Ulysses, RIP...

One of our most productive robotic explorers is nearly at the end of its road. Ulysses was launched (via space shuttle) in 1990, and reached it's orbit around the sun in 1992. Ever since then – nearly 18 years – it's been doing great science. Its measurements of the sun, and most especially the sun's magnetic field, have contributed enormously to humanity's knowledge about the solar system.

Ulysses is yet another JPL/ESA project that far exceeded its original expectations, sending home years more science data than was originally planned. Last year the Ulysses team was almost ready to end the mission due to some failures – but some very clever engineering eked out yet another year of successful operation.

But now a combination of circumstances has brought a decision to shut down Ulysses. The biggest factor appears to be this: it's low-powered radio transmitter and great distance means that Ulysses can only be heard on JPL's 70 meter antenna network. This network has great demands upon it, so its time is valuable. Ulysses has been getting by with “spare time” use of the antenna network, meaning that it took whatever dregs other missions made available through last-minute scheduling changes, etc. Ulysses is getting further and further from earth, so its signal is weaker and weaker – which means a lower and lower bitrate on the data even when it can get antenna time. Simultaneously the demands on the 70 meter antenna network are getting even more intense. So the mission controllers decided that Ulysses had finally reached the point where the science value of its data was no longer worth the cost, both in terms of antenna time and in terms of maintaining the mission team.

So on June 30 (this coming Tuesday), the mission controllers will send a signal to Ulysses to tell it to turn itself off. It will remain permanently in orbit around the sun, a monument to mankind's achievments that will remain no matter what we manage to do to ourselves...

More information here, here, and here.