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

[Jonfliesgoats]

What is the best telescope that can fit in a cubesat?  How would you improve upon it?

[Steel]

Not a particularly good one if your maximum mirror size is 10 cm

[Jonfliesgoats]

Do you think we could engineer a reflective membrane to fit in an inflateable ring?  Maybe control the reflective membrane's geometry with magnets?  Is that feasible?

Looks like someone beat us to it:

http://www.techbriefs.com/component/content/article/ntb/tech-briefs/mechanics-and-machinery/7062

https://www.alibaba.com/product-detail/Inflatable-Mirror-ball-For-Decoration-Large_60460426774.html?s=p

Edited December 22, 2016 by Jonfliesgoats

[Steel]

In theory it's possible, as long as you have (A) the ability to control the membrane to reasonable accuracy (+/- 1 mm would be on the loose end of the spectrum, you'd probably want much better than that) and (B) also have the power to ensure that the membrane doesn't flex or change shape in any way

EDIT: also with any cubesat, even with extending arms e.t.c your focal length is going to be limited to a few tens of centimeters

Edited December 22, 2016 by Steel

[Jonfliesgoats]

Getting away from inflateables, that project to see planets around Alpha Centauri is based on cube sats.  Do we have any design information about their telescopes?

That could be a cool project for an undergrad ro graduate student.  Inflateable, electro-reactive mirrors, I mean.

Edited December 22, 2016 by Jonfliesgoats

[Steel]

1 minute ago, Jonfliesgoats said:

Getting away from inflateables, that project to see planets around Alpha Centauri is based on cube sats.  Do we have any design information about their telescopes?

Which project exactly?

[Jonfliesgoats]

Let me dig up the link.  Just a sec.

http://www.space.com/34340-project-blue-alpha-centauri-earthlike-alien-planet.html

Project Blue

[Steel]

Well they're talking about a half-metre mirror and an instrument package about the size of a refrigerator, so it's fair to say that its a fair bit bigger than a cubesat

Edited December 22, 2016 by Steel

[Jonfliesgoats]

I wonder why I thought this was based on cubesats?  This is why I can't be trusted.  Still,  it's a lot smaller than Hubble.  Miniaturization is coming.

Found the cubesat telescopes I was thinking of.  I got mixed up on the Alpha Centauri thing.  This uses two satellites to make one telescope.

http://www.skyandtelescope.com/astronomy-news/the-rise-of-cubesat-astronomy-08032016/

13 minutes ago, Steel said:

Well they're talking about a half-metre mirror and an instrument package about the size of a refrigerator, so it's fair to say that its a fair bit bigger than a cubesat

 

 

This too:

https://www.nasa.gov/feature/goddard/2016/nasa-eyes-first-ever-carbon-nanotube-mirrors-for-cubesat-telescope

[Jonfliesgoats]

This too!

http://www.jpl.nasa.gov/cubesat/missions/asteria.php

I have no idea how they will keep two satellites properly positioned with accuracy to make a decent telescope. 

[Tullius]

4 minutes ago, Jonfliesgoats said:

I have no idea how they will keep two satellites properly positioned with accuracy to make a decent telescope.

Micro-Newton thrusters, i.e. your normal RCS system in XXS. And it is certainly part of the engineering challenge of building this telescope. But if they succeed, there is no risk of frying the imaging sensor while observing the solar corona, since there is nothing from which direct solar light may be reflected.

[_Augustus_]

Maximum size would be less than 4". I own 2 telescopes bigger than that. No sense in launching such a little one into orbit.

Project Blue is not a CubeSat. And in any case the program failed because of lack of funds.

Edited December 22, 2016 by _Augustus_

[Streetwind]

The planned Arkyd spacecraft from Planetary Resources are pretty much telescopes in slightly-above-cubesat format, right? And then there's Planet (formerly Planet Labs) with their constellation of 6U Earth observation cubesats.

However, both of those are fairly short range. Low Earth orbit for the latter, Earth's immediate neighborhood for the former. Neither of them would be able to make a useful observation of another planet in our own solar system, much less of other stars or exoplanets. Even that Asteria mission linked above will only be able to look at our stellar neigborhood. It's meant to free up larger, better specced telescopes from having to spend time on long-term observations of known objects, not to do exciting new stuff.

