Space: the Final Frontier. These are voyages of the blah blah blah... Even if you hate science fiction you will have probably heard those immortal lines at some point! However, as its continuing popularity shows, we love Star Trek and the idea of travelling to the stars and meeting distant alien cultures. Yet it all seems just a distant fantasy. Most of us believe we will never see such flights of fantasy, nor will our grandchildren, but in reality might we? Dr Charles Pellegrino seems to think so. Pellegrino is a fascinating man, a scientist who has written books on subjects ranging from Pompeii and Atlantis to the sinking of the Titanic1. Working with scientists Jim Powell, Hiroshi Takahashi and, vitally, Pierre Noyes, Pellegrino has designed a spaceship that he believes could have mankind leaving earth and visiting the stars by the year 2070.
Why Go to the Effort?
The chance of there being life elsewhere in space is statistically quite probable and an equation known as the Drake Equation was created in 1961 to calculate the odds. If you look at the following figures, for example, you can see the likelihood of there being extraterrestrial life somewhere.
Say that only 0.01% of stars in our galaxy contain a planet with similar conditions to Earth. There are somewhere between 3 to 100 billion stars in our galaxy, so using these figures, we have some 30,000 million Earth-like planets in our galaxy alone! Now, say that life will only appear on 0.001% of these Earth-like planets — this means there could still be some 3 million planets with life evolving on them in our galaxy alone! So the odds are good so far — add in the fact there are an estimated 600 billion stars in the nearest galaxy to our own, Andromeda, and it becomes even more likely. Finally, factor in the estimated 300 billion galaxies in the visible universe. The bare statistics mean we are probably not alone in the universe!
So the chances of there being life are good, but the chances of us meeting it by staying at home is not. If we want to achieve this next giant leap, we need to at least get out into our own solar system and then our own galaxy. However, this is the start of the problem: size. The distances and dimensions involved in the universe are immense. It is a mere 6,560km from London to New York, but compared to the 41,000km circumference of the Earth, that's a tiny figure. Yet if you were then to measure the distance from the Atlantic Ocean to the Sea of Tranquillity, where Neil Armstrong and Buzz Aldrin stepped out on to the Moon's surface in 1969, you'd encounter a distance of some 385,000km. In space terms, that's not just next-door, but actually sat on our lap! If we wanted to go flying off to visit another planet, the nearest one, Mars, is at its closest point some 56 million kilometres away. If we wanted to go to the nearest star system, the Alpha Centauri system is some 41 trillion kilometres or about four-and-a-half light years from Earth. Our galaxy, the Milky Way, is 2,500 times wider than the distance from Earth to Alpha Centauri! In space, distance is a relative concept: what's far to us on Earth is relatively small out there. Strangely, this is the big problem. Relativity is the major stumbling block when it comes to our explorations.
Einstein's famous theory means that we are unable to travel faster than the speed of light. In fact, it would actually be impossible for an object with 'normal' mass to achieve the speed of light. Until we discover the real version of the warp drive used in science fiction, we have to play within the confines of real physics. However, that doesn't mean we cannot travel at unbelievably high speeds which are still below light speed. In fact, the spaceship that Dr Pellgrino has designed is believed to be capable of achieving a maximum cruising speed of 92% of the speed of light2, or some 992,912,611kph (616,967,298mph)! At these sorts of velocities, according to relativity, time would slow by a third. This means that six years would pass on earth for every two years on board ship. Although we'd never be able to explore the far reaches of the galaxy, which are hundreds of light years away, we could explore our corner of the galaxy. Our next-door neighbour Alpha Centauri, for example, is 'only' four-and-a-half light years away. Travelling at maximum speed and taking the time dilation into account, the crew will be experience travel times of a similar duration to other great explorers such as Columbus or Cook.
The basic concept of Dr Pellgrino's Valkyrie ship design is not new. However, it has many subtle changes which overcome many of the previous design problems. Up until now, most spacecraft designs have used a large thruster rocket at the base of the ship and therefore all the necessary support structure to hold the thruster. Valkyrie does away with all this structure, as it is heavy. In spacecraft design, weight is bad because it starts a downward spiral. Extra weight needs extra fuel to provide enough power to move the craft along, though the extra fuel itself generates weight and therefore requires still more fuel. This spiral continues until a spaceship's total weight could easily become almost 99.7% fuel. In fact, the scientists Donald Goldsmith and Tobias Owen calculated that a ship designed along the old methods with the range to fly to the nearest stars would weigh some 400 million tonnes. Valkyrie in comparison weighs a mere 200 tonnes, with only half that mass being fuel.
Alternative designs such as the Bussard Ramjet have worked around this problem, but the Valkyrie concept has simply scaled it down. The ship really only consists of an anti-matter containment pod feeding a reactor chamber. This is attached to a large magnetic coil and together they act as the engines. Tethered to the power unit on a large cable is the crew/living quarters, being towed some 10km behind. This, in turn, is towing another reactor, magnetic coil and containment pod on a similar cable 10km behind it — more on this second engine later. The whole arrangement is more like a waterskier, the crew compartment, being towed by a speed boat, the magnetic coil/reactor engine, — in comparison to the ocean liners that are older spaceships!
