RS-56
RS-56 engines on an Atlas II | |
| Country of origin | United States |
|---|---|
| First flight | 1991 |
| Manufacturer | Rocketdyne |
| Predecessor | RS-27A |
| Status | Retired |
| Liquid-fuel engine | |
| Propellant | LOX / RP-1 |
| Cycle | Gas-generator |
| Performance | |
| Thrust, sea-level | RS-56-OBA: 207,000 lbf (920.8 kN) RS-56-OSA: 60,500 lbf (269.0 kN) |
| Chamber pressure | 4.8 MPa (48 bar) |
| Specific impulse, vacuum | RS-56-OBA: 299 s (2.93 km/s) RS-56-OSA: 316 s (3.10 km/s) |
| Specific impulse, sea-level | RS-56-OBA: 263 s (2.58 km/s) RS-56-OSA: 220 s (2.2 km/s) |
| Burn time | RS-56-OBA: 172 RS-56-OSA: 283 sec |
| Dimensions | |
| Length | RS-56-OBA: 11.3 ft (3.43 m) 8.9 ft (2.7 m) |
| Diameter | RS-56-OBA: 8.0 ft (2.45 m) 10.0 ft (3.05 m) |
| Used in | |
| Atlas II | |
RS-56 (Rocket System-56) was an American liquid-fueled rocket engine, developed by Rocketdyne. RS-56 was derived from the RS-27 engine, which itself is derived from the H-1 engine used in the Saturn I and Saturn IB.
Two variants of this engine were built, both for use on the Atlas II first stage. This was the last Atlas rocket to use the "stage-and-a-half" technique, where it ignited all three engines at liftoff and then jettisoned the two side engines and their support structure during ascent.
The two RS-56-OBA engines, with high thrust but moderate efficiency, were integrated into a single unit called the MA-5A and shared a common gas generator. They burned for approximately 164 seconds before being jettisoned, when acceleration reached approximately 5.0–5.5 g.
The central sustainer engine on the first stage, an RS-56-OSA, would burn for an additional 125 seconds. It featured less thrust but better efficiency at high altitudes than the RS-56-OBAs.