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Model: Able. Gross Mass: 1,884 kg (4,153 lb). Empty Mass: 429 kg (945 lb). Thrust (vac): 34.690 kN (7,799 lbf). Isp: 270 sec. Burn time: 115 sec. Propellants: Nitric acid/UDMH. Diameter: 0.81 m (2.65 ft). Span: 0.84 m (2.75 ft). Length: 5.67 m (18.60 ft). Country: USA. No Engines: 1. Motor: AJ10-40. Status: Retired 1960. First Flight: 1956. Last Flight: 1960. No Launched: 35. No Failed: 5. Used as: Able. Other designations: Able. Release conditions: Aerojet.

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.

Engine for Vanguard was AJ10-37; for later Able models AJ10-41 and AJ10-42. Total of 21 stages built and delivered by Aerojet.

Model: Delta A. Gross Mass: 2,164 kg (4,770 lb). Empty Mass: 694 kg (1,530 lb). Thrust (vac): 33.803 kN (7,599 lbf). Isp: 271 sec. Burn time: 115 sec. Propellants: Nitric acid/UDMH. Isp(sl): 0 sec. Diameter: 0.84 m (2.75 ft). Span: 0.84 m (2.75 ft). Length: 5.36 m (17.58 ft). Country: USA. No Engines: 1. Motor: AJ10-118. Status: Retired 1965. Cost $ : 1.160 million. First Flight: 1959. Last Flight: 1965. No Launched: 6. No Failed: 1. Other designations: Able.

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.

Model: Delta 104. Gross Mass: 4,472 kg (9,859 lb). Empty Mass: 590 kg (1,300 lb). Thrust (vac): 35.098 kN (7,890 lbf). Isp: 278 sec. Burn time: 296 sec. Propellants: Nitric acid/UDMH. Isp(sl): 0 sec. Diameter: 1.40 m (4.50 ft). Span: 1.40 m (4.50 ft). Length: 5.88 m (19.29 ft). Country: USA. No Engines: 1. Motor: AJ10-104. Status: Retired 1962. Cost $ : 1.740 million. First Flight: 1960. Last Flight: 1962. No Launched: 12. No Failed: 1.

Model: Able-Star. Gross Mass: 4,497 kg (9,914 lb). Empty Mass: 599 kg (1,320 lb). Thrust (vac): 36.024 kN (8,099 lbf). Isp: 280 sec. Burn time: 296 sec. Propellants: Nitric acid/UDMH. Isp(sl): 210 sec. Diameter: 1.40 m (4.50 ft). Length: 4.52 m (14.82 ft). Country: USA. No Engines: 1. Motor: AJ10-104. Status: Out of production. Cost $ : 5.000 million. First Flight: 1957. Last Flight: 1965. No Launched: 19. Release conditions: Aerojet.

As is almost always the case in such programs, the Air Force requested increases in the propulsion system capabilities in an effort to meet their ever-expanding mission requirements. As a result, the stainless steel version of the basic Able engine was selected, and it was uprated to increase thrust 34.7 kN to 37.0 kN and to increase the duration 2-1/2 times (easily done with the stainless steel thrust chamber) - and this configuration was called Ablestar. The Ablestar also included modifications that allowed in-space restarting - a first in the industry. The time required for developing and qualifying the Ablestar propulsion system was eight months, most of which was needed for the design, development and qualification of the much larger propellant tanks and titanium helium spheres. These remarkably short development times was a result of the basic simplicity of the Able design - mainly the low chamber pressure, hypergolic propellants, and gas pressurized propellant tanks. This simplicity also resulted in a number of additional very desirable features:

