What's Up With Ulysses?, alive? dead? cancelled soon? Options

[deglr6328]

What is up with the tiny Ulysses spacecraft that was launched in 1990 to study the solar whatever at high lattitudes? Last I heard it was in danger of dying because the RTG power was running low and at aphelion there was a risk of the hydrazine freezing/exploding in its propulsion system. Well that was like a year ago and I haven't heard anything since. It looks like it should've passed aphelion by now and should be out of danger.....

Its been going up there for over a full solar cycle, is it one of the missions on the chopping block because of the new humans on moon/mars thing?

[nprev]

I agree with ustrax; the longevity of this spacecraft (and others) is astounding. These are arguably among the most complex devices ever built, yet without hands-on maintenance, periodic overhauls, etc., they just keep going. Wonder if the space agencies might be interested in building a few cars on the side...

All that aside, how much longer can Ulysses keep going given this new power conservation strategy? Also, is there any possibility that it will re-encounter Jupiter at some point?

[Paolo]

Also, is there any possibility that it will re-encounter Jupiter at some point?

Back when I was in university, a dozen of years ago I played with simulating Ulysses' orbit. In that occasion I "discovered" the second flyby of 2003.
Ulysses crosses Jupiter's orbit every 6.5 years, and approaches it every 13 years, but IIRC, the encounter distance is increasing and there will be no more flybys during all of the 21st century.

[IM4]

Back when I was in university, a dozen of years ago I played with simulating Ulysses' orbit. In that occasion I "discovered" the second flyby of 2003.
Ulysses crosses Jupiter's orbit every 6.5 years, and approaches it every 13 years, but IIRC, the encounter distance is increasing and there will be no more flybys during all of the 21st century.

I explored Ulysses orbit evolution with JPL HORIZONS system. Here are some interesting encounters till the end of XXI century:

CODE

          Date (CT)       Body  CA Dist      Vrel
  ----------------------  -----  --------  ------
  A.D. 1992 Feb 08.78380  Juptr  0.006795  20.895
  A.D. 2004 Feb 04.98546  Juptr  0.804396  13.984
  A.D. 2086 Nov 13.65625  Juptr  0.780194  14.070
  A.D. 2095 Nov 01.78213  Mars   0.056797  37.722
  A.D. 2098 Nov 07.59152  Juptr  0.004053  24.594

November 7, 2098 Ulysses will be kicked out of the Solar system by Jupiter's gravity. Spacecraft's final trajectory will be highly hyperbolic (eccentricity~1.42), so it will be travelling very fast and one day, thousands years from now, Ulysses will reach some star.

[ugordan]

November 7, 2098 Ulysses will be kicked out of the Solar system by Jupiter's gravity. Spacecraft's final trajectory will be highly hyperbolic (eccentricity~1.42), so it will be travelling very fast and one day, thousands years from now, Ulysses will reach some star.

I'm wondering how accurate HORIZONS data can possibly be for such distant dates. There has to be a number of unmodelled factors affecting orbital evolution of the spacecraft that the system doesn't take into account such as solar radiation pressure, slow outgassing from the spacecraft, etc. These will, given enough time, measurably perturb the orbit and I'm wondering what the real flyby distance and slingshot effect will be in 2098. Even tiny perturbations now can lead to large deviations in the future predicted passes.

I wouldn't put my hand into the fire and say Ulysses is heading out of the solar system, let alone heading out on a highly hyperbolic trajectory. Move the closest approach point to Jupiter by a million km in one direction and it could end up being decelerated by Jupiter instead.

EDIT: To give a sense of what I'm talking about, consider Jupiter's orbital velocity is 13 km/s and so it needs some 21 hours to cross a million kilometers. If Ulysses is early in its orbit by a mere 20 hours at the time of the 2098 flyby, the outcome could be radically different. A 20 hour cumulative in 90 years is really not much, especially since weak forces like light pressure tend to not change orbits much, but change their circumference a bit, which then brings timing differences that accumulate over time.

[tedstryk]

For most of that time it should be away from major influences. However, when I run the numbers, I am seeing a Jupiter flyby in 2092 that is fairly close and would extend the orbit too far out to be thrown out of the solar system in 2098. In fact, at least on the "kiloyear" level, the orbit looks stable.