View source for Engineering:Liquid fly-back booster

{{short description|Launch vehicle study}}
{{EngvarB|date = July 2020}}
{{No orbit for payload}}
[[File:Ariane 5 Liquid-Fly-Back Booster.jpg|thumb|The LFBB model used in wind tunnel tests by the German Aerospace Center (DLR)|alt=The LFBB model used in wind tunnel tests by the German Aerospace Center (DLR)]]
'''Liquid Fly-back Booster''' (LFBB) was a [[Organization:German Aerospace Center|German Aerospace Center]]'s (DLR's) project concept to develop a [[Engineering:Liquid rocket booster|liquid rocket booster]] capable of [[Astronomy:Reusable launch system|reuse]] for [[Engineering:Ariane 1|Ariane 1]] in order to significantly reduce the high cost of space transportation and increase environmental friendliness.<ref name="Satellitenkatapult"/> lrb would replace the existing [[Engineering:Liquid rocket booster|liquid rocket booster]]s, providing main thrust during the countdown. Once separated, two winged boosters would perform an [[Astronomy:Atmospheric entry|atmospheric entry]], go back autonomously to the French Guiana, and land horizontally on the airport like an aeroplane.

Additionally a family of derivative launch vehicles was proposed in order to take an advantage of [[Finance:Economies of scale|economies of scale]], further reducing launch costs. These derivatives include:
* A reusable booster in a class of [[Engineering:Small-lift launch vehicle|small]],[[Engineering:Medium-lift launch vehicle|medium-lift launch]] and [[Engineering:Heavy-lift launch vehicle|heavy lift boosters]] like [[Engineering:Vega (rocket)|Vega]] and [https://www.youtube.com/watch?v=CdTnwmLMaDY SLS].<ref name=near70/><ref name="Wiederverwendbare"/>{{rp|15}}
* A super-heavy-lift launch vehicle capable of lifting nearly {{convert|70|t|lb}} to the orbit.<ref name=near70/><ref name="Wiederverwendbare"/>{{rp|15}}
* A [[Astronomy:Two-stage-to-orbit|two-stage-to-orbit]] system operating a dedicated reusable orbiter.

German Aerospace Center studied Liquid Fly-back Boosters as a part of future launcher research programme from 1999 to 2004.<ref name="longTermApplications"/> After the cancellation of the project, publications at DLR continued until 2009.{{cn|date=October 2016}}

