RS-68 (rocket engine)
Encyclopedia
The Pratt & Whitney Rocketdyne
RS-68 (Rocket System 68) is a liquid-fuel rocket engine that burns liquid hydrogen
(LH2) with liquid oxygen
(LOX). It is the largest hydrogen-fueled engine in the world. Development of the engine started in the 1990s with the goal of producing a simpler, less-costly, heavy-lift engine for the Delta IV launch system. The engine has three versions: the original RS-68, the improved RS-68A, and the RS-68B for NASA
.
Propulsion and Power, located in Canoga Park, Los Angeles, California
, to power the Delta IV
Evolved Expendable Launch Vehicle (EELV
). The combustion chamber burns liquid hydrogen and liquid oxygen at 1486 lbf/in2 at 102% with a 1:6 engine mixture ratio.
At a maximum 102% thrust, the engine produces 758000 pound-forces (3,371.8 kN) in a vacuum and 663000 pound-forces (2,949.2 kN) at sea level. The engine's mass is 14560 pounds (6,604.3 kg) at 96 inches (2.4 m). With this thrust, the engine has a thrust-to-weight ratio of 51.2, and a specific impulse
of 410 s (4 kN·s/kg) in a vacuum and 365 s (3.58 kN·s/kg) at sea level. The RS-68 is gimbaled hydraulically and is capable of throttling between 58% and 101% thrust.
A leading goal of the RS-68 program was to produce a simple engine that would be cost-effective when jettisoned after a single launch. To achieve this, the RS-68 has 80% fewer parts than the multi-launch Space Shuttle Main Engine
(SSME). Simplicity came at the cost of lower thrust-efficiency versus the SSME: the RS-68's thrust-to-weight ratio is significantly lower and the RS-68's specific impulse is 10% lower. The benefit of the RS-68 is its reduced construction cost: To build an RS-68 for the Boeing
Delta IV program costs about $14 million, compared to $50 million for the SSME. While the SSME's higher costs were designed to be spread across multiple launches, the larger, less-costly, more powerful (50% more thrust) RS-68 was a more cost-effective engine for an expendable launch vehicle.
The engine itself is a gas generator cycle
engine with two independent turbopump
s. The combustion chamber uses a channel-wall design to reduce cost. This design, pioneered in the former Soviet Union
, features inner and outer skins brazed
to middle separators, forming cooling channels. This method is heavier, but much simpler and cheaper than the tube-wall design (using hundreds of tubes, bent into the shape of the combustion chamber and brazed together) used in other engines. The lower nozzle has an expansion ratio of 21.5 and is made from an ablative
material. The nozzle's lining is designed to burn away as the engine runs, dissipating heat. This is also heavier than the tube-wall nozzles used in other engines, but is also much easier and cheaper to manufacture. The presence of a Carbonaceous fuel, or in this case an ablative coating utilizing a carbon containing material, can be inferred by the yellow color of the engine exhaust, this is in contrast to the engine exhaust of another LOX/LH2 engine, the RL-10
.
The engine design was done at the Canoga Park, California facility, where the SSME is manufactured. The initial development engines were assembled at the nearby Santa Susana Field Laboratory
where the Saturn V
F-1
engines were developed and tested for the Apollo missions to the Moon. The RS-68 had initial testing done at Air Force Research Lab, Edwards AFB
and later at NASA's John C. Stennis Space Center. The first successful test firing at AFRL was completed on September 11, 1998, and the first successful test firing at Stennis on September 22, 1999. The RS-68 was certified for use on Delta IV in December 2001. The first successful launch using the new engine and launch vehicle occurred on November 20, 2002.
The RS-68 is part of the Common Booster Core
(CBC) used to create the five variants of the Delta IV family of launch vehicles. The largest of the launch vehicles includes three CBCs mounted together for the Heavy.
(CaLV). NASA chose the RS-68 because of its lower cost, about $20 million per engine after NASA upgrades. The modifications to the RS-68 for the Ares V include a different ablative nozzle to accommodate a longer burn, a shorter start sequence, hardware changes to limit free hydrogen at ignition, and changes to reduce helium use during countdown and flight. Thrust
and specific impulse
increases will occur under a separate upgrade program for Delta IV. Later the Ares V was changed to use six RS-68 engines. The engine version for NASA's Ares V is designated RS-68B. The DIRECT
alternative launch project included two or three RS-68 engines in "version 2.0" of the team's proposal, but switched to the Space Shuttle Main Engine
(SSME) for "version 3.0".
