Thirty years ago, on 6 October 1990 the joint ESA-NASA spacecraft Ulysses was launched on board the US-Space Shuttle Discovery, beginning its study of the Sun. Seven and a half hours after lifting-off from Cape Canaveral, Ulysses, which was designed and built at what is today’s Airbus Defence and Space Friedrichshafen (Germany) plant, was sent on its way into a heliocentric orbit via a special upper stage/PAM-S motor combination. The escape velocity of 15.4 kilometres per second, was the fastest velocity ever achieved by a human-made object at the time.
The Ulysses deep-space mission was designed to study the heliosphere - the region of space influenced by the Sun and its magnetic field. The primary scientific goal was to study the never-before-examined north and south poles of the Sun. Other areas of investigation included determination of the global properties and behaviour of the solar wind, the study of energetic particles of solar and interplanetary origin, measurement of the magnetic field of the Sun and the heliosphere, galactic cosmic rays, how the heliosphere interacts with interstellar space, and participation in a programme to identify the origin of gamma-ray bursts.
The spacecraft also performed a number of technical feats including making an unprecedented gravity assist manoeuvre at Jupiter (1992) to hurl itself out of the ecliptic plane, bringing it below the ecliptic plane, past the solar South Pole and then above the ecliptic to fly over the North Pole. It was the first spacecraft to fly out of the ecliptic plane.
Some of Ulysses’ principal findings showed that there is a weakening of the solar wind over time (which was at a 50-year low in 2008) and that the solar magnetic field at the poles is much weaker than previously estimated. They also found that the Sun’s magnetic field ‘reverses’ direction every 11 years, and that small dust particles coming from deep space into the solar system are 30 times more abundant than previously thought.
Three times during its mission, the spacecraft unexpectedly passed through comet tails and revealed that they are much longer than predicted.
Far outliving its planned mission lifetime Ulysses became one of the most prolific contributors to knowledge of the solar activity cycle. On 30 June 2009, the Ulysses mission ended after 6,842 days (18 years 8 months 24 days) in orbit.
With the Solar Heliospheric Observatory SOHO (launched in 1995 and still operational!) and Solar Orbiter (launched in February 2020), two Airbus-built operating space probes are studying our star. Solar Orbiter is expected to reach the closest distance to the Sun within 42 million kilometres in October 2022.