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The Stars in their Courses

Here’s hoping Centauri Dreams readers in the States enjoyed a restful Thanksgiving holiday, though with travel problems being what they are, I often find holidays can turn into high-stress drama unless spent at home. Fortunately, I was able to do that and, in addition to a wonderful meal with my daughter’s family, spent the rest of the time on long-neglected odds and ends, like switching to a new Linux distribution (Mint 16 RC) and fine-tuning it as the platform from within which I run this site and do other work (I’ve run various Linux flavors for years and always enjoy trying out the latest release of a new version).

Leafing through incoming tweets over the weekend, I ran across a link to Stephen Cass’ article in IEEE Spectrum on Plotting the Destinations of 4 Interstellar Probes. We always want to know where things are going, and I can remember digging up this information with a sense of awe when working on my Centauri Dreams book back around 2002-2003. After all, the Voyagers and the Pioneers we’ve sent on their journeys aren’t going to be coming back, but represent the first spacecraft we’ve sent on interstellar trajectories.

And if the Pioneers have fallen silent, we do have the two Voyagers still sending back data, as they will for another decade or so, giving us a first look at the nearby interstellar medium. For true star traveling, of course, even these doughty probes will fall silent at the very beginning of their journeys. Voyager 1 is headed on a course that takes it in the rough direction of the star AC+79 3888 (Gliese 445), a red dwarf 17.6 light years away in the constellation Camelopardalis. Here’s the star chart the IEEE Spectrum ran to show Voyager 1’s path — the article offers charts for the other interstellar destinations as well, but I’ll send you directly to it for those.


Notice anything interesting about Voyager 1? The IEEE Spectrum article says the spacecraft will pass within 1.6 light years of the star in 40,000 years, and indeed, this is a figure you can find mentioned in two authoritative papers: Rudd et al., “The Voyager Interstellar Mission” (Acta Astronautica 40, pp. 383-396) and Cesarone et al. ,”Prospects for the Voyager Extra-Planetary and Interstellar Mission” (JBIS 36, pp. 99-116). NASA used the 40,000 year figure as recently as September, when Voyager project manager Suzanne Dodd (JPL) spoke of the star to Space.com: “Voyager’s on its way to a close approach with it in about 40,000 years.” I used the figure as well in my Centauri Dreams book.

But wait: I’ve often cited how long it would take Voyager 1 to get to Alpha Centauri if it happened to be aimed in that direction. The answer, well over 70,000 years, is obviously much longer than the 40,000 years NASA is citing to get to the neighborhood of Gliese 445. How can this be? After all, Voyager 1 is moving at 17 kilometers per second, and should take 17,600 years to travel one light year. In 40,000 years, it should be a little over 2 light years from Earth.

I’m drawing these numbers from Voyager 1 and Gliese 445, a fascinating piece that ran in the Math Encounters Blog in September of this year. The author, listed as ‘an engineer trying to figure out how the world works,’ became interested in Voyager 1’s journey and decided to work out the math. It turns out NASA is right because the star Gliese 445 is itself moving toward the Solar System at a considerable clip, about 119 kilometers per second. Gliese 445 should be making its closest approach to the Solar System approximately 46,000 years from now, closing to within 3.485 light years, a good deal closer than the Alpha Centauri stars are today.

Never forget, in other words, that we’re dealing with a galaxy in constant motion! Voyager 1’s sister craft makes the same point. It’s headed toward the red dwarf Ross 248, 10 light years away but also moving briskly in our direction. In fact, within 36,000 years, the star should have approached within 3.024 light years, much closer indeed than Proxima Centauri. Voyager 2, headed outbound at roughly 15 kilometers per second, thus closes on Ross 248 in about the same time as Voyager 1 nears Gliese 445, 40,000 years. Voyager 2 then presses on in the direction of Sirius, but 256,000 years will have gone by before it makes its closest approach.

As for the Pioneers, Pioneer 10 is moving in the direction of Aldebaran, some 68 light years out, and will make its closest approach in two million years, while Pioneer 11 heads toward Lambda Aquilae, an infant star (160 million years old) some 125 light years away, approaching it four million years from now. We could throw New Horizons into the mix, but remember that after the Pluto/Charon encounter, mission controllers hope to re-direct the craft toward one or more Kuiper Belt objects, so we don’t know exactly where its final course will take it. Doubtless I’ll be able to update this article with a final New Horizons trajectory a few years from now. Until then, be sure to check out the IEEE star charts for a graphic look at these distant destinations.


