Robot Explorers: US Unmanned Space Missions: page 19

Ulysses is the first mission to study the environment of space above and below the poles of the Sun.
Its data have given scientists their first look at the variable effect that the Sun has on the space around it.

ulysses1.jpg (33281 bytes)
Artist's rendering of Ulysses orbiting the Sun.

A joint mission between the European Space Agency (ESA) and NASA, Ulysses was orginally slated for launch from the Space Shuttle in mid 1986. However, the Challenger disaster ocurred in January of 1986, and all shuttle launches were stopped. The Ulysses spacecraft was dismantled and sent back to Europe. Several years later Shuttle missions began again, and Ulysses was reassembled and successfully carried into space aboard the Space Shuttle Discovery on October 6, 1990.

 ulysses-launch.jpg (24612 bytes)
Space Shuttle Discovery launch.
It is important to study our star's environment in order to build a complete picture of how the Sun works and how it effects the Solar System. Ulysses is focusing on studying the Sun's complex magnetic field and the solar wind that is continually released from the Sun. This solar wind is different from winds on Earth. The solar wind is a plasma of charged particles (mostly protons and electrons) moving at very high speed which produces a large bubble in space called the heliosphere. Variations in the solar wind effect its interaction with our magnetic field and atmosphere, sometimes causing aurorae and magnetic storms on Earth.

Ulysses has explored the solar wind from all angles, producing the first three-dimensional picture of the heliosphere. The wind from the regions around the Sun's poles spreads out to fill two thirds of the heliosphere and travels around 460 miles per second, much faster than the 210 miles per second wind that flows from the equatorial region of the Sun.

ulysses-heliosphere.jpg (59141 bytes)
Artist's rendering of Sun's solar wind and heliosphere.
ulysses-orbit.jpg (73064 bytes) Ulysses has been so successful that in February of 2004, ESA once again decided to extend the mission until March of 2008. This third extension will allow Ulysses to fly over the poles of the Sun for a third time under different conditions than the first two passes. The 2000 and 2001 passes ocurred near the maximum of the Sun's activity cycle. Conditions are expected to be much quieter for the 2007/2008 passes, and similar in nature to those in 1994/1995. There will be one important difference.

The Sun's activity follows the well-known 11-year sunspot cycle. However, conditions in the heliosphere are driven by the 22-year solar magnetic cycle. "The Sun's magnetic field is rather like that of a bar magnet, with a north and a south pole", says Richard Marsden, ESA's Mission Manager for Ulysses. "The north and south poles changed places at the time of the recent solar maximum, so the Sun's magnetic polarity in 2007/2008 will be opposite to that of the previous solar minimum." The magnetic field of the Sun influences the way in which charged particles (cosmic rays, solar energetic particles, and even interstellar dust grains) move through the heliosphere. "We'll be looking for differences in behaviour related to the magnetic reversal", says Marsden.

For more information on Ulysses visit http://ulysses.jpl.nasa.gov/

Previous

Index

Next

Copyright ©2004 Colleen Gino

Images and content courtesy ESA, JPL and NASA.