Encyclopedia Astronautica
Agena A



agena04.jpg
Agena in orbit
Credit: NASA
Nitric acid/UDMH propellant rocket stage. Loaded/empty mass 3,790/885 kg. Thrust 68.95 kN. Vacuum specific impulse 276 seconds. The Agena space vehicle was used in large numbers during the 1960s and 1970s as upper stage with SLV-2 Thor, SLV-3 Atlas and SLV-5 Titan boosters to launch a variety of military and civilian payloads into orbit. The Agena itself was actually the first general-purpose satellite, and formed the core for many operational satellites and experimental space vehicles.

In 1955, the U.S. Air Force began the WS-117L program, calling for the development of a strategic satellite system. The initial goal was the development an orbital photo-reconnaissance platform, and in October 1956, Lockheed became prime contractor for the system. The core element of WS-117L was a new multipurpose spacecraft with boost and manoeuvering engines, which would act as the second stage of the launch vehicle as well as the carrier vehicle for the reconnaissance system. Lockheed's Agena stage was built around the Bell XLR81 liquid-propellant rocket engine, and was initially known informally as Hustler because the XLR81 was originally developed for a cancelled rocket-powered weapons pod for the B-58 Hustler bomber. The first launch of a Thor-Agena combination in January 1959 was a failure, but on 28 February that year, Agena scored its first success and placed the Discoverer 1 satellite into polar orbit. The first few Agena A's flown used a Bell XLR81-BA-3 rocket engine, but later vehicles in the series used an XLR81-BA-5 (Bell Model 8048). The engine had gimballed nozzles for pitch and yaw control, and could deliver a thrust of 68.9 kN (15,500 lb) for up to 120 s.

Historical Essay © Andreas Parsch

Lockheed RM-81 Agena

The Agena space vehicle was used in large numbers during the 1960s and 1970s as upper stage with SLV-2 Thor, SLV-3 Atlas and SLV-5 Titan boosters to launch a variety of military and civilian payloads into orbit. The Agena itself was actually the first general-purpose satellite, and formed the core for many operational satellites and experimental space vehicles. It is included in this missile directory, because the U.S. Air Force allocated the formal missile designator RM-81 to the Agena (see section on RM-81 Designation for details).

In 1955, the U.S. Air Force began its Weapons System 117L program, calling for the development of a strategic satellite system. The initial primary goal of WS-117L was the development an orbital photo-reconnaissance platform, and in October 1956, Lockheed became prime contractor for the system. The core element of WS-117L was a new multipurpose spacecraft with boost and manoeuvering engines, which would act as the second stage of the launch vehicle as well as the carrier vehicle for the reconnaissance system. Lockheed's Agena spacecraft was built around the Bell XLR81 liquid-propellant rocket engine, and was initially known informally as Hustler, because the XLR81 was originally developed for a (later cancelled) rocket-powered weapons pod for the B-58 Hustler bomber. The first launch of a Thor-Agena combination in January 1959 was a failure, but on 28 February that year, Agena scored its first success when a Thor-Agena launcher placed the Discoverer 1 satellite into polar orbit.

Agena A

The first few Agenas, including the vehicle used in the Discoverer 1 launch, used a Bell XLR81-BA-3 rocket engine, but most vehicles of the initial Agena A series used an XLR81-BA-5 (Bell Model 8048). The engine had gimballed nozzles for pitch and yaw control, and could deliver a thrust of 68.9 kN (15500 lb) for up to 120 s.

Launch Vehicle Combination Number of Launches First-Last Launch
Thor (SLV-2) + Agena A 16 21-Jan-1959 - 13-Sep-1960
Atlas (LV-3A) + Agena A 4 26-Feb-1960 - 31-Jan-1961
Total for Agena A 20 21-Jan-1959 - 31-Jan-1961

Launch summary for Agena A

The Thor-Agena A launched the initial reconnaissance satellites of the CORONA (publicly named Discoverer) series (KH-1 system), while the Atlas-Agena A was used for the first two launches of both the Midas (Missile Detection And Surveillance) early-warning system and Samos (Satellite and Missile Observation System) ELINT satellite series.

Agena B

The Agena B had an improved XLR81-BA-7 engine (Bell Model 8081), which could be restarted in space, and was stretched to carry much more propellant, doubling the total burn time to 240 s. Both features greatly increased the versatility of the Agena vehicle. When launched into low orbits, the Agena B had plenty of fuel left for extensive orbital manoeuvers, an important requirement for a reconnaissance platform. Later models of the Agena B used a further improved XLR81-BA-9 (Bell Model 8096) engine, which (among other changes) increased the thrust to 71.1 kN (16000 lb) by using a different type of fuel.

