A satellite, often known as an artificial satellite, is an object that has been launched into orbit in space on purpose. To this day, The Earth is orbited by thousands of artificial satellites. Communication relay, weather forecasting, navigation, broadcasting, scientific research, and Earth observation are just a few of the many applications for satellites.
Satellites have a variety of uses, including communication relay, weather forecasting, navigation, broadcasting, scientific research, and Earth observation. Some take pictures of the planet that help meteorologists predict weather and track hurricanes. Some take pictures of other planets, the sun, black holes, dark matter or faraway galaxies to better understand the universe and solar system.
Only 4,852 of the 8,261 satellites orbiting the Earth as of January 2022, according to UNOOSA records, are functioning (as at the end of December 2021). Where do these satellites go when they die? Satellites come in many shapes and sizes and there are different classes of satellites, which drive you to longer or shorter lifespans. Depending on how high the satellite is now, there are two options. Engineers will utilize the remains of the satellite's fuel to slow down smaller, closer-to-Earth satellites, which will cause the satellite to fall out of orbit and burn up in the atmosphere. The only option for bigger satellites that orbit higher in space is to alter the velocity of the object to send it far away from the orbit.
There is a design lifetime, and an environment lifetime for a satellite. The cost of launch to GEO is substantially higher, so satellites must be built to make better use of that cost for a longer period of time to justify the budget, which contributes to the short design lifetime in LEO. LEO satellites will experience higher drag than a GEO satellite because they are less expensive and often not planned for as long a lifetime. One of the most crucial design factors that should be considered while doing mission design is the lifetime of a satellite. There are many distinct types of satellites with various purposes, including spy, communication, and GPS satellites. They all function under a very diverse set of circumstances, and their design lives vary accordingly.
Image credits: NASA
Various perturbing factors can change the orbit of any satellite in Earth orbit. Atmospheric drag is a major factor for satellites in low Earth orbit, with perigee altitudes below 2000 km. Slowly but surely, this force seeks to circularize the orbit and lower its altitude. At heights below 200 km, the orbit's "decay" rate becomes extremely rapid, and by the time the satellite descends to 180 km, it will only have a few hours to live before making a violent reentry back to Earth. In most cases, the temperatures reached during this re-entry are high enough to melt the majority of the satellite, but in other cases, such as when the satellite is especially massive or under specific circumstances, component pieces may reach the ground.
An orbit below an altitude of roughly 2,000 kilometers is known as a low Earth orbit (LEO) (1,200 mi). Since air molecules are present at this height, there is a rise in drag, which results in orbital decay (more so during solar maxima, due to the expansion of gasses in the atmosphere). Because of this drag, these LEO orbited satellites require frequent reboots; otherwise, their orbital velocity drops, and they spiral towards the lower atmosphere.
The geostationary orbit is a circular orbit 35,786 km (22,236 mi) above the equator, and at high altitudes, air drag is comparably less than LEO orbit. Geosynchronous orbit satellites typically have a practical lifetime of 15 years, which is a restriction imposed mostly by the depletion of onboard propellant. The propellant is required for "station-keeping," which is the process of keeping the satellite in its orbital slot and maintaining its in-orbit attitude so that its solar panels and antennae are oriented in the right directions. And in that way, the longevity of an orbiting satellite is determined by the architecture of the satellite and its environmental design itself.
Written by Zira A.
References:
Boag, S. (2019). The Lifespan of Orbiting Satellites. [online] European Space Imaging. Available at: https://www.euspaceimaging.com/the-lifespan-of-orbiting-satellites/.
May, S. (2014). What Is a Satellite? [online] NASA. Available at: https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-satellite-58.html.
Via Satellite. (2012). Satellite Life Extension: the Technology and the Economics - via Satellite -. [online] Available at: https://www.satellitetoday.com/telecom/2012/03/01/satellite-life-extension-the-technology-and-the-economics/ [Accessed 4 Jan. 2023].
www.spaceacademy.net.au. (n.d.). Orbital Lifetimes. [online] Available at: http://www.spaceacademy.net.au/watch/debris/orblife.htm [Accessed 4 Jan. 2023].
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