Satellite Heaven and Hell - the 2 Strategies for their Decommissioning

By Adjunct Associate Professor Todd Hutchison

Ever wondered what happens to satellites at the end of their useful life, and how their operational life is measured?

There are specifically two orbits for these satellites: geosynchronous and geostationary. The geosynchronous orbit provides for any inclination, which is an angle of the orbit in relation to the Earth’s equator as it synchronizes with the rotation of the Earth. Geostationary orbits fall in the same category as geosynchronous orbits, however lie on the same place as the equator that is referred to as having zero inclination. This is shown below:

Image taken from GISGeography[1].

These satellites occupy a high Earth orbit, being approximately 42,164 kilometres from the centre of the Earth (i.e., 35,786 kilometres above the Earth’s surface) at latitudes above about 81°[2] with a general life span of 15-18 operational years[3].

Satellites in this orbit generally provide telecommunications, meteorology monitoring, navigation, military and remote sensing functionality. The antennas point to Earth to receive and transmit data to, and between, Earth stations. The physical distance between a geostationary satellite and Earth stations causes approximately a 250-millisecond delay when consisting voice communications.

Its orbital period is 24 hours, making it matching the rotation of the Earth, thereby making it appearing fixed at one point in the sky from the Earth’s perspective.  In 1945, Arthur C. Clarke in his paper entitled Extra-Terrestrial Relays – Can Rocket Stations Give Worldwide Radio Coverage?, acknowledged three satellites suitably located around the equator could provide cover to almost all the Earth's surface useful for broadcasting and relaying communications signals[4]. Others argue up to 6 satellites[5], however the orbit height plays a key factor to its surface area coverage.

Image from ScienceDirect[6]

It was US Navy technician and electrical engineer, Harold Rosen, who led the team (who included Don Williams, Tom Hudspeth and John Mendel) to design and build the first successful Syncom 2 geosynchronous orbit satellite in 1963 in time to relay live television signals from the Tokyo Summer Olympics, although the first Syncom 1 attempt failed due to an electronics issue. The US President John F. Kennedy also phoned the Nigerian prime minister Abubakar Tafawa Balewa from a ship on the August 23 1963[7]. Its size had a diameter of 76 centimetres (30 in), height of 38 centimetres (15 in), and weighed 11.3 kilograms (25 lb). Syncom 3 was the first geostationary orbit-based satellite that was launched by Dekta D Rocket in 1994[8], with the commercialisation of such satellites occurring only two years later in 1965.

There are a limited number of slots available to place the satellite, and with their spacing being important to avoid harmful radio-frequency interference from other satellite that can interfere with signal quality.

Unfortunately, geostationary satellite antennae does move off course due to coriolis forces (the separation of electronic and nuclear motions[9]), the moon’s attraction and solar flux. This requires the need to maintain its antennae position through a process called stationkeeping. This process involves releasing repositioning gas in spurts that is transformed into a plasma that brings useful energy to provide propulsion from the thrusters that will effectively move the azimuth or elevation of the satellite, bringing it pointing back to the Earth stations.

A geostationary satellite’s life usage comes to at end as it runs out of propulsion fuel used in staionkeeping. This fuel source helps keep the satellite antenna to point to the earth station, however as it runs. There are two options for the post-operational disposal of the satellite, one going up towards heaven and the other going down in a fiery ball in hell (so to speak).  

The first and historic option is where satellites use their last propellant fuel to push it a few hundred kilometres above the operational orbit. The amount of fuel to do this is reportedly the same as maintaining its position for 3 months in operation[10]. They end up in the graveyard orbit, otherwise known as the junk orbit or the spacecraft graveyard.

Such space junk creates risk to other satellites or spacecrafts called the kessler effect after NASA scientist Donald J. Kessler in 1978 theorised where a collusion could cause a cascade of space debris[11]. As all geostationary orbits in the same plane, attitude and speed allows for lower collision speed of space debris, with any debris less than 10cam in diameter not being able to be seen by Earth[12]. Unfortunately, spacecraft collisions have occurred. (Click here to see satellite debris from the Telkom-1 satellite incident[13]).

The following diagram shows the graveyard orbit distances:

Image from Wikipedia[14]

The fact that there are thousands of used satellites now occupying space a new solution was needed. Based on the Union of Concerned Scientists (UCS) database[15], there are currently 2,666 active satellites known to be orbiting Earth with 1,918 in a low Earth orbit [16], which interestingly is the same number reported back in 2005[17].  There is expected to be around the same number that are no longer active and floating in space.

