How Long Would It Take to Travel to the Nearest Star?

The nearest star to the Sun is Proxima Centauri, about 4.24 light-years away. It belongs to the Alpha Centauri system, a triple star that includes two brighter companions, Alpha Centauri A and B, about 4.34 light-years from us. On the scale of the Milky Way, which is on the order of 100,000 light-years across, that is a short hop. On the scale of human spaceflight it is almost absurdly far.

Light covers the gap in 4.24 years. Voyager 1, the most distant spacecraft ever built, moves at about 17 kilometers per second and would need roughly 75,000 years. This article walks through what different technologies could achieve, what stops them, and why the honest answer is "no one knows how to do it within a lifetime yet."

Key takeaways

• Proxima Centauri is about 4.24 light-years away, which is about 40 trillion kilometers (25 trillion miles).
• At Voyager 1's speed (about 17 km/s), the trip takes roughly 75,000 years.
• Even the Parker Solar Probe, the fastest human-made object at about 191 km/s, would need around 6,650 years if it could hold that speed, which it cannot.
• A one-way trip in 20 years requires an average speed of about 21 percent of the speed of light. A 42-year trip needs 10 percent.
• Laser sails and fusion rockets have both been studied, but neither has been built. The rocket equation is the main reason chemical rockets cannot do the job.
• Time dilation saves meaningful time only at very high speeds, roughly half the speed of light or faster.

The scale of the distance

A light-year is the distance light travels in one year, about 9.46 trillion kilometers. Multiply by 4.24 and you get roughly 40 trillion kilometers, or about 268,000 astronomical units (an astronomical unit, or AU, is the average Earth-Sun distance of about 150 million kilometers).

Here is one way to feel that. Voyager 1 left Earth in 1977. NASA projects that on November 18, 2026, it will reach a distance of one light-day from Earth, about 25.9 billion kilometers, just over 49 years after its 1977 launch (NASA). One light-day is about 0.065 percent of the way to Proxima. In roughly five decades, the spacecraft has covered about one part in 1,500 of the distance.

The nearest star is visible to the naked eye only in the form of its brighter neighbors, Alpha Centauri A and B, which merge into one bright point in the southern sky. Proxima itself is a dim red dwarf that requires a telescope. The light reaching your eye from Alpha Centauri left it a little more than four years ago.

For a broader sense of how this distance compares to everything else out there, see how big the universe is.

What today's spacecraft can do

Travel time is simple arithmetic: distance divided by speed. The distance is fixed at about 4.01 × 10¹³ kilometers. What changes is the speed.

Vehicle or concept	Speed	Fraction of light speed	Time to Proxima Centauri
International Space Station (orbital speed, about)	7.7 km/s	0.0026%	about 165,000 years
Voyager 1 (relative to the Sun)	about 17 km/s	0.0057%	about 75,000 years
Parker Solar Probe at perihelion, Dec. 24, 2024	about 191 km/s	0.064%	about 6,650 years
Constant 1% of light speed	about 3,000 km/s	1%	about 424 years
Dyson's Orion design, momentum-limited	up to 10,000 km/s	about 3.3%	about 130 years
Daedalus cruise speed	about 12% of c	12%	about 35 years of cruise
Breakthrough Starshot target	15 to 20% of c	15 to 20%	about 21 to 28 years
Constant 50% of light speed	about 150,000 km/s	50%	about 8.5 years
Constant 90% of light speed	about 270,000 km/s	90%	about 4.7 years

The times in the table are calculated from the speeds and ignore acceleration, deceleration, and relativistic effects. They show what the cruise phase alone would cost.

Two entries deserve a closer look.

Voyager 1 is moving at about 17 km/s, or about 61,000 kilometers per hour, relative to the Sun, according to the Voyager 1 article. It crossed the heliopause, the edge of the Sun's wind, on August 25, 2012. It is heading toward the constellation Ophiuchus, not toward Alpha Centauri. Its path was set by a close flyby of Saturn's moon Titan, and it was never aimed at any other star. For more about both Voyagers, see Voyager 1 and 2, the most distant human-made objects.

