The internal link does not appear to be working (at least for me)...
http://cubesat.ifastnet.com/forum/viewtopic.php?f=1&t=119
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Monroe L. King Jr.
Sent: Monday, December 11, 2017 1:17 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Cubesats orbital grenades ?
Imaging optically is not the only use for satellites in fact it's not even
common for satellites! Most satellites don't do any imaging optically.
But if you wanted to do some imaging with a cubesat I did design a telescope
that is compact enough to fit on a 1U cubesat with a 80mm reflector.
It's a Gregorian reflector on one side of the cubesat that has an extendable
shield and secondary mirror.
It's the only type of telescope that would work on a 1U cubesat and it has
almost no impact on the internals or solar panels of the satellite.
That telescope could possibly double as a small parabolic radio antenna as well.
No you can't put much of an imager on a cubesat but why do you need to?
There are so many other possibilities!
Here is 100Mb of cubesat payload ideas.
http://cubesat.wikidot.com/forum/t-306927/100-mbytes-of-cubesat-payload-ideas-and-proposals
Satellites are just about the same as drones in fact they are drones in space.
Monroe
-------- Original Message --------
Subject: [AR] Re: Cubesats orbital grenades ?
From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
Date: Mon, December 11, 2017 10:23 am
To: Arocket List <arocket@xxxxxxxxxxxxx>
On Mon, 11 Dec 2017, Galejs, Robert - 1007 - MITLL wrote:
One obvious counter-example: If you are trying to get high
resolution ground images from space, you need optical apertures
larger than cubesats can handle . From 300 km altitude at nadir,
you'd need a 2 ft diameter circular aperture for 1 ft resolution at
550 nm. That's hard to fit on a cube sat...
In principle that can be overcome using formation flying and imaging
interferometry, but that is *MUCH* easier said than done, especially
in visible wavelengths. (The astronomers have enough trouble making
it work in near-IR -- where the longer wavelengths make everything
easier -- with all the telescopes bolted firmly to solid rock.)
And then square and cube that if you're also trying to look at
something relatively faint, i.e. looking up instead of down. Imaging
interferometry needs enough photons per millisecond to form detectable
interference fringes, so it pretty much works only on bright sources.
For dim stuff, you've got to gather photons the old-fashioned way if you want
results.
Especially if you want to do spectroscopy or zillion-pixel imaging:
the finer you slice the photons, the more of them you need.
Our BRITE astronomy nanosats do good astrophysics, but the small
apertures do limit them to working only on fairly bright stars; our
first satellite, MOST, did better but at the cost of being a 53kg
microsat. (We could make it smaller now, but I don't know if it could
go into a 12U cubesat, and just its telescope alone is rather bigger
than a 3U.)
Sometimes there is no substitute for aperture. And that applies to
radio too -- when working with faint signals or long distances or high
data rates, you quickly find yourself needing dishes or long helixes
or whatever on the satellite, not just little omni antennas. And
those are sized by the radio wavelength and can't shrink without losing
performance.
Henry
