought a second extended mission of about 2 years. NASA has done a pretty good job w/ Ulysses.

Meanwhile, given the extreme hostility of space and the complete impossability of making repairs once launched, the practice of overdesign for the primary mission is justifiable. The extended secondary mission is the simple practicality of if it's still working, might as well enjoy it.