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05 February 2021


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Barbara Ann

My first thought when looking at this was "why not just build it in space?". If you are going to go to all the trouble of packing it origami-like into a spacecraft and sending it to the moon only to deal with the tremendous difficulties of assembling it in a crater, surely simply expanding/assembling it in place in zero-G is easier. Space telescopes can be lighter & can be pointed in any direction too.

I have to wonder whether this is a NASA's boondoggle which has skipped the most important part of the feasibility study and settled on the Moon due to terrestrial thinking bias; i.e. assuming huge radio telescopes have to look like Arecibo. Shades of Space Shuttle's hugely expensive & complex air frame design vs. Musk's much simpler conception of a reusable spacecraft?

Didn't know Arecibo had been destroyed until I read the link in the article btw.

The Twisted Genius

Barbara Ann,

According to the presentation, placing the antenna inside the crater shields it from strong side radiation coming from our own galaxy as well as from Earth. It's akin to light pollution. That can't be done with a space antenna. I would think maintaining the shape of a 1 km antenna floating in space may also be problematic without sufficient structure. Gravity maintains the structure of the crater antenna.

I would like to see a 1 km solar sail. The Planetary Society's Light Sail 2 is still going, but that's only 32 square meters.

Arecibo collapsed on 1 Dec 2020. There are several videos available on YouTube.


At 1000 meters it is more than three times the diameter of the former Arecibo Observatory. And it would be more than ten times Arecibo's area.

Low surface gravity of the moon will ease construction. But I am a bit leery of those wall-climbing DuAxel robots. And I wonder about the effect on the structure of temperature extremes on the moon: from plus 260 degrees Fahrenheit dipping to minus 280 when the sun goes down. Modern aluminum alloys can withstand that, but for how long with that constant heating and cooling?

Barbara Ann

Ah, that makes sense thanks. In that case I wish them luck, would love to be an engineer on the project.

The Twisted Genius


Those DuAxel robots are being tested on rocky slopes in the Mojave. What I don't yet understand is how the cables will be anchored around the rim of the crater. Will it need a bigger version of Curiosity's drill?





Thanks for that link to Curiosity drill holes. For sure a lunar radio telescope, even with low gravity, would need deeper and stronger anchors than the two-inch deep drill holes by curiosity. Could they do it with counterweights instead?

Wiki has opined some other potential problems for the telescope: fine lunar dust and solar flares.



Leith, the trick is that the dish will have very little mass so the forces the anchors will be very low. It can't weight that much just due the logistics of getting it there on a rocket. Think of the suspended cameras at a football game. The dish will be a conductive spiderweb. The anchors will probably be the robot's lander stages that get filled/buried with soil by the robots like large flower pots before they decent into the crate to pickup their cable.

Antenna deployment will be the hard part given how fragile it will be.


EE -

Thanks for the insight on anchoring. What effect do you think thermal strain might have? Or solar flares?


I would think that it would deform at sunset and sunrise while it was partially lit and partially in shadow. That would have the effect of putting it out of focus. Maybe a day every 14 days. RF is just like light, it's still a photon, just a way longer wavelength. I design electronics for lasers and optical equipment BTW.

A large conductor looks like the shorted secondary of a transformer when hit by a magnetic field. That's how induction cook-tops work and how the foil seals on food packages are heated. Assuming the "horn" was moved away from the focus when a storm was approaching and the dish was pointed at the sun the main risk is the "dish" over heating like the foil layer of CD in the microwave. Not my area of expertise, but I'd guess a field that powerful would trash the earth's electrical grid long before it melted the dish.

