Aerospike engine
Encyclopedia
The aerospike engine is a type of rocket engine
that maintains its aerodynamic efficiency across a wide range of altitude
s through the use of an aerospike nozzle. It is a member of the class of altitude compensating nozzle
engines. A vehicle with an aerospike engine uses 25–30% less fuel at low altitudes, where most missions have the greatest need for thrust
. Aerospike engines have been studied for a number of years and are the baseline engines for many single-stage-to-orbit
(SSTO) designs and were also a strong contender for the Space Shuttle Main Engine
. However, no engine is in commercial production. The best large-scale aerospikes are still only in testing phases.
The terminology in the literature surrounding this subject is somewhat confused—the term aerospike was originally used for a truncated plug nozzle
with a very rough conical taper and some gas injection, forming an "air spike" to help make up for the absence of the plug tail. However, frequently, a full-length plug nozzle is now called an aerospike.
Instead of firing the exhaust out of a small hole in the middle of a bell, an aerospike engine avoids this random distribution by firing along the outside edge of a wedge-shaped protrusion, the "spike". The spike forms one side of a virtual bell, with the other side being formed by the outside air—thus the "aerospike".
The idea behind the aerospike design is that at low altitude the ambient pressure compresses the wake against the nozzle. The recirculation in the base zone of the wedge can then raise the pressure there to near ambient. Since the pressure on top of the engine is ambient, this means that base gives no overall thrust (but it also means that this part of the nozzle doesn't lose thrust by forming a partial vacuum, thus the base part of the nozzle can be ignored at low altitude).
As the spacecraft climbs to higher altitudes, the air pressure holding the exhaust against the spike decreases, but the pressure on top of the engine decreases at the same time, so this is not detrimental. Further, although the base pressure drops, the recirculation zone keeps the pressure on the base up to a fraction of 1 bar
, a pressure that is not balanced by the near vacuum on top of the engine; this difference in pressure gives extra thrust at altitude, contributing to the altitude compensating effect. This produces an effect like that of a bell that grows larger as air pressure falls, providing altitude compensation.
The disadvantages of aerospikes seem to be extra weight for the spike, and increased cooling requirements due to the extra heated area. Further, the larger cooled area can reduce performance below theoretical levels by reducing the pressure against the nozzle. Also, aerospikes work relatively poorly between Mach
1-3, where the airflow around the vehicle has reduced pressure, and this reduces the thrust.
In the linear aerospike the spike consists of a tapered wedge-shaped plate, with exhaust exiting on either side at the "thick" end. This design has the advantage of being stackable, allowing several smaller engines to be placed in a row to make one larger engine while augmenting steering performance with the use of individual engine throttle control.
Rocketdyne
conducted a lengthy series of tests in the 1960s on various designs. Later models of these engines were based on their highly reliable J-2
engine machinery and provided the same sort of thrust levels as the conventional engines they were based on; 200,000 lbf
(890 kN) in the J-2T-200k, and 250,000 lbf (1.1 MN) in the J-2T-250k (the T refers to the toroidal combustion chamber). Thirty years later their work was dusted off again for use in NASA
's X-33 project. In this case the slightly upgraded J-2S engine machinery was used with a linear spike, creating the XRS-2200. After more development and considerable testing, this project was cancelled when the X-33's composite fuel tanks repeatedly failed.
Three XRS-2200 engines were built during the X-33 program and underwent testing at NASA's Stennis Space Center
. The single-engine tests were a success, but the program was halted before the testing for the 2-engine setup could be completed. The XRS-2200 produces 204420 lbf (909,305.5 N) thrust with an Isp
of 339 seconds at sea level, and 266230 lbf (1,184,250 N) thrust with an Isp of 436.5 seconds in a vacuum.
The RS-2200 Linear Aerospike Engine was derived from the XRS-2200. The RS-2200 was to power the VentureStar
single-stage-to-orbit
vehicle. In the latest design, seven RS-2200s producing 542,000 pounds of thrust each would boost the VentureStar into low earth orbit. The development on the RS-2200 was formally halted in early 2001 when the X-33 program did not receive Space Launch Initiative
funding. Lockheed Martin
chose to not continue the VentureStar program without any funding support from NASA.
Although the cancelling of the X-33 program was a setback for aerospike engineering, it is not the end of the story. A milestone was achieved when a joint academic/industry team from California State University, Long Beach
(CSULB) and Garvey Spacecraft Corporation successfully conducted a flight test of a liquid-propellant powered aerospike engine in the Mojave Desert
on September 20, 2003. CSULB students had developed their Prospector 2 (P-2) rocket using a 1,000 lbf (4.4 kN) LOX/ethanol aerospike engine. This work on aerospike engines is ongoing; Prospector-10, a ten-chamber aerospike engine, was test-fired June 25, 2008.
