Can you make a really good telescope fit in a cube sat?

[DBowman]

1 hour ago, kunok said:

This will have a brutal aberration :| but I suppose you can do the corrections in the rest of the optical system.

I was thinking the same thing. I don't know if one could improve things by spinning up the bubble and/or putting some charge on it and on other inner/outer metalized bubbles - anything to move to better than spherical. I don't know enough about what shape you'd want your telescope to be. Sounds like a lot of infrastructure to produce the mirror ... shame to make just one ... inteferometry of 100 m mirrors? nice

 

55 minutes ago, wumpus said:

There are also radio telescope arrays as well, but I suspect that uses more straightforward DSP tricks.

I think the longer wavelength for radio makes it 'much less demanding' than optical frequencies. The optical ones have big evacuated tubes (long) with mirrors that they use to adjust the 'optical distance' within wavelength scale distances.

 

Just now, Jonfliesgoats said:

Does this mean networked cubesats can bring .1 or .01 meter resolution earth imagery to organizations with smaller budgets?

Oh interesting idea, look down, for sure lots of photons... 

[YNM]

Once I saw someone here carry a tele camera lens with Maksutov-like anatomy. I suppose those kinds would fit in easily ? Add with some high-def sensor, guess trying to look at the stars or at the ground won't be much of a hassle.

Also, never try to do lucky imaging of Earth's surface. You won't have any stackable images I suppose - any short delay and the whole thing is off-sync...

Edited December 23, 2016 by YNM

[Shpaget]

3 hours ago, YNM said:

Once I saw someone here carry a tele camera lens with Maksutov-like anatomy. I suppose those kinds would fit in easily ? Add with some high-def sensor, guess trying to look at the stars or at the ground won't be much of a hassle.

I have one of those.

Samyang 800 mm f8

It's really light, long focal distance and rather cheap, but optically useless. I ended up mounting an exterior stepper motor for focusing with optical sensors so I don't need to touch anything to focus, but still couldn't get good image. Yes I did get a few more details than with my 100 mm macro lens, but the macro is so much better all around.

I don't have my camera with me ATM, it's at my workplace, but if you guys want, I can shoot some pictures with it later today.

Edited December 23, 2016 by Shpaget

[YNM]

Perhaps your problem is with the manufacturer...

https://www.google.com/search?q=samyang&prmd=ivns&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiaxuOR84nRAhVLRY8KHTAvAoEQ_AUIBigB

 

EDIT : On Topic :

Just for proper reference of the general appearence of the object/tool that I referenced :

Edited December 23, 2016 by YNM

[Shpaget]

Sure, there are poor manufacturers and better ones, however, there are no excellent mirror lenses. Perhaps my particular one is poorer than usual, or just it's a matter of opinion. Perhaps what is crap for me is acceptable to somebody else.

In any case, I forgot to bring my camera home, so I can't shoot some comparison photos. Will report back.

[_Augustus_]

13 hours ago, YNM said:

Once I saw someone here carry a tele camera lens with Maksutov-like anatomy. I suppose those kinds would fit in easily ?

A Mak just shoves a longer focal length into a shorter package. It is not as versatile due to the long focal length. One would probably be better off using a standard reflector or refractor and having a Barlow lens that can flip in to lengthen the focal length when needed.

[YNM]

1 hour ago, Shpaget said:

Sure, there are poor manufacturers and better ones, however, there are no excellent mirror lenses. Perhaps my particular one is poorer than usual, or just it's a matter of opinion. Perhaps what is crap for me is acceptable to somebody else.

I suppose I have to apologize here, I didn't mean to insult the manufacturer (yes I know it actually shown first when searching that word) or anyone else, just a little bit of connection (and perhaps a silly one). I'm sorry if you were to feel offended or insulted.

15 minutes ago, _Augustus_ said:

A Mak just shoves a longer focal length into a shorter package. It is not as versatile due to the long focal length. One would probably be better off using a standard reflector or refractor and having a Barlow lens that can flip in to lengthen the focal length when needed.

But you do get the ability to take very fast photograph of very fast-moving object while not having saturation thanks to (often) higher f/D. And most (bar Newtonian or Schmidt camera) reflectors are having that reduction in length. I mean, perhaps for the best results ever one can go for Ritchey-Cheretien but that'd be "quite expensive", hence my initial applicable suggestion.

There's another possibility : tiny collapsible dobsonians.

Edited December 23, 2016 by YNM

[Shpaget]

I'm not offended. I'm well aware that it's a poor quality lens. After all, you get what you pay for, and right at the beginning I said it was a cheap lens.

