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Hayabusa2 (はやぶさ2)
Hayabusa2 (はやぶさ2) is a Japanese asteroid sample return mission led by JAXA that collected 5.4 grams from the C-type asteroid Ryugu and returned it to Earth in December 2020.
Health threat from cosmic rays
The health threat from cosmic rays is the risk space radiation poses to astronauts outside Earth's protective magnetic field, including cancer, nervous system damage, and cataracts.
Heliocentric orbit
A heliocentric orbit, also known as a solar orbit, is an orbit around the Sun, followed by every planet, dwarf planet, asteroid, and comet in the solar system.
Helios (spacecraft)
Helios was a pair of German-American solar probes, Helios 1 and Helios 2, launched in 1974 and 1976 into orbits carrying them closer to the Sun than any earlier spacecraft.
Helios-B
Helios-B, also called Helios 2, was a West German–American solar probe launched in January 1976 that held the records for closest approach to the Sun and highest speed until 2018.
Hemispherical resonator gyro
A hemispherical resonator gyro is a gyroscope that senses rotation with a vibrating fused silica shell and no rotating parts, used in spacecraft like Cassini and Webb.
HETE (satellite)
HETE, the High Energy Transient Explorer, was a series of two small NASA satellites designed to detect and localize gamma-ray bursts; HETE-2 launched in 2000 and operated until 2008.
HETE-2
HETE-2 (High Energy Transient Explorer 2) was a small astronomical satellite built by MIT that detected gamma-ray bursts from 2000 until 2008, transmitting burst positions to ground observers within seconds.
HIFI (Herschel instrument)
HIFI, the Heterodyne Instrument for the Far Infrared, was a spectrometer aboard the European Space Agency's Herschel Space Observatory, covering 480 to 1910 GHz and identifying individual molecules in space.
High Earth orbit
High Earth orbit (HEO) is defined as an orbit around Earth above 35,786 kilometers or 2,000 kilometers. It covers geostationary and highly elliptical orbits used for communications and astronomy.
High-gain antenna
A high-gain antenna (HGA) is a directional antenna that concentrates radio power into a narrow beam, the principal dish antenna spacecraft use to communicate across interplanetary distances.
High-power rocketry
High-power rocketry is the branch of amateur sport rocketry using motors of H impulse class and above, over 160 Newton-seconds, with fliers certified by national associations.
Highly elliptical orbit
A highly elliptical orbit (HEO) is an Earth orbit with eccentricity above 0.25, used by Molniya and Tundra satellites to serve high northern latitudes where geostationary coverage fails.
HiPEP
HiPEP (High Power Electric Propulsion) is a high-power gridded ion thruster developed by a NASA Glenn Research Center-led team for the proposed Jupiter Icy Moon Orbiter mission.
Hipparcos
Hipparcos (High Precision Parallax Collecting Satellite), a European Space Agency satellite launched in 1989, was the first space mission dedicated to astrometry, precisely measuring star positions and distances.
HiRISE
HiRISE (High Resolution Imaging Science Experiment) is a camera on NASA's Mars Reconnaissance Orbiter that images the Martian surface at the highest resolution available from orbit.
Hispasat (satellite operator)
Hispasat is a Spanish satellite communications operator constituted in 1989 and based in Madrid, operating a geostationary fleet from 30° West and 61° West, controlled since 2025 by Indra.
History of SpaceX
The history of SpaceX covers the American launch company Elon Musk founded in 2002, which became the first private company to send a liquid-fueled rocket to orbit.
Hiten (ひてん) (spacecraft)
Hiten (ひてん), pre-launch name MUSES-A, was a Japanese ISAS spacecraft launched in January 1990 as Japan's first lunar mission, ending with a controlled impact on the Moon in April 1993.
Hitoshi Kuninaka
Hitoshi Kuninaka is a Japanese aerospace engineer at JAXA's Institute of Space and Astronautical Science who invented the ion engines powering the Hayabusa and Hayabusa2 asteroid sample-return missions.
Hohmann transfer orbit
The Hohmann transfer orbit is an elliptical orbit connecting two coplanar circular orbits with two engine burns; Walter Hohmann described it in 1925 as the minimum-propellant transfer.
Hosted payload
A hosted payload is a sensor or instrument attached to another party's satellite, sharing its power and communications; a NASA study found it saves nearly half the mission cost.
Hot Bird
Hot Bird is a family of Eutelsat broadcasting satellites at 13 degrees East, relaying around 900 television channels to homes across Europe, North Africa, and the Middle East.
Houston, we have a problem
"Houston, we have a problem" is a popular phrase signaling something has gone wrong, adapted from the Apollo 13 crew's 1970 radio transmission during an oxygen tank explosion.
HS-376
HS-376 is a spin-stabilized commercial communications satellite bus built by Hughes, carrying data, voice, and television; 58 satellites using it were launched between 1980 and 2003.
HS-601
The HS-601 is a three-axis, body-stabilized geostationary communications satellite bus developed by Hughes Space and Communications in California, introduced in 1987, with 84 spacecraft ordered by 17 customers.
HTPB
HTPB, or hydroxyl-terminated polybutadiene, is a liquid synthetic rubber used chiefly as the fuel-binder of composite solid rocket propellants and as the liner bonding propellant grains to motor cases.
Huang Hai CZ-11 launch zone
The Huang Hai CZ-11 launch zone, also called the Yellow Sea launch area (Haiyang), is China's sea-based launch area in the Yellow Sea off Shandong.
Huanjing
Huanjing (环境减灾), formally the Environment and Disaster Monitoring and Forecasting Small Satellite Constellation, is a Chinese Earth-observation constellation approved in 2003, with satellites launched from 2008.
Hubble (film)
Hubble (Hubble 3D, IMAX: Hubble) is a 2010 43-minute IMAX 3D documentary directed by Toni Myers, narrated by Leonardo DiCaprio, covering the Hubble telescope and the May 2009 STS-125 Atlantis servicing mission, grossing $52.5 million in the US.