Figure 2.5 Paths of Voyager 1 and Voyager 2 through the solar system. Both probes used the gravitational pull of Jupiter and Saturn to accelerate them further out into the solar system. This process is called gravity assist.

Voyager 2 in August 1981. The probes discovered seven new moons and returned spectacular photographs of the planet's ring system.

After passing Saturn, Voyager 1 left the solar system, but Voyager 2 was able to visit Uranus onJanuary 1986 and Neptune in August 1989. Voyager 2 discovered several new moons around each planet as well as ring systems. Triton, a moon of Neptune, was found to have active geyser-like structures and an atmosphere. After passing over Neptune's north pole, this space probe also headed out of the solar system.

These two space probes provided spectacular close-up views of the four outer planets, known as the gas giants. Both space probes continue to operate beyond the solar system, and are returning data about cosmic rays in outer space and ultraviolet sources among the stars. Communication

Did You Know?

Halley's comet passed the Earth in 1985-86, and a number of countries sent space probes to observe the comet. The probe that got the closest to the comet was Giotto, launched by the European Space Agency. Giotto passed within 600 km of the nucleus of Halley's comet on 13 March 1986. The probe carried 10 instruments including a colour camera. Giotto was severely damaged by high-speed dust encounters as it neared the comet and it was placed into hibernation soon after. In 1990, Giotto was reactivated and some of its instruments still worked. On 2 July 1990, Giotto came close to Earth and was re-targeted to a successful fly-by of comet Grigg-Skjellerup on 10 July 1992.

The US space probes Pioneer Venus, Pioneer 7 and Dynamics Explorer 1 also collected data on Halley's comet. The comet's nucleus was found to be dark in colour, irregularly shaped, about 16 km by 8 km in size, and covered in dust. The comet's inner coma contained a mixture of 80 per cent water vapour, 10 per cent carbon monoxide, and 3.5 per cent carbon dioxide and some organic compounds.

with the probes is expected to continue until 2015, when the radioisotope thermoelectric generators on the probes are expected to run out of power. Voyager 1 passed the Pioneer 10 space probe on 17 February 1998 and is now the most distant human-made object in space.


NASA placed the Magellan space probe into orbit via a space shuttle in May 1989. The craft was named after the sixteenth-century Portuguese explorer who first sailed around the Earth. Magellan reached its destination, Venus, in August 1990, with the aim of mapping the surface of Venus using radar. The synthetic aperture radar (SAR) imaging of features on Venus was more than 10 times sharper than previous radar images taken from other orbiting space probes. Other data from Magellan were used to prepare a comprehensive gravity field map for most of the planet, and it executed a first-ever aero-braking manoeuvre, dipping into the atmosphere to change its speed and circularise its orbit. This fuel-saving technique was r

Low-gain antenna

Altimeter antenna

Aero Braking Probe System

Figure 2.6 The Magellan space probe.

Forward — equipment module



Low-gain antenna

Altimeter antenna

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