The descent propulsion system (DPS - pronounced 'dips') or lunar module descent engine (LMDE), internal designation VTR-10, is a variable-

throttle A throttle is the mechanism by which fluid flow is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle'' ...

hypergolic A hypergolic propellant is a rocket propellant combination used in a rocket engine, whose components spontaneously ignite when they come into contact with each other. The two propellant components usually consist of a fuel and an oxidizer. T ...

rocket engine A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accorda ...

invented by Gerard W. Elverum Jr. and developed by

Space Technology Laboratories TRW Inc., was an American corporation involved in a variety of businesses, mainly aerospace, electronics, automotive, and credit reporting.http://www.fundinguniverse.com/company-histories/TRW-Inc-Company-History.html TRW Inc. It was a pionee ...

(TRW) for use in the

Apollo Lunar Module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed ...

descent stage. It used

Aerozine 50 __NOTOC__ Aerozine 50 is a 50:50 mix by weight of hydrazine and unsymmetrical dimethylhydrazine (UDMH), originally developed in the late 1950s by Aerojet General Corporation as a storable, high-energy, hypergolic fuel for the Titan II ICBM rocket e ...

fuel and dinitrogen tetroxide () oxidizer. This engine used a pintle injector, which paved the way for other engines to use similar designs.

Requirements

The propulsion system for the descent stage of the lunar module was designed to transfer the vehicle, containing two crewmen, from a circular lunar parking orbit to an elliptical descent orbit with a pericynthion of , 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 propellant A hypergolic propellant is a rocket propellant combination used in a rocket engine, whose components spontaneously ignite when they come into contact with each other. The two propellant components usually consist of a fuel and an oxidizer. Th ...

s and a

gimballed A gimbal is a pivoted support that permits rotation of an object about an axis. A set of three gimbals, one mounted on the other with orthogonal pivot axes, may be used to allow an object mounted on the innermost gimbal to remain independent of ...

pressure-fed ablative cooled engine that was capable of being

d. A lightweight cryogenic helium pressurization system was also used. The exhaust

nozzle extension A nozzle extension is an extension of the nozzle of a reaction/rocket engine. The application of nozzle extensions improves the efficiency of rocket engines in vacuum by increasing the nozzle expansion ratio. As a rule, their modern design assu ...

was designed to crush without damaging the LM if it struck the surface, which happened on Apollo 15.

Development

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 crewed spacecraft. Very little advanced research had been done in variable-thrust rocket engines up to that point.

Rocketdyne Rocketdyne was an American rocket engine design and production company headquartered in Canoga Park, California, Canoga Park, in the western San Fernando Valley of suburban Los Angeles, California, Los Angeles, in southern California. The Rocke ...

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 The Lyndon B. Johnson Space Center (JSC) is NASA's center for human spaceflight (originally named the Manned Spacecraft Center), where human spaceflight training, research, and flight control are conducted. It was renamed in honor of the late U ...

(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 AS-201 (or SA-201), flown February 26, 1966, was the first uncrewed test flight of an entire production Block I Apollo command and service module and the Saturn IB launch vehicle. The spacecraft consisted of the second Block I command module ...

, 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. Grumman held a bidders' conference on March 14, 1963, attended by

Aerojet General Aerojet was an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California, with divisions in Redmond, Washington, Orange and Gainesville in Virginia, and Camden, Arkansas. Aerojet was owned by GenCorp. I ...

, Reaction Motors Division of

Thiokol Thiokol (variously Thiokol Chemical Corporation(/Company), Morton Thiokol Inc., Cordant Technologies Inc., Thiokol Propulsion, AIC Group, ATK Thiokol, ATK Launch Systems Group; finally Orbital ATK before becoming part of Northrop Grumman) was an ...

, United Technology Center Division of

United Aircraft The United Aircraft Corporation was an American aircraft manufacturer formed by the break-up of United Aircraft and Transport Corporation in 1934. In 1975, the company became United Technologies. History Pre-1930s 1930s The Air Mail scandal ...

, and Space Technology Laboratories, Inc. (STL). In May, STL was selected as the competitor to Rocketdyne's concept. STL proposed an engine that was gimbaled as well as throttleable, using flow control valves and a variable-area pintle injector, in much the same manner as does a shower head, to regulate pressure, rate of propellant flow, and the pattern of fuel mixture in the combustion chamber. The first full-throttle firing of Space Technology Laboratories' LM descent engine was carried out in early 1964. NASA planners expected one of the two drastically different designs would emerge the clear winner, but this did not happen throughout 1964. Apollo Spacecraft Program Office manager Joseph Shea formed a committee of NASA, Grumman and Air Force propulsion experts, chaired by American spacecraft designer

Maxime Faget Maxime Allen "Max" Faget (pronounced ''fah-ZHAY''; August 26, 1921 – October 9, 2004) was a Belizean-born American mechanical engineer. Faget was the designer of the Mercury spacecraft, and contributed to the later Gemini and Apollo spa ...

