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The Incentive Trap: When to Launch a Starship

Richard Trevithick’s name may not be widely known today, but he was an important figure in the history of transportation. A mining engineer from Cornwall, Trevithick (1771-1833) built the first high pressure steam engine, and was able to put it to work on a railway known as the Penydarren because it moved along the tramway of the Penydarren Ironworks, in Merthyr Tydfil, Wales, running 14 kilometers until reaching the canal wharf at Abercynon. The inaugural trip marked the first railway journey hauled by a locomotive, and it proceeded at a blistering 4 kilometers per hour. The year was 1804.


Image: The replica Trevithick locomotive and attendant bar iron bogies at the Welsh Industrial & Maritime Museum in 1983. Credit: National Museum of Wales.

Consider, as René Heller (Max Planck Institute for Solar System Research) does in a new paper, how Trevithick’s accomplishment serves as a kind of bookend for 211 years of historical data on the growth in speed in human-made vehicles from the Penydarren to Voyager 1. The world’s first production car was the Benz Velocipede (1894), whose top speed of 19 kilometers per hour far surpassed the Trevithick railway, but was put to shame by a Stanley Steamer racing car that reached a then incredible 204 kilometers per hour in 1903.

I mused about the nature of speed in a 2013 post called The Velocity of Thought, and Heller’s new paper has me doing it again, though in entirely different directions. A few more waypoints and I’ll explain what I mean. When the Wright Brothers took to the air in 1903, their Wright Flyer first flew at about 11 kilometers per hour, and we began to see how quickly aviation records could be superseded. A Sopwith Camel of World War I vintage could reach 181 kilometers per hour. By 1944, German test pilot Heini Dittmar was able to take a ME-163 rocket plane to 1130 km/h, a number that wouldn’t be reached again for almost ten years.


Image: Typical appearance of a Me-163 Komet after landing, waiting for the airfield’s Scheuch-Schlepper tractor and lifting trailer to tow it back for reattachment of its “dolly” maingear. Credit: Wikimedia Commons.

When we get into space, we can note Voyager 1’s 17 kilometers per second as it leaves the Solar System. The Helios solar probes launched in 1974 and 1976 set the current record at 70.22 km/s. And looking forward, the Solar Probe Plus mission is to perform a close flyby of the Sun, reaching a top heliocentric speed of 195 kilometers per second, which works out to 6.5 × 10 −4 c. If Breakthrough Starshot realizes its goal, an interstellar lightsail may one day head for Proxima Centauri at fully 20 percent of the speed of light.

Part of what occupies René Heller in his new paper is the exponential growth law we can construct between the 1804 Penydarren locomotive and the 17 kilometers per second of Voyager 1 in 2015. From wind- to steam-driven ships and into the realm of automobiles, then aircraft and, finally, rockets, we can extrapolate speeds that may take us into interstellar probe territory some time in this century or the next. Given that an interstellar mission may take longer than the average human lifetime, we thus need to ask a key question. When do we launch?

Screenshot from 2017-05-08 08-29-36

Image: Figure 1 from the Heller paper, showing historical speed records. From the paper: “All these values are symbolized with black-rimmed circles in Figure 1, with additional top speed measurements of trains, cars, planes, and rockets shown with different symbols (see legend). The dashed black line illustrates an exponential growth law connecting the 1 m s −1 speed of the “Penydarren” steam locomotive in 1804 with the 5.7 × 10 −5 c Solar System escape speed of Voyager 1 in 2015. Credit: René Heller.

For the problem, a classic in science fiction, is to work out the most efficient timing. If we launch a starship at a particular level in our technology, will it not be caught by a faster ship launched at a much later date? Given sufficient technological improvements, a later launch (incorporating the necessary ‘wait time’) could result in an earlier arrival.

Those who have read A. E. van Vogt’s story “Far Centaurus” will recall precisely that scenario, when an Alpha Centauri mission reaches destination only to find it populated by humans who arrived by faster means. It’s a theme that shows up in Heinlein’s Time for the Stars and many other places.

Heller calls this problem ‘the incentive trap.’ And he refers back to Andrew Kennedy’s 2006 paper, which looked at the problem with the assumption of an exponential growth of the interstellar travel speed. Kennedy was assuming a 1.4 % average growth rate, under which a minimum time to reach Barnard’s Star could be calculated: some 712 years from 2006.

What that means is this: There is a total time that includes the waiting time (waiting for improved technology) and the actual travel time, and we can calculate a minimum value for this total time by using our assumption about the exponential growth of the interstellar travel speed. Calculating the minimum value shows us when we can launch without fear of being overtaken by a faster future probe, in hopes of avoiding that “Far Centaurus” outcome.

