When you arrive at Jupiter, take a left

Colin Pillinger takes a guided tour around the facts of space voyaging.

A journey of 1,000 miles starts with just one step, so they say, but in the case of space it is the first 50 miles that are all important. Fifty miles does not sound much on top of the Earth's radius of 4,000 miles: it is the equivalent of going from London to Cambridge to reach the final frontier and get above the atmosphere.

Conquering the first 50 miles of man's efforts to fly is a great story in itself. But onwards and upwards. The first staging post is at 22,730 miles, where a spacecraft's orbital velocity will match that of the Earth's rotation (the geosynchronous orbit). Beyond 50,000 miles (twice the circumference of our planet) and you are off towards the sun or another planet depending on your direction. Most people probably do not realise it, but if you want to journey very close to the sun, it is easier to fly past Jupiter to obtain the necessary braking effect, otherwise your vehicle ends up in orbit further from our star than you imagine. By-passing Jupiter, your spacecraft can travel out of the solar system (3.6 billion miles) to the nearest star (1014 miles), the Andromeda Galaxy (1018 miles) and end up at the edge of the observable universe (1024 miles). Even if you travelled there at the speed of light (not actually possible), to reach the edge would take you a good proportion of the time the universe has already existed.

Such are the difficulties of space voyaging that would-be astronauts get to take very little baggage. Mass is the most important commodity in the space business; it gets consumed incredibly quickly, both in fuel and in the fuel's storage tanks. The journey to Mars could be done in 1.5 days if only the spacecraft could be accelerated at just 1g (the acceleration due to gravity on Earth) for the first half of the journey and braked at 1g for the descent to the planet. This would be quite comfortable for would-be astronauts (no weightlessness) but very heavy in miles-per-gallon. The size of the tank needed for a journey with those characteristics would be the size of the Earth!

Nevertheless, you, as a Martian astronaut, might just have room for the little book A Tribble's Guide to Space in the luggage compartment. During a first read, you could amuse yourself by learning the sorts of information that would stand you in good stead for Trivial Pursuit while you are camping out on the red planet. Test yourself against the following questions: (i) Why was it entirely appropriate that Buzz Aldrin was chosen as Neil Armstrong's companion on Apollo 11? (ii) How many Nasa astronauts have there been? (I will allow an error of plus or minus ten.) (iii) Where do astronauts originate? (In other words, name all the countries who have supplied astronauts to the United States and Russian programmes.) (iv) What is the starting pay for a Nasa astronaut? (v) On the way back, how fast do you have to be travelling to escape Martian gravity? (vi) Astronauts cannot be over a certain height, so who is prevented from joining the corps? Answers below.

If you scored more than ten, either you are a complete anorak, you have read Alan Tribble's book already, or you impress the contestants at your local pub on quiz nights by telling them you are a rocket scientist. Joking aside, this book is a compendium of facts carefully disguised in an easily assimilable form, in other words hard information mixed with things to make it readable.

One of the beauties is that Tribble is a real rocket scientist, a child of the space generation born three months after Alan Shepard reached space. To prove it, he tells his readers the who, what, when, where, why and how of space exploration. The anecdotes remind you this man is an insider, who has been involved in numerous missions. His informal style allows him to introduce Newton's theory of gravity, Kepler's laws of planetary motion, Einstein's theory of relativity, radiation environments, magnetic fields, three-axis stabilisation, momentum wheels, attitude (the spacecraft's -not yours), planetary slingshots and so on -all without your realising that concepts from mathematics, physics, chemistry and engineering are being implanted into your brain. Speaking of slingshots, did you know that accelerating a spacecraft by 1,000 miles per hour with the assistance of the Earth's gravity slows the earth by less than the diameter of one small molecule per hour? Although nothing is free, Tribble reckons this cost is very cheap, considering the expense of taking huge quantities of fuel into space.

I have just one quarrel with the author. He favours space as a place to scatter the ashes of the rich and famous. I would rather that my successors in the space-science community, who will study the composition of various extraterrestrial bodies in the solar system, would not have to contend with analysing anyone's ashes.

Tribble's book is a great read: a guide to space technology with a light touch for those who believe they do not understand what it takes to be a rocket scientist. The trouble is, the book is so easy to read it will not last you through one of the very long, boring voyages after passing the final frontier that will remain the rule until some new form of propulsion is invented (Tribble discusses some possibilities). His book is more suited to a train journey; under the recent speed restrictions, a journey of 50 miles just seems like going to the ends of the Earth.

Colin Pillinger is professor of planetary science, Open University.