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A Self-Assembling Space Telescope?

Scaling up our space telescopes calls for new thinking. Consider this: The Hubble telescope has a primary mirror of 2.4 meters. The James Webb Space Telescope takes us to 6.5 meters. But as we begin to get results from missions like TESS and JWST (assuming the latter gets off safely), we’re going to need much more to see our most interesting targets. Imagine what could be done with a 30-meter space telescope, and ponder the challenge of constructing it.

This is what Cornell University’s Dmitry Savransky has been doing, developing a NIAC study that looks at modular design and self-assembly in space. Savransky’s notions take me back to a much earlier era, when people like Bob Forward talked about massive structures in space that dwarf any engineering project we’ve yet attempted. Forward saw these projects — his vast Fresnel lens between the orbits of Saturn and Uranus 1000 kilometers in diameter, for example — as ultimately achievable, but his primary concern was to be sure the physics worked.

Image: Cornell’s Dmitry Savransky. Credit: Cornell University.

Rather than imagining spacesuited work crews in the tens of thousands welding metal to metal, I have long thought that the only way to conceive of structures on this scale is through nanotechnology and self-assembly, harvesting materials from the asteroid belt and achieving a robotic cascade of structural growth that, once programmed, would run with human oversight. So the idea of self-assembly in space on the scale of a 30-meter telescope is music to my ears.

But that kind of technology is in the future. Where do we stand today? Here’s Cornell’s Mason Peck on the matter:

“As autonomous spacecraft become more common, and as we continue to improve how we build very small spacecraft, it makes a lot of sense to ask Savransky’s question: Is it possible to build a space telescope that can see farther, and better, using only inexpensive small components that self-assemble in orbit?”

Peck’s credentials here are hard to surpass, given his extensive work on the nanocraft he calls ‘sprites,’ which are essentially spacecraft on a chip. You can see why Peck’s insights have proven so valuable to the Breakthrough Starshot concept, which envisions sending swarms of tiny payloads to nearby stars (exactly which stars, as we saw yesterday, is a question that has yet to be decided). But just how do we do self-assembly at our current level of technology?

What Savransky has in mind is discussed in the précis on his ideas published by NASA along with the other Phase I projects for 2018. The concept: Every part of the telescope, and that includes not just the primary and secondary mirrors but the support structures and the sunshield, are to be constructed from mass-produced spacecraft modules. Each module is a hexagonal spacecraft about 1 meter in diameter that houses an active mirror assembly.

We’re not at the level of nanoengineering, but the self-assembly is ingenious. Rather than trying to launch a single, massive space telescope, the heavy lifting is done by launching separate modules as payloads of opportunity. Each of the modules has the ability to navigate on its own to the Sun-Earth L2 point using a deployable solar sail. The concept wastes no materials — the planar telescope sunshield is built out of the solar sails during the assembly process.

Image: Graphic depiction of Modular Active Self-Assembling Space Telescope Swarms. The schematic shows one module, lower left, and what the finished telescope might look like, with approximately 1,000 modules assembled together. Credit: D. Savransky/Cornell University.

Construction of the 30-meter space telescope is thus as much a matter of programming as it is of mechanics. But Savransky’s $125,000 Phase 1 grant could be on to something big, a solution for the scaling problem we face with space instrumentation. Says its creator:

“James Webb is going to be the largest astrophysical observatory we’ve ever put in space, and it’s incredibly difficult. So going up in scale, to 10 meters or 12 meters or potentially even 30 meters, it seems almost impossible to conceive how you would build those telescopes the same way we’ve been building them.”

Whether or not modular self-assembly in the Savransky mode makes it through the initial feasibility study — this is essentially what Phase I NIAC work is all about — will determine whether the idea progresses up the ladder to a more detailed and focused Phase II. More specifically, the NIAC précis lays out where the scientist hopes to go in Phase I:

In the NIAC Phase I, we propose to carry out detailed simulations of the spacecraft flight and rendezvous dynamics in order to set requirements on the solar sail area and loading, along with analyses of the mirror assembly to validate the ability to achieve the required surface figure in the assembled primary and secondary mirrors.

