Hypertelescope capable of direct high-resolution imaging with a high limiting magnitude have been built and tested on Earth. The Hypertelescope group have proposed giant telescopes 10-25 kilometers across in lunar impact craters.
Many small mirrors can be dilutely arrayed in a lunar impact crater spanning 10 to 25km.
The light from two Keck telescopes were combined into an 85-meter (279 ft) baseline, near infrared, optical interferometer. This long baseline gave the interferometer an effective angular resolution of 5 milliarcseconds (mas) at 2.2 µm, and 24 mas at 10 µm. Several back-end instruments allowed the interferometer to operate in a variety of modes, operating in H, K, and L-band near infrared, as well as nulling interferometry. As of mid-2012 the Keck Interferometer has been discontinued for lack of funding.
The imaging resolution for giant moon telescopes with 25 kilometer and even several hundred kilometer wide hypertelescope arrays expected can reach 100 nano-arcseconds on the Moon. This would 50,000 times better resolution than the Keck interferometer. The moon space telescopes would not have to look through atmosphere.
There are 6,972 moon craters greater than 20 km (12 mi) in diameter.
Nested Lunar Hypertelescope (NLH) with cable-suspended focal optics
The “Ubaye hypertelescope” terrestrial prototype is a fixed-mirror array, nested in a deep valley. Its focal optics is suspended from a single crossing cable, and 6 oblique tethers actuated by small winches control its position and attitude while it tracks the focal image of the observed star. It does not require optical delay lines, and may thus have hundreds of sub-apertures, a significant advantage compared to interferometers such as the VLTI.
The experience gained in a decade of testing suggests that it can be replicated in a lunar impact crater. If and when a manned lunar station becomes installed. A fully robotic construction and operation on the Moon would be possible.
There are optical interferometer arrays that combine the light of several telescopes. The Magdalena Ridge Optical Interferometer (MROI) is an optical and near infrared interferometer under construction at MRO. When the MROI is completed, it will have ten 1.4 m (55 in) telescopes located on three 340 meters (1,120 ft) arms. Each arm will have nine stations where the telescopes can be positioned, and one telescope can be positioned at the center. This array would combine light spread across 600 meter wide baselines.
And a larger version, modified for a flat lunar site and spanning up to several hundred kilometers can be later built if needed for a higher resolution and limiting magnitude.
Concept for a Larger and Flat Lunar Hypertelescope (LFLH)
For a large array, nearly flat at the scale of several hundred kilometers, optical delay lines are needed. The optical delay lines needed with a flat array of mirrors, coplanar with the combined focus and science camera, can be achieved with extra flat mirrors, movable and arranged as a hierarchy of deformable elliptical loci.
A first prototype of Hypertelescope type “Carlina” is currently under study in France in the Ubaye Valley in the Alps of Haute Provence. When it is completed, it will be 200 m in diameter. With 800 mirrors 15 centimeters, it will accumulate two times more of collecting area than the Hubble Space Telescope and a visual acuity almost one hundred times greater. It will be five times as powerful in resolution that the future EELT from 39 meter in diameter whose construction is scheduled for 2024 by ESO to the Chile.
The current prototype model will consist of a set of mirrors on the ground already totaling 57 metres in diameter that can in principle be enlarged to 200 meters. It will have a resolution of 0.5 millisecond of arc, or 80 times better than the Hubble space telescope when the effect of atmospheric turbulence will be corrected by an adaptive optics system.
The scientific team has estimated they can build a Hypertelescope extra large with a diameter of the order of 1 km and install it in the depression of a former impact crater, in the crater of a dormant volcano or some high valleys of the Andes or of the Himalayas.
