View source for Aerospike engine

{{short description|Type of rocket engine that maintains its aerodynamic efficiency across a wide range of altitudes}}
{{use dmy dates |date=August 2020}}
[[File:Twin Linear Aerospike XRS-2200 Engine PLW edit.jpg|thumb|upright=1.5|[[Rocketdyne XRS-2200|XRS-2200]] linear aerospike engine for the [[X-33]] program being tested at the [[Stennis Space Center]]]]

The '''aerospike engine''' is a type of [[rocket engine]] that maintains its [[aerodynamic]] efficiency across a wide range of [[altitude]]s.<ref name=factsheet>{{Cite web|url=https://www.nasa.gov/centers/marshall/news/background/facts/aerospike.html|title=NASA - Linear Aerospike Engine fact sheet (08/00)|website=www.nasa.gov|language=en|access-date=2020-01-21}}</ref> It belongs to the class of [[altitude compensating nozzle]] engines.<ref>{{cite journal|last1=Defusca|first1=Albert|last2=Craddock|first2=Christopher|date=November 1, 2017|title=Affordable Access to Low Earth Orbit|url=https://www.dsiac.org/resources/journals/dsiac/fall-2017-volume-4-number-4/affordable-access-low-earth-orbit|journal=DSIAC Journals|volume=4|issue=4|access-date=June 16, 2019}}</ref> Aerospike engines were proposed for many [[single-stage-to-orbit]] (SSTO) designs. They were a contender for the [[Space Shuttle main engine]]. However, as of 2023 no such engine was in commercial production, although some large-scale aerospikes were in testing phases.<ref>{{Cite web|url=https://www.hq.nasa.gov/office/pao/History/x-33/aerospik.htm|title=Aerospike Engine Homepage|website=www.hq.nasa.gov|access-date=27 August 2020|archive-date=23 May 2022|archive-url=https://web.archive.org/web/20220523204457/https://www.hq.nasa.gov/office/pao/History/x-33/aerospik.htm|url-status=dead}}</ref>

The term ''aerospike'' was originally used for a truncated [[plug nozzle#In rockets|plug nozzle]] with a rough conical taper and some gas injection, forming an "air spike" to help make up for the absence of the plug tail. However, a full-length plug nozzle may also be called an aerospike.

==Principles==
The purpose of any engine bell is to direct the exhaust of a rocket engine in one direction, generating thrust in the opposite direction. The exhaust, a high-temperature mix of gases, has an effectively random momentum distribution (i.e., the exhaust pushes in any direction it can).  If the exhaust is allowed to escape in this form, only a small part of the flow will be moving in the correct direction and thus contribute to forward thrust.  The bell redirects exhaust moving in the wrong direction so that it generates thrust in the correct direction.  Ambient air pressure also imparts a small pressure against the exhaust, helping to keep it moving in the "right" direction as it exits the engine.  As the vehicle travels upward through the atmosphere, ambient air pressure is reduced.  This causes the thrust-generating exhaust to begin to expand outside the edge of the bell.  Since this exhaust begins traveling in the "wrong" direction (i.e., outward from the main exhaust plume), the efficiency of the engine is reduced as the rocket travels because this escaping exhaust is no longer contributing to the thrust of the engine.  An aerospike rocket engine seeks to eliminate this loss of efficiency.<ref name=factsheet/>

[[File:Aerospikeprinciplediagram.svg|thumb|Comparison between the design of a [[bell-nozzle]] rocket (left) and an aerospike rocket (right)]]

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", which serves the same function as a traditional engine bell. The spike forms one side of a "virtual" bell, with the other side being formed by the outside air.<ref name=factsheet/>

The idea behind the aerospike design is that at low altitude the ambient pressure compresses the exhaust against the spike. Exhaust recirculation in the base zone of the spike can raise the pressure in that zone to nearly ambient. Since the pressure in front of the vehicle is ambient, this means that the exhaust at the base of the spike nearly balances out with the drag experienced by the vehicle.  It gives no overall thrust, but this part of the nozzle also doesn't ''lose'' thrust by forming a partial vacuum.  The thrust at the base part of the nozzle can be ignored at low altitude.<ref name=factsheet/>

