# OHMOrbiter addon challenge. The Beacon Project

#### Donamy

Donator
Beta Tester
This challenge is to Orbinauts to discuss and possibly create an addon that would launch aboard a Falcon Heavy, to deliver a payload to Lunar orbit that would be able to be seen from Earth.

Lets hear some ideas.

#### Urwumpe

##### Not funny anymore
Donator
What about stacking a lot of mirrors or solar sails? With the right amount of origami, you should be able to fit a large surface into the fairing. Since it doesn't need to be scientific and the orbit around Earth has a long period, attitude control by paddles (like Mariner attempted) could be sufficient. How long does it have to be visible?

#### Donamy

Donator
Beta Tester
It would be nice to see it forever. Even if it was only through a cheap telescope.

#### BrianJ

It would be nice to see it forever. Even if it was only through a cheap telescope.
This got me doing some mental arithmetic on the basis of it being a naked-eye object.

The ISS is ~ mag. -4 when it goes overhead at ~400km, and say the faintest star you can see is ~ mag.6 (yeah, maybe 7, but 6 is convenient). That's a difference of mag.10, which is a difference of 10,000x in brightness.
Say the Moon is ~400,000km away, thats 1000x as far away as the ISS, so you would need 1,000,000 ISS's to appear at mag.-4 at the distance of the Moon. But only 100 ISS's to be visible at mag.6.

So something with the cross section area of 100 ISS's - or smaller if you made it more reflective

How big is that?

Cheers,
Brian

#### Max-Q

##### 99 40
So something with the cross section area of 100 ISS's - or smaller if you made it more reflective
It's only the ISS's solar wings that are reflective.
And with a material like shiny mylar, more light per unit area is going to be reflected than from a solar wing as you said.
ISS has about 2,500 square meters of solar wings, so assuming twice the reflectiveness that's 125,000 square meters.
That's a total mass of just the mylar of 5,000 - 10,000 kg, depending on thickness by my rough guess.

#### Boxx

Donator
I would love to see standard (habitable) modules of a wheel station brought by Flacon Heavy to Lunar orbit that could be assembled there, hence with auto-docking systems to one another, eventually forming the wheel. The size and rotation would recreate 1G at the perimeter, it could be seen from Earth with correct phase angle.

Docking would occur at the center of the wheel (of course) and the vessel, after docking, would be moved to the periphery of the wheel (where there is 1G). Animations in Orbiter allow that. Undocking would occur from that location. Many parking lots on the wheel (1 per standard habitable module, typically).

#### Felix24

##### Active member
How about a giant space laser that shines back at earth?

#### Max-Q

##### 99 40
How about a giant space laser that shines back at earth?
How you gonna power and cool it?

#### Donamy

Donator
Beta Tester
Something simple is better. Also in the near term, because I'd like to see it for real. Maybe it would finally shut up the Lunatics (get it).
Maybe get BarryGolden to pitch it At SpaceX.

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#### BrianJ

This is a very useful paper if you're going the "large and reflective" route....

#### Boxx

Donator
By the way, is there a potential to design retroreflectors in Orbiter? We can already design light emission, but retroflector is another story: emitting only when the observer points a light to it. I guess it would request coupling the observer's light and the observed object. Could help see structures at the Moon from some distance

#### LordCroussette

##### Quebec City's Resident Base Builder
Donator
Not to be a bummer but I do not believe it is possible to see something orbiting the Moon from the Earth in Orbiter. I thought the idea was really funny and decided to make this thing to test things out:

This thing is massive, at 378km wide. It should be visible from Earth but, for some reason, I couldn't see anything. Looking at it closer, I realized there was an issue.
First, here is the "spacecraft" visible from a distance of 97M.

And here it is from a distance of 101M. The thing has vanished.

It seems that Orbiter has a render limit for its mesh of 100M (millions of kilometers?) which means that nothing on the Moon, not matter how big or small, or reflective or not, will be visible from the Earth.

PS: It didn't unload because it was too far away for the size of the spacecraft. The marker (visible by pressing F9) is visible from Earth (at FOV 10 at least). It's just the mesh that disappears.

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#### dgatsoulis

##### ele2png user
Not to be a bummer but I do not believe it is possible to see something orbiting the Moon from the Earth in Orbiter. I thought the idea was really funny and decided to make this thing to test things out:
View attachment 34666
This thing is massive, at 378km wide. It should be visible from Earth but, for some reason, I couldn't see anything. Looking at it closer, I realized there was an issue.
First, here is the "spacecraft" visible from a distance of 97M.
View attachment 34667
And here it is from a distance of 101M. The thing has vanished.
View attachment 34668
It seems that Orbiter has a render limit for its mesh of 100M (millions of kilometers?) which means that nothing on the Moon, not matter how big or small, or reflective or not, will be visible from the Earth.

PS: It didn't unload because it was too far away for the size of the spacecraft. The marker (visible by pressing F9) is visible from Earth (at FOV 10 at least). It's just the mesh that disappears.
Here is a Carina mesh, scaled to ~35 km wide, placed on Brighton Beach. Config file size set to 1e6.

In Orbiter2016 it can be seen from Earth with Camera MFD (FoV 0.5)

External MFD window enlarged to full width of screen (1920):

Same pic taken from 300 km altitude above Earth:

Zoomed in 50%

#### LordCroussette

##### Quebec City's Resident Base Builder
Donator
Here is a Carina mesh, scaled to ~35 km wide, placed on Brighton Beach. Config file size set to 1e6.
View attachment 34673

In Orbiter2016 it can be seen from Earth with Camera MFD (FoV 0.5)
View attachment 34672
External MFD window enlarged to full width of screen (1920):
View attachment 34674
Same pic taken from 300 km altitude above Earth:
View attachment 34675
Zoomed in 50%
View attachment 34676
Yeah but that's as a surface base object. It is interesting that it works, but it's not in lunar orbit, which is what the challenge was about. Maybe you can try that though. Who knows, maybe my Orbiter is broken.

