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 is going to 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, as well as 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 via the use of 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 to 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. If the crew could be induced to hibernate, the issues of survival become more straightforward to solve. Hibernating astronauts can be immobilized in special capsules and would no longer need pressurized living space or artificially generated gravity.

NASA News 

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 the form of deuterium fuel is blended with antimatter and annihilates each other generating vast quantities of energy. This energy is mediated through the dilithium crystals and is funnelled to the warp nacelles which in turn warp space-time permitting ships to travel faster than light. Travelling at warp speed means that solar systems can be reached in days rather than a millennium.

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 way of navigating the Slipstream. Slipstream is a series of "strings" connected between planetary systems by gravity. A Gravity Field Generator greatly reduces the mass of the ship after which a slipstream drive opens a slip point which the ship enters. The pilot then navigates the sequence of slipstream "tunnels" 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 not any science behind the slipstream, there are several theories which 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, which establishes a wormhole in which matter can be transported. Wormholes are theoretical tunnels through the fabric of space-time that might potentially permit rapid travel between widely separated points.

While wormholes are conceivable under Einstein's theory of general relativity, such exotic voyages will most probably remain in the realm of science fiction. There are very strong indications that wormholes that a human could travel through are forbidden by the laws of physics. Also, traversable wormholes - if they may be able to exist at all - almost without a doubt 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" after which the ship "jumps" in an instant 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 then teleports to some other location.

I would not get too serious about this being a chance any time 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, chemical rockets have pretty much 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 space craft would never leave Earth's atmosphere. Future refinements to the chemical rocket are not anticipated to produce any 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 when it comes to power to weight, the overall thrust may be very small, so their use has been restricted to satellites orbiting the Earth. They had been developed in the 1970s and continue to be used as of late.

Ion drive

The subsequent generation of space engines are looking like a contender for long-range missions. The thrust produced could be very low, however, can be sustained for a very long time, and is cumulative. Throughout an extended-range mission, Ion drive engines can deliver 10 times as much thrust per kilogram of fuel than a chemical rocket can.

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

Particles of light (called photons) carry momentum, like ping pong balls bouncing off a wall. The solar sail concept is to catch sufficient of them to pick up important thrust. 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 resulting in much less thrust.

Plasma Propulsion Engine

These engines are like beefed-up variations of the ion drive. Instead of the use of 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), being developed by the Ad Astra Rocket Company in Texas. 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

Back 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 would heat a propellant to extraordinarily high temperatures and generate thrust. The venture was about to be built-in 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.