The Parker Solar Probe holds the record for the fastest human-made object. On December 24, 2024, at 11:53 UTC, it passed the Sun at about 191 km/s (roughly 690,000 km/h), about 6.16 million kilometers above the solar surface (Parker Solar Probe article). That figure is a speed relative to the Sun at the point of closest approach, as the Sun's gravity pulls the probe into a plunging orbit. It is not a cruising speed that could be sustained away from the Sun. Once the probe climbs back out, it slows down. See the Parker Solar Probe explained for how its orbit works.

Why chemical rockets cannot do it

The central problem is the rocket equation, worked out by Konstantin Tsiolkovsky. It says the change in speed a rocket can achieve equals its exhaust velocity multiplied by the natural logarithm of the ratio of its fueled mass to its empty mass. The key point is the logarithm: fuel needs grow exponentially with the speed you want.

Take a typical chemical rocket with an effective exhaust velocity of 4.5 km/s, the value used in the rocket equation article. To reach orbit, which needs a change in speed of about 9.7 km/s including losses, the mass ratio is about 8.6, so almost 88 percent of the rocket at liftoff is propellant. That is already hard.

Now ask for 10 percent of the speed of light, about 30,000 km/s. The required mass ratio is e raised to the power of 30,000 divided by 4.5, which is about 10 raised to the power of 2,895. That is a one followed by nearly three thousand zeros, a ratio no conceivable rocket could have. Chemical propulsion is out. Getting a rocket to a significant fraction of light speed requires a very different kind of engine, one with an exhaust speed that is itself a good fraction of light speed.

That is the logic behind every design in the sections below. Each tries to change something about the rocket equation: use exhaust that moves much faster, leave the fuel behind, or push from outside the vehicle. For the basics of how rockets work today, see how rocket engines actually work.

The concept ladder

Nuclear pulse: Project Orion

Project Orion ran from 1955 to 1964. The idea, which Stanisław Ulam first proposed in 1946, was to propel a ship by detonating a series of small nuclear bombs behind a massive pusher plate. General Atomics led the design work in San Diego, with Ted Taylor in charge and physicist Freeman Dyson taking a year off from the Institute for Advanced Study to contribute. Model flights using chemical explosives took place in 1959, the most successful flying 56 meters in 23 seconds. The project ended in 1964, mainly because the 1963 Partial Test Ban Treaty banned nuclear detonations in the atmosphere and in space (Orion article).

In 1968, Dyson wrote a paper on interstellar versions of the idea using fusion explosions in place of fission bombs. His "momentum-limited" design was a 100-meter, 100,000-tonne ship reaching a maximum of 10,000 km/s (about 3.3 percent of light speed) at an average acceleration of 1 g, with a one-way trip to Alpha Centauri of about 133 years. That is a multi-generation voyage, though a fast one by the standards of the other options of that era.

Fusion: Daedalus and Longshot

Between 1973 and 1978, the British Interplanetary Society studied Project Daedalus, an uncrewed two-stage fusion starship. Its target was Barnard's Star, about 5.9 light-years away, not Alpha Centauri. The craft would have weighed 54,000 tonnes at launch, of which about 50,000 tonnes were fuel, and cruised at about 12 percent of light speed for a total trip of about 50 years. It would not have slowed down at its destination, so it would have been a flyby (Daedalus article).

The later Project Longshot, developed in 1987 and 1988 by the US Naval Academy and NASA, aimed at Alpha Centauri B and would have entered orbit around it. It would have used helium-3 and deuterium fuel pellets ignited by lasers, with an onboard fission reactor powering the lasers. Launch mass was about 396 tonnes, including 264 tonnes of fuel, and the trip would have taken about a century (Longshot article).

These studies shared a limit. Controlled fusion that produces net energy is still a laboratory problem on Earth, let alone in a starship engine. The fusion that powers the Sun is explained in nuclear fusion energy explained. The designs are valuable as feasibility studies, not as blueprints.

Laser sails: Breakthrough Starshot

Breakthrough Starshot was announced on April 12, 2016, in New York by Yuri Milner and Stephen Hawking, with $100 million in initial funding. The idea is to avoid carrying fuel altogether. A ground-based array of lasers, with a combined power of up to 100 gigawatts, would push a sail no larger than 4 meters by 4 meters. The payload would be a "StarChip" weighing a few grams, and about 1,000 of them would be carried into orbit by a mothership.

