RM-81 Agena
Encyclopedia
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
rocket upper stage and satellite support bus which was developed by Lockheed
Lockheed Corporation
The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1912 and later merged with Martin Marietta to form Lockheed Martin in 1995.-Origins:...
initially for the canceled WS-117L reconnaissance satellite program. Following the split-up of WS-117L into SAMOS
Samos (satellite)
The Samos E or SAMOS program was a relatively short-lived series of reconnaissance satellites for the United States in the early 1960s, also used as a cover for the intitial development of the KH-7 Gambit system...
and Corona
Corona (satellite)
The Corona program was a series of American strategic reconnaissance satellites produced and operated by the Central Intelligence Agency Directorate of Science & Technology with substantial assistance from the U.S. Air Force...
for image intelligence, and MIDAS
Missile Defense Alarm System
The Missile Defense Alarm System was an American system of 12 early-warning satellites that provided limited notice of Soviet intercontinental ballistic missile launches between 1960 and 1966...
for early warning, the Agena was later used as an upper stage, and an integrated component, for several programs, including Corona
Corona (satellite)
The Corona program was a series of American strategic reconnaissance satellites produced and operated by the Central Intelligence Agency Directorate of Science & Technology with substantial assistance from the U.S. Air Force...
reconnaissance satellites and the Agena target vehicle
Agena Target Vehicle
The Agena Target Vehicle was an unmanned spacecraft used by NASA during its Gemini program to develop and practice orbital space rendezvous and docking techniques and to perform large orbital changes, in preparation for the Apollo program lunar missions.-Operations:Each ATV consisted of an Agena-D...
used to demonstrate rendezvous
Space rendezvous
A space rendezvous is an orbital maneuver during which two spacecraft, one of which is often a space station, arrive at the same orbit and approach to a very close distance . Rendezvous requires a precise match of the orbital velocities of the two spacecraft, allowing them to remain at a constant...
and docking during Project Gemini
Project Gemini
Project Gemini was the second human spaceflight program of NASA, the civilian space agency of the United States government. Project Gemini was conducted between projects Mercury and Apollo, with ten manned flights occurring in 1965 and 1966....
. It was used as an upper stage on Atlas
Atlas-Agena
The Atlas-Agena was an American expendable launch system derived from the SM-65 Atlas missile. It was a member of the Atlas family of rockets, and was used for 119 orbital launches between 1960 and 1978....
, Thor
Thor-Agena
Thor-Agena was a series of orbital launch vehicles. The rockets used Thor first stages and Agena second stages. They are thus cousins of the more famous Thor-Deltas, which founded the Delta rocket family. The first attempted launch of a Thor-Agena was in January 1959...
, Thorad
Thorad-Agena
The Thorad-Agena was an American expendable launch system, derived from the Thor and Delta rockets. The first stage of the rocket was the stretched variant of the Thor which had been developed for the Delta programme. The second stage was the Agena-D, which had already been used in conjunction with...
and Titan IIIB rockets, and considered for others including the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
and Atlas V
Atlas V
Atlas V is an active expendable launch system in the Atlas rocket family. Atlas V was formerly operated by Lockheed Martin, and is now operated by the Lockheed Martin-Boeing joint venture United Launch Alliance...
. A total of 365 Agena rockets were launched between February 28, 1959 and February 1987, when the last Agena D was launched.
On some missions, the payload was built directly into the Agena, which provided it with electric power, communications and three-axis stabilization. Payload components were usually located ahead of the Agena's standard bulkhead. On missions where the payload was not built into the Agena, and instead separated after launch, the Agena was known as an Ascent Agena. The Agena was upgraded twice from the original Agena-A in order to support heavier and more sophisticated satellites, such Corona spacecraft with multiple and more powerful cameras.