== Development ==
The German Aerospace Center (DLR) studied potential future launch vehicles of the [[Social:European Union|European Union]] under the ''Ausgewählte Systeme und Technologien für Raumtransport'' (ASTRA; English: Systems and Technologies for Space Transportation Applications) programme from 1999 to 2005, with additional studies continuing until 2009.<ref name="Satellitenkatapult">{{cite news|url=http://www.astronews.com/news/artikel/2007/04/0704-003.shtml|title=Sonnensegel und Satellitenkatapult|language=DE|publisher=astronews.com|date=4 April 2007|accessdate=9 June 2015}}</ref><ref name="longTermApplications"/> The LFBB design was one of two projects within the ASTRA program, the other being Phoenix RLV.<ref name="SART">{{cite web|url=http://www.dlr.de/irs/en/desktopdefault.aspx/tabid-6639/11294_read-25975/|title=Space Launcher Systems Analysis (SART)|publisher=DLR|accessdate=9 September 2014|url-status=dead|archiveurl=https://web.archive.org/web/20140330043102/http://www.dlr.de/irs/en/desktopdefault.aspx/tabid-6639/11294_read-25975/|archivedate=30 March 2014}}</ref><ref name="RLVSdesign">{{cite report|url=http://www.la.dlr.de/ra/sart/publications/pdf/2002-5220.pdf|title=Progress in the Design of a Reusable Launch Vehicle Stage|publisher=American Institute of Aeronautics and Astronautics, Inc.|via=[[Organization:German Aerospace Center|German Aerospace Center]] (DLR)|year=2012|accessdate=9 September 2014|url-status=dead|archiveurl=https://web.archive.org/web/20060110171054/http://www.la.dlr.de/ra/sart/publications/pdf/2002-5220.pdf|archivedate=10 January 2006}}</ref><ref name="DLRsiteLFBBmain">{{cite web|url=http://www.dlr.de/irs/desktopdefault.aspx/tabid-7582/12834_read-32243/ |title=Liquid Fly-back Booster (LFBB) |publisher=DLR |accessdate=9 June 2015 |url-status=dead |archiveurl=https://web.archive.org/web/20150610050518/http://www.dlr.de/irs/desktopdefault.aspx/tabid-7582/12834_read-32243/ |archivedate=10 June 2015 }}</ref> During development, scale models were constructed for testing various configurations in DLR's [[Supersonic speed|supersonic]] ''Trisonische Messstrecke Köln'' (TMK; English: Trisonic measuring section at Cologne) and in their ''Hyperschallwindkanal 2 Köln'' (H2K; English: [[Physics:Hypersonic speed|Hypersonic]] wind canal at Cologne) [[Physics:Wind tunnel|wind tunnel]]s.<ref>{{cite book |last=Gülhan |first=Ali |year=2008 |title=RESPACE - Key Technologies for Reusable Space Systems |location=Cologne |publisher=[[Physics:Springer-Verlag|Springer-Verlag]] |page=20,22,26 |isbn=978-3-540-77819-6}}</ref><ref>{{cite web|url=http://www.la.dlr.de/ra/sart/publications/pdf/2003-7056.pdf|title=Experimental studies on a Liquid Fly-Back-Booster configuration (LFBB) in wind tunnels|page=4,5|publisher=[[Organization:American Institute of Aeronautics and Astronautics|American Institute of Aeronautics and Astronautics]]|date=December 2003|accessdate=21 September 2015|url-status=dead|archiveurl=https://web.archive.org/web/20150610105732/http://www.la.dlr.de/ra/sart/publications/pdf/2003-7056.pdf|archivedate=10 June 2015}}</ref> The preliminary mechanical design of other major elements was done by the companies ESA and [[Organization:NASA|NASA]].<ref name="longTermApplications"/>{{rp|213}}

The advantages of reusable boosters include simplicity from using only one type of fuel, environmental friendliness, and lower reoccurring costs. Studies concluded that reusable fly-back boosters would be the most affordable and the least risky way for European space launch systems to start becoming reusable. These fly-back boosters had the potential to reduce launch costs. However, when other projects, such as [[Engineering:Space Shuttle|Space Shuttle]] or [[Engineering:VentureStar|VentureStar]], undertook this objective, they failed to meet their goals. Supporting technologies needed for LFBB construction can be developed within 10 years, and additional launchers can be developed based on fly-back boosters to minimise costs and provide maintenance synergy across multiple classes of launch vehicles.<ref name="Wiederverwendbare"/> 

Eventually, the hardware grew too large and the LFBB project was scrapped, with one member of the French space agency ([[Organization:CNES|CNES]]) remarking:

{{quote|The thing that shocked me was that at the beginning, this reusable flyback booster was just a cylinder with engines and little wings, just a turbo fan in the back. And three years later these were complete Airbuses in terms of size with four engines in each of them.|Christophe Bonnal, [[Organization:CNES|CNES]] launcher directorate<ref>{{cite magazine|url=http://aviationweek.com/blog/nasa-cnes-warn-spacex-challenges-flying-reusable-falcon-9-rocket|title=French Debris-mitigation Law Could Pose Issue for Arianespace|magazine=Aviation Week|date=5 May 2014|accessdate=9 June 2015}}</ref>}}

