The joint ESA-NASA Ulysses mission made nearly three complete orbits of the Sun during more than 18 years in service. The probe operated more than four times its expected lifetime and made many important discoveries. Ulysses’ principal findings included data that showed there is a weakening of the solar wind over time (which was at a 50-year low in 2008). Data from the mission indicated the solar magnetic field at the Sun’s poles is much weaker than previously assumed. Ulysses helped determine that the Sun’s magnetic field “reverses” in direction every 11 years. The spacecraft’s May 1996 encounter with comet Hyakutake revealed comet tails are far longer than expected. SSL built the gamma-ray and soft X-ray sensors.