Further progress came in March 2004 when two successful tests were carried out at the NASA Dryden Flight Research Centre using small-scale rockets manufactured by Blacksky Corporation, based in Carlsbad, California
. The aerospike nozzles and solid rocket motors were developed and built by Cesaroni Technology Incorporated. The two rockets were solid-fuel powered and fitted with non-truncated toroidal aerospike nozzles. They reached an apogee of 26000 ft (7,924.8 m) and speeds of about Mach
1.5.
Small-scale aerospike engine development using a hybrid rocket
propellant configuration has been ongoing by members of the Reaction Research Society
.
Rocket engine
A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
that maintains its aerodynamic efficiency across a wide range of altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
s through the use of an aerospike nozzle. It is a member of the class of altitude compensating nozzle
Altitude compensating nozzle
An altitude compensating nozzle is a class of rocket engine nozzles that are designed to operate efficiently across a wide range of altitudes.- Conventional designs :...
engines. A vehicle with an aerospike engine uses 25–30% less fuel at low altitudes, where most missions have the greatest need for 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....
. Aerospike engines have been studied for a number of years and are the baseline engines for many single-stage-to-orbit
Single-stage-to-orbit
A single-stage-to-orbit vehicle reaches orbit from the surface of a body without jettisoning hardware, expending only propellants and fluids. The term usually, but not exclusively, refers to reusable vehicles....
(SSTO) designs and were also a strong contender for 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...
. However, no engine is in commercial production. The best large-scale aerospikes are still only in testing phases.
The terminology in the literature surrounding this subject is somewhat confused—the term aerospike was originally used for a truncated plug nozzle
Plug nozzle
The plug nozzle is a type of nozzle which includes a centerbody or plug around which the working fluid flows. Plug nozzles have applications in aircraft, rockets, and numerous other fluid flows.-In Rockets:...
with a very rough conical taper and some gas injection, forming an "air spike" to help make up for the absence of the plug tail. However, frequently, a full-length plug nozzle is now called an aerospike.
Principles
The basic concept of any engine bell is to efficiently direct the flow of exhaust gases from the rocket engine into one direction. The exhaust, a high-temperature mix of gases, has an effectively random momentum distribution, and if it is allowed to escape in that form, only a small part of the flow will be moving in the correct direction to contribute to forward thrust.Instead of firing the exhaust out of a small hole in the middle of a bell, an aerospike engine avoids this random distribution by firing along the outside edge of a wedge-shaped protrusion, the "spike". The spike forms one side of a virtual bell, with the other side being formed by the outside air—thus the "aerospike".
The idea behind the aerospike design is that at low altitude the ambient pressure compresses the wake against the nozzle. The recirculation in the base zone of the wedge can then raise the pressure there to near ambient. Since the pressure on top of the engine is ambient, this means that base gives no overall thrust (but it also means that this part of the nozzle doesn't lose thrust by forming a partial vacuum, thus the base part of the nozzle can be ignored at low altitude).
As the spacecraft climbs to higher altitudes, the air pressure holding the exhaust against the spike decreases, but the pressure on top of the engine decreases at the same time, so this is not detrimental. Further, although the base pressure drops, the recirculation zone keeps the pressure on the base up to a fraction of 1 bar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
, a pressure that is not balanced by the near vacuum on top of the engine; this difference in pressure gives extra thrust at altitude, contributing to the altitude compensating effect. This produces an effect like that of a bell that grows larger as air pressure falls, providing altitude compensation.
The disadvantages of aerospikes seem to be extra weight for the spike, and increased cooling requirements due to the extra heated area. Further, the larger cooled area can reduce performance below theoretical levels by reducing the pressure against the nozzle. Also, aerospikes work relatively poorly between Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
1-3, where the airflow around the vehicle has reduced pressure, and this reduces the thrust.
Variations
Several versions of the design exist, differentiated by their shape. In the toroidal aerospike the spike is bowl-shaped with the exhaust exiting in a ring around the outer rim. In theory this requires an infinitely long spike for best efficiency, but by blowing a small amount of gas out the center of a shorter truncated spike, something similar can be achieved.In the linear aerospike the spike consists of a tapered wedge-shaped plate, with exhaust exiting on either side at the "thick" end. This design has the advantage of being stackable, allowing several smaller engines to be placed in a row to make one larger engine while augmenting steering performance with the use of individual engine throttle control.
Performance
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...
conducted a lengthy series of tests in the 1960s on various designs. Later models of these engines were based on their highly reliable J-2
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...
engine machinery and provided the same sort of thrust levels as the conventional engines they were based on; 200,000 lbf
Pound-force
The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...
(890 kN) in the J-2T-200k, and 250,000 lbf (1.1 MN) in the J-2T-250k (the T refers to the toroidal combustion chamber). Thirty years later their work was dusted off again for use in 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...
's X-33 project. In this case the slightly upgraded J-2S engine machinery was used with a linear spike, creating the XRS-2200. After more development and considerable testing, this project was cancelled when the X-33's composite fuel tanks repeatedly failed.
John C. Stennis Space Center
The John C. Stennis Space Center , located in Hancock County, Mississippi, at the Mississippi-Louisiana border, is NASA's largest rocket engine test facility.- History :...
