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A Relativistic Probe to Alpha Centauri

Good space science comes from unexpected quarters. When I interviewed the Jet Propulsion Laboratory’s James Lesh about his thinking on communicating with a probe around Alpha Centauri, he pointed out how much can be gained by simply studying the signal sent by a spacecraft. Here in the Solar System, we’ve seen how that signal is affected by passing through a planetary atmosphere as the vehicle moves behind a distant world, an event that tells us much about the atmosphere in question. So in many cases it’s not just the data carried by the communications signal, but how that signal behaves, that tells the tale.

Can we imagine something similar around Alpha Centauri? Lesh envisaged a 20-watt laser communications system sending data from a sophisticated probe. But a new paper takes a different approach, imagining a fast probe moving at relativistic speeds, one that would announce its arrival in the Centauri system and create effects that could be studied from Earth. At 10 ounces, such a probe wouldn’t carry instrumentation (at least, not until our nanotechnology becomes more sophisticated), but it would be the first manmade object ever to reach another star, and it might teach us valuable lessons about the art of starflight.

The authors, Wade Hobbs Jr. (a researcher at the Library of Congress) and Daniel Junker, a spaceflight consultant in Arlington VA, presented this work at the Fourth International Symposium on Beamed Energy Propulsion in Nara, Japan. Much of their effort is devoted to assessing the parameters of the journey in relation to the power of the laser that would drive it. They propose a matrix of laser beams on Earth’s surface, a further reduction in cost over previous beamed energy concepts for space-based lasers. Such a system would allow the probe, the duo calculates, to reach the Centauri stars in between five and ten years.

Confirming the probe’s arrival depends upon detecting the effects of this relativistic craft as it impacts the dust ring surrounding the Centauri system, looking for data anomalies via x-ray instruments like COAST (the Cambridge Optical Aperture Synthesis Telescope) or the Compton x-ray telescope. Other detection methods are also discussed, including tiny but forseeable laser options, or planned collisions between sequentially launched probes timed to coincide with their arrival in Centauri space, the latter perhaps more detectable from distant Earth.

Centauri Dreams‘ take: Lightweight probes bring back memories of Robert Forward’s ‘Starwisp’ mission, an unmanned, microwave-driven mesh a kilometer in diameter that would weigh no more than sixteen grams. Forward hoped to put microchips at each intersection in the mesh and push Starwisp with a 10-billion watt microwave beam, reaching Centauri in 21 years and beaming back images of the encounter. The idea fell apart when Geoffrey Landis demonstrated that the needed microwave power would simply turn the Starwisp mesh into slag, but it seemed a grand notion in its day.

The Junker/Hobbs probe, by sharp contrast, seems a flyable mission, a major question being whether it is worth our while to send a probe whose sole contribution to science would be in our measurements of its effects on the Centauri debris disk. The thinking here, though, is that there is another reason for such a probe.

The Tau Zero’s Foundation’s motto is ad astra incrementis, meaning we go to the stars one step at a time, hoping that each step is bigger than the last. More valuable than the science the probe could show us in the Centauri system is what we would learn from the first attempt to accelerate a craft to relativistic speeds. That this could be accomplished at much lower cost than previously believed puts such a mission into the realm of the forseeable. In other words, get something there, examine what you have learned in the attempt, and then build the next iteration, bigger and better.

Or perhaps better but not bigger. For we are advancing into an era when nanotechnology will make tiny probes that carry significant instrumentation possible. The Junker/Hobbs probe could be seen as a forerunner of equally small (and smaller) vehicles that sacrifice little in terms of the science they can do. It may be possible one day to send the kind of probe nanotech pioneer Robert Freitas talks about, a vehicle the size of a sewing needle capable of reaching its target and constructing a scientific base via assembler technologies on, say, a moon or asteroid in the Centauri system. Small may, in fact, be better when the speeds demanded are a significant fraction of light speed.

The paper is D. Junker and W. D. Hobbs, Jr., “Sending a Probe to Alpha Centauri on a Voyage of Five to Ten Years,” AIP Conference Proceedings Volume 830 (May 2, 2006), pp. 605-611 (abstract available here).

Comments on this entry are closed.

  • andy July 10, 2006, 10:14

    Is there actually an observed debris disk around Alpha Centauri, or is this a “let’s hope there is one, and hope the probe hits it” kind of thing?

  • Administrator July 10, 2006, 14:42

    Good question. As far as I know, the dust or debris disk around Centauri A and B is an extrapolation based upon disks around other stars, but I’ll be seeing Wade Hobbs next week and I’ll ask him. I know of no observational evidence for a Centauri disk at present.

  • Rui Pimentel July 10, 2006, 15:55

    What will be first? Man on Mars or an high-resolution photo (of a planet from Centarui B system) taken by a probe ? I hope to be around to see both.