Comments on this entry are closed.

  • Alex Tolley December 2, 2013, 19:34

    It is interesting that we normally just assume that flight time is a function of the ship’s velocity and do not take into account the relative motion of the target star. As another thread indicated, just waiting (a long time) will get other stars within relatively close range of the sun for a shorter starflight.
    Has anyone done calculations for flight times at various STL velocities for the nearer stars, especially those moving towards us at a high velocity?

    I’m reminded of the metaphor of the Polynesian migration in the context of STL worldships. It seems to me that the movement of the target stars is in some ways analogous to the differing ocean currents. Targeting a star that is rapidly moving towards you is like catching the ocean current that will carry your ship/raft faster to your target island.

  • Eniac December 2, 2013, 23:43

    I wonder if the New Horizon team could be pursuaded to finagle the trajectory such that after its last useful flyby it will be headed directly towards a (by then) nearby star in 50,000 years or so. Not a light year or two, but within an AU or less. Is that possible?

  • Paul Gilster December 3, 2013, 10:22

    Interesting notion! Let me put that question to Alan Stern.

  • Paul Gilster December 3, 2013, 17:17

    Alan Stern’s response puts this one out of the question, I’m afraid:

    “Not enough fuel for that– by orders of magnitude.”

  • Christopher Phoenix December 3, 2013, 19:07

    Yeah, people often don’t remember that the so-called “fixed stars” are moving relative to our solar system… and at a fast clip, compared to our space probes. The old neighborhood will have rearranged itself in a few tens of thousands of years. Stellar navigators had better update their star maps before then, and if you are traveling at the crawl of the Pioneer and Voyager probes, the motion of the stars actually shortens the travel time ’til projected stellar encounters by quite a bit- the star is literally racing at many km/sec to meet our probe.

    I was first introduced to this concept in the chapter of the redoubtable The Starflight Handbook titled “The Not-So-Fixed Stars”!!

    Mr. Chung discusses how to adjust for the motion of stars and envision the galactic maps of other eras at his Project Rho pages, noting that the stars of a long vanished galactic empire will be scattered across the galaxy over millions of years, complicating efforts to find “forerunner” planets and plunder ancient artifacts.

    Over “deep time”, the effect is apparently something like an explosion in a glitter factory…

  • ljk December 4, 2013, 12:57
  • steven rappolee December 5, 2013, 16:23

    perhaps we could ask Allen Stern where the solid Star motor wil be centuries from now?

  • ljk December 6, 2013, 11:36

    steven rappolee said on December 5, 2013 at 16:23:

    “perhaps we could ask Allen Stern where the solid Star motor wil be centuries from now?”

    See here:


    and here:


    Steven, as you have importantly pointed out in the past on Centauri Dreams, these final booster stages tend to be forgotten in favor of the space probes, although most of the deep space missions have them traveling into the wider Milky Way galaxy as well.

    These rocket stages most certainly carry no useful or easily decipherable information about humanity and our world for any finders. A detailed analysis of their trajectories are in order, as they are larger than the probes they sent into deep space. Would they also have any remaining fuel on board?

    Just as we would be utterly grateful to find information on an ancient alien probe that came drifting through our Sol system and we were able to capture it, the same situation should apply to those rocket stages.

  • Eniac December 7, 2013, 0:55

    “Not enough fuel for that– by orders of magnitude.”

    I had thought that it should not require any extra fuel, just a very accurate aim at the last target such that its gravity would provide the small delta-V needed to aim directly at a star instead of just past it. Looks like I was wrong….

  • ljk June 13, 2014, 10:18


    Heather Smith

    June 13, 2014

    On June 13, 1983, Pioneer 10 left our solar system and began its journey into interstellar space after 30 years of flight. It succeeded as becoming the first spacecraft to survey Jupiter, Pioneer 10 became the first spacecraft to achieve escape velocity from the Solar System.

    Full article here:


    By leaving the Sol system in this case they meant Pioneer 10 passed the orbit of Neptune, which at the time was closer than Pluto and before the anti-planet decision of the IAU in 2006. Pioneer 10 was the first to achieve escape velocity to wander the Milky Way galaxy, even if Voyager 1 over took it later.