But was Kennedy right? Heller’s own take on the incentive trap takes into account the possibility that Breakthrough Starshot may achieve a velocity of 20 percent of lightspeed within several decades, an outcome that would, in Heller’s words, “…fundamentally change both the assumptions and the implications of the incentive trap because the speed doubling and the compounded annual speed growth laws would collapse as v approaches c.” And whatever happens with Breakthrough Starshot, the speed growth of human-made vehicles turns out to be much faster than previously believed.

Intriguing results flow out of Heller’s re-examination of what Kennedy had called the ‘wait equation,’ and tomorrow I want to go deeper into the paper to explain how the scientist uses exponential growth law models to show us a velocity which, once we have attained it, will no longer be subject to the incentive trap of faster, later technologies. The results are surprising, particularly if Breakthrough Starshot achieves its goal in the planned 30 years. The implications for our reaching well beyond Alpha Centauri, as we’ll see, are striking.

The Heller paper is “Relativistic Generalization of the Incentive Trap of Interstellar Travel with Application to Breakthrough Starshot” (preprint). The Kennedy paper is “Interstellar Travel: The Wait Calculation and the Incentive Trap of Progress,” Journal of the British Interplanetary Society Vol. 59, No. 7 (July, 2006), pp. 239-247.


Comments on this entry are closed.

  • Phil Freedman May 8, 2017, 13:12

    Without having time to follow up on the votes papers, I have to wonder if relativistic effects are considered in these exponential extrapolations. To the extent that a constant exponent might apply at all, we should remember that our baseline tech growth model is derived at low relative velocities where linear Newtonian equations remain more or less applicable.

  • Ron S May 8, 2017, 13:22

    Of course another reading of the chart is that Starshot is unreasonably optimistic and that speed will not be achieved until a century later than projected.

    • Joe May 8, 2017, 19:29

      This ties in with my beliefs that at some point we are going to encounter the law of diminishing returns in our efforts to reach the stars.

  • Douglas Dwyer May 8, 2017, 13:26

    Friction is the other ignored parameter 200 years ago more important than motive force.
    Important in the atmosphere and in inter stellar space approaching the speed of light

  • Marshall Eubanks May 8, 2017, 13:48

    “By 1944, German test pilot Heini Dittmar was able to take a ME-163 rocket plane to 1130 km/h, a number that wouldn’t be reached again for almost ten years. ”

    The X1 achieved 1,600 km/h in 1948.

    • Alexander Tolley May 8, 2017, 16:38

      Good catch. He should consider this part of peer review.

      According to Wikipedia, the Me163 record was beaten unofficially in 1947 by Yeager in the Bell X-1. The author is correct if official records are used when an F-86 broke that record in 1953.

      Flight airspeed record

      • Paul Gilster May 9, 2017, 10:52

        Alex, it wasn’t Heller who made the mistake about the ten years — that was my own insertion. He simply noted the speeds attained by the Me-163 without reference to how long it took to pass them.

        • Alexander Tolley May 9, 2017, 12:26

          That’s what comes from reading both and making assumptions. I see that Heller just mentioned Me rocket planes reaching around 1000 km/h.

          If we consider Penna’s point about manned vs unmanned, why not include the V2 rocket which reached 1000’s km/h during the same WWII period? Looking backward, cannon and firearms projectile speeds were already much higher than transport speeds, if only for relatively short distances, although WWI guns could deliver shells for many miles, certainly far further than the Wright Brother’s flyer.

          I also think that including the speculative Breakthrough Starshot probe is a stretch. It is like including rocket flight based on Tsiolkovsky’s designs.

          Transport speeds are usually considered as logistic curves that have overlapped. It might best be assumed that spaceflight using chemical rockets has reached the upper end of its logistic curve and we are waiting to see if new propulsion developments can extend the upper velocity bound. We most certainly shouldn’t really aggregate these curves and assume some sort of Moore’s Law for velocity.

          Closer reading of Heller’s paper indicates that he uses the term “man-made vehicles” as a catchall for his ideas. He does seem to premise his paper on unmanned probes to the stars, rather than manned ones. While acknowledging the uncertainty of his parameters, it does seem to me that he has cherry-picked his examples and timeline in order to make his case, even while noting that BS is orders of magnitude outside the predicted speeds for its projected date.

