Interstellar Space Travel - What Does It Take to Get to the Stars?A look at the challenges of interstellar space travel, current and emerging technologies might one day be able to take us to the stars.
Interstellar space travel is the term used for travel between the stars. Interstellar space travel will be a lot more tricky than interplanetary spaceflight since the distances are generally hundreds of thousands of AU and, in most cases, expressed in light-years.
You can read more about AU and Light Years in my distance guide.
Science fiction writers and TV shows have shown us countless visions of humanity spread out across the Universe and countless spaceships capable of faster-than-light speed. Let's look at a few of them and the science behind the fiction.
Alien
In the classic 1979 movie Alien, the crew aboard the deep space towing vessel Nostromo can travel huge distances using hypersleep. This permits them to survive travelling lengthy distances. The hypersleep chambers can suspend the body's autonomic functions whilst maintaining the well-being of every individual cell during stasis. This is not the same as freezing; hypersleep is more like hibernation.
Could cryogenics be used for real-life interstellar space travel? It's no doubt a possibility, and NASA has invested significant resources in this issue. In the not-too-far-off future, interplanetary journeys to other planets will require months of travel through the vacuum of space. Maintaining the crew's well-being is a crucial concern. Survival issues would become more straightforward if the crew were induced to hibernate. Hibernating astronauts can be immobilised in special capsules, no longer needing pressurised living space or artificially generated gravity.
Star Trek
For interstellar travel, hypersleep would not be as effective; it will still take thousands of years to reach different solar systems. The key to interstellar space travel is travelling very, very fast. In Star Trek, this is accomplished with the use of Warp Drive. Matter in deuterium fuel is blended with antimatter and annihilates each other, generating vast energy. This energy is mediated through the dilithium crystals and is funnelled to the warp nacelles, which warp space-time, permitting ships to travel faster than light. Travelling at warp speed means solar systems can be reached in days rather than a millennium.
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The bulk of scientific knowledge concludes that it's not possible, particularly when considering Einstein's Theory of Relativity; then again, a concept for a real-life warp drive was once suggested in 1994 by Mexican physicist Miguel Alcubierre. Subsequent calculations discovered that this type of device would require prohibitive amounts of energy; however, just lately, physicists say that adjustments can also be made to the proposed warp drive that might enable it to run on significantly less power, potentially bringing the concept back from the realm of science fiction into science. Link.
Andromeda
In Gene Roddenberry's Andromeda, the Andromeda Ascendant can travel faster than light by navigating the Slipstream. Slipstream is a series of "strings" connected by gravity between planetary systems. A gravity field generator greatly reduces the ship's mass, after which a slipstream drive opens a slip point at which the ship enters. The pilot then navigates the slipstream "tunnels" sequence until they exit via the desired slip point. Usually, one has to enter and exit the Slipstream several times before reaching their final destination.
While there is no science behind the Slipstream, several theories suggest that it may be conceivable to "surf" gravitational waves, which themselves travel at the speed of light. Surf's up!
Stargate SG-1
In Stargate SG-1, our intrepid heroes discover the galaxy using a network of Stargates. Each Stargate can dial any other gate, establishing a wormhole where matter can be transported. Wormholes are theoretical tunnels through space-time fabric that might permit rapid travel between widely separated points.
While wormholes are conceivable under Einstein's theory of general relativity, such exotic voyages will remain in science fiction. There are very strong indications that the laws of physics forbid wormholes that a human could travel through. Also, traversable wormholes - if they may be able to exist at all - cannot occur naturally, so we would need to devise a way of constructing them artificially, and that may take an incredible quantity of power.
Battlestar Galactica
Spacecraft in Battlestar Galactica use an FTL Drive for faster-than-light travel. Before a jump, the drive is "spooled up", and the ship "jumps" instantly to some other point in space using a dimensional transportation effect. The series by no means explains how the theoretical jump drive works, only that once the drive spools up, presumably reaching an operating speed, building up momentum or charging the flux capacitor, the ship teleports to another location.
I would not get too serious about this being a chance soon. Current theory indicates that teleportation is not possible. Quantum teleportation does not teleport matter; it's more of a communication of data between two previously quantum-entangled particles.
Current and Emerging Technology
Science fiction writers have given us many pictures of interstellar space travel however travelling at the speed of light is just imaginary at present; on the other hand, several privately funded initiatives such as the Tau Zero Foundation, Project Icarus and Breakthrough Starshot have emerged in recent times, each hoping to bring us just a little bit closer to reaching throughout the cosmos.
Chemical Rockets
The powerhouses of the space age and chemical rockets have reached the end of their existence. They require massive quantities of fuel and supply only enough thrust to escape orbit. Even a round trip to Mars is not feasible since the fuel required would weigh so much, and the spacecraft would never leave Earth's atmosphere. Future refinements to the chemical rocket are not anticipated to produce substantial gains in thrust or power-to-weight ratio.
Electrothermal Engines
These engines use electric power to create a super-heated plasma and fire it through a supersonic nozzle to generate thrust. While they are fuel efficient regarding power to weight, the overall thrust may be very small, so their use has been restricted to satellites orbiting the Earth. They were developed in the 1970s and continue to be used today.
Ion drive
The subsequent generation of space engines looks like a contender for long-range missions. The thrust produced could be very low; however, it can be sustained for a very long time and is cumulative. Throughout an extended-range mission, Ion drive engines can deliver ten times as much thrust per kilogram of fuel as a chemical rocket.
Ion drives work by using ionising molecules of an unreactive fuel, such as xenon, and accelerate them through an electric field to be shot out the back.
The Dawn space probe used its ion drive to become the first spacecraft to enter and leave the orbits of more than one celestial body.
Solar Sails
Light particles (photons) carry momentum, like ping-pong balls bouncing off a wall. The solar sail concept is to catch enough of them to pick up important thrusts. Like Ion drives, the thrust may be very small; however, over a long period, the effect is cumulative. Unlike ion drives, solar sails depend on the sun's energy, so heading further out of the solar system results in much less solar pressure and much less thrust.
Plasma Propulsion Engine
These engines are like beefed-up variations of the ion drive. Instead of using a non-reactive fuel, magnetic currents and electrical potentials accelerate ions in the plasma to generate thrust.
The most powerful plasma rocket in the world is currently the Variable Specific Impulse Magneto plasma Rocket (VASIMR), which the Ad Astra Rocket Company in Texas is developing. Ad Astra calculates it could power a spacecraft to Mars in 39 days. However, the concept hasn't yet made it into space.
Nuclear Fission
In the 1960s and 1970s, several designs for a nuclear-powered engine had been constructed and tested on the ground in the US. These nuclear reactors heat a propellant to extraordinarily high temperatures and generate thrust. The venture was about to be built right into a spacecraft. However, the Nixon administration shelved the concept of sending people to Mars and cut the project's funding, so the plans had been shelved.
