The ULYSSES Mission

Image 1: Sectional view of Ulysses with it’s Instruments

The ULYSSES-Mission

ULYSSES is a cooperative ESA/NASA scientific mission. The space probe was built by the firm Dornier in Friedrichshafen. Launch was on October 6, 1990. The mission: flight to Jupiter in ecliptic, Jupiter fly-by (encounter) on February 5, 1992, rotation of the orbit plane by 80 degrees from Jupiter’s gravitation, first orbit nearly to the sun’s polar orbit until February 1998, second orbit until February 2004, third orbit only party observable. The mission will probably end this year

Scientific goals and results

Mission to the poles of the sun: 3-D Structure und Dynamics of the Heliosphere
The sun is the central body in our solar system. Every second, millions of tons of hot plasma (ionized hydrogen and helium gas) are spewed from its atmosphere into interplanetary space at speeds from 300 to 800 km/s. This flow of plasma is called solar wind. Magnetic field lines from the sun are also carried out with the solar wind. Because the sun rotates with a period of 27 days, the magnetic field lines form Archimedean spirals in interplanetary space. High energy particles also move in spirals along these magnetic field lines. Therefore, magnetic field lines are the most important structural element in the heliosphere. They can be considered as the long arms of the sun that it uses to extend its sovereignty to at least 130 km away. The sun is extremely variable with time and place. Sunspots, coronal holes and the 11-season cycle of solar activity, which really takes 22 years, are the most well-known variable aspects of the sun, which also affects the heliosphere

The sun’s corona: Link between the sun and the heliosphere
The corona is the outer most atmosphere of the sun. It is heated up to several million Kelvin and is extremely turbulent. At a total eclipse it is visible with a coronagraph, a telescope that blocks the solar disk. Solar wind originates from the corona and carries the corona’s local and momentary characteristics out into interplanetary space. The corona is not directly observable with ULYSSES. However, conclusions can be drawn from the in-situ measurements. The best corona measurements at the moment are being sent from SOHO.

Solar wind and high energy particles: acceleration and distribution
Solar wind, suprathermal and high energy particles are accelerated in the corona of the sun. Their composition can shed light on the elemental and isotopic frequency as well as the temperature of the corona. The origin of the particles can be calculated from information about the interplanetary magnetic fields and the velocity of the solar wind

Jupiter: a rebel planet, dangerous, but fascinating
Like the earth, Jupiter has a strong magnetic field and a magnetosphere in which charged particles can be accelerated and momentarily held. The electron intensity in Jupiter’s radiation belt is the highest in the solar system and magnitudes higher than the earth’s. Jupiter rotates so fast that a day on the planet lasts only 10 hours. Thereby, Jupiter’s magnetosphere is constantly undergoing restructuring and is very active. Jupiter’s magnetosphere is a large source of high energy electrons in the solar system. Whenever electrons from Jupiter’ magnetosphere reach Ulysses along magnetic field lines, it measures a higher electron intensity. This can even be observed at a distance of 150 million km (1 AU). The intensity increases tenfold as Jupiter is approached. As Ulysses entered Jupiter’s magnetosphere, the intensity increased to a thousand times as much and continued to increase to a very high particle density in the inner magnetosphere at the closest distance of 6 Jupiter radii. While Ulysses was moving away, it was repeatedly overtaken by the volatile magnetosphere until the intensity finally went back to interplanetary levels. The time variation of the electron measurement values is observed as a period of Jupiter’s rotation called a Jupiter-hour. Since its discovery in 1973, it has stayed remarkably constant. After 16,058 revolutions, the deviations amount to less than 30 minutes. After 12 years, Ulysses was close to Jupiter again on February 5, 2004, if only within a relatively large distance of 0.8 AU (120 million km). And as expected, the electrons from Jupiter were again observed.

Kiel’s instruments on board Ulysses

Kiel’s Electron-Telescope (KET)
Particle detectors: semiconductor detectors, Cherenkov-detectors, and Scintillators
Energy range: 2,50 MeV - > 6000 MeV
Elektrons and 5 MeV/n – > 2000 MeV/n H und He

Solar Wind Ion Composition Spectrometer
Data analysis and interpretation in cooperation with the University of Maryland, USA.