This UCS database reports the 2,666, being owned by[18]:

• United States: 1,327
• Russia: 169
• China: 363
• Other: 807

Orbits are elliptical in shape (i.e., an oval shape). Satellites must be at least 100 kilometres from the Earth’s surface to be in space. In fact that is the definition of where space begins, known as the Karman line[19]. Satellite placements are recorded and categorised by orbit:

• Low Earth Orbit (LEO): 1,918 satellites (160 – 2,000 km from Earth’s surface)
• Medium Earth Orbit (MEO): 135 satellites (2,000 – 25,786 km from Earth’s surface)
• Elliptical Orbit: 59 satellites (37.015 km from the Earth’s surface).
• Geostationary Orbit (GEO): 554 satellites (24,786 km from the Earth’s surface).

The following diagram depicts a non-scale version of these orbits.

Image by Jagran Josh[20]

In comparison, the International Space Station is in the Low Earth Orbit (LEO) that is 161 to 322 kilometres from the Earth’s surface that about 90 minutes to complete one orbit cycle[21].

An object in motion in an orbit will stay in motion until some force pulls or pushes it[22]. This provides an opportunity to take a different strategy for destroying in-active satellites. Modern satellites now use the propulsion fuel to slow the satellite’s speed down to cause it to drop towards Earth, through a process called deorbiting to what is known as the disposal orbit. This results in a decay of the satellite’s body as it enters into the Earth’s atmosphere due to atmospheric drag and ultimately it burns up from the heat friction of air as it descends. This takes approximately 12 months from its decommissioning.

Given the dependence on communications and GPS devices, that also help guide military armoury, space is being increasingly militarised, with a race to control the space above the sky[23]. This is seeing countries expand from their navy, army and air forces to now include space forces.

ABOUT THE AUTHOR

Adjunct Associate Professor Todd Hutchison began his career in broadcast engineering, working in both territorial and satellite microwave engineering, including installing the first 13-metre digital satellite solutions for commercial television in Australia.

Todd's role was the Microwave Link Manager and working in RF with high voltage transition and Satellite Earth stations. He has worked in commercial television and as a operator in the master control rooms of earth stations communicating with satellites in both the Indian and Pacific Ocean regions, and working for commercial television stations, including STW9, TVW7, ABW2, NEW10 and TVNZ.

This is an image of a younger Todd Hutchison in a commercial television’s master control room, controlling earth stations transmissions in both the Indian Ocean and Pacific Ocean regions.

Todd now teaches in Curtin University’s Masters of Engineering.  He has an MBA in Technology Management and a Master of Commerce in Information Systems.  He is an international bestselling author and listed in the Who's Who of Business in Australia.

REFERENCES

[1] https://gisgeography.com/geosynchronous-geostationary-orbits.

[2] https://en.wikipedia.org/wiki/Geostationary_orbit

[3] https://en.wikipedia.org/wiki/Geosynchronous_orbit

[4] https://en.wikipedia.org/wiki/Geostationary_orbit

[5] https://ral.ucar.edu/~djohnson/satellite/coverage.html.

[6] https://www.sciencedirect.com/topics/engineering/geostationary-satellites

[7] https://www.latimes.com/nation/la-na-syncom-satellite-20130726-dto-htmlstory.html

[8] https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1964-047A

[9] https://www.sciencedirect.com/topics/chemistry/coriolis

[10]https://en.wikipedia.org/wiki/Graveyard_orbit.

[11] https://en.wikipedia.org/wiki/Kessler_syndrome

[12] https://spacenews.com/exoanalytic-video-shows-telkom-1-satellite-erupting-debris/

[13] https://www.youtube.com/watch?v=4FXX1kSNljU&feature=emb_logo

[14] https://en.wikipedia.org/wiki/Graveyard_orbit

[15] https://ucsusa.org/resources/satellite-database

[16] https://www.geospatialworld.net/blogs/how-many-satellites-orbit-earth-and-why-space-traffic-management-is-crucial/

[17] https://www.ucsusa.org/resources/satellite-database

[18] https://ucsusa.org/resources/satellite-database

[19] https://www.sciencelearn.org.nz/resources/272-launching-satellites

[20] https://www.jagranjosh.com/general-knowledge/definition-of-low-earth-orbit-1553683068-1

[21] https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-orbit-58.html

[22] https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-orbit-58.html

[23] https://www.aljazeera.com/ajimpact/space-force-race-control-space-sky-190829095755687.html