  • NS July 13, 2006, 0:43

    The proposed Innovative Interstellar Explorer uses almost-current technology to get out 200 astronomical units by 2044 (assuming a 2014 launch). Since I’ll be 88 years old by then (God willing) I wonder if it wouldn’t be better to concentrate on more advanced propulsion and instrumentation but maybe end up getting there sooner.

  • ljk July 13, 2006, 11:43

    At first I was thinking how we would not be able to fit a
    Voyager-style/size data information device on such a
    small star probe, but then it quickly dawned on me that
    I was thinking too old school in this area, to say nothing
    of not big enough.

    The star probe discussed here may not be able to carry
    much in the way of instrumentation, but I could see a
    lot of information about humanity and our world put on
    many of these probes and spread out into the galaxy
    like seeds.

    Forget just a few large probes with a rather limited amount
    of information: We could have thousands of little probes sent
    all over the nearby galactic realm, increasing the chances of
    someone finding them and learning more about us.

    And no, I am not worried about some hostile ETI finding out
    that we exist and where we live via these probes. My
    presumptions for this are as follows:

    * A truly nasty species probably does not have the means or
    the interest in conquering the galaxy and is likely in the process
    of destroying itself.

    * Truly advanced ETI would not want anything from such small
    and comparatively primitive creatures outside of maybe some
    basic information to update their galactic database.

    * With all the resources in the Milky Way galaxy and its 400
    billion star systems, why go after one small system that is
    already occupied?

    * If there are ETI who do want to take over Earth and the
    Sol system, there is blessed little we could do about it at
    this point. And they wouldn’t even need fancy weapon
    systems to do it: Just aim some space rocks at key areas
    of our civilization and wait for the dust to settle.

    * Sharing information might be interpreted as a friendly
    gesture, since the probes would only be carrying these
    data packets.

    * If some catastrophe does befall the human race, these
    probes may contain the only records of our existence,
    preserved for the ages in deep space in multiple places.

    Could we place as much information on such a tiny craft as
    I think we can? I also presume that anyone who could find
    these star probes would also be able to find the data and
    decode it.

    As for the pros of sending interstellar messages via physical
    means as opposed to radio or light waves, see this Web site:

    http://www.winlab.rutgers.edu/~crose/cgi-bin/cosmicB.html

  • Wade Hobbs July 21, 2006, 17:27

    I’d like to comment on this assertion in your article: “The Junker/Hobbs probe, by sharp contrast, seems a flyable mission, a major question being whether it is worth our while to send a probe whose sole contribution to science would be in our measurements of its effects on the Centauri debris disk.”

    I strongly disagree that the sole contribution of the Centauri probe would be in its measurement of the dust debris around the star. A flyby mission to Alpha Centauri would be a tremendous scientific achievement in itself.

    When the Russians sent a dumb probe to the moon, it was good science. It had never been done before, and enormous technical challenges had to be overcome before such a project could be conducted. In itself, reaching the moon was quite a monument in the advance of science. So too here, reaching Alpha Centauri will itself be a significant contribution to science.

  • Administrator July 21, 2006, 17:57

    I agree with this so strongly that I wonder if you saw the next paragraph in the story: “More valuable than the science the probe could show us in the Centauri system is what we would learn from the first attempt to accelerate a craft to relativistic speeds. That this could be accomplished at much lower cost than previously believed puts such a mission into the realm of the forseeable. In other words, get something there, examine what you have learned in the attempt, and then build the next iteration, bigger and better.” I think we’re on the same page.

