Ulysses’s odyssey comes to an end

By Phil Plait | February 26, 2008 11:15 am

You may have already heard that scientists have decided that is it time for the solar satellite Ulysses to shed this mortal coil.

Ulysses was launched from the Space Shuttle back in 1990, and was designed to operate for 5 years. Now, over 17 years later, its radioactive power source has finally decayed to the point where power is a serious issue. They’ve decided that in a few months they’ll shut it off, after an extraordinary mission.

Ulysses didn’t take pictures, so you may never have heard of its breakthrough science. It was the first machine to directly detect interstellar dust particles and helium atoms in our solar system, literally, interlopers from another star. It took unprecedented data of the Sun and its magnetic field, and did so continuously for so long that we now have an excellent baseline for such measurements, including over an entire sunspot cycle*.

For me, the most interesting aspect of the mission was that it was in a solar polar orbit: instead of sticking to the orbital plane of the planets like most probes, it was actually sent into an orbit nearly perpendicular to the orbit of the planets, so that it could peer straight down over the solar poles, an aspect we had never witnessed before.

Getting a probe into an orbit like this is hard. Why? Because the Earth orbits the Sun pretty quickly, at 30 km/s (18 miles/second). You need to mostly negate that velocity for a probe to end up perpendicular to the plane of Earth’s orbit, and then you need to give it a huge velocity "down", south if you will, to get it in that orbit (or up, of course, but in this case Ulysses was sent down). No rocket we have now (or in 1990) could do that.

So we borrowed energy from one of the biggest sources we have: Jupiter. Ulysses was launched toward the giant planet, and using a slingshot maneuver launched itself down, down, and away, into the polar orbit around the Sun. While it was at Jupiter it took lots of scientific measurements, and has been sending back data ever since.

But now that’s over. With the power source dying, it cannot keep energy flowing to its instruments, communication devices, and also be able to heat the hydrazine fuel it uses for maneuvering (this is the same stuff the spysat that was recently destroyed — and many other satellites — use for fuel). When Ulysses’s orbit takes it out to Jupiter’s distance once again, it’s so cold that the probe has a hard time keeping its fuel from freezing. All of these together mean it’s time for Ulysses to say its goodbyes.

My only regret for this mission? It didn’t swing by the asteroid 201 Penelope.

*Pedantically, you could say it’s half a cycle since the Sun’s magnetic field reverses every 11 years, and therefore a full cycle is 22 years. But it’s a full sunspot cycle of minimum numbers of sunspots to maximum and back to minimum, so that counts.


Comments (20)

  1. You thought the leaden winter would bring you down forever,
    But you rode upon a steamer to the violence of the sun.

  2. Why wasn’t Ulysses fitted with a solar panel?

  3. Tom


    Solar panels aren’t of much use out by Jupiter. Out there, the panels would only get about 4% of the light they would get if near the Earth.

  4. ioresult

    I went to the probe’s site a few times, looking for pictures. I was always disappointed and I supposed it didn’t have a camera. They could say it on the main page at least: “people looking for pictures beware: the probe does not carry a camera”.

    I wonder how it navigates. Isn’t a star tracker some kind of camera?

    Pieter: solar panels are nearly useless at Jupiter’s distance from the Sun.

  5. Phil,

    I was thinking about writing a little homage to Ulysses because it was one of the two spacecraft whose data I used in projects that helped put me through grad school.

    We took advantage of Ulysses’s extreme polar orbit to sample the varying regimes of the solar wind and use that data to project how those regimes would affect comet plasma tails. We were able to characterize the high and low-speed streams and predict what those streams would do the plasma tails of comets of interest to our team. Sweet stuff!

    I’m sorry to see the spacecraft go, but it has had a good long run. May its data archives live forever!

  6. fos

    I am always amazed by the ingenuity shown by the scientists that design, build, and fly these robotic probes. They are an inspiration for us mere mortals.