== Description ==
[[Image:LFBB line drawing plain.svg|thumb|400px|A line drawing of DLR's LFBB, showing top, front, and side views|alt=A line drawing of DLR's liquid fly-back booster, showing top, front, and side views]]
The overall concept of the liquid boosters in the LFBB programme was to retain the Ariane 5's core and upper [[Astronomy:Multistage rocket|stages]], along with the [[Engineering:Payload fairing|payload fairing]]s, and replace its [[Engineering:Solid rocket booster|solid rocket booster]]s (EAP P241, from French ''Étages d’Accélération à Poudre'') with reusable [[Engineering:Liquid rocket booster|liquid rocket booster]]s. These boosters would provide the main thrust during take-off. After separation, they would return to a spaceport in French Guiana for landing. This vertical take-off, horizontal landing (VTHL) mode of operation would allow liquid fly-back boosters to continue operating from the [[Organization:Guiana Space Centre|Guiana Space Centre]], thus avoiding any major changes to the ascend profile of Ariane 5. Launch vehicle payload performance of the [[Physics:Cryogenic fuel|Cryogenic]] Evolution type-A (ECA) variant would increase from {{convert|10500|kg|abbr = on}} to {{convert|12300|kg|abbr = on}}.<ref name="Wiederverwendbare">{{cite news|url=http://elib.dlr.de/64860/1/RC-56-LFBB.pdf|title=Wiederverwendbare Boosterstufen für Ariane 5|trans-title=Reusable booster stages for Ariane 5|language=DE|publisher=Raumfahrt Concret|date=January 2009|accessdate=9 June 2015}}</ref><ref name="longTermApplications" />{{rp|214}}

In the reference design, each LFBB consists of three engines installed in a circular arrangement at the [[Engineering:Aft|aft]] of the vehicle. Each engine is a [[Engineering:Vulcain (rocket engine)|Vulcain]] engine with reduced [[Physics:Expansion ratio|expansion ratio]]. An additional three [[Engineering:Turbofan|turbofan]] air-breathing engines, installed in the [[Engineering:Nose cone|nose]] section, provide power for fly-back. The [[Engineering:Fuselage|fuselage]] is {{convert|41|m|abbr = on}} long, with an outer tank diameter of {{convert|5.45|m|abbr = on}}, specifically designed to match the existing Ariane 5 core stage and to reduce manufacturing costs. A low-wing V-tail [[Engineering:Canard (aeronautics)|canard]] configuration was selected,<ref name="longTermApplications"/> with a [[Wingspan|wingspan]] of approximately {{convert|21|m|abbr = on}} and an area of {{Convert|115|m2|abbr = on}}.<ref name=near70/> The aerofoil was based on a [[Physics:Transonic|transonic]] profile from the Royal Aircraft Establishment (RAE 2822). The gross lift-off mass (GLOW) of each booster is {{convert|222.5|t|ST}}, with {{convert|54|t|ST}} upon separation and {{convert|46.2|t|ST}} dry mass. In comparison, the GLOW for EAP P241 is {{convert|273|t|ST}}.<ref name="longTermApplications">{{cite journal|url=http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.elsevier-bc3ae811-c581-3b79-b123-8acfded8f087|title=Long-term/strategic scenario for reusable booster stages|first1=Martin|last1=Sippel|first2=Chiara|last2=Manfletti|first3=Holger|last3=Burkhardt|journal=Acta Astronautica|issue=4|publisher=[[Company:Elsevier|Elsevier]]| pages=209–221| doi=10.1016/j.actaastro.2005.09.012| issn=0094-5765| publication-date=2006|date=28 September 2005|volume=58|bibcode=2006AcAau..58..209S}}</ref>{{rp|209,210,214}}

The booster was designed to have four independent propulsion systems, the first of which – main rocket propulsion – would be based on three [[Engineering:Gimbaled thrust|gimbaled]] [[Engineering:Vulcain (rocket engine)|Vulcain]] engines fueled by {{convert|168500|kg|abbr = on}} of propellant. Second, [[Engineering:Eurojet EJ200|Eurojet EJ200]] fly-back turbofan engines would be propelled with hydrogen to reduce fuel mass. Further, ten {{Convert|2|kN|abbr = on}} thrusters placed on each side of the vehicle would be used by the [[Engineering:Reaction control system|reaction control system]]. Finally, the fourth propulsion system would be based on solid rocket motors that separate the boosters from the core stage. An up-scaled version of the motors used in existing EAP boosters would be mounted in the attachment ring and inside the wing's main structure.<ref name="longTermApplications" />{{rp|211,212}}

