Spinning Membrane Space Telescopes Would Be Big, Cheap and Easy

Robert Zubrin has proposed using rotating membranes to create Enormous Space Telescopes (ESTs) that can scale to over 1000 meter diameter or match current space telescopes for thousands of time lower cost. They would also not require the construction of large structures.

A demonstration cubesat EST could have an aperture larger than the Webb Space Telescope. The Webb Space Telescope has a 6.5-meter mirror and costs over $10 billion.

The EST employs a hoop to deploy a slack reflector membrane, such as solar sail material or radio dish. The EST is simultaneously rotated around its center and accelerated along its axis of rotation, the membrane will assume a parabolic shape, thereby creating a reflector for a very large aperture telescope. The EST reflector can be accelerated along its linear axis by tethering its deployment hoop to a tug spacecraft.

Linear acceleration will shape the telescope membrane into a parabola.

A little demonstration EST, with a total mass less than 20 kg, including optics that would be positioned along or suspended from the tether at the parabola focal point, would have four times the light gathering capacity of Webb (about thirty times that of Hubble), while costing on the order of 1/1000th as much.

A 50 kWe argon-ion drive spacecraft would weigh 1000 kilograms and could deploy a 130-meter diameter EST telescope. The 65-meter radius operational EST would have a mass of about 2000 kg.

A single SpaceX Super Heavy Starship could deploy a 120 ton EST space telescope with a diameter of 1000 meters.

If there was a multi-decade nuclear power source, then the 20 kilogram systems could be deployed to the gravititional lensing points twenty times further than Pluto.

Making lighter but highly capable cubesat space telescopes would make it more affordable to send thousands of these telescopes out to the gravitational lensing point. The gravity of the sun would then enhance the images by millions of times. A 1-meter space telescope at the gravitational lensing point would be like an 80-kilometer diameter regular space telescope. A 12-meter diameter space telescopes at the gravitational lensing point would be able to image like a regular 1000 kilometer space telescope.

SpaceX has mass produced krypton fed hall effect thrusters for the Starlink satellites.

The SpaceX Starlink satellites cost less than $1 million each.

We could get space telescopes out to the gravitational lens point using near term technology within 8 to 15 years using a slightshot around the sun.

The earlier plan would be first create the cubesat demos of the spinning membrane telescopes and then scaling up to the 1-kilometer space telescopes over the next 5 years. In 5-10 years, we would perfect long-duration nuclear power source cubesat EST and then send those out to the gravitational lens points. The gravitational lens telescopes would reach their observation points in the 2040s.

Other Attempts to Get a Breakthrough for Larger and Cheaper Telescopes

There have been attempts to make large ground based telescopes that are a hundred times cheaper than the traditional approach.

The Large Zenith Telescope (LZT) was a 6.0-meter diameter liquid-mirror telescope located in the University of British Columbia’s Malcolm Knapp Research Forest, about 70 km (43 mi) east from Vancouver, British Columbia, Canada. It was one of the largest optical telescopes in the world, but still quite inexpensive. The telescope was completed in the spring of 2003 and decommissioned by 2019. The Large Zenith Telescope is now decommissioned and all its liquid mercury stored for other projects.

This mirror was a test, built for $1 million, but it was not suitable for astronomy because of the test site’s weather. The University planned a larger 8-meter liquid-mirror telescope named ALPACA for astronomical use at an estimated first-light cost of $5 million, $3 million contingency, $10 million for the camera, $5 million for a spectrograph, and $0.3 million operating costs per year. A larger project is planned, called LAMA, with 66 individual 6.15-meter telescopes with a total collecting power equal to a 55-meter telescope, resolving power of a 70-meter scope.

SOURCES- Centauri Dreams, Robert Zubrin
Written by Brian Wang, Nextbigfuture.com

16 thoughts on “Spinning Membrane Space Telescopes Would Be Big, Cheap and Easy”

  1. Correct, you see an Einstein ring a few arc-seconds across. That's why you need a line of detectors spaced out, with each one gathering light from the ring, but not the Sun. So you need an occulting disk for each detector. Each detector produces one pixel of the final image.

  2. An additional complication is that the "image" doesn't actually appear as anything you'd see as an image. It's a *ring* around the sun representing light from any source exactly opposite you from the star, at an angle that moves out the further away from the sun you get. You have to combine the whole ring from one location for a given pixel, then move.

    A really large parabolic mirror would, I think hopelessly blur the image, because the rings would be overlapping. Though I suppose a really heroic effort at deconvolution might salvage things.

  3. Brian doesn't seem to understand how gravitational lensing works. The Sun's gravity brings the entire sky into a focal sphere. Any given point on that sphere only sees what is exactly opposite. If you want to image a planet orbiting Alpha Centauri, you need to position yourself opposite that star. The size of the image will be reduced by the ratio of the distance of the planet from the Sun to the distance you are observing from. In this case the ratio is 275,000 AU to ~800 AU, or 344:1.

