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Planet: Imaging the entire Earth every day

nbremer.github.io

31–40 of 144 posts

Re: Planet: Imaging the entire Earth every day

#32

I can't believe I've never wondered this before, but I wonder how possible it is to deliberately create a satellite-blocking cloud above one's own property. What height and size it would have to be, etc.

If you could track the satellite could you not shine a laser, or bright light (maybe a mirror reflecting the sun) directly at the camera to mess up the imaging while over your region?

And if an aircraft flies over your property you could get charged with a federal offense (pointing a laser at an aircraft).

Re: Planet: Imaging the entire Earth every day

#34
Stupid question: how do they measure speed of the satellite? I mean, on the website they've mentioned the speed of one of their satellite as ~7.6 kmps. Is that the actual speed of the satellite or it's a measure of how much land the the satellite covers per second?

Re: Planet: Imaging the entire Earth every day

#36

Stupid question: how do they measure speed of the satellite? I mean, on the website they've mentioned the speed of one of their satellite as ~7.6 kmps. Is that the actual speed of the satellite or it's a measure of how much land the the satellite covers per second?

They can measure it by altitude. An orbiting object always has a defined velocity at any point of its orbit. For example, a circular orbit 500km above Earth's surface amounts to velocity of 7.61 km/s everywhere on it.

Re: Planet: Imaging the entire Earth every day

#38
post #33
post #25

"This visualization doesn't work right on Firefox+Linux, sorry! You could try Chrome/Chromium instead." No Thanks.

Chromium doesn't have all that tracking stuff right. What's wrong with it?

Not true. Chromium talks a lot to Googles servers.

Additionally, "websites" that are made for chrome drive even more people into this monoculture which is bad for the web.

Re: Planet: Imaging the entire Earth every day

#39

Stupid question: how do they measure speed of the satellite? I mean, on the website they've mentioned the speed of one of their satellite as ~7.6 kmps. Is that the actual speed of the satellite or it's a measure of how much land the the satellite covers per second?

The orbital velocity and the ground track velocity only differ by about 6.6% for their 450km orbit, so it's not a big difference. But because they have a relatively circular orbit, you can use the formula sqrt(G*M/R) which gives 7.639km/sec -- so it looks like they are referring to true orbital velocity.

Re: Planet: Imaging the entire Earth every day

#40

Stupid question: how do they measure speed of the satellite? I mean, on the website they've mentioned the speed of one of their satellite as ~7.6 kmps. Is that the actual speed of the satellite or it's a measure of how much land the the satellite covers per second?

Not an expert. But there are a few ways to look at this.

Bodies that are in stable orbit can have only a specific velocity which is a function of its distance from & mass of whatever it is orbiting. So orbiting satellite's speed can be inferred from its orbital height.

There are ground based tracking stations that can technically measure the speed of any orbiting body.

Also read somewhere that LEO satellites could use GPS receivers to get a fix on their position. measuring change in this position also gives velocity. There a bunch of limiting conditions around max-height and velocity for this to work though.

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