The final Agena launch was of an Agena-D on 12 February 1987, configured as the upper stage of a Titan 34B. In all, 365 Agena vehicles were launched by NASA and the US Air Force
Characteristics
The Agena was 5.0 feet (1.5 m) in diameter, three-axis stabilized (for the benefit of the reconnaissance system cameras) and its Bell 8096 engine produced 16,000 lbs. (71 kN) of thrust using unsymmetrical dimethyl hydrazineHydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
(UDMH
UDMH
Unsymmetrical dimethylhydrazine is a toxic volatile hygroscopic clear liquid, with a sharp, fishy, ammoniacal smell typical for organic amines. It turns yellowish on exposure to air and absorbs oxygen and carbon dioxide. It mixes completely with water, ethanol, and kerosene. In concentration...
) as the fuel, and inhibited red fuming nitric acid
Red fuming nitric acid
Red fuming nitric acid is a storable oxidizer used as a rocket propellant. It consists mainly of nitric acid , also containing 13% dinitrogen tetroxide and 3% water. The dissolved nitrogen dioxide is very concentrated and can be found at room temperature...
(IRFNA) as the oxidizer. This is a hypergolic fuel/oxidizer combination, and as such, it does not need an ignition system. This rocket engine could be restarted multiple times in orbit, by radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
command, and it frequently was. The engine was notable for its unusual aluminum construction. The regeneratively-cooled channels that cooled the throat and nozzle were formed from straight gun drill
Gun drill
Gun drills are straight fluted drills which allow cutting fluid to be injected through the drill's hollow body to the cutting face. They are used for deep drilling—a depth-to-diameter ratio of 300:1 or more is possible. Gun barrels are the obvious example; hence the name...
formed channels. The engine was derived from the XLR-81 propulsion unit for the canceled rocket-propelled nuclear warhead pod of the Convair
Convair
Convair was an American aircraft manufacturing company which later expanded into rockets and spacecraft. The company was formed in 1943 by the merger of Vultee Aircraft and Consolidated Aircraft, and went on to produce a number of pioneering aircraft, such as the Convair B-36 bomber, and the F-102...
B-58 Hustler
B-58 Hustler
The Convair B-58 Hustler was the first operational supersonic jet bomber capable of Mach 2 flight. The aircraft was designed by Convair engineer Robert H. Widmer and developed for the United States Air Force for service in the Strategic Air Command during the 1960s...
bomber. Until 1959, the Agena was also known as Discoverer Vehicle or Bell Hustler. The manned Project Apollo
Project Apollo
The Apollo program was the spaceflight effort carried out by the United States' National Aeronautics and Space Administration , that landed the first humans on Earth's Moon. Conceived during the Presidency of Dwight D. Eisenhower, Apollo began in earnest after President John F...
Lunar Module ascent stage engine was modeled closely on the Agena engine.
Attitude control of the horizontal flying Agena was provided by an inertial reference package with three gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...
s, two horizon sensors, and micro-jets using a nitrogen-freon mixture of cold gas. Pitch and roll
Aircraft principal axes
An aircraft in flight is free to rotate in three dimensions: pitch, nose up or down about an axis running from wing to wing), yaw, nose left or right about an axis running up and down; and roll, rotation about an axis running from nose to tail. The axes are alternatively designated as lateral,...
were sensed by two hermetic integrating gyro units. A rate gyro unit determined yaw error by sensing orbital rate. Pitch and roll gyro errors were corrected from the horizon sensors, which were later supplemented by Sun and star trackers. This enabled Agena to accommodate the higher pointing stability required for better ground resolution imaging with the improved Corona cameras.
As Agena was designed to hold a fixed orientation in space while orbiting Earth, a passive thermal control system was devised.
The main source of Agena's electrical power were Silver peroxide-zinc batteries
Silver-oxide battery
A silver oxide battery , not to be confused with a similar but different silver–zinc battery, which is a secondary cell, is a primary cell with relatively very high energy/weight ratio. They are costly due to the high price of silver...
