Could we carve a large radio dish in the Antarctic ice?

  • Could we carve a large radio dish in the Antarctic ice that could replace the Arecibo Observatory? Could this work, and what would be some potential limitations?


    I think there would be a small limit on the amount of sky observed with it being on one of the poles.

    Could you please add more details?

    Seems easier to carve a very large telescope in a self supporting material. Also there is very little light pollution

    @fasterthanlight like what? If a question is clear then details are not necessary. There is no rule that questions must be at least X in length, It looks fine to me.

    Would be a good one for Worldbuilding, maybe?

    @BrianDrake with +7/-1 voting it seems that people felt that in this particular case the question was of a nature where a bit of research just for the sake of adding "evidence of research" just wasn't worth it or necessary. SE has very few *absolute* rules; sometimes a well-received question can simply be the title. It doesn't happen often but it does happen, and there's no rule against it.

    Surely the question is about making the dish itself out of ice? not building something on top of the ice? If so I would be worred about the heating effect of the radio waves that are being captured.

  • uhoh

    uhoh Correct answer

    one year ago

    Great question!


    There are many open and active antarctic permanent bases and several antarctic astronomical observatories. There are even major large projects that involve substantial drilling and removal of ice such as the IceCube Neutrino Observatory. The biggest construction project is probably the Amundsen–Scott South Pole Station.


    This is certainly a valid idea to consider and should not be dismissed out of hand by "Antarctica is hard".


    There's no bedrock on which to affix your dish; it will be floating in creeping ice and subject to drifting snow.


    From Amundsen–Scott South Pole Station:



    The new station included a modular design, to accommodate rises in population, and an adjustable elevation to prevent it from being buried in snow. Since roughly 20 centimetres (8 in) of snow accumulates every year without ever thawing the building's designers included rounded corners and edges around the structure to help reduce snow drifts.



    Basically I think @PeterErwin's comment summarizes the problem nicely. For more details see their link and also Challenges That Face South Pole Architecture which mentions the following:


    WIND



    • Constant winds result in snow pile-up on buildings.

    • The new station faces into the wind, and is airfoil-shaped.

    • The airfoil forces air into a compressed space where it accelerates.

    • The fast wind scours out built-up snow.

    • Years later, if snow still builds up, the building can be lifted two more
      stories on its columns.


    ICE FLOW



    • The station sits atop a 2-mile deep layer of ice.

    • Each year, the geographic South Pole is marked.

    • Ice (cold water), slowly drips down to the ocean with gravity.

    • The trail of yearly South Pole markers shows that the ice moves 33 feet per year.


    ICE CREEP



    • The weight of the building also causes the ice to move locally.

    • Ice compresses and shifts away from sources of pressure.

    • Resulting variable rates of sinking make keeping the building level a challenge.

    • Architectural elements built into the design will help meet that challenge


    Basically everything is built up on stilts above the surface. This lets wind blow under things and prevents snow drifting which would quickly burry a surface structure.


    The South Pole Telescope consisting of a 10 meter point-able dish is also built on an elevated platform sitting on stilts to prevent drifting (see below).


    You could propose heating the entire dish to de-ice and de-snow it regularly, and pumping out the melt water, but power is at a premium at the South Pole. Fuel is flown in on airplanes during a short summer season and burned in electrical generators for power. Building something that requires electrical power to constantly melt drifting snow has serious practical hurdles.


    Radio telescope dishes built into fixed surface depressions


    At least two very large, single dish telescopes have been built into naturally occurring depressions in local rock: Arecibo at 18.3° N and FAST at 25.7° N latitudes. Both telescope designs have large primary focus structures (small buildings where people can work) suspended high above the ground at the primary focus of the dish, and in order to view the celestial equator and to track objects as the Earth rotates, moveable cables suspended from very tall towers were designed allow these structures to move around by about in two directions by roughly +/-19° and +/-26°.


    For more on that see this answer to Is there an advantage to the equatorial region of the far side of the moon for a radio telescope or would any crater on the far side work?


    Arecibo succumbed to deterioration of its cables caused by environmental factors and fell down.



    Maintaining these kinds of necessary tall structures in the high winds and snow storms at the South Pole would be quite a challenge as well.