The target is 15 to 20 percent of light speed, reached in about 10 minutes, at an average acceleration on the order of 100 km/s², or roughly 10,000 times Earth's gravity. Each sail would absorb around 1 terajoule of light energy. The trip would take 20 to 30 years, plus about four years for the signal home (per the Starshot article). The official Breakthrough Initiatives page describes a flyby mission with "just over 20 years" of travel time from launch.

The physics of pushing with light is real. Photons carry momentum, and a mirror that reflects them gets a tiny push. Solar sails have flown, and why solar sails can move without fuel explains the principle. Starshot scales it up by many orders of magnitude, and the challenges are about engineering:

• Sail survival. The sail must absorb almost none of the laser energy, or it will vaporize.
• Atmospheric focusing. Turbulence in the atmosphere makes it hard to hold a beam steady on a target far away, which has led some to suggest space-based lasers.
• Dust. The probe would hit interstellar dust grains at a large fraction of light speed. Starshot's planners expected on the order of 1,000 particles of at least 0.1 micrometers per square centimeter of frontal area along the trip.
• Communications. A laser link from a gram-scale probe over four light-years would deliver between 2.6 and 15 baud per watt of transmitted power, assuming a 30-meter receiving telescope on Earth.
• Technology gap. The Economist reported that at least a dozen off-the-shelf technologies would need orders of magnitude of improvement.

The project did some early tests. Small precursor chips called Sprites flew on an Indian PSLV rocket in 2017, and 105 Sprites were deployed from the International Space Station aboard KickSat-2 in March 2019. As of a September 2025 report in Scientific American, the project had been put on hold indefinitely, with physicist Philip Lubin estimating that about $4.5 million of the proposed $100 million had been spent.

Antimatter

Antimatter is the most compact energy source imaginable. When matter and antimatter meet, they annihilate and convert their mass entirely into energy. For more on the physics, see what is antimatter.

The obstacle is production. According to CERN, its Antimatter Factory delivers about 400 million antiprotons per hour to experiments, which capture roughly 10 percent of them (CERN). Running non-stop for a year, that comes to about 300 billion antiprotons, or about 3 × 10⁻¹⁶ kilograms. That is not "nanograms per year," a figure sometimes quoted. It is roughly three thousand times smaller than a single nanogram. A starship would need many tonnes.

The relativistic rocket

If you could build an engine with unlimited efficiency, how fast could you go? The standard textbook case is a rocket that accelerates at a constant 1 g (the gravity felt on Earth's surface), flips halfway, and decelerates. The formulas, summarized in the relativistic rocket FAQ, give a trip to a star 4.3 light-years away that stops there with a ship time of about 3.6 years. Calculating from the same equations, the time on Earth is about 5.9 years, and the top speed at the halfway point is about 95 percent of light speed.

That sounds appealing, but the fuel is the problem. Even for a perfect photon rocket with exhaust moving at light speed, the same source gives a fuel-to-payload mass ratio of about 38 to 1 for a trip that stops at 4.3 light-years, and about 10 to 1 for a flyby. Real engines are far from perfect. The relativistic rocket is a limit, not a design.

The deceleration problem

Most of the numbers above describe how long it takes to arrive, not how long it takes to stay. A probe that flies by at 20 percent of light speed crosses the entire Alpha Centauri system, about 35 AU wide between A and B at the farthest, in a matter of days. Useful for a snapshot, not for a survey.

Stopping requires removing all the speed you gained. A rocket that carries its own fuel must carry the fuel for braking up to speed too, which multiplies the mass problem. Proposed alternatives include:

• Magnetic braking using a magnetic sail that interacts with the stellar wind of the destination star. The effectiveness is uncertain.
• Laser braking with a beam from a second installation at the destination. That needs a previous mission to build it.
• Staged sails where part of the sail detaches and reflects light back to slow the rest. This idea has been studied for light-driven missions to Alpha Centauri.
• Aerobraking in a stellar atmosphere is not practical at these speeds, since the heating would be extreme.