I mean, there's such a thing as synthetic aperture techniques to improve resolution by combining many cubesats, but that's not useful for increasing range. It works more like a microscope, improving the detail that's right in front of you. A microscope can't make proper long distance observations, no matter how good its magnification factor is.

See, the thing with really far away stuff is that any light it gives off has so much distance to spread itself thin that, from our point of view, it practically gives off no light worth mentioning at all. How do you take a picture of something like that? Well, you build a bigger mirror. The more mirror area you have, the more light emitted from your target you can capture. When Hubble took the famous Ultra Deep Field picture, it had its aperture open (in intervals) for a grand total of over eleven days. That's how long it had to stare at the exact same patch of sky - an area equal to what's obscured by one square millimeter of paper held at arms length in front of you - just to catch enough light to make a useful picture out of it. It was literally capturing photons almost one by one. And Hubble has 4.5 square meters of mirror area - from a mirror taller than an adult human. James Webb will have five times that mirror surface area. This is why JWST is a (literally) big deal, and why its capabilities will exceed Hubble's. Advancements in technology have little to do with it... it's almost all down to mirror size. JWST needed advancements in technology to build and use that size of mirror, not to improve its capabilities independently from it.

Too look really far, and get good results in practical timeframes, you simply need giant mirrors. This is not something that can be miniaturized away - this is a law of nature. Optical systems simply work that way. You might as well expect new generations of aircraft to be less affected by gravity than older ones... but that's not how it works, is it now? Gravity is a law of nature, you can't make an object be less affected. And in the same way, you can't collect light with a small mirror as well as you could with a large mirror. It's a part where reality tells us "not open for discussion, guys"

[Jonfliesgoats]

Great responses!  What actually got me into the telescopes-in-cubesats mind frame was another discussion about cubesat-sized reconnaissance satellites.  There, light collection is less of an issue.

Also, what about arrays of telescopes with better image processing?  In my previous life, folks smarter than myself solved some challenging imaging problems with software improving the resolution by compensating for atmospheric effects and other things.

Theoretically can software integrate imagery collected from a formation of cubesats into something better?

I guess an array wouldn't be able to catch that one photon from the far side of the universe, but they may be able to resolve things in our neighborhood, right?

[kerbiloid]

https://en.wikipedia.org/wiki/Diffraction-limited_system

[Shpaget]

37 minutes ago, Streetwind said:

it's almost all down to mirror size. JWST needed advancements in technology to build and use that size of mirror, not to improve its capabilities independently from it.

I was about to say that it's pretty much exactly all down to mirror size, but then @kerbiloid ninja'd me by linking to diffraction limited system wiki entry.

We've had the technical capability for building diffraction limited telescopes for quite a while; Hubble being the famous one, but definitely not the first one. Its mirror has been polished to about 10 nanometer accuracy, which should be a good enough argument for discarding any proposition for inflatable mirrors.

Just to explain what diffraction limited system is, it's the maximum theoretical resolution an optical system can achieve, and it is directly linked to the size of the primary mirror. Bigger mirror means better image. It's not just light gathering capabilities (although that's a nice bonus).

So, a good 10 cm mirror in orbit would make a good telescope, but not a spectacular one. It would be outperformed by many ground based handmade mirrors of larger diameter.

[Nibb31]

2 hours ago, Jonfliesgoats said:

Theoretically can software integrate imagery collected from a formation of cubesats into something better?

Software can extrapolate to enlarge a low resolution image into a high resolution one, but it can't invent detail that wasn't perceived because of a poor sensor. 

2 hours ago, Jonfliesgoats said:

I guess an array wouldn't be able to catch that one photon from the far side of the universe, but they may be able to resolve things in our neighborhood, right?

 

[wumpus]

4 hours ago, Jonfliesgoats said:

Still,  it's a lot smaller than Hubble.  Miniaturization is coming.

Mirror (or lens) size is still crucial to telescopes. Miniaturization will likely only happen in thinness (although a sparse array of telescopes will have certain advantages) and allow for in-space inflation.  I suspect that the electronics/optics necessary to link up a sparse array of telescopes isn't within the means of microsats yet.

