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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.
If you go to the publications page for Ulysses, you'll see that about 60 PhDs have been awarded for Ulysses research, in addition to vast numbers of research papers and other article. By any count, this mission has been a success. Congratulations to all involved.
We all know what to do, but we don't know how to get re-elected once we have done it
"4 times the usefulness" is a bit of NASA doublespeak. They plan a mission in terms of Primary Mission and Extended Mission. Primary Mission is based on the bare minimum, critical science measurements that should or must be taken in order to make the mission worthwhile. The same sort of thinking that goes, "if the house were on fire, what things would I grab on my way out the door?". The time of the mission and engineering of the spacecraft is set around guaranteeing this stuff happens. As you might expect, this results in extreme overdesign in some respects, which leads to: The Extended Mission. The Extended Mission is all the things you want to do AFTER the Primary goals have been hit. They get prioritized and executed in phases over an Extended time. This is more like, "a flood will probably hit the house in two to three days. What should I move out, just in case, and what should go first?"
Behold, this dreamer cometh. Come now, and let us slay him... and we shall see what will become of his dreams.
What about the Lunakhod rovers? Lunakhod 1 lasted 322 earth days, Lunakhod 2 lasted 4 months.
Comment forecast: Bits of genius surrounded by a sea of mediocrity.
STS-41 Launch: ESA Ulysses Oct. 6, 1990
http://www.youtube.com/watch?v=bqmYWgivsHw
Thank you Ulysses!
If you had read the article you would know that this originally was intended to be a five year mission,
Just sit right back and you'll hear a tale,
A tale of a successful trip
That started from a tropic space-port
Aboard this tiny ship.
The console-mate was a mighty science man,
The project manager brave and sure.
Seven instruments set sail that day
For a five year tour, a five year tour.
The sun's plasma started getting rough,
The tiny ship was tossed,
If not for the courage of the fearless controllers
Ulysses would be lost, the Ulysses would be lost.
Table-ized A.I.
This kinda makes me wonder if NASA and other space agencies purposely over-estimate the useful lives of their spacecraft.
It appears that if the craft survives the initial launch and landing (if there is one), then lifetimes often exceed expectations. Thus, the average estimated lifetime is sort of distorted by initial problems during launch and landing. It is kind of like how infant deaths distort average human lifespan statistics such that they usually exclude them.
Further, various instruments seem to be rated for about an 80-percentile. For example, Spirit's wheels were designed for an 80-chance of lasting 3 months (I don't know the exact contract). And, it is true that various parts of Spirit starting failing after 3 months: the front wheel started sticking and the grinder's diamond surface wore off, making it nearly useless. Thus, the chance of most of the instruments lasting past the lifetime estimate is fairly high (assuming critical non-redundant systems don't fail).
Table-ized A.I.
For those that havn't seen pictures, Ulysses is one of the most beautiful spacecraft ever built. Some future archeologist will love getting this for their museum: http://upload.wikimedia.org/wikipedia/commons/6/68/Ulysses_spacecraft.jpg
Covered mostly in gold and other types of metals, the craft looks more like something out of a movie than a real craft.Here's to losing my Karma Bonus again....
Predictable doesn't mean easy. Lunar temperatures have something like a +/- 250 degree temperature range between day and night, and the day/night cycles are 2 weeks long each, meaning your rover gets really hot soaked alternating with really cold soaked. Martian day/night temperatures are not so extreme, and the days/nights are only about 12-1/4 hours long each. The atmosphere helps moderate the temperature.
Sure, Mars has winds where Luna doesn't, but given the thin atmosphere, it's not like you have to worry about them blowing the rover away or anything. As it turned out, they were just right to blow accumulated dust off the solar panels. Yes, the wind means dust might be more likely to get into the mechanisms, but at least it's smooth rounded dust. Lunar dust is jagged fractal surfaces all the way down, highly abrasive; the saving grace is that it only gets kicked up by your wheels spinning or a nearby impact. (That's another difference -- the Martian atmosphere is enough that you don't have to worry about micrometeorite impacts, which you do on the Moon.)
Venus is of course a different question; nobody's gotten a Venus-lander to last for more than a few hours. The surface temperature is twice as hot as a pizza oven (hotter, in fact, than Mercury's surface), and the pressure is about the same as 3000 feet underwater.
-- Alastair