Descent Propulsion System
| Country of origin | United States |
|---|---|
| Date | 1964-1972 |
| Manufacturer | TRW |
| Application | Lunar Descent Stage/Spacecraft propulsion |
| Successor | TR-201 |
| Status | Retired |
| Liquid-fuel engine | |
| Propellant | N2O4 / Aerozine 50 |
| Cycle | Pressure-fed |
| Configuration | |
| Chamber | 1 |
| Performance | |
| Thrust (vac.) | 10,125 pounds-force (45.04 kN) maximum, throttle between 10% and 60% of full thrust |
| Chamber pressure | 100 psia |
| Isp (vac.) | 311 seconds (3.05 km/s) |
| Dimensions | |
| Length | 90.5 inches (230 cm) |
| Diameter | 59.0 inches (150 cm) |
| Dry weight | 394 pounds (179 kg) |
| Used in | |
| Lunar Module as Descent Engine | |
The Descent Propulsion System (DPS) or LMDE (Lunar Module Descent Engine) is a variable throttle hypergolic rocket engine developed by Space Technology Laboratories (TRW) for use in the Apollo Lunar Module Descent Stage. It used Aerozine 50 fuel and N2O4 oxidizer. This engine used a pintle injector, a design also used later in the SpaceX Merlin engine.
The propulsion system for the descent stage of the Lunar Module was designed to transfer the vehicle, containing two crewmen, from a 60-nautical-mile (110 km) circular lunar parking orbit to an elliptical descent orbit with a pericynthion of 50,000 feet (15,000 m), then provide a powered descent to the lunar surface, with hover time above the lunar surface to select the exact landing site. To accomplish these maneuvers, a propulsion system was developed that used hypergolic propellants and a gimballed pressure-fed ablative cooled engine that was capable of being throttled. A lightweight cryogenic helium pressurization system was also used. The exhaust nozzle extension was designed to crush without damaging the LM if it struck the surface, which happened on Apollo 15.
According to NASA history publication Chariots for Apollo, "The lunar module descent engine probably was the biggest challenge and the most outstanding technical development of Apollo." A requirement for a throttleable engine was new for manned spacecraft. Very little advanced research had been done in variable-thrust rocket engines up to that point. Rocketdyne proposed a pressure-fed engine using the injection of inert helium gas into the propellant flow to achieve thrust reduction at a constant propellant flow rate. While NASA's Manned Spacecraft Center (MSC) judged this approach to be plausible, it represented a considerable advance in the state of the art. (In fact, accidental ingestion of helium pressurant proved to be a problem on AS-201, the first flight of the Apollo Service Module engine in February 1966.) Therefore, MSC directed Grumman to conduct a parallel development program of competing designs.
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