A typical mission profile would begin with the ignition of a main stage and both boosters, followed by an acceleration to {{Convert|2|km/s|abbr = on}} and then a separation at the altitude of {{Convert|50|km|abbr = on}}. As the main stage continues its flight into orbit, the boosters follow a ballistic trajectory, reaching an altitude of {{Convert|90|-|100|km|abbr = on}}. After low-energy [[Astronomy:Atmospheric entry|atmospheric entry]], the boosters reach denser layers of the atmosphere where they perform a [[Physics:Banked turn#Banked turn in aeronautics|banking turn]] toward the target airfield. Gliding continues until they achieve an altitude that is optimal for engaging turbofan engines and entering cruise flight. At this point, about {{Convert|550|km|abbr = on}} from the launch point, the boosters would be flying over the [[Earth:Atlantic Ocean|Atlantic Ocean]]. The cruise back to the airport requires about {{convert|3650|kg|abbr = on}} of hydrogen fuel and takes over two hours to complete. An undercarriage is deployed and each booster lands autonomously. After separation, the boosters are not under threat of collision until they land due to small differences in their initial flight trajectories.<ref name="Wiederverwendbare">{{cite news|url=http://elib.dlr.de/64860/1/RC-56-LFBB.pdf|title=Wiederverwendbare Boosterstufen für Ariane 5|trans-title=Reusable booster stages for Ariane 5|language=DE|publisher=Raumfahrt Concret|date=January 2009|accessdate=9 June 2015}}</ref><ref name="longTermApplications" />{{rp|215}}

==Derivatives==
The development of liquid fly-back boosters has the potential to enable three additional space transportation systems with an objective of increasing production and creating [[Finance:Economies of scale|economies of scale]]. The aim of the LFBB project at DLR was to reduce Ariane 5 operational costs and to develop future derivatives, including a reusable first stage of a small-to-medium launch vehicle, a super-heavy launch vehicle capable of lifting {{Convert|67|tonnes|ST}}<ref name=near70>{{cite web|url=http://www.dlr.de/irs/desktopdefault.aspx/tabid-7593/12849_read-32301/|title=ASTRA LFBB configuration|publisher=[[Organization:German Aerospace Center|German Aerospace Center]]|accessdate=30 September 2015|url-status=dead|archiveurl=https://web.archive.org/web/20150923225812/http://www.dlr.de/irs/desktopdefault.aspx/tabid-7593/12849_read-32301/|archivedate=23 September 2015}}</ref> to [[Astronomy:Low Earth orbit|Low Earth orbit]], and a reusable [[Astronomy:Two-stage-to-orbit|two-stage-to-orbit]] launch vehicle.<ref>{{Cite web|title = DLR - Institut für Raumfahrtsysteme - ASTRA LFBB configuration|url = http://www.dlr.de/irs/desktopdefault.aspx/tabid-7593/12849_read-32301/|website = www.dlr.de|accessdate = 30 September 2015|first = Sabine|last = Lindemann|url-status = dead|archiveurl = https://web.archive.org/web/20150923225812/http://www.dlr.de/irs/desktopdefault.aspx/tabid-7593/12849_read-32301/|archivedate = 23 September 2015}}</ref> Initially, LFBBs would be used only on Ariane 5. Over time, alternative configurations could phase out Arianespace Soyuz and [[Engineering:Vega (rocket)|Vega]].<ref name="longTermApplications" />{{rp|215}}

