How Long Would It Take to Travel to Other Stars?

Proxima Centauri is our nearest stellar neighbor, a dim red dwarf 4.24 light-years away. Light — the fastest thing in the universe — takes 4.24 years to make the trip. The New Horizons spacecraft, which flew past Pluto in 2015 and is now the third-fastest human-made object ever launched, is traveling at about 14 kilometers per second relative to the Sun. At that speed, reaching Proxima Centauri would take approximately 78,000 years. The Voyager 1 probe, humanity's most distant artifact, would take about 73,000 years to reach a comparably close star.

Interstellar travel, with current propulsion technology, is not merely difficult. It is effectively impossible on any timescale that means anything to a civilization. But physics does not forbid it. It demands only that we think on a scale we have never been forced to before.

Key takeaways

• The nearest star system is 4.24 light-years away; at current spacecraft speeds, the journey would take ~75,000 years
• Nuclear pulse propulsion (Project Orion) could theoretically reach 3-10% of the speed of light, cutting transit time to 40-150 years
• Laser sail concepts like Breakthrough Starshot aim to accelerate gram-scale probes to 20% the speed of light using ground-based lasers
• Relativistic travel at speeds above ~10% of light introduces time dilation — the crew ages slower than people on Earth

The Tyranny of Distance

To feel the scale of interstellar distances, it helps to shrink the solar system to a model where the Sun is a basketball. On this scale, Earth is a small marble about 29 meters away. Jupiter, the outermost gas giant, is about 150 meters from the Sun-basketball. The outer edge of the Kuiper Belt, where New Horizons is now, is about 750 meters away. Voyager 1, the farthest human-made object, is about 2.3 kilometers from the basketball-Sun.

And on this same scale, the nearest star — Proxima Centauri — is about 7,700 kilometers away. From New York, it would be in western China.

This is the tyranny of interstellar distance. Our solar system is enormous by human standards; interstellar distances are enormous compared to our solar system.

A light-year — the distance light travels in one year — is approximately 9.46 trillion kilometers. Proxima Centauri is 4.24 of these. The Milky Way is 100,000 light-years across. The Andromeda Galaxy, our nearest large galactic neighbor, is 2.5 million light-years away.

Current Technology: Chemical and Ion Propulsion

Every spacecraft launched to date has relied primarily on chemical propulsion — burning rocket fuel to generate thrust. The fundamental limit of chemical propulsion is set by the chemical energy available in the propellants. The exhaust velocity of the best chemical rockets (liquid hydrogen/oxygen) is about 4.4 kilometers per second. The most efficient use of this — multiple stages, gravity assists, aerobraking — can get spacecraft to about 10-20 km/s relative to the Sun.

This is breathtaking by human standards and utterly inadequate for interstellar travel. Even at 20 km/s — faster than any spacecraft has actually achieved on an interstellar trajectory — reaching Proxima Centauri would take 63,000 years.

Ion drives, which accelerate ionized particles to extremely high velocities with electric fields, are far more fuel-efficient than chemical rockets. NASA's Dawn spacecraft and others have used ion drives. But their thrust is extremely low — comparable to the weight of a piece of paper — and they are powered by solar panels that become ineffective far from the Sun. Ion drives are excellent for solar system exploration; they change the interstellar calculus only marginally.

Nuclear Propulsion: A Serious Possibility

The most credible near-term route to significantly higher speeds is nuclear propulsion. Two main concepts have received serious engineering study.

Nuclear thermal propulsion heats a propellant (typically hydrogen) using a nuclear reactor and expels it to generate thrust. This roughly doubles the specific impulse (efficiency) of chemical rockets. NASA's DARPA nuclear thermal rocket program (DRACO) aims to demonstrate this technology in the late 2020s for use in the inner solar system. For interstellar purposes, it is a step in the right direction but not a game-changer — maximum speeds might reach 100 km/s, cutting transit time to Proxima to about 13,000 years.

Nuclear pulse propulsion is far more capable. Project Orion, studied seriously by physicists including Freeman Dyson in the 1950s and 1960s, proposed detonating nuclear bombs behind a massive shock-absorber plate. Each explosion pushes the spacecraft forward. A sufficiently large Orion ship could reach 3-10% of the speed of light — transit times of 42-140 years to Proxima Centauri. The idea was technically feasible (Dyson believed it could have been built with 1960s technology) but was killed by the Partial Nuclear Test Ban Treaty of 1963, which prohibited nuclear explosions in space.

