by Stuart Carter

It may be the oldest cliché in town, but in the not too distant future science fiction will turn into science fact. The fantastic spaceships of sci-fi comic books and novels will no longer be a figment of our creative imagination; they may be the real vision of our future. 

Engineers and designers are already designing craft capable of propelling us beyond Earth's orbit, the Moon and the planets. They're designing interstellar spaceships capable of travel across the vast emptiness of deep space to distant stars and new planets in our unending quest to conquer and discover. Our Universe contains over a billion galaxies; star cities each with a hundred billion inhabitants. Around these stars must exist planets and perhaps life. The temptation to explore these new realms is too great.

First things first - we'll have to build either a giant orbiting launch platform, far bigger than the International Space Station (ISS), or a permanently manned lunar base to provide a springboard for the stars. Some planners feel we should limit ourselves to robotic probes, but others are firmly committed to sending humans. "There's a debate right now about how to explore space" says astronaut Bill Shepherd, destined to be the first live-aboard Commander of the ISS. "Humans or machines - I think they're complementary".

The human problem
Space is the most hostile environment we will ever explore. Even a single five-hour spacewalk requires months of training, and a vast technical backup to keep it safe. The astronauts and cosmonauts who live aboard the ISS will be there for only a few weeks or months; if we want to travel into deep space it could take years. First we'll have to find out just how long the human body can survive in a weightless environment. In zero gravity, four pints of body fluid rush from the legs to the head where it stays for the duration of the mission. Astronauts often feel as if they have a permanent cold, and disorientation can become a major problem. In space there's no physical sensation to let you know when you're upside down and astronauts have to rely on visual clues from their surroundings. A few hours after reaching orbit, one in three of all astronauts will experience space sickness - a feeling rather like carsickness. And weightless conditions lead to calcium being leached from the bones, and problems with the astronauts' immune systems.  

Trillions of rocky fragments - meteoroids - roam our Solar System at speeds of up to 150,000 miles an hour. A meteoroid no bigger than a grain of salt could pierce a spaceship window. Protection from the extreme hazards of space is going to need some clever technology. Space is also full of lethal radiation - X-rays, gamma rays and the high-speed particles called cosmic rays.

Down here on Earth we are protected by the atmosphere and by our planet's magnetic field, but in space long haul astronauts suffer gradual but irreversible radiation sickness unless they are carefully shielded. Commander Shepherd is confident the ISS will help us crack the problems "The ISS is going to answer a number of questions about long range exploration in space. A lot of things are going to be pioneered on the space station for future exploration".

Stepping stones
Saturn V is still the most powerful rocket ever built. But even this vast 3000 tonne giant carried only enough fuel to send a tiny manned capsule with just three men on a 250,000 mile journey - a mere drop in the cosmic ocean. It's over a quarter of a century since the last man stood on the Moon (Commander Gene Cernan on the Apollo 17 mission in 1972), and it seems that it will be another quarter of a century before we return to build a permanently manned base there. Bob Forward - who earns his living from designing spaceships of the future - believes we'll have to find a cheap way of reaching the Moon before we think of living there. His slingshot concept may seem radical at the start of the 21st century, but it is certainly ingenious. "If you have something rotating quite fast around another thing on the end of a string, it has a tendency to fly away. You have to decide when to let go (from Earth-orbit) and - like a trapeze artist catching his partner - you have to decide when to catch the payload (in lunar orbit)". A lunar base would become a viable stepping stone to deep space. In the 1990s, the Clementine and Lunar Prospector spacecraft detected frozen water below the lunar surface. This could be mined, melted and broken down to make liquid oxygen and hydrogen rocket fuel needed to blast off into deep space.

But before we leave the Solar System on our interstellar quest we will have to conquer it. Mars will become our first target. Whether we'll reach it directly from Earth, from Earth's orbit or from the Moon is anyone's guess but Mars is far from being a barren desert like the Moon.

Mars probably has plentiful supplies of frozen water below the surface and even has 24-hour days! Unfortunately the atmosphere is 95% carbon dioxide, with just a fraction of the Earth's atmospheric pressure and no protective ultraviolet layer. Martian astronauts will have to live in sealed modules, and wear spacesuits to venture outside. Mars would be a tiny colony, like the remote outposts of the early Earth explorers. Mars itself will probably never be a stepping stone to the stars, but it will help us learn if we can live in such a remote and harsh place for years or even a lifetime.

The round trip to Mars will take at least two years - on the most fuel-economical route, the travel time alone will be 9 months each way. So we either have to find much faster propulsion system or ways of helping the human body to cope.

It's only rocket science
Scientists are already experimenting with propulsion systems that may travel much faster than today's conventional chemical rockets. Franklin Chang's plasma rocket may be the answer. "In a plasma rocket you're continually accelerating," he explains.

A trip to Mars could be cut to 90 days, claims Chang. His rocket harnesses a nuclear process to produce a hot gas plasma. The plasma is magnetically held in a rocket the shape of a bottle and then expelled at very high velocity to provide propulsion. The plasma has to be heated to millions of degrees. Chang believes his system will be too good just to reach Mars. "I think it will quickly be developed for interplanetary travel within our Solar System". The plasma rocket is now under development at NASA's Houston laboratories.

Another new method of propulsion is already flying through our Solar System. Pushed only by an electronically driven 'ion engine', Deep Space One is already over 100 million miles from Earth. It works by ionising xenon gas and expelling it with the aid of electric fields, so providing a gentle but constant thrust. The ion engine provides a force about the same as a single sheet of paper exerts on your hand - far too weak to lift a spacecraft from the surface of a planet - but the continuous acceleration has already pushed Deep Space One to a speed ten times higher than any of the manned rockets we use today.

Interstellar travel
To leave the Solar System and carry humans to the stars we will have to find a way of travelling near to the speed of light. Even then a journey could take hundreds or thousands of years. Travelling at 1/10 the speed of light it would take over forty years to reach the nearest star, Alpha Centauri.

One giant source of free energy is our Sun. Bob Forward has designed the solar sail, a craft that doesn't have to carry its own fuel supply. It's driven by the power of the Sun's rays, and it will be the fastest machine ever built. "The sunlight bounces off the aluminium sails and in the process gives it a tiny push," explains Forward. Like the ion probe it will accelerate and accelerate. And it's not a total dream. NASA is already experimenting with deploying large sails in Earth-orbit. Propelled by light, solar sails will travel thousands of times faster than Apollo or the Shuttle.

Asleep or awake?
Even with the perfect spaceship it isn't going to be easy. In his classic sci-fi novel 2001, Arthur C. Clarke used the concept of suspended animation as a way for humans to cope with long space flights. He imagined that we would be able to put the human body into hibernation - suspended animation - to escape the boredom of long interstellar missions.

An even more drastic measure might be to freeze the astronauts. We already use cryogenic techniques to preserve dead bodies and store human embryos. Freezing living adults may not be so far away, but perhaps we won't have to do that. Perhaps we should use our existing technology and send frozen embryos across to the far corners of the cosmos.

It could certainly save on space. Then hundreds of years from now, billions and billions of miles away, the embryos will be thawed and their hearts will start beating. These space-farers of the future will not grow inside a mother's body but will be incubated in a machine. They will be brought up by robot. It may seem strange and radical but one day it might just happen…

"Who's to say in 25 years what we'll be doing in space? I think all estimates may be wildly short of the mark," muses Commander Shepherd.

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