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3 hours ago by loudmax

Youtube channel Launch Pad Astronomy discussed some of the challenges for a lunar telescope: https://www.youtube.com/watch?v=QKJY7gH2n9I

One of the problems is moon dust. There's a lot of it. If you build a big parabolic dish on the moon, you'll need some way to either remove dust or prevent it from accumulating in the first place.

Another issue is the change in temperature. Without an atmosphere stabilize the temperature, day times become extremely hot and night times are extremely cold. This means that you need to engineer something that can withstand very significant swings in temperature over the course of the lunar day.

Challenges like these highlight the benefit of placing James Webb space telescope at Lagrange Point L2. The temperature remains constant and there's far less interplanetary dust than moon dust.

That isn't to say that we shouldn't build a lunar telescope, but we should have a clear understanding of the difficulties.

2 hours ago by goodcanadian

One of the problems is moon dust.

Well, yes, but at radio wavelengths, it would take an awful lot of dust to significantly impact the performance of the telescope. My gut says centuries worth if not millennia. And the article is proposing a wire mesh primary reflector, so dust will mostly just fall through.

Another issue is the change in temperature.

Similar answer to the above. The wire mesh reflector would expand and contract. I suspect the main impact would be to change the location of the focal point. We can handle that by moving the receiver up and down similar to what we do with telescopes on Earth.

2 hours ago by lmilcin

I think the wire mesh expansion and contraction is not such a huge issue for a number of reasons.

First of all, you will probably want to make observations when not illuminated by the Sun, so that the receiver is shielded by the mass of the Moon from the Sun interference.

Second, on the Moon there is no weather. You basically have only two conditions, it either is illuminated by the full sun or it is not (with some time while it is partly illuminated, but most of the time is just basically two temperatures). During night the temperature will be rather predictable for the entire length of the night.

So I think the simplest solution would be to just use the telescope for about 50% of the time when its geometry is stable and is shielded from the Sun.

It is not such a huge issue, the basic fact of this kind of telescope is that you can't steer it so you still rely on orbital mechanics of the body on which you place to move the part of the sky which it listens to.

In this case even restricting to 50% of the time does not change much as it still requires 1 whole year to make observation of entire part of the sky it can observe.

2 hours ago by eterevsky

> One of the problems is moon dust. There's a lot of it. If you build a big parabolic dish on the moon, you'll need some way to either remove dust or prevent it from accumulating in the first place.

Moon doesn't have atmosphere, so once you've built the dish and cleaned it, it should stay clean unless a meteorite strikes nearby.

20 minutes ago by knappe

One my favorite quotes from one of my astronomy professors is: "Everything has an atmosphere, no matter how tenuous."

This is a reminder that he used to make sure we checked our assumptions and always considered constantly changing conditions.

2 hours ago by rtkwe

Solar winds can also kick up moon dust. It would be a long slow process though and I think the reflector would still work under a thin layer of dust. By the time it’s a problem we’ll hopefully be there in person to either dust it off or build a bigger better one.

2 hours ago by adamcharnock

AFAIK, these telescopes produce a lot of data. Do we send this data back to Earth, or keep it on the moon and work on it remotely? Do we have the bandwidth to send it back to Earth? I’m really interested to know how much bandwidth can be achieved with an Earth-Moon link.

an hour ago by markbnine

LROC, which may be the closest we have in volume to a lunar telescope, sends its data back to Earth. http://lroc.sese.asu.edu/about

LROC is one of seven instruments on board LRO. Together, these instruments have a downlink allocation of 310 Gbits per Ka band pass and up to 4 passes per day. That translates into 155 GBytes per day of data or 56,575 GBytes per year (55 TBytes). These data are processed by each respective instrument's Science Operation Center (SOC) with the final products being delivered to the NASA Planetary Data System (PDS).

12 minutes ago by mciancia

If someone wonders, 155GB per day is 14.35Mb/s on average

an hour ago by adamcharnock

That’s a great answer, thank you. And that’s actually a lot more link capacity than I expected.

For anyone reading, Google states that the aka band is between 26.5 GHz and 40 GHz.