An advanced version — nuclear pulse propulsion using fusion bombs instead of fission — could reach 10-12% of the speed of light. The British Interplanetary Society's Project Daedalus (1970s) designed a fusion-propelled probe along these lines. The calculations closed; the engineering and the fusion fuel acquisition were the challenges.

Laser Sails: The Most Promising Near-Term Concept

Breakthrough Starshot, announced in 2016 by Yuri Milner and Stephen Hawking with $100 million in funding, proposes a radically different approach: instead of carrying propellant, use photon pressure from a powerful ground-based laser array to accelerate an ultra-lightweight sail.

The concept: a laser array with a total power of about 100 gigawatts illuminates a sail made of a material a few hundred atoms thick, a few meters across, attached to a gram-scale "StarChip" carrying miniaturized cameras, sensors, and a laser communications system. Over a few minutes, the sail is accelerated to 20% of the speed of light.

At 0.2c, the transit time to Proxima Centauri is about 20 years. Adding time for signals to return (4.24 years), humanity could receive data from another star system within about 24 years of launch — within a human lifetime.

The engineering challenges are formidable: the laser array must be focused on a moving sail with extraordinary precision over thousands of kilometers; the sail must survive the laser intensity; the StarChip must survive 20 years of cosmic ray bombardment; and the communication laser on the chip must be powerful enough to be detectable from 4 light-years away. None of these challenges violates any known physics. All of them require significant technological development.

Relativistic Travel: Time Dilation as a Possible Advantage

For speeds above roughly 10% of light, special relativity's time dilation becomes significant. Time on the spacecraft passes more slowly than time on Earth. At 90% of the speed of light, the crew experiences only 43% as much time as Earth observers. At 99.5% of light, only 10%.

This means that while a round trip to Proxima Centauri would take about 8.5 years of Earth time even at the speed of light, the crew could reach much more distant destinations — the galactic center, 26,000 light-years away — in a few decades of their own subjective time, even as tens of thousands of years pass on Earth.

This is not useful for keeping in contact with human civilization — anyone who left at 99% of light speed for the galactic center would return to an Earth 52,000 years in the future — but it raises the profound possibility of a "generation-less" starship where the original crew arrives at their destination, old but alive.

The energy requirements for relativistic travel are staggering. Accelerating even a modest spacecraft to 10% of light speed and decelerating it at the destination requires energy comparable to all of humanity's current energy consumption for years. Getting to 90% of light requires thousands of times more. Without some form of antimatter propulsion or access to energy sources far beyond current technology, relativistic crewed travel is not feasible in the near-term.

FAQ

Is there any star closer than Proxima Centauri? No. Proxima Centauri, at 4.24 light-years, is definitively the closest star to our Sun. It is part of the Alpha Centauri triple-star system; the other two members (Alpha Centauri A and B, gravitationally bound to Proxima) are 4.37 light-years away.

Does Proxima Centauri have any Earth-like planets? Yes — Proxima Centauri b, discovered in 2016, is a planet in the star's habitable zone with a mass slightly greater than Earth's. However, Proxima Centauri is a flare star that produces intense ultraviolet and X-ray flares; whether Proxima b can maintain an atmosphere and liquid water under this bombardment is uncertain and actively debated.

What about warp drives? The Alcubierre warp drive is a mathematical solution to Einstein's field equations that would allow faster-than-light travel by expanding spacetime behind a ship and contracting it in front. The problem: it requires exotic matter with negative energy density, which may not be physically realizable. Some researchers have proposed modifications requiring less exotic matter, but no known physical mechanism for achieving it exists. It is an interesting mathematical curiosity, not an engineering proposal.

Could a generation ship work? A generation ship — a slow-moving spacecraft where many generations of crew are born, live, and die during the voyage — is physically feasible but faces severe psychological, genetic, and social challenges. The minimum viable population to avoid genetic bottlenecks over a multi-thousand-year voyage is estimated at hundreds to thousands of people. Keeping a stable, functional society over that timescale, with no outside contact, is a sociological problem for which we have no precedent.

Would suspended animation make long voyages feasible? Hypothetically, yes — if crew metabolism could be slowed dramatically, subjective voyage time could be reduced to manageable periods. No current technology can achieve this for more than a few hours in medical contexts, let alone years. Research into torpor states (the hibernation-like reduced metabolism seen in some mammals) is ongoing, and NASA has funded early studies, but it remains far from operational for space missions.

---

Read next:

• How Long Would It Take to Travel to the Nearest Star?
• How Rocket Engines Actually Work — From Kerosene to Ion Thrusters
• How Rockets Work: The Physics Behind Getting to Space