In a final version, deployed in space, the Hypertelescope diameter may be extended at least eight to ten times more than the diameter of the Earth. This will produce sharp images of the surface of exoplanets.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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Geez Brian, you didn’t even reference your previous article in 2019, the previous crowdfunding effort for the terrestrial prototype, or the organization doing it?
https://www.nextbigfuture.com/2019/10/ground-based-hypertelescope-has-first-operational-components.html
https://www.kickstarter.com/projects/hypertelescope/hypertelescope-tomorrows-telescope-le-telescope-du/
https://hypertelescope.org/hypertelescope-en/
There are loads of articles I have written on space telescopes, hypertelescopes and gravitational lensing. I will write a follow up on this with goat Guys comments and other follow up.
Instead of spraying….perhaps the feed horn tower could be part of a pendulum system that could give a more even flow.
First they need to make it work for ordinary 30-40 m class Earth based telescopes. Even with them they have problems and delays are huge.
I seem to recall reading somewhere (and a few decades ago) that a really big space-based array might be capable of “seeing” things down to a level of 50 meters wide on exoplanets (although they probably called them “extra-solar” worlds back then).
Not sure if that’s doable or not, especially without moving way further out and using gravitic lensing.
“Hypertelescope diameter may be extended at least eight to ten times more than the diameter of the Earth. This will produce sharp images of the surface of exoplanets.”
A telescope with an appetite 10× the diameter of Earth would have a Dawes’ limit of 0.9 nanoarcseconds. That would mean the apparent diameter of a 1 AU object at 1 billion parsecs. Stellar parallax of intergalactic objects is now possible.
Must be more useful to have such telescopes hanging in space so they can be pointed to targets in all directions.
Or, is it easier to send many small telescopes out to solar gravity lens points?
As per previous articles on NBF, the resolution of a SGL-telescope will be in the 0.5 nano arcsec ballpark.
I suppose interferometers can have a ‘resolution’ slightly higher than the Raleigh’s limit formula. A bit. Using just the numbers BOLD highlighted about the Keck interferometer, 85 m baseline and 2.2×10⁻⁶ m wavelength:
AR = 1.22λ/D
AR = (1.22 × 2.2×10⁻⁶) ÷ 85
AR = 3.16×10⁻⁸ radians
AR = (…) ÷ 2π • ( 360° × 60 min × 60 sec × 1000 milliarcsec/sec )
AR = 6.51 milliarcsec
6.51 being somewhat larger (less resolving) than the quoted 5 mas. Comes more in line if the 85 m baseline is added with the 10 m diameters of each of Keck’s telescopes (comes down to 5.61 mas). Even more likely, is that the ‘resolution’ of interferometers is somewhat better technically than straight optical imaging mirrors. You know, convolution, edge interpolation, all that.
So … it is kind of a relief: the basic physics ‘checks out’, giving confidence that the OTHER projections might also be similarly evaluated. Let’s see.
10,000 m (10 km) dia, 2.2×10⁻⁶ λ = 0.055 mas or 55,000 nanoarcsec
25,000 m (25 km) dia, 2.2×10⁻⁶ λ = 0.022 mas or 22,000 nanoarcsec
And for that ‘could be hundreds of kilometers’ bit:
250,000 m (250 km) dia, 550×10⁻⁹ λ = 0.000554 mas or 554 nanoarcsec
Note ^^ that I also changed wavelength to 550 nanometers, being the middle of the green part of the optical spectrum. CLEARLY no-where near 100 nano-arcsec. Clearly.
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ONE of the most annoying aspects of all synthetic aperture optical (or even RADAR!!!) systems is that the need to align the little imaging reflectors to within fractions-of-a-wavelength grows, and grows, and grows, the bigger the synthetic aperture itself.
Perspective: Setting aside for the moment the Keck interferometer, and just the actual Keck mirrors (10 m diameter each, consisting of 36 hexagonal 1.6 m sub-mirrors apiece too), The figuring (optical term for ‘precision of shape) of the actual paraboloids was better than ¹⁄₁₀₀th of a wäve. … because, at the actual focal point, wäve errors get multiplied by the square-root of diameter. (This is why small backyard hobbyist telescopes can easily ‘get away with’ quarter wäve optics. Square-root of diameter.)