2 days ago by iseewhatyousaw

With the Artemis Program hopefully establishing a permanent lunar presence, it'll be interesting to see what massive radio telescope arrays will be planned and built in the decades to come.

The one thing I do wonder about is if building such telescopes will somehow restrict the amount/type of human activity that can take place on the far-side of the moon without it also impacting radio astronomy?

7 hours ago by TeMPOraL

If my understanding of physics is correct (and if it isn't, I'd appreciate a correction because this would be some fundamental problem), if they stuck the antennas in a crater that's opaque to most radio frequencies, and make a wall around the edges - making sure no point in the (extended) inner surface can see anything else other than the inner surface and the sky, then there shouldn't be a problem with radio interference.

Radio waves are light, and to a good approximation, radio emitters are like lightbulbs. On Earth, we have a problem because atmosphere scatters radiation. On the Moon, if you can't see the radio source directly or through a set of reflections, its signal won't get to you, period. So if you stick the antennas at the bottom of a well, they should not get any interference even if there's plenty of human activity nearby.

One problem I see is that human activity near the telescopes could create dust clouds, and those would definitely scatter radiation - and in low gravity, it could take some time for them to settle. I imagine it would make sense to prohibit rocket launches and construction work involving explosives in the vicinity of the telescopes.

EDIT: I'm looking at the picture in the TFA:


The crater shown there is already the kind of well I'm describing - its edges go above the nearby surface, and at least on the diagram, at no point the inner edge can see the rest of the Moon's surface.

7 hours ago by versteegen

Not quite, radio waves can diffract around obstacles/edges, and lower-frequency waves apparently do this more efficiently. https://en.wikipedia.org/wiki/Ground_wave#Radio_propagation


Edit: It seems that diffraction around edges and electromagnetic ground waves are two quite different phenomena. (A third separate effect being a refractive index vertical gradient in the atmosphere causing diffraction, acting as a waveguide.) EM ground waves require that the ground is partially conductive, which the Earth is, but I suspect the Moon isn't particularly because it's dry. Still, diffraction will occur.

Edit2: A better link for diffraction: https://en.wikipedia.org/wiki/Radio_propagation#Diffraction

"However, the angle cannot be too sharp or the signal will not diffract. ... Lower frequencies diffract around large smooth obstacles such as hills more easily."

2 hours ago by rtkwe

Fortunately we can control our intentional emissions really well and could test for unintentional ones, most intentional communications will be in the higher bands anyways because it's higher bandwidth, the antennas are more manageable, and it's the standard currently anyways.

7 hours ago by TeMPOraL

Thank you! That's the glaring hole in my knowledge I was hoping someone would point out!

(Also I suppose this means I should turn in my HAM license...)

2 hours ago by kadoban

I believe that even despite the low gravity of the moon, dust settles out quite quickly. There's just nothing to stop it from free-fall, nothing to push against or mix with.

7 hours ago by tjmc

Despite the low gravity, the complete lack of atmosphere would allow the dust to settle as fast as if you dropped a brick from the same height.

7 hours ago by TeMPOraL

Right. I'm mostly worried about dust reaching near-escape velocities, allowing it to take its sweet time as it falls back down. I'd have to do some math to see if this is an actual problem - it might be that it's very hard to create such a cloud.

6 hours ago by SiempreViernes

Satellites overflying would be an obvious problem...

an hour ago by rtkwe

Those satellites would be operating in higher frequency bands than most radio telescopes care about. If it does turn out to be an issue they can also be programmed to stop transmitting when they’re ‘in view’ of the telescope.

6 hours ago by rbanffy

A great reason to build an array on Pluto.

9 hours ago by femto

Maybe the convention should be that all permanent settlements go on the side of the Moon closest to Earth? That way Moon bases get 24/7 communications with Earth and are sited on the side of the Moon that gets all the electromagnetic noise from Earth. The quiet side of the Moon could be an "EM sanctuary" reserved for research.

Worth a try, even if the agreement falls apart with the first mineral discovery on the quiet side?

10 hours ago by KZerda

Depends on the radio frequencies used. This dish is designed to look at relatively low frequencies -- 6mhz to 30mhz. So I imagine that any potential new far-moon missions would probably just avoid those frequencies. These frequencies wouldn't be as useful as they are on earth anyways, because there's relatively low bandwidth, and there's no useful ionosphere to bounce signals are for long-range propogation like there is on earth.


