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Gravity-2
Gravity-2 (引力二号, also romanized Yinli-2) is a two-stage, partially reusable Chinese launch vehicle under development by Orienspace, designed to place 21.5 tonnes into low Earth orbit with a recoverable first stage.
Gravity-gradient stabilization
Gravity-gradient stabilization is a passive spacecraft attitude control method using the torque from gravity's variation across a spacecraft to keep one axis pointed toward Earth, requiring no propellant.
Great Observatories program
NASA's Great Observatories program comprises four large astronomical satellites observing different wavelengths: Hubble, Compton, Chandra, and Spitzer, launched between 1990 and 2003, with Hubble and Chandra still operating.
Gregory Jarvis
Gregory Jarvis, also known as Greg Jarvis, was an American Hughes Aircraft satellite engineer who flew on the Space Shuttle Challenger and died when it broke apart in 1986.
Grid fin
A grid fin, also called a lattice fin, is an aerodynamic control surface of small cells used to steer missiles and rockets during atmospheric flight.
Gridded ion thruster
A gridded ion thruster is an electric propulsion device that accelerates ions through grids, first flown in space in 1964 and used on NASA's Deep Space 1 and Dawn.
Griffin Mission One
Griffin Mission One (Griffin-1) is a lunar lander mission by Astrobotic under NASA's CLPS, launching to Nobile Crater on a Falcon Heavy no earlier than 2026.
Ground station
A ground station, also called a tracking station or Earth terminal, is a terrestrial facility with antennas that communicates with spacecraft, sending commands and receiving data.
GSAT
GSAT (Geosynchronous Satellite) is a series of Indian geostationary communication satellites developed and operated by ISRO since 2001, carrying India's telecommunications, TV broadcasting, DTH, and broadband services.
Guiana Space Centre
The Guiana Space Centre, also known as Europe's Spaceport or Centre Spatial Guyanais, is a CNES-operated spaceport near Kourou, French Guiana, from which every ESA-developed launcher, including Ariane, has flown since 1968.
Guion Bluford
Guion Bluford, also known as Guy Bluford, is an American engineer and former NASA astronaut who became the first African American in space in 1983.
Guowang (国网)
Guowang (国网) is China's national low Earth orbit satellite internet constellation, planned at 12,992 satellites under a 2020 ITU filing and operated by China Satellite Network Group.
Gwynne Shotwell
Gwynne Shotwell, born 1963, is an American mechanical engineer and President and COO of SpaceX, where she joined in 2002 as employee No. 11 and won the 2008 NASA resupply contract.
H-I
The H-I (H-Iロケット) was a Japanese expendable launch vehicle developed by NASDA and flown nine times between 1986 and 1992, bridging the N series and the H-II.
H-II
The H-II was a two-stage Japanese expendable launch vehicle developed by NASDA as Japan's first fully domestic rocket, flying seven times from 1994 to 1999 with five successes before retirement in favor of the H-IIA.
H-II Transfer Vehicle
The H-II Transfer Vehicle (HTV), nicknamed Kounotori, was a Japanese uncrewed cargo spacecraft flown by JAXA to resupply the ISS nine times between 2009 and 2020.
H-IIA
The H-IIA, also written H2A, is a Japanese expendable liquid-fuel launch vehicle, Japan's mainstay rocket for satellites and probes, flown by JAXA from 2001 to 2025.
H-IIB
The H-IIB was a Japanese heavy-lift rocket developed by JAXA and Mitsubishi Heavy Industries, flying nine successful HTV cargo missions to the ISS from 2009 to 2020.
H3 (rocket)
The H3, or H3 Launch Vehicle, is a two-stage expendable rocket developed by JAXA and Mitsubishi Heavy Industries as Japan's flagship launcher, replacing the H-IIA in 2023.
Habitation and Logistics Outpost
The Habitation and Logistics Outpost (HALO) was a pressurized module Northrop Grumman built as the first crew cabin, command center, and docking hub of NASA's planned Gateway lunar space station.
Hainan Commercial Space Launch Site
The Hainan Commercial Space Launch Site, also called the Wenchang Commercial Space Launch Site, is China's first launch site dedicated to commercial missions, opened in Wenchang in November 2024.
Haiyang (satellite series)
Haiyang (海洋, meaning ocean) is a Chinese series of civil ocean-monitoring Earth-observation satellites in four generations, HY-1 through HY-4, operated by NSOAS and developed by CAST, begun with HY-1A in 2002.
HALCA
HALCA (はるか) was a Japanese radio astronomy satellite and the first spacecraft to perform Very Long Baseline Interferometry from space, launched in February 1997 with an 8-meter radio telescope.
Hall-effect thruster
The Hall-effect thruster, or Hall thruster, is an ion thruster in which trapped electrons ionize xenon, producing thrust for spacecraft, first flown in 1971 on the Soviet Meteor-1-10 satellite.
Halo orbit
A halo orbit is a periodic, three-dimensional orbit around a Lagrange point, first used by the ISEE-3 spacecraft in 1978 and now used by the James Webb Space Telescope.
Hard X-ray Modulation Telescope
The Hard X-ray Modulation Telescope (HXMT), renamed Insight-HXMT after launch, is China's first X-ray astronomy satellite, launched on June 15, 2017 to study black holes, pulsars, and gamma-ray bursts.
Hartebeesthoek Radio Astronomy Observatory
The Hartebeesthoek Radio Astronomy Observatory (HartRAO) is a radio astronomy and space geodesy facility near Johannesburg, South Africa, begun in 1961 as a NASA deep-space tracking station.
Haven-1
Haven-1 is a planned single-module commercial space station in low Earth orbit, developed by Vast of Long Beach, California, targeted to launch in 2027 on a SpaceX Falcon 9.
HawkEye 360
HawkEye 360 is an American signals intelligence company in Herndon, Virginia, founded in 2015, that geolocates radio frequency emissions using a low Earth orbit satellite constellation.
Hayabusa (はやぶさ)
Hayabusa, originally designated MUSES-C, was a JAXA asteroid probe launched in 2003 that returned the first asteroid surface sample, from 25143 Itokawa, to Earth in 2010.