, which from the early 1960s on were supplemented by solar arrays. An S-band beacon enable Agena to receive ground command sequences (image motion compensation, altered attitude, ...), which could be stored for later execution
Versions
Three versions of the Agena were flown:| Variant | Engine | Thrust | Burn time | Rockets | number of launches |
|---|---|---|---|---|---|
| Agena-A | Bell 8048 | 69 kN | 120 seconds | Atlas, Thor | 20 |
| Agena-B | Bell 8081 | 71 kN | 240 seconds | Atlas, Thor | 76 |
| Agena-D | Bell 8096 (Bell 8247 on Agena Target Vehicle) | 71 kN | 265 seconds | Atlas, Thor, Thorad, Titan IIIB | 269 |
Agena-A
The Agena A was the first type of Agena to be built. It was launched atop Thor and Atlas rockets, mostly into polar orbits from Vandenberg Air Force BaseVandenberg Air Force Base
Vandenberg Air Force Base is a United States Air Force Base, located approximately northwest of Lompoc, California. It is under the jurisdiction of the 30th Space Wing, Air Force Space Command ....
Launch Complex 75 and Point Arguello
Point Arguello
Point Arguello is a headland used as a launch site by the United States Navy. Point Arguello was first used in 1959 for the launch of military and sounding rockets. It was transferred to the United States Air Force in 1964, at which time it became part of Vandenberg Air Force Base.There were 6...
Launch Complex 1
Vandenberg AFB Space Launch Complex 3
Space Launch Complex 3 is a launch site at Vandenberg Air Force Base that has been used by Atlas and Thor rockets. It was built in the early 1960s and consists of two pads, SLC-3E and SLC-3W . The East-West coastline at Vandenberg allows SLC-3 to launch over-ocean polar trajectories that avoid...
respectively. Two Atlas launches occurred from Launch Complex 14
Cape Canaveral Air Force Station Launch Complex 14
Launch Complex 14 is a launch site at Cape Canaveral Air Force Station, Florida. LC-14 was used for various manned and unmanned Atlas launches, including the Friendship 7 flight aboard which John Glenn became the first American to orbit the Earth....
at Cape Canaveral
Cape Canaveral Air Force Station
Cape Canaveral Air Force Station is an installation of the United States Air Force Space Command's 45th Space Wing, headquartered at nearby Patrick Air Force Base. Located on Cape Canaveral in the state of Florida, CCAFS is the primary launch head of America's Eastern Range with four launch pads...
. The Agena-A was propelled by a Bell 8048 (XLR81) engine, which could produce 69 kilonewtons of thrust for two minutes. Agena-A launches occurred between 1959 and 1961.
Agena-B
The Agena B was the second type of Agena to be built. It was equipped with a Bell 8081 engine, which could generate 71 kilonewtons of thrust, and be restarted in orbit. The stage carried enough propellant for the engine to burn for a total of four minutes. These launched the SAMOS-ESamoš
Samoš is a village in Serbia. It is situated in the Kovačica municipality, in the South Banat District, Vojvodina province. The village has a Serb ethnic majority and its population numbering 1,247 people .-See also:...
, SAMOS-F (ELINT Ferret), and MIDAS
Missile Defense Alarm System
The Missile Defense Alarm System was an American system of 12 early-warning satellites that provided limited notice of Soviet intercontinental ballistic missile launches between 1960 and 1966...
(Missile Defense Alarm System) military early-warning satellites and the Ranger
Ranger program
The Ranger program was a series of unmanned space missions by the United States in the 1960s whose objective was to obtain the first close-up images of the surface of the Moon. The Ranger spacecraft were designed to take images of the lunar surface, returning those images until they were destroyed...
and Lunar Orbiter lunar probes.
Agena-D
The Agena D was the result of a proposal by LockheedLockheed Corporation
The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1912 and later merged with Martin Marietta to form Lockheed Martin in 1995.-Origins:...
engineering executive Lawrence Edwards
Lawrence Edwards
Lawrence K. Edwards is an accomplished American innovator in aerospace and ground transportation. Early in his career, he pioneered cutting-edge technologies for U.S. space and missile defense programs. He went on to invent and promote high-speed Gravity-Vacuum Transit and monobeam rail transit...