      • jJonathan Ratzlaff May 10, 2017, 22:28

        Chuck Yeager broke the sound barrier in October 14, 1947. I am not sure what the fixation on speed records is, considering that the earliest records in this article don’t have the same conditions

        • Alexander Tolley May 11, 2017, 10:41

          Records are just proof of achieving a standard. For aircraft, the record has to be achieved under certain rules, e.g. level flight and not a gravity assisted dive. The Me 163 had a very short flight duration, mostly in non-level flight. Even Spitfires pushed close to the sound barrier in steep dives.

          At best, I would use the author’s chart as an imperfect guide, something to hang his calculations on. Its deficiencies have been pointed out by many commenters on this post.

  • Ron S May 8, 2017, 14:29

    Well, I have other things that need doing, but even so I went and read through the paper. Although I did not review the mathematics in any detail it seems fine. Putting that aside a couple of issues not covered in the paper occurred to me, things that I believe are important in assessing the waiting time impact.

    First, if we’re sending robots (automated probes) the waiting time is fine as is. If we’re sending people it is not. The waiting time is described from the perspective of those at home, not those on the trip. If I’m to do the trip it matters a great deal whether the trip takes 30 years or 10 years (due to relativistic velocities). The cost of waiting would be measured very differently by travelers and those staying at home.

    The second item is cost. In computing and other fast moving fields is that while some metric (e.g. FLOPs) increases rapidly the cost for a constant FLOPs declines. That can be quite important. Granted, energy tends not to scale with time in the same manner (my daily energy costs are not declining). However the technology cost required for the project will most likely decline over time.

  • Alexander Tolley May 8, 2017, 14:57

    The author’s chart conveniently leaves out:

    1. Horses can gallop at 45 mph for short distances, chariots, and carriages up to 20 mph.
    2. Sailing ships (up to 25 mph for clippers, up to 15 mph for mediaeval sailing ships)

    Both these exceeded the early trains so that the pre-1800 curve is much flatter than shown. The author’s chart suggests people were almost frozen in the ancient world ;)

    For things that can be transmitted and reproduced by printing, lightspeed was already available by no later than the mid 19th century, and arguably signaling was far earlier.

    The author takes a naive approach to relativistic travel. A slow world ship (0.05c) would have to be far more massive than a near c ship where the occupants experienced time dilation and therefore might have a much smaller ship. This would impact the energies needed to accelerate the ship and would be worth waiting for if that development came later than slower ships.

    The other issue is the payload. Suppose the original ship was just a receiver. Once in place, the volume of travelers, all traveling at c could be vast, making it worthwhile to use this system rather than a smaller population on a sub-light ship, or even a slow world ship with a large [potential] population.

    Finally, should we find means to travel faster than c, then the assumptions break down.

    • Joe May 8, 2017, 19:46

      “the volume of travelers, all traveling at c could be vast.” I recall the calculations Lawrence Krauss did in “The Physics of Star Trek.” The storage capacity needed to make teleportation work would require a stack of hard drives reaching from Earth the to moon. This was based on 1990s technology. IMO the odds are better of building a warp drive than getting teleportation to work.

      • Alexander Tolley May 8, 2017, 21:28

        I recall that calculation too. I just wasn’t thinking of ST beaming. For humans, it might be more like mind beaming as in Richard Morgan’s “Altered Carbon”. But I see intelligent robots as the star farers, so mind transmission is almost a done deal for such machines, and with factories stamping out bodies suitable for the environment at the other end, robots could beam themselves around the galaxy, and their civilization could probably out-reproduce any human civ, ensuring their kind dominated.

    • Rogério Penna May 8, 2017, 21:29

      More than that, the author conveniently mixes manned transportation with unmanned “things”.

      Why do we consider a waffer ship but not a 5000 BC arrow? Why not a 15 century bullet? A chinese firework from 1300?

  • Joe May 8, 2017, 15:20

    An interesting article, Paul. It seems to me though that the incentive trap involves more than just speed and time. It also involves breaking. Just getting to a star faster isn’t all that valuable if you can’t slow down to take a look once you arrive.

    I was very impressed by Rene Heller’s presentation at the Breakthrough Discuss Conference. He made an excellent point that a slower journey to Proxima B would allow a probe to spend more time imaging the planet. So the extra time needed to insure a more productive mission needs to be factored in to the incentive trap.

    Another possibility is that in the 20 years it takes to get to the Proxima system at 20% of the speed of light, we might be able to build space telescopes capable of taking better images of Proxima B than the ultralight spacecraft envisioned by the Breakthrough Initiative.

