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Sierra Nevada Corporation
Sierra Nevada Corporation (SNC) is a privately held American aerospace and national security company, founded in 1963 and owned by Eren and Fatih Ozmen since 1994.
Sierra Space
Sierra Space is an American commercial aerospace and defense company in Louisville, Colorado, spun off from Sierra Nevada Corporation in 2021; it develops the Dream Chaser spaceplane and LIFE habitats.
Simplified Aid For EVA Rescue
The Simplified Aid For EVA Rescue (SAFER) is a small propulsive backpack worn on spacewalks, letting a drifting astronaut fly back to the spacecraft if a tether fails.
Single-stage-to-orbit
A single-stage-to-orbit (SSTO) vehicle, also called one stage to orbit, reaches low Earth orbit using a single rocket stage. No Earth-launched SSTO has ever flown.
Sirius Satellite Radio
Sirius Satellite Radio, also known as CD Radio, was one of the two licensed US satellite radio companies. It launched in 2002 and merged with XM in 2008 to form Sirius XM.
Sirius XM
Sirius XM is an American subscription audio entertainment company broadcasting music, sports, and talk channels by satellite and streaming, formed when Sirius and XM merged in 2008.
Sky Group
Sky Group, formerly British Sky Broadcasting (BSkyB) and Sky plc, is a European entertainment company owned by Comcast since 2018, operating Sky News and Sky Sports.
Sky Italia
Sky Italia is an Italian pay television and broadband company launched in 2003 from the merger of Stream and Telepiù, headquartered in Milan and part of Comcast's Sky Group.
SkyFall (helicopter)
SkyFall is a NASA mission announced in 2026 that will send three Mars helicopters evolved from Ingenuity to map subsurface water ice and scout future landing sites.
Skylab
Skylab was the first United States space station, a laboratory built from a Saturn V stage that hosted three crews in 1973 and 1974 and reentered in 1979.
Skylab 2
Skylab 2 was the first crewed mission to the Skylab space station, launched in May 1973, whose crew repaired the damaged station during a 28-day flight.
Skylab 3
Skylab 3 was the second crewed mission to Skylab, the first United States space station, launched July 28, 1973 with astronauts Alan Bean, Owen Garriott, and Jack Lousma aboard.
Skylab 4
Skylab 4 was the third and final crewed mission to Skylab, keeping astronauts Carr, Gibson, and Pogue in orbit for a record 84 days in 1973 and 1974.
Skylab B
Skylab B was the backup Skylab orbital workshop built for NASA, never flown and displayed at the Smithsonian's National Air and Space Museum since 1976.
Skylark (rocket)
Skylark was a British solid-fuel sounding rocket developed by the Royal Aircraft Establishment between 1954 and 1956, first flown at Woomera in 1957 and retired in 2005 after 441 launches.
Skylon (spacecraft)
Skylon, also known as Reaction Engines Skylon, is a British concept for a fully reusable, unpiloted spaceplane powered by the air-breathing SABRE engine, developed from 1989 until 2024.
Skynet (satellite)
Skynet is the United Kingdom Ministry of Defence's family of military communications satellites, in service since 1969 and now supplying NATO under an agreement running from 2020.
SkySat
SkySat is a commercial Earth-observation constellation of 21 high-resolution imaging satellites built by Skybox Imaging and operated by Planet Labs since 2017, delivering 50 cm imagery and full-motion video.
SLATS (satellite)
SLATS, nicknamed TSUBAME, was a Japanese JAXA engineering test satellite that operated at super low altitudes down to 167.4 km from 2017 to 2019 using an ion engine.
SLIM (lunar lander)
SLIM, short for Smart Lander for Investigating Moon, was a JAXA lunar lander that landed within 55 meters of its target near Shioli crater on January 20, 2024.
SLV (Indian rocket)
The SLV-3 was India's first satellite launch vehicle, an all-solid four-stage rocket developed by ISRO, led by A. P. J. Abdul Kalam and flown four times between 1979 and 1983.
SM-65 Atlas
The SM-65 Atlas, also known as the Atlas ICBM, was the United States Air Force's first operational intercontinental ballistic missile, deployed from 1959 to 1966.
Small satellite
A small satellite, or SmallSat, is an artificial satellite commonly defined as having a wet mass below 500 kilograms, built at a fraction of conventional spacecraft cost.
SMART-1
SMART-1 was a European Space Agency lunar orbiter launched in 2003, Europe's first Moon mission, which flight-tested solar-electric ion propulsion before being deliberately crashed onto the Moon in 2006.
SMOS (satellite)
SMOS (Soil Moisture and Ocean Salinity) is a European Space Agency Earth observation satellite launched in 2009 to measure soil moisture over land and sea surface salinity.
Sojourner (rover)
Sojourner, also known as Mars Sojourner, was NASA's six-wheeled solar-powered rover deployed by the Mars Pathfinder lander on July 4, 1997, the first wheeled vehicle operated on another planet.
Solar and Heliospheric Observatory
The Solar and Heliospheric Observatory (SOHO) is a joint ESA-NASA solar observatory launched in 1995 to study the Sun from a point 1.5 million kilometers sunward of Earth.
Solar Anomalous and Magnetospheric Particle Explorer
SAMPEX, the Solar Anomalous and Magnetospheric Particle Explorer, was the first NASA Small Explorer satellite, launched in 1992 to study charged particles and operated until 2004.
Solar Dynamics Observatory
The Solar Dynamics Observatory (SDO) is a NASA solar-physics spacecraft launched on February 11, 2010, observing the Sun nearly continuously to understand solar variability and space weather.
Solar Maximum Mission
The Solar Maximum Mission, known as SolarMax, was a NASA solar observatory launched in February 1980 that observed solar flares and was repaired in orbit in 1984, the first such servicing.