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Equatorial Low Orbit Schmidt Cassegrain Sintering Satellite for Lunar Regolith

11/22/2020 4:54 PM

I have seen papers on heliostat and rover regolith sintering for lunar manufacturing. It struck me that a more bitmapped approach on a much grander scale could be very cost effective. A very large, zero G, long focal length telescope mirror mounted in an equatorial low orbit satellite could trace out paths on the surface with a high energy focused beam pass after pass without expending significant energy in movement. Two opposing mirrors much like a very long focal length schmidt cassegrain telescope with the smaller mirror obstructing the center of the light headed into the large mirror from the sun and with the axis of the two mirrors on a radius from the center of the moon would be focusing the sunlight on the surface for a significant distance on the current orbit bright side of the moon with no gross motor movements. Fine motor movements could be tasked with tracing the desired sintered path. Yes, the focus will be slightly off at the edges of the active area. Do coarser resolution plotting near the edges. Yes, you must shift the tilt of your smaller mirror slightly as you scan a line.

The active area being 3D printed would move around the moon as the sunlight does and a moderately large percentage of each orbital pass would be non-functional. Ignore that dead time since you get a huge solar power rating for your sinterer and over many passes you access a huge lunar surface area. Since the process is efficient with delivered material and consumables, over time, you win. You can build a complete equatorial road for rovers using the technique and you can collect the product of your efforts when and where it is convenient from the edges of that road. Leave abrupt elevation changes(steep craters) fallow, Very slowly shift your orbit to circumnavigate fallow areas.

Techniques may need to be developed to precisely refresh the unsintered dust layer during the dead time of each orbit but realize that natural meteorite activity will be doing this some anyway and a minor trailing charged particle(electron/alpa) gun scan might provide enough particles attracted to the active area to collect a desired amount of new regolith dust where you want it. Fire the alphas so they embed into the target and the betas at surrounding dust.

For those who have a need for a question: Are we planning to do this already ? If not, why not ? The sooner we get it up there the sooner we will have an equatorial rover road lined with bricks to use to construct shelter.

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#1

Re: equatorial low orbit schmidt cassegrain sintering satellite for lunar regolith. Not an imaging telescope.

11/22/2020 5:45 PM

This telescope sinterer may be a bit different from most schmidt cassegrain telescopes with which you may be familiar. Specifically, there is only the mirror pair and no refractive lens involved. I was just trying to express the two mirror concept with the focusing beam passing through the center of the larger mirror. The sinterer would not likely have shortening the tube as a major goal like many telescopes do. Also the smaller mirror may not necessarily be curved. We are going for energy density (per area in the focal spot) and for the in-one-end-and-out-the-other geometry rather than for optical perfection and sharp imaging.

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#2

Re: equatorial low orbit schmidt cassegrain sintering satellite for lunar regolith

11/22/2020 6:39 PM

The problem with this is "very long focal length". The sun subtends an angle of 1/2 degree. The size of a focused image of the sun would thus be

D = (0.5 deg / 57.3 deg/radian x focal length).

If the orbit were 15 km from the surface, the focused image of the sun would be 131 meters in diameter. The light reflected from the satellite would be spread over a circle of 131 meters in diameter (best case, neglecting diffraction and imperfect focussing). The mirror in orbit would have to be very large to significantly increase the energy in this large circle.

Of course, the satellite is not standing still, so it can't stay focused on the same spot with the same focal length. It either must move on with closest focus or suffer an expanded focus size as it increases in distance.

The sun is not a point source and that's as sharp as you can focus the sun's rays.

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#3

Re: equatorial low orbit schmidt cassegrain sintering satellite for lunar regolith

11/22/2020 7:17 PM

We just need faster dune buggies....

Roads?! We don't need no stinking roads!

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#4
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Re: equatorial low orbit schmidt cassegrain sintering satellite for lunar regolith. Emmett Brown.

11/23/2020 8:41 AM

I was hoping that a low orbit would function as a virtual "stinkin' road" but...