, who suggested standardising the basic Agena configuration, and adding additional features depending on payload requirements, and a requirement from the Pentagon that the Agena be made compatible with the Titan
Titan (rocket family)
Titan was a family of U.S. expendable rockets used between 1959 and 2005. A total of 368 rockets of this family were launched, including all the Project Gemini manned flights of the mid-1960s...
rocket. David N. Spires summarizes the standardisation as follows:
- The Agena D's common configuration included four usable modules containing the major guidance, beacon, power, and telemetry equipment, a standard payload console, and a rear rack above the engine for plug-in installation of optional gear-like solar panels, "piggyback" subsatellites, and an optional Bell Aerosystems engine that could be restarted in space as many as sixteen times.
Its orbital configuration had a diameter of 60 in (1.5 m) and a length of 248 in (6.3 m), and provided 19,500 Wh of electrical power from batteries. As of 2010, the Agena-D is the most-launched American upper stage. A special production line was set up to turn out 40 Agena-D spacecraft per year. Edwards remained responsible for the engineering for several years until the Air Force declared the Agena-D operational froze its design. By the time of its retirement, the reliability of the Agena-D exceeded 95 percent.
The Agena-D was used to launch KH-7
KH-7
Codenamed Gambit, the KH-7 was a reconnaissance satellite used by the United States from July 1963 to June 1967. Like the older CORONA system, it acquired imagery intelligence by taking photographs and returning the undeveloped film to earth. It achieved a typical ground-resolution of to...
GAMBIT spy satellites, three Mariner probes to Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
and the two Mariner
Mariner program
The Mariner program was a program conducted by the American space agency NASA that launched a series of robotic interplanetary probes designed to investigate Mars, Venus and Mercury from 1963 to 1973...
space probes to Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
.
Other variants
In the early 1970s Lockheed studied the use of Agena as a payload in the Space Shuttle bay.An Agena-C with an increased diameter was proposed, but never built.
The Agena-2000 was intended as a modernised Agena, and would have been used on the Atlas V
Atlas V
Atlas V is an active expendable launch system in the Atlas rocket family. Atlas V was formerly operated by Lockheed Martin, and is now operated by the Lockheed Martin-Boeing joint venture United Launch Alliance...
Light Evolved Expendable Launch Vehicle. The Atlas V Light was cancelled in favour of standardising on the Medium configuration, and as a result the Agena-2000 was never built.
Agena Target Vehicle
The Agena Target Vehicle was based around the Agena-D, with equipment fitted to support use as a rendezvous and docking target for missions conducted as part of Project GeminiProject Gemini
Project Gemini was the second human spaceflight program of NASA, the civilian space agency of the United States government. Project Gemini was conducted between projects Mercury and Apollo, with ten manned flights occurring in 1965 and 1966....
. It was equipped with a Bell Aerospace Model 8247 engine, which was qualified for up to 15 restarts. On later missions, the Agena's engine was fired whilst the Gemini spacecraft was docked, in order to boost the spacecraft to a higher orbit, and to bring it back again. During the Gemini 11
Gemini 11
Gemini 11 was the ninth manned spaceflight mission of NASA's Project Gemini, which flew from September 12 to 15, 1966. It was the 17th manned American flight and the 25th spaceflight to that time . Astronauts Charles "Pete" Conrad, Jr. and Richard F. Gordon, Jr...
mission, an elliptical orbit with an apogee of 1375 kilometres (854.4 mi) was reached, which set an altitude record
Altitude record
Altitude record may refer to:*Flight altitude record, the highest altitude to have been reached in an aircraft*World altitude record , the highest altitude to have been reached by mountaineers...
for manned spaceflight that held until Apollo 8
Apollo 8
Apollo 8, the second manned mission in the American Apollo space program, was the first human spaceflight to leave Earth orbit; the first to be captured by and escape from the gravitational field of another celestial body; and the first crewed voyage to return to Earth from another celestial...
, the first manned mission to the Moon, was launched.