Launch Vehicle Combination Number of Launches First-Last Launch
Thor (SLV-2) + Agena B 44* 26-Oct-1960 - 28-Aug-1964
Thrust-Augmented Thor (SLV-2A-C) + Agena B 3* 29-Jun-1963 - 15-May-1966
Atlas (LV-3A) + Agena B 28 12-Jul-1961 - 21-Mar-1965
Atlas (SLV-3) + Agena B 1 9-Jun-1966
Total for Agena B 76 26-Oct-1960 - 9-Jun-1966

Launch summary for Agena B

* Thor variant counts slightly differ between sources, but Thor-Agena total is not in question

Most of the Thor-Agena B vehicles launched KH-series reconnaissance systems (all KH-2-3 CORONAs, and some satellites of the KH-4 CORONA and KH-5 ARGON series). The remainder included e.g. some ELINT systems of the Samos program. The Atlas-Agena B launched a variety of spacecraft, the major ones being Midas early-warning systems, Samos ELINT systems and Ranger space probes.

Agena C

The designation Agena C was reserved for a proposed enlarged variant, which was to have doubled the capability of the Agena B (most likely by doubling the fuel tank size). However, this version was not built.

Agena D

The majority of Agenas were of the final Agena D variant. This was essentially a "standardized" Agena B, which could accept a variety of payloads (in a conical payload section in the nose) and be fitted to Atlas, Thor or Titan launchers without changes to the basic Agena. The earlier Agena A-B vehicles were tailor-made for their respective payloads and launcher types. The Agena D launched a large number of military and scientific payloads, including e.g. the Gemini-Agena target vehicles used by NASA for space capsule docking experiments in 1966.

Launch Vehicle Combination Number of Launches First-Last Launch
Thor (SLV-2) + Agena D 22* 28-Jun-1962 - 31-May-1967
Thrust-Augmented Thor (SLV-2A-C) + Agena D 60* 28-Feb-1963 - 17-Jan-1968
LTTAT** (SLV-2G-H) + Agena D 22* 9-Aug-1966 - 16-Jul-71
Thorad (SLV-2G-H) + Agena D 21* 18-May-1968 - 25-May-72
Atlas (LV-3A) + Agena D 15 12-Jul-1963 - 20-Jul-1965
Atlas (SLV-3) + Agena D 48 14-Aug-1964 - 5-Nov-1967
Atlas (SLV-3A) + Agena D 12 4-Mar-1968 - 7-Apr-1978
Atlas F + Agena D 1 27-Jun-1978
Titan 3B (SLV-5B) 29 29-Jul-1966 - 23-Oct-1970
Titan 23B 2 21-Jan-1971 - 22-Apr-1971
Titan 33B 3 21-Mar-1971 - 21-Aug-1973
Titan 24B 23 12-Aug-1971 - 21-Aug-1973
Titan 34B 11 10-Mar-1975 - 12-Feb-1987
Total for Agena D 269 28-Jun-1962 - 12-Feb-1987

Launch summary for Agena D

* Thor variant counts slightly differ between sources, but Thor-Agena total is not in question
** LTTAT = Long-Tank Thrust-Augmented Thor (quoted by some sources as identical to Thorad)
Titan 3B was the designation for the Titan 3 + Agena D combination
These derivatives of the Titan 3B are sometimes called 3(23)B, 3(33B), 3(24)B and 3(34)B, respectively.

The majority of Agena D missions on Thor-type boosters launched KH-series reconnaissance systems, mostly CORONA (KH-4-4A-4B), but also ARGON (KH-5) and LANYARD (KH-6). Most of the initial Atlas-Agena D vehicles (LV-3A-SLV-3) launched GAMBIT satellites (KH-7 reconnaissance system) into orbit, but payloads also included the Mariner series of interplanetary probes and the GATV (Gemini-Agena Target Vehicle). The SLV-3A-Agena D was used to launch the CANYON and RHYOLITE-AQUACADE series of ELINT-SIGINT satellites into geostationary orbits.

The Titan 3B-23B-24B series launched GAMBIT (KH-8 reconnaissance system) satellites, while the payloads of the larger Titan 33B-34B boosters consisted of JUMPSEAT SIGINT and SDS communications satellites.

A total of 365 Agena vehicles of all types were launched into space by the U.S. Air Force and NASA between January 1959 and 12 February 1987, when the last Agena D was launched with a USAF payload (SDS communications satellite #7) as upper stage of a Titan 34B booster.