    A planet the size of the Earth would then be projected 37 km across. If you want to image the whole planet, then what you want is a linear array of photodetectors as long as you can make it, and let the planet move through your field of view. Then move the array sideways, and repeat for as many strips as it takes to cover the whole thing.

    A 1 meter diameter telescope will only image 344 meters of the planet at a time.

  4. It would be possible to use the refraction of planetary atmospheres as a large primary lenses. Also a floating flotilla of mirrors could make a very large telescope. But my favorite idea would be to mass produce a set of large telescopes to observe the entire sky from space. Mass production to make them cheap, from $100 million to a $billion. Ten to twenty telescopes. Launch them using Starship. They would be used to look for changing phenomena across the universe.

  5. The spinning membrane would want to point gyroscopically in one direction, so a pull constantly trying to turn it to face away from the planet would distort the mirror.

  6. Ohh. Didn't think of the sun. Yes, you'd need to deal with that.

    And true, you can point DOWN too. So either a hubble or a spysat for your university. The astronomy and the geography/political science departments can bid on the direction.
    Or, just have one at each end of the cable…

    One issue with being above geosync is that the higher the orbit, the longer the cable needs to be for tidal forces to give any decent tension.

  7. They could definitely build the small demonstrator, see how it (and i.e. electrostatics) interacts in LEO or GEO with magnetic field, dust or impingement of solar particles. But you don't need really electrostatics, it could complicate interactions; Zubrin's design seems to be meant to be spin stabilized only. However, if you could do it purely electrostatically, and still keep the dish perfectly curved, you would need less fuel to change the attitude of the probe, as it no longer acts as a giant gyroscope. Test it.

  8. If Robert Zubrin's idea can made to work we might be observing features like some of the lakes in Minnesota. Maybe the method would involve the two oppositely facing parabolas pulled toward one another by electrostatic force, which was mentioned here last week.

  9. My thoughts exactly! They would always point toward, or away from the mass they orbited, but they would be so cheap you could make thousands of them.
    In polar orbits they would continually sweep the entire sky. Equatorial orbits would concentrate on the ecliptic. If you placed them above geosynchronous orbit there would be very little to interfere with them, and their slow skew would make observations easier.
    You'd need some mechanism to dump the light when pointing near the sun.

  10. It looks like 95% of the cost is the space tug needed to keep tension on the central cable.

    What if you just had a long cable, and had them in orbit around a planet/moon/star, with the cable running radially out from the gravitational centre. Now tidal forces will put tension in the cable and you only need the 20 kg telescope, without the 1000 kg tug.

    Being in orbit, it will scan the sky, not concentrate on a single spot, but that is probably more suited to a lower precision mirror anyway.

    Now you can have a 30-times-the-hubble space telescope launched for well within most university's budgets.

  11. One problem with these allegedly ultra-cheap telescopes is that you can't just point them at what you're interested in. The spinning mercury mirrors would only point to the zenith of where they're at. Any changes in the direction the spinning space membrane was being dragged towards would need a while for perturbations in the image to settle down. And the gravitational lens 'point' wouldn't be a point, but a sphere, or more likely, considering it has to slingshot off a planet to get there, a ring. Any point on that ring could only view the antipodal point to it on the other side of the sun, and a change of viewpoint would require the telescope to move distances comparable to those it crossed to get out there in the first place.

  12. Interesting. One of the most mind blowing things would be to see direct clear image of habitable exoplanet with its continents, oceans. So many people would get motivated to get a job in space related occupations and find a way to get there.

    With my amateur astronomical knowledge I still doubt it. With larger mirror you get more light which is great for deep sky at least ground. On the other hand, James Webb's mirrors need high degree of precision and accuracy, wouldn't that also be the case for spinning space membranes and that method? I doubt you can get such accuracy and without too large distortions. Perhaps you can do radio telescope, on the other hand I doubt if optical one? All right, you can use some kind of software control, so that everything is aligned perfectly, but still.

  13. 1/20th!. The fact that they can do so well on Earth with correcting mirror shapes means easy in Space, I bet.

  14. I had a similar idea for just putting a sliver of a mirror up (out of a stiff metal alloy) and just spin it around to create the entire optical surface. This way you could fit a 10-20 meter diameter telescope in a 11-15meter long 3-5m diameter fairing depending on what you use as the central mass a radial slice or diameter slice spins around. The secondary mirror would pop out after reaching destination orbit. In this digital age processing the collected light would not be an issue.

    Do you think the engineering issues would be surmountable?

  15. Cheap, big, easy, and incredibly unlikely to have 1/8 wavelength figures, let alone 1/2th.

    When you're focusing light to concentrate energy, you just need sort of right.

    When you're doing astronomy, you need the mirror surface to be accurate to a fractional wavelength of light.

    Now, in zero G you might achieve that with an actively controlled membrane mirror. Using continuous measurement and active electrostatic feedback, say.

    But just passively spinning up and accelerating a membrane? Fat chance.

Comments are closed.