Looking back: The Sky at Night
7 April 2008
On the 7 April 2008 episode of The Sky at Night, Patrick Moore took a look at the European Space Agency’s Ulysses mission, which had spent almost two decades studying the Sun.
Unlike solar observation missions that had come before it, Ulysses didn’t fly around the equator of the Sun. Instead, it flew over the solar poles – an important area for anyone studying the Sun’s magnetic field.
The mission launched on 6 October 1990 on board Space Shuttle Discovery. A Shuttle launch meant the probe itself could carry more fuel for its flight beyond Earth orbit. If it was to get up over the poles, the spacecraft had to leave the plane of the ecliptic, requiring a huge amount of energy. It was only possible with a gravitational assist from
Jupiter in 1992, which propelled Ulysses into an orbit inclined at 79˚.
The probe made its first fly-by of the southern solar pole in 1994, before swinging around to the northern side a year later. Between these, it made its closest approach to the Sun: 1.35 times the Earth–Sun distance away. It conducted two more fly-bys in 2000/2001 and 2007/2008 before the mission finally ended in 2009.
The long period between passes meant Ulysses saw the Sun at different times during its 11-year solar cycle. The first and last were during solar minimum, while the middle occurred near the highly active solar maximum. Ulysses was able to provide direct evidence that the magnetic field of the Sun reversed between each minimum.