Artificial satellites of Earth

Artificial satellites of Earth
Name	Artificial satellites of Earth
First	Sputnik 1
Operator	Roscosmos, National Aeronautics and Space Administration, European Space Agency, China National Space Administration, Indian Space Research Organisation
Applications	Global Positioning System, International Telecommunication Union, Landsat, Hubble Space Telescope

Artificial satellites of Earth are human-made objects placed into orbit around Earth to perform functions ranging from communications and remote sensing to navigation satellite services and scientific observation. They have enabled programs such as Sputnik program, Apollo program, International Space Station, Landsat program, and Global Positioning System to transform activities in United States, Soviet Union, Russia, China, India, and European Space Agency member states. Modern fleets include platforms from SpaceX, Arianespace, Roscosmos, China Aerospace Science and Technology Corporation, and ISRO.

Overview

Artificial satellites operate under frameworks like the Outer Space Treaty and coordination bodies such as the International Telecommunication Union and United Nations Office for Outer Space Affairs. Notable platforms include Sputnik 1, Explorer 1, Vanguard 1, Ariel 1, Telstar 1, Intelsat, Inmarsat, Iridium, Galileo, GLONASS, and BeiDou. Observational missions include Landsat 8, Sentinel-1, Terra, Aqua, Envisat, Hubble Space Telescope, James Webb Space Telescope, and scientific probes like GOES, NOAA-20, ICESat-2, and GRACE.

History and development

The launch of Sputnik 1 by the Soviet Union in 1957 initiated the Space Race between United States and Soviet Union, leading to programs such as Explorer 1, Project Vanguard, Project Mercury, Gemini, and Apollo program. Cold War satellite development saw the rise of reconnaissance systems like CORONA and KH-11, meteorological series like TIROS, and communication networks exemplified by Telstar and Intelsat I (Early Bird). Later milestones include civil constellations GPS by the United States Department of Defense, GLONASS by Soviet Union/Russia, and commercial ventures by SpaceX's Starlink and OneWeb.

Types and functions

Satellites serve roles in Earth observation, meteorology, communications, navigation, astronomy, and military intelligence. Examples: Landsat program for land imaging, Sentinel satellites for Copernicus, GOES for weather monitoring, Intelsat for transoceanic communications, Iridium for mobile voice, GPS/Galileo/GLONASS/BeiDou for positioning, Hubble Space Telescope for astrophysics, and reconnaissance systems like KH series. Scientific platforms include Swift, Chandra X-ray Observatory, Planck, and ICRAR-collaborated missions.

Orbits and orbital mechanics

Satellites occupy orbits classified as LEO (e.g., International Space Station), MEO (e.g., GPS), GEO (e.g., Intelsat), and HEO (e.g., Molniya orbit). Launch vehicles like Soyuz, Saturn V, Space Launch System, Falcon 9, Ariane 5, and Long March place spacecraft into transfer trajectories such as Hohmann transfer orbit and employ maneuvers informed by Kepler's laws and the patched conic approximation. Key parameters include inclination, eccentricity, apogee, perigee, and nodal precession as addressed in orbital perturbation models used by Jet Propulsion Laboratory and agencies like European Space Operations Centre.

Launch and deployment

Launch sites such as Baikonur Cosmodrome, Kennedy Space Center, Guiana Space Centre, Tanegashima Space Center, Satish Dhawan Space Centre, and Vostochny Cosmodrome support vehicles from Roscosmos, NASA, ESA, JAXA, CNSA, and ISRO. Rideshare programs, deployers like P-POD, ESPA ring, and separation systems release cubesats and microsatellites such as CubeSat constellations deployed by universities and corporations. Notable missions include Sputnik 1 launch by R-7, Explorer 1 by Jupiter-C, and commercial launches by SpaceX for Starlink and OneWeb.

Operations, control, and lifecycle

Ground segments run by NASA Deep Space Network, European Space Operations Centre, Roscosmos control centers, and commercial mission control handle telemetry, tracking, and command. Onboard subsystems—power (solar arrays, batteries), attitude control (reaction wheels, CMGs), thermal control, and payload—are designed for lifetimes ranging from months to decades (e.g., Vanguard 1). End-of-life practices include controlled reentry (e.g., Skylab), transfer to graveyard orbit for GEO craft, and passivation to reduce explosion risk, coordinated via databases like the Space-Track catalog.

Environmental and legal issues

Space debris from collisions (e.g., Iridium–Kosmos collision), fragmentation events, and anti-satellite tests (e.g., 2007 Chinese antisatellite test, 2019 Indian ASAT test) threatens assets; mitigation guidelines are promoted by Inter-Agency Space Debris Coordination Committee and enforced by norms under the Outer Space Treaty and Liability Convention. Spectrum coordination is managed through the International Telecommunication Union; liability and registration obligations stem from the Registration Convention and disputes have involved states including United States, Russia, China, and members of European Union. Environmental concerns on Earth include launch exhaust impacts addressed in studies by National Research Council and regulatory oversight by agencies such as Federal Aviation Administration and national space agencies.

Category:Satellites