For any crewed mission, deceleration is non-negotiable.

What time dilation does and does not do

Special relativity says a moving clock runs slow compared with a stationary one. A traveler going fast enough could cross the 4.24 light-years in less ship time than it takes for the light to travel it. The effect is described by the Lorentz factor, and the fraction of Earth time that passes on the ship is the inverse of that factor.

Speed (fraction of c)	Ship clock rate vs. Earth clock	One-way trip, Earth frame	Ship time for the trip
0.1	99.5%	42.4 years	42.2 years
0.2	98.0%	21.2 years	20.8 years
0.5	86.6%	8.5 years	7.3 years
0.9	43.6%	4.7 years	2.1 years
0.99	14.1%	4.3 years	0.6 years
0.999	4.5%	4.2 years	0.19 years

These values are calculated from the standard Lorentz factor formula and assume the whole journey is at one steady speed. At the speeds that Starshot or fusion designs aim for, 10 to 20 percent of light speed, the time savings are small: a percent or two. Dilation becomes a major factor only at speeds that exceed anything proposed except in the idealized relativistic rocket. For how it works, see the twin paradox explained. The clock effect cuts the traveler's experience, not the time on Earth, so people at home would still wait at least 4.24 years.

The destination

Alpha Centauri is a triple system. Alpha Centauri A is a Sun-like G2V star of about 1.1 solar masses, and B is a cooler K1V star of about 0.9 solar masses. They orbit each other every 79.8 years or so, with a separation that varies from about 11.2 AU to 35.6 AU. Proxima Centauri is a dim red dwarf of about 0.12 solar masses, roughly 13,000 AU (0.21 light-years) from the pair. These numbers are from the Alpha Centauri article.

Proxima has the best-known planet. Proxima b was announced by the European Southern Observatory on August 24, 2016, from Doppler measurements by the Pale Red Dot project, led by Guillem Anglada-Escudé. It orbits about 0.048 AU from its star every 11.2 days, has a minimum mass of about 1.06 Earth masses, and sits in the star's habitable zone. A habitable zone is the range of distances where liquid water could exist on a planet's surface. That does not make the planet habitable. Proxima is a flare star, and the planet may receive 10 to 60 times the ultraviolet and X-ray radiation Earth gets. Flares and stellar wind could strip off any atmosphere, and no atmosphere has been detected (Proxima b article).

The planet is probably tidally locked, with one hemisphere always facing the star, but if its orbit is even slightly eccentric it could settle into a 3:2 spin-orbit resonance like Mercury's instead. Proxima d, a smaller planet orbiting much closer to the star, was reported in 2022. A third candidate, Proxima c, remains unconfirmed.

Around the bigger stars, the picture is open. In August 2025, researchers using NASA's James Webb Space Telescope reported evidence of a possible gas giant, roughly Saturn's mass, orbiting Alpha Centauri A at about 2 AU. Follow-up observations did not detect it again, which the team says is consistent with the planet's orbit carrying it too close to the star in roughly half of the simulated orbits. It is a candidate, not a confirmed planet, and NASA's Roman Space Telescope, which NASA's mission page lists as launched on August 30, 2026 and now in commissioning, could help. For the search methods, see how we actually find exoplanets, and for why red dwarfs complicate habitability, see why red dwarf stars matter for life searches. A catalog of worlds within reach is in nearest exoplanets that could host life.

Talking to a probe four light-years away

Radio and laser signals travel at light speed, so a message takes 4.24 years to cross the distance. Any instruction sent to a probe and answered right away would produce a reply at least 8.5 years later. Real-time control is impossible. A probe has to make its own decisions, and the people who built it have to wait.

For Starshot, the timeline adds up as follows: roughly 20 to 30 years of flight and then about four years for the first data to arrive. Those who start such a mission would hand it to a generation that had not been born at launch.

What about crewed missions?

A crewed ship adds mass, life support, and radiation shielding. Even at 10 percent of light speed, a 1,000-tonne ship would carry a kinetic energy of about 4.5 × 10²⁰ joules, which is 450 exajoules, before counting deceleration. The arithmetic is half the mass times the speed squared. Generation ships, in which several generations live and die in transit, appear in fiction and in some early studies, but no design exists that shows how a closed ecosystem could stay stable for a century or more. Closed life-support systems are hard even in low Earth orbit; see how astronauts survive in space.

For a speculative look at what a civilization that did make the jump might look like, see what if humanity became an interstellar civilization. Ideas such as wormholes would change the arithmetic entirely, but they depend on exotic physics that has not been shown to exist; wormholes explained covers what theory does and does not allow.

Common misunderstandings

"Voyager is headed to Alpha Centauri." It is not. It is heading toward Ophiuchus, and its trajectory was set by a Saturn flyby, not by a stellar target.

"The Parker Solar Probe could get us there in a few thousand years." Its record speed is a speed at the bottom of a gravity well relative to the Sun. It cannot hold that speed on the way out.

"Time dilation will make the trip short for the crew." Only at speeds above roughly half the speed of light, which are far beyond any studied design except idealized ones.

"We could build Starshot now." Not with existing technology. The laser array, the sail material, and the communication link all need large advances, and as of September 2025 the project was reported to be on hold.

"Antimatter is just an expensive fuel." The issue is quantity, not price. Present production is vastly smaller than what a starship would need.

FAQ

Q: How far away is the nearest star? A: Proxima Centauri, a red dwarf, is about 4.24 light-years away, which is about 40 trillion kilometers (25 trillion miles). The brighter pair, Alpha Centauri A and B, is slightly farther, at about 4.34 light-years.

Q: How long would it take Voyager 1 to reach the nearest star? A: About 75,000 years, if it were aimed at Proxima Centauri, using its speed of about 17 km/s. It is not aimed there. It is heading toward the constellation Ophiuchus.

Q: What is the fastest spacecraft ever built? A: The Parker Solar Probe, which reached about 191 km/s (about 690,000 km/h) relative to the Sun on December 24, 2024. At that speed, maintained forever, the trip to Proxima would take about 6,650 years, but the probe cannot maintain it away from the Sun.

Q: Could a human reach another star in their lifetime? A: Not with any propulsion that exists. A trip of about 40 years requires an average speed near 10 percent of light speed. Studies of fusion and nuclear pulse ships suggest that speed is possible on paper, but none has been built, and the fuel masses involved are enormous.

Q: What is Breakthrough Starshot? A: A research program announced in 2016 to send gram-scale probes on laser-driven sails to Alpha Centauri at 15 to 20 percent of light speed, with a trip of roughly 20 to 30 years. It would send no crew. A 2025 report said the project was on hold.

Q: Is there a planet we could go to? A: Proxima b is the best-known candidate. It lies in the habitable zone of its star, but the star's flares and the planet's possible lack of an atmosphere make its habitability very uncertain. A gas giant candidate around Alpha Centauri A is still unconfirmed.

Q: Why not just go faster than light? A: Relativity forbids accelerating ordinary matter to light speed, and faster-than-light travel would require physics that has not been shown to exist.

The takeaway

The nearest star is close in the cosmic sense and far in every practical sense. Four light-years is a few hundred times the distance our fastest probes can cover in a century, and the limits that matter are not only about money. The rocket equation punishes chemical fuel exponentially, so the only routes forward either throw exhaust at a huge fraction of light speed or leave the fuel behind. The studied options, from nuclear pulse ships to fusion starships to laser-driven sails, all trade one problem for another. For now, the most realistic first visit to another star is a gram-sized probe, and its builders would have to be willing to hand the results to the next generation.

Sources

• NASA: Where are Voyager 1 and Voyager 2 now?
• NASA: Voyager 1
• Breakthrough Initiatives: Breakthrough Starshot
• CERN: Antimatter
• The Relativistic Rocket (University of California, Riverside)
• Wikipedia: Breakthrough Starshot
• Wikipedia: Project Daedalus
• Wikipedia: Parker Solar Probe

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• The International Space Station Explained — How It Works and What's Next
• The James Webb Space Telescope Explained — How It Works and What It's Found
• How Rocket Engines Actually Work — From Kerosene to Ion Thrusters
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• The Mysteries of Time: Why Aging Slows Down in Space