Interstellar Travel » First Baby Steps towards Interstellar Travel

The 1970s saw the launching by NASA of the first four space vehicles to venture into the outer Solar System. They made history in two ways. Firstly they crossed the asteroid belt and carried out flybys of the four outer planets Jupiter, Saturn, Uranus and Neptune. Secondly they are going on towards the Heliopause where the combined 'wind' that comes from the rest of the galaxy is equal to the strength of the Solar Wind. It is true that the Sun's gravitation still operates on the Oort Cloud which lies outside this region but in many ways we can think of the heliopause as marking the frontier between the 'Kingdom of the Sun' and interstellar space.

The Space Craft were:

Pioneer 10 launched on 2 March 1972. It was the first spacecraft to cross the asteroid belt. It made the closest encounter to Jupiter and passed within about 130,000 kilometres above the cloud tops. It used the gravity and orbital momentum of Jupiter to hurl it towards interstellar space at 40,000 kilometres per hour which was enough to reach a velocity which would send it out of the Solar System forever into interstellar space. This is known as the sling shot effect. Its last message to Earth was received on 23 January 2003. Long after the Sun has become a red giant and then a white dwarf, Pioneer 10 will cruise on through interstellar space bearing on its framework a gold anodised plaque, shown on the right above, designed by Carl Sagan and Frank Drake. It will tell any race of creatures that may find it who we were and to which star we belonged. Although the chances of it ever being found are extremely unlikely it adds a little poetry to the first space craft designed to cross the vast emptiness of interstellar space.

In 1977, two unmanned spacecraft, designed and built by NASA’s Jet Propulsion Laboratory, were launched on reconnaissance missions to the outer planets. They were Voyagers 1 and 2 and were sent towards Jupiter in September and August 1977. The launch window during 1977-79 which the Voyager missions took advantage of to fly by all four planets in our Outer Solar System happens only once every 176 years. If this window had occurred in 1965-66-67, we wouldn’t have had the technology to fly such a mission. The primary mission was the exploration of Jupiter and Saturn. Both probes studied not only the gas giants themselves but also their moons. Voyager 2 went on to explore Uranus and Neptune, and is still the only spacecraft to have visited those outer planets. Current interest lies in the Voyager Interstellar mission (VIM) which will explore the outer limits of the Solar System. There is a more definitive and unambiguous frontier, which the Voyagers will approach and pass through. This is the heliopause, which is the boundary area between the solar and the interstellar winds. When Voyager 1 crosses the solar wind termination shock, it will have entered into the heliosheath, the turbulent region leading up to the heliopause. When the Voyagers cross the heliopause, hopefully while the spacecraft are still able to send science data to Earth, they will be in interstellar space even though they will still be a very long way from the “edge of the Solar System”. The Oort Cloud which is still gravitationally bound to the Sun lies beyond the Heliopause. Once Voyager is in interstellar space, it will be immersed in matter that came from explosions of nearby stars. So, in that sense, one could consider the heliopause as the final frontier between the Sun's dominion and interstellar space. The trajectories ot the two Voyager Spacecraft passing Jupiter and Saturn on their way to the Heliopause are shown on the right above. (Illustration Credit NASA.)

By August 2010, Voyager 1 had reached a distance of 17.1 Billion Kilometers from the Sun and Voyager 2 a distance of 13.9 Billion kilometres. Voyager 1 is departing the Solar System at a speed of 62,400 kilometres per hour (39,000 miles per hour). Voyager 2 is departing the Solar System at a speed of 56,000 kilometres per hour (35,000 miles per hour). The Voyagers have enough electrical power and thruster fuel to operate until at least 2020. By that time, Voyager 1 will be 19.9 billion kilometres (12.4 billion miles) from the Sun and Voyager 2 will be 16.9 billion kilometres (10.5 billion miles) away. Eventually, the Voyagers will pass other stars. In about 40,000 years, Voyager 1 will drift within 1.6 light years of AC+79 3888, a star in the constellation of Camelopardalis. In some 296,000 years, Voyager 2 will pass 4.3 light years from Sirius, the brightest star in the sky. The Voyagers are destined—perhaps eternally—to wander the Milky Way. These space vessels are hardly travelling at Star Trek speeds!!!

An illustration by Edward Stone of Caltech given on the right above, shows the four spacecraft entering the Heliopause and all travelling in diferent directions towards interstellar space.

Ray Goodwin

Somewhere there are mountains
Glistening in the snow
Somewhere there are mountains
That we shall never know

Somewhere there are rivers
Flowing fast and free
Somewhere there are rivers
That we can never see

Somewhere there are oceans
And sun drenched island sands
Forests full of creatures
In vastly distant lands

Somewhere there’s a planet
Beneath an alien star
The people watch our tiny sun
And wonder where we are

One day perhaps we’ll find them
Across the void of space
Perhaps through ways as yet unknown
We’ll meet them face to face

The author of this web site Ray Goodwin holds B.Sc. Degrees from London University in Chemistry, Geology and Physiology and an M.Sc. in Biochemistry. He has spent most of his professional life teaching in Colleges of Technology. On his retirement he has entered the fields of astronomy, astrochemistry, astrobiology and space sciences. He has spent a great deal of his retirement in visiting amateur astronomy societies and in attending European Space Agency Symposia in ESTEC in the Netherlands and other scientific conferences in England and Sweden. He regularly attends the yearly European Astrofest in South Kensington London and other meetings in the UK. He has written scientific articles and given a number of lectures on diverse scientific subjects.

Readers of this web site are invited to e-mail the author ( and discuss their opinions of the topics dealt with and suggest any changes which they think may be helpful.

Life in the Cosmos Website
Version 01.00 - April 20, 2015.