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Thought Experiment: The Asteroid Belt Astronomical Telescope

Could laser light be used to shape and polish an asteroid to high optical standards? That’s the question raised in an imaginative essay in Physics Today that posits the creation, a century from now, of the Asteroid Belt Astronomical Telescope (ABAT). It’s science fiction today, part of the series of speculations that the magazine has been running to explore possible futures, but what a concept for an SF novel, and perhaps someday real astronomy (thanks to Centauri Dreams reader Klaus Seidensticker for sending me the link).

Author Robert Austin (Florida Polytechnic University) creates a backstory involving a “self-described over-the-hill assistant professor at Purdue University” who uses a research grant to polish a 1-centimeter sphere of pyrolytic carbon magnetically levitated in a vacuum. He achieves the needed flat optical surface along with a reflective hemispherical ‘bump’ on the object’s backside that can be used to reorient the mirror by photon pressure.

Soon the idea of using lasers to form and manipulate mirror components takes off, and by the end of the 21st Century an actual 2-meter asteroid is shaped and steered, using equipment originally developed for asteroid mining. The Asteroid Belt Astronomical Telescope that grows out of all this will eventually reach billions of mirror facets in imaging arrays in space, a 5 AU diameter astronomical mirror. Austin’s essay is written as a scientific report from the future, at a time 100 years from now when ABAT is 1% finished but already achieving stunning imagery.


Image: The Asteroid Belt Astronomical Telescope (ABAT) focuses light from laser-polished asteroids onto dual imaging arrays above and below the solar system; other intense laser pulses maneuver the arrays to different locations, thus allowing ABAT to point at multiple celestial targets. Asteroid ablation residue corralled into a pair of Devil’s Footprints shields the focal regions from solar illumination. Credit: Robert Austin/Physics Today.

The ‘Devil’s Footprint’ reference in the caption above is to Munich’s Frauenkirche, which has a part of the floor in which no windows are visible — how it got its name is an entertaining part of the essay, which I’ll send you to for more. The point is that asteroid residue is a helpful way to block sunlight, and by the era depicted in this piece, asteroid mining is assumed to have become so widespread an activity that industrial operations at 5 AU are all but routine.

Bob Forward would, I’m sure, have loved the mega-engineering involved in creating something like this which, if built, would be the most ambitious scientific project ever undertaken. Austin’s ABAT would see its imaging arrays maneuvered through coordinated pulses of laser light, creating minuscule torques to turn each facet in the desired direction. As for enabling this vast cloud of technology to produce the needed data, here’s Austin’s take, based as is the whole article on the assumption of yet to be developed technologies:

Developing a conventional monolithic sensor array to span ABAT’s focal plane would be impractical, so Kim’s team hit upon a new approach based on diatoms, the microscopic organisms with silica skeletons that hold such a special place in the hearts of nanotechnologists. Group biologists genetically engineered diatoms to produce several specialized organs. Some of the organs convert light to electrical signals. Some store the microwave input power necessary for operating the array. Still others use CPS (celestial positioning system) signals to determine three-dimensional location, measure time, and digitally encode the data for transmission.

The result: Trillions of self-reproducing sensors are grown in a vat and deployed in space, manipulated as clouds of microscopic optical sensors.

Image readout begins when maser beams wake the sensors and provide transmission instructions. Guided by the electromagnetic field of the masers, the sensors align themselves toward a receiving antenna to which they beam their data. The vast data set is then relayed to ABAT’s brain, which puts the information together to form an image.


So there you have it, an array of 10 billion asteroids polished into mirror facets, all coordinated through artificial intelligence in a century-long project that might get underway, perhaps, by 2100. It’s a fascinating speculation, and I like the way Physics Today presents these explorations, in the form of articles you might read in the future issue that explains the project at hand. It makes for convincing reading, like good science fiction, and at times, I confess, it does make the hair stand up a bit on the back of the neck. Because imagine what we could see with something this vast, and imagine how much bigger still it could grow.

Image: Imaginary view. The exoplanet Gliese 832c as the future ABAT might see it early in the process of construction. Credit: Robert Austin/Physics Today.

If we ever do begin to see exoplanets at the level of detail promised in the artist’s rendering above, it’s worth speculating on what that might mean for interstellar exploration. Breakthrough Starshot puts the first interstellar crossing somewhere in the latter half of this century, assuming major breakthroughs in laser array technologies and engineering. Would a new ability to see exoplanets like this put a damper on future mission ideas, or would the view of prospective targets actually act as an incentive to get a payload into their systems?


Comments on this entry are closed.

  • Resonanz December 5, 2016, 13:54

    Kepler 8462852, Tabby’s star!