  7. morley

    darn moist, i was gonna put some cream references

  8. David

    @moist and morley

    Me too, oh, well its not too late, I guess.
    Tiny purple fishes swim, laughing
    through your fingers
    and you want to take them with you
    to the hardlands of the winter

  9. There’s hydrazine on board? Quick! To the missile launchers!

  10. I’ve always wondered why polar orbits were so rare … even among planets.
    So now I know!

  11. morley

    dear david,

    You rock

  12. Nick Rudzicz

    Obligatory “Operation: Annihilate” retro-reference.

    I suppose there’s no feasible way to somehow brake the probe enough to send it — in a reasonable amount of time — hurtling back down into the sun, so that it might be “finally free”?

    I dunno, I’ve always enjoyed watching NASA (intentionally) de-orbit their probes in spectacular fashion. The pics might not always be the greatest, but the concept is great — I likes me some fireworks, I does.

  13. My only regret for this mission? It didn’t swing by the asteroid 201 Penelope.

    Moreover, it didn’t hang around here for a few years as part of the mission. Bummer.

  14. Troy

    When the MESSENGER data was delayed because of a com issue with Ulysses I was SHOCKED that it was still going. I’m surprised that the radioactive supply is shot after only 17 years though since the Pu 238 half life is something like 85 years. Voyager is still communicating more than 30 years later. My understanding is that it isn’t the amount of radioactive materials, rather it is the degrading of the thermocouple that harvests the energy.

  15. Patrik

    A Science@NASA article from 2004 mentioned that the power level is down to 207 W from 285 W (30W of which should be due to decay if Pu 238 is used) which already then caused problems with the propellant heaters if they tried to use all the instruments and communicate at the same time. My guess is that the Voyeger probes where more overengineered and that they usually don’t run all their instruments.

  16. Dunc

    Props to the Cream fans, but surely Ulysses 31 is the more appropriate reference?

    ” Ulysses, Ulysses, soaring through all the galaxies, in search of Earth, flying in to the night.”

  17. Buzz Parsec

    The article I read (spaceflightnow.com) was a little confusing, but I think they turned off one of the transmitters to save power so they could redirect that power to the heaters to keep the hydrazine from freezing, but then when they tried to turn the transmitter back on, it didn’t work, so they figured without the transmitter and with the general wearing out of the other systems, it wasn’t worth keeping it going. (The article didn’t say, but I presume Ulysses is still communicating with the Earth using a low-power transmitter, so they know it’s still alive, but the high-power transmitter is needed to send back significant quantities of scientific data, rather than just “yup, I got that message” stuff.)

  18. Wayne

    I don’t remember the source, but I think you’re right about the transmitters. That’s not to say that you can’t get science data from a low-gain antenna (see Galileo mission), but it certainly puts a crimp in things.

  19. Are we sure it stole energy from Jupiter to get into the tighter orbit? There’s less energy in a tighter orbit, so maybe Jupiter stole energy from the probe rather than the other way around?

  20. Plutonium being from Pluto

    Vale Ulysses (Launched 1990 October, finished 2009.)

    Voyager to Jove & thrice around the Solar poles.
    Catcher of the fainter wisps of solar wind
    And gamma ray bursts galore,
    Ion tails of passing comets and more.
    Traveller in the deepest dark,
    High flung above the plane
    Long journey in sacred black
    Your home eternity.

    A remarkable odyssey indeed & congrats to the JPL-ESA team that operated it. :-)

    Here is a probe that has been through the ion tails of two comets – Hyakutake and McNught-Hartley & visited the poles of our Sun. Also, & I’d have thought the BA would have mentioned (perhaps I missed it), Ulysses additionally helped fix the position of Gamma ray bursts.A truly remarkable and sadly under-appreciated & too little known mission.

    See : http://en.wikipedia.org/wiki/Ulysses_(spacecraft) & links from there too.

    Plus :


    @ 16. Dunc Says:

    Props to the Cream fans, but surely Ulysses 31 is the more appropriate reference?

    ” Ulysses, Ulysses, soaring through all the galaxies, in search of Earth, flying in to the night.”

    Ah yes definitely – that one brings back a few childhood memories. Good reference. :-)


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