===Reusable first stage===
[[Image:LFBB RFS.svg|thumb|Top view of RFS configurations: Vega and Ariane 5 derivatives (top), large cryogenic upper stage (bottom) with the LFBB shown in blue]]
The LFBB was studied with the three upper stage composites, to attain a Reusable First Stage (RFS) configuration. The first was a [[Engineering:Vega (rocket)|Vega]] derivative, with a Zefiro 23 second stage, a Zefiro 9 third stage and an AVUM upper stage. With the LFBB replacing the [[Engineering:P80 (rocket stage)|P80 stage]], the payload to [[Astronomy:Sun-synchronous orbit|Sun-synchronous orbit]] (SSO) would increase to {{convert|1882|kg|abbr = on}}, compared to the {{convert|1450|kg|abbr = on}} of the Vega. The second was an [[Engineering:Ariane 4|Ariane 4]] derivative called H-25<!-- spelled with a hyphen in a source-->. It was  based on an H10 upper stage with a Vinci rocket engine and {{Convert|25|tonnes|ST}} of [[Physics:Cryogenic fuel|cryogenic fuel]]. Depending on the method of deceleration, the payload to SSO is between {{Convert|1481|and|2788|kg|abbr = on}}. The third was a large cryogenic upper stage, called H-185, based on an alternative, yet-to-be-developed Ariane 5 main stage with {{Convert|185|tonnes|ST}} of cryogenic fuel. Its payload to SSO is {{convert|5000|kg|abbr = on}}.<ref name="longTermApplications"/>{{rp|216}}

Two of the lighter configurations (the Zefiro 23 and the H-25) use upper stages mounted on top of the booster. Due to the lower weight, it might have been necessary to lower the amount of fuel in a booster to ensure that the separation velocity, the flight path, and the reentry do not exceed design bounds. In the case of H-25, it might be necessary to accelerate the fly-back boosters to above {{Convert|2|km/s|abbr = on}} to help the upper stage achieve its desired orbit. Consequently, two solutions were proposed to decelerate the boosters after separation. The first option was to actively decelerate them using {{Convert|10|tonnes|ST}} of fuel and reduce the velocity by {{Convert|300|m/s|abbr = on}}. However, launch performance would drop below that of the Vega derivative. Another option is to use aerodynamic forces to decelerate. However, a [[Physics:Hypersonic speed|hypersonic]] parachute was deemed too expensive and too complex. As a result, an alternative [[Engineering:Ballute|ballute]] was proposed. Flight dynamics simulation revealed that a ballute with a cross-section of {{Convert|45|m2|abbr = on}} offered the best compromise between loads on the booster and deceleration by aerodynamic forces. In this configuration, a launch performance of up to {{convert|2788|kg|abbr = on}} could be achieved, partly thanks to a higher separation velocity.<ref name="longTermApplications" />{{rp|216}}

The heaviest configuration uses a single booster with an asymmetrically mounted, large, expendable cryogenic stage designated H-185<!-- spelled with a hyphen in a source-->. It was proposed as a future variant of the Ariane 5 core stage (H158), eventually meant to phase out the main stage in a standard launch configuration with LFBB. H-185 would use a new Vulcain&nbsp;3 main engine, with increased vacuum thrust. When launched with a single booster, both stages would be operated in parallel, and be delivered to a {{Convert|180 by 800|km|abbr = on}} orbit before separation. The remaining upper stage composite would weigh {{convert|7360|kg|abbr = on}}, with a {{convert|5000|kg|abbr = on}} payload performance to SSO. When launching to [[Astronomy:Low Earth orbit|Low Earth orbit]], payload mass can be increased to over {{convert|10000|kg|abbr = on}}.<ref name="longTermApplications" />{{rp|215–217}}

===Super-Heavy Lift Launcher (SHLL)===
[[Image:LFBB SHLL.svg|thumb|Top view of the SHLL configuration with the LFBB shown in blue]]
The Super-Heavy Lift Launcher (SHLL) would consist of a new cryogenic main stage, five liquid fly-back boosters, and a re-ignitable injection stage. This configuration was designed to provide increased capabilities for complex missions, including crewed explorations to the Moon and to Mars, as well as the launch of large solar-powered satellites.<ref name="Wiederverwendbare"/>{{rp|15}}