, in November 1964 to recommend a choice, but their results were inconclusive. Grumman chose Rocketdyne on January 5, 1965. Still not satisfied, MSC Director

Robert R. Gilruth Robert Rowe Gilruth (October 8, 1913 – August 17, 2000) was an American aerospace engineer and an aviation/space pioneer who was the first director of NASA's Manned Spacecraft Center, later renamed the Lyndon B. Johnson Space Center. He worked ...

convened his own five-member board, also chaired by Faget, which reversed Grumman's decision on January 18 and awarded the contract to STL. To keep the DPS as simple, lightweight, and reliable as possible, the propellants were pressure-fed with

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

gas instead of using heavy, complicated, and failure-prone

turbopump A turbopump is a propellant pump with two main components: a rotodynamic pump and a driving gas turbine, usually both mounted on the same shaft, or sometimes geared together. They were initially developed in Germany in the early 1940s. The purpo ...

s. Cryogenic supercritical helium was loaded and stored at 3500 psi.Apollo Experience Report – Descent Propulsion System – NASA Technical Note: March 1973
/ref> The helium was pressure regulated down to 246 psi for the propellant tanks. Pressure from the helium would gradually rise as it warmed and would eventually be vented. The system was also equipped with a rubber diaphragm that would burst when the helium pressure reached a certain level and allow the gas to vent harmlessly into space. Once the helium was gone however, the DPS would no longer be operable. This was not seen as an issue since normally, the helium release would not occur until after the lunar module was on the Moon, by which time the DPS had completed its operational life and would never be fired again. The design and development of the innovative thrust chamber and pintle design is credited to TRW Aerospace Engineer Gerard W. Elverum Jr. The engine could throttle between and but operation between 65% and 92.5% thrust was avoided to prevent excessive nozzle erosion. It weighed , with a length of and diameter of .

Performance in LM "life boat"

The LMDE achieved a prominent role in the Apollo 13 mission, serving as the primary propulsion engine after the oxygen tank explosion in the

Apollo Service Module The Apollo command and service module (CSM) was one of two principal components of the United States Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functioned as a mother sh ...

. After this event, the ground controllers decided that the

Service Propulsion System The Apollo command and service module (CSM) was one of two principal components of the United States Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functioned as a mother shi ...

could no longer be operated safely, leaving the DPS engine in ''Aquarius'' as the only means of maneuvering Apollo 13.

Modification for Extended Lunar Module

In order to extend landing payload weight and lunar surface stay times, the last three

s were upgraded by adding a

to the engine to increase thrust. The nozzle exhaust bell, like the original, was designed to crush if it hit the surface. It never had on the first three landings, but did buckle on the first Extended landing,

Apollo 15 Apollo 15 (July 26August 7, 1971) was the ninth crewed mission in the United States' Apollo program and the fourth to Moon landing, land on the Moon. It was the first List of Apollo missions#Alphabetical mission types, J mission, with a ...

TR-201 in Delta second stage

After the Apollo program, the DPS was further developed into the TRW

TR-201 The TR-201 or TR201 is a hypergolic pressure-fed rocket engine used to propel the upper stage of the Delta rocket, referred to as Delta-P, from 1972 to 1988. The rocket engine uses Aerozine 50 as fuel, and as oxidizer. It was developed in the ...

engine. This engine was used in the second stage, referred to as

Delta-P The Delta-P is an American rocket upper stage, stage, developed by McDonnell Douglas and TRW, first used on November 10, 1972 as the second stage for the Delta 1000 series. It continued to serve as the second stage for subsequent Delta 2000 and ...

, of the Delta launch vehicle (

Delta 1000 The Delta 1000 series (also referred to as Straight-Eight) was an American expendable launch system which was used to conduct eight orbital launches between 1972 and 1975. It was a member of the Delta family of rockets. Several variants existed, d ...

Delta 2000 The Delta 2000 series was an American expendable launch system which was used to conduct forty-four orbital launches between 1974 and 1981. It was a member of the Delta family of rockets. Several variants existed, which were differentiated by a ...

Delta 3000 The Delta 3000 series was an American expendable launch system which was used to conduct 38 orbital launches between 1975 and 1989. It was a member of the Delta family of rockets. Several variants existed, which were differentiated by a four ...

series) for 77 successful launches between 1972–1988.

References

External links

NASA Technical Note: Apollo Experience Report – Descent Propulsion System. March 1973
31 pages, much detail on both designs, and the testing.
Apollo Lunar Module Propulsion Systems Overview, NASA

{{TRW Rocket engines Rocket engines using hypergolic propellant Apollo program hardware TRW Inc. Rocket engines using the pressure-fed cycle