  • Wade Meyer August 1, 2006, 16:08

    When we lived in Kansas in the early 1960s as small children. We used to live on the North end of Great Bend, Kansas on the North end of Morton St. One night in 1964 or 65, I looked out of the kitchen window and saw a White cube that glowed like a light bulb. It had a red light glowing on the inside of it. There are or were quite a few radio towers there and one huge TV 2 tower farther to the North. The cube shaped thing flew around that radio tower like a moth flies around a light bulb of all things, only slower than a moth and it never hit the tower. I ran to get my dad but he said don’t brother him right now. So I ran back to the kitchen yelling for my two brothers to come here. When I got back to the window it was still flying near the tower. Just before my brothers got to the window it came across the field then towards me and it started hovering around 75 feet above the ground maybe 200 yards away. That is when my two brothers made it to the window and started saying what is that, what is that? Also, I might add that the red light was fading on an off like the tower light was. I believe perhaps it was trying to communicate with it. Then it spun so fast that it turned into a ball and in a white streak it went almost stright up but at a little angle towards the north west and was gone. We saw what we saw so because of that I know we are not alone. Sure makes you wonder why that thing was flying around that radio tower? I can also tell you that well we did anyway, still had black and white TV as it was still the early years for TV. The large TV 2 tower first broadcast was Nov. 28, 1954. Just for the fact that signals can travel at the speed of light and maybe it too could travel at or near the speed of light too. Then maybe it could have came from a near by star system that would be within 5 or 6 light years from us? But if it was a craft or a type of probe that was just passing by then who knows where it could have came from? Another possibility is that, what if it was some type of life form itself? And it roams the cosmos like the buffalo roomed our prairies long ago? I have done my homework on about everything it could have been and my conclusion is that it was extraterrestrial, why? Because the thing I saw showed intelligence and there is no doubt about it. I know it was looking at things by the way it was behaving. At the North end of the street was a wheat field then to the North edge of that about 1 mile is the Dry Walnut Creek and on the North edge of that was the radio tower. The radio tower was around one and a quarter mile from the kitchen window where I first saw it. The houses including ours 15 houses or so lined up along the wheat field east and west. The houses that are there now on the East side of the field were not there then. Here is the part that I did not include, when I got back to the window it just moved off the tower and was spinning (like a white glowing box spinning) it was spinning towards the South southeast towards town. Then it turned toward the West very quickly and staying over the field run along the row of houses staying out over the field around 200 yards or so and up in the air like I said around 75 feet. When it saw me looking out the window like I said, it stopped and that is when my 2 brothers made it to the window and started saying what is that, what is that? To me that shows a form of intelligence don’t you think? It was about the size of a small box truck like 20feetx20feet Sq. This is a true story and I wanted to share it. Sincerely, Wade Meyer

  • David Wade September 10, 2006, 20:58

    I just got a copy of Beamed Energy Propulsion. I have a question Do we have a laser powerful enough to do this? As I read the Chart in the paper a one megawatt laser could accelerate a 10 gram probe to relativistic speeds.

    If this is the case shouldnt this be a serious goal: to cost this out and do it in a decade? Also if we have the equipment why not shoot them to all the nearbt stars?

    We need something more inspiring than the misnamed Orion-Lets really send something somewhere!

  • Abdul Ahad October 2, 2006, 14:59

    Wouldn’t there be a cost-conflict between NASA’s Terrestrial Planet Finder mission funding and the relativistic probe concept? I’m thinking if the latter is going to be a faster, cheaper, better alternative to examining the proximity of nearby stars to find Earth-like planets, then it should be given more priority and developed sooner…

  • Abdul Ahad October 3, 2006, 17:12

    I’m behind with the times… just found this on the web:

    http://www.spaceref.com/news/viewnews.html?id=1092

    Looks like they’ve cancelled TPF! Oh, what a big mistake that seems to me :(

    I do have one question on the relativistic probe idea that still puzzles me. How do you expect a micro-sized 10-gramme probe to relay anything ( and I mean absolutely *anything* ) by way of telemetry data back across 4 light years? I just can’t get my head around extrapolating to the lowest level of nanotechnology miniaturization, that a probe so small would be visible if it emitted back at any electromagnetic frequency on passing the vicinity of Alpha Centauri.

    Can someone please shed some light on this for my benefit. Many thanks in advance…

  • Administrator October 4, 2006, 8:32

    Re the question above: “How do you expect a micro-sized 10-gramme probe to relay anything ( and I mean absolutely *anything* ) by way of telemetry data back across 4 light years?”

    The probe discussed in this mission concept is actually a ‘dumb probe’ — i.e., it would carry no instrumentation. Its arrival in the Alpha Centauri system would be detectable only through our observations of its effects on the assumed debris disk around the Centauri stars. As I understand it, Hobbs and Junker argue that these effects would be pronounced enough to measure given that the probe would enter the system at relativistic speeds.

  • Abdul Ahad October 8, 2006, 15:56

    Thanks. It seems virtually a forgone conclusion that a probe of this type will never be able to send back any data or images of a planetary body which may be in orbit in the Centauri system.

    If such a probe were designed to be large enough to have the capability to do this, by carrying a camera, a telemetry antenna and other science instruments, then it would be far too heavy to accelerate that fast in the first place and it would take of the order of centuries as a minimum to get there.

    This means our only hope of ever detecting an Earth-like planet around one of the nearby stars is by using interferometry-based telescopes in orbit around the Earth. TPF was going to be such a superbly accommodating mission, and I fail to understand why they would want to cancel something as smart as that, whatever the cost.

  • Administrator October 8, 2006, 17:57

    Fortunately, good things may rise from the ashes of the original TPF concept. See this story, for example:

    https://centauri-dreams.org/?p=557

  • Wade Hobbs, Jr. October 9, 2006, 15:57

    First, let me apologize if our relativistic probe idea had anything to do with someone else having their funding for space research cut. I think it’s a tragedy anytime funding for space research is reduced.

