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{{short description|Facility from which rockets are launched}}
{{About|the structure from which rockets are launched||Launchpad (disambiguation)}}
{{redirect|Space Launch Complex|other uses|Launch Complex (disambiguation)}}
{{refimprove|date=August 2008}}
[[File:Stspad39baerial.jpg|thumb|upright=1.6|Launch pad at [[Kennedy Space Center Launch Complex 39B]] on [[Merritt Island, Florida]]]]
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A '''launch pad''' is an above-ground facility from which a [[rocket]]-powered [[missile]] or [[space vehicle]] is vertically launched.<ref>{{cite book |title=A Dictionary of Aviation |first=David W. |last=Wragg |isbn=9780850451634 |edition=first |publisher=Osprey |year=1973 |page=175}}</ref> The term ''launch pad'' can be used to describe just the central launch platform ([[mobile launcher platform]]), or the entire complex ('''launch complex'''). The entire complex will include a ''launch mount'' or ''launch platform'' to physically support the vehicle, a [[service structure]] with umbilicals, and the infrastructure required to provide [[liquid-propellant rocket|propellants]], [[cryogenic]] fluids, electrical power, communications, [[telemetry]], rocket assembly,{{Not verified in body|date=December 2020}} payload processing,{{Not verified in body|date=December 2020}}<!-- seems only some launch pads do rocket assembly and have facilities for payload processing --> storage facilities for propellants and gases, equipment, access roads, and [[drainage]].

Most launch pads include fixed service structures to provide one or more access platforms to assemble, inspect, and maintain the vehicle and to allow access to the spacecraft, including the loading of crew. The pad may contain a [[Flame deflector|flame deflection structure]] to prevent the intense heat of the rocket exhaust from damaging the vehicle or pad structures, and a [[sound suppression system]] spraying large quantities of water may be employed. The pad may also be protected by [[lightning arrester]]s. A [[spaceport]] typically includes multiple launch complexes and other supporting infrastructure.

A launch pad is distinct from a [[missile launch facility]] (or '''missile silo''' or '''missile complex'''), which also launches a missile vertically but is located underground in order to help harden it against enemy attack. 

The launch complex for liquid fueled rockets often has extensive [[ground support equipment]] including propellant tanks and plumbing to fill the rocket before launch. [[Cryogenic propellant]]s ([[liquid oxygen]] oxidizer, and [[liquid hydrogen]] or [[liquid methane]] fuel) need to be continuously topped off (i.e., boil-off replaced) during the launch sequence ([[countdown]]), as the vehicle awaits liftoff. This becomes particularly important as complex sequences may be interrupted by planned or unplanned holds to fix problems.

Most rockets need to be supported and held down for a few seconds after ignition while the engines build up to full [[thrust]]. The vehicle is commonly held on the pad by hold-down arms or [[explosive bolt]]s, which are triggered when the vehicle is stable and ready to fly, at which point all umbilical connections with the pad are released.<ref>{{Cite web |title=A8FJ - Day 1: Launch and Ascent to Earth Orbit |url=https://www.nasa.gov/history/afj/ap08fj/01launch_ascent.html |access-date=2024-11-20 |website=www.nasa.gov}}</ref>

== History ==

Precursors to modern rocketry, such as fireworks and rocket launchers, did not generally require dedicated launch pads. This was due in part to their relatively portable size, as well as the sufficiency of their casings in sustaining stresses. One of the first pads for a liquid-fueled rocket, what would later be named the [[Goddard Rocket Launching Site]] after [[Robert H. Goddard]]'s series of launch tests starting in 1926, consisted of a mount situated on an open field in rural Massachusetts. The mount consisted of a frame with a series of gasoline and liquid oxygen lines feeding into the rocket. 

It wasn't until the 1930s that rockets were increasing enough in size and strength that specialized launch facilities became necessary. The [[Verein für Raumschiffahrt]] in Germany was permitted after a request for funding in 1930 to move from farms to the [[Berlin rocket launching site]] ({{langx|de|Raketenflugplatz Berlin}}), a repurposed ammunition dump.<ref>{{cite web|url=http://history.msfc.nasa.gov/german/highlights.html|archive-url=https://web.archive.org/web/20070821043454/http://history.msfc.nasa.gov/german/highlights.html|archive-date=21 August 2007|title=Highlights in German Rocket Development|access-date=14 June 2016}}</ref> 

A test stand was built for liquid-propellant rockets in [[Kummersdorf]] in 1932, where the early designs from the [[Aggregat]] series of ballistic missiles were afterwards developed. This site was also the location of the first casualties in rocket development, when Dr. Wahmke and 2 assistants were killed, and another assistant was injured. A propellant fuel tank exploded, while experimenting with mixing 90% [[hydrogen peroxide]] and alcohol, before combustion.<ref name=walter>{{cite book |last1=Dornberger |first1=Walter |title=V-2 |date=1954 |publisher=The Viking Press, Inc. |location=New York |pages=27–42}}</ref>{{rp|35}}<ref name="wf">{{cite book |last1=Fleischer |first1=Wolfgang |title=The Wehrmacht Weapons Testing Ground at Kummersdorf |date=1997 |publisher=Schiffer Publishing Ltd. |location=Atglen |isbn=9780764302732 |pages=9–46}}</ref>{{rp|52–53}}

In May 1937, Dornberger, and most of his staff, moved to the [[Peenemünde Army Research Center]] on the island of [[Usedom]] on the [[Baltic Sea|Baltic]] coast which offered much greater space and secrecy. Dr. Thiel and his staff followed in the summer of 1940. Test Stand VI at Pennemünde was an exact replica to Kummersdorf's large test stand.<ref name=walter/>{{rp|56,60}}<ref name=wf/>{{rp|57}} It was this site which saw the development of the [[V-2 rocket]]. [[Test Stand VII]] was the principle testing facility at the [[Peenemünde Airfield]] and was capable of static firing rocket motors with up to 200 tons of thrust.

Launch pads would increase in complexity over the following decades throughout and following the [[Space Race]]. Where large volumes of exhaust gases are expelled during engine testing or vehicle launch, a [[flame deflector]] might be implemented to mitigate damage to the surrounding pad and direct exhaust. This is especially important with [[reusable launch vehicles]] to increase efficiency of launches while minimizing time spent refurbishing.

== Construction ==
{{main|Spaceport#Location}}
The construction of a launch pad begins with site selection, considering various geographical and logistical factors. It is often advantageous to position the launch pad on the coast, particularly with the ocean to the east, to leverage the Earth's rotation and increase the [[specific impulse]] of launches. Space programs such as [[Soviet space program]] or the [[French space program]] without this luxury may utilize facilities outside of their main territory such as the [[Baikonur Cosmodrome]] or [[Guiana Space Centre]] to launch for them. This orientation also allows for safe trajectory paths, minimizing risks to populated areas during ascent.<ref>{{cite web |author=National Aeronautics and Space Administration |title=Building KSC's Launch Complex 39 |url=https://public.ksc.nasa.gov/partnerships/wp-content/uploads/sites/15/2023/03/Buildings-KSC-pad-VAB-LCC-O_C.pdf |website=NASA |access-date=2024-07-12 |date=2006}}</ref>

== Facilities ==
=== Transport of rockets to the pad ===
{{main|Mobile launcher platform}}
{{original research|section|date=November 2018}}
[[File:Soyuz Rolls Out.jpg|thumb|upright=1.2|Transport of [[Soyuz rocket]] to pad by train]]
[[File:STS-114 rollout.jpg|thumb|upright=1.2|Transport of [[Space Shuttle]] and [[Mobile launcher platform|MLP]] to pad on [[Crawler-transporter]]]]
[[File:Falcon 9 preparing to launch DSCOVR (16673054016).jpg|thumb|upright=1.2|[[SLC-40]] with SpaceX [[Falcon 9]] launch infrastructure. The four towers surrounding the rocket are [[lightning arrester]]s, and acts like a giant [[Faraday cage]]]]
[[File:Pas-de-tir-du-lanceur-KSLV-II-à-Naro-3.jpg|thumb|upright=1.2|The second launch pad at [[Naro Space Center]] in South Korea is a fixed launch tower.]]
Each launch site is unique, but a few broad types can be described by the means by which the [[space vehicle]] gets to the pad.{{cn|date=November 2018}}

* Horizontally integrated rockets travel horizontally with the tail forward to the launch site on a [[transporter erector launcher]] and are then raised to the vertical position over the flame duct. Examples include all large Soviet rockets, including [[Soyuz (rocket family)|Soyuz]], [[Proton (rocket)|Proton]], [[N1 (rocket)|N1]], and [[Energia (rocket)|Energia]]. This method is also used by the [[SpaceX launch vehicles|SpaceX]] and [[Electron (rocket)|Electron]] launch vehicles.
* Silo launched rockets are assembled inside of a [[missile silo]]. This method is only used by converted ICBMs due to the difficulty and expense of constructing a silo that can contain the forces of a rocket launch.
* Vertically integrated rockets can be assembled in a separate [[hangar]] on a [[mobile launcher platform]] (MLP). The MLP contains the umbilical structure and is carried to the launch site on a large vehicle called [[Crawler-transporter]]. [[Launch Complex 39]] at the [[Kennedy Space Center]] is an example of a facility using this method.<ref>{{cite web |url=http://www-pao.ksc.nasa.gov/kscpao/release/1985/252-85r.htm |title=LAUNCH COMPLEX 39, PADS A AND B |publisher=NASA KSC |year=1992 |url-status=dead |archive-url=https://web.archive.org/web/20080921222509/http://www-pao.ksc.nasa.gov/kscpao/release/1985/252-85r.htm |archive-date=2008-09-21 }}</ref> A similar system is used to launch [[Ariane 5]] rockets at [[ELA-3]] at [[Guiana Space Centre]].
* Vertically assembled vehicles can also be transported on a mobile launcher platform resting on two parallel standard gauge railroad tracks that run from the integration building to launch area. This system is in use for the [[Atlas V]] and future [[Vulcan (rocket)|Vulcan]].
* At [[Vandenberg AFB Space Launch Complex 6|SLC-6]] and [[Cape Canaveral Air Force Station Launch Complex 37|SLC-37]], rockets are assembled on the launch mount. A windowless rail-mounted building encloses the launch pad and gantry to protect the vehicle from the elements, and for purposes of military secrecy. Prior to launch,<ref>{{cite web |url=https://cpsblaunchpad.com/cpsb-launchpad-4/ |title=Cpsb Launchpad |publisher=Viswanath |year=2023 |url-status=dead |access-date=2023-06-16 |archive-date=2023-06-16 |archive-url=https://web.archive.org/web/20230616125001/https://cpsblaunchpad.com/cpsb-launchpad-4/ }}</ref> the building is rolled away. This method is also used at [[Kagoshima Space Center|Kagoshima]] for the [[M-V]].
* The former [[Sea Launch]] service used the converted self-propelled oil drilling platform ''[[Ocean Odyssey]]'' to transport [[Zenit 3SL]] rockets horizontally to the [[Equator]], and then to erect and launch them from a [[floating launch platform]] into [[geostationary transfer orbit]]s.

=== Service structure ===
{{main|Service structure}}
A service structure is a steel framework or tower that is built on a launch pad to facilitate assembly and servicing. 

An umbilical tower also usually includes an [[elevator]] which allows maintenance and crew access. Immediately before ignition of the rocket's motors, all connections between the tower and the craft are severed, and the bridges over which these connections pass often quickly swing away to prevent damage to the structure or vehicle.{{Citation needed|date=October 2021}}

=== Flame deflector systems ===
{{main|Flame deflector}}
A flame deflector, flame diverter or flame trench is a structure or device designed to redirect or disperse the flame, heat, and [[exhaust gas]]es produced by [[rocket engine]]s or other propulsion systems.<ref name=":1">{{Cite web |title=Moonport, CH11-7 |url=https://www.hq.nasa.gov/pao/History/SP-4204/ch11-7.html |access-date=2023-09-01 |website=www.hq.nasa.gov |archive-date=2023-09-01 |archive-url=https://web.archive.org/web/20230901192218/https://www.hq.nasa.gov/pao/History/SP-4204/ch11-7.html |url-status=live }}</ref> The amount of thrust generated by a rocket launch, along with the sound it produces during liftoff, can damage the [[Launch pad|launchpad]] and [[service structure]], as well as the launch vehicle.<ref name=":0">{{Cite web |last=Wessels |first=Wessel |date=2022-10-26 |title=The Purpose Of A Flame Trench At A Rocket Launch Site |url=https://headedforspace.com/flame-trench/ |access-date=2023-09-01 |website=Headed For Space |language=en-US |archive-date=2023-09-01 |archive-url=https://web.archive.org/web/20230901192219/https://headedforspace.com/flame-trench/ |url-status=live }}</ref> The primary goal of the diverter is to prevent the flame from causing damage to equipment, infrastructure, or the surrounding environment. Flame diverters can be found at [[rocket launch sites]] and [[Engine test stand|test stands]] where large volumes of exhaust gases are expelled during engine testing or vehicle launch.

=== Sound suppression systems ===
{{main|Sound suppression system}}
Sites for launching large rockets are often equipped with a sound suppression system to absorb or deflect [[Sound|acoustic energy]] generated during a rocket launch.  As engine exhaust gasses exceed the [[speed of sound]], they collide with the ambient air and [[Shock wave|shockwaves]] are created, with noise levels approaching 200 db. This energy can be reflected by the [[Transporter erector launcher|launch platform]] and pad surfaces, and could potentially cause damage to the launch vehicle, payload, and crew. For instance, the maximum admissible overall [[sound power]] level (OASPL) for payload integrity is approximately 145 db.<ref>Dougherty, N. S., &amp; Guest, S. H. (2012, August 17). A correlation of scale model and flight aeroacoustic data for the Space Shuttle Vehicle. ''Aeroacoustics Conferences''. Retrieved November 16, 2022, from https://arc.aiaa.org/doi/10.2514/6.1984-2351</ref> Sound is dissipated by huge volumes of water distributed across the launch pad and launch platform during liftoff.<ref name=":0sss">{{Cite journal|last=Lubert|first=Caroline Parsons|date=2017|title= Sixty years of launch vehicle acoustics|journal= The Journal of the Acoustical Society of America|volume=142|issue=4 |page=040004|doi=10.1121/1.5014084|bibcode=2017ASAJ..142.2489L|doi-access=free}}</ref><ref>{{Cite journal|last1=Walsh|first1=E. J.|last2=Hart|first2=P.M.|date=Nov 1982|title=Liftoff Ignition Overpressure-A Correlation|journal=Journal of Spacecraft and Rockets|language=en|volume=19|issue=6|pages=550–556|doi=10.2514/3.62300|bibcode=1982JSpRo..19..550W|issn=0022-4650}}</ref>

Water-based acoustic suppression systems are common on launch pads.  They aid in reducing acoustic energy by injecting large quantities of water below the launch pad into the exhaust plume and in the area above the pad. [[Flame deflector|Flame deflectors]] or flame trenches are designed to channel rocket exhaust away from the launch pad but also redirect acoustic energy away.<ref name=":0sss" /><ref>{{Cite web|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710023719.pdf|title=Acoustic Loads Generated by the Propulsion System (NASA SP-8072)|last=|first=|date=June 1971|website=|access-date=}}</ref>

=== Hydrogen burn-off systems ===
In rockets using [[liquid hydrogen]] as their source of [[Rocket propellant|propellant]], hydrogen burn-off systems (HBOI), also known as radially outward firing igniters (ROFI), can be utilized to prevent the build up of free gaseous hydrogen (GH2) in the aft engine area of the vehicle prior to engine start. Too much excess hydrogen in the aft during engine start can result in an [[overpressure]] blast wave that could damage the launch vehicle and surrounding pad structures.<ref>{{cite web |last=Gebhardt |first=Chris |title=Heritage hardware: Testing the hydrogen burn off system for SLS |url=https://www.nasaspaceflight.com/2015/06/heritage-hardware-hydrogen-burn-off-system-sls/ |website=NASASpaceFlight.com |date=June 1, 2015}}</ref>

== Validating engine performance and system readiness ==
The SpaceX launch sequence includes a hold-down feature of the launch pad that allows full engine ignition and systems check before liftoff. After the first-stage engine starts, the launcher is held down and not released for flight until all propulsion and vehicle systems are confirmed to be operating normally. Similar hold-down systems have been used on launch vehicles such as [[Saturn V]]<ref name="NASA Hold-Down Arms">{{citation-attribution|1={{cite web|url=https://www.hq.nasa.gov/pao/History/SP-4204/ch13-4.html|title=Hold-Down Arms and Tail Service Masts|publisher=NASA|access-date=June 24, 2017|archive-url=https://web.archive.org/web/20161102234513/http://www.hq.nasa.gov/pao/History/SP-4204/ch13-4.html|archive-date=November 2, 2016|url-status=live}} }}</ref> and [[Space Shuttle]]. An automatic safe shut-down and unloading of propellant occur if any abnormal conditions are detected.<ref name="falcon9-2010">{{cite web|url=http://www.spacex.com/falcon9.php|archive-url=https://web.archive.org/web/20101222155322/http://www.spacex.com/falcon9.php|title=Falcon 9 Overview (2010)|publisher=SpaceX |access-date=8 May 2010|archive-date=22 December 2010}}</ref> Prior to the launch date, [[SpaceX]] sometimes completes a test cycle, culminating in a three-and-a-half second first stage engine static firing as well.<ref>{{cite web|last1=Clark|first1=Stephen|title=Falcon 9 completes full-duration static fire|url=http://spaceflightnow.com/2014/12/20/falcon-9-completes-full-duration-static-fire/|publisher=Spaceflight Now|access-date=10 May 2015|date=20 December 2014|quote=SpaceX conducts the static fire test — that typically ends with a 3.5-second engine firing — before every launch to wring out issues with the rocket and ground systems. The exercise also helps engineers rehearse for the real launch day.|archive-url=https://web.archive.org/web/20150605035551/http://spaceflightnow.com/2014/12/20/falcon-9-completes-full-duration-static-fire/|archive-date=5 June 2015|url-status=live}}</ref><ref>{{cite web|last=Clark|first=Stephen|title=Starlink satellite deployments continue with successful Falcon 9 launch|publisher=Spaceflight Now|url=https://spaceflightnow.com/2020/06/13/starlink-satellite-deployments-continue-with-successful-falcon-9-launch/|access-date=27 July 2020|archive-date=17 October 2020|archive-url=https://web.archive.org/web/20201017190720/https://spaceflightnow.com/2020/06/13/starlink-satellite-deployments-continue-with-successful-falcon-9-launch/|url-status=live}}</ref>

== See also ==
{{Portal|Spaