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

by Ian O'Neill on July 8, 2008

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Project Orion, using nuclear explosions as a propellant (NASA)
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?

Hertzsprung-Russell Diagram (NAU)

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.

Red Dwarf star and planet. Artists impression (NASA)

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.

The SMART-1 mission, slow, but economical (ESA)

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.

Ion engine test (NASA)

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 Helios solar mission (Deep Space Network)
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.

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
Project Orion, using nuclear explosions as a propellant (NASA)
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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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!

Jon Hanford July 9, 2008 at 3:21 PM

Along the lines of Marcellus regarding Proxima Cen as a viable destination for humans, the star ( a red dwarf) much less luminous than Sol, is classified as a ‘flare star’ (as are most magnetic dwarf stars) capable of producing flares intense enough to create copious amounts of X-rays (see Wiki listing for Proxima Cen for details). Alpha Cen A and-or B would seem more stable, luminous stars with a better likelihood of habitable planets (or moons orbiting gas giant planets). In any case, a great article on interstellar flight & great food for thought.

Chuck Lam July 10, 2008 at 5:26 AM

Great article! Great posts!

Ken in Shanghai July 10, 2008 at 2:14 AM

Thank You Stanton, I was thinking about your work on the Nerva & Phoebus systems when I read this. We could learn a lot by just looking at all the fantastic space technology that was developed 50 years ago.

MC July 10, 2008 at 3:49 AM

Are there any theories relating to what space would be like between solar systems? would it be more of a vacuum so maybe more acceleration could be reached? or maybe you would get stuck in the spin of the milky way outside of the protection of our solar system and never get anywhere… (random thought i know)

Peter K July 10, 2008 at 7:27 AM

MC, both ideas go kablooie. Space is a near vacuum anywhere you go, even in a nebulae. There are no meteor storms to watch out for in interstellar space. (Nothing to keep them together) It would be like watching out for meteorites while you are driving…not a major concern. The Milky way affects us here the same way it would outside our solar system. The heliopause affects atomic size particles, not spaceships. The Oort cloud is invisible mostly because “cloud” poorly defines it. It’s far more tenuous than whales in the ocean. How many times have you dived in to land on one’s back?
I personally think it’s hilarious anyone is worried about radioactivity in space. It’s got to be a red herring or simply the worries of bureaucrats with little astro-education. There is a radioactive belt or two surrounding the earth even now. Space is filled with radioactivity. Nasty place. As described in one post, bomb detritus would spread to near nothingness in little time. It would probably take off from moon orbit anyway. Too big to launch from earth surface.
And the blast absorbtion plate would have to be enormous? Where does that thinking come from? The blasts are smallish and continuous. It doesn’t have to be a Hiroshima every ten minutes. And whatever distance from the ship that works, doesn’t have to be just 15 metres away.
I think anti-matter will probably be the answer that gets us there. Massive energy from smallest quantity, and lacking in need for extra-dimensional travel which will probably always remain a tantalizing theory at best.

Derek Mathias July 10, 2008 at 5:25 PM

Here’s my suggestion:

Within two or three decades, we should have sufficient molecular manufacturing technology to create extremely efficient, small, light and highly intelligent robots, as well as small nanofactories capable of creating any object from patterns stored in computer memory. Sending them out to the nearest stars would take far less energy than sending humans.

If a robot arrived at a suitable exoplanet, it could use the nanofactory to construct a laser receiving station (or similar device), as well as living accommodations for humans.

The same technology that would allow the construction of the robots and nanofactories should allow us to disassemble human beings and reassemble them. This may allow us to store entire humans as digital information.

We could then beam the information to the receiving station on the exoplanet. The nanofactory would reassemble the human patterns, creating exact duplicates of the original human templates, and those humans would have living accommodations already waiting for them.

Of course that would still take a while: probably hundreds or thousands of years to get the robots to the exoplanets, then at least a few years to establish a connection with Earth (beaming info at lightspeed), and then a few more years to beam the human patterns to the exoplanets.

By that time we’ll likely have populated the entire solar system and probably won’t resemble modern humans in mind or body much at all.

So…forget it. At least for now. Maybe some AI will come up with a way to shorten the trip, so just wait a few decades and find out.

Robert Ryukyu July 11, 2008 at 9:51 PM

Thanks so much for the article and reader comments. Exciting visions. Always dreamt of such possibilities as a small boy.

Unfortunately, nowadays, the negative consequences of global warming accelerate faster than the development of interstellar propulsion engines.

Trying to be realistic, I only hope that there will be human astronauts after 2050 or so to board space ships.

R Eccles July 11, 2008 at 9:57 PM

Maybe we could travel to other planets with our mind rather than our bodies. OOBE’s anyone?

Chuck Lam July 12, 2008 at 7:24 AM

To: Peter K., While space is a near vacuum, I suspect there are chunks of unknown quantity and material within this near vacuum that can easily destroy a space vehicle. A couple of probes NASA has lost contact with over the years comes to mind. Another thought, for mankind to do any serious space traveling, it would be necessary to develop a means to exceed the speed of light several magnitudes. Attempting a trip to the Alpha C system, at just a fraction the speed of light, doesn’t make much sense.

Jon Doh July 14, 2008 at 5:40 PM

Maybe we need to learn to live on this planet before we go to another?
Planet starbucks haha….drill for oil on planet exxon…kinda reminds me of several sci fi films where the lifeforms are called a disease or virus, they jump from planet to planet destroying each in the process and the only solution is to find another host.
Did anyone mention suspension, cryonic or other?
Wake up 20,000 years later orbiting a strange planet …

Chip August 20, 2008 at 1:11 AM

“Imagine travelling 80 to 1,000 years to the nearest star, and then finding out there is absolutely nothing of interest there.”

You miss the point of space travel. The trip between the stars is the interesting part.

I would love nothing more than the chance to travel alone in a spaceship to another star, even knowing I would die of old age before making it to that star, just for the chance to be out there, every day, watching the stars from outside of Earth’s atmosphere, knowing I am that much closer to another star.

If you have ever had the chance to look at stars through an actual telescope, not the internet pictures, taking the time to just look at some random name-unknown group of stars, it is fascinating. I am enthralled by the fact that I am looking at real suns live (minus light year distance of course). There is something about it that overwhelms.

I am not one who would immediately plant a carbon copy of human society on another planet. What difference does it make what planet you watch TV on?

It is the chance to leave this society behind and be out there with no one else except the stars that draws me like nothing else in life. Pick any one star, no matter how far, and head for it. Reaching it doesn’t matter, the chance to be out there does.

asd November 4, 2008 at 11:00 PM

well for the G forge thingy you can be put in a room filled with some sort of material that dampens the effect of the inertial forces… or some sort. easy to be done, and there are some results in achieving this kind of material, for example Asics (shoe manufacturing) uses some kind of rubber on which u can drop an egg from 3-5 meters and it won’t break (the layer was just 1-2″ thick). so it can be done the means of propulsion must be developed more.

Tobias Holbrook of the Dragonfire November 5, 2008 at 3:22 PM

Intersting article. And even more interesting comments.

Aside from the fact that you’ve neglected to mention beamed power, it’s okay. But I’m sure that 80 year figure can be improved. Perhaps by launching the nukes ahead of the starcraft, or maybe by some other means.

“I would love nothing more than the chance to travel alone in a spaceship to another star, ”

Agreed. Although I’d quite like to have someone with me on the Starcraft.

householdutensils November 28, 2008 at 5:41 AM

We could always build a massive coil gun, preferably orbiting one of the outer planets. Build it in an elliptical shape, like a particle accelerator, accelerate a small craft to the maximum % of c we can get from storing power from nuclear generators and solar power in superconducting capacitors and then let it fly, using nuclear pulse propulsion or some other form of propulsion for additional thrust. Realistically, we can get a lot higher speeds and lower mass crafts by using robotics rather than manned voyages.

This method reduces the problem of on-board fuel. It all depends on how much power we can store, and what velocity we can accelerate the projectile to.

roger December 15, 2008 at 2:54 PM

OK. We now can accellerate a stream of particles to 99.99% the speed of light. granted, these particles have very low mass and are easily pushed around CERNs tubing. How much energy would it take to accelerate a larger object to those speeds. Also the G forces from just the curvature of the earth would be enough to destroy any device we send around. But I propose that we create an orbital TRACK, one that works just like a particle accelerator that pushes an object around untill we reach the right velocity then it opens upon on end to let it fly. We could get a robot or transmitter to a distent star pretty fast, however there would be NO way to slow it down. in fact something going the speed of light that had any mass to it at all would literaly pass straight through ANything unscathed. We would need on accelerator to throw and another at the destination, to catch. But heaven forbid we should miss. lol. see ya

Dragonfire: Tobias Holbrook January 3, 2009 at 2:02 PM

I suggested the coil gun over at NewMars. The unfortunate thing about it is how long it takes to get up to speed without killing its occupents and such.

So I suggested launching Ion beams instead. Others suggested Aluminum pellets. Those could work to, if they could perhaps be vaporised to form high speed Ions hitting the craft.

Decelerate at the target system using a combination of MagSail and Orion. Aim for a top speed of say maybe 25% of c, although I’m fine with 5% (extended lifespan, remember), But 20 years to Alpha Centauri would be good. Although I’d trade it in for 50 years to Tau Ceti or Epsilon Eridani (much more promising places).

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