And if we eventually build space telescopes in the 30-meter class? Mapping the surface of Earth-like planets around nearby stars becomes a possibility, as does resolved imaging of stellar populations at a level never before possible. Self-assembly in and of itself, if demonstrated through missions like this one, obviously becomes a major factor in future mission design. Up next for Savransky is a NIAC orientation meeting in early June as the study begins.

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{ 23 comments… add one }
  • matterbeam May 2, 2018, 13:55

    How is the Sunshield and mirror assembly rotated to point towards the Sun at all times?

    What temperature is the mirror expected to cool down to if permanent shadow is maintained?

  • David H May 2, 2018, 13:59

    I know that asteroid mining is still a ways off, but then again, we’re spending decades between launches of big-mirror space telescopes, and some asteroid mining might be up an running in 25 years. My question is: How realistic would it be to build a (huge) telescope mirror from asteroid stuff and polish it in space? In microgravity there would be no reason to cast glass. You could just melt it, spread it over an approximately parabolic backplate, and let it cool gradually to anneal. The grinding, measuring and polishing could be done robotic instruments lowered into the dish from a temporary scaffolding. Of these there could be many, and they could work in parallel. In space there would be no issue of sagging, so you wouldn’t have to optimize the mass of the backplate. Would glass even be the right material to use for the reflector? Might it not be enough to use a thin coat of mercury, spin up the dish while the mercury is liquid to make it parabolic, and then let it cool to 3K?

    What would be the physical limitations of a mirror telescope built in this way? Could we achieve multi-kilometer reflector diameters? Turning and aiming such a behemoth would obviously have to be slow, because sudden jerks would vibrate like a giant drumhead, but a dampening system plus great care should not make this impossible, right? I’m curious partly because a telescope built in this was will appear in a scifi story I’m writing, and don’t want to overlook scientific dealbreakers and details that undermine the story’s plausibility.

    • Michael Fidler May 2, 2018, 16:58

      Spin casting Mercury will not work in space, it will just fly off the edge, no gravity to hold it down. One idea that would be much easier to do is blowing bubbles in space and letting it cool to solid, believe it is one of the NIAC concepts. This was also a sci-fi concept for spacecraft from asteroid smelting, but cannot remember which book?

      • J. Jason Wentworth May 3, 2018, 0:24

        One–which might or might not be the one you have in mind–is science fiction author Larry Niven’s real-world idea for building a “slow-boat” asteroid starship. A suitable one would have tanks of water installed at its center, after which the rotating asteroid would be slowly melted by a nearby solar mirror as the evaporating water blew it up like a balloon. After the expanded asteroid cooled, it would be outfitted with engines, attitude thrusters, airlocks and “shuttle locks” (docking hangars), and an interior habitat.

      • AlexT May 4, 2018, 3:09

        Ther is no gravity, but mercury can interact with magnetic field.

    • Michael May 4, 2018, 17:40

      “Might it not be enough to use a thin coat of mercury, spin up the dish while the mercury is liquid to make it parabolic, and then let it cool to 3K?”

      If liquid mercury is spun in zero g it will take on the shape of the object it is in contact with it to a degree i.e. via adhesive forces. It will not form a parabolic shape unless the shape of the holding vessel forces it to be. The problem with mercury freezing is that it forms a rough surface due to phase changes. It should be able to be polished or coated though to a fair finish.

  • Alex Tolley May 2, 2018, 17:44

    Conceptually this is the right way to go. Use the advanced facilities on earth to build the components, then assemble the modules in space. You could fit quite a few of the mirrors with their sails in the payload fairing of a rocket like the Atlas/Delta/F9.

    What I am skeptical of, is the self-assembly of the elements via navigation using only the solar sail. Nor do I see the sails being able to self-assemble into the shade. I suspect other assembly modules will be needed too.

    Having said that, I really hope that this concept passes muster and can be applied not just to the telescope, but also to other structures that can be built out of small, replicate modules.

