Orbit your own satellite

[ravingdave]

Only $8,000.00 .


http://spacefellowship.com/2009/08/01/i ... llite-kit/

David

[Aero]

Great - At that price you could build your own Transit system (A precursor to GPS) for $Millions instead of $Billions!

[Skipjack]

I thought I had remembered something along those lines from a long time ago in a galaxy... cough... sorry.
So, I went and asked Clark Lindsey of Hobby Space fame about these guys. According to him, they have been arround for a few years, making rather impressive claims, but have never managed to show anything, but concepts. That is great, but they better back them up with some substance too...

Aero, there would be two problems with that: These tube- sat orbits are not stable for very long and they are not geostationary...

[Aero]

Yes. Orbit stability is desirable but a good ground tracking network would help with that problem. Add a lot of costs, too.
Transit satellites were in low, polar orbits for world wide coverage. Tube sats, not being in polar orbits, would cause a coverage problem.
That's OK though, because I don't really need my own system. GPS is good enough for me.

[KitemanSA]

These folks are touting orbital INstability as a benefit, i.e. they don't add to orbital clutter. Interesting business model.

[kurt9]

You could build and send up your own spy satellite. One that has a resolution sufficient to image individuals.

[pfrit]

You could build and send up your own spy satellite. One that has a resolution sufficient to image individuals.

Could you? What would be the minimum appeture that you would need to resolve a human at 100 miles? Is the canister that wide? I wouldn't think so, but I have been wrong before. Often. How big are the appetures of the telescopes that google earth uses? How high are they?

[Skipjack]

I think it should be almost possible. Leica just released a camera capable of 37.5 megapixels resolution. In a 4:3 format (it isnt exactly that, but to make things easier on me) this would result in a horizontal resolution of a little more than 7000 pixels. Now if we assume a lens set that is available on the open market, no big custom stuff or something, then I think we can get a 1300mm lens (Phoenix Zoom Super Telephoto 650-1300mm ). This means that in a distance of 300km you would have a horizontal field of view of roughly 5km. This would mean about 0.75 meters/pixel.
That should be enough to see a pixelsized smudge where a person is. This is of course assuming ideal weather and lighting- conditions. Super Teles need a lot of light. If the sensor does not get enough light, you will get noise and it will be difficult to differenciate noise from a person.
Still it would be pretty close to resolving a person. I am not sure what tele lenses are available beyond 1300mm on the open market. Chances are, that you can get something better somewhere.

Edit: I just checked, no chance that this would fit into a tubesat. These tubesats are only 10 cm long...

[D Tibbets]

I think it should be almost possible. Leica just released a camera capable of 37.5 megapixels resolution. In a 4:3 format (it isnt exactly that, but to make things easier on me) this would result in a horizontal resolution of a little more than 7000 pixels. Now if we assume a lens set that is available on the open market, no big custom stuff or something, then I think we can get a 1300mm lens (Phoenix Zoom Super Telephoto 650-1300mm ). This means that in a distance of 300km you would have a horizontal field of view of roughly 5km. This would mean about 0.75 meters/pixel.
That should be enough to see a pixelsized smudge where a person is. This is of course assuming ideal weather and lighting- conditions. Super Teles need a lot of light. If the sensor does not get enough light, you will get noise and it will be difficult to differenciate noise from a person.
Still it would be pretty close to resolving a person. I am not sure what tele lenses are available beyond 1300mm on the open market. Chances are, that you can get something better somewhere.

Edit: I just checked, no chance that this would fit into a tubesat. These tubesats are only 10 cm long...

Um, I'm too lazy to actually calculate the numbers for the resolving power of a lens in feet directly. But, a lens will resolve ~ 1 arcsecond for each 4 inches of aperature (Daw's or Ralieh's limits). At ~ 120 miles 1 arcsecond would be equivalent to ~ ? feet (need some trigonometry which I hate (it is mutual)).
For comparison I have heard that the Hubble telescope could resolve ~ 100 meters at the distance of the moon. At low Earth orbit that would be = 100yrds/~300,000 miles= x yrds / 120 miles= ~1/2 inch. That is with a 96 inch mirror. That would be equivalent to ~ 2 feet resolution for a 4 inch aperature lens.
But, that assumes extreamly good optics and no air. Atmospheric turbulance and scattering decreases the resolution considerably. There are two ways to combat this. One is with adaptive optics, a very complex and difficult process. The other is to take alot of short exposures (<several hundreths of a second each), then choose those rare exposures when the atmospheric turbulance just happens to be optically neutral. This gives an intermediate resolution image. Not as good as it would be without intervening air, but it serves as a poor mans 'adaptive optics'. Amatuer astronomers use this method to obtain remarkably detailed images of planets and even the ISS(perhaps several meters resolution). You can image dimmer objects by stacking the good images, but the short exposures limit this. The "Lucky imaging system" works in the same way.
http://en.wikipedia.org/wiki/Lucky_imaging

Again for comparison, a good amatuer observing site might allow 2 arcsecond seeing on good nights. Most places average 4 arcsecond or greater seeing. Excellent sites like Mona Kia (sp?) may average ~ 0.5 arcsecond seeing conditions.


Dan Tibbets

[Skipjack]

I did not have to calculate, I used my trusty 3d- app to do the calc for me