Odd question. (Satelite)

buzzardsbay

Does anyone know how fast (eg speed per hour or rate) a satelite can travel in the atmosphere of the earth. Say how fast could it move between Boston and New York. Also does anyone know the angle of view the satelite would have (eg field of vision)?



I've been told the imagery they have is so strong they can tell what kind of cigarette someone is smoking on a clear day. But they can only look straight down because of how far up they are.



Thanks for your time.



Cheers,

Dan

drewprops

Why do you want to know this....comrade?

buzzardsbay

Just out of curiosity, I was looking at terraerver online and thought of the question.



I hope someone hear has the answers.



Dan.

towel

I suppose anything I've learned from Tom Clancy is unclassified...



Spy satellites orbit rather low, actually, since resolution decreases with distance. They're usually in low polar orbits, making an orbit every 90 minutes or so. That works out to about...[smoke emerging from ears] 18,000 mph. It can see as far as the horizon (doesn't have to be straight down), but again, resolution drops with distance and takes a further hit from having to look through more smog-filled atmosphere at an oblique angle. You can probably do some trig to calculate how much of the 24,000-mile-circumference earth is visible from a satellite orbiting at 80-100 miles above its surface.



Edit: You realize, though, that the images on microsoft.terraserver.com aren't satellite images? They're all aerial photos, taken at 20,000 feet. Yet spy satellites orbiting fifty times higher can have a resolution several-fold greater. Pretty cool.



[ 03-03-2003: Message edited by: Towel ]</p>

ghost_user_name

Simple high school physics can answer the first part of your question. As for the second part, that all depends on the type of lense on the satellite's camera.



G * m1 * m2 / r^2 = m1 * v^2 / r



m1 is the mass of the satellite, m2 is the mass of the earth, and G is the gravitational constant. m1 cancels leaving you with v and r as your two variables. v is the velocity of the satellite and r is the radius from the center of the earth.



Here I've solved v as a function of r.



v = sqrt(G * m2 / r)



To use an altitude above earth's surface rather than a radius from the center, here's a final equation for you. I've input the constants already:



v = sqrt((6.67 * 10^-11) * (5.98 * 10^24) / (6.38 * 10^6 + d))



d is now the distance from the earth's surface or the altitude.



Sufficient?



edit: important vote: velocity is measured in meters per second and distance is measured in meters.



another important note: this does not take into account air resistance of a satellite *in* the earth's atmosphere. Most are high enough that this isn't a factor.



[ 03-03-2003: Message edited by: Brad ]</p>

ebby

Satellites can only look straight down because lightwaves become distorted when they pass through the atmosphere. (The less atmosphere, the less distortion) I heard some satellites have the magnification to read the date off a quarter, but it is currently impossible (* ) because of the heat distortion in the atmosphere.



*I was told this information a few years ago by an UNCREDITABLE source. However, I do think it is possible to map heat distortion by measuring the distortion's effect on an inferred laser and running it through a simple computer program. This would allow satellites to see clearer and/or sideways. (Even through windows <img src="graemlins/surprised.gif" border="0" alt="[surprised]" /> :eek: )



[ 03-03-2003: Message edited by: Ebby ]</p>