Encyclopedia Astronautica
Delta A


Nitric acid/UDMH propellant rocket stage. Loaded/empty mass 2,164/694 kg. Thrust 33.80 kN. Vacuum specific impulse 271 seconds. Able was only the first of many engine and application programs that flowed from the Vanguard experience base. These included Able, Ablestar, Delta, Fat Delta, the Japanese N II, and applications or offshoots such as Hydra, Saint (Satellite Intercept), and other classified programs.

Included in all this were numerous upratings and incremental changes in the thrust chambers, tanks, and complete systems. Derivative programs included Transtage and Apollo SPS, and ultimately, the Shuttle OME. Delta thrust chamber assemblies of a considerably advanced configuration were still being produced by Aerojet well into the 21st Century - a total of over 50 years of continuous activity in this family.

The associated large number of different missions, vehicles, stages, and thrust chamber assemblies, and modifications thereof, has led to a nomenclature problem, and considerable confusion as to program details, relationships, and relative timing. A major example of this is that in the early years the Air Force called the vehicles that they procured "Thor-Able" or "Thor-Ablestar," but, NASA called all their Thor-based vehicles "Delta." No matter what they were called, they were all really Vanguard second stages, either with the original or larger diameter tanks. In those days Able or Ablestar meant Air Force, and Delta meant NASA. However, several years later, the name Delta was also applied to Aerojet's ablative thrust chambers and stages, even though some were procured by the Air Force.

Continuing development of the Vanguard aluminum thrust chamber assembly resulted in selection of this system by the Air Force for use with a Thor booster that was to be used to demonstrate the Atlas guidance system, and to explore nose cone reentry problems. This was called the Able program, and it began in November 1957. Thor was basically a single stage IRBM built by Douglas Aircraft that used essentially the same thrust chamber assembly as Atlas, and reached flight status before Atlas. Space Technology Laboratories (STL), and later the Aerospace Corporation (which was formed from part of STL in 1960), acted as system manager for the Thor-Able program and its Air Force successors. The Able system included the thrust chamber assembly, valves, tanks, pressurizing system, and any additional components to make up a complete second stage. The oxidizer was changed from the WFNA used in Vanguard, to RFNA. The first few Thor-Ables were delivered before the formation of NASA.

The minor modification of the Vanguard aluminum tube thrust chamber to meet the Able requirements was accomplished in the record time of only three months. The major effort during this time was the testing of six aluminum tube thrust chambers for durations longer than the full burn time. This was done to develop confidence that the expected burn-through failure in the throat would occur at least 30% beyond the nominal duration, that it would be repeatable, and that the total impulse would be within specification limits. This was accomplished, and it provided the first opportunity for Aerojet's aluminum tube bundle engine to perform successfully in space.

Cost $ : 1.160 million.

AKA: Able.
Status: Retired 1965.
Gross mass: 2,164 kg (4,770 lb).
Unfuelled mass: 694 kg (1,530 lb).
Height: 5.36 m (17.58 ft).
Diameter: 0.84 m (2.75 ft).
Span: 0.84 m (2.75 ft).
Thrust: 33.80 kN (7,599 lbf).
Specific impulse: 271 s.
Burn time: 115 s.
Number: 6 .

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Associated Countries
Associated Engines
  • AJ10-118 Aerojet Nitric acid/UDMH rocket engine. 33.8 kN. Out of Production. Isp=271s. Engine originally developed for the Vanguard launch vehicle, and then for use on the Able and Delta upper stages and as the Apollo Service module engine. Flown 1957-1962. More...

Associated Launch Vehicles
  • Delta A American orbital launch vehicle. Three stage vehicle consisting of 1 x Thor DM-21 + 1 x AJ10-118 + 1 x Altair More...
  • Thor DSV-2G American orbital launch vehicle. Two stage vehicle consisting of 1 x Thor DM-18A + 1 x AJ10-118 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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