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Satellites Taking Pictures of Rockets Carrying More Satellites

planet.com

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Re: Satellites Taking Pictures of Rockets Carrying More Satellites

#41

Post by vonuebelgarten »

jofer wrote: post #35
nine_k wrote: post #29

Earlier quoted context omitted.

I suspect it's related to the need to possibly re-orient the satellite to have a particular place visible by the camera. It must be relatively slow, and possibly even cost reaction mass, thus the commitment to shoot more of the same area.

Rapideye and SkySat aside, Planet primarily operates a monitoring constellation, rather than a tasking constellation. The doves (satellites used to take this and the satellites being launched) are focused on imaging the land surface of the Earth with an approximately daily cadence. They don't target a particular area, try to reorient, or even have active propulsion (just reaction wheels). This is an exception -- the…

Their strategy is particularly awesome: a hundred of small short-lived satellites (really small, they're 3-unit cubesats, 30x10x10 cm) operating in a swarm. No big deal if a single one is lost: operation can continue with other ones once they are in position. Also, costs are spread due the possibility of servicing several customers simultaneously in separate locations around the globe.

Re: Satellites Taking Pictures of Rockets Carrying More Satellites

#43

Post by natch »

ChuckMcM wrote: post #7
natch wrote: post #2

Would love to see an actual speed version of this... what's the hurry?

Think about the system[1], you've got to take a picture, store it, and then downlink it. If you take too many pictures your downlink is overloaded and you run out of memory. Assuming that an HD frame is about 2 megabytes once it is compressed, that is a 2 - 5 mbs downlink speed (depending on error correction). The satellites they launch are tiny and low power so they will have a limited budget for down link bandwidth…

Whoosh. Nobody is arguing that they don't have the frames that they have. As we can plainly see, they have plenty of frames from which to make a video that runs in closer to real time.

All they need to do is adjust the frame playback rate to make the video last longer. Yes it will have little jerky movements but it would give time for the viewer to enjoy and ponder what they are seeing.

Re: Satellites Taking Pictures of Rockets Carrying More Satellites

#44

Post by natch »

andrewstuart2 wrote: post #11
jessriedel wrote: post #8

Earlier quoted context omitted.

If bandwidth were the main limiting factor, they would just take video intermittently and downlink it over a long period of time. This would be useful for documenting real-time changes on the ground during important isolated events (e.g., rocket launches). But they apparently don't have this capability, and I think it's because the hardware for taking many frames per second just isn't worth the cost and complexity.

As mentioned in parent, the rate you can capture depends on the resolution (i.e. image size in bytes), downlink speed, available memory, and length of the event. As the length of the event approaches infinity, the framerate you can capture is basically bandwidth / image size. `(mb/s)/mb = 1/s` (aka hz). Beyond that limit, the memory size / image size gives you a hard limit for the number of additional frames you can…

The playback speed can also be adjusted by changing the frame rate of playback. Each frame just stays on the screen for a longer time. Similar to the -delay parameter when creating a GIF in ImageMagick.

Re: Satellites Taking Pictures of Rockets Carrying More Satellites

#45

Post by nickelbackfan »

natch wrote: post #43
ChuckMcM wrote: post #7

Earlier quoted context omitted.

Think about the system[1], you've got to take a picture, store it, and then downlink it. If you take too many pictures your downlink is overloaded and you run out of memory. Assuming that an HD frame is about 2 megabytes once it is compressed, that is a 2 - 5 mbs downlink speed (depending on error correction). The satellites they launch are tiny and low power so they will have a limited budget for down link bandwidth…

Whoosh. Nobody is arguing that they don't have the frames that they have. As we can plainly see, they have plenty of frames from which to make a video that runs in closer to real time. All they need to do is adjust the frame playback rate to make the video last longer. Yes it will have little jerky movements but it would give time for the viewer to enjoy and ponder what they are seeing.

You could play the video at a slower speed if that is what you want, the youtube player goes down to 0.25x speed.

Re: Satellites Taking Pictures of Rockets Carrying More Satellites

#46

Post by andrewstuart2 »

natch wrote: post #44
andrewstuart2 wrote: post #11

Earlier quoted context omitted.

As mentioned in parent, the rate you can capture depends on the resolution (i.e. image size in bytes), downlink speed, available memory, and length of the event. As the length of the event approaches infinity, the framerate you can capture is basically bandwidth / image size. `(mb/s)/mb = 1/s` (aka hz). Beyond that limit, the memory size / image size gives you a hard limit for the number of additional frames you can…

The playback speed can also be adjusted by changing the frame rate of playback. Each frame just stays on the screen for a longer time. Similar to the -delay parameter when creating a GIF in ImageMagick.

That's not in question. Yes, playback framerate is independent from recording framerate.

The question is the availability of resources (memory and bandwith) to the satellite and how many frames it can store without needing to transmit them over its slow downlink.

Re: Satellites Taking Pictures of Rockets Carrying More Satellites

#47

Post by natch »

andrewstuart2 wrote: post #46
natch wrote: post #44

Earlier quoted context omitted.

The playback speed can also be adjusted by changing the frame rate of playback. Each frame just stays on the screen for a longer time. Similar to the -delay parameter when creating a GIF in ImageMagick.

That's not in question. Yes, playback framerate is independent from recording framerate. The question is the availability of resources (memory and bandwith) to the satellite and how many frames it can store without needing to transmit them over its slow downlink.

The frames are already back on earth now, as evidenced by the video being on Youtube. Adjusting the playback rate of those frames is what I'm talking about...

Re: Satellites Taking Pictures of Rockets Carrying More Satellites

#48

Post by natch »

nickelbackfan wrote: post #45
natch wrote: post #43

Earlier quoted context omitted.

Whoosh. Nobody is arguing that they don't have the frames that they have. As we can plainly see, they have plenty of frames from which to make a video that runs in closer to real time. All they need to do is adjust the frame playback rate to make the video last longer. Yes it will have little jerky movements but it would give time for the viewer to enjoy and ponder what they are seeing.

You could play the video at a slower speed if that is what you want, the youtube player goes down to 0.25x speed.

Indeed. That gets us part of the way there.

Re: Satellites Taking Pictures of Rockets Carrying More Satellites

#49

Post by Gravityloss »

notahacker wrote: post #21
Pica_soO wrote: post #20

Earlier quoted context omitted.

Has somebody recombined low res data from many satellites to a high res free version? Sort of like many synced cheap oscilloscopes can form a expensive one?

There is pansharpening (effectively improving the spatial resolution of colour images by combining them with sharper, higher spatial-resolution monochrome images) and using processing techniques to combine low-res images can certainly improve the effectiveness of detecting features which are smaller than the image pixel size, but I don't think anyone's likely to get comparable detail to a sub-1m or even a 5m pixel im…

Why not? You can treat it as a statistical problem where you are given low Res samples of the actual data. I've done it myself on a school assignment. A matrix inversion was required. There are things like sensor shift cameras commercially available too. And stacking software for astronomers etc...
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