In science fiction movies, we see crews being frozen in cryogenic chambers so that they can make long trips across the universe. The crew being placed in an induced state of hibernation at the start of their mission would not only leave them in a mentally and physically healthier state by the time they arrive at their destination months or years later, but would also limit the necessity for large living quarters, and various types of heavy equipment.
While we obviously don’t have that type of technology at our disposal at the moment, it does still raise questions about how realistic the prospect are of travelling to far off distant worlds. For instance, is the nearest star so far away that we couldn’t make it there in a single lifetime? How long would it take using the methods currently available, and what methods of interstellar transportation might be available in the future that would be faster?
Let’s take a look at some existing and theoretical methods of space travel to find the answers. For the sake of this article, we’ll be discussing how long it would take to reach Proxima Centauri, the closest star to our solar system. It is about 4.24 light years away as a frame of reference.
Current Methods of Space Travel
Ionic Propulsion has been developed to move unmanned space probes across the universe at faster speeds. The latest craft use solar power to make their ion thrusters move, resulting in a very fuel efficient system in which only small amounts of xenon or another propellant are needed for the journey. Its fuel efficiency would make ionic propulsion the most practical and inexpensive method of journeying to the next closest star. In 1998, Deep Space 1 (DS1) became the first spacecraft to use ion drive technology, and during its mission to test the new technology, DS1 managed to attain a velocity of 35,000 miles/hr (56,000 km/hr). At that rate it would take 81,000 Years to reach Proxima Centauri; however, improvements in the design of ion thrusters could reduce the travel time but not to that of an average human’s lifespan.
At the present time, the fastest way to travel through the universe is with Gravity Assist, a method by which a spacecraft uses the gravity and orbit of nearby planets to help propel it at a fast pace. In 1974, it was used for the Mariner 10 spacecraft’s trip to Mercury, where the gravitational field of Venus was used to catapult the vessel forward. NASA Helios 2 space probe in 1976 then became the fastest man-made object ever made after reaching a maximum velocity of over 150,000 miles/hr (240,000 km/hr), using the orbital speed attained from the gravitational pull of the Sun. At this rate, it would take 19,000 to 76,000 Years to reach Proxima Centauri, depending upon the velocity that the space craft was able to reach.
This type of propulsion has never been used in a spacecraft, but basically uses nuclear engines to produce thrust. Both Nuclear Thermal Propulsion (NTP) rockets and Nuclear Electric Propulsion (NEP) rockets involve using uranium or deuterium-based reactions to propell the spacecraft through either nuclear fission or nuclear fusion, rather than using chemical propellants. If it could be safely perfected, NTP/NEP would be cost effective, and would allow for lightning fast transport through space with minimal costs. Using this method, the time required to reach Proxima Centauri could be reduced to 1000 years.
The electromagnetic propulsion drive (EM Drive) has been built here on Earth but has never actually been used in a spacecraft. Some speculate that it would not actually work, and that it goes against the law of momentum conservation. Basically, this type of propellant-less thruster does not require any type of mass such as ionized particles to power its movement, but instead uses solar power to produce multiple microwaves which bounce back and forth inside an enclosed cone to create thrust in the direction of the cone’s narrow end. Likened to the Starship Enterprise’s Impulse Drive, some studies have shown that the thruster could theoretically be used to travel through space at faster speeds that we have so far been able to manage, and that Proxima Centauri could be reached in just 100 years.
Theoretical Methods of Space Travel
Since all of the following methods of space travel are still little more than concepts, it’s not possible to know just how quickly they could get us from Earth to Proxima Centauri; however, if any of them were available, they would be likely to drastically reduce the travel time, potentially making it possible to make the trip in significantly fewer years than the modes of travel currently available.
Nuclear Pulse Propulsion
First proposed in 1946, Nuclear Pulse Propulsion was studied briefly during the 1950s and 1960s by a team at Princeton University. A simple explanation of this technology is that a spacecraft equipped with the propulsion system explodes a series of thermonuclear warheads behind it that create a wave of energy that is absorbed by a pusher pad which subsequently drives the vehicle forward.
