Editing Category:Satellites (section)

== Applications ==

=== Earth observation ===
Main article: Earth observation satellite
[[File:Earth Radiation Budget Satellite.jpg|thumb|Deployment of the Earth Radiation Budget Satellite on STS-41-G, collecting data on Earth's weather and climate]]
Earth observation satellites are designed to monitor and survey the Earth, called remote sensing. Most Earth observation satellites are placed in low Earth orbit for a high data resolution, though some are placed in a geostationary orbit for an uninterrupted coverage. Some satellites are placed in a Sun-synchronous orbit to have consistent lighting and obtain a total view of the Earth. Depending on the satellites' functions, they might have a normal camera, radar, lidar, photometer, or atmospheric instruments. Earth observation satellite's data is most used in archaeology, cartography, environmental monitoring, meteorology, and reconnaissance applications. As of 2021, there are over 950 Earth observation satellites, with the largest number of satellites operated with Planet Labs.

Weather satellites monitor clouds, city lights, fires, effects of pollution, auroras, sand and dust storms, snow cover, ice mapping, boundaries of ocean currents, energy flows, etc. Environmental monitoring satellites can detect changes in the Earth's vegetation, atmospheric trace gas content, sea state, ocean color, and ice fields. By monitoring vegetation changes over time, droughts can be monitored by comparing the current vegetation state to its long term average. Anthropogenic emissions can be monitored by evaluating data of tropospheric NO<sub>2</sub> and SO<sub>2</sub>.

=== Communication ===
Main article: Communications satellite

=== Spy satellites ===
Main article: Reconnaissance satellite

When an&#x20;Earth observation satellite or&#x20;a communications satellite is deployed for&#x20;military&#x20;or&#x20;intelligence&#x20;purposes, it is known as a spy satellite or reconnaissance satellite.

Their uses include early missile warning, nuclear explosion detection, electronic reconnaissance, and optical or radar imaging surveillance.

=== Navigation ===
Main article: Satellite navigation

Navigational satellites are satellites that use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few meters in real time.

=== Telescope ===
Main article: Space telescope
[[File:Hubble Space Telescope (27946391011).jpg|thumb|The Hubble Space Telescope]]
Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects.

=== Experimental ===
Tether satellites are satellites that are connected to another satellite by a thin cable called a tether. Recovery satellites are satellites that provide a recovery of reconnaissance, biological, space-production and other payloads from orbit to Earth. Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation. Space-based solar power satellites are proposed satellites that would collect energy from sunlight and transmit it for use on Earth or other places.

=== Weapon ===
Main articles: Space weapon, Anti-satellite weapon, and Early warning satellite

Since the mid-2000s, satellites have been hacked by militant organizations to broadcast propaganda and to pilfer classified information from military communication networks. For testing purposes, satellites in low earth orbit have been destroyed by ballistic missiles launched from the Earth. Russia, United States, China and India have demonstrated the ability to eliminate satellites. In 2007, the Chinese military shot down an aging weather satellite, followed by the US Navy shooting down a defunct spy satellite in February 2008. On 18 November 2015, after two failed attempts, Russia successfully carried out a flight test of an anti-satellite missile known as ''Nudol''. On 27 March 2019, India shot down a live test satellite at 300&#x20;km altitude in 3 minutes, becoming the fourth country to have the capability to destroy live satellites.

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