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RapidEye
RapidEye was a commercial Earth-observation constellation of five identical satellites, launched on a single rocket in August 2008 and operated until March 2020, delivering 5-meter multispectral imagery for agriculture.
Rassvet (ISS module)
Rassvet is a Russian ISS module attached to Zarya, launched in 2010, used for cargo storage and as a docking port for Soyuz and Progress vehicles.
RD-170
The RD-170 is a Soviet liquid-oxygen and kerosene rocket engine made by NPO Energomash in Moscow, powering Energia strap-on boosters and the Zenit first stage from 1985.
RD-180
The RD-180 (РД-180) is a Russian liquid oxygen and kerosene rocket engine developed by NPO Energomash that has powered the first stage of the Atlas V since 2002.
RD-214
The RD-214 (GRAU index 8D59) was a Soviet four-chamber liquid-propellant engine developed by Valentin Glushko's bureau to power the first stage of the R-12 missile and the Kosmos-2 launcher.
Reaction control system
A reaction control system (RCS) is a set of small rocket thrusters on a spacecraft or aircraft, used for attitude control, small maneuvers, and station keeping, unlike main propulsion.
Reaction wheel
A reaction wheel, also called a momentum wheel, is a flywheel spun by an electric motor to control a spacecraft's orientation; three or four wheels give precise three-axis pointing.
Real-time kinematic positioning
Real-time kinematic positioning (RTK) is a satellite-navigation surveying technique in which a base station sends corrections to a moving receiver, giving centimeter accuracy in real time.
Reconnaissance satellite
A reconnaissance satellite, also known as a spy satellite, is an unmanned spacecraft in orbit that collects intelligence, chiefly imagery and intercepted signals; the first successes reached orbit in 1960.
Red fuming nitric acid
Red fuming nitric acid (RFNA) is a storable liquid rocket oxidizer, made of concentrated nitric acid with dissolved nitrogen dioxide, which gives it a reddish color and toxic fumes.
Reduced-gravity aircraft
A reduced-gravity aircraft, nicknamed the Vomit Comet, flies steep parabolic arcs giving passengers about 20 seconds of weightlessness, used by space agencies to train astronauts and test equipment.
Reentered spacecraft, 1970–1979
The reentered spacecraft of 1970–1979 include the Soyuz 11 crew lost during descent in 1971, Cosmos 954's reactor over Canada in 1978, and Skylab in July 1979.
Reentered spacecraft, 1980–1989
Covers spacecraft reentries from 1980 to 1989, a decade averaging about 100 large reentries yearly, from routine Shuttle landings to Soviet stations deorbited over the Pacific.
Reentered spacecraft, 1990–1999
Reentered spacecraft, 1990–1999 surveys roughly 50 to 110 cataloged reentries each year, defined by the uncontrolled 1991 reentry of the 40-tonne Salyut 7 station over Argentina.
Reflect Orbital
Reflect Orbital is an American aerospace startup, founded in 2021 and based in the Los Angeles area, that plans to sell "sunlight on demand" by reflecting sunlight from satellites onto the ground at night.
Reflection Grating Spectrometer
The Reflection Grating Spectrometer (RGS) is a pair of X-ray spectrometers aboard ESA's XMM-Newton observatory, the first to use reflection gratings, covering the 0.33 to 2.5 keV band.
Regenerative cooling
Regenerative cooling is a rocket engine technique in which a propellant flows through channels in the chamber and nozzle walls to cool them, then returns the absorbed heat to combustion.
Relative navigation
Relative navigation is the determination of a spacecraft's position, velocity, and attitude relative to another vehicle rather than a ground reference, enabling autonomous rendezvous, docking, on-orbit servicing, and planetary landing.
RemoveDEBRIS
RemoveDEBRIS was a British-led technology demonstration satellite deployed from the ISS in 2018 that tested space debris removal with a net, harpoon, and drag sail.
Repulsor (rocket)
The Repulsor was a series of small liquid-propellant rockets built by Klaus Riedel of the German amateur society VfR, flown near Berlin in 1931 and 1932.
Resilience (lander)
Resilience was a Japanese lunar lander built by ispace, launched in January 2025 and destroyed in a June 2025 landing attempt after a faulty laser rangefinder.
Resistojet
A resistojet is an electrothermal spacecraft thruster in which an electrical resistance heater heats a gaseous propellant that expands through a nozzle, first flown on a US Navy satellite in 1965.
Resonant orbit
A resonant orbit is a spacecraft orbit whose period is commensurate with a repeating cycle, usually Earth's rotation, so it passes over the same ground points on schedule.
Resourcesat
Resourcesat is a series of Indian Earth observation satellites operated by ISRO for land-resource remote sensing, launched between 2003 and 2016 and carrying three cameras that combine wide coverage with fine detail.
Resurs-F
Resurs-F (Ресурс-Ф, "Resource") was a Soviet and Russian family of film-return Earth observation satellites built by TsSKB in Samara, photographing Earth in visible and near-infrared light from 1979 to 1999.
Reusability (launch vehicles)
Reusability in launch vehicles is the practice of recovering and reflying rocket hardware like the first stage, pioneered by the Space Shuttle and made routine by SpaceX's Falcon 9.
Reusable spacecraft
A reusable spacecraft is a space vehicle designed to fly multiple missions, recovering its hardware instead of discarding it, ranging from the Space Shuttle to SpaceX's Falcon 9 and Starship.
Reusable Vehicle Testing
Reusable vehicle testing is the sequence of ground and flight campaigns proving reusable launch vehicles can survive launch, reentry, landing, and reflight, tracing to NASA's 1990s demonstrators.
RFA One
RFA One is a three-stage small orbital launch vehicle developed by Rocket Factory Augsburg, a German company majority-owned by OHB, designed to carry small satellites to low Earth orbit.
RHESSI
RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager), originally HESSI, was a NASA satellite launched in 2002 to study solar flares in X-rays and gamma rays.