A joint ESA and NASA mission, Ulysses (named after the hero of Greek legend) orbits the Sun in an elliptical polar orbit, that takes it it high over the poles of the Sun. The unique vantage points allow for the charting of these regions of space, and the orbital period of 6.2 years provide a sampling time in step with the Sun's cycle of activity.
Original Ulysses Mission science objectives
As originally formulated, the science objectives of the Ulysses mission are:
Exploring our star's environment is vital if scientists are to build a complete picture of the Sun, how it works and its effect on the solar system. In particular, the satellite is studying the solar wind that blows nonstop from the Sun and carves a huge bubble in space called the heliosphere. Ulysses is providing the first-ever map of the heliosphere from the equator to the poles.
As well as mapping the heliosphere in three spatial dimensions, Ulysses is also investigating its behaviour in the fourth dimension - time. The Sun's character undergoes dramatic changes over the course of its 11-year activity cycle, from being relatively quiescent around sunspot minimum, to becoming violently active at sunspot maximum. These changes are reflected in the state of the solar wind and the heliosphere. Near solar minimum, the solar wind can exhibit large-scale, stable structures that persist for many 25-day rotations of the Sun. At solar maximum, on the other hand, the wind is highly variable, and the heliosphere is frequently disrupted by huge clouds of material blown from the Sun during solar storms. Ulysses, in its high-inclination orbit around the Sun, is uniquely placed to study these changing conditions.
Ulysses does more than study the solar wind, however. Its scientific instruments, many of which are even today state-of-the-art, are returning data of importance to a wide variety of studies in space plasma physics and astrophysics. Questions being addressed include the origin, acceleration and transport of energetic charged particles of solar and interplanetary origin, the transport of galactic cosmic rays in the heliosphere, the nature of the interstellar gas and dust that flows through the heliosphere, the origin of cosmic gamma-ray bursts, and the characteristics of the many natural radio signals emitted by the Sun and the interplanetary plasmas. Studies of the solar wind itself to which Ulysses is making major contributions encompass its origin in the solar corona, the nature of the magnetic field it carries away from the Sun, and its interaction with the interstellar gas and plasma that surrounds the heliosphere. In short, Ulysses is more than living up to its name as an explorer of unknown territory.
Future science objectives
Ulysses' third orbit of the Sun began in 2004. Important new observations in a different phase of the sunspot cycle and in the second half of the solar magnetic cycle can be made in this orbit. As noted above, Ulysses has already characterized the 3-dimensional heliosphere at solar minimum and solar maximum, helped develop techniques to map solar wind fields and particles back to their solar sources, carried out joint radio burst triangulation studies with NASA's Wind spacecraft, determined properties of the local interstellar medium and magnetars, and revealed an important need for additional measurements relating to energetic particle dynamics in the second half of the 22-year Hale solar magnetic cycle.
Now well into its third solar orbit, Ulysses' science future goals include:
Ulysses will enhance these studies by collaborating with SOHO, Wind, ACE, Solar-B, STEREO and the upcoming SDO mission.