#### n72.75

##### Move slow and break things
Orbiter Contributor
Tutorial Publisher
Donator
There are some limitations on draw distance, I believe imposed by the Orbiter Core. They are based on angular size or the angular distance subtended by the vessel's "Size", at its distance from the camera. This also makes optical rendezvous difficult for NASSP, where LMs and SIVBs should technically be visible through the telescope.

For a realistic solution to this question in the OP, probably a large chemical laser, but even that would be difficult. The moon is verrrrry far away and light has a lot of space to spread out on the way from there to here.

#### dgatsoulis

##### ele2png user
Yeah but that's as a surface base object. It is interesting that it works, but it's not in lunar orbit, which is what the challenge was about. Maybe you can try that though. Who knows, maybe my Orbiter is broken.
I get that. It was just to point out that it is possible bypass the "100M limit" and view things on the Moon from Earth, as long as they are not the focused vessel (and you change the size in the config file).
In the example above, the mesh size is 35km and the config file size is 1e6 meters.

Donamy mentioned this:
It would be nice to see it forever. Even if it was only through a cheap telescope.
I think that the first thing we need is something that simulates the view from a cheap telescope.
According to this (source from 2008) , an 8" apperture should be able to discern ~1km wide features on the Moon. Stands to reason that it's irrelevant if said "feature" is on the lunar surface or in orbit.

I'll recompile the Generic Camera MFD to be able to zoom in more (current minimum is at 10° FoV), and we can take it from there.

#### LordCroussette

##### Quebec City's Resident Base Builder
Donator
I think that the first thing we need is something that simulates the view from a cheap telescope.
According to this , an 8" apperture should be able to discern ~1km wide features on the Moon. Stands to reason that its irrelevant if said "feature" is on the lunar surface or in orbit. (It's a source from 2008).
Stellarium simulates telescope views, though I'm not sure if it's possible to create your own telescope preset to simulate one that isn't included by default.

#### dgatsoulis

##### ele2png user
Here is a replacement for the Generic Camera that comes with the D3D9 client. Keep a backup, because this was hastily put together just to change the FoV limit.
It can zoom in up to 0.0001° FoV. (At 0.002 - 0.001° you can "clearly" see the ISS on Brighton Beach).
Targeting is tricky.
Create an attachment point at your ship's nose, select it from the MFD and aim at the Moon. Use 0.1 timewarp and zoom in. Make fine adjustments with rcs to get to your target.
It shouldn't be too difficult to convert this to a proper "TelescopeMFD". It needs a proper targeting system for that though, because manual is very tedious.

#### Attachments

• GenericCamera.zip
71.9 KB · Views: 2

#### Boxx

Donator
Here is a replacement for the Generic Camera that comes with the D3D9 client. Keep a backup, because this was hastily put together just to change the FoV limit.
It can zoom in up to 0.0001° FoV. (At 0.002 - 0.001° you can "clearly" see the ISS on Brighton Beach).
Targeting is tricky.
Create an attachment point at your ship's nose, select it from the MFD and aim at the Moon. Use 0.1 timewarp and zoom in. Make fine adjustments with rcs to get to your target.
It shouldn't be too difficult to convert this to a proper "TelescopeMFD". It needs a proper targeting system for that though, because manual is very tedious.
could see an exoplanet?

0.0001° = 0.36 arcsec.... Proxima Centauri b orbits at 0.037 arcsec from its star, i.e. 1/10 of the FoV this MFD isn't anymore a "cheap" telescope, but fun to think at it

#### dgatsoulis

##### ele2png user

Bagged the ISS in a 500 km orbit around the Moon. Not a cheap telescope for sure, probably outperforms Hubble. (Cheap for Musk?)
Date selected was November 25th 2034 (super moon date) and the Earth observation location was Sriharikota Base, with the Moon almost directly overhead.
A custom targeting system was used (constantly changing the dir and rot of an attachment point) to keep the iss in view.

The actual size of ISS's mesh wasn't changed at all. (113m x 76.7m x 37.4m), but the Size parameter was set to 30km in its config file. Less than that wasn't visible from Earth. (Actually it was much less than I expected).
To clarify, the size parameter was used to alter the draw distance, so that the ISS was drawn at this distance in Orbiter. It didn't affect the ISS's actual size.
The actual size of the ISS in the pics is 113 meters at its longest axis.

So we have proof of concept, that a telescope view can be simulated in Orbiter for a vessel located on Earth aiming at a target vessel in orbit around the Moon. Perhaps some more knowledgeable forum members can help with the following:

Considering a modern CMOS camera sensor, "lucky imaging" and stacking techniques available from free software and a reasonably "cheap" telescope setup, (1000$-2000$ ballpark price for everything: scope, mount, camera ) what's the smallest size of target on the Moon you'd expect to image relatively clearly?
By that I mean "be able to make out what it is", not "read its license plate number".
How does that size translate to Orbiter's FoV?

Having this info will help us define what kind of payload to create for the proposed addon.
My guess is that a a solar sail would have the largest area to weight ratio, but the largest ones so far are in the 1600 m² - 1700m² range ~40mx40m.

Probably need an array of those flying in formation to be able to see them from Earth.

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