    So this possibility would also have to be factored into the incentive trap. Therefore I don’t think the incentive trap is going to disappear just because spacecraft speed continues to improve. Instead the estimates and calculations required in planning interstellar missions are going to grow more complex.

  • Jesús May 8, 2017, 16:14

    “Walking was not fast enough, so we ran. Running was not fast enough, so we galloped. Galloping was not fast enough, so we sailed. Sailing was not fast enough, so we rolled merrily along on long metal tracks. Long metal tracks were not fast enough, so we drove. Driving was not fast enough, so we flew. Flying isn’t fast enough, not fast enough for us. We want to get there faster. Get where? Wherever we are not. But a human soul can only go as fast as a man can walk, they used to say. In that case, where are all the souls? Left behind. They wander here and there, slowly, dim lights flickering in the marshes at night, looking for us. But they’re not nearly fast enough, not for us, we’re way ahead of them, they’ll never catch up. That’s why we can go so fast: our souls don’t weigh us down.”
    -Margaret Atwood, “Faster” (from ‘The Tent’)

    • ajay May 9, 2017, 10:11

      The idea of the limited speed of the human soul is not original to Atwood; William Gibson came up with it in “Pattern Recognition” (2003), as a metaphor for the effect of jetlag, and well before him Terry Pratchett invented it in “Strata” as an unexplained side-effect (“soul-lag”) of FTL travel.

  • DJ Kaplan May 8, 2017, 16:35

    I think it’s deceptively easier and simpler to map velocity rather than technology. The technology gap that bridged steam locomotives and jet/rocket-powered aircraft is likely of a very different nature than that gap that reaches to near-light speed.

    • J. Jason Wentworth May 9, 2017, 14:40

      I agree–as nuclear physicist Stanton Friedman points out (in just one of his examples regarding technological advances versus what they make possible, over what was possible before they occurred): “Lasers aren’t just better light bulbs.”

      Like light bulbs, lasers put out light, but the type of light that they emit (coherent, of course)–and its far greater intensity and control-ability–enables lasers to do many more things than can light bulbs. Just plotting increases in velocity itself over time doesn’t even *begin* to cover the many other capabilities that the different *methods* of achieving those higher velocities make possible. Now:

      This doesn’t make the author’s work useless by a long shot, but it does omit important implications of the numerous technologies involved. As Arthur C. Clarke pointed out in “The Promise of Space,” technological advances do not merely add together; they multiply our capabilities.

  • djlactin May 8, 2017, 18:25

    All of the transports considered in this article (and I presume also in the paper) have on-board propulsion. The StarChips will not. I think this difference invalidates use of the curve presented here. Apples ain’t oranges.

  • Carl May 8, 2017, 19:23

    I would be interested in a parallel analysis of sensing capabilities improvement over time. In deciding a destination for a spaceship, choosing appropriate targets would be better informed with better telescopes (at a variety of wavelengths).

    If sensory technology advances faster than ship speed there’s little problem. But if it cannot, there is some further factor of deciding whether to send a ship or wait longer to knowing choose a better target, informed by better survey knowledge. If the stars within 40 light-years are all unsuitable for colonization (or not worth even exploring with humans) than that indicates only relativistic ship technology is worth using.

  • MICHEL LAMONTAGNE May 8, 2017, 20:50

    For a full scale generation worldship, I think this is a false problem since the trip is as important, or even more important, than the destination. And I don’t see why the worldship inhabitants would not be aware of the developments back home, and why there would not be fast ships going between the worldship and the home planet.

    • xcalibur May 9, 2017, 11:37

      You raise a good point. Even if a worldship traveled at under 1% of c, their observations/communications would still be 100% of c. There may be years of delay as they crossed the parsecs, but they would still be generally aware of developments back home and at their destination. There’s no reason to believe a worldship would be completely cut off from the rest of the human race until it arrived. It’s also likely that a far faster ship would rendezvous with the slower worldship along the way, assuming it could quickly change its velocity.

  • Rogério Penna May 8, 2017, 21:24

    Breakthrough Starshot should not be counted together with those means of transportation, because Breakthrough Starshot is NOT a human transport, as with all other human transports shown in the graph.

    Actually I guess some of the later points on the graph probably also belong to unmanned rockets and probes and thus should ALSO not be counted.

    If you count unmanned rockets and probes, why not count anything launched by human hands? Like arrows, bolts, etc?