[Green Baron]

I doubt that 100 cubesats will make a good telescope, since the small surface areas won't collect enough photons for a meaningful application. Also, how would such a swarm be controlled ? You need a mirror, a camera, a little computer, a transmitter for the data, a maneuvering unit ... all in a 1l-box. or a quart or two pints if you like it that way :-)

A single 1,2m-mirror would already be a better solution. But esa/nasa/other are already a few steps ahead. For example, it is planned to do really (like: ludicrously) large baseline interferometers in the 20s. Example https://www.lsst.org/lsst/ on earth and http://sci.esa.int/euclid/ in earth-sun-L2. Challenging but possible and planned.

 

[Jonfliesgoats]

Yeah, the more I think about it, arrays of little, orbiting data to mimic single, big telescopes rapidly hit a point where complications in coordination, network communication and processing are greater than simply launching or building bigger assets.  Complexity is an enemy of good design, and arrays of satellites get complex fast.

Lots of IMINT or SIGINT cubesats can do some important things in a network, though.  Generally sensorsnhave to choose between coverage area and resolution.  Do we want to look through a sofa straw at fine detail or look through a sewer pipe at rough detail?  More, cheap sensors in cube sats can provide global "sewer pipe" coverage that gets fed through an algorithm.  That allows us to rapidly decide where we want to aim better sensors to see or hear interesting things.

It means an organization with lots of small, cheap satellites can run through an OODA or other decision loop faster than other organizations.

[mikegarrison]

On 12/22/2016 at 7:25 AM, Jonfliesgoats said:

Miniaturization is coming.

But you can't miniaturize the wavelength of light. The limits for telescopes are based on whatever wavelength they are looking for.

Perhaps you could use a multi-satellite telescope, however. Just as there are virtual telescopes on the ground, made up of many smaller telescopes instead of one large one, you could perhaps do something like that in space. But the problem, of course, is that any two things in orbit will be moving at different speeds and will never stay at a constant distance.

[Jonfliesgoats]

Yeah, I am aware of wavelength limitations.  The array idea was appealing for a while, but then you have to have really good fidelity of communication between satellites in the array along with really good fidelity of position and velocity information.  The more I thought it about it, the more complex the inter-sensor communication and position requirements become for an orbiting array.  At that point the cost and complexity savings offered by cubesat arrays are more than offset by processing and communications difficulties.

Using a constellation of cubesats for wide field change detection may by more useful.  You could cover most of earth's surface, or figure out which parts of the cosmos deserve attention from more expensive assets, like the JWST.

[YNM]

Apparently it's not that impossible, though. But for small swarms I suppose more precision are needed, which is why it'd be a bit harder.

Edited December 24, 2016 by YNM

[Shpaget]

You need much, much better accuracy and precission for optical telescope interferometry.

[Shpaget]

Ok, so I got around to take some photos. Here are some details about it.

The camera used was Canon 40D, mounted on a tripod, with 10 second shutter delay and mirror lockup, all in an effort to eliminate the camera shake. I would say the camera was sufficiently stable and not moving.
The lens under test is Samyang 800mm f8 mirror lens. It is a manual focus, fixed aperture. It is Cassegrain, Maksutov or similar design. It's hard to tell and impossible to find in specs. In any case the primary mirror is about 10 cm in diameter.
For comparison I used a Canon 100mm f/2,8 macro, a refractor, obviously.

Just for comparison, the Canon lens is about 2,5 times more expensive.

Since it is -2°C outside, I left the camera and both lenses outside for a bit more than an hour so they can cool down. Perhaps some of you may appreciate that.

Anyway, here are the photos. The building is about 150-200 meters away.

First, the Canon 100 mm f/2,8 macro.
ISO 100
f/6,3
1/80s 

The insert is 100% zoom.

Next, it's Samyang
ISO 100
f/8
1/80s

As you can see there is an awful lot of fuzziness and even some ghosting.

This is not zoomed in. That's straight out of camera, just resized for sanity.

Next I artificially stepped down the lens. You basically make a small hole in an opaque material which you place over the lens. It's not possible to measure the aperture very accurately, but we can make some conclusions based on other parameters. In this case the effective aperture was reduced to approximately f/20.

ISO 100
f/20
1/10s

Again, the insert is 100% zoom.

There is significant difference between wide open and stepped down Samyang. Much more detail is visible in the third photo than in the second, but the overall sharpness is still much lower than on the Canon. Perhaps if the Canon lens was mounted on a camera with higher resolution sensor, the image would contain even more detail. I can't be sure, I don't have such a camera, but it's clear that the Samyang has reached it's potential on this old sensor and that it would benefit very little from an increased sensor resolution.

Yes, the (stepped down) Samyang offers more information, but it's far from good.

Of course, this test speaks more about this particular Samyang lens than about good reflector telescopes in general. A small (10cm) space based telescope would without a doubt have significantly better optics than this lens, but it would never be comparable to larger ones, which was the starting point of this topic.