On April 4, 2008, the Air Force awarded Boeing Launch Services of Huntington Beach, Calif., a modified contract for $20 million. This contract modification will authorize Boeing to perform demonstration testing on a rebuilt RS-68 engine. The government has authorized work under the Assured Access to Space initiative to develop hardware that will reduce or eliminate these risks and increase the reliability of the RS-68 engine.
On September 25, 2008, the upgraded RS-68A successfully completed its first test firing. The RS-68A is an updated version of the RS-68, with changes to provide increased specific impulse and thrust (to over 700000 pound-forces (3,113,755.1 N) at sea level). The RS-68A is planned to be certified in 2010, with initial launch capability in early 2011. The first flight that will use RS-68A engines will use three of them. On March 8, 2011 Pratt & Whitney Rocketdyne announced that the Hardware Acceptance Review for the first of those three engines had been successfully completed. The remaining two engines for that flight are scheduled for Hardware Acceptance Review in March and April 2011, respectively.
standards. NASA states several changes are needed to human-rate the RS-68, including health monitoring, removal of fuel-rich environment at liftoff, and improved subsystems robustness.
Rocketdyne
Rocketdyne was a Rocket engine design and production company headquartered in Canoga Park, California, United States. The company was related to North American Aviation for most of its history. NAA merged with Rockwell International, which was then bought by Boeing in December, 1996...
RS-68 (Rocket System 68) is a liquid-fuel rocket engine that burns liquid hydrogen
Liquid hydrogen
Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...
(LH2) with liquid oxygen
Liquid oxygen
Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...
(LOX). It is the largest hydrogen-fueled engine in the world. Development of the engine started in the 1990s with the goal of producing a simpler, less-costly, heavy-lift engine for the Delta IV launch system. The engine has three versions: the original RS-68, the improved RS-68A, and the RS-68B for NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
.
Design and development
The RS-68 was developed at RocketdyneRocketdyne
Rocketdyne was a Rocket engine design and production company headquartered in Canoga Park, California, United States. The company was related to North American Aviation for most of its history. NAA merged with Rockwell International, which was then bought by Boeing in December, 1996...
Propulsion and Power, located in Canoga Park, Los Angeles, California
Canoga Park, Los Angeles, California
Canoga Park is a district in the San Fernando Valley region of Los Angeles, California, United States about 25 miles northwest of Downtown Los Angeles....
, to power the Delta IV
Delta IV rocket
Delta IV is an active expendable launch system in the Delta rocket family. Delta IV uses rockets designed by Boeing's Integrated Defense Systems division and built in the United Launch Alliance facility in Decatur, Alabama. Final assembly is completed at the launch site by ULA...
Evolved Expendable Launch Vehicle (EELV
EELV
Evolved Expendable Launch Vehicle is an expendable launch system program of the United States Air Force , intended to assure access to space for Department of Defense and other United States government payloads...
). The combustion chamber burns liquid hydrogen and liquid oxygen at 1486 lbf/in2 at 102% with a 1:6 engine mixture ratio.
At a maximum 102% thrust, the engine produces 758000 pound-forces (3,371.8 kN) in a vacuum and 663000 pound-forces (2,949.2 kN) at sea level. The engine's mass is 14560 pounds (6,604.3 kg) at 96 inches (2.4 m). With this thrust, the engine has a thrust-to-weight ratio of 51.2, and a specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
of 410 s (4 kN·s/kg) in a vacuum and 365 s (3.58 kN·s/kg) at sea level. The RS-68 is gimbaled hydraulically and is capable of throttling between 58% and 101% thrust.
A leading goal of the RS-68 program was to produce a simple engine that would be cost-effective when jettisoned after a single launch. To achieve this, the RS-68 has 80% fewer parts than the multi-launch Space Shuttle Main Engine
Space Shuttle main engine
The RS-25, otherwise known as the Space Shuttle Main Engine , is a reusable liquid-fuel rocket engine built by Pratt & Whitney Rocketdyne for the Space Shuttle, running on liquid hydrogen and oxygen. Each Space Shuttle was propelled by three SSMEs mated to one powerhead...