    The moment we consider ONLY manned ships, Breakthrough Starshot makes no difference in the graph because the same principles of laser propulsion would still take many decades after Breakthrough Starshot to be used for humans:

    1 – Breakthrough Starshot must accelerate the waffer ship to a fraction of the speed of light in a few seconds, tremendous acceleration. To continuously accelerate a manned ship at comfortable 1G for a few months until relativistic speeds would require huge laser stations spread around the solar system.

    2 – the wafer ship will just go through the destination star and never stop. A human ship would need to stop at a destination. How to do that without FIRST building a lot of facilities at the destination?

    3 – we still do not have the tech to launch a ship weighing a few grams. We will need many decades and breakthroughs to get the tech to launch a ship weighing several hundred tons, with a lot of cargo in the form of food for humans in the several years journey.

    • Michael May 10, 2017, 9:02

      ‘Breakthrough Starshot should not be counted together with those means of transportation, because Breakthrough Starshot is NOT a human transport, as with all other human transports shown in the graph.’

      There is no reason why Starshot can’t be used for human transport.

      ‘1 – Breakthrough Starshot must accelerate the waffer ship to a fraction of the speed of light in a few seconds, tremendous acceleration…’

      It is around 10 minutes.

      ‘To continuously accelerate a manned ship at comfortable 1G for a few months until relativistic speeds would require huge laser stations spread around the solar system.’

      We could moderate the gravity load by say higher g when sleeping and less when working.

  • Robin Datta May 9, 2017, 1:10

    Even counting the slower passage of time at those velocities, if humans (and other biological beings) have to expend several generations during the travel phase, then they will need to assemble biological ecosystems that are sustainable over that period of time, to absorb their wastes and provide thew resources. The ability to do so has yet to be demonstrated.

    Suspended animation is a slower consumption of resources unless metabolism is completely stopped.

  • Tony May 9, 2017, 1:19

    The graph is extremely poorly done.

    The highest black-rimmed point is the projected perihelion speed of the solar probe plus. A heliocentric velocity is always going to be high when you fall towards the sun and is not particularly relevant to interstellar travel.

    The speeds of interplanetary craft leaving Earth are ignored back through the 1960s (and have not appreciably increased), and the Voyager probe’s velocity should be placed back in the 1970s when it was launched rather than today.

    New planes are not included on the speed graph in the last few decades since they have saturated.

    The exponential growth trend has nothing to support it for forty years.

  • Ray Perreault May 9, 2017, 8:28

    Interesting, although there is a flaw in the logic. When plotted on a logarithmic scale, it implies that ANY flight, will be caught by a later flight. Using a Moore’s Law analogy, is tricky.

  • Michael May 9, 2017, 8:33

    The beauty of the ‘Starshot’ concept is not only the modularly of the design i.e. if just gets bigger over time it has multiple uses. And then once we get into space and use free electron lasers we can compensate for the Doppler shift issue and then we can accelerate probes at much higher velocities only limited by the material properties and energy amount.

  • ole burde May 9, 2017, 9:40

    One of the most efective general strategies of practical problem solving , is to prepare two esentially diferent solutions ( Plan A and Plan B) , in order to maximize the chances of at least one of them to sucseed . …In this stategy , the time to make a final choice between A an B is ONLY when one of them has sucseded beyond any doubt . If we apply this to the ‘incentive trap ‘ , things become more clear : the time to give up on a slow moving generation ship is only when a faster mooving vessel has established a thriving colony in another starsystem , and seen from this perspective it becomes perfectly acceptable if a slowmoving generationship find an other solution to have sucseeded as well

  • neutrino78x May 9, 2017, 10:05

    I still wonder: what is the maximum speed that a crewed spacecraft could achieve using the “sundiver” technique? Let’s say we immerse them in liquid (US Navy does research on that…I was Navy submariner lol) so they can tolerate high acceleration. We make a sail with A carbon layer that burns off when close to the Sun.

    My first boat, USA Florida SSBN-728, displaced roughly 16,000 metric tonnes while running on the surface, and since she was positive buoyant on the surface, her actual weight was a little less (to submerge, we take water into the ballast tanks, so the weight of the boat is greater than the water we displace… Archimedes law). So let’s say that’s the mass of the spacecraft, including the solar sail.

    Anybody study calculus? Could we get to say 20% light speed that way? Or would a laser array still be needed? :)

    • J. Jason Wentworth May 9, 2017, 16:45

      If the people onboard were encapsulated in water (with air supplies, of course), the only limit might be the rate of acceleration/deceleration that the structure of the solar sail starship itself could withstand. (The fierce solar–and stellar, at the other end of the trajectory [unless electrostatic braking was used instead of photonic braking]–heating that the ship would experience would affect the strength of its materials). Balanced against this heating would be its possibly short duration, as the ship would–after “blasting off” from behind its occulter, very close to the Sun–rapidly accelerate away, pushed by the powerful sunlight pressure so close to the solar surface.

