Buzz
Many of the foremost thinkers in physics and engineering have dedicated considerable effort to imagining interstellar travel. They have devised detailed concepts and models for spacecraft capable of transporting humans to distant stars. Each proposed design tackles the primary hurdle of interstellar travel: the vast distances between the stars.
Proxima Centauri, located 4 light-years away, is the closest star to Earth (aside from our own Sun). Using conventional rocketry, reaching it would take approximately 137,000 years. The purpose of these spacecraft designs is to propel the ships to a fraction of the speed of light, making the journey achievable within a human lifetime. These proposals are seen as potential solutions that could one day become a reality.
10. Ion Drive Propulsion
Ion propulsion is an advanced engine technology that has seen significant development in recent years. Rockets utilizing ion propulsion generate much less thrust compared to traditional rockets.
Unlike conventional rockets, which stop accelerating once they leave Earth, ion propulsion rockets can continue to propel the spacecraft for extended periods, even decades. The engine's purpose is to steadily accelerate the rocket, enabling it to reach speeds of up to 145,000 kilometers per hour (90,000 mph) over several years.
However, this speed is still insufficient to reach the closest stars. This type of spacecraft would be more effective for missions aimed at exploring the outer reaches of our solar system.
Ion propulsion operates by utilizing the electrostatic behavior of particles, where particles with similar charges repel each other and particles with opposite charges attract. The process begins by injecting an inert gas, typically xenon, into an ionization chamber. Then, a stream of electrons is introduced into the chamber using electricity generated by solar panels or nuclear reactors.
As the electrons interact with the xenon atoms, they knock off some of the atoms' electrons, creating positively charged ions. The like charges of these ions push against each other, causing the ions to accelerate.
Using a negatively charged grid, the ions are drawn toward holes at the end of the chamber. Once there, they are expelled from the spacecraft at extremely high speeds, propelling the spacecraft forward.
Xenon is an exceptionally efficient propellant that can be stored in large quantities, making it an excellent fuel choice. Furthermore, ion propulsion systems emit a bright blue glow, resembling the spaceships seen in space operas.
9. Nanotechnology
Researchers at the University of Michigan have enhanced ion propulsion technology with a development called nanoFET. Instead of using xenon atoms, this technology employs large, man-made particles known as carbon nanotubes. These particles can be charged and accelerated similarly to xenon atoms, if not more effectively. Due to their greater mass, their ejection provides the spacecraft with a significantly stronger thrust.
However, this method is quite messy and complicated. A spacecraft would need to constantly expel trillions of these particles. NanoFET still has a long way to go.
8. Nuclear Explosions
Yes, this is legitimate. Nuclear bombs could potentially be used to power interstellar spacecraft. While it may seem barbaric, this is one of the more feasible designs on this list.
Every three seconds, a small nuclear explosion, or 'bomblet,' would detonate at the rear of the spacecraft. The energy from the explosion would be absorbed by shock absorbers attached to a 'pusher plate,' which would propel the spacecraft to 3 percent of the speed of light.
You might think that passengers aboard these spacecraft would endure the most intense turbulence imaginable. However, the energy from the explosions is expected to be distributed efficiently, resulting in a surprisingly smooth journey.
7. Ramjet Engines
Nuclear fusion is a reaction that takes place at the cores of all stars, producing the immense heat emitted by stars. Fusion occurs when atoms are exposed to extreme temperatures and pressures, causing lighter atoms to combine into heavier ones. This process releases vast amounts of thermal energy as a byproduct.
Fusion is significantly more powerful and energetic than fission (the process used in nuclear bombs to split atoms). The most common form of fusion is hydrogen fusion, which results in the creation of helium. Various designs for interstellar spacecraft harness the power of hydrogen fusion.
By using powerful lasers or magnets, hydrogen is compressed and heated until fusion occurs. The thermal energy produced by the fusion reaction is transferred to surrounding atoms, causing them to accelerate. These atoms are then expelled from the spacecraft through a nozzle, propelling the spacecraft to an astonishing 90 million kilometers per hour (55.9 million mph).
Hydrogen can either be stored onboard the spacecraft or collected from the interstellar medium (the matter and radiation that exists between stars) as the ship travels. Spacecraft that gather hydrogen as they move are referred to as ramjets.
6. Antimatter
A particle of antimatter possesses the opposite characteristics of its regular matter counterpart. For instance, a proton carries a positive charge, whereas an antiproton carries a negative charge.
What does antimatter look like? You’ve never seen it because it’s only created in laboratories. The reason for this is that when a particle of antimatter comes into contact with a regular matter particle, they annihilate each other in a spectacular explosion. The entire mass of both particles is converted into a tsunami of energy.