This really does sound like science fiction, but anti-matter does exist. Scientists all over the world have been creating small amounts of anti-protons in their atom smashers and particle accelerators for years. In fact, in these colliders anti-protons are collected in magnetic 'bottles' called Penning traps for future use. This is achieved by combining the anti-proton with an anti-electron or positron to form an atom of the element hydrogen. However, instead of becoming normal hydrogen, this becomes an atom of anti-hydrogen. In the Valkyrie, large amounts of anti-hydrogen are stored in the magnetic bottles at -272°C, one degree above absolute zero. At this temperature, the anti-hydrogen forms into solid 'white flakes' that can be conveniently stored as fuel pellets. The engine operates by controlling the temperature of the anti-hydrogen so that it evaporates at a controllable and constant rate. This evaporated anti-hydrogen enters an atomic accelerator, where it is accelerated to around 750km per second and then fired at a target containing normal hydrogen. Here the matter target and anti-matter stream crash into one another and almost all the mass is turned into energy — as shown by the famous E=mc2 equation3.
So How is the Thrust Generated?
Valkyrie uses two methods to achieve its thrust. The first is to use the energy of the matter/anti-matter collison to trigger nuclear fusion within the extra hydrogen that makes up the target. The engine effectively becomes an anti-matter-controlled fusion reaction. By controlling the rate of the evaporation, the amount of fusion can be monitored and fine-tuned. The thrust is created by directing a spray of 'heavy elements'4, created as a byproduct of the fusion reaction. These 'heavy elements' leave the reaction travelling at 12 - 20% of light speed. They are then captured by a magnetic coil and forced into leaving the craft in the same direction, thus providing thrust. This nuclear fusion-based thrust is similar to earlier designs such as the Orion Project and the more sophisticated Daedalus Project. However, unlike these two designs, which where more like strapping the spaceship to a large nuclear bomb, Valkyrie's thrust is more like a nuclear power station. It is a controllable reaction rather than a powerful, violent, uncontrolled one.
However, the sharp-eyed reader will have noticed that this first stage of thrust is still far from the claimed top speed of 92% of the speed of light. As the ship starts to approach 12 - 20% of light speed, the fusion reaction is starting to run out of force. Basic Newtonian physics states that if the exiting particles are travelling 12 - 20% of the speed of light, we cannot move faster than this. However, by increasing the rate of evaporation, more anti-hydrogen meets hydrogen. There will be less free hydrogen for the fusion reaction but more fuel for the matter/anti-matter reaction. Eventually, the fusion reaction will slow and then stop altogether, as the only reaction occurring is the matter/anti-matter one. A lot of complicated physics takes place during these matter/anti-matter reactions because instead of totally annihilating each other to form pure energy, the matter and anti-matter also produce a particle called a meson. The mesons decay very swiftly, but as they exit the ship they are electrically charged and are travelling close to the speed of light. This enables the magnetic coils to capture the force they generate and propel the ship up to its top speed. Confused? You probably will be unless you're a physicist, but the science is all correct!
By using the first stage of 'heavy' but slow-moving particles, the Valkyrie is accelerated up to 20% of light speed. Then by switching over to the 'light' but high-speed particles, Valkyrie is able to reach its claimed top speed. This is what makes the engine design on Valkyrie so new: the ship's engine changes its thrust characteristics to suit the situation and it achieves this without using huge fuel reserves.
The Tether System
As was mentioned earlier, the Valkyrie ship consists of the reactor, magnetic coils and containment bottles towing a long cable that is attached to the small crew compartment. The reason for this is that the engine produces large amounts of gamma radiation. By towing the crew compartment 10km behind the engine, you minimise the effects of the radiation .This can also be helped by placing a 20cm-thick tungsten shield on this tether, about 100 meters behind the matter/antimatter reactor. This shield acts like an umbrella, creating a large shadow-like area free from the dangerous gamma rays. The other advantage of this tether system is the second engine. When you wish to slow down to a stop, it is simply a case of shutting off the first engine that is pulling you and switching on the second engine. This engine, which has been redundant up till now, fires in the opposite direction and can be used to slow the craft down. In fact, as the first engine is now no longer needed, it can be jettisoned — thus shedding its extra mass and making the second engine more efficient.
As Han Solo once said:
Travelling through hyperspace isn't like dusting crops, kid! Without precise calculations we could fly right through a star or bounce too close to a supernova and that'd end your trip real quick, wouldn't it?
Okay, so the Valkyrie isn't going to be travelling faster than light, but even at our non-relativistic 92% of light speed, a single piece of space dust could tear through the hull of the ship like a hot knife through butter. In fact, a stationary piece of dust weighing a gram, if struck by the ship travelling at 92% of light speed, will impact with the same force as a 1-ton car travelling at 992kph (616mph) — and remember, most space dust is not stationary! However, Jim Powell and Dr Pellegrino have solved this problem and have worked out how to shed any excess heat the engine creates at the same time. First, by pumping the heat into a tank of organic fluid mixed with metal particles, the heat can be transferred to the liquid. If this liquid is subsequently sprayed out in front of the ship as a fine mist, that heat will be lost through radiation into space. As there are metal particles embedded within the fluid droplets, magnetic collectors can be used to continually recollect the spray for re-use as the ship accelerates into the mist cloud. This cloud is also what will protect from dust and meteorite impact. When the interstellar dust impacts into this field, its constituent particles will break up5 and ultimately be recycled in the spray. The other advantage of the spray shield is that unlike a solid ablative shield, it is continually replacing itself.
So there we have it, the design of a machine which, in concept at least, could enable us to travel at 0.92% of light speed. Coupled with the recent breakthroughs in quantum teleportation for possible communications, perhaps we are already a step closer to the universe as imagined by science fiction writers. The Valkyrie design could see within a generation or two the kind of exploration we have up till now only dreamed of. This generation's great-grandchildren could one day be staring down onto the surface of a planet in another star system. The future is out there, just waiting for us to grasp hold of it...
Of course, the Valkyrie design is a lot more complicated and goes into more detail than can be covered in this short Entry. If you are interested, more about it can be read in Charles Pellegrino's article about the ship.