≡ Menu

Starship Detection: The K2 Perspective

‘Classical’ SETI, if I can use that term, is based on studying the electromagnetic spectrum primarily in the radio wavelengths thought most likely to be used for communication by an extraterrestrial civilization. SETI’s optical component is largely focused on searching for signals intended as communication. What is now being called Dysonian SETI is a different approach, one based on gathering observational evidence that may already be in our archives, data that demonstrate the existence of extraterrestrial activity far beyond our capability.

Just as a Dyson Sphere would reveal the workings of a civilization of Kardashev Type II — producing something like ten billion times the energy of a Type I culture — the detection of a starship would show us technology in action, even if the craft were, as Ulvi Yurtsever and Steven Wilkinson have speculated, a vehicle pushing up against light speed millions of light years away. As physicist Al Jackson has tackled starship detection in recent years, he has taken note of the work of D. R. J. Viewing and Robert Zubrin, which dealt with some but not all design and detection possibilities. Beamed propulsion, for example, does not turn up in these sources.


Jackson also points to a caveat in such work: If we are hoping to detect a starship using many of the methods described in previous studies, we need to be inside the engine’s exhaust cone or the transmitter cone of the energy beam. We also know that the cone will be narrow. Even so, there are a number of ways to proceed, ranging from the craft’s interactions with the interstellar medium to detection of its own waste heat.

Image: Physicist Al Jackson. I can’t remember who took this (it may even have been me).

Imagine a highly advanced ship built by a Kardashev Type II civilization. Give it a gamma factor of 500, which translates to 0.999998 times the speed of light. Assume the ship is as hot as 5000 K (near the melting temperature of graphene). All these are extreme assumptions (see below) but we’re pushing the envelope here. This is, after all, K2.

Would we be able to detect such a craft? Waste heat can be modeled as isotropic radiation, says Jackson, in the rest frame of the ship, while to an observer in another inertial frame, this radiation appears beamed. We get this result:

Considering a ship of modest size and mass, a K2 ship accelerating at one gravity. For instance, if we have a ship 1000 meters long and 50 meters in diameter, generating 11402 terawatts in its rest frame, Doppler boosting will generate approximately 1.2×108 terawatts beamed into the forward direction. However… unless the ship is headed straight at the observer, it will be hard to see. Take into account the Doppler shifting of the characteristic wavelength, from near green in the rest frame to soft x-ray in the observer’s frame. One might look for small anomalies in data from a host of new astrophysical satellite observatories.

Not very encouraging, but then, detecting the signature of a starship is not going to be easy. One possible place to look is in the realm of what Jackson calls ‘gravitational machines,’ such as the massive binaries Freeman Dyson once suggested could be used as gravitational slingshots. We might consider not just white dwarf and neutron star binaries but even black hole binaries. A gravitational assist in such scenarios might reach as high as .006c.

On the other hand, wouldn’t a civilization that could already reach binaries like these have acquired capabilities greater than those it would gain by using the binaries in the first place? Perhaps better to consider black holes as a source of direction change for fast-moving starships. Jackson points out that a starship orbiting a black hole will have visible waste radiation. In fact, a close-orbiting ship will have fluctuating emissions peaked at those times that the ship, black hole and observer line up, a phenomenon that is the result of gravitational focusing.

Figure 2

Other extreme astronomical objects may be worthy of investigation in these terms. Jackson points to SS 433, a neutron star or black hole orbited by a companion star, with material being drawn from the companion into an accretion disk. Jets of particles are being blown outward from the poles. While at SS 433 the particles in the jets are moving at 26 percent of the speed of light, jet material in configurations like these can reach 95 percent of lightspeed. Using such jets to propel magsails that reach .5 times the speed of light would allow a K2 civilization an abundant source of energy for repeated missions at a high percentage of c.

Image: Magsail ‘jet riding’. Credit: Doug Potter.

We don’t know what a K2 civilization will choose to do, but exploiting naturally occurring resources like these may be an attractive proposition. There may be interesting prospects not just for magsails but so-called ‘lightsails’ around extreme astronomical objects:

Consider a K2 civilization taking advantage of a Schwarzschild or Kerr black hole as a means of focusing radiation from a beaming station onto a sail. The advantage of this is the tremendous amount of amplification possible. One of the most promising modes of interstellar flight propulsion is the use of a sail, a transmitter, and maybe a ‘lens’ to focus a beam of laser light or microwaves. Extrapolate to a K2 civilization the use of a black hole as the focusing device. An approximate calculation for a Schwarzschild black hole shows that beamed radiation can be amplified by a factor 105 to 1015.