  • The ability to achieve rapid, relatively low cost modifications, and high reliability for a variety of missions
  • The ability to shift back to the aluminum thrust chamber and injector which provided an extremely good thrust to weight ratio (180, based on 3500 kgf thrust and a weight of 19.5 kg)
  • Very light weight tankage based on heat treated 410 stainless steel
  • Easily adjustable run time (in the stainless steel version) based on simply varying the length of the cylindrical section of the tanks.
In addition, the basic philosophy of pressure fed, low chamber pressure and ablative (rather than regeneratively cooled) thrust chambers for upper stage engines produced outstanding reliability and scalability. In a vacuum engine, a low chamber pressure still provides a reasonable expansion ratio, and thus reasonable performance. Secondly, low chamber pressure allows use of a very simple, pressure fed propellant system with relatively light and inexpensive tanks. Thirdly, the low chamber pressure results in lower heat transfer rates, thus making ablative chambers more practical - and they are inherently less expensive, and much mere reliable. And finally ablative chambers greatly simplify restarts in a vacuum environment because there are essentially no problems with cooling jacket and manifold fill times or coking in the coolant system.
Model: Delta D. Gross Mass: 2,693 kg (5,937 lb). Empty Mass: 545 kg (1,201 lb). Thrust (vac): 33.695 kN (7,575 lbf). Isp: 278 sec. Burn time: 170 sec. Propellants: Nitric acid/UDMH. Isp(sl): 0 sec. Diameter: 0.84 m (2.75 ft). Span: 0.84 m (2.75 ft). Length: 5.58 m (18.30 ft). Country: USA. No Engines: 1. Motor: AJ10-118D. Status: Retired 1969. Cost $ : 1.160 million. First Flight: 1962. Last Flight: 1969. No Launched: 24.

Model: Delta E. Gross Mass: 6,009 kg (13,247 lb). Empty Mass: 785 kg (1,730 lb). Thrust (vac): 35.098 kN (7,890 lbf). Isp: 278 sec. Burn time: 400 sec. Propellants: Nitric acid/UDMH. Isp(sl): 0 sec. Diameter: 1.40 m (4.50 ft). Span: 1.40 m (4.50 ft). Length: 6.28 m (20.60 ft). Country: USA. No Engines: 1. Motor: AJ10-118E. Status: Retired 1982. Cost $ : 2.320 million. First Flight: 1966. Last Flight: 1982. No Launched: 13.

Model: Delta P. Gross Mass: 5,434 kg (11,979 lb). Empty Mass: 820 kg (1,800 lb). Thrust (vac): 41.923 kN (9,425 lbf). Isp: 301 sec. Burn time: 322 sec. Propellants: N2O4/Aerozine-50. Isp(sl): 0 sec. Diameter: 1.38 m (4.52 ft). Span: 1.38 m (4.52 ft). Length: 5.97 m (19.58 ft). Country: USA. No Engines: 1. Motor: TR-201. Status: Retired 1988. Cost $ : 4.350 million. First Flight: 1972. Last Flight: 1988. No Launched: 95. No Failed: 1. Other designations: TR-201.

Model: Delta F. Gross Mass: 5,629 kg (12,409 lb). Empty Mass: 784 kg (1,728 lb). Thrust (vac): 41.364 kN (9,299 lbf). Isp: 280 sec. Burn time: 335 sec. Propellants: Nitric acid/UDMH. Isp(sl): 0 sec. Diameter: 1.40 m (4.50 ft). Span: 1.40 m (4.50 ft). Length: 6.28 m (20.60 ft). Country: USA. No Engines: 1. Motor: AJ10-118F. Status: Retired 1987. Cost $ : 2.320 million. First Flight: 1972. Last Flight: 1987. No Launched: 19. No Failed: 1.

Model: Delta K. Gross Mass: 6,954 kg (15,330 lb). Empty Mass: 950 kg (2,090 lb). Thrust (vac): 43.630 kN (9,808 lbf). Isp: 319 sec. Burn time: 431 sec. Propellants: N2O4/Aerozine-50. Diameter: 1.70 m (5.50 ft). Span: 2.40 m (7.80 ft). Length: 5.89 m (19.32 ft). Country: USA. No Engines: 1. Motor: AJ10-118K. Status: Active. Cost $ : 4.350 million. First Flight: 1982. Last Flight: 2007. No Launched: 254. No Failed: 1.

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