Projecting to the 10 to 25 kilometer scale, the positioning accuracy would need to exceed ¹⁄₁₀₀₀₀ wäve across the whole synthetic aperture diameter!!! On good old Earth, we have wind, air, seismicity, heating/cooling, tides, position of Moon, and even movement of large equipment that affects the active correction going on at Keck. A lot is done to counteract these effects.
Positioning on the Moon — in a crater — doesn’t exactly alleviate this list.
Sure … no wind per se, precious little atmosphere. Yet, there’s still seismicity, there’s a LOT of heating/cooling at least on a 28.5 day cycle. There actually are ‘tides’ (every action has an equal-and-opposite reaction, so Earth tides are also Lunar tides), yada, yada. More critically on Luna as opposed to Earth, our precious synthetic aperture telescope would be literally bombarded 24–7 by, oh, you know: Solar wind (protons, helium ions), Interstellar particles (“low energy Cosmic rays”), Intergalactic denizens (High energy CRs). And the wavering magnetic field of Old Sol, along with unpredictable blasts of Coronal Mass Ejections. And X-Rays. Lots of X-Rays.
Now, I’m not saying really that it couldn’t be done. But it is pretty glib to project the magnificence of such a beast without trotting out the shortcomings that its developers will face.
Are these shortcomings ‘terminal’? Hmmm… maybe: the aggregate of influences (in my estimate) feel large enough to prevent imaging even a small fraction of the theoretical limit, calculated above. Thus then, what’s the point?
One might argue that ‘the point’ is that with massive light gathering, the very, very dim planets (compared to their overwhelmingly bright stars) still could reasonably imaged in a ‘science sense’. You know, not pretty pictures at the back of the 25 kilometer wide Polaroid camera, but rather, lots of juicy pixels of data, fed through spectrographs, polarizers, and other filters looking for signatures of life, and with sufficient density-of-observation that way more than ‘just a hint’ could be achieved. More like, “well, how about that, Planet Zorcon is TEAMING with critters and forests!”
That’d be something, if even the Polaroid picture ain’t so clear. Moreover, the enormous potential light gathering could in a way RELIEVE those crazy-precise positioning and local influence counteracting requirements. Video, taken at thousands of frames per second, could ‘stop action’ the quivering telescope mirrors, allowing their correction to be computed, frame by frame, mathematically. Solves most of the problem, and likely could deliver pretty Polaroids too. Certainly Astronomy and National Geographic front-cover quality images. After awhile.
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I think I am more fond of sending all this magic imaging stuff to hover in Space, free from planetary body influences. The same solar-wind and heating, and other problems need address. But the whole structure, as Webb has aptly demonstrated, is (un?)surprisingly stabile, drifting about in Space. Oh, sure, needed a humungous heat-shield to deflect Sol’s super-bright hot rays away, but this didn’t exactly break the bank, or the science budget.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
Yeah, I’m a fan of free space telescope arrays. No physical connection needed between the mirror segments, you can have each mirror segment flying freely, using something really low thrust and long term, like fission fragment thrusters.
I suppose that, if you’re using optical delay lines, you could at the same time track some really distant point source, like a star in another galaxy, to update the necessary delays in real time.
How does it scale on a phased array telescope?
Like you said, it might be easier to brute force solve the data with computer, rather than finesse it with mirrors.
You can also set up gravity wave detectors on the moon using crater rims. No need to supply vacuum or long metal tubes.
Moon dust is a huge problem. It is electrostatically charged and sticks to everything. It’s also super abraisive. That’s gonna cause problems for any moon based optical system and the larger the system, the more of a problem it will be.
Whats the advantage in being on the moon? There are still some moonquakes, and still some atmosphere. A trivial amount, but still relevant at nano-meter precision. Just leave it hanging in space. If gravity is an advantage when assembling, then assemble it on the moon and launch it into space after.
When you get to that kind of size (8-10 Earth radii) you’d be talking about construction at the Jupiter-Sun L2, surely? That’s about the only thing you could hide behind to block out the Sun effectively at that size, even then you’re kind of limited to ~5 Earth radii.