Moons of our Solar System
Moons of our Solar System

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

1.1 The Grand Tour

In the 1960s and 1970s, NASA was the only space agency with the capability to send a probe to the outer Solar System. Proposals were made to take advantage of a rare alignment of the planets to allow a single mission to fly past Jupiter, then onwards in turn to Saturn, Uranus and Neptune and maybe even onwards to Pluto. This was dubbed the ‘Grand Tour’. It wasn’t so much the shortness of the route from planet to planet that was important; it was that a spacecraft could take advantage of the first planet’s gravity to swing its trajectory onwards towards the next target, and so on, in a so-called ‘gravitational slingshot’ manoeuvre – known more prosaically as a ‘gravity-assist manoeuvre’. You may recall that it was just such a manoeuvre round the Moon that was critical in getting Apollo 13 home safely.

At that time, the prime goals for exploration were the planets themselves. Few people expected their moons to be anything like as fascinating as we have now discovered them to be. In preparation for this proposed Grand Tour, NASA launched two trial probes: Pioneer 10 in 1972 and Pioneer 11 in 1973. Pioneer 10 flew past Jupiter in 1973. Pioneer 11 flew past Jupiter in 1975 and past Saturn in 1979. By today’s standards, these were very simple probes, lacking anything that we would count as an on-board computer, and able to store only a very limited number of commands transmitted from Earth. The images they beamed back were of poor quality (and few were of the moons). However, they did prove that a space probe can survive passage through the Asteroid Belt, which lies between Mars and Jupiter. These probes also showed the strength of the magnetic fields and radiation belts close to Jupiter and Saturn that future missions would need to withstand.

Neither of the Pioneers passed close to any more-distant planets, but being the first probes from Earth whose trajectories would ultimately take them beyond the Solar System and into interstellar space, each carried an engraved gold-coated plaque bearing symbolic greetings from Earth and other graphics intended to allow the point of origin to be traced by any beings who might one day salvage the craft.

This is an image of the plaque carried by Pioneers 10 and 11. Actual size 23 cm by 16 cm.
Figure 2 The plaque carried by Pioneers 10 and 11. Actual size 23 cm by 16 cm.

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371