Discussion
I was watching a news program the other day and they talked about how spy satellites capture images each time the satellite passes over head, also watched a program on Starlite and why so many satellites are needed is because earth moves out of range
but you have TV satellites receiving and transmitting constantly now, so i am really quite confused
Can anyone explain?
but you have TV satellites receiving and transmitting constantly now, so i am really quite confused
Can anyone explain?
Spy satellites need to be close to the Earth (known as Low Earth Orbit) to get high resolution on the images.
TV satellites are desired to be in a fixed position in the sky (known as Geostationary orbit).
LEO is between 100 and 1200 miles. Although lower than 400 will experience atmospheric drag and eventually fall out of orbit without maintenance.
GEO is ~36000 miles.
TV satellites are desired to be in a fixed position in the sky (known as Geostationary orbit).
LEO is between 100 and 1200 miles. Although lower than 400 will experience atmospheric drag and eventually fall out of orbit without maintenance.
GEO is ~36000 miles.
Some modern communication satellites are quite low earth orbit too - particularly ones used for the internet. The problem with these types of orbits is that the satellite crosses the sky in around 5 minutes so you will only be able to link to it for that length of time. In order to have continuous coverage, you need to have other satellites in the system available to link to as each one rises and sets quickly. This is why the Starlink system consists of hundreds of satellites all whizzing about in low earth orbit.
Eric Mc said:
Some modern communication satellites are quite low earth orbit too - particularly ones used for the internet. The problem with these types of orbits is that the satellite crosses the sky in around 5 minutes so you will only be able to link to it for that length of time. In order to have continuous coverage, you need to have other satellites in the system available to link to as each one rises and sets quickly. This is why the Starlink system consists of hundreds of satellites all whizzing about in low earth orbit.
Thousands, but yes, currently over 3300.Target is 12000
annodomini2 said:
Thousands, but yes, currently over 3300.
Target is 12000
True.Target is 12000
The problem with low earth orbit satellites is that the satellite experiences aerodynamic drag and will fall back into the atmosphere after a relatively short period of time - unless boosted to a higher orbit on a regular basis. That technique is limited by the amount of fuel on board.
One of the reasons why Starlink requires thousands of satellites is because they need to replenish the "constellation" on a regular basis. Quite a few Starlink satellites have already re-entered.
Eric Mc said:
annodomini2 said:
Thousands, but yes, currently over 3300.
Target is 12000
True.Target is 12000
The problem with low earth orbit satellites is that the satellite experiences aerodynamic drag and will fall back into the atmosphere after a relatively short period of time - unless boosted to a higher orbit on a regular basis. That technique is limited by the amount of fuel on board.
One of the reasons why Starlink requires thousands of satellites is because they need to replenish the "constellation" on a regular basis. Quite a few Starlink satellites have already re-entered.
what is the altitude at which aerodynamic drag is no longer a problem, if so is it really that much more expensive to reach, I'd have thought it would be cheaper than having to conduct more launches and build more satellites to replace those lost? Or is it a case of at that altitude they wouldn't actually be able to do what they're required to?
The lower the altitude, the greater the aerodynamic drag experienced. Drag can be experienced out to a few thousand miles.
The problem is that sometimes low altitude orbit is what is required for the mission, such as spy satellites for example.
You just have to put up with the inconvenience of low earth orbit drag in order to use the satellite as effectively as possible.
The problem is that sometimes low altitude orbit is what is required for the mission, such as spy satellites for example.
You just have to put up with the inconvenience of low earth orbit drag in order to use the satellite as effectively as possible.
annodomini2 said:
Spy satellites need to be close to the Earth (known as Low Earth Orbit) to get high resolution on the images.
TV satellites are desired to be in a fixed position in the sky (known as Geostationary orbit).
LEO is between 100 and 1200 miles. Although lower than 400 will experience atmospheric drag and eventually fall out of orbit without maintenance.
GEO is ~36000 miles.
GEO is ~36000km, or 22000 miles.TV satellites are desired to be in a fixed position in the sky (known as Geostationary orbit).
LEO is between 100 and 1200 miles. Although lower than 400 will experience atmospheric drag and eventually fall out of orbit without maintenance.
GEO is ~36000 miles.
Dr Jekyll said:
How much does it cost to launch a small satellite these days? How does it compare with the cost of building the satellite?
SpaceX have a rideshare price calculator, for various orbit options, and details of current availability. Looks like you can get up to 50kg to a sun-synchronous orbit for $300K.This is a map of the Starling satellites.
https://satellitemap.space/
Hard to imagine what it will be like when they're all up there!
You can see the most recently launched as they are still all in line.
https://satellitemap.space/
Hard to imagine what it will be like when they're all up there!
You can see the most recently launched as they are still all in line.
A while back, on a clear night, I was watching satellites go over and doing a count of them whilst waiting for meteors. From memory I counted about 11 which were doing polar orbits for some sort of earth observation.
Now, I saw 8 going North to south in direction and 3 going south to north. Which popped a question into my mind " is there any preference for one over the other?" or , to put it another way, what causes a preference ? I assumed it must be due to launch location, whether the launch direction has to avoid areas such as population or neighbouring countries, but I don't have any evidence for this. I tried looking online but didn't really come up with much.
Any thoughts or better internet sleuthing ?
Now, I saw 8 going North to south in direction and 3 going south to north. Which popped a question into my mind " is there any preference for one over the other?" or , to put it another way, what causes a preference ? I assumed it must be due to launch location, whether the launch direction has to avoid areas such as population or neighbouring countries, but I don't have any evidence for this. I tried looking online but didn't really come up with much.
Any thoughts or better internet sleuthing ?
As an aside (ie not disagreeing with Eric, just raising an interesting point) - are you sure they were all satellites?
I was doing similar last year and using an app to work out what each satellite was - a remarkable number of satellites were in fact space junk (notably a failed Chinese launcher that had been up there about 20 years).
Have a look here https://satellitemap.space/ - you can see how just the StarLinks (and others) move - the idea is there's a 'web' of satellites overhead and in order to do that they need to travel in different directions.
I was doing similar last year and using an app to work out what each satellite was - a remarkable number of satellites were in fact space junk (notably a failed Chinese launcher that had been up there about 20 years).
Have a look here https://satellitemap.space/ - you can see how just the StarLinks (and others) move - the idea is there's a 'web' of satellites overhead and in order to do that they need to travel in different directions.
Anything orbiting a planet, moon or star can be classified as a "satellite" even if it is dead or not providing any sort of useful function - such as an expired satellite, a spent upper stage or even a glove or tool box (the latter two have become satellites in the past).
Generally, a spent upper stage will remain in the orbit that it was left in after it had deployed its payload.
If the upper stage is fairly long, it may enter a tumbling mode which you can spot because the light levels rise and fall as it rotates. I watched something of that nature go overhead last July. I timed the rotations at precisely eight seconds.
Generally, a spent upper stage will remain in the orbit that it was left in after it had deployed its payload.
If the upper stage is fairly long, it may enter a tumbling mode which you can spot because the light levels rise and fall as it rotates. I watched something of that nature go overhead last July. I timed the rotations at precisely eight seconds.
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