However, on the other hand, there could potentially be a lot of unintended low-frequency broadcasters -- microchips, etc. So I imagine there would still be a need for hold-out zones, but they'd probably not be as impactful as there are on earth.

10 hours ago by lacker

You wouldn't want to put up cell towers near the radio telescopes. Green Bank has a 10 mile zone where radio activity is restricted, and on the moon you could probably get much more space dedicated to telescopes for a long time. But even if one day there starts to be some radio interference due to activity on the moon, the lack of atmosphere will probably always cause there to be orders of magnitude less interference, and there are some wavelengths that simply can't be observed from the earth because of atmospheric interference.

8 hours ago by garmaine

> and there are some wavelengths that simply can't be observed from the earth because of atmospheric interference.

Of particular relevance is the frequency associated with the transition from opaque plasma to neutral matter, which made interstellar space transparent. This coincides with the first stars, and is as close to the Big Bang as we can observe. Cosmologists are very interested in generating a detailed cosmic map at these frequencies, but they are unfortunately blocked by (1) the ionosphere of the Earth's atmosphere, and (2) subject to tons of radio interference. It's like right smack in the middle of the most commonly used frequency bands. Lunar far-side observatories are pretty much the best path towards making these measurements.

3 hours ago by rbanffy

How large would a lander need to be to still be able to make useful observations from a point on the far side? Or even the near side, as the noise would come from the Earth and a directional antenna can always look the other way. A 3m dish would fit on an LM-sized lander and that’s “relatively simple” tech.

6 hours ago by femto

Given the lack of weather and other disturbances, I wonder if it would work to spray a conductive layer directly onto the crater's interior surface, maybe using a hovering rocket with the conductive material injected into its exhaust? I gather craters are hyperbolic [1, 2], but maybe the middle portion is close enough to a parabola to focus waves onto a receiver?

It might not be very environmentally friendly though, as it would be difficult to remove in the future.

[1] https://pubmed.ncbi.nlm.nih.gov/29755255/

[2] https://pubmed.ncbi.nlm.nih.gov/17994980/

6 hours ago by iSnow

If I read this right, they want to do the whole wiremesh/DuAxi robot dance because the craters are not parabolic enough. They use them because they allow to build a parabola without ferrying thousands of tons of material to the moon but they are not suitable on their own.

6 hours ago by SiempreViernes

I expect craters are not very smooth surfaces at cm-scales, and just spraying something on top will not make it smooth on it's own.

11 hours ago by carabiner

Holy shit. Can some crazy tech billionaire just fund this thing as some branded vanity project? This looks fucking awesome.

11 hours ago by garyfirestorm

Did you mean can NASA do it? Yeah I think NASA should do it.

an hour ago by dylan604

I'm all about having the SR Hadden Lunar Radio if that's what it takes to get the thing. If NASA builds it, if ESA builds it, if JAXA builds it, I don't care. Private funding is not a new thing for getting telescopes built, but the private funders are not the ones doing the building. They just write the checks.

8 hours ago by ncmncm

If it's un-crewed, it should be brilliant.

Another pair of telescopes should be sited in Shackleton Crater, 21 km across, at the exact south pole of the moon. https://apod.nasa.gov/apod/ap110423.html

One of them would be a conventional radio telescope. The other, an infrared telescope.

The temperature within the crater is a nearly-constant 90K. You could power it with solar panels rotating on vertical axes posted at strategic points on the crater rim, that are almost always in sunlight.

The crater is so big that, for the infra scope, you could build it out of optically flat mirrors placed around the circumference.

The crater always points to the same spot in the sky, so you could get really, really long exposures. That you can't point it is OK, because there is so much to see if you are looking far enough away. At some distance and red-shift it would be an X-ray telescope, others an ultraviolet scope. Maybe a gamma-ray scope, at the extremum?

3 hours ago by travisporter

Bezos could save some face by investing in something like this after his recent legal antics.

