(26) Number of engines (reduce):
Shuttle Benchmark: 3 SSME’s, 2 OMS engines, 2 SRB’s
Derivation:
The number of engines is a multiplier of maintenance and test requirements for any given configuration. Where more engines are used to reduce power levels, enhancing life limitations on components and increasing reusability, there is a benefit. Being able to achieve that same benefit with fewer engines is always desirable. This is synergistic with the criteria "number of components with demonstrated high reliability (increase)".
Engines |
Total |
|
| Atlas IIAR (Liquid*, Centaur) | 1, 1 |
2 |
| Access to Space Airbreather / Rocket | 2+2 |
4 |
| Shuttle (Main Propulsion, SRB’s, OMS) | 3, 2, 2 |
7 |
| Atlas IIAS (Liquid*, Liquid, Solids, Centaur) | 1, 1, 4, 2 |
8 |
| Access to Space All Rocket Bipropellant SSTO (Main and OMS) | 7, 2 |
9 |
| Saturn Apollo Moon Rocket (Stage 1, 2, 3, 4) | 5, 5, 1, 1 |
12 |
| Soviet N-1 Moon Rocket3 (Stage 1, 2, 3, 4, 5) | 30, 8, 4, 1, 1 |
44 |
| *2 Thrust chambers per
engine Note: Varying payload, launch rate capabilities, staging events. Italics = Planned or conceptual, not flown. |
Table 6: Various engine count examples. Note that a requirement for "engine out" capability possibly increases the number of engines for a vertical take-off rocket whereas with horizontal take-off, imposing the same requirement, it is still possible to reduce engine count.
The number of engines on a vehicle is strongly related to the ease of integration and the maintainability of the propulsion system.
Level: 1 - This is information available early in the conceptual phases of vehicle definition.
Visions of Improvement:
Basic improvement begins by altering the definition of an "engine". The sharing of components, such as at the turbopump level should a failure occur, begins to reduce parts count or to provide more fault tolerance. Reduced power levels are required to enable this. Further, integration, combined with increased throttle capability and control, could eliminate separate systems for orbital maneuvering such as the 2 Shuttle OMS pods. This is synergistic with reducing the number of different fluids which also enables fewer active ground systems for servicing.
Ideal levels of improvement would be enabled by a few high reliability engines. Similar to aircraft, the number of engines could be a targeted architectural feature once highly reusable space transportation is enabled similar to airline preferences for twin jet aircraft versus aircraft with 3 or more engines.
Target for Improvement:
Targets for improvement over the current 3+2+2 configuration could (1) target commonality (of fluids, hardware, tankage) and then (2) target fewer remaining engines.
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Edgar Zapata, NASA Kennedy Space Center
Shuttle Process Engineering Directorate, Fluid Systems Division