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Emily LakdawallaMarch 14, 2008

Stretching out Ulysses' life as long as possible

A reader pointed me to an item on ESA's Ulysses website that indicates the mission is getting very creative in its attempts to spin out the mission for just a few more days. As I mentioned in an earlier blog post, Ulysses is running low on power and is also receding from the Sun; as a result, it is facing the imminent freezing of its hydrazine fuel. Once the fuel freezes, the mission is effectively over, as the spacecraft will no longer be able to point its remaining antenna toward Earth. So the mission is now starting to intentionally bleed fuel from its thrusters, which will advance the fuel in the fuel lines and hopefully prolong the time before it freezes. Of course, spitting fuel out thrusters imparts torque to the spacecraft, so the fuel bleeding is being done by firing one set of spin-up and spin-down thrusters simultaneously, so their effects should cancel. Each bleed, performed at two-hour intervals, uses up 1.2 grams of hydrazine, advancing the remaining fuel 40 millimeters down the fuel lines. I'm not sure how much hydrazine fuel Ulysses has left after its long mission, or whether it's likely to use up its hydrazine or freeze first.

In preparation for the mission's end I started rereading the Odyssey to look for a good epitaph. I haven't come across anything yet but I've been greatly enjoying the Robert Fagles translation, which I hadn't read before.

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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Emily Lakdwalla
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