RM-81 Designation

In 1958 (or early 1959), the U.S. Air Force allocated the formal "Research Missile" designation RM-81 to the Agena space vehicle. The reasons for this remain unclear, but the USAF possibly needed to assign a designator for formal purposes and there was no better alternative at that time. USAF serial number listings show a total order of 341 Agenas, designated as XRM-81, RM-81, SRM-81 and SRM-81A. Because I cannot connect these four designators in any way to the documented basic Agena variants (Agena A-B-D), I don't know what the significance of the different RM-81 designations is. The table below is a detailed listing of allocated Agena serial number blocks, sorted by type designation:

    Serial Range Designation Total Number Ordered
    59-2544-2557
    60-606-615
    60-5454-5463
    60-6594-6630
    60-6914-6922
    62-12585
    XRM-81 81
    60-3710-3719 RM-81 10
    63-7368-7406
    63-12759-12764
    65-10657-10685
    66-4390-4432
    66-9249-9262
    67-14544-14579
    SRM-81 167
    61-4530-4536
    62-3876-3878
    62-4614-4625
    62-12202-12213
    62-12289-12291
    63-13040-13085
    SRM-81A 83

Notes:
1. The Agena did not receive a new designation in June 1963, when the joint DOD missile designation system was introduced, because spacecraft were not originally part of the new system.
2. One would expect that SRM-81A designated a newer version than SRM-81 (before 1962, an "A" suffix designated the second version), but the latest blocks are all attributed to plain SRM-81. However, after June 1963 the Agena's designation was no longer covered by any official regulation, so it's possible that the general SRM-81 designator was not meant to designate any specific variant, but was only retained in the serial number list for informal purposes.
3. The 341 serials do not account for the full number of Agenas built (at least 365).

Specifications

Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate! Because exact numbers for each Agena depend on payload configuration, the data are to be regarded as "typical" values.

Data for Agena A, Agena B, Agena D:

  Agena A Agena B-D
Length 5.94 m (19.5 ft) 7.56 m (24.8 ft)
Diameter 1.52 m (5 ft)
Weight 3850 kg (8500 lb)
Fuel: 2945 kg (6500 lb)
7160 kg (15800 lb)
Fuel: 6115 kg (13500 lb)
Propulsion Bell XLR81-BA-5 liquid-fuel rocket;
68.9 kN (15500 lb) for 120 s
Bell XLR81-BA-9 liquid-fuel rocket;
71.1 kN (16000 lb) for 240 s
Main Sources

[1] Jos Heyman: "World Spacecraft Digest 1957-2002", Tiros Space Information, 2003
[2] Jos Heyman: "Spacecraft Tables 1957-2002", Tiros Space Information, 2003
[3] Ren J. Francillon: "Lockheed Aircraft since 1913", Putnam, 1987
[4] Norman J. Bowman: "The Handbook of Rockets and Guided Missiles", Perastadion Press, 1963
[5] Mark Wade: Encyclopedia Astronautica
[6] Gunter Krebs: Gunter's Space Page
[7] USAF Aircraft Serial Number Records (data provided by Jos Heyman)


Cost $ : 5.800 million.

AKA: RM-81.
Status: Retired 1961.
Gross mass: 3,790 kg (8,350 lb).
Unfuelled mass: 885 kg (1,951 lb).
Height: 4.73 m (15.51 ft).
Diameter: 1.52 m (4.98 ft).
Span: 1.52 m (4.98 ft).
Thrust: 68.95 kN (15,501 lbf).
Specific impulse: 276 s.
Burn time: 120 s.
Number: 26 .

More... - Chronology...


Associated Countries
Associated Engines
  • Bell 8048 Bell Nitric acid/UDMH rocket engine. 68.9 kN. Out of production. Isp=276s. Used on Agena A, derived from Rascal engine. Regeneratively cooled; used drilled holes to create the same effect as more costly stacked spaghetti rubes. First flight 1959. More...

Associated Launch Vehicles
  • Thor Agena A American orbital launch vehicle. Two stage vehicle consisting of 1 x Thor DM-18A + 1 x Agena A More...
  • Atlas Agena A American orbital launch vehicle. Atlas D + 1 x Agena A upper stage. Agena originally called 'Hustler', based on engine for cancelled rocket-propelled nuclear warhead pod for B-58 Hustler bomber. More...

Associated Propellants
  • Nitric acid/UDMH Drawing on the German World War II Wasserfall rocket, nitric acid (HNO3) became the early storable oxidiser of choice for missiles and upper stages of the 1950's. To overcome various problems with its use, it was necessary to combine the nitric acid with N2O4 and passivation compounds. These formulae were considered extremely secret at the time. By the late 1950's it was apparent that N2O4 by itself was a better oxidiser. Therefore nitric acid was almost entirely replaced by pure N2O4 in storable liquid fuel rocket engines developed after 1960. Unsymmetrical Dimethylhydrazine ((CH3)2NNH2) became the storable liquid fuel of choice by the mid-1950's. Development of UDMH in the Soviet Union began in 1949. It is used in virtually all storable liquid rocket engines except for some orbital manoeuvring engines in the United States, where MMH has been preferred due to a slightly higher density and performance. More...

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