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Tracking and Data Relay Satellite System
The Tracking and Data Relay Satellite System (TDRSS) is NASA's constellation of geostationary communications satellites, operating since 1983, that gives the International Space Station and Hubble near-continuous contact with Earth.
Trans-lunar injection
Trans-lunar injection (TLI), also called a lunar transfer orbit, is the burn sending a spacecraft from Earth orbit toward the Moon, used by Apollo and Artemis missions.
Transit 5
Transit 5 was a series of United States Navy navigation satellites in the Transit program, the precursor to GPS, developed by the Johns Hopkins Applied Physics Laboratory.
Transiting Exoplanet Survey Satellite
The Transiting Exoplanet Survey Satellite (TESS) is a NASA space telescope led by MIT that hunts exoplanets by an all-sky survey; it launched in 2018 and has found nearly 6,000 planets.
Transponder
A transponder is a receiver-transmitter combination that receives a signal at one frequency and retransmits it at another, relaying traffic between satellite ground stations and controlling spacecraft.
Transporter-1
Transporter-1 was a SpaceX Falcon 9 rideshare mission launched on January 24, 2021, the first dedicated SmallSat Rideshare flight, deploying a record 143 satellites into sun-synchronous orbit.
Transtage
The Transtage was a restartable hypergolic upper stage built by Martin Marietta for the Air Force's Titan III and Titan 34D rockets, flying 47 missions between 1964 and 1989.
Trimble RTX
Trimble RTX is a real-time Precise Point Positioning correction technology from Trimble Inc., introduced in 2011, delivering centimeter-level GNSS accuracy without a local base station or VRS network.
Tripoli Rocketry Association
The Tripoli Rocketry Association (TRA) is an American non-profit, incorporated in 1986, that certifies high-power rocketry with the NAR and runs the annual LDRS and BALLS national launches.
Tselina-2
Tselina-2 (Целина-2) was a series of Soviet and later Russian electronic intelligence satellites that combined area survey and detailed direction finding in one spacecraft, launched 23 times between 1984 and 2007.
Tselina-D
Tselina-D was a Soviet electronic intelligence satellite, launched from 1970 until 1994, that determined the exact location and operating characteristics of radars detected by its companion satellites.
Tselina-OM
Tselina-OM (Целина-ОМ, GRAU index 11F616M) is a Soviet electronic intelligence satellite, the modernized wide-area Tselina-O, with 34 satellites launched from Plesetsk on Kosmos-3M rockets between 1968 and 1982.
Tsiklon-2
Tsiklon-2, also written Tsyklon-2 and known as Tsyklon-M, was a Soviet and later Ukrainian two-stage orbital launch vehicle that flew 106 times from 1969 to 2006.
Tsiklon-3
Tsiklon-3 (Циклон-3, also Tsyklon-3) was a Soviet and later Ukrainian three-stage orbital launch vehicle derived from the R-36 missile, flying 122 missions from Plesetsk between 1977 and 2009.
Tsukuba Space Center
Tsukuba Space Center (TKSC, 筑波宇宙センター) in Tsukuba, Japan, opened in 1972, is JAXA's largest research complex, controlling the Kibo ISS module, training astronauts, and tracking satellites.
Turksat
Türksat is the Turkish state-owned satellite operator, Türksat A.Ş., and its fleet of six active communications satellites, including the indigenously built Türksat 6A launched in 2024.
Two-line element set
A two-line element set (TLE) is a standardized two-line, 69-character format describing the mean orbital elements of a cataloged Earth-orbiting object, used with the SGP4 or SDP4 models.
u-blox PointPerfect
u-blox PointPerfect is a family of high-precision GNSS correction services sold by the Swiss company u-blox, launched in 2021 to bring satellite positioning to centimeter accuracy.
U.S. Space & Rocket Center
The U.S. Space & Rocket Center is a state-owned space museum in Huntsville, Alabama, opened in 1970, home of Space Camp, and official visitor center for NASA's Marshall Space Flight Center.
Uchinoura Space Center
Uchinoura Space Center, formerly Kagoshima Space Center, is a JAXA launch facility in Kagoshima Prefecture, Japan, established in 1962, from which Japan's first satellite, Ohsumi, launched in 1970.
Udupi Ramachandra Rao (ಉಡುಪಿ ರಾಮಚಂದ್ರ ರಾವ್)
Udupi Ramachandra Rao (ಉಡುಪಿ ರಾಮಚಂದ್ರ ರಾವ್), known as U. R. Rao, was an Indian space scientist who supervised India's first satellite, Aryabhata, and chaired ISRO from 1984 to 1994.
Uhuru (satellite)
Uhuru, also designated Explorer 42 or SAS-1, was an American X-ray astronomy satellite launched in 1970, the first satellite entirely devoted to studying cosmic X-ray sources.
UK Space Agency
The UK Space Agency, also known as the United Kingdom Space Agency, is the government body for UK civil space policy, founded in 2010 and merged with DSIT in 2026.
Ultraviolet Explorer
The Ultraviolet Explorer (UVEX) is a NASA space telescope selected in 2024 to survey the entire sky in ultraviolet light, with a planned launch in 2030 and a two-year prime mission.
Ulysses (spacecraft)
Ulysses was a joint ESA/NASA space probe that, from 1990 to 2009, made the first surveys of the Sun's polar regions from a near-polar solar orbit.
Umbra (satellite constellation)
Umbra is a commercial X-band synthetic aperture radar satellite constellation operated by Umbra Lab in Santa Barbara, California, imaging Earth day and night in any weather at 25 cm resolution.
Uncrewed spacecraft
An uncrewed spacecraft, also called a robotic spacecraft, is a vehicle that operates in space without people on board; the first was Sputnik 1, launched in 1957.
Underwater habitat
An underwater habitat, or undersea habitat, is a pressurized seafloor structure where people live and work underwater for extended periods, entering through a moon pool.
United Kingdom Rocketry Association
The United Kingdom Rocketry Association (UKRA), founded in 1996, is the national body representing model, high power, and amateur rocketry in the United Kingdom, providing safety codes and certification.
United Launch Alliance
United Launch Alliance (ULA) is a 50-50 joint venture of Boeing and Lockheed Martin, formed in 2006, whose rockets include the Atlas V and the Vulcan Centaur.