    If the shade can be constructed this way, then why not large solar sails? We tend to envision them as monolithic, requiring careful deployment. But if small sails can be assembled into a large structure with relatively low mass overhead, then why not choose that route, as it offers far more flexibility, as well as removing a single point of failure? This approach was suggested by John Mankins for building solar power sats. He made the case that many small modules would allow the overall price to fall compared to a large, single module. A similar case was made for many small asteroid mining craft rather than a large craft. With a specified module, multiple manufacturers can engage in supply, competing with each other and finding further ways to drive down costs, so that further structures can be built at ever decreasing costs.

    • J. Jason Wentworth May 3, 2018, 12:13

      I’m a bit skeptical about such “high-level” self-assembly and “collective control” myself (at our current level of technology, at least). There is, however, a simpler form of it that we could implement right now; in fact, it was proposed at least as far back as the mid-1970s:

      Although it was proposed for creating reusable manned interplanetary spaceships, the technology involved would be equally applicable to large space telescopes. In his 1975 book, “Manned Spacecraft to Mars and Venus: How They Work,” the aerospace writer Walter B. Hendrickson, Jr. described the NASA and contractor plans for modular spaceships. Their propulsion (nuclear thermal, solar thermal, or nuclear [or solar] electric), propellant tankage, communications, life support, and habitation modules were designed so that they could be docked together to make up a complete spaceship. They could also be “mixed-and-matched” as needed or desired, to replace worn-out modules or to replace existing modules with upgraded ones.

  • Michael Fidler May 2, 2018, 20:29

    Kilometer Space Telescope.

    https://www.nasa.gov/directorates/spacetech/niac/2018_Phase_I_Phase_II/Kilometer_Space_Telescope

    https://www.google.com.ph/amp/s/www.nextbigfuture.com/2018/04/kilometer-space-telescope.html/

    Blowing bubbles is the way to go. When this will be practical could be an issue but thin, lightweight and easy to maneuver plus the possibility of very high precision are big pluses.

  • Michael Fidler May 2, 2018, 20:32

    Big problem with space scopes is upgrading the instruments, JWST instruments may be obsolete by the time it is at full power!

    • J. Jason Wentworth May 3, 2018, 12:42

      Unfortunately, yes. This, perhaps ironically, is a good “excuse” for developing either manned or tele-operated (or perhaps AI-operated, with tool accessorize-able robotic manipulator arms, in any case) reusable space tugs, the “low-powered, inter-orbital shuttles” that Arthur C. Clarke advocated (first for LEO to GEO trips, for servicing geosynchronous satellites), and:

      As observatory and other types of spacecraft positioned at (or orbiting around, in halo orbits) the Sun-Earth and Earth-Moon Lagrangian points become more popular (and more expensive), their (current) inaccessibility for servicing and upgrades will become increasingly frustrating. Just as an effective and economically viable maritime and coastal river transportation infrastructure requires tugboats, so does such a space transportation infrastructure need space tugs.

      • Jim Baerg May 3, 2018, 21:15

        I keep thinking an actual good use for a space station, like the ISS or a new one made from Bigelow’s modules, would be to have humans assemble or at least check out a large spacecraft like the James Webb Telescope in LEO & then send it to where ever in space it is needed with an ion drive.

        • ljk May 4, 2018, 10:51

          JWST has so many complicated procedures that it must accomplish automatically in order to work I am both deeply impressed and very concerned with its design.

          That NASA does not have an official plan (or spaceship) to fix and repair any problems the astronomical satellite may have once it is in space is very troubling, especially since they are already encountering issues before the robotic observatory has even left Earth:

          http://spacenews.com/jwst-suffers-new-problem-during-spacecraft-testing/

          Perhaps SpaceX should start ramping up its manned Dragon vessel for a JWST rescue mission. Imagine if there had been no access to HST after all its problems, which were not discovered until after it had been delivered into Earth orbit.

          Yes, I know there is Orion, but it will not be ready until 2022 at the earliest. I also doubt the Russians can or will help not only for technical reasons but politically.

          If you are going to spend over 8 billion dollars on a satellite and years in development, you should have a space rescue/repair plan already in place.