To put it in perspective, the largest nuclear bombs today convert only 0.1 percent of their mass into energy. However, before all the mass is transformed into pure energy, a few short-lived particles are created as a result of the reaction. These particles are mostly known as pions.
In an antimatter-powered rocket, these pions would serve as fuel and be expelled from the spacecraft before they fully convert into energy. It’s estimated that a spacecraft powered by antimatter annihilation could reach speeds of 40 percent of the speed of light. Unfortunately, antimatter is exceedingly difficult to produce, and we currently lack the technology to generate enough of it.
5. Solar Sails
You may have seen them in Star Wars, but solar sails are very real. NASA and The Planetary Society have already carried out tests with these spacecraft.
These spacecraft function similarly to a sailboat. Instead of wind, however, they use sunlight as their propellant. The ship consists of a small payload connected to a gigantic, ultrathin mirror, which can be as large as 30 meters (100 feet) in diameter.
Pressure is applied to the sail as an immense number of photons are reflected from the surface of the mirror. As time passes, the pressure accumulates, allowing the spacecraft to accelerate to speeds of up to 241,000 kilometers per hour (150,000 mph).
Although these spacecraft are fast, they still don’t reach the speeds necessary for interstellar travel. However, as you’ll soon discover, the concept of solar sails can be adapted to achieve some of the fastest velocities on this list.
4. Laser Beams
The concept of using powerful laser beams to propel spacecraft at extremely high speeds has gained the backing of influential figures, including Mark Zuckerberg and the late Stephen Hawking. This idea, known as Breakthrough Starshot, aims to launch thousands of small probes to Proxima Centauri, the closest star to Earth after the Sun, located 4 light-years away.
Proxima Centauri is not only close but is also a prime candidate for exploration because it hosts an Earth-like exoplanet called Proxima Centauri b (also known as Proxima b), which orbits within the habitable zone. The mission’s objective is to capture images and gather other crucial data on the exoplanet to determine whether Proxima Centauri b could be habitable or possibly already home to life.
The probes will be minuscule, wafer-thin pellets equipped with various valuable instruments, weighing only a few grams. Similar to solar sails, they will be attached to “lightsails” and launched into space.
From a station on Earth, large arrays of high-powered lasers will focus 100 gigawatts of energy on the lightsails, accelerating them to 20 percent of the speed of light—about 160 million kilometers per hour (100 million mph). At such high speeds, even the smallest particles of space dust could destroy a probe.
To maximize the chances of success, thousands of probes will be dispatched, ensuring that at least a few will successfully reach their target. The Breakthrough Starshot probes are expected to arrive at Proxima Centauri b within 20 years.
3. Black Hole Starship
Among all the starships proposed in this list, the black hole starship stands out as the most far-fetched. However, it is certainly a captivating concept. This idea leverages Hawking radiation, a phenomenon first theorized by Stephen Hawking.
Hawking radiation is the radiation emitted by a black hole as it gradually evaporates. Throughout its existence, a black hole releases radiation and decreases in size. For starships, the key insight is that the radiation emission accelerates as the black hole shrinks. By artificially creating a microscopic black hole, the Hawking radiation it emits could potentially be reflected away from the spacecraft, providing thrust.
2. Gas Station On Saturn’s Moon
Traditional rocket fuel is composed of liquid hydrogen and an oxidizer, often liquid oxygen. These fuels are not only toxic but also challenging to store due to their low density, which limits how much can be stocked. Furthermore, they must be maintained at extreme temperatures of -252.9 degrees Celsius (-423.2 °F).
As a result, innovators like Elon Musk and Jeff Bezos have shifted their focus to methane fuel. Methane (CH4) is a safer, non-toxic alternative that can be stored at much higher temperatures and is denser than hydrogen, making it more efficient for storage.
However, there’s a challenge. Despite its abundance on Earth, methane is not easily harvested. Fortunately, a nearby location offers vast reserves of liquid fuel waiting to be collected. Saturn's largest moon, Titan, is home to lakes of methane, ethane, and propane, making it an ideal source for rocket fuel.
If a launchpad were constructed on Titan’s surface, we could fuel a rocket with large quantities of methane. Moreover, Titan’s weaker gravity would significantly reduce the amount of fuel needed for liftoff, which is typically the most fuel-consuming phase of a journey. A spacecraft launched from Titan could potentially carry us to the stars.
1. Beamed Particle Propulsion
One issue with Breakthrough Starshot involves a phenomenon known as 'beam spreading.' This occurs when light beams spread out as they travel, reducing the impact they can have on a lightsail. Some researchers have suggested using jets of particles instead of light beams, but these too suffer from the same spreading effect.
Researchers at Texas A&M have devised a groundbreaking approach: combining both lasers and particles. Their project, called PROCSIMA, aims to eliminate beam spreading in lasers by altering the properties of particles, and to counteract spreading in particles by adjusting the properties of light.