(SSME). Simplicity came at the cost of lower thrust-efficiency versus the SSME: the RS-68's thrust-to-weight ratio is significantly lower and the RS-68's specific impulse is 10% lower. The benefit of the RS-68 is its reduced construction cost: To build an RS-68 for the Boeing
Boeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
Delta IV program costs about $14 million, compared to $50 million for the SSME. While the SSME's higher costs were designed to be spread across multiple launches, the larger, less-costly, more powerful (50% more thrust) RS-68 was a more cost-effective engine for an expendable launch vehicle.
The engine itself is a gas generator cycle
Gas-generator cycle (rocket)
The gas generator cycle is a power cycle of a bipropellant rocket engine. Some of the propellant is burned in a gas-generator and the resulting hot gas is used to power the engine's pumps. The gas is then exhausted...
engine with two independent turbopump
Turbopump
A turbopump is a gas turbine that comprises basically two main components: a rotodynamic pump and a driving turbine, usually both mounted on the same shaft, or sometimes geared together...
s. The combustion chamber uses a channel-wall design to reduce cost. This design, pioneered in the former Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
, features inner and outer skins brazed
Brazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...
to middle separators, forming cooling channels. This method is heavier, but much simpler and cheaper than the tube-wall design (using hundreds of tubes, bent into the shape of the combustion chamber and brazed together) used in other engines. The lower nozzle has an expansion ratio of 21.5 and is made from an ablative
Ablation
Ablation is removal of material from the surface of an object by vaporization, chipping, or other erosive processes. This occurs in spaceflight during ascent and atmospheric reentry, glaciology, medicine, and passive fire protection.-Spaceflight:...
material. The nozzle's lining is designed to burn away as the engine runs, dissipating heat. This is also heavier than the tube-wall nozzles used in other engines, but is also much easier and cheaper to manufacture. The presence of a Carbonaceous fuel, or in this case an ablative coating utilizing a carbon containing material, can be inferred by the yellow color of the engine exhaust, this is in contrast to the engine exhaust of another LOX/LH2 engine, the RL-10
RL-10
The RL10 was USA's first liquid hydrogen fueled rocket engine. An updated version is used in several current launch vehicles. Six RL10 engines were used in the S-IV second stage of the Saturn I rocket. One or two RL10 engines are used in the Centaur upper stages of Atlas and Titan rockets...
.
The engine design was done at the Canoga Park, California facility, where the SSME is manufactured. The initial development engines were assembled at the nearby Santa Susana Field Laboratory
Santa Susana Field Laboratory
The Santa Susana Field Laboratory is a complex of industrial research and development facilities located on a 2,668 acre portion of the Southern California Simi Hills in Simi Valley, California, used mainly for the testing and development of Liquid-propellant rocket engines for the United States...
where the Saturn V
Saturn V
The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...
F-1
F-1 (rocket engine)
The F-1 is a rocket engine developed by Rocketdyne and used in the Saturn V. Five F-1 engines were used in the S-IC first stage of each Saturn V, which served as the main launch vehicle in the Apollo program. The F-1 is still the most powerful single-chamber liquid-fueled rocket engine ever...
engines were developed and tested for the Apollo missions to the Moon. The RS-68 had initial testing done at Air Force Research Lab, Edwards AFB
Edwards Air Force Base
Edwards Air Force Base is a United States Air Force base located on the border of Kern County, Los Angeles County, and San Bernardino County, California, in the Antelope Valley. It is southwest of the central business district of North Edwards, California and due east of Rosamond.It is named in...
and later at NASA's John C. Stennis Space Center. The first successful test firing at AFRL was completed on September 11, 1998, and the first successful test firing at Stennis on September 22, 1999. The RS-68 was certified for use on Delta IV in December 2001. The first successful launch using the new engine and launch vehicle occurred on November 20, 2002.
The RS-68 is part of the Common Booster Core
Common Booster Core
The Common Booster Core is an American rocket stage, which is used on the Delta IV rocket as part of a modular rocket system. Delta IV rockets flying in the Medium and Medium+ configurations each use a single Common Booster Core as their first stage, whilst the Heavy configuration uses three; one...
(CBC) used to create the five variants of the Delta IV family of launch vehicles. The largest of the launch vehicles includes three CBCs mounted together for the Heavy.
Future use
On May 18, 2006, NASA announced that five RS-68 engines would be used instead of SSMEs on the planned Ares VAres V
The Ares V was the planned cargo launch component of the Constellation program, which was to have replaced the Space Shuttle after its retirement in 2011. Ares V was also planned to carry supplies for a human presence on Mars...