As the vehicle climbs to higher altitudes, the air pressure holding the exhaust against the spike decreases, as does the drag in front of the vehicle. The recirculation zone at the base of the spike maintains the pressure in that zone to a fraction of 1 [[bar (unit)|bar]], higher than the near-vacuum in front of the vehicle, thus giving extra thrust as altitude increases.  This effectively behaves like an "altitude compensator" in that the size of the bell automatically compensates as air pressure falls.<ref name=factsheet/>

The disadvantages of aerospikes seem to be extra weight for the spike. Furthermore, the larger cooled area can reduce performance below theoretical levels by reducing the pressure against the nozzle. Aerospikes work relatively poorly between [[Mach number|Mach]] 1–3, where the airflow around the vehicle has reduced the pressure, thus reducing the thrust.<ref name="nozzledesign">{{Cite web|url=http://ww17.pwrengineering.com/articles/nozzledesign.htm|archive-url=https://web.archive.org/web/20100402105625/http://www.pwrengineering.com/articles/nozzledesign.htm|url-status=dead|title=Pwrengineering.com|archive-date=April 2, 2010|website=ww17.pwrengineering.com}}</ref>

===Variations===
Several versions of the design exist, differentiated by their shapes. 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 of the center of a shorter truncated spike (like [[base bleed]] in an artillery shell), 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==
<!-- Deleted image removed: [[File:Annular-Aerospike.jpg|thumb|[[Rocketdyne]]'s [[J-2 (rocket engine)|J-2T-250k]] annular aerospike test firing.]] -->
[[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 (rocket engine)|J-2]] engine machinery and provided the same sort of thrust levels as the conventional engines they were based on; 200,000 [[pound-force|lbf]] (890 [[Newton (unit)|kN]]) in the '''J-2T-200k''', and 250,000&nbsp;lbf (1.1 MN) in the '''J-2T-250k''' (the T refers to the toroidal combustion chamber). Thirty years later their work was revived 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 '''[[Rocketdyne XRS-2200|XRS-2200]]'''. After more development and considerable testing, this project was cancelled when the X-33's composite fuel tanks repeatedly failed.
 
[[File:Aerospike close-up.jpg|thumb|[[CSULB]] aerospike engine]]
Three XRS-2200 engines were built during the X-33 program and underwent testing at NASA's [[John C. Stennis Space Center|Stennis Space Center]]. The single-engine tests were a success, but the program was halted before the testing for the two-engine setup could be completed. The XRS-2200 produces {{convert|204420|lbf|abbr=on}} thrust with an [[Specific impulse|I<sub>sp</sub>]] of 339 seconds at sea level, and {{convert|266230|lbf|abbr=on}} thrust with an I<sub>sp</sub> of 436.5 seconds in a vacuum.

The RS-2200 Linear Aerospike Engine<ref>{{cite web|title=RS-2200|url=http://www.astronautix.com/r/rs-2200.html|archive-url=https://web.archive.org/web/20161228055938/http://astronautix.com/r/rs-2200.html|url-status=dead|archive-date=28 December 2016|website=Astronautix.com|access-date=4 February 2018}}</ref> 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 {{convert|542000|lbf|kN}} 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. An engine of this type is on outdoor display on the grounds of the NASA Marshall Space Flight Center in Huntsville Alabama.

[[File:Non-truncated toroidal aerospike nozzle.jpg|thumb|[[NASA]]'s Toroidal aerospike nozzle]]
The [[Lockheed Martin X-33#Cancellation|cancellation of the Lockheed Martin X-33]] by the federal government in 2001 decreased funding availability, but aerospike engines remain an area of active research. For example, 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&nbsp;lb<sub>f</sub> (4.4&nbsp;kN) LOX/ethanol aerospike engine. This work on aerospike engines continues; Prospector-10, a ten-chamber aerospike engine, was test-fired June 25, 2008.<ref>{{Cite web|url=http://www.csulb.edu/colleges/coe/mae/views/projects/rocket/|archive-url=https://web.archive.org/web/20080615154007/http://www.csulb.edu/colleges/coe/mae/views/projects/rocket/|url-status=dead|title=CSULB CALVEIN Rocket News and Events|archive-date=June 15, 2008}}</ref>