      • Michael May 10, 2017, 7:46

        Starshot can also be used to propel much larger space craft, no need to go near the sun. If we get into space proper we can use a large lens together with photo recycling which would be a huge boost. But slowing down is an issue, maybe if we send out a large number of ‘fuel cells’ on these sails towards the target star and we pick them up ‘burn’ them and use them to slow down with.

        Although we can use water or low density fluid we must take care in that although the body is supported certain organs such as the tongue will weight a lot more than normal. We should be able to handle much higher g forces than normal been support by a liquid or semi-liquid.

    • George King May 9, 2017, 22:22

      Not a rocket scientist, but I believe that a principal constraint would be that the escape velocity close to the Sun is far below relativistic speed. If the sundiver were able to reach and exceed escape velocity at a particular distance from the Sun, it then would go on a hyperbolic trajectory. That would start taking it increasingly further from the Sun, such that the additional boost provided by solar irradiance thereafter would diminish as the craft got further from the Sun.

      If my liberal arts major Wikipedia-based math is correct, twenty percent of c is roughly 60,000 km/s. The escape velocity at the very surface of the Sun is 617.5 km/s. The sundiver of course would not be able to get quite that close. In comparison, the solar escape velocity still fairly close in but out at at the orbit of Mercury is only 67.7 km/s.

      I believe that Professor Matloff has conceptualized a very light payload sundiver probe mission with yet-to-be-developed materials that potentially might attain 1400 km/s.

      But I don’t believe that 60,000 km/s is attainable via that method, particularly with the much larger payloads necessary for human rated craft. If I understand the situation correctly, the sundiver would not be able to remain close enough to the Sun for long enough for solar irradiance to boost the craft to 60,000 km/s.

      I really like the sundiver mission concept, too. But I believe that it is more ideally suited for sending probes to the deep outer reaches of the solar system rather than for reasonable duration interstellar missions. Such as, for example, Professor Maccone’s FOCAL gravitational lensing mission. Or a mission to Planet X (or 9) if confirmed and located.

      So, yes, I believe that a laser will be necessary to cross interstellar distances with lightsails within a reasonable time, especially if we’re talking heavy payloads. Going to be challenging enough as it is to do it with hyperlight chip craft.

      Some of the math/science types here may be able to provide a more mathematically precise response, but I believe that the above is roughly right in the (purportedly) Keynesian sense (“it’s better to be roughly right than precisely wrong”).

      That immersion thought might be useful, though, if they use lasers or some other method of propulsion involving high rates of acceleration. Also would provide some marginal individual radiation protection as well.

      • J. Jason Wentworth May 10, 2017, 19:37

        I agree; I was referring to the maximum acceleration/deceleration forces that the structure of a “Sundiver” (and its crew and passengers, if immersed in liquid during the high-g maneuvers) could withstand. There is, of course, another limit when the possible sunlight pressure-“induced” velocities of sail vehicles are considered. Not only does the Sun’s gravity deduct from the hypothetical “no solar gravity” velocity (just as the Earth’s gravity deducts 9.8 m/s from the velocity of a vertically-rising rocket each second), but the Sun’s light pressure, while powerful, can only impart so much velocity to a sail.

  • james stilwell May 9, 2017, 11:10

    Without navigation charts wouldn’t a trip to the nearest star system possibly encounter dust lanes or worse…slowing down would also take time…all becoming part of the transit time…very high speed to the stars may have terrible consequences…unless the dust lane thought is just in my imagination…

  • RobFlores May 9, 2017, 11:51

    As I have previously conjectured, the practical maximum speed over normal space is about 45% of the speed of light. Nearing those speeds capabilities there should be no hesitation about launching.

    This is just a practical limit for manned ships.
    Because, at this speed you can still scan the space in
    front of you for significant debris, and have time to evade it, accounting for
    the round trip time of speed of light echo from debris location.

    Sure you could push to 99.9% to get relativistic effects.
    But your time dilation of 1 year from 22 1/3 years is coupled with:

    1) needing a titanic amount of Power to speed up beyond 45% C to 99.9% C
    2) Shielding against 1 gram impact the equivalent of the energy released
    in TNT quantity more than the mass of a dwarf planet.

    Only Khadashev 3 type CIV would probably have this capability.