  • ljk December 5, 2016, 14:23

    Real astronomers just detected and studied a real two-meter wide planetoid that is also very reflective! See here:


  • Tom Mazanec December 5, 2016, 14:35

    Will this ever be expanded to the Edgeworth-Kuiper Belt?

  • Michael December 5, 2016, 14:53

    It would be easier to have starshot send out mirrors by the tens of thousands into orbits around the sun.

  • Wikisteff December 5, 2016, 16:51

    I thought of much the same thing back in 2005, although I put it in the Oort cloud for better heat rejection and a longer baseline, and had aliens make it. They could then spy on in-system and out-of-system exoplanets with very high acuity, while keeping a low profile and having very high energy efficiency.

  • Daniel de França Diniz Rocha December 5, 2016, 17:20

    Maybe this is a solution for the Fermi Paradox. ETs don’t need to move much. They can take pictures and simulate the environment in 3D.

  • Geoffrey Hillend December 5, 2016, 18:58

    This thought experiment is impracticable for the following reasons: 1) A laser will NOT polish pyrolytic carbon. Like graphite it is highly resistant to heat. 2) A pyrolytic carbon is not made with lasers. 3) pyrolytic carbon does not have the reflectivity to make a telescope mirror without adding some kind of coating like silicon dioxide or aluminum. Pyrolytic carbon can be used as a lightweight support structure or most of the mirror. Making such a mirror is very expensive.

    How many years will it take to shape the asteroids and add mirrors to them which could be measured in many millenia. We could build huge space telescope by combining many smaller mirrors like the James Webb space telescope and make an interferometer of of several of them within a few decades.

  • Wojciech J December 5, 2016, 20:02

    Reminds me of the Galactic Life Imager idea


  • DJ Kaplan December 5, 2016, 20:28

    I don’t know. It’s hard enough to get a decent mirror ground planetside.

    • Matt December 5, 2016, 21:55

      Would being in zero G make it easier to grind a mirror? I don’t think the asteroid belt would be a good clean room though.

      • Mark Zambelli December 14, 2016, 6:18

        I would imagine the vacuum at 5 AU would compare very favorably to even our best attempts at a clean room. Shading from the solar wind would provide an even better environment.

        If we could control the rotation of the asteroid at will then how about melting the surface and allowing it to freeze into the parabola of choice… may be easier than using lasers for the shaping.

  • xcalibur December 5, 2016, 20:43

    Wouldn’t dust and micrometeoroids present an obstacle to space mirrors?

    I would think that any sort of space engineering must take small impacts into account, especially around the asteroid belt.

  • Michael Fidler December 5, 2016, 21:45

    How about a Poisson spot telescope made up of millions of small ball bearing keep aligned via a web of wires generating a stabilizing magnetic field. This could be done very cheaply and could even be launch by small rockets to keep the cost down – need to be sent to one of the Lagrange points for stability. It would work as a huge Poisson spot interferometer that may be able to block the starlight when looking for or imaging exoplanets. Any suggestions for improvements or similar concepts – maybe glass ball bearings, make the whole array into an arc or like a bubble to focus it! What we need is cheap and easy to do!

    • Michael C. Fidler December 6, 2016, 19:18

      ljk, thanks for the link to the Aragoscope (Poisson spot), here is an update from NBF that give more details for different optical designs of such a system, courtesy of NASA’s NIAC.
      The advantage in using ball bearings would be the much greater light grasp across the array improving the contrast of the exoplanets. The Aragoscope use one single huge disk, whereas the millions of ball bearings would fill in the area that is being blocked. The other advantage is that making high precision ball bearings is easy to do so no problem with the accuracy that a large disk would need. The requirements for launching would also make for a cheaper solution. Just think of this as millions of small lenses combines to form a high resolution image.

  • Eniac December 6, 2016, 0:31

    Great Concept!

    However, even with all the asteroids in existence this would be an exceedingly sparse mirror, which means it would be needlessly large for its light gathering power. It does not help if you can resolve a square meter on an exoplanet if only a single photon from that square meter makes it into the detector every year. With weak light sources, like planets, it is better to put the same number of mirrors much closer together, say as a multi-kilometer swarm at L2, where there is some shade.

    Also, if I read this correctly, each asteroid would have only one side of it polished into a mirror. It is much more effective to mass-produce thin, flat mirrors, from asteroid materials or from Earth. You can then have many more of them at much lower cost and they can be oriented much more easily. Equip each with a navigation system and use light pressure for propulsion, with an LCD type attitude control system like the IKAROS sail uses. Except, these “sails” would be solid and have one side polished to be an optically perfect paraboloid. In the absence of gravity, they can still be very thin.

    We are lacking the experience in optically precise formation flying, but everything else is pretty much today’s technology.

  • DCM December 6, 2016, 5:09

    Worth a try once we could afford it. How long will that be?