Because of my Earth bias and the biggest(175 m deep, Barringer Crater) remaining terrestrial crater rims being less than 200 m in height reduced only by a bit of wind and water erosion I incorrectly assumed that moon craters would be of similar magnitude. I should have looked up moon crater depth before posting but that ship has already sailed. I thought that regolith splash from other impacts would tend to level out moon craters to some (almost comparable to Earthly water and wind) degree but that effect seems to be unimportant relative to a snowball Earth megaglacier grader scraping off kilometers of rock. I could start my satellite sinterer at max surface elevation and hope to fill in the troughs but that sharply reduces the active sintering area per orbit and would dramatically reduce productivity until a genuine leveled road could be substantially developed, but that requirement sharply increases my "full production rate" startup time. So, Emmett Brown, "Who needs a stinkin' road ?" All the way around the equator of the moon at a uniform elevation ? I do.
And it ain't there to start with, so I cannot limit my focal length overhead to something effective at orbital speeds with a "reasonably" large primary mirror with a short enough focal length for focusing on a small enough spot to achieve sintering at speed. And now I know why no one is planning such a large 3D printer for lunar development. Thanks(GA), Rixter, for your lunar crater depth of knowledge. I have looked a little more and found this:
"
The missing piece of the puzzle comes from the study of Earth’s past climate records. Bottke showed that the paucity of ancient craters on Earth may coincide with periods in Earth’s history when its surface was completely covered with ice, the "Snowball Earth" scenario. The most compelling evidence for a Snowball Earth in the distant past comes from geology, which records evidence of glaciation near the equator. As glaciers move across continents, they cause deep erosion, removing kilometers' worth of material from the surface. Bottke proposed that glacial erosion during the Snowball Earth was such an extensive erosional process, especially in the period just before 650 million years ago, that it led to erasure of most of the large impact craters on Earth. However, extremely large impact craters like those at Sudbury (Canada) and Vredefort (Africa), which have very deep roots, survived the glacial scraping.
"
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#5
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Re: equatorial low orbit schmidt cassegrain sintering satellite for lunar regolith. Kinetic Diamond Production?

11/23/2020 8:50 AM

Kinetic Diamond Production ?

On a bit of a tangent, it is interesting that Sudbury and also South Africa are both known as diamond sources. This suggests that perhaps more terrestrial diamonds may have impact sources than many people realize.

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#6
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Re: equatorial low orbit schmidt cassegrain sintering satellite for lunar regolith. Kinetic Diamond Production?

11/23/2020 9:12 AM

An important distinction is whether kinetic delivery or kinetic excavation or kinetic pressure and heat are responsible for transporting or revealing or creating diamonds.

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#8
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Re: equatorial low orbit schmidt cassegrain sintering satellite for lunar regolith. Kinetic Diamond Production?

11/24/2020 2:14 AM

Why hasn't the Moon rover detected any diamonds? they should be everywhere...

https://en.wikipedia.org/wiki/Extraterrestrial_diamonds

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#9
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Re: equatorial low orbit schmidt cassegrain sintering satellite for lunar regolith. Diffusion in the limit is Oblivion.

11/24/2020 9:09 AM

Proposed Mechanisms for Why Lunar Rovers are Not Finding Diamonds on the Moon

As a wild guess: Earth has a very important elemental carbon concentrator, namely life. Additionally, the atmospheric erosion tends to pack that life modified, predominantly pure, elemental carbon tightly underground in (coal, oil, and graphite) layers with silicon rich layers of sediment on top of it. This geometry forms an anvil gasket for meteorites to use to achieve high temperatures and pressures on nearly pure elemental carbon caches underground. Wham ! visible sized diamond production, but it is still at depth. Now, over time, more glacial, and water and wind erosion and, voila, large, sparkly diamonds brought to or near the surface and worn right out of their surroundings.

Still guessing.... The carbon on the moon and in most meteors is predominantly chemically bound and unconcentrated carbon. Those non-carbon elements and pre-contaminated carbon compounds interfere with high temp, high pressure "pure carbon crystal" production. Even if a meteor arrives with some existing diamonds, it comes with and strikes material with carbon(and non-carbon) compounds which make large diamond production less likely and may even further reduce any existing crystal diamond load due to recombination. Furthermore, with no subsequent low temperature erosion to speak of, whatever diamonds (existing or produced) remain sequestered in rock or get blasted into microscopic specs too small to be noticed in huge quantities of normal regolith.

"they should be everywhere..." may be a large part of the problem since being everywhere frustrates being "precisely somewhere enough" to get noticed. Diffusion in the limit is oblivion.

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#7
In reply to #5

Re: equatorial low orbit schmidt cassegrain sintering satellite for lunar regolith. Kinetic Diamond Production?

11/23/2020 5:11 PM

Apparently, some diamonds do come from meteor strikes...

"For decades the Popigai crater has fascinated paleontologists and geologists, but the entire area was completely off limits because of the diamonds found there. However, a major investigatory expedition was undertaken in 1997, which greatly advanced understanding of the enigmatic structure.[7] The impactor in this event has been identified as either an 8 km (5.0 mi) diameter chondrite asteroid, or a 5 km (3.1 mi) diameter stony asteroid.

The shock pressures from the impact instantaneously transformed graphite in the ground into diamonds within a 13.6 km (8.5 mi) radius of the impact point. These diamonds are usually 0.5 to 2 mm (0.020 to 0.079 in) in diameter, though a few exceptional specimens are 10 mm (0.39 in) in size. The diamonds not only inherited the tabular shape of the original graphite grains but they additionally preserved the original crystals' delicate striations.[7]"

https://en.wikipedia.org/wiki/Popigai_crater

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