  • J. Jason Wentworth May 9, 2017, 14:10

    This article is strangely, personally, very timely, because I was pondering this very question over the weekend (while reading Dr. Ronald N. Bracewell’s book, “The Galactic Club: Intelligent Life in Outer Space,” in which he addressed the same question, with regard to dispatching both messenger-type and non-messenger-type interstellar probes). My own answer is “relatively soon,” and here is why:

    These two recent Centauri Dreams articles (see: https://centauri-dreams.org/?p=37514 and https://centauri-dreams.org/?p=37527 ) suggest that relatively fast solar sail and/or laser-pushed lightsail micro-probes—capable of reaching the Alpha Centauri system in a human lifetime or less—may be feasible before the second half of the 21st century. This also means that slower sail probes (made using sail materials that are now available, or soon will be), which we could build now, could be launched even sooner. Because the electronics and the spaceframes (bodies) of such micro-probes could be mass-produced easily (the sails could also be fabricated in quantity, using automated machines and human effort), it would be worthwhile to launch many of them—in all directions from the Sun, with some being targeted at neighboring stars (as well as on flyby trajectories to Kuiper belt objects [and Planet X, if it exists])—for the following reasons:

    [1] Three-dimensional coverage of the outer heliosphere, its bow shock region, and the interstellar medium beyond would be of great scientific interest in its own right. It would also provide engineering data on the total amounts, rates, and types of erosion that interstellar probes—especially faster ones—would encounter when traveling to stars lying in different directions from the Sun (some will have more—or less—gas, dust, or both). VLBI (Very Long Baseline Interferometry) astronomical observations could also be possible using such widely-separated probes. These missions, like the tiny Vanguard 1 “grapefruit” satellite, would be engineering tests with “bonus” scientific results—their purpose would be to perfect the solar “fry-by” (or high-speed laser) launch technique, then function as long as possible in interstellar space, possibly long enough to reach and return data & images from other stellar systems;

    [2] Because interstellar probes will have to remain functional for at least decades, or even centuries, in space while in transit to their destinations, these missions would provide ample opportunities to find out how long our best-devised electronics can last in the interstellar environment, and how they would degrade (hopefully “gracefully,” as engineers say). Fortunately, while radiation is a problem, the deep cryogenic cold out there greatly slows down the degradation of transistors and other solid-state electronic components (not terribly unlike the much-discussed theoretical cryonic hibernation of human star travelers), as Ronald Bracewell pointed out in his book. Experience gained from the probes’ flights—along with continuous technology development back home—would enable subsequent models of the probes to be greatly improved. These missions would also provide much-needed experience in tracking and controlling extremely distant spacecraft, and;

    [3] The idea that we shouldn’t launch slower interstellar missions because they would be overtaken by later, faster missions would be true *IF* human beings were logical beings, whose societies advanced steadily and predictably in their economic and engineering capabilities. But they aren’t, as history makes abundantly clear (the very long “pause” in manned deep space travel since Apollo 17 is a depressingly glaring example of this). Large, dramatic advances occur suddenly for all kinds of reasons (“hot” and “cold” wars are common ones, but not the only ones; an unusual individual like an Einstein, von Braun, Bezos, or Musk sometimes comes along and triggers a huge leap), whose causes are usually unpredictable, transient, and unable to be recreated at will. Therefore:

    Whenever the opportunity to launch interstellar probes presents itself—or is brought into being by the efforts of the right people—we should “Go while the getting’s good!” (And if the first, slower probes *do* happen to be passed by later-launched, faster probes, so what? That would be a welcome bonus!) Just as with robotic lunar and planetary probes, which gradually developed their own academic and industry lobbying constituencies (and came to be seen by governments as having prestige and propaganda benefits), an interstellar medium/interstellar probe program, once started, will also develop its own economic/academic/political momentum, especially after the first data and images from Kuiper belt worlds, Planet X (if it’s there), the Alpha Centauri system—or maybe a closer brown dwarf exoplanetary system, if we’re lucky—are received on Earth.

  • Michael C. Fidler May 22, 2017, 10:34

    First Breakthrough for Future Air-Breathing Magneto-Plasma Propulsion Systems.