  • Andrew Palfreyman December 6, 2016, 5:28

    Perhaps we can do even better by working to sparsely populate the enormous area out beyond 550 AU for Maccone’s solar gravscope.

  • Alexander McLin December 6, 2016, 10:21

    Reminds me of the Oculus interferometry telescope in Alastair Reynolds’ “Blue Remembered Earth. Except he used imaging elements constructed out of Trans Neptunian materials and spherically distributed at nearly Oort scale distances with the focus located in Mercury orbit. Beautiful visualization of a plausible near-future human solar scale technology.

    From the ABAT picture, it seems the telescope wouldn’t be focus on any objects located on or near the elliptic plane?

  • jonW December 6, 2016, 11:15

    “Would a new ability to see exoplanets like this put a damper on future mission ideas, or would the view of prospective targets actually act as an incentive to get a payload into their systems?”

    I’d say the answer is definitely that it would depend what the exoplanets look like! The imagined image of Gliese 832c would spur us on, but a lifeless hunk of rock or a gas giant like one of “ours” might suggest there’s no urgency.

    • ljk December 6, 2016, 13:29

      Maybe an advanced alien culture that is hiding for whatever reason would want other species to think its home world is a lifeless rock. Would not be terribly hard to do if their society was underground.

    • Mark Zambelli December 14, 2016, 6:10

      It would allow us to be more selective and allow us to tailor each mission payload depending on the destination targets of choice.

  • ljk December 6, 2016, 12:24

    Some other giant space-based telescopes on the proverbial drawing board:

    High-Definition Space Telescope (HDST):



    DARPA’s Membrane Optical Imager for Real-Time Exploitation (MOIRE) program, a folding polymer space telescope:


    The Aragoscope:


    The late great Robert Bradbury envisioned telescopes that an advanced ETI could make out of something the size of Earth’s Moon: Not much need to travel to other star systems after having an instrument like that (I am being somewhat facetious, but only somewhat).

  • Michael Spencer December 6, 2016, 15:23

    The ideas expressed by Dr. Austin are lovely!

    Centuries-long projects imply an attention span (and funding) not often seen among humans with a few exceptions: European cathedrals come to mind, as do various pyramids around the globe, and perhaps a few Stone Age projects like Stone Henge (though admittedly nobody knows how much time was required to place those tablets).

    All of those efforts had the “advantage” of steady-state technology, of course, although it is true that flying buttresses affected the cathedrals. Still the examples represented very long commitments.

    Our times are so different, aren’t they? Our capabilities change so quickly that I wonder if anything so particular would be attempted.

  • ljk December 7, 2016, 12:25

    New telescope chip offers clear view of alien planets

    6 December 2016

    Scientists have developed a new optical chip for a telescope that enables astronomers to have a clear view of alien planets that may support life.

    Seeing a planet outside the solar system which is close to its host sun, similar to Earth, is very difficult with today’s standard astronomical instruments due to the brightness of the sun.

    Associate Professor Steve Madden from The Australian National University (ANU) said the new chip removes light from the host sun, allowing astronomers for the first time to take a clear image of the planet.

    “The ultimate aim of our work with astronomers is to be able to find a planet like Earth that could support life,” said Dr Madden from the ANU Research School of Physics and Engineering.

    “To do this we need to understand how and where planets form inside dust clouds, and then use this experience to search for planets with an atmosphere containing ozone, which is a strong indicator of life.”

    Physicists and astronomers at ANU worked on the optical chip with researchers at the University of Sydney and the Australian Astronomical Observatory.

    Full article here:


    • Alex Tolley December 7, 2016, 16:57

      Larry, please make sure you follow up with technical details as they are released. This sounds very interesting at first blush.

      • ljk December 7, 2016, 18:52

        I certainly will. You could also contact the Australian National University (ANU) Research School of Physics and Engineering:


        • Michael Fidler December 7, 2016, 23:34

          Did a little digging and found this: On the APPC-AIP program guide;
          MIR Nulling on a
          Chalcogenide Photonic Chip
          for Exoplanet Detection
          Harry-Dean Kenchington
          Which I Googled and found this:
          Chalcogenide glass planar MIR couplers for future chip based Bracewell interferometers
          Photonic integrated circuits are established as the technique of choice for a number of astronomical processing functions
          due to their compactness, high level of integration, low losses, and stability. Temperature control, mechanical vibration
          and acoustic noise become controllable for such a device enabling much more complex processing than can realistically
          be considered with bulk optics. To date the benefits have mainly been at wavelengths around 1550 nm but in the
          important Mid-Infrared region, standard photonic chips absorb light strongly. Chalcogenide glasses are well known for
          their transparency to beyond 10000 nm, and the first results from coupler devices intended for use in an interferometric
          nuller for exoplanetary observation in the Mid-Infrared L’ band (3800-4200 nm) are presented here showing that suitable
          performance can be obtained both theoretically and experimentally for the first fabricated devices operating at 4000 nm.