The cost for such a spacecraft would probably run around $2.5 trillion and bans on nuclear testing make it virtually impossible to study the method of propulsion in order to determine if it could ever be made feasible. Nevertheless, estimates suggest a spacecraft could reach 5% the speed of light using this method, or 33,353,083 miles/hr.
Fusion rockets were studied briefly during the 1970s and are another potentially fast way to move through the galaxy. In this type of spacecraft, deuterium and helium-3 pellets are detonated inside of a fusion reactor to produce plasma energy to power the rocket. There are a number of obstacles that would need to be overcome in order to bring this concept to reality, one of the biggest of which is that helium-3 would need to be mined in outer space as it is not readily found on Earth. Gradually accelerating up to 12% the speed of light, or 80,473,995 miles/hr, a craft could travel to Proxima Centauri in 36 years.
Robert W. Bussard introduced the idea of a ramjet spacecraft in 1960. Building on the idea of the nuclear fusion rocket, this vehicle would have an electromagnetic funnel that would bring hydrogen from space into the rocket’s reactor and compress it until thermonuclear fusion occurs. Continuously refueling the spacecraft in this way would make the spacecraft very cost efficient, and could potentially allow the craft to reach 4% the speed of light.
A completely different concept for space travel is the laser sail, developed off of the concept of the solar sail, a spacecraft that moves solely using power harnessed from the sun. A laser sail in space would receive a photon boost from an array of powerful lasers located on the Earth or stationed around Earth’s orbit, with their highly focused and perfectly synchronized beam providing an irradiation 100,000 times greater than the Sun’s. This could lead to astonishing speeds being attained, with a 1 meter (3 ft) diameter laser sail reaching about 26 percent the speed of light in just 10 minutes, and Proxima Centauri in a mere 15 years.
Studies are still being done to explore this possible method of interstellar travel but so far the high cost that it would take to craft the sail out of a material that could withstand the heat has made moving forward with the technology impractical.
Fans of Star Trek will known that warp-capable Federation starships are powered by a matter/anti-matter reaction that produces vast amounts of energy. Anti-particles have the same mass but an opposite electrical charge to its corresponding particle, and it was only in 1928 that Paul Dirac revised Einstein’s E = mc2 equation to allow for a + or – value for Energy (E).
Basically, an antimatter engine slams particles of hydrogen and antihydrogen together, with the resulting reaction producing huge amounts of energy, together with a subatomic particles traveling one-third the speed of light, which are subsequently channeled out of a magnetic nozzle to produce thrust. Is is believed that a spacecraft using an antimatter engine could travel at half the speed of light, and reach Proxima Centauri within 9 years. On the downside, antiparticles are extremely rare, are not easy to store, and to date scientists have only been able to create 20 nanograms of anti-matter by collisions inside large particle accelerators, with the cost of producing even one gram of anti-matter apparently costing trillions of dollars.
Alcubierre Warp Drive
In 1994, Mexican physicist Miguel Alcubierre proposed his concept for a propulsion system (Alcubierre Warp Drive), that would allow spacecraft to travel faster-than-light speeds without contradicting Einstein’s laws. According to his speculative idea, a spacecraft fitted with such a device would be able to use gravitational effects to contract the space-time in front of it, and expand the space-time behind, creating a warp bubble that carries the craft through space-time distances faster than light could have managed. In this instance, there is no violation of Einstein’s relativity theory beause while nothing can exceed the speed of light, space itself is able to expand or contract faster than any photon ever could.
The spacecraft would then travel at zero gravity within a bit of flat spacetime inside the warp bubble, and ride the wave of compressed and expanded spacetime at superluminal speed. Such a craft would theoretically be able to travel up to 10 times the speed of light, cutting a journey to Proxima Centauri to less than 5 months. Some of the many problems associated with the idea, however, include the huge amount of energy required to power the warp drive, dangers of the gravitational fields produced ripping any spaceship apart, and also Alcubierre’s mathematical model violating some of nature’s fundamental laws.