[[File:Nozzle performance comparison.svg|thumb|Nozzle performance comparison of [[bell nozzle|bell]] and aerospike nozzle]]

Further progress came in March 2004 when two successful tests sponsored by the NASA [[Dryden Flight Research Center]] using high-power rockets manufactured by [[Blacksky Corporation]], based in [[Carlsbad, California]]. The aerospike nozzles and solid rocket motors were developed and built by the rocket motor division of [[Cesaroni Technology Incorporated]], north of Toronto, Ontario. The two rockets were solid-fuel powered and fitted with non-truncated toroidal aerospike nozzles. Flown at the Pecos County Aerospace Development Center, Fort Stockton, Texas, the rockets achieved apogees of {{convert|26000|ft|m|abbr=on}} and speeds of about [[Mach number|Mach]] 1.5.

Small-scale aerospike engine development using a [[hybrid rocket]] propellant configuration has been ongoing by members of the [[Reaction Research Society]].

In 2020 the [[TU Dresden]] and [[Fraunhofer IWS]] started their CFDμSAT-Project for research on additively manufactured aerospike-engines. A prototype has already been tested in a test cell at TU Dresden's Institute of Aerospace Engineering, achieving a
burn time of 30 seconds.<ref>{{cite web|title=TU-Dresden Homepage|url=https://tu-dresden.de/tu-dresden/profil/exzellenz/news/3D-Raketentriebwerk?set_language=en|website=tu-dresden.de|access-date=23 April 2021}}</ref>

== Implementations ==
=== Firefly Aerospace ===
In July 2014 [[Firefly Aerospace|Firefly Space Systems]] announced its planned Alpha launcher that uses an aerospike engine for its first stage. Intended for the small satellite launch market, it is designed to launch satellites into low-Earth orbit (LEO) at a price of US$8–9&nbsp;million, much lower than with conventional launchers.<ref name=giz1407>{{cite web|url=http://www.gizmag.com/firefly-alpha-aerospike-launch-vehicle/32892 |title=Firefly Space Systems unveils Alpha launch vehicle design with aerospike engine |publisher=Gizmag.com |date= 14 July 2014|access-date=2014-07-14}}</ref>

[[Firefly Alpha]] 1.0 was designed to carry payloads of up to {{convert|400|kg}}. It uses carbon composite materials and uses the same basic design for both stages. The plug-cluster aerospike engine puts out {{convert|90000|lbf|kN}} of thrust. The engine has a bell-shaped nozzle that has been cut in half, then stretched to form a ring with the half-nozzle now forming the profile of a plug.<ref name=giz1407/>

This rocket design was never launched. The design was abandoned after Firefly Space Systems went bankrupt. A new company, [[Firefly Aerospace]], has replaced the aerospike engine with a conventional engine in the Alpha 2.0 design. However, the company has proposed Firefly Gamma, a partially reusable spaceplane with aerospike engines.

=== ARCA Space ===
In March 2017 [[ARCA Space Corporation]] announced their intention to build a [[single-stage-to-orbit]] (SSTO) rocket, named Haas 2CA, using a linear aerospike engine. The rocket is designed to send up to 100&nbsp;kg into low-Earth orbit, at a price of US$1&nbsp;million per launch.<ref name="ARCA">{{cite web|title=ARCA News|url=http://www.arcaspace.com/en/news.htm|website=ARCA Space|access-date=30 May 2018}}</ref> They later announced that their Executor Aerospike engine would produce {{convert|50500|lbf|kN}} of thrust at sea level and {{convert|73800|lbf|kN}} of thrust in a vacuum.<ref>{{cite web |title=Haas 2CA Specs |url=http://www.arcaspace.com/en/Haas_2CA/specs.htm |website=ARCA Space |access-date=30 May 2018 |archive-date=30 May 2018 |archive-url=https://web.archive.org/web/20180530002103/http://www.arcaspace.com/en/Haas_2CA/specs.htm |url-status=dead }}</ref>

