# OHMOrbiter addon challenge. The Beacon Project

#### Boxx

Donator
Whatever the CMOS pixel size, whatever the image processing or stacking.

Dura Lex Difractionis, Sed Lex Difractionis ==> If you can "model" (i.e. assume) a telescope on Earth with an aperture D (in meters), the resolution of your telescope CANNOT be better than lambda/D in radians, with lambda = 500nm (mid of visible spectrum). If you can play with interferometry, the largest baseline of your interferometer (maybe 100s of km!) is D (but it's difficult in visible light). Any other assumption is a "fictional" telescope.

#### dgatsoulis

##### ele2png user
Whatever the CMOS pixel size, whatever the image processing or stacking.

Dura Lex Difractionis, Sed Lex Difractionis ==> If you can "model" (i.e. assume) a telescope on Earth with an aperture D (in meters), the resolution of your telescope CANNOT be better than lambda/D in radians, with lambda = 500nm (mid of visible spectrum). If you can play with interferometry, the largest baseline of your interferometer (maybe 100s of km!) is D (but it's difficult in visible light). Any other assumption is a "fictional" telescope.

Using some online calculators, I find that the diffraction limit for a 6" aperture is about 0.8 arcseconds. The Moon's angular size is 1900 arcseconds, so that translates to objects ~ 1.5 km in size.
For double the aperture, we get half the size, so about 750 meters.
But what does that mean? If I image the Moon with a 12" telescope, each pixel will be 750 meters across?

Also, what is the relation between arcseconds and Orbiter's FoV? [it's a simple arsceconds to decimal degrees conversion]

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#### Boxx

Donator
With D = 6 inches = 0.15m, we've got an affordable telescope that could even be integrated in a Delta Glider (the Arrow Freighter could easily get a 1m telescope, 7 times better resolution). Then, the angular resolution in visible light is lambda/D = 550E-9/0.15 = 3.7E-6 [rad] = 3.7E-6 * 180 / pi [deg] = 2.1E-4° = 2.1E-4*3600 [arcsec] = 0.76 [arcsec].

At the Moon distance, it corresponds to details of 3.7E-6*300000 [km] = 1.1km => you CANNOT distinguish the ISS in Lunar orbit, you'd see only a blur dot (nothing better with a 1m telescope on the Arrow Freighter, smallest details would be 150m). Sorry! But you could see an unresolved spot of light if it is illuminated.

But what does that mean? If I image the Moon with a 12" telescope, each pixel will be 750 meters across?
No, the pixel size is another story => if the angular size of your pixel is smaller than the resolution (say 1px = 0.2 arcsec), then the smallest detail with your 6'' telescope, say 1km at the Moon, will simply spread over 4 pixels, i.e. your camera (your pixel size) is oversized considering your resolution, it is a bad combination for telescope + camera, a waste of hardware. That's why smartphones ads that claim a huge number of pixels mean simply nothing without telling the lens diameter (about 2mm?)... ok, different story.

Coming back to my own dream .... you could see a wheel station at the Moon (with retroreflectors?) with a 1m telescope from the Arrow Freighter in Earth orbit !

#### Donamy

Donator
Beta Tester
How about a reflective chaff dispenser ?

#### Urwumpe

##### Not funny anymore
Donator
How about a reflective chaff dispenser ?

The cloud would quickly spread out and after about a week turn into a faint ring around the moon. And be gone after a year or two.

#### Donamy

Donator
Beta Tester
But would it be visible ? It would be good for a start.

#### Urwumpe

##### Not funny anymore
Donator
But would it be visible ? It would be good for a start.

The Sodium cloud experiment as visible to telescopes and likely much better than any chaff experiment. Also you need to make sure that the Westford needle problem does not repeat.

(Damn, I learned something in that Space Debris lecture 20 years ago)

#### Boxx

Donator
Also, @Urwumpe put in the shoutbox some very interesting material (IMO) about a huge modular wheel station:
• https://www.nasa.gov/sites/default/files/files/Longman_2013_PhI_Tensegrity.pdf
Yesterday at 9:33 PM
• Urwumpe: Interesting paper. A toroid space station, that can be initially deployed with just 3 (superheavy) launches, and then grow over time to about 950 times the initial size, turning into space habitat for up to 10000 people, while staying manned and operational during the construction period. Yesterday at 9:33 PM

Ok, it's fictional because too expensive, but here we can imagine things like this: see Fig 4.3.... By the way, the water is an excellent shielding against cosmic rays (protons at least), maybe not all around but in small cylindrical units with available space in the center to serve as a shelter when space weather events occur. Also, think Bigelow Inflatable, add docks everywhere (to park vessels and leave the station) and incoming dock in the center, with an animation to move the vessel from the center to the periphery.

#### BrianJ

The cloud would quickly spread out and after about a week turn into a faint ring around the moon. And be gone after a year or two.
That might be rather pretty - I'd like to see that! (problems for astronomers, space debris, etc.etc. notwithstanding)

My only idea so far is a big white sphere ~ 150m radius, which would be seen as a 6 mag. star, around full-moon.
A large cylinder would be more visible either side of full-moon - but would look like a "giant toilet roll in space".

Cheers,
Brian

#### Donamy

Donator
Beta Tester
Make it look like a death star.

#### Felix24

##### Active member
How about an inflatable hoop a few hundred meters in diameter with a thin reflective aluminum mylar membrane stretched across. It orients itself to always reflect the sun towards earth. Kinda like a big reflective solar sail. It would do a full rotation relative to earth every two months. Things to contend with: solar wind/radiation pressure, lunar gravity gradient.

#### Donamy

Donator
Beta Tester
Maybe once in awhile, use the solar wind for Orbital boost ?

#### Urwumpe

##### Not funny anymore
Donator
Maybe once in awhile, use the solar wind for Orbital boost ?

That was my solar sail idea initially in the thread - just position it to counter the orbital pertubations all the time and use paddle-like small control surfaces to control rotation rate. Since we want to see the wide area illuminated by the sun, somewhere close to a L point would be ideal for this, so only small tilts from "down the wind" would be necessary and the balance of gravity, centrifugal force and radiation pressure keeps it stable.

#### Donamy

Donator
Beta Tester
So it probably wouldn't need much pressure to inflate the ring. I don't think MMD would be an issue.

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