John Merryman

Having followed cosmology for over four decades, I would like to make a prediction of what will be found at some point, possibly by the James Webb. That the cosmic background radiation is not a relic of some primary event, but the light of ever further sources, redshifted down into the radio spectrum. That the universe is infinite.
It first occurred to me there were various basic misconceptions built into Big Bang Theory, back in 89, reading Hawking's, A Brief History of Time, where he made the point that for the universe to be as stable as it is, "Omega" has to be very close to one. What this means is the expansion and gravity have to basically be inversely proportional. Which would seem to totally invalidate the assumption of the entire universe expanding, if the observed expansion is effectively balanced by gravity. In essence it would be Einstein's original "Cosmological Constant." The force balancing out gravity, to maintain a stable universe.
To use the ball on a rubber sheet analogy of gravity, consider that if the sheet were over water, where it would be pressed down by the ball, would cause empty areas of the sheet to be pushed up equally. Such that what is measured as curving inward, into the vortices of galaxies, is balanced by equivalent expansion between them.
Consider that BBT cannot be falsified, as whenever there is a gap between prediction and observation, some enormous new force of nature is proposed and everyone runs off looking for it. What if your accountant could just write in a figure and call it "dark money," whenever he finds a gap in the books?
Before Inflation, Dark Matter and Dark Energy, the original patch was when they realized that as redshift increases proportional to distance in all directions, it creates the effect that we appear to be at the center of this expansion. So the theory was changed from an expansion in space, to an expansion of space, because Spacetime!
Which totally ignores the central premise of SR, that the speed of light is constant in any frame. If intergalactic light is being redshifted, it isn't constant to intergalactic space. More lightyears, not expanded lightyears. The expansion is still being denominated in the metric of the speed of light. As Einstein said, space is what you measure with a ruler and the ruler in this theory remains the speed of light, not the redshifted spectrum of the same light.
Multispectrum light "packets" do redshift over distance, as the higher frequencies dissipate faster than lower ones, but this would mean we are sampling a wave front, not observing individual photons traveling billions of years and that really opens a Pandoras Box, as to the indivisibility of quanta. The information we can extract from the energy, is not the same as the energy.
Safe to say, this will get you banned in any academic physics discussion, since it's all about the math, not the logic, but just putting the prediction out there.
Epicycles were brilliant math, as a description of our view of the cosmos, but the crystalline spheres were lousy physics, as explanation. Beware trusting your models.

The Twisted Genius

John Merryman,

I can't say I understand that at all, except that there remains many questions about the universe and its origins. If it takes math, I may never find out. I gutted my way through a year of calculus convinced it was a cruel hoax foist upon us unwashed non-STEM students. Happily I found a book from 1914 for us unwashed that may reveal the calculus in terms even we can understand. Thanks to Chris Hadfield for the link.


Barbara Ann


Re calculus & ventures on the moon; blame the plague:

At the beginning of 1665, when Isaac Newton was twenty-three years old, he returned to his native village for a period of two years to escape the plague that had closed down Cambridge University. He later wrote that these years were his most fruitful and creative, and recalls in particular that in 1666 he developed the integral calculus, experimentally verified the composite nature of light, and refined his gravitational theory to the point that he was able to satisfy himself through calculation that the earth's gravity holds the moon in orbit
17th century lockdowns were evidently highly productive for some. No Netflix to distract from the serious business of inventing a whole new branch of mathematics - just so you can do the calculations on your epoch-defining theories about how the universe works.


John Merryman

TTG, (The Twisted Genius)

I was never very good with math, as most of my life required reacting instinctively, in order not to get hurt. Then thinking it through afterwards.
As I see it, reality is that cycle of emergence and consolidation. It is just that our minds can only see the clarity of the complete form, rather than the dynamic processes leading up to it. so we tend to work backwards, but mostly by breaking the form into all its varied components, rather than the processes that generated them. To wit, if we reduce a body down to its most stable parts, we have the skeleton, not the egg.
Math is all about the stable structures and relationships. Like Plato's ideal forms, it is assuming some essential shape as the basis.
So think of math as the map, rather than the territory.
For instance, is space really three dimensional, or is that a mapping device, like longitude, latitude and altitude? If we use two different coordinate systems to map the same space, would that make it six dimensional?
Look at it from a political perspective, in terms of different peoples applying different maps to the same territory, like Israelis and Palestinians, backed by different narrative histories, aka the time dimension.
One point I keep trying to make to the book minded, is that time is not some narrative we read from start to finish, past to future, but change, turning future to past. Tomorrow becomes yesterday, because the earth turns. There is no literal dimension of time, because the past is consumed by the present, to inform and drive it. Causality and conservation of energy. Cause becomes effect.
Energy is "conserved," because it is the present, not some dimensionless point between past and future. So the energy goes past to future, while the patterns generated go future to past.
The energy drives the wave, while the fluctuations rise and fall.
Consciousness goes past to future, while emotions and thoughts go future to past.
Yet it's the digestive, respiratory and circulatory systems processing the energy driving us, while the central nervous system sorts the information. Motor and steering.
So time is an effect and measure of activity, similar to temperature, pressure, color, sounds. Time is frequency, events are amplitude.
Ideal gas laws correlate volume with temperature and pressure, but we don't call them the 5th and 6th dimensions of space, because they are only foundational to our emotions, bodily functions and environment, not the sequence of thought we require as mobile organisms, to navigate.
I could go on, but this, if you are willing to mentally digest it, is a small example of how conceptually primitive we still remain.


If you build it in space, you could point it anywhere in the universe anytime you want, this would be a huge limit on the moon.

Can't wait for October and the James Web, potential is incredible.

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