          • J. Jason Wentworth May 5, 2018, 10:24

            The expensive loss of the OAO-1 (Orbiting Astronomical Observatory-1) satellite, which is still in orbit today (774 x 783 km, 35.0°), just hours after it had been injected into a perfect orbit on April 8, 1966, was a heart-breaking blow. It was one of the most complex satellites yet developed, with 440,000 separate parts, 30 miles of wiring, and a battery of telescopes (the largest having an aperture of 16 inches), and:

            With OAO-1, the United States had gambled enough to build half a dozen Palomar Mountain telescopes, and had lost–due to a power supply problem that could have been fixed by a technician on the spot with a screwdriver. Given that long-dead satellites have come back to life decades later (such as AMSAT-OSCAR 7 and LES 1 [Lincoln Experimental Satellite 1]), while others–such as LES 8 and 9–have operated for decades past their expected lifetimes, it isn’t impossible that OAO-1 (whose mission was terminated after 20 orbits without activating its experiments) could be repaired and put in service, if a mission was launched to do so. Also:

            This costly loss prompted Arthur C. Clarke to more strongly advocate for space station-based, low-powered inter-orbital shuttles (what we call space tugs today). SpaceX’s Dragon V2 with trunk could function as a low/medium orbit tug, while–with added consumables in the trunk–it could serve as a deep-space tug for servicing spacecraft like the JWST and SOHO, out at the Sun-Earth L1 point nearly a million miles away. (Missions that far out would also overcome a psychological barrier, enabling gradual manned forays into interplanetary space; such missions could also visit Earth’s temporarily-captured asteroidal moons [statistically, there’s always one or two–they’re just a few meters across], which orbit a million or more miles away from the Earth.)

        • J. Jason Wentworth May 4, 2018, 14:45

          That concept of “human-tended automated spacecraft” (microgravity factories, space observatories, etc.) was advocated as the Space Shuttle program began to gel in the early 1970s. Such spacecraft would contain one or more pressurized modules stocked with space parts, test equipment and consoles, and tools, which would enable occasionally-visiting astronauts to do maintenance, upgrades, and replenishment of expendables in the convenience of shirt-sleeves comfort. Bigelow’s expandable habitat modules might be perfect for such applications.

          • J. Jason Wentworth May 4, 2018, 14:46

            Argh–I meant “spare parts,” not “space parts.”

  • Robert May 3, 2018, 12:35

    The concept of self assembly and related topics was discussed in the 1980 NASA/ASEE summer study Advanced Automation for Space Missions edited by Freitas and Gilbreath. See chapter five.

    https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19830007077.pdf

    My two cents worth is in the form of a concept. Can the solar sail material, the thin metalized foil, be stretched on a frame to make a very light and extremely large mirror surface. Yes, the reflection of the foil is less than optical quality mirrors but the immensity of the size one could make out of small stretched segments may more than make up for that. I’ve seen such material stretched into adequate solar mirrors for solar energy applications. I’ve seen paraboloid surfaces made with stretched metalized film. In this scenario, the mirror might also be the sunshade. One could test the concept by making a telescope here on earth.

    • Ron S. May 4, 2018, 13:08

      Considering that the mirror accuracy over its entire surface needs to be a small fraction of a wavelength I don’t see how this is possible with a thin film. Even if it could be somehow accomplished in isolation from the environment that would count for little. Solar energy mirrors are not comparable since these “photon buckets” do not form images.

  • Brett Bellmore May 5, 2018, 10:41

    I’d like to see some work on making smaller mirrors, on the order of 1 meter, fly independently with sufficient positional stability to form a larger mirror by flocking. This would allow a very large mirror to be assembled by increments, without any disturbances propagating through a physical structure.

    You could have a large sail/mirror shadowing the array, a selection of sensors flying into and out of the focal point, and keep everything located by a reference system using vacuum UV interfereometry.

  • Robert May 7, 2018, 14:53

    Still, I wonder if between specially designed thin films and support structures a decent compromise might work. At least the concept should be explored fully before final rejection.

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