Starships

Starships

by : Aria Ratmandanu

NUCLEAR ROCKET

       Scientists have also considered using nuclear energy to drive a starship. Beginning in 1953, the Atomic Energy Commission began to look seriously at rockets carrying atomic reactors, beginning with Project Rover. In the 1950s and 1960s, experiments with nuclear rockets ended mainly in failure. They tended to be unstable and too complex to handle properly. Also, an ordinary fission reactor, one can easily show, simply does not produce enough energy to drive a starship. A typical nuclear power plant produces about a billion watts of power, not enough to reach the stars.

        But in the 1950s, scientists proposed using atomic and hydrogen bombs, not reactors, to drive a starship. The Orion Project, for example, proposed a rocket propelled by a succession of nuclear blast waves from a stream of atomic bombs. A starship would drop a series of atomic bombs out its back, creating a series of powerful blasts of X-rays. This shock wave would then push the starship forward.

In 1959, physicists at General Atomics estimated that an advanced version of Orion would weigh 8 million tons, with a diameter of 400 meters, and be powered by 1,000 hydrogen bombs.

      One enthusiastic proponent of the Orion project “was physicist Freeman Dyson. “For me, Orion meant opening up the whole solar system to life. It could have changed history,” he says. It would also have been a convenient way to get rid of atomic bombs. “With one trip, we’d have got rid of 2,000 bombs,” he says.

      What killed Project Orion, however, was the Nuclear Test Ban Treaty of 1963, which prohibited aboveground testing of nuclear weapons. Without tests, physicists could not refine the design of the Orion, and the idea died.

RAMJET FUSION

        Yet another proposal for a nuclear rocket was made by Robert W. Bussard in 1960; he envisioned a fusion engine similar to an ordinary jet engine. A ramjet engine scoops air in the front and then mixes it with fuel internally. By igniting the mixture of air and fuel, a chemical explosion occurs that creates thrust. He envisioned applying the “same basic principle to a fusion engine. Instead of scooping air, the ramjet fusion engine would scoop hydrogen gas, which is found everywhere in interstellar space. The hydrogen gas would be squeezed and heated by electric and magnetic fields until the hydrogen fused into helium, releasing enormous amounts of energy in the process. This would create an explosion, which then creates thrust. Since there is an inexhaustible supply of hydrogen in deep space, the ramjet fusion engine can conceivably run forever.

          Designs for the ramjet fusion rocket look like an ice cream cone. The scoop traps hydrogen gas, which is sent into the engine, where it is heated and fused with other hydrogen atoms. Bussard calculated that if a 1,000-ton ramjet engine can maintain the acceleration of 32 feet per second squared (or the gravity felt on the earth), then it will approach 77 percent of the speed of light in just one year. Since the ramjet engine can run forever, it could theoretically leave our galaxy and reach the Andromeda galaxy, 2,000,000 light-years from earth, in just 23 years as measured by the astronauts in the rocket ship. (As stated by Einstein’s theory of relativity, time “slows down in a speeding rocket, so millions of years may have passed on earth, but the astronauts will have aged only 23 years.)

         There are several problems facing the ramjet engine. First, since mainly protons exist in interstellar space, the fusion engine must burn pure hydrogen fuel, which does not produce that much energy. (There are many ways in which to fuse hydrogen. The method preferred on earth is to fuse deuterium and tritium, which has a large yield of energy. But in outer space, hydrogen is found as a single proton, and hence ramjet engines can only fuse protons with protons, which does not yield as much energy as deuterium-tritium fusion.) However, Bussard showed that if one modifies the fuel mixture by adding some carbon, the carbon acts as a catalyst to create enormous amounts of power, sufficient to drive a starship.

         Second, the scoop would have to be huge—on the order of 160 kilometers—in order to collect enough hydrogen, so it would have to be assembled in space.

        There is another problem that is still unresolved. In 1985, engineers Robert Zubrin and Dana Andrews showed that the drag felt by the ramjet engine would be large enough to prevent it from accelerating to near light speed. The drag is caused by the resistance that the starship encounters when it moves in a field of hydrogen atoms. However, their calculation rests heavily on certain assumptions that may not apply to ramjet designs of the future.

           At present, until we have a better grasp of the fusion process (and also drag effects from ions in space), the jury is still out on ramjet fusion engines. But if these engineering problems can be solved, then the ramjet fusion rocket will definitely be on the short list.

