The RL-10 was America's first liquid hydrogen fueled rocket engine, and an updated version is used in several current launch vehicles. Six RL-10 engines were used in the S-IV second stage of the Saturn I rocket. One or two RL-10 engines are used in the Centaur upper stages of Atlas and Titan rockets. One RL-10 is used in the upper stage of Delta IV rockets. There were proposals to use RL-10 powered Centaur upper stages on Saturn I, Saturn IB and Saturn V rockets, and the Space Shuttle.


The RL-10 was first flown in 1961. [ [http://www.astronautix.com/engines/rl10.htm] ]

Original RL10 specifications

Thrust (altitude): 15,000 lbf (66.7 kN)
Burn Time: 470 s
Design: Expander cycle
Specific impulse: 433 s (4.25 kN·s/kg)
Engine weight - dry: 298 lb (135 kg)
Height: 68 in (1.73 m)
Diameter: 39 in (0.99 m)
Nozzle expansion ratio: 40 to 1
Propellants: LOX & LH2
Propellant flow: 35 lb/s (16 kg/s)
Contractor: Pratt & Whitney
Vehicle application: Saturn I / S-IV 2nd stage - 6-engines
Vehicle application: Centaur upper stage - 2-engines

Current design

The RL10 has been upgraded over the years. One current model, the RL10B-2, powers the Delta IV second stage, as well as the Delta III second stage. It has been significantly modified from the original RL10 to improve performance. Some of the enhancements include an extendable nozzle and electro-mechanical gimbaling for reduced weight and increased reliability. Current specific impulse is 462 s (equivalent to an exhaust velocity of 4.53 km/s).: [http://www.spaceandtech.com/spacedata/engines/rl10_specs.shtml Specifications]

; RL10B-2
*Thrust (altitude): 24,750 lbf (110.1 kN)
*Design: Expander cycle
*Burn time: 1,152 seconds
*Specific impulse: 462 s (4.53 kN·s/kg)
*Engine weight - dry: 664 lb (301 kg)
*Height: 163 in (4.14 m)
*Diameter: 87 in (2.21 m)
*Expansion ratio: 250 to 1
*Mixture ratio: 5.88 to 1
*Propellants: Liquid oxygen & liquid hydrogen
*Propellant flow: Oxidizer 41.42 lb/s (20.6 kg/s), fuel 7.72 lb/s (3.5 kg/s)
*Contractor: Pratt & Whitney
*Vehicle application: Delta III, Delta IV second stage (1 engine)A flaw in the brazing of an RL10B-2 combustion chamber was identified as the cause of failure for the Delta III launch carrying the Orion-3 communications satellite. [cite web | title = Delta 269 (Delta III) Investigation Report | url = http://www.boeing.com/defense-space/space/delta/delta3/d3_report.pdf | publisher = Boeing|format=PDF]

; RL10A-4-2The other current model, the RL10A-4-2, is an upper stage engine used on Atlas V.

Future use of the RL10

In 2005 NASA announced the decision to use an Apollo-like spacecraft configuration for the proposed Orion spacecraft. At that time NASA decided that the descent stage of the new Lunar Surface Access Module (LSAM) would be powered by liquid hydrogen and liquid oxygen. The original plan called for the ascent stage to use liquid methane and liquid oxygen, but that has changed and the ascent stage will now also use LH2/LOX.

Because of the choice of propellents, along with the need to land the spacecraft in the polar regions of the Moon from an equatorial orbit, NASA decided to use the RL10 as the main powerplant for the descent stage engine. Current specifications call for four RL10 engines to be used on the descent stage and a single RL10 for the ascent stage. Currently, the RL10B-2 engines used on the Delta III and Delta IV can thrust at 20% of maximum thrust. Because of the need for the LSAM to hover above the lunar surface, along with providing a smooth landing, the new RL10 engines must be able to thrust as low as 10%. The use of the RL10 will allow NASA to keep costs on the lunar program down by using existing hardware, albeit modified to enhance performance or allow for manned spaceflight.

Common Extensible Cryogenic Engine

The Common Extensible Cryogenic Engine (CECE) is a testbed to develop RL10 engines that throttle well. It has demonstrated operability (with some "chugging") at 11-to-1 throttle ratios. [cite web | url = http://science.nasa.gov/headlines/y2007/16jul_cece.htm | title = Throttling Back to the Moon | date = 2007-07-16 | publisher = NASA] NASA has contracted with Pratt & Whitney Rocketdyne to develop the CECE demonstrator engine. [cite web | url = http://www.pw.utc.com/vgn-ext-templating/v/index.jsp?vgnextrefresh=1&vgnextoid=91380e78738ee010VgnVCM100000c45a529fRCRD | title = CECE | publisher = United Technologies Corporation]

Other Rockets using RL10

Four modified RL10A-5 engines, all of them with the ability to be throttled, were used in the McDonnell Douglas DC-X. It is not known if the very similar Blue Origin rocket, which is based on the DC-X, has these type of RL10 engines.


ee also

*Spacecraft propulsion

External links

* [http://www.astronautix.com/engines/rl10b2.htm RL10B-2 at Astronautix]
* [http://www.spaceflightnow.com/news/n0708/16rl10valve/ Spaceflight Now article]

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