    A new breakthrough in jet propulsion technology since the invention of the jet engine is achieved. The first critical tests for future air-breathing magneto-plasma propulsion systems have been successfully completed. In this regard, it is also the first time that a pinching dense plasma focus discharge could be ignited at one atmosphere and driven in pulse mode using very fast, nanosecond electrostatic excitations to induce self-organized plasma channels for ignition of the propulsive main discharge. Depending on the capacitor voltage (200-600 V) the energy input at one atmosphere varies from 52-320 J/pulse corresponding to impulse bits from 1.2-8.0 mNs. Such a new pulsed plasma propulsion system driven with one thousand pulses per second would already have thrust-to-area ratios (50-150 kN/m²) of modern jet engines. An array of thrusters could enable future aircrafts and airships to start from ground and reach altitudes up to 50km and beyond. The needed high power could be provided by future compact plasma fusion reactors already in development by aerospace companies. The magneto-plasma compressor itself was originally developed by Russian scientists as plasma fusion device and was later miniaturized for supersonic flow control applications. So the first breakthrough is based on a spin-off plasma fusion technology.


    Get Ready For Low-Cost Jet Engines That Reach Space Without Burning Fossil Fuels


    • Alexander Tolley May 22, 2017, 13:34

      Great minds think alike! Below is an arvix link to their work that gives more detals.


      It sounds as though the engine doesn’t scale so they need clusters.

      My thought is to use the engine in mixed mode, like Skylon, to launch small payloads like CubeSats to orbit. Laser power beaming to solar cells on the wings for the needed energy. The high exhaust velocity if enough to overcome the remaining air drag should be good for low mass ratio vehicles. Potentially a very low cost, reusable, vehicle for small payloads.

  • Michael C. Fidler May 22, 2017, 20:11
    • J. Jason Wentworth May 23, 2017, 4:45

      So *that’s* how UFOs are propelled… :-) But seriously, I wonder if the MPC system might have interstellar potential? Here’s why:

      Dr. Robert Duncan-Enzmann designed–in addition to his famous Enzmann Starship–a photonic ramscoop-equipped interstellar ramjet (see: http://enzmannstarship.blogspot.com/2013/05/starship-main-drive-propulsion-systems.html , http://enzmannstarship.blogspot.com/2013/03/anatomy-of-echolance.html [about 1/3 of the way down the “screen-page”], and http://3.bp.blogspot.com/-IMnXg2PYBRg/UTraaTxqWWI/AAAAAAAACwg/SwGbydCdvyw/s1600/ath.jpg ), whose ramscoop is a low-drag device (because, consisting of laser beams, it doesn’t transmit drag forces to the ship, as a magnetic scoop would). Now:

      While this design of Enzmann’s is a full-blown fusion ramjet, the MPC might work in interstellar space if Enzmann’s photonic ramscoop was used to collect interstellar hydrogen, which would serve as the MPC’s reaction mass. Such an arrangement–perhaps using a fission reactor to provide the electricity it would need–might be a near-term propulsion system that could propel reasonably fast (“arrival at Alpha Centauri within a human lifetime”) interstellar probes.

  • Michael C. Fidler May 23, 2017, 2:39

    Plasma propulsion could become effective and useful for higher altitude aviation, airships and eventually space access
    A little more digestible info in this article:


    First Breakthrough for Future Air-Breathing Magneto-Plasma Propulsion Systems

    Berkant Göksel

    Managing Director of Electrofluidsystems


    I Ch Mashek
    Investigation of Magneto-Plasma Compressors with Internal Initiation to Develop High Momentum Pulsed Plasma Jet Actuators for Flow Control

    Guess who is the coauthor of this article, none other then Martin Tajmar of EMDrive and Evaluation fame!
    Laser-induced MW discharge


    Microwave energy release regimes for drag reduction in supersonic flows

    Read More: https://arc.aiaa.org/doi/abs/10.2514/6.2002-353
    Some interesting articles relating to Plasma and Dust and Supersonic flows!



    Bow Shock Wave Mitigation by Laser-Plasma Energy
    Addition in Hypersonic Flow


    I Ch Mashek and Russian article on Zeemen splitting – so what does this have to do with the rest of these articles on microwaves, plasma rockets and high magnetic fields?

    Zeeman splitting, its specific features, and gyromagnetic ratios for configurations 1snf (n = 4–10) of the helium atom

    The Zeeman magnetic split effect is exactly what would be seen from an alien spacecraft in the earths atmosphere using a microwave driven Air-Breathing Magneto-Plasma Propulsion System!

    The Russians or the USA did not build it in 1947, so go figure.

  • J. Jason Wentworth May 23, 2017, 8:47

    Michael, some of those links (including your first one) give “404 alarms,” at least on my end.

  • Michael C. Fidler May 23, 2017, 18:59

    Yes, they become truncated or garbled when they are copied, they work on the lenr-forum so try that, the last comment has the correct links: