Ulysses solar orbiting spacecraft says: "Mission Accomplished"

After whirling around the sun since its launch in 1990, Ulysses has accomplished its mission. It has provided earthlings data on interstellar dust particles and interstellar helium atoms in the solar system. Experiments were conducted by more than 120 scientists world wide. Data was gathered from instruments that includedmeasurements of the interplanetary magnetic field, determination of the solar-wind ion-composition, quantification of ion and electron fluxes, gamma ray detection, and review of interstellar neutral gas.

The data collected during Ulysses’ Solar Minimum Mission make up eight CD-ROMS and are available from ESA.

Ulysses Space craft with its key elements...
Ulysess space craft with its key systems… bear in mind that this unit was launched almost 20 years ago… a lot of things changed since then.

How did Ulysses do it? The spacecraft is radiation-resistant, and spin stabilized. Its main parts include the body, an Earth-pointing high-gain antenna that provides the communications link, and the RTG that supplies the electrical power. A radial boom keeps three groups of experiments far enough away from the spacecraft to avoid interference. A set of antennas form a long, three-axis radio wave/plasma wave antenna. Experiment electronics and spacecraft subsystems are enclosed in the main body.

The well-equipped Ulysses orbited every six years over the north and south pole of the Sun during both calm and turbulent periods. Observations sent back to Earth redefined how scientists think about space weather.

An unexpected revelation showed that the Sun’s magnetic field is carried into the Solar System in a more complicated manner than we had thought.. Science Daily explains: "Particles expelled by the Sun from low latitudes can climb up to high latitudes and vice versa, even unexpectedly finding their way down to planets."

More than 1,300 scientific papers resulted from Ulysses triumphant journey. Discoveries provided scientists with tons of new information. The flux of galactic cosmic rays is essentially the same over the polar caps as at the solar equator. The lengths of comet tails can exceed an Astronomical Unit. Ulysses direct measurement of interstellar gas for the first time, hints at the presence of a "bow shock" for interstellar radiation beyond the heliosphere. The abundance of neutral interstellar atoms (Hydrogen, Helium, Oxygen, Nitrogen, Neon) have been inferred from observations of their ionization and pickup by the heliospheric magnetic field.

A year ago, although the project team thought that Ulysses’ weakened power supply would have problems rendering the satellite uncontrollable, a work-around fended off the inevitable. Finally, as the cost/benefit ratio waned, they decided to end the mission.

The final communication pass with a ground station will start at 17:35 CEST and run until 22:20 CEST (15:35-20:20 UTC) or until the final command is issued to switch the satellite’s radio communications into ‘monitor only’ mode. No further contact with Ulysses is planned.

Ulysses was definitely a joint effort: Dornier Systems of Germany built Ulysses, while NASA supplied the launch using a space shuttle and upper stage boosters. The generator that powers the spacecraft came from the US Department of Energy. The scientific instruments on board came from both the European and US investigators. Ulysses is operated from the Jet Propulsion Lab in California.


Editor’s note: This is the second part of our three-part tribute to Ulysses. Part I and Part III are also available, if you click on their respective links:

Part I: Ulysses space craft says goodbye to Earth
Part II: Solar orbiting spacecraft says "Mission Accomplished"
Part III: Rendezvous with the comet Hyakutake in outerspace