Some Orbits That Need Additional Attention

There are many many "orbital regimes" or ways to categorize orbits - there are low inclination orbits, high inclination orbits, orbits that are closer or further from the surface of the Earth. One type of orbit that gets a lot of attention is the geosynchronous orbit - where many communications satellites are stationed. Some other orbits are heavily used and yet seem to get less attention.

As a place to start to see which orbital regimes are more or less popular, look here:

World Meteorological Organization satellite page

Sun Synchronous Orbit

One is the "sun synchronous" orbit, often used for "Earth resources" kind of remote sensing satellites, these are not close to the Earth as you might expect for a photographic satellite, they are at approximately 800 km altitude. This orbital regime is use by many government satellites such as the (stand by for a hurricane of acronyms) National Oceanographic and Atmospheric Administration's (NOAA) Polar Operational Environmental Satellite (POES). Also the US Air Force's Defense Meteorological Support Program (DMSP). And the Landsat constellation, and the "A-Train" environmental satellites, the commercial WorldView imaging satellites, and many many others. These satellites are often put into "planes" that are defined by the time that they cross the equator going South to North. These planes are filled by payloads but also by the upper stages that delivered them to orbit. For instance the European Environmental Satellite (ENVISAT) or satellite number 27386 - it was in the process of being retired and so was lowered somewhat below the sun synchronous orbit - but it's upper stage (satellite number 27387) was not lowered. Now ENVISAT is in an orbit with an apogee and perigee of approximately 765 km but 27387 has an apogee of almost 800 km, though the perigee is 750 km. So the apogee is right in a very crowded altitude.

Unfortunately this orbital regime has a number of types of satellites that have tended to break up and shed pieces, as detailed in:

Satellite Breakups And Related Events

Since I wrote that I have gone back over and looked at some of the pieces shed by the DMSP satellites and they are pieces that were intentionally shed during activation. There is a bit more detail on my Errors page.

Many of these planes are getting very full of satellites and pieces of debris, of course there is a LOT of volume for satellites to spread out, but they are not evenly distributed around the planet and some orbital regimes are getting crowded. This plot shows a few satellites, none of them are upper stages. Both the NOAA and DMSP satellites have broken up, scattering pieces in their planes.

We have to make educated guesses about why some of these satellites have broken up, we don't have any firm information. My article on satellite breakups has some more information.

Again I must recognize my colleague Brian Chambers for generating this plot!

These satellites are distributed around the Earth and that does separate them, to show that I have generated this ground trace:

Trying to make something like this that is readable is not easy; I need to replace this with a ground trace from JSatTrak, to eliminate the yellow circles. But here you can see that DMSP B5D2-6, 7, and 8 are in the same plane but are distributed in their orbit. DMSP F16 and NOAA-19 (almost hidden over southern Greenland) are in a very similar orbit. These satellites are also in somewhat different altitudes.

What is needed is more understanding of why these satellites break up, it would also be very useful to have a way to (if a potential break up is identified) help prevent future breakups. Another useful capability would be something that would allow us to lower the orbit of these large upper stages and payloads - so that if they did break up the pieces would be below the operational satellites. Still, they would likely be far above other operational satellites such as the ISS! Lowering a sun synchronous satellite to below 400 km would be expensive.

There are MANY objects in these orbits - both payloads and upper stages. Just a very few examples are:

Having worked with objects like ISS a lot, I wondered how much objects would separate in plane after having been in orbit for years. If they are of different sizes and densities they might separate in altitude and then their planes would precess at different rates. So I looked at some representative launches and it looks like they do not. Here is a launch from Plesetsk, 2003-031 or Monitor-E and some small sats that went into orbit with the payload.

The bottom blue line is the payload - object 27840 - which is the largest object. The other objects are small sats, some or most of them are CubeSats. Even over 14 years, the are still in the same plane. They do not appear to be dispersing in altitude or plane (altitude would drive dispersal in plane). This indicates to me that drag due to the atmosphere does not affect them much - due to being at such a high altitude.

One very odd thing to note is that there was another payload on that flight - Mimosa (object 27841) which was a payload from the Czech Republic. It was recorded as decaying in Dec 2011, while the rest of the payloads (presumably very similar in density) are still at 830 km circular orbits. Hmmm.

This is one set of satellites where I wish I could see the raw observations - these small, older, satellites are often not tracked much. They are probably maintained by the computer and the computer can mix them up. But the TLEs show very regular trends.

ISS Orbit (A Low Altitude Orbit)

Some people have noticed that there are many small satellites being deployed, both from the International Space Station (ISS) and from expendable rockets. The ISS orbits only just above the appreciable atmosphere (at about 400 km) and so small satellites that are deployed from it will not last long. Many small satellites only survive for approximately 6 months, when they get down to about 160 km they will soon reenter.

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as of: 10 Feb 2019