(CaLV). NASA chose the RS-68 because of its lower cost, about $20 million per engine after NASA upgrades. The modifications to the RS-68 for the Ares V include a different ablative nozzle to accommodate a longer burn, a shorter start sequence, hardware changes to limit free hydrogen at ignition, and changes to reduce helium use during countdown and flight. Thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
and specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
increases will occur under a separate upgrade program for Delta IV. Later the Ares V was changed to use six RS-68 engines. The engine version for NASA's Ares V is designated RS-68B. The DIRECT
DIRECT
DIRECT is a proposed alternative heavy lift launch vehicle architecture supporting NASA's Vision for Space Exploration, which would replace the space agency's planned Ares I and Ares V rockets...
alternative launch project included two or three RS-68 engines in "version 2.0" of the team's proposal, but switched to the Space Shuttle Main Engine
Space Shuttle main engine
The RS-25, otherwise known as the Space Shuttle Main Engine , is a reusable liquid-fuel rocket engine built by Pratt & Whitney Rocketdyne for the Space Shuttle, running on liquid hydrogen and oxygen. Each Space Shuttle was propelled by three SSMEs mated to one powerhead...
(SSME) for "version 3.0".
On April 4, 2008, the Air Force awarded Boeing Launch Services of Huntington Beach, Calif., a modified contract for $20 million. This contract modification will authorize Boeing to perform demonstration testing on a rebuilt RS-68 engine. The government has authorized work under the Assured Access to Space initiative to develop hardware that will reduce or eliminate these risks and increase the reliability of the RS-68 engine.
On September 25, 2008, the upgraded RS-68A successfully completed its first test firing. The RS-68A is an updated version of the RS-68, with changes to provide increased specific impulse and thrust (to over 700000 pound-forces (3,113,755.1 N) at sea level). The RS-68A is planned to be certified in 2010, with initial launch capability in early 2011. The first flight that will use RS-68A engines will use three of them. On March 8, 2011 Pratt & Whitney Rocketdyne announced that the Hardware Acceptance Review for the first of those three engines had been successfully completed. The remaining two engines for that flight are scheduled for Hardware Acceptance Review in March and April 2011, respectively.
Human-rating
It would reportedly require over 200 changes to the RS-68 to meet human-ratingHuman-rating certification
Human-rated or man-rated are terms used to describe the certification of a spacecraft, launch vehicleor airplaneas worthy of transporting humans. NASA and the U.S. GAO now uses "Human-rating" when describing requirements for these systems...
standards. NASA states several changes are needed to human-rate the RS-68, including health monitoring, removal of fuel-rich environment at liftoff, and improved subsystems robustness.
Variants
- RS-68 is the initial engine version. It produces 663000 pound-forces (2,949.2 kN) thrust at sea level.
- RS-68A is an improved engine version. It produces 705000 lbf (3,136 kN) thrust at sea level and 800000 lbf (3,558.6 kN) thrust in vacuum. Certification testing was completed in November 2010.
- RS-68B is the proposed engine version for NASANASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Constellation program.
See also
- SSMESpace Shuttle main engineThe RS-25, otherwise known as the Space Shuttle Main Engine , is a reusable liquid-fuel rocket engine built by Pratt & Whitney Rocketdyne for the Space Shuttle, running on liquid hydrogen and oxygen. Each Space Shuttle was propelled by three SSMEs mated to one powerhead...
- RS-83Rs-83The RS-83 was a rocket engine design for a reusable liquid hydrogen/liquid oxygen rocket larger and more powerful than any other. The RS-83 was designed to last 100 missions, and was intended for use on the first stage of a two-stage-to-orbit reusable launch vehicle.- Development :It was developed...
- RS-84Space Launch InitiativeThe Space Launch Initiative was a NASA and U.S. Department of Defense joint research and technology project to determine the requirements to meet all the nation’s hypersonics, space launch and space technology needs...
- J-2 (rocket engine)J-2 (rocket engine)Rocketdyne's J-2 rocket engine was a major component of the Saturn V rocket used in the Apollo program to send men to the Moon. Five J-2 engines were used on the S-II second stage, and one J-2 was used on the S-IVB third stage. The S-IVB was also used as the second stage of the smaller Saturn IB...