I have two questions regarding satellites. From my understanding, there is a specific altitude that satellites can be placed in to maintain a certain position relative to the earth, generally directly above the equator. I have heard reference to satellites being at 110 degrees or 119 degrees and so on. Since space is limited at this specific altitude, what is the accepted minimum distance that satellites are spaced apart?
Second, if for some reason, man stopped sending any control signals to space, how long before all of the current man-made satellites fell back to earth and/or burned up in the atmosphere? I would guess that satellites at a higher orbit take longer to fall back to earth. Would having a higher mass speed up, slow down, or have no effect on the orbit decay?
Is the space around the earth self-cleaning if we just stop shooting stuff up there?
A geosynchronous orbit is one that has an orbital period of 24 hours (well, 23 hours, 56 minutes) so the satellite appears to remain stationary over an equatorial point. Orbital “slots” are typically 2 degrees apart, with radio interference between satellites being the major concern. Thus, there’s a maximum number of equatorial geosynch sats of 180, though an “inclined” orbit (the sat is not perfectly circling the equator but has an orbit slightly tilted relative to it - from a fixed point on the ground, the satellite will appear to move in a circle) may be acceptable, with the nuisance of having to constantly adjust earthbound parabolic dishes in response. The altitude is ~22,300 miles.
Vanguard 1 was launched in 1958 and is likely to remain up there for another ~200 years. It wouldn’t surprise me if dozens of other sats are up there with even longer projected orbital lifespans.
You’re correct that satellites in higher orbits will take longer to come down. In fact, a satellite at geosynchronous height will last essentially forever. They could be knocked out by a very near pass by an asteroid, or something of the sort, but things like that are basically unpredictable. Failing that, they’ll come down in a few billion years when the Sun dies.
Space really isn’t limited. The circumference of the orbit is something like 160,000 miles.
The problem occurs if more than one satellites use the same radio frequency for communication or broadcast. Large ground-based antennas have narrow beam width, so if you use 10-ft antennas on the ground, you can put satellites 2 degrees apart transmitting at the same frequency and you can pick out one satellite by aiming your antenna. If you use non-directional antennas on the ground (e.g. satellite radio receivers), you can put only 2 or 3 satellites transmitting at the same frequency, so anywhere on earth you get signals from only one of them.
Low-orbit satellites will fall down in a matter of years or decades. Geostationary satellites probably won’t fall down at all. For a given size, the heavier the satellite, the slower the orbit decays.
I once had the privilege of visiting the uplink station (in Betzdorf, Luxembourg) for the ASTRA satellites which transmit TV signals to Europe. They are in geosynchronous orbit, but what isn’t generally realised is that they only stay there because they have onboard rocket engines which are fired every two weeks to stop them drifting out of that position. Without this it wouldn’t be long until they drifted far enough away to be unusable. Though that doesn’t mean they’d crash into the Earth - they’d probably stay in orbit for many years. The lifetime of a communications satellite is determined by the amount of fuel it can carry to power its rocket engines.
The angle that is most generally used is the inclination with respect to the Earth’s ecliptic (the plane running throught the equator). Note that while satellites have to orbit in a plane going through the center of the Earth (with a couple of oddball exceptions) they don’t need to be at the same altitude, so as long as they pass reasonably far away (~5km is a comfortable distance) it’s no worry if the orbit intercept. Most satelllites, in fact, do not orbit at the equator, and many have highly elliptical orbits to permit long dwell times over a specific area, particularly telecommunications or imaging satellites serving high latitudes.
Low satellites, like those used for ham radio signals, can only last a decade or so before drag slows the orbit and drops them into the upper atmosphere. In higher orbits, it takes much longer. At geostationary altitude (~36,000 km altitude) there is no atmosphere and the only real drag they see is from solar wind and the occasional odd tug by the Moon. I doubt the orbit would last billions of years, but certainly millions or tens of millions; probably much longer thatn it would take for them to be pulverized by dusk or destroyed by a random meteor.
Low LEO? Yes, although first it gets worse as debris from damaged satellites impacts more satellites, creating more debris in a chain reaction. This is known as the Kessler Syndrome or orbital cascading ablation.
Here is a fun tool. It displays the real-time location of 900+ satellites including the geosynchronous ones. You can also zoom and click on them to get the name, orbit and ground trace (where it will fly over). Unfortunately it is difficult to judge distance between them.
BTW, if a space elevator were to be built, the geosynchronous orbit is where the far end would be, which means the tether/ribbon will be ~22K miles long.
Geostationary orbit, at 22,240 statute miles (35,790 km) altitude. You’d actually want to extend your counterweight a little bit beyond that to maintain positive tension on the cable.