Figure 1. Fusion Rocket 

ANTIMATTER ROCKETS

         Another distinct possibility is to use the greatest energy source in the universe, antimatter, to power your spaceship. Antimatter is the opposite of matter, with the opposite charge; for example, an electron has negative charge, but an antimatter electron (the positron) has positive charge. It will also annihilate upon contact with ordinary matter. In fact, a teaspoon of antimatter has enough energy to destroy the entire New York metropolitan area.

         Antimatter is so powerful that Dan Brown had the villains in his novel Angels and Demons build a bomb to blow up the Vatican using antimatter stolen from CERN, outside Geneva, Switzerland. Unlike a hydrogen bomb, which is only 1 percent efficient, an antimatter bomb would be 100 percent efficient, converting matter into energy via Einstein’s equation E = mc².

          In principle, antimatter makes the ideal rocket fuel for a starship. Gerald Smith of Pennsylvania State University estimates that 4 milligrams of antimatter will take us to Mars, and perhaps a hundred grams will take us to the nearby stars. Pound for pound, it releases a billion times more energy than rocket fuel. An antimatter engine would look rather simple. You just drop a steady stream of antimatter “ particles down the rocket chamber, where it combines with ordinary matter and causes a titanic explosion. The explosive gas is then shot out one end of the chamber, creating thrust.

        We are still far from that dream. So far, physicists have been able to create antielectrons and antiprotons, as well as antihydrogen atoms, with antielectrons circulating around antiprotons. This was done at CERN and also at the Fermi National Accelerator Laboratory (Fermilab), outside Chicago, in its Tevatron, the second-largest atom smasher, or particle accelerator, in the world (second only to the Large Hadron Collider at CERN). Physicists at both labs slammed a beam of high-energy particles at a target, creating a shower of debris that contained antiprotons. Powerful magnets were used to separate the antimatter from ordinary matter. These antiprotons were then slowed down and antielectrons were allowed to mix with them, creating antihydrogen atoms.

        One man who has thought long and hard about the practicalities of antimatter is Dave McGinnis, a physicist at Fermilab. While standing next to the Tevatron, he explained that the daunting economics of antimatter. The only known way to produce steady quantities of antimatter, he emphasized, is to use an atom smasher like the Tevatron; these machines are extremely expensive and produce only minuscule amounts of antimatter. For example, in 2004, the atom smasher at CERN produced several trillionths of a gram of antimatter at a cost of $20 million. At that rate, it would bankrupt the entire economy of earth to produce enough antimatter to power a starship. Antimatter engines, he stressed to me, are not a far-fetched concept. They are certainly within the laws of physics. But the cost of building one would be prohibitive for the near future.

       One reason antimatter is so prohibitively expensive is because the atom smashers necessary to produce it are notoriously expensive. However, these atom smashers are all-purpose machines, designed mainly to produce exotic subatomic particles, not the more common antimatter particles. They are research tools, not commercial machines. It is conceivable that costs could be brought down considerably if one designs a new type of atom smasher specifically to produce copious amounts of antimatter. Then, by mass-producing these machines, it might be possible to create sizable quantities of antimatter. Harold Gerrish of NASA believes that the cost of antimatter might eventually go down to $5,000 per microgram.

        Another possibility lies in finding an antimatter meteorite in outer space. If such an object were found, it could supply enough energy to power a starship. In fact, the European satellite (Payload for Antimatter Matter Exploration and Light-Nuclei Astrophysics) was launched in 2006 specifically to look for naturally occurring antimatter in outer space. If large quantities of antimatter are found in space, one can envision using large electromagnetic nets to collect it.

       So although antimatter interstellar rockets are certainly within the laws of physics, it may take until the end of the century to drive down the cost. But if this can be done, then antimatter rockets would be on everyone’s short list of starships.”

NEXT 100 YEARS

       By 2100, it is likely that we will have sent astronauts to Mars and the asteroid belt, explored the moons of Jupiter, and begun the first steps to send a probe to the stars.

      But what about humanity ? Will we have space colonies to relieve the world population by finding a new home in outer space? Will the human race begin to leave the earth by 2100 ?

     No. Given the cost, even by 2100 and beyond, the majority of the human race will not board a spaceship to visit the other planets. Although a handful of astronauts will have created tiny outposts among the planets, humanity itself will be stuck on earth.

     Given the fact that earth will be the home of humanity for centuries to come, this raises another question: How will civilization itself evolve ? How will science affect our lifestyle, our jobs, and our society? Science is the engine of prosperity, so how will it reshape civilization and wealth in the future ?