So-called ‘strong focusing’ is tricky to model and, as Jackson explains in some detail, the astronomical configuration — the location of a source and the best location for the sail — are topics that need much more work. But the idea that a K2 civilization would use the immense energies available in the area of black holes makes them a natural hunting ground for Dysonian SETI activity. Could a black hole in the vicinity of a starship’s destination be used for braking?

Robert Bussard’s 1960 paper on interstellar ramjets posited a spacecraft that could collect gas from the interstellar medium, compressing it to a plasma that could be brought to fusion temperatures. Carl Sagan would later suggest that a magnetic scoop would be the ideal way for this gas collection to proceed, but later work by Dana Andrews and Robert Zubrin revealed how much drag such a magnetic scoop would produce. The ‘magsail’ actually acts like a brake.

Why not, then, use these magsail properties, shedding energy and momentum as a spacecraft nears its destination? Craft moving at relativistic velocities might find this an efficient way to arrive, one that produces a ‘bow shock’ whose radiation ranges from the optical to the X-ray bands. “A starship will be much smaller than a neutron star,” writes Jackson, “but detection of the radiation signature of a starship’s bow shock could imply a very peculiar object.”

Figure 3

Image: Two examples of neutron star bow shock, the one on the right an artist’s concept. Credit: Wikimedia Commons.

Jackson’s paper is a work in progress, with an early version printed in Horizons, the AIAA bulletin for the organization’s Houston chapter. A journal submission is in the works as he refines the draft. It’s a fascinating discussion that reminds us how much we have to speculate about when we talk K2 civilizations. Jackson notes the major assumptions: Ships can run ‘hot,’ and that means as high as 5000 K; material structural strength limits have been overcome; extreme accelerations are allowable and dust/gas shielding issues resolved. We can argue about the limits here, but it’s clear that a K2 civilization will have capabilities far beyond our science, and it may be the random anomaly in astronomical data that flags its existence.


Comments on this entry are closed.

  • Michael March 26, 2015, 14:38

    @Al Jackson

    ‘Give it a gamma factor of 500, which translates to 0.999998 times the speed of light. Assume the ship is as hot as 5000 K (near the melting temperature of graphene). Would we be able to detect such a craft? Waste heat can be modeled as isotropic radiation, says Jackson, in the rest frame of the ship, while to an observer in another inertial frame, this radiation appears beamed.’

    If the radiation is dopplered into the X-ray part of the spectrum we would not even see the craft until around 2.5 months before arrival if it travelled across the galaxy because of the closeness to the speed of light the craft was. 2.5 months is not a lot of time to observe a beam that would be as narrow as the emission zone, the front end, and we would be extremely lucky to see this beam given the huge area the sky presents.

  • Wojciech J March 26, 2015, 15:31

    Just like radio SETI this concep does assume some pretty far reaching technological wonders so to speak. I asked in previous entry this question and would like to repeat it, since there was no answer. How detectable would be spaceships using more realistic speeds of say 0.3c ? Would they be detectable easily? And if yes in what radius?

  • Michael March 26, 2015, 16:06

    Mind you 1.2×10^8 terawatts beamed into the forward direction is a lot of intensity for 2.5 light months out provide we are lucky to be in that narrow beam. So I think it is detectable and when the craft slows down the spectrum will change back towards the optical side.

  • Al Jackson March 26, 2015, 17:02


    The opening solid angle of the beamed radiation is 1/gamma, which at a of gamma = 500 is ~ .12 steradians , the probability of observation would be this angle divided by four pi steradians or ~ .005, which makes observation very difficult.
    I once computed* that if Gamma Ray Bursts were due to starships then there was a fleet of several thousand bearing down on us right now!
    (That’s not the case by the way.)
    *Correspondence: A. A. Jackson, IV, “Ultra-Relativistic Starships,” JBIS, 32, 240 (1979).

  • Alex Tolley March 26, 2015, 18:05

    When I read things like this, I am reminded of Clarke’s point that we are like isolated islanders thinking we are alone as we don’t hear drums from across the ocean, while unknown to us there are radio waves passing by undetected. I would go further and suggest that those same islanders might speculate on how big and loud those drums have to be in order to hear them at various distances.

    While the universe doesn’t preclude the use of huge drums, and it is worth listening for them, we should bear in mind that if interstellar travel is going to be by star ship, the technology may not impact the medium as we might expect.

  • Alex Tolley March 26, 2015, 18:29

    What is the operational benefit of trying to push a starship to very high gamma? Time dilation is the only advantage I can think of, and that would be largely irrelevant to non-biological life. In terms of populating the galaxy, there seems little advantage in very high c ships.

