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Hubble Space Telescope
The Hubble Space Telescope, also known as the Hubble Telescope, is a 2.4-meter NASA/ESA observatory launched in 1990 that observes ultraviolet, visible, and near-infrared light from above Earth's atmosphere.
HughesNet
HughesNet is a satellite internet service operated by Hughes Network Systems, an EchoStar company, launched in 1996 as one-way DirecPC and now running on the JUPITER Ka-band satellite fleet.
Human Landing System
The Human Landing System is the NASA program of commercially built lunar landers carrying Artemis astronauts to the Moon: SpaceX's Starship and Blue Origin's Blue Moon.
Human mission to Mars
A human mission to Mars is a proposed crewed spaceflight to Mars, with no official landing date; NASA, SpaceX, and China are the main actors.
Human Research Program
The Human Research Program (HRP) is a NASA program established at Johnson Space Center in 2005 that investigates and reduces spaceflight risks to astronaut health and performance.
Human spaceflight
Human spaceflight, also called manned spaceflight, is the flight of people to and from space in life-supporting vehicles, beginning with Soviet cosmonaut Yuri Gagarin in 1961.
Huygens (spacecraft)
Huygens was a European Space Agency probe that landed on Saturn's moon Titan on 14 January 2005, the first landing in the outer Solar System.
Hybrid-propellant rocket
The hybrid-propellant rocket, or hybrid rocket motor, is a chemical rocket combining a solid fuel with a separately stored liquid or gaseous oxidizer, allowing throttling and shutdown by controlling oxidizer flow.
Hydrazine
Hydrazine, also called diazane, is a toxic, fuming compound of nitrogen and hydrogen used as a rocket propellant and to make agricultural chemicals and blowing agents.
Hyperbola-1
Hyperbola-1 (双曲线一号, SQX-1) is a four-stage solid-propellant orbital rocket developed by the private Chinese company iSpace, the first privately funded Chinese rocket to reach orbit in 2019.
Hyperbolic trajectory
A hyperbolic trajectory, also called a hyperbolic orbit, is the open path of a body moving under gravity with more than escape energy, corresponding to eccentricity greater than 1.
Hypergolic propellant
A hypergolic propellant, also called hypergolic fuel, is a rocket propellant combination whose fuel and oxidizer ignite spontaneously on contact, typically monomethylhydrazine and dinitrogen tetroxide, making engines reliable and storable for years in spacecraft.
Hypersonic inflatable aerodynamic decelerator
A hypersonic inflatable aerodynamic decelerator (HIAD) is a deployable aeroshell that acts as both heat shield and drag device, packing small and inflating larger than any rocket fairing.
I-2K
I-2K, also written I-2000 for INSAT-2000, is a geostationary satellite bus from ISRO's U R Rao Satellite Centre, used for missions including GSAT, INSAT, and Hylas-1.
I-3K
The I-3K, also known as INSAT-3000, is a geostationary satellite bus developed by ISRO's U R Rao Satellite Centre for 3,000 to 3,500 kg communication satellites.
iBOSS (spacecraft)
iBOSS (intelligent Building Blocks for On-Orbit Satellite Servicing) is a German modular spacecraft architecture in which satellites are assembled from cubic modules joined by a multifunctional interface.
ICESat-2
ICESat-2, the Ice, Cloud, and land Elevation Satellite-2, is a NASA satellite launched in 2018 that measures the height of ice sheets, sea ice, and forests from orbit.
Igor Cherepinsky
Igor Cherepinsky is a Ukrainian-born American aerospace engineer who directs Sikorsky Innovations, works on rotorcraft autonomy and flight controls, and joined the National Academy of Engineering in 2025.
IKAROS (イカロス)
IKAROS (イカロス) is a solar sail demonstrator built by JAXA, launched on May 21, 2010, and the first spacecraft to demonstrate solar-sail propulsion and thin-film solar power generation.
IKONOS
IKONOS was a commercial Earth-observation satellite, launched in September 1999 after the first spacecraft was lost, that delivered the world's first commercial one-meter satellite imagery until 2015.
Ilan Ramon (אילן רמון)
Ilan Ramon (אילן רמון), born Ilan Wolferman, was an Israeli Air Force colonel who became the first Israeli astronaut, dying in the 2003 Columbia disaster.
Illness and injuries during spaceflight
Illness and injuries during spaceflight are the medical events, from rashes to evacuations, that astronauts experience before, during, and after missions in the spaceflight environment.
IM-1
IM-1, also known as Intuitive Machines IM-1, was a 2024 lunar mission by Intuitive Machines whose Nova-C lander Odysseus made the first commercial Moon landing near the lunar south pole, the first US landing since 1972.
IM-2
IM-2, also known as Intuitive Machines IM-2, was a 2025 robotic lunar mission that landed closer to the Moon's South Pole than ever before, but its lander Athena tipped over.
IM-3
IM-3, or Intuitive Machines IM-3, is the third CLPS lunar lander mission of Intuitive Machines, targeted to land the Nova-C lander Trinity at Reiner Gamma in 2027.
Imaging X-ray Polarimetry Explorer
The Imaging X-ray Polarimetry Explorer (IXPE) is a NASA space observatory, launched in December 2021 with the Italian Space Agency, that measures X-ray polarization from black holes, neutron stars, and pulsars.
IMAP (spacecraft)
IMAP (Interstellar Mapping and Acceleration Probe) is a NASA heliophysics observatory that launched in 2025 and orbits the Sun-Earth L1 point, mapping the heliosphere's boundary and providing early warning of harmful space radiation.
Impulse Space
Impulse Space is an American in-space mobility company founded in 2021 in Redondo Beach, California, by Tom Mueller, SpaceX's first employee, building spacecraft that move payloads between orbits.
Indian Human Spaceflight Programme
The Indian Human Spaceflight Programme, also known as the Indian manned space program, is ISRO's effort to fly Indians to low Earth orbit via the Gaganyaan missions.
Indian National Satellite System
The Indian National Satellite System (INSAT) is India's multipurpose geostationary satellite system for telecommunications, television broadcasting, meteorology, disaster warning, and search and rescue, operated by ISRO since 1983.