# What would be a “big picture” understanding of how the orbits of Earth satellites are monitored?

In preparation for another question, I typed "keeping track of satellites in orbit" into a search engine, and found a website called keeptrack.space which has a bunch of features that look cool but I don't understand.

There are dropdown menus that list some locations where I assume there is equipment that keeps track of Earth satellites. They may be a mix of radar and optical (vis and IR) but I don't know.

In fact I don't even know what the official term for keeping track of (all of) Earth satellites is. I always thought there was some giant farm of megaWatt radar antennas in some government facility in the US and something similar in a few other big countries, but it's a vague notion, and that may be more for total awareness of space debris including the very small objects.

Question: What would be a "big picture" understanding of how the orbits of Earth satellites are monitored? Are there a few main facilities that do this, or is it a distributed effort? Is it mostly optical, or radar, or are both roughly equally important?

For some background, a discussion of an optical vis-NIR telescope for satellite monitoring can be found in Aerospace.org's article Ground-Based Telescopes for Space Awareness.

below: screen shots of pull-down menus from http://keeptrack.space/

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below: "Aerotel captured this image of three actively maintained geostationary satellites (center) with another satellite nearby (lower left). For this observation, the telescope was staring at one spot, with no tracking movement. Thus, the stationary satellites appear as dots, while the background stars, which are moving at the natural sidereal rate, appear as streaks." From here.

Satellites are routinely monitored by the likes of US, Russia and China. China for example is known to blind American spy satellites with lasers.

The goal is to track the approx 23000 (sources vary from 10 to 25000) objects, which could be anything from a satellite, debris from launches and even lost items from EVAs.

US monitoring systems

radar USSSN - US space surveillance network

Monitoring is accomplished in the US by the USSSN, the US space surveillance network. The majority of sensors are radars. They allow tracking of smaller objects, that cannot be tracked optically, they are distributed around the globe, they can track under any weather conditions. Facilities of the USSSN are located everywhere around the world, Alaska, California, Spain, Norway, Greenland, UK, and various islands in the atlantic, indian and pacific ocean. The objective is cpmplete coverage of the geosynchronous belt. There are dedicated sensors as well as civilian sensors that share their data. Optical sensors operate in favorable weather at night or during sun set/rise.

The organizational unit responsible is the US Strategic Command's Joint Functional Component Command for Space.

optical

GEODSS - Ground based electro-optical deep space surveillance

is a dedicated optical system and is part of the USSSN. They can detect 20cm objects in geo orbit, which is not bad.

The telescopes can either track the stars, then the stars appear as dots and orbiting objects appear as streaks. This is SOP. The complementary mode is target track, which means, that the telescope tracks a space object, all other objects, such as stars, appear as streaks.

Radar is just radar. Depending on the system the output is either a data stream of tracks, video or pictures.

The tracking information of all these sensors is sent in realtime to Cheyenne Mountain Air Station, Colorado, where they.

facilities

The list of observing facilities in the screenshot is identical to the USSSN locations. Clear is Clear AFB in Alaska. Xuanhua is a chinese phased array radar on a mountain in northern china. The RUS sensors are from the SKKP.

US space catalogs

military

All the data is fed into the US space catalog, which tracks everything from small debris left over from space walks to the space station. The Air Force and the Navy maintain separate catalogs.

civilian

NASA publishes all non-classified objects. The offical catalog is available at https://www.space-track.org/

Classified tracks are not available, but it will come as no surprise that this information is readily available on the internet as this seems to be a rather popular hobby in astronomy circles.

A reasonably proficient hobbyist can track satellites with an optical telescope

Tracking is not as complicated as it may sound at first. Two observations are usually enough to determine the track. Usually everything stays in the same orbit or as a decaying orbit, if it is in a low orbit. Some satellites can maneuver and are therefore harder to track, but far from impossible.

Tracking every piece in orbit is very important to ensure safe access to space and safe operation in space. The ISS had to make maneuvers to avoid debris in the past.

Russia

Russia operates a similar system to the USSSN named SKKP. No further information is available

China

The Chinese satellite telemetry tracking and control network consists of the Xian satellite control center (XSCC), a number of fixed posts and three mobile units under the command of XSCC and ocean going instrumentation ships. source NAIC