Groundbreaking Solar Mission Faces Chilly Death

iamlucky13 writes "Over 17 years ago, the Ulysses spacecraft was launched aboard the space shuttle Discovery for a unique NASA/ESA mission. While nearly all other probes travel along our solar system's ecliptic plane, Ulysses used a Jupiter gravity assist to swing 80 degrees out of plane, carrying it over the sun's poles for an unprecedented view. During a mission that lasted four times longer than planned, it has flown through the tails of several comets, helped pinpoint distant gamma-ray bursts, and provided data on the sun and its heliosphere from the better part of two solar cycles. Unfortunately, the natural reduction of power from its radioisotope thermal generator means it is now unable to even keep its attitude control fuel from freezing, and NASA has decided to formally conclude the mission on July 1."

Re:solar power?

[Anonymous Coward]

it does not provide thrust. for that you need to throw out some mass. or use HUGE solar sails.

Re:I'd send it into the sun for one last splash

[PMBjornerud]

"Attitude control" means the thrusters to change its orientation, as opposed to changing the course. You could likely make the probe spin real fast. Not sure if that would give you any more exciting data, though.

I think you can safely assume the engineers on the project have gone through the possible options.

Re:I'd send it into the sun for one last splash

[cyclone96]

To change the orbit to intersect the sun, a tremendous amount of velocity would need to be removed from the current orbit. It would take more propellant to get it to the sun than it took to launch it from the earth in the first place.

It's actually quite difficult to "hit the sun", the Messenger [jhuapl.edu] spacecraft will need to do one earth, two Venus, and 3 Mercury flybys over 7 years to "slow down" enough so that it can finally brake into orbit around Mercury with it's insertion motor.

Re:I'd send it into the sun for one last splash

[u38cg]

Absolutely no way, is the short answer.

Long answer - in order to get it into the sun, you have to reduce its rotational velocity from numerous miles per second down to zero. You'll remember your 0.5mv^2 - that's how much calorific energy has to be in those tanks to achieve that. Also, at those kind of distances, almost any kind of rotational velocity will be enough to achieve orbit - meaning the damn thing will almost certainly miss and turn into a rather odd comet, which will no doubt baffle our ancestors.

Re:I'd send it into the sun for one last splash

[ozbird]

It doesn't carry anywhere near enough fuel for a sun dive.

Most of the energy to get into its current orbit came from its PAM-S and IUS solid rocket boosters, with Jupiter kicking it out of the ecliptic. Until New Horizons was launched recently, Ulysses was the fastest ever artificially-accelerated object - that's how much energy we're talking about. Ulysses started out with 33.5kg of hydrazine maneuvering fuel, and was down to 8.4kg in May 2002. In a nutshell, you could use up all of the remaining fuel and not get anywhere near the Sun (perhelion distance is around 1 AU.)

Re:RTG lifetime

[deglr6328]

Because the problem of failing RTGs is not due to radioactive decay. RTGs use Pu-238 which has a half life of 88 years. It's just as hot as when it launched. The problem is dopant migration in the semiconductor heterojunctiontions (peltier junctions) of the part that creates the electricity. They degrade over time and put out less electricity for the same reason an LED fails gradually over time slowly emitting less and less light for the same amount of energy put in.

Re:Mission's over?

[Anonymous Coward]

Did you see that big dish on it? "Floating around aimlessly" = not pointing at the earth. You can't transmit to the earth without attitude control.

Re:NASA-style journalism

[Anonymous Coward]

Except in this case it isn't even a NASA spacecraft, sure NASA lauched it and did lots of the science equipment, but the spacecraft itself was built by the ESA.

Re:solar power?

[NathanBFH]

While this was certaintly true 17 years ago, it's interesting to note that we are now able to sufficiently power science craft with solar panels even as far as Jupiter. Check out Juno: http://en.wikipedia.org/wiki/Juno_(spacecraft) [wikipedia.org]

Re:Don't know how to mod this

[Pathwalker]

What term would you use for the ions in the junction of two different metals than "heterojunction ions"?

Seems perfectly clear to me.

Re:Don't know how to mod this

[jschen]

Definitely informative. Slowly failing RTG's due to degradation of the thermocouples that convert heat into electricity is a likely cause of the eventual end of the Voyager missions. More info at http://voyager.jpl.nasa.gov/spacecraft/spacecraftlife.html [nasa.gov]

Re:solar power?

[hubie]

"Sufficiently power," of course, depends on your mission goals as well. An RTG will give you consistent power for a long time, whereas the solar cells will have issues managing eclipses and long-term degradation from radiation exposure. A Voyager-like flyby would be better suited for an all-solar approach rather than a Galileo-type orbit (and eclipse) all the time in strong radiation belts. History has also shown that it is far from trivial to deploy large solar arrays, even when you have humans present, and the size of these arrays are huge.

A very nice summary [usra.edu] of solar cell technology and future plans can be found over at the USRA site.

Re:RTG lifetime

[Free the Cowards]

And if wishes were horses we'd all be eating steak.

It's easy to say things like, just double the mass of the RTG and just use an isotope with a longer half-life. It's much harder to actually find an isotope with that longer half life (the isotopes which have an appropriate half life and can be synthesized in the appropriate quantities, and to actually change the design of the spacecraft to accommodate the extra mass.

It's an extremely complex engineering problem with a lot of tradeoffs involved. If they could get more life "for free" then they certainly would, but unfortunately it's far from free when you get into the details.

Re:yeah but

[Tubal-Cain]

Ulysses was launched on October 6, 1990. Linux was announced August 25, 1991. (hurray for wikipedia!) Draw your own conclusions.

Re:The Real Ulysses

[Petrushka]

Yeah, because he sucked at navigation. Additionally, he was an idiot: All the things the gods warned him not to do because they would turn out to be bad, he did - and they went bad.

Not a single statement there accurately reflects the Odyssey. The actual story, as opposed to the one you've made up, relates that:

1. he took ten years because his men continually disobeyed his orders -- that's made clear in the first few lines --;
2. he shacked up with Circe for a year (voluntarily);
3. after he washed up on Calypso's island she basically held him prisoner for seven years. The story also relates how
4. any time a god told him to do something, he did exactly that; and
5. he is repeatedly described as having practically divine intelligence, and this is borne out by the various schemes he devises in the story. Even Athena compliments him on his deviousness.

The reason you do not understand his appeal to the ancient Greeks is because your memory of the story bears little resemblance to the actual story.

Here there's more

[Dusty]

The European Space Agency had a press conference about the end of Ulysses on Thursday. Brief note and audio feed [esa.int]. Longer press release [esa.int].

The video the Ulysses Legacy [esa.int] has a great summary of the mission, and of the problems it now faces.