9 hours ago by Evidlo

What's the advantage of doing this with a filled aperture vs using synthetic aperture with satellites?

9 hours ago by japanuspus

Signal strength. Synthetic aperture might match the spatial resolution of filled aperture, but signal strength still depends on collected area. For radars you can compensate by upping the transmitted power, not so for passive listening.

8 hours ago by eminemence

What is going to protect this from all those meteoroids,asteroids and cosmic rays?

7 hours ago by marcyb5st

For this approach I don't know. It's a wire mesh so I think it can resist some damage.

I read about other approaches that make me marvel at mankind's genius. For instance, on the moon you could slowly spin a pool of liquid Mercury to obtain a radio telescope that is basically immune from microimpacts. Not sure how it would work once the mercury freezes solid due to lack of sunlight, but I think it's such a beautiful (but maybe impractical) idea :).

6 hours ago by Ginden

> Not sure how it would work once the mercury freezes solid due to lack of sunlight, but I think it's such a beautiful (but maybe impractical) idea :).

Can't you heat it through induction heating? Vacuum is good isolation, so it won't lose heat too fast. Keeping whole pool above -30 °C probably won't require too much energy.

5 hours ago by marcyb5st

Maybe. I honestly don't know and just read about it quite a while ago and can't remember the details.

6 hours ago by iSnow

But mercury is a heavy metal. It must be prohibitively expensive to transfer the amount needed to the moon from earth.

5 hours ago by marcyb5st

Agreed, that's why I wrote maybe impractical. I just find it fascinating :)

6 hours ago by tiborsaas

Statistics :) The chance of a wire is hit by something is probably extremely low. Electronics working in space is also an understood problem so I don't think it's an issue.

7 hours ago by ComodoHacker

Probably the proposed wire-mesh design, it won't be a solid reflecting surface. Total exposed surface would be comparable to orbit telescopes.

8 hours ago by Out_of_Characte

Cosmic rays are a solved problem. at most you will run out of backup computers. asteroids, you just hope you'll not win the cosmic lottery of collisions.

6 hours ago by hutzlibu

Like we do on earth with the big ones.

But since there is no atmosphere stopping the small ones on the moon, who also can do damage: this likely will be a problem, because there are a lot of them over time.

So a laser shield might sound science fiction, but will maybe be necessary, for longtime operation?

Or is it possible to build some protective sphere, that does not hinder transmission too much?

11 hours ago by gpt5

How limiting is the fact that the telescope can’t be aimed, but is moving with the moons rotation?

Naively I’d assume that beyond the inability to aim it as a specific spot, it would also mean that we can’t do a long exposure of anything, as the image would get smeared with the moon’s movement.

an hour ago by adolph

Earth rotates at 1670 kilometers/hour, the Moon travels at 3,683 kilometers per hour, tidally locked to Earth so the telescope travels at that speed. However, the Moon has a lot further to travel so a more meaningful measure is change in angle over time. For the purpose of a "long exposure" the Moon would have a lot less smear.

Earth: 7.2921159 × 10−5 radians/second (sidereal, not including solar orbit, at equator)

Moon: 0.2.66169 × 10−5 radians/second (on average for its eliptical orbit)



10 hours ago by _Microft

The „Five-hundred Meter Aperture Spherical Telescope“ (FAST) can deform its wiremesh mirror to target different directions and to remove the spherical aberration issue by turning the surface shape into a paraboloid.

If that’s possible for a robotically constructed and maintained structure is more than questionable.


10 hours ago by Laremere

This is a limitation known to several radio telescopes. For example, the Arecibo telescope couldn't aim much until they added the arm in 1997. They could aim the telescope not by moving the dish, but by moving the focal point/receiver. This only works with spherical dishes, but it is an option.

9 hours ago by sennight

Arecibo was distance limited by the Earth's rotation speed, since radar returns had to make it back before the target shifted out of the telescopes steerability window. As the Moon is tidally locked - that long stare limitation remains.

an hour ago by rtkwe

That's just if you're doing active radar ranging to objects instead of passive radio observations which is most of what radio telescopes do anyways.

8 hours ago by ncmncm

Advantage is, the rotation rate will be 28x slower.

8 hours ago by undefined


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