  • Wade Hobbs, Jr. October 9, 2006, 16:07

    Mr. Wade,

    I’m sure we could develop a computer simulation of the relativistic probe’s voyage – would you be in a position to fund such a project, presuming it would be completed within a matter of months?

  • David Wade October 21, 2006, 23:04

    I really wish I could
    How Much would it cost. I echo all the comments above Its depresssing that these truly vital projects go begging.
    I keep Hoping we could have a visionary adminstration that would get us out of our stone age pretroleum economy and reruns of 50 year old space technology

    Maybe we could sell Europe or Russia on the idea?

  • Wade Hobbs, Jr. October 31, 2006, 18:07

    On the Existence of a Dust Cloud Around Alpha Centauri

    The inference of a dust cloud around Alpha Centauri is based on two theories. The first theory is the Big Bang Theory (Gamow et. al.); the second theory is the Theory of Gravitation (Newton’s theory as modified by Einstein). What follows is a short explanation of why that cloud probably exists.

    George Gamow, then a professor at George Washington University, first presented the theory that came to be known as the Big Bang Theory in a 1948 paper co-authored with Alpher and Herman. (Others who contributed to the idea include Friedmann, Penzias and Wilson, LeMaitre, Guth, Smoot and the COBE team, Hawking and Penrose, Dicke and Peebles.) Essentially, the theory is that the universe began in a singularity of enormous intensity and heat. Eventually, after billions of years, the stars and galaxies formed.

    They formed because of Gravitation (Newton’s theory as modified by Einstein). According to the Theory of Gravitation, a force – Gravity – exists between any two masses. This force tends to compel each mass towards the other. Applied here, minute dust particles emanating from the Big Bang gravitate towards massive stars. The star Formalhaut, as shown in the picture from NASA and ESA, draws innumerable particles towards it.

    The overwhelming implication from the Big Bang and Gravity theories is that each star has a dust ring or cloud around it. That ring or cloud may vary in density: It may be far less (or more) dense than the cloud that surrounds Formalhaut. That we may not have formal recordation of the dust cloud or ring around the Alpha Centauri group results either from our primitive instrumentation or our failure to make observations of that star group. The reader should note, finally, that for purposes of this short explanation, the possibility of an anisotropic universe has been ignored.

  • Wade Hobbs, Jr. October 31, 2006, 18:16

    The computer simulation project could be done for US$200,000. That would allow for the purchase of computer equipment and software, rental of office space, funding for graduate students, and expenses.

  • andy November 1, 2006, 18:09

    “This force tends to compel each mass towards the other. Applied here, minute dust particles emanating from the Big Bang gravitate towards massive stars. The star Formalhaut, as shown in the picture from NASA and ESA, draws innumerable particles towards it.”

    Stars form from clouds of gas and dust, some of which goes to form the star, other parts are not accreted by the star and form the disc. Fomalhaut is a young star and so has a massive disc around it – this is not due to it drawing in particles. As the star ages, processes such as light pressure, etc. will tend to deplete the dust, either pushing it out of the system or causing it to fall into the star.

    The problem with Alpha Centauri is that the binary system would tend to disrupt debris in orbit around the stars – also, the Alpha Centauri system is much older than Fomalhaut (5-6 billion years, as opposed to a few hundred million for Fomalhaut), which gives the system a lot of time for the dust levels to fall off. In addition to the two main stars, there is also Proxima Centauri in a distant orbit, which would provide further disruption to the system, making it even less likely to find significant orbiting dust.

  • andy November 1, 2006, 18:12

    Further point: for a star as old as Alpha Centauri, you’d need some kind of reservoir of orbiting bodies (e.g. an asteroid/Kuiper belt) to keep on generating dust in the system to replenish the dust being depleted. The multiple nature of the system isn’t going to help this – while asteroid belts and hence dust discs around one or other of the components should be possible, a circumbinary belt is going to have to be a long way out, and Proxima Centauri should have cleared out such belts a long time ago.

  • Wade Hobbs, Jr. November 8, 2006, 16:56

    Got any mathematics to support your assertions?

  • DennisP November 30, 2007, 18:13

    Let me get this, a tiny uninstrumented probe with no propulsion system, pushed all the way to Centauri by lasers pointed at it from earth. Right.

  • Adam December 1, 2007, 17:36

    Hi Paul

    A bunch of fast, dumb nanoprobes sent towards Alpha Centauri would produce gamma-ray flashes if they collide with interstellar debris – which would tell us a lot about the ISM. That would be very handy information for sending actual smart probes and manned vehicles. And it would be practice for learning how to launch relativistic pellets in a mass-beam launcher system.