In June 2017, ARCA announced that they would fly their Demonstrator3 rocket to space, also using a linear aerospike engine. This rocket was designed to test several components of their Haas 2CA at lower cost. They announced a flight for August 2017.<ref name="ARCA"/>  In September 2017, ARCA announced that, after being delayed, their linear aerospike engine was ready to perform ground tests and flight tests on a Demonstrator3 rocket.<ref name="ARCA"/>

On December 20, 2019, ARCA tested the LAS 25DA aerospike steam rocket engine for the Launch Assist System.<ref>{{cite web |title=Flight of the Aerospike: Episode 34 - LAS 25DA Aerospike Engine |url=https://www.youtube.com/watch?v=WnrTrsRskp8  |archive-url=https://ghostarchive.org/varchive/youtube/20211211/WnrTrsRskp8| archive-date=2021-12-11 |url-status=live|website=Youtube |publisher=ARCA Space |access-date=August 5, 2020}}{{cbignore}}</ref>

===KSF Space and Interstellar Space===
Another spike engine concept model, by KSF Space and Interstellar Space in Los Angeles, was designed for orbital vehicle named SATORI. Due to lack of funding, the concept is still undeveloped.<ref name="ksf">{{cite web | url=https://www.ksf.space/satori-ksf-space.html | title=SATORI Space Vehicle Rocket | website=KSF Space}}</ref>

=== Rocketstar ===
Rocketstar planned to launch its 3D-printed aerospike rocket to an altitude of 50 miles in February 2019 but canceled the mission three days ahead of liftoff citing safety concerns. They are working on a second launch attempt.<ref>{{Cite web|date=2021-09-27|title=RocketStar ready for second suborbital flight attempt|url=https://spacenews.com/rocketstar-ready-for-second-suborbital-flight-attempt/|access-date=2021-12-14|website=SpaceNews|language=en-US}}</ref>

=== Pangea Aerospace ===
In November 2021, Spain-based [[Pangea Aerospace]] began hot-fire testing of its small-scale demonstration methane-oxygen aerospike engine DemoP1.
<ref>{{cite web
 | title = Pangea Aerospace tests aerospike engine
 | url = https://spacenews.com/pangea-aerospace-tests-aerospike-engine/
 | website = SpaceNews
 | date = November 20, 2021
 | access-date = January 2, 2022}}</ref><ref>{{cite web
 | title = Research Activities in the Development of DemoP1: A LOX/LNG Aerospike Engine Demonstrator
 | url = https://www.researchgate.net/publication/350800053
 | website = ResearchGate
 | date = March 2021
 | access-date = December 22, 2022}}
</ref>

After successfully testing the demonstrator DemoP1, Pangea plans to up-scale to the 300&nbsp;kN ARCOS engine.<ref>{{cite web
 | title = Aerospike Propulsion
 | url = https://pangeaaerospace.com/technology/
 | website = Pangea Aerospace
 | access-date = December 22, 2022}}
</ref>

=== Stoke Space ===
Headquartered in Kent, Washington, [[Stoke Space]] is building and testing a distributed architecture LH2/LOX aerospike system for its reusable second stage.<ref>{{Cite web|date=2022-10-10|title=Stoke Space aims to build rapidly reusable rocket with a completely novel design|url=https://arstechnica.com/science/2022/10/stoke-space-aims-to-build-rapidly-reusable-rocket-with-a-completely-novel-design/|access-date=February 13, 2023|website=Arstechnica|language=en-US}}</ref>