  • John March 26, 2015, 19:05

    Very interesting, but I’m not sure I agree with the assumption of a very massive craft travelling at a significant fraction of C. Why would a K2 civilisation build such a vehicle? The available surface area they would have for imaging would be staggering, and they would need to be past masters of nano-tech to have reached the K2 level. Effectiove immortaliy at an individual level is also a possibility…

    Of course, without a K2 civ to examine we cannot rule the building of such artifacts out…. I just don’t see why they’d need one.

  • william March 26, 2015, 23:16

    Doppler boosting will generate approximately 1.2×108 terawatts beamed into the forward direction.

    What is Doppler boosting?

  • william March 26, 2015, 23:20

    Forgot to ask these two questions:

    why would the following occur?
    Waste heat can be modeled as isotropic radiation, says Jackson, in the rest frame of the ship, while to an observer in another inertial frame, this radiation appears beamed.

    What I mean by the question is; why would the radiation in a rest frame suddenly have the appearance of a beam in a non-rest frame ? And what is the cause of the forward production of energy as the craft is moving ?

  • swage March 27, 2015, 7:19

    That depends to a large degree on their motivation. It is conceivable that advanced civilizations turn to a nomadic approach, especially as we know that stellar evolution mandates, at least to some degree, a kind of mass exodus sooner or later.

    To be frank: complete planetary mass evacuations do not seem like a feasible approach from here.

    Maybe i am too pessimistic here, as i am reminded by Arthur C. Clarke’s “Rescue Party”, a thought for which he has earned my respect and far more aspiring than Lovecraft/Barlow’s dystopian vision in “Till A’ the Seas”.

    But there is clearly an end to this world and other worlds due to the sequence of their main star in the far future, if not sooner, but i also do not think our species, as conceivable as that definition may be with regards of the involved time frame, will go down without fighting if it survives for that long in any case. There will be survivors for the time being. Living through such a catastrophe may change their attitude regarding colonization efforts quite a bit. If you had access to the kind of technology allowing you to build more or less self sufficient habitats in space you may start to deem natural habitats as rather unstable and dangerous, for example.

    I’d say there is a increase in ambition for space programs over the course of a habitable time frame on a planetary system and also with the evolution of technology, which may or may not be a similar evolution the respective species go through, complicated more or less by their environment (burning fossil fuel may be complicated for an aquatic species, for example and lead to an entirely different perception of things).

    The key driving factor initially, in our case, was military interest in improving ballistic weapons. Then, with the dawn of nuclear power, focus shifted towards high precision long range delivery systems, improving missile systems up to the point making a manned moon landing feasible.

    It also lead to the practical impossibility of large scale conflicts due the introduction of self-annihilation potential. For the first time in history humans couldn’t wage war against each other indiscriminately. Its almost ironic if not so serious.

    Secondly the introduction of nuclear propulsion concepts in effect opens up the solar system, if we should choose so.

    We are still trapped in that kind of pause in between those two consequences where we try to adapt to the new reality and quite frankly also are frightened of the capabilities we have opened up. A particularly dangerous phase, too, but the worst successfully transcended in 1962, relapses are not totally inconceivable, tho and do seem to happen.

    What we can see here clearly that it is not enough to come up with the right technologies, but also to come up with the maturity to use the advancements for the benefit of the species and not destroying it or to keep it locked away for personal use, dragging down the entire development of the species. It also, since we are basically constrained into peace by our technology, gives a hint where our deficits lie.

    With this level of technology, as we are very well aware today, also a host of secondary effects surface, such as overpopulation or ecological disruption, which will not be solved by interplanetary endeavors in the solar system anytime soon. And again we will be measured by our maturity to tackle those problems.

    This also may tell us something important about the level of necessary social sophistication in an interstellar civilization.

  • Harry R Ray March 27, 2015, 9:42

    BREAKING NEWS: In a futile attempt to detect the transit of Alpha Centauri Bb, HST came up with a very interesting signal that may be one (ONLY) transit of an earth-sized planet with a much longer orbital period (but much shorter than Mercury’s)! Since this is a very tentative signal at best, a HUMONGOUS lightsail cannot be ruled out. This single “transit” reminds me of the frustrating UCF 1.02 signal. Could this transit be persued with existing telescopes in addition to Hubble PRIOR to TESS (or PLATO, if TESS is not sensitive enough)?

  • Al Jackson March 27, 2015, 10:39


    Beaming (sometimes called the ‘headlight effect’ ) is due to Special Relativity, how two relative frames see the physics as one frame relates to another.

    Doppler Boosting:
    See in the link above the section “Doppler effect on intensity”.

  • Michael March 27, 2015, 15:59

    Just thinking about when these Aliens want to slow down to a stop! All of a sudden we will have the exhaust which would burn millions of times hotter pointed at us which will then be doppler amplified by 10000 times, at least initially. That would push the radiation well into the gamma ray part of the spectrum.

  • Al Jackson March 27, 2015, 18:15


    Eugen Sänger noted in 1961 that for his matter – antimatter 100 tonne photon star ship one could not turn it on in the solar system!*
    Beam would fry everybody!

    *Handbook of astronautical engineering, New York, McGraw-Hill, 1961.

  • Wojciech J March 27, 2015, 19:10

    Why this ideas and attempts are interesting , I think the assumptions here are reaching to very unrealistic levels. Speeds that near the speed of light raise enormous issues when it comes to energy demands and materials needed to withstand potential collisions. While I definitely love such attempts being made, I think a more realistic expectations should be taken into consideration. Required speeds are IMHO very highly unlikely to be achieved. Nothing wrong in searching for them(you never know) but I would be wary of making the public and enthusiasts expecting such spaceships to be detected and then disappointed as none are found, while search for more likely probes and spaceships was not undertaken(simply because it would be far more difficult).It is a similar problem radio SETI had with its unrealistic expectations that were taken for granted for a long time with eventually disappointing results and disillusionment.

  • william March 28, 2015, 1:57

    @Al Jackson

    Eugen Sänger noted in 1961 that for his matter – antimatter 100 tonne photon star ship one could not turn it on in the solar system!*
    Beam would fry everybody!

    *Handbook of astronautical engineering, New York, McGraw-Hill, 1961

    a simple thought here – if you couldn’t turn it on in the solar system, then ‘exactly’ what was it doing to the occupants of the craft that was riding the beam !?

  • Harry R ray March 28, 2015, 14:39

    Andrew@www.drewexmachina.com: Thank you for answering ALL of my questions (see above comment) on your website. Thoughe this CLEARLY a TCE, I still have nagging doubts as to whether follow-up observations will produce anything positive (UCF 1.01 and 1.02 were also CLEARLY TCE’s, but were not confrmed).

  • Al Jackson March 28, 2015, 16:22


    Sänger was into Dyson-think before there was Dyson-think! He figured our future selves would be able to figure out the technology to protect the crew. Just think of how to collimate a beam of gamma rays, he did it using plasmas , no idea how one would do this!
    Speaking of Dyson, here is an extended quote of his for any who wish to pursue Big Thinks technology:

    “My argument begins with the following idea. If it is true, as many chemists and biologists believe, that there are millions of places in the universe where technology might develop, then we are not interested in guessing what an average technological society might look like. We have to think instead of what the most conspicuous out of a million technologies might look like. The technologies, which we have a chance to detect is by definition one which has grown to the greatest possible extent. So the first rule of my game is: think of the biggest possible artificial activities, within limits set only by the laws of physics and engineering, and look for those. I do not need to discuss questions of motivation, who would want to do these things or why. Why does the human species explode hydrogen bombs or send rockets to the moon? It is difficult to say exactly why. My rule is there is nothing so big nor so crazy that one out of a million technological societies may not feel itself driven to do, provided it is physically possible.”
    — Freeman Dyson

    Freeman Dyson, The Search for Extraterrestrial Technology,
    Perspectives in modern physics: essays in honor of Hans A.Bethe on the occasion of his 60th birthday, July 1966

  • Eniac March 29, 2015, 21:54

    Al Jackson: Thank you for that Dyson quote. He puts his finger on exactly why it is futile to to argue that something would not happen because “The ETI” might chose not to do it. Because there is not one ETI. There is either none or countless many, and we have to assume that anything that is physically possible is eventually going to be done by one of them.

  • ljk March 31, 2015, 11:38

    Trying to determine what ETI may or may not do in terms of interstellar communications technology is one big reason why Optical SETI, or OSETI, did not come into its own in the mainstream SETI community until around 1998.

    Despite the fact that none other than Charles Townes had promoted communications between worlds with lasers back in 1961, just one year after Project Ozma, the radio SETI community dominated the situation for decades with one big reason being that since humanity wasn’t quite up to firing laser messages across the stars back in the day, technological aliens would not either!

    This is why only recently have we started to get past radio SETI into other areas of the electromagnetic spectrum, a paradigm shift that if it had happened sooner might have produced a discovery by now. And yes, we should still look in the radio realm as it still makes sense, but limiting ourselves regarding beings we know next to nothing about does not make sense. Oh yeah, and SETI in general could do with a lot more funding and support.

    Here are two sources of the history of Optical SETI which should serve as valuable lessons for conducting such searches from now on. In summation, anything reasonable should be tried and more than just once in a while.