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

by Ian O'Neill on July 8, 2008

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We’ve all asked this question at some point: How long would it take to travel to the stars? And could I do it in my lifetime? There are many answers to this possibility, some very simple, others in the realms of science fiction. To make this easier to answer, we’ll address how long it would take to travel to the nearest star to the solar system, Proxima Centauri. Unfortunately, any route you take to the stars will be slow, even if you are powered by the most powerful nuclear propulsion technology…

In April, I examined how long it takes to travel to the Moon. We took the fast-track with New Horizons Pluto mission, powering past Earth’s only natural satellite in a mere eight hours and 35 minutes. We also had the leisurely ion drive-propelled SMART-1 mission that trundled its way to the Moon for 13 months. So, from the speedy rocket-propelled spacecraft to the economical ion drive, we have a few options open to us when flying around local space (plus we could use Jupiter or Saturn for a hefty gravitational slingshot). But say if we build a dedicated mission to somewhere a little more extreme?

The nearest star to Earth is our Sun. It is a fairly “average” star in the Hertzsprung – Russell diagram’s “Main Sequence.” Our Sun is surprisingly stable, providing Earth with just the right sunlight for life to evolve on our planet. We know there are planets orbiting other stars near to the Solar System, but could they support life as efficiently as our Sun? In the future, should mankind wish to leave the Solar System, we’ll have a huge choice of stars we could travel to, and many could have the right conditions for life to thrive. But where would we go and how long would it take for us to get there?

First choice would probably be Proxima Centauri, the closest star to the Solar System. Part of a triple star system called Alpha Centauri; Proxima is 4.22 light years from Earth. Alpha Centauri is actually the brightest star of the three in the system, and so the system is named after this star. Alpha Centauri is part of a closely orbiting binary about 4.37 light years from Earth, but Proxima Centauri (the dimmest of the three) is an isolated red dwarf star 0.15 light years from the binary. Red dwarf stars generate far less energy than our Sun, so we’d have to find a planet in a closer orbit to this red dwarf to sustain life as we know it.

Interstellar travel probably conjures up some outlandish theories about the technology we could use to get there. Star Trek‘s warp drive will have to wait and stay in the “sci-fi” category for now, it is more likely any deep space trip will take generations rather than a few days. So, starting with one of the slowest forms of space travel, how long will it take to get to Proxima Centauri? Remember, this is all conjecture as there is currently no benchmark for interstellar trips…

Slowest: Ion drive propulsion, 81,000 years
Ion drive propulsion was considered to be science fiction only a few decades ago. In recent years however, the technology to support ion propulsion has moved from theory and into practice in a big way. The ESA SMART-1 mission for example successfully completed its mission to the Moon after taking a 13 month spiral path from the Earth. SMART-1 used solar powered ion thrusters, where electrical energy was harvested from its solar panels and used to power its Hall-effect thrusters. Only 82 kg of xenon propellant was used to propel SMART-1 to the Moon. 1 kg of xenon propellant provided a delta-v of 45 m/s. This is a highly efficient form of propulsion, but it is by no means fast.

One of the first missions to use ion drive technology was the 1998 Deep Space 1 mission to Comet Borrelly. DS1 also used a xenon-powered ion drive, consuming 81.5 kg of propellant. Over 20 months of thrusting, DS1 was designed to reach a cometary flyby velocity of 56,000 km/hr (35,000 miles/hr).

Ion thrusters are therefore more economical than rocket technology as the thrust per unit mass of propellant (a.k.a. specific impulse) is far higher, but it takes a long time for ion thrusters to accelerate spacecraft to any great velocity. As the maximum velocity of ion thruster-powered spacecraft depends on the amount of fuel it can carry and the amount of electricity it can generate, although slow, if ion thrusters were to be used for a non-time critical mission to Proxima Centauri, the ion thrusters would need a huge source of energy production (i.e. nuclear power) and a large quantity of propellant (although not as large as less-economical forms of space travel, such as rockets). As interstellar ion engines do not exist yet, I will quickly calculate how long it would take for an interplanetary ion engine spacecraft, like Deep Space 1 to travel to our nearest stellar neighbour.

Assuming all the 81.5 kg of xenon propellant translates into a maximum velocity of 56,000 km/hr (assuming there is no other forms of propulsion, such as a gravitational slingshot, and this velocity remains constant for the duration of the journey), Deep Space 1 would take over 81,000 years to travel the 4.3 light years (or 1.3 parsecs) from Earth to Proxima Centauri. To put that time-scale into perspective, that would be over 2,700 human generations. So I think we can categorically say, interplanetary ion engine mission speeds are far too tiny to be considered for manned interstellar missions. But, should ion thrusters be made bigger and more powerful (i.e. ion exhaust velocity would need to be higher), with enough propellant for the spacecraft’s entire 4.3 light year trip, the 81,000 years would be greatly reduced.

Fastest: Gravitational assists, 19,000 years

The 1976 Helios 2 mission was launched to study the interplanetary medium from 0.3AU to 1AU to the Sun. At the time, Helios 1 (launched in 1974) and Helios 2 held the record for closest approach to the Sun. However, to this day, Helios 2 holds the record for fastest ever spacecraft to travel in space. Helios 2 was launched by a conventional NASA Titan/Centaur launch vehicle (the craft itself was built in Germany) and placed in a highly elliptical orbit. Due to the large eccentricity (e=0.54) of the 190 day solar orbit, at perihelion Helios 2 was able to reach a maximum velocity of over 240,000 km/hr (150,000 miles/hr). This orbital speed was attained by the gravitational pull of the Sun alone.

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Gravitational assists are a very useful spaceflight technique, especially when using the Earth or massive planets for a much needed boost in velocity. The Voyager 1 probe for example used Saturn and Jupiter for gravitational slingshots to attain its current 60,000 km/hr (38,000 miles/hr) interstellar velocity. Technically, the Helios 2 perihelion velocity was not a gravitational slingshot, it was a maximum orbital velocity, but it still holds the record for being the fastest manmade object regardless.

So, if Voyager 1 was travelling in the direction of the red dwarf Proxima Centauri, how long would it take to get there? At a constant velocity of 60,000 km/hr, it would take 76,000 years (or over 2,500 generations) to travel that distance. And what if we could attain the record-breaking speed of Helios 2′s close approach of the Sun? Travelling at a constant speed of 240,000 km/hr, Helios 2 would take 19,000 years (or over 600 generations) to travel 4.3 light years.

Again, these speeds are prohibitively slow for any quick forms of transportation to the stars. Other technologies are required (wormholes, warp drives and teleportation will remain in the “sci-fi” drawer for now)…

Fastest (theoretical): Nuclear Pulse Propulsion, 85 years

Nuclear pulse propulsion is a theoretically possible form of fast space travel. Very early on in the development of the development of the atomic bomb, nuclear pulse propulsion was proposed in 1947 and Project Orion was born in 1958 to investigate interplanetary space travel. In a nutshell, Project Orion hoped to harness the power of pulsed nuclear explosions to provide a huge thrust with very high specific impulse. It is a major advantage to extract maximum energy from a spacecraft’s fuel to minimize cost and maximize range, therefore a high specific impulse creates faster, longer-range spaceflight for minimum investment.

For archived prototype video of pulsed propulsion using conventional explosives, watch this video »

The Partial Test Ban Treaty of 1963 is largely attributed to the cancellation of Project Orion (due to the obvious design flaw that huge amounts of radioactive waste would be pumped into space), but what kind of velocities could a nuclear pulse propulsion spaceship attain? Some estimates suggest a ballpark figure of 5% the speed of light (or 5.4×10⁷ km/hr). So assuming a spacecraft could travel at these speeds, it would take a Project Orion-type craft approximately 85 years to travel from the Earth to Proxima Centauri.

In conclusion, if you were hoping to travel to the nearest star within your lifetime, the outlook isn’t very good. However, if mankind felt the incentive to build an “interstellar ark” filled with a self-sustaining community of space-faring humans, it might be possible to travel there in a little under a century if we developed nuclear pulse technology. So your descendents may touch down on a planet closely orbiting Proxima Centauri, but unless we make a breakthrough in interstellar travel (and science fiction becomes more like science fact), we’ll be stuck with long-term, pedestrian transits for the foreseeable (and distant) future…

Sources:
NASA
ESA SMART 1
NASA Helios 2

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About Ian O'Neill

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Hello! My name is Ian O'Neill and I've been writing for the Universe Today since December 2007. I am a solar physics doctor, but my space interests are wide-ranging. Since becoming a science writer I have been drawn to the more extreme astrophysics concepts (like black hole dynamics), high energy physics (getting excited about the LHC!) and general space colonization efforts. I am also heavily involved with the Mars Homestead project (run by the Mars Foundation), an international organization to advance our settlement concepts on Mars. I also run my own space physics blog: Astroengine.com, be sure to check it out!

David

Excellent article, as usual. I’ll go out on a limb and sound like a wingnut. But what about theoretical aspects? We seem so hopelessly confined to conventional understandings of space travel, but I still wonder about the possibilities of interdimensional travel. Mathematics suggests the existence of a multi-dimensional universe. Could they be utilized to get from point a to point b in this dimension? What about alterations in space time, a-la black holes and worm holes? I understand gravity would prove a nasty foe to using these monsters, but is there still a possibility of creating one or finding one that could be used for human use? At least in our present understanding, we appear to have hit a wall in long distance space travel. Even if we utilize the above, even with suspended animation…our efforts would seem rather existential at best given that the round trip would return us to a home where we would not know anyone, where all our friends and family would long since have expired. It would seem we need to return to imagination in our theoretical constructs or resign ourselves to being confined to the solar system.
Don Alexander

Well, some people are already seriously thinking of going way beyond nuclear pulse drives…

http://arxiv.org/pdf/astro-ph/0410511
James

David, I think reaching a black hole would take longer than it’d take to reach the star, so using one of those would be counter-productive? Unless we made our own temporarily, or something.
As for the other theoretical things, for all we know now we could say we could get there before we even left using interdimensional/time travel. Nobody knows for sure, though, and this article just sticks to conventional methods we’ve got down (or theories with a definitive speed like nuclear pulse propulsion). Maybe one day traveling anywhere in the universe can happen in the blink of an eye with those other ideas!
This article is cool, I love seeing answers to unorthodox questions like this.
One thing I always think of, though, is how people tend to think we’ll pick up the whole human race and relocate them. But in the actual case of us inhabiting another planet, only a few people would really go (at least, that’s how we’d do it now). Taking more than a few vital people would be too much added weight and supplies and the mission would never work out!
Jorde

Hmm, not sure Nuclear Pulse would be a valid form of travel for us lowly humans. Wouldn’t the g force from such a pulse transform us into small piles of goo? Though for probes it would be nice.

Also, how do theoretical antimatter engines stack up? If we can eventually find a way to produce the stuff in sufficient quantity, that may be able to get us there.
Alex

im most interested in the last one

85 years , ok
but
does that include i mean , i would imagine to actually arrive there you would need to slow down , and any slowing down at those supposed speeds would take a long ass time ,
so is that factor in , when you say it’ll take 85 years to arrive to our closest star?
sps

Great article.
I believe they figured out the g force problem for Project Orion. Something about a shock absorber. Smart, imaginative people back then I suppose.
Van

Before we think about sending people to Alpha Centuari, we need to send a robot probe. Our government did a study and made a plan. There are a few problems to solve yet:

http://en.wikipedia.org/wiki/Project_Longshot
Yael Dragwyla

Excellent article, but “The Partial Test Ban Treaty of 1963 is largely attributed to the cancellation of Project Orion (due to the obvious design flaw that huge amounts of radioactive waste would be pumped into space)” sort of misses the point. That waste, injected into the near-total vacuum of interstellar space, would very quickly become an extremely tenuous, rapidly expanding mist of particles whose intense radioactivity would be far and away offset by the egregiously low density of the mist. Something like one atom of the stuff for every, what, 10,000 cubic miles? Anywhere near Earth, of course, that waste would definitely be a liability — but we could build the craft somewhere in the Solar System where Earth wouldn’t be in the firing line, and send it on its way from there. Other than that, great article.
Astrofiend

Jorde Says:
July 8th, 2008 at 3:16 pm

“Hmm, not sure Nuclear Pulse would be a valid form of travel for us lowly humans. Wouldn’t the g force from such a pulse transform us into small piles of goo? Though for probes it would be nice.”

>>>>Google Project Orion. The space craft was designed to utilise a thrust plate and massive shock absorbers that reduced the apparent acceleration to something manageable for humans. You can actually see the concept drawing in this article – it’s the very first picture. The thrust plate is the big dish at the back of the craft near the explosion, and the shocks are those linear-looking poles between the plate and the spacecraft…

What we really need to do is get ourselves a technology that will get us up near the speed of light. Then good old Lorentz contraction will shorten the distance we need to travel considerably… Hmmm – easier suggested than done, me thinks.
http://apnea.cz trux

I am sorry for the criticism, but unlike what told above, I think that this article is really of a exceptionally low quality, that I am surprised to see here on this blog. Not only it completely ignores that such long travel necessarily includes accelerating and decelerating phases (likely half of the journey each), it ignores maximal possible long-time acceleration and deceleration (which could not be much higher than 1G for human flights), but it also looks like the author completely misunderstood the principle of ion drive propulsion, and of gravitational assist.

At ion propulsion (or any other similar one), the thrust results in acceleration force, and that again in the acceleration. You need to dimension the propulsion according to available power and propellant supplies, and the mass that needs to be accelerated (including the propellant). The time the propulsion is active plays a role too, of course (ideally it would be accelerating 1/2 way, and decelerating the other half). And of course, as already written, you are limited by the maximal acceleration (at human travels it could not be much more than 10m/s2, but also at robotic probes there would be limits). So basing the calculation on the constant maximal speed achieved by DS1 is a nonsense. You can scale it up (technologically no big issue) to get higher acceleration, and let it on much longer (both for the acceleration and the deceleration), but you are limited by the power supply and by the weight of the entire system (including propellant tanks). The calculation would be much more complex, but the result would be quite different from the one shown in this article.

And as for the gravitational assist – you cannot use the Sun for assisting a space ship – the boost it gives the ship when it falls to the Sun, the vessel loses again when flying away. You can only use assist of planets that gravitationally pull the ship behind them, but that force is quite limited and not of a big interest for interstellar trips. You could only use pull of the Sun if you made huge spirals in the galactic space around the Solar system, using it relative speed to the galaxy center, but that would make the travel many times longer.
Qev

Yeah, the Orion designed called for a ‘pusher plate’, effectively a giant shock absorber at the back of the craft. The nuclear charges would be fired out the back, through an opening in the pusher plate, detonating behind the ship, and the pusher plate would convert the sudden impulse into a longer, gentler push, solving the ‘strawberry jam problem’.

I’m surprised Robert Forward’s solar-laser sail design didn’t rate a mention. It’s a little beyond our technology right at the moment, but could get a ship up to around 0.2c in reasonable time…
Frank Kokot

I’ll propose a possible scenario. Lets say we develop, in the not too distant future, say a highly focused beam of energy that could be transmitted to our craft, or perhaps fission drive with a hydrogen scoop for fuel/thrust. The important thing is we have a craft that can accelerate/decelerate to proxima all the way there ( decelerating at 1g halfway there). So our craft (freighter) can carry a crew and supplies and can accelerate/decelerate at a constant 1g. How long would it take? As a matter of fact lets skip this first model and go straight to a second model which has the ability to accelerate/decelerate at up to 8g, but would only be used as a reasonably healthy crew could withstand for short periods, then 1g.
http://duoquartuncia.blogspot.com/ Duae Quartunciae

The gravitational assist one stood out to me as wrong.

You can get a boost from a planet, by a hyperbolic fly-by. You end up moving away from the planet with the same relative velocity you had on approach (with comparatively minor course adjustments if necessary). This gives a boost in velocity with respect to some other reference point, due to the motions of the planet. You effectively grab a little bit of momentum from the planet. That can’t work with the Sun.
http://apnea.cz trux

If you go 1g half-way and brake 1g the other half, you can calculate the necessary time with the following formula:

t = 2*SQRT(0.5*d/a)

where t is the time, d is distance, and a is the acceleration. In this case the a would be equal to g, which is 10m/s2. So you get these numbers:

t = 2*SQRT(0.5*4.37*365*24*60*60*300,000,000 / 10) = 90932608 s = 2.88 years

However, that’s impossible, because with 1g you would get close to the speed of light pretty soon, and there the relativistic laws apply, increasing the mass and decreasing the accelaeration. It would require a more complex formula to get the real time needed, but likely the journey would not be that long even with a more moderate acceleration rate (assuming sufficient energy for the propulsion is available during the entire flight).
http://apnea.cz trux

>> The nuclear charges would be fired out the back, through an opening
>> in the pusher plate, detonating behind the ship, and the pusher plate
>> would convert the sudden impulse into a longer, gentler push

I did not see the numbers, so I do not know in what force and acceleration the nuclear explositions would result, but my very raw guess is that the absorber would need to be several miles long to allow for sufficient aborbtion. And that again would represent huge mass that needs to be accelerated, hence requiring much more additional energy.
Ken

A planet that can support life will have life, and we will have zero immunity to it. It’s better to just send our genetic information so if there is intelligent life they can simulate us and perhaps send back some suggestions.
tacitus

Unless we discover a potentially life-sustaining planet about Alpha Centauri, I doubt we will attempt to send any spacecraft there until it can be done in less than 100 years — and that’s a long way off. I just don’t think there will be any incentive to invest in a multi-century mission unless there is some other factor involved, like a critical threat to our existence on Earth.

As for a manned mission, I reckon 40 years (averaging 0.1c) will be the longest attempted. I believe that fast a ship is theoretically possible, but again we’re a long long way off.

So for the next few decades at least, we are better pouring our resources into better and beefier telescopes to do long range surveys of the nearer solar systems. My guess is that before we set foot outside our own system, we will have a catalog of tens of thousands of exoplanets from which to choose from to visit first.
SUGARAT

Instead of trying to force the universe to act how we think it should act(something we do here on earth), the whole of science would benefit greatly by working with natures grain not against it. Nature has already figured everything out for us, we just need to learn how we can tap into the inherant knowlege in such a way that we join with it in a “natural”manner.
The broader our perception becomes the more we need to keep in mind that all things interact.
An infant has a narrow understanding of what it sees. As it learns that understanding spreads to include bits of information that previously were isolated and not related in perception. This concept can be true when compared to science as a whole, humanity has not put much energy into trying to blend all scientific disceplines together to create a GUT.
Renniassance man= multi discepline learning= potential for great understanding.
I know we have the ability, I know we do not yet have the focus or long sightedness it would take to achieve any great things, such as interstellar travel or world harmony.
James

I think some of you are taking the article too seriously. He just answered a question, providing us with nothing other than the answer of ‘how long would it take us to reach our nearest neighboring solar system?”
This article doesn’t suggest any of them are that logical, nor that we need to invest in it. Because obviously right now it’d take way too long to reach it.
It was just food for thought, really.

In regards to the life on another planet, there are 3 possibilities.
1) Neither affect eachother
2) They lack immunity and some of them die off (perhaps all of them?)
3) We lack immunity and some of us die off (perhaps all of us?)
Of course, when the time comes to study other life, we’ll assume that #3 to be what we’re dealing with, to prevent getting stuck in a worst-case scenario, #2 to be of slightly-less-but-still-great importance, and #1 to be how we hope it turns out.
The way you spoke of it, you make it seem like you know 100% we’ll get destroyed by the life we find.
Again, the article is using estimations to just give us a general idea. You guys are like ‘MAN SENDING A SHIP TO ANOTHER STAR NEXT YEAR WOULD BE DUMB.” Yeah, obviously.
http://elsofista.blogspot.com/2008/07/cunto-tiempo-tomara-viajar-la-estrella.html El Sofista – Â¿CuÃ¡nto tiempo tomarÃa viajar a la estrella mÃ¡s cercana?

Todos alguna vez nos preguntamos cuÃ¡nto tiempo tomarÃa viajar a las estrellas y si ese viaje serÃa posible en el transcurso de la vida propia. Hay muchas respuestas para esta posibilidad, de las cuales algunas son muy simples y otras pertenecen al reino de la ciencia ficciÃ³n. [...] Fuente: Ian O’Neill para Universe Today.

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