=== Polaris Spaceplanes ===
The [[Bremen]]-based German startup [[POLARIS Raumflugzeuge GmbH]] received a [[Bundeswehr]] contract to design and flight test a linear aerospike engine in April 2023. The company is set to test this new engine on board of its fourth spaceplane demonstrator, DEMO-4 MIRA, in late 2023<ref>{{Cite web |title=POLARIS Raumflugzeuge - POLARIS receives Bundeswehr Study Contract for Linear Aerospike Rocket Engine Design and Flight-Testing |url=https://polaris-raumflugzeuge.de/News/POLARIS-receives-Bundeswehr-Study-Contract-for-Linear-Aerospike-Rocket-Engine-Design-and-Flight-Testing |access-date=2023-07-25 |website=polaris-raumflugzeuge.de |language=de-DE}}</ref><ref>{{cite web|url=https://europeanspaceflight.com/polaris-spaceplanes-begins-testing-its-mira-light-vehicle/|title=POLARIS Spaceplanes Begins Testing its MIRA-Light Vehicle|author=Andrew Parsonson|date=August 25, 2023|website=European Spaceflight}}</ref> at Peenemünde,<ref>{{cite web | url=https://www.bundeswehr.de/de/organisation/ausruestung-baainbw/aktuelles/wtd61-unbemanntes-raumflugzeug-getestet-5594484 | title=Aus "ATHENA" wird "NOVA" - Unbemanntes Raumflugzeug getestet | date=13 March 2023 }}</ref> the same place where the V-2 ballistic missiles were developed. If successful, MIRA will be the first aerospace vehicle to be powered by a linear aerospike rocket engine during flight.<ref>{{Cite web |title=POLARIS Spaceplanes on LinkedIn: 𝐄𝐱𝐜𝐢𝐭𝐢𝐧𝐠 𝐝𝐚𝐲 𝐚𝐭 𝐏𝐎𝐋𝐀𝐑𝐈𝐒 ✨: Primary structure of our... |url=https://www.linkedin.com/posts/polaris-spaceplanes_%3F%3F%3F%3F%3F%3F%3F%3F-%3F%3F%3F-%3F%3F-%3F%3F%3F%3F%3F%3F-activity-7089522177368027136-rJp6 |access-date=2023-07-25 |website=www.linkedin.com |language=en}}</ref>{{Primary source inline|date=October 2023}}

== See also ==
* [[Expanding nozzle]]
* {{annotated link|Linear Aerospike SR-71 Experiment|LASRE}}  <!-- a-l doesn't work with redirect! -->
* {{annotated link|Rotary Rocket}}
* {{annotated link|SABRE (rocket engine)|Sabre}}
* [[Expansion deflection nozzle]]

==References==
{{Reflist}}

==External links==
{{Commons category|Aerospike rocket engines}}
*[http://www.aerospaceweb.org/design/aerospike/main.shtml Aerospike Engine]
*[https://web.archive.org/web/20050219153713/http://astronautix.com/stages/satt250k.htm Advanced Engines planned for uprated Saturn and Nova boosters] — includes the J-2T
*[https://web.archive.org/web/20041030222947/http://www1.msfc.nasa.gov/NEWSROOM/background/facts/aerospike.html Linear Aerospike Engine — Propulsion for the X-33 Vehicle]
*[http://www.nasa.gov/centers/dryden/news/X-Press/stories/2004/063004/res_spike.html Dryden Flight Research Center]
*[https://web.archive.org/web/20071007072409/http://www.pwrengineering.com/dataresources/AerospikeEngineControlSystemFeaturesAndPerformance.pdf Aerospike Engine Control System Features And Performance]
*[https://web.archive.org/web/20071009152233/http://www.pwrengineering.com/dataresources/X-33AttitudeControlUsingTheXRS-2200LinearAerospikeEngine.pdf X-33 Attitude Control Using The XRS-2200 Linear Aerospike Engine]
*{{cite book |doi=10.2514/6.2005-3797 |chapter=Flight Research of an Aerospike Nozzle Using High Power Solid Rockets |title=41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit |year=2005 |last1=Bui |first1=Trong |last2=Murray |first2=James |last3=Rogers |first3=Charles |last4=Bartel |first4=Scott |last5=Cesaroni |first5=Anthony |last6=Dennett |first6=Mike |isbn=978-1-62410-063-5 }}
* [https://www.youtube.com/watch?v=D4SaofKCYwo Are Aerospikes Better Than Bell Nozzles?]

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