Ulysses' extended mission, as before, is to study the sun. But at the moment Ulysses is far from our star. It's having an encounter with Jupiter, studying the giant planet and its magnetic field. Sunlight out there is 25 times less intense than what we experience on Earth, and Ulysses is getting perilously cold. Back in the 1980's, when Ulysses was still on Earth and being assembled, mission planners knew that the spacecraft would have to endure some low temperatures. So they put dozens of heaters onboard, all powered by a Radioisotope Thermoelectric Generator, or
Fuel lines are critical to the mission. They deliver hydrazine propellant to the ship's eight thrusters. Every week or so, ground controllers fire the thrusters to keep Ulysses' radio antenna pointing toward Earth. The thrusters won't work if the hydrazine freezes. No thrusters means no communication. The mission would be lost. About eight meters of fuel line snake through the spaceship. Every twist and turn is a possible cold spot, a place where the hydrazine can begin to solidify. The temperature at any given point along the fuel lines is bewilderingly sensitive to what's going on elsewhere in the spacecraft. Turning on a scientific instrument
'As long as men are free to ask what they must; free to say what they think; free to think what they will; freedom can never be lost and science can never regress. '
J. Robert Oppenheimer