The new core stage would stand {{convert|28.65|meters|abbr = on}} tall and have a diameter of {{convert|10|meters|abbr = on}}, feeding {{convert|600|tonnes|ST}} of [[Physics:Liquid oxygen|LOX]]/[[Chemistry:Liquid hydrogen|LH<sub>2</sub>]] to three Vulcain&nbsp;3 engines. The increased circumference of the main stage allows five LFBBs to be integrated with either retractable or variable-geometry wings. The upper stage would be a derivative of the Ariane 5 ESC-B, with the size upped to {{convert|5.6 x 8.98|m|ft|abbr = on}}, and strengthened to bear higher loads. The Vinci engine was proofed to be sufficiently powerful for orbital insertion. Payload would be enclosed in an {{convert|8 x 29.5|m|ft|abbr = on}} [[Engineering:Payload fairing|fairing]]. The launch vehicle would have a total height of {{convert|69|meters|abbr = on}} and a mass of {{convert|1900|tonnes|ST}}. The payload to [[Astronomy:Low Earth orbit|LEO]] would be {{convert|67280|kg|abbr = on}}.<ref name="longTermApplications" />{{rp|218}}

When launched to a {{Convert|200 x 600|km|abbr = on}} Low Earth transfer orbit, the LFBBs would separate at an altitude of {{convert|51|km|abbr = on}}, at a speed of {{Convert|1.55|km/s|abbr = on}}. To avoid simultaneous separation of all boosters, either a cross-feed to the main stage, or throttling could be used. The return flight of the boosters would require an estimated {{convert|3250|kg|abbr = on}} of fuel, including a 30% reserve.<ref name="longTermApplications" />{{rp|218–219}}

===Two-stage-to-orbit===
[[Image:LFBB TSTO.svg|thumb|Top view of the TSTO configuration with the LFBB shown in blue]]
The reusable [[Astronomy:Two-stage-to-orbit|two-stage-to-orbit]] (TSTO) launch vehicle variant of LFBB was planned to be implemented about 15 years after the addition of LFBBs to Ariane 5.<ref name="longTermApplications" />{{rp|216}} However, only a preliminary analysis of TSTO was completed. The proposed configuration consisted of two boosters with retractable wings attached to the external fuel tank, and a reusable orbiter with fixed wings carrying payload on top of it. During [[Astronomy:Geostationary transfer orbit|geostationary transfer orbit]] (GTO) missions, an additional, expandable upper stage would be used.<ref name="longTermApplications" />{{rp|219}}

The external tank, being a core of the system, would have a diameter of {{convert|5.4|m|ft}} and a height of {{convert|30.5|m|ft}}, carrying {{convert|167.5|tonnes|ST}} of propellant. The attached orbiter would be {{convert|28.8|m|ft}} tall and {{convert|3.6|m|ft}} in diameter, carrying {{convert|50|tonnes|ST}} of propellant. The payload fairing mount atop the orbiter would be {{convert|5.4 x 20.5|m|ft}}. For LEO missions, the launch vehicle would be {{convert|57.3|m|ft}} tall, with a gross lift-off mass of {{convert|739.4|tonnes|ST}}. The payload to LEO would be {{convert|12800|kg}}, with an increase to {{convert|8500|kg}} to GTO when using an expandable upper stage.<ref name="longTermApplications" />{{rp|219}}

==See also==
* {{Annotated link|Baikal (rocket booster)}}
* {{Annotated link|Falcon Heavy}}
* {{Annotated link|RETALT}}
* {{Annotated link|Reusable Booster System}}

==External links==
* [https://web.archive.org/web/20150610050402/http://www.dlr.de/irs/desktopdefault.aspx/tabid-7593/12849_read-32301/ ASTR LFBB] with technical details

==References==
{{Reflist|colwidth=30em}}

{{Reusable launch systems}}
{{European launch systems}}
{{European Space Agency}}

[[Category:European Space Agency]]
[[Category:Ariane (rocket family)]]

{{Sourceattribution|Liquid fly-back booster}}