. The single-engine tests were a success, but the program was halted before the testing for the 2-engine setup could be completed. The XRS-2200 produces 204420 lbf (909,305.5 N) thrust with an Isp
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 339 seconds at sea level, and 266230 lbf (1,184,250 N) thrust with an Isp of 436.5 seconds in a vacuum.
The RS-2200 Linear Aerospike Engine was derived from the XRS-2200. The RS-2200 was to power the VentureStar
VentureStar
VentureStar was a proposed spaceplane design for a single-stage-to-orbit reusable launch system by Lockheed Martin. The program's primary goal as a United States federally funded program was to develop a reusable unmanned spaceplane for launching satellites into orbit at a fraction of the cost of...
single-stage-to-orbit
Single-stage-to-orbit
A single-stage-to-orbit vehicle reaches orbit from the surface of a body without jettisoning hardware, expending only propellants and fluids. The term usually, but not exclusively, refers to reusable vehicles....
vehicle. In the latest design, seven RS-2200s producing 542,000 pounds of thrust each would boost the VentureStar into low earth orbit. The development on the RS-2200 was formally halted in early 2001 when the X-33 program did not receive Space Launch Initiative
Space Launch Initiative
The 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...
funding. Lockheed Martin
Lockheed Martin
Lockheed Martin is an American global aerospace, defense, security, and advanced technology company with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It is headquartered in Bethesda, Maryland, in the Washington Metropolitan Area....
chose to not continue the VentureStar program without any funding support from NASA.
California State University, Long Beach
California State University, Long Beach is the second largest campus of the California State University system and the third largest university in the state of California by enrollment...
(CSULB) and Garvey Spacecraft Corporation successfully conducted a flight test of a liquid-propellant powered aerospike engine in the Mojave Desert
Mojave Desert
The Mojave Desert occupies a significant portion of southeastern California and smaller parts of central California, southern Nevada, southwestern Utah and northwestern Arizona, in the United States...
on September 20, 2003. CSULB students had developed their Prospector 2 (P-2) rocket using a 1,000 lbf (4.4 kN) LOX/ethanol aerospike engine. This work on aerospike engines is ongoing; Prospector-10, a ten-chamber aerospike engine, was test-fired June 25, 2008.
Further progress came in March 2004 when two successful tests were carried out at the NASA Dryden Flight Research Centre using small-scale rockets manufactured by Blacksky Corporation, based in Carlsbad, California
Carlsbad, California
-2010:The 2010 United States Census reported that Carlsbad had a population of 105,328. The population density was 2,693.1 people per square mile . The racial makeup of Carlsbad was 87,205 White, 1,379 African American, 514 Native American, 7,460 Asian, 198 Pacific Islander, 4,189 from other...
. The aerospike nozzles and solid rocket motors were developed and built by Cesaroni Technology Incorporated. The two rockets were solid-fuel powered and fitted with non-truncated toroidal aerospike nozzles. They reached an apogee of 26000 ft (7,924.8 m) and speeds of about Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
1.5.
Small-scale aerospike engine development using a hybrid rocket
Hybrid rocket
A hybrid rocket is a rocket with a rocket motor which uses propellants in two different states of matter - one solid and the other either gas or liquid. The Hybrid rocket concept can be traced back at least 75 years....
propellant configuration has been ongoing by members of the Reaction Research Society
Reaction Research Society
The Reaction Research Society is the oldest continuously operating amateur experimental rocket group in the United States. Founded by George James on 6 January 1943, originally as the Southern California Rocket Society, the organization's name was changed to the Glendale Rocket Society two months...
.
See also
- Expanding nozzleExpanding nozzleThe expanding nozzle is a type of rocket nozzle that, unlike traditional designs, maintains its efficiency at a wide range of altitudes. It is a member of the class of altitude compensating nozzles, a class that also includes the plug nozzle and aerospike...
- LASRELASRELASRE was NASA's Linear Aerospike SR-71 Experiment which took place at the Dryden Flight Research Center at Edwards Air Force Base, California, until November 1998...
- Rotary RocketRotary RocketRotary Rocket, Inc, was a rocketry company headquartered in a facility at Mojave Airport that developed the Roton concept in the late 1990s as a fully reusable single-stage-to-orbit manned spacecraft. Roton was intended to reduce costs of launching payloads into low earth orbit by a factor of...
- Lockheed Martin X-33Lockheed Martin X-33The Lockheed Martin X-33 was an unmanned, sub-scale technology demonstrator suborbital spaceplane developed in the 1990s under the U.S. government-funded Space Launch Initiative program. The X-33 was a technology demonstrator for the VentureStar orbital spaceplane, which was planned to be a...
- Sabre
External links
- Aerospike Engine
- Advanced Engines planned for uprated Saturn and Nova boosters — includes the J-2T
- Linear Aerospike Engine — Propulsion for the X-33 Vehicle
- Dryden Flight Research Centre
- Aerospike Engine Control System Features And Performance
- X-33 Attitude Control Using The XRS-2200 Linear Aerospike Engine