    Architectural challenges to a South Pole Station Architectural challenges to a South Pole Station


    Sources: nsf.gov news and South Pole Station Destination Alpha


    Architectural challenges to a South Pole Station


    Source: nsf.gov news


    South Pole Telescope Arecibo dish and focal plane structure


    Sources left and right


    South pole telescope during polar night


    Source


    enter image description here enter image description here


    Sources for both: Antarctic Bases and Buildings - 3 Building at The South Pole via @PeterErwin's comment.


    left: "The South Pole radio telescope, the very clear and dry air at the pole make it the best place on earth to have a space telescope.
    Photo Christopher Michel from San Francisco Creative Commons Attribution 2 Generic license" right: "In the 6 months of night time of the South Polar winter with the Aurora Australis overhead, July 2008 Photo: Patrick Cullis - National Science Foundation"


    Minor nitpick: "drilling" the holes for the IceCube detector strings didn't involve much "removal of ice", since it was done by *melting* vertical tunnels with high-pressure hot water, then lowering the detector strings into the holes before the water froze. (Otherwise, very nice answer!)

    @PeterErwin That's a good point! For a few seconds I wondered playfully if the dish could be frozen in ice; backfill it and smooth the top. For the lower RF frequencies (pure) ice is pretty transparent. Of course one would have to go shovel off the snow every day and then run a Zamboni over it then flood it with water and let it freeze flat again (with a dome to protect from the wind). But it might be somewhat pointable. I thought about it for less time than it took to write this, but it was fun.

    @PeterErwin And then there is the Fresnel loss at the top surface; from here $n \approx 5$ at 1 cm and goes up to nearly 10 at longer wavelengths. So in that case maybe ice radio lenses would work well as long as they have a micro-patterned antireflection texturing on each surface.

    A *"space telescope"*? It is not in space. Do you mean *"radio telescope"*?

    Re *"very clear and dry air"*: Why would that matter for a radio telescope? Some microwave band? What frequencies? Is elevation also a factor or not (smaller air mass)? Can you elaborate a little bit in your answer?

    @PeterMortensen those quotation marks help to indicate that those are quoted from the caption under the image in the linked source. They're not my words. But I can say that for short wavelengths you need very dry air, that's why ALMA is at the Atacama for example. And "the best place on earth to have a space telescope" is a bit of humor; if you have a telescope that you'd like to put in space but can't afford it, then I guess they are suggesting that this "best place on Earth" is the next-best thing. ˀ

    @PeterMortensen you might consider posting these as a new question, that would provide more space and allow several people to add answers.

    "There's no bedrock" is not entirely exact. There is one, it's just buried under a loooooot of snow and ice which moves (so attaching to it would probably not be a good idea, if it were even possible in the first place).

    @jcaron If I ask "Where's the coffee?" and someone says "Oh, there is no coffee." Do I then accuse them of eliminating all traces of coffee from the planet? Or do I know that there is an implicit assumption that this refers to the local proximity or readily available space only? If one go to Antarctica and ask "Where is the bedrock? Can you show me some bedrock I can attach this antenna to?" and someone replies "There is no bedrock." one will not think that the Earth as disappeared. One will naturally understand the unspoken but implicit "...that you can attach your antenna to."

    @uhoh Perhaps "the bedrock is inaccessible" would be clearer.

    @AndrewMorton you are welcome to make any reasonable edit to any post at any time. But as I've just demonstrated your proposed alternate interpretation is not reasonable. The meaning is *clear* to anyone.

    @uhoh: Speaking only for myself, I didn't understand what "There's no bedrock" meant until I got to "The station sits atop a 2-mile deep layer of ice" (which I hadn't known until now), and even then I wasn't 100% sure until I saw jcaron's comment and your reply. To you it may seem obvious that there's bedrock under every point on Earth, but given how astronomers define "metal", not all of us are so confident that we can guess how they define "bedrock"!

    @ruakh we're talking about a *section heading*, not even a sentence. A section heading should entice the reader to read further, not give the false impression that all's been explained and so the content below it can be skipped. For those who find it curious-sounding and not intuitive (and I think it will be few) then all the better that they go ahead and read the section below the heading. It's done it's intended job nicely. But as an answer to a question about *carving a large radio dish in the Antarctic ice* I think even astronomers should understand what "there is no bedrock" means.

    @ruakh nonetheless, the heading has been adjusted

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Content dated before 7/24/2021 11:53 AM