[PB666]

6 hours ago, Steel said:

Not a particularly good one if your maximum mirror size is 10 cm

Better than a cell phone camera.

 

[Theysen]

If you want to look deep into space you need close to 0 movement of the craft. Hard to achieve to fit all this precision attitude control into a tiny cubesat plus the telescope. 

[PB666]

1 hour ago, wumpus said:

Mirror (or lens) size is still crucial to telescopes. Miniaturization will likely only happen in thinness (although a sparse array of telescopes will have certain advantages) and allow for in-space inflation.  I suspect that the electronics/optics necessary to link up a sparse array of telescopes isn't within the means of microsats yet.

Its not possible except at great distances from gravitational bodies. dx,dy,dz/dt differs for any two objects in a circular object around a gravitational orbit. CUbesats do not have the range.

[DBowman]

5 hours ago, Streetwind said:

Too look really far, and get good results in practical timeframes, you simply need giant mirrors. This is not something that can be miniaturized away - this is a law of nature.

You can cheat the law kind of using interferometery - the light from two 0.1 m mirrors 10 m apart can be combined to give the diffraction limited resolving power of a 10 m mirror. They still only have the light gathering power of two 0.1 m mirrors but you can get the same image as the 10 m mirror if you look for 'long enough'. This approach has problems:

1. 'station keeping' & combining the light correctly is 'fiddly', probably the more so the more mirrors you combine
2. using long exposures is not good for transient events e.g. star transiting behind planet atmosphere, planets rotate, stars rotate, planets move - some of these you might be able to compute away after increasing exposure even more

It seems like on wavelengths that pass the atmosphere / don't have interference modern ground based telescopes with adaptive optics and computation can out deliver orbital systems. It's just so much cheaper to make them and service / update them.

Once we start doing techniques like putting a star blocker some kilometers in front of the telescope (so the planet light does not have to 'compete' with the star light) space systems will have an advantage again. These guys have plans to inflate 'soap bubbles' (some kind of uv setting resin) hundreds of meters in diameter and deposit metal vapor in them. Maybe going huge will put the advantage back on orbital systems.

[kunok]

1 hour ago, DBowman said:

Once we start doing techniques like putting a star blocker some kilometers in front of the telescope (so the planet light does not have to 'compete' with the star light) space systems will have an advantage again. These guys have plans to inflate 'soap bubbles' (some kind of uv setting resin) hundreds of meters in diameter and deposit metal vapor in them. Maybe going huge will put the advantage back on orbital systems.

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

[wumpus]

3 hours ago, PB666 said:

Its not possible except at great distances from gravitational bodies. dx,dy,dz/dt differs for any two objects in a circular object around a gravitational orbit. CUbesats do not have the range.

I was thinking about tricks already used on Earth (at least my understanding is that there are optically linked telescopes on Earth).  The microthrusters mentioned in a previous thread might come in hand (I suspect you would still have to adjust mirrors to accuracy>>wavelengths of light, but it might be possible to simply move the mirror relative to the spacecraft).  Hopefully nothing once things are aligned, there isn't any real movement (presumably a solved issue on Hubble).

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

 

[Jonfliesgoats]

Pretty fascinating ideas, guys.  I get that tiny mirrors simply can't collect the light to peer deep into space.  Huge, terrestrial telescopes seem to be advantageous.  Still optical arrays of cubesats could be pretty powerful for earth observation, it seems.

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

I get maneuvering and attitude control would have to be pretty stupendous for the cubes.  I suppose relative a position and motion of individual sensors would have to be actively monitored and compensated for by image processing software.

Would it be more advantageous for orbiting sensors in a cubesat array to broadcast position and image date to another processing and relay sat or have the sensors broadcast image and position data to a ground station for image processing?

To this point I have been imaging arrays of cubesats taking a simultaneous snapshot of whatever they want to look at.

Would a swarm of cubesats be able to continuously monitor the earth and provide successively greater resolution by pushing more data through image processing to eventually get higher resolution imagery?  

 

Orbital mechanics being what they are, clouds of cubesats could be maneuvered so that the constellation gets clustered over points of interest.  The networked sensors could switch array networks they are part of, thus each sensor would not have to dedicated to a single array and out of use for the majority of its orbit.