          Here is something a little shorter, on page 47:

  • Geoffrey Hillend December 7, 2016, 17:16

    Lik, the chip idea sounds promising. It would make the space telescope interferometer which needs to use two telescopes to cancel out the star light obsolete. I think a large telescope is still needed to resolve the faint light of an exoplanet especially if we have to look through Earths atmosphere. Maybe we get that chip into a space telescope or James Webb space telescope.

  • ljk January 4, 2017, 11:28

    NASA Plans to Build a Gigantic Space Telescope from 2 Tiny CubeSats

    The distance between the satellites would serve as the telescope’s focal length.

    By Jeremy Hsu | Scientific American January 2017 Issue

    More than 400 years after Galileo handcrafted his first spyglass, NASA and South Korea’s Yonsei University aim to create a “virtual” telescope in space by using two separate spacecraft. To test the concept, scientists have built two small satellites called cubesats that will practice lining up in orbit to construct a single telescope with a focal length as large as the distance between them. Scheduled for launch in early 2017, the roughly $1-million mission could pave the way for a new class of instrument that can peer through the sun’s glare or at distant alien planets, without requiring a massive single scope.

    The six-month mission—called “CubeSat Astronomy by NASA and Yonsei using Virtual telescope ALignment eXperiment” (CANYVAL-X)—will try out a technique for forming a telescope that would otherwise be much heavier to launch. The plan requires two spacecraft (together the size of a bread loaf) to orbit together in a straight line, always pointed at their target. “Flying two spacecraft in coordination, aligning them to a distant source and holding that configuration is a capability that has never been attempted,” says Neerav Shah, an aerospace engineer at the NASA Goddard Space Flight Center.

    Full article here:


  • ljk March 15, 2017, 16:29

    A Vision That Could Supercharge NASA

    Posted on 2017-03-15

    by Marc Kaufman

    Let your mind wander for a moment and let it land on the most exciting and meaningful NASA mission that you can imagine. An undertaking, perhaps, that would send astronauts into deep space, that would require enormous technological innovation, and that would have ever-lasting science returns.

    Many will no doubt think of Mars and the dream of sending astronauts there to explore. Others might imagine setting up a colony on that planet, or perhaps in the nearer term establishing a human colony on the moon. And now that we know there’s a rocky exoplanet orbiting Proxima Centauri — the star closest to our sun — it’s tempting to wish for a major robotic or, someday, human mission headed there to search for life.

    All are dream-worthy space projects for sure. But some visionary scientists (and most especially one well-known former astronaut) have been working for some time on another potential grand endeavor — one that you probably have not heard or thought about, yet might be the most compelling and achievable of them all.

    It would return astronauts to deep space and it would have them doing the kind of very difficult but essential work needed for space exploration in the far future. It would use the very costly and very powerful Space Launch System (SLS) rocket and Orion capsule being built now by NASA and Lockheed Martin respectively. Most important, it would almost certainly revolutionize our understanding of the cosmos near and far.

    At a recent meeting of the House Science Committee, chairman Lamar Smith, said of the hearing’s purpose that, “Presidential transitions offer the opportunities to reinvigorate national goals. They bring fresh perspectives and new ideas that energize our efforts.”

    That said, here’s the seemingly feasible project that fires my imagination the most.

    It has been quietly but with persistence promoted most visibly by John Grunsfeld, the former astronaut who flew to the Hubble Space Telescope three times to fix and upgrade it, who has spent 58 hours on spacewalks outside the Shuttle, and towards the end of his 40 years with the agency ultimately became an associate administrator and head of the agency’s Science Mission Directorate.

    His plan: Build a segmented space telescope mirror that is 16 meters (52 feet) in diameter or larger, package it into one or several payload fairings and launch it into deep space. Accompanying astronauts would put it together either at its final destination or at a closer point where it could then be propelled to that destination.

    This would provide invaluable humans-in-space experience, would put the Orion and SLS to very good use in advance of a projected human mission to Mars, and would deploy the most penetrating telescope observing ever. By far.

    Full article here:


    To quote:

    What Grunsfeld’s space behemoth would provide is an unprecedented power and resolution to see back to the earliest point possible in the history of the universe, and doing that in the ultraviolet and visible wavelengths. But perhaps more significantly and revolutionary, it would supercharge the agency’s ability to search for life beyond Earth.

    Like nothing else currently in use or development, it would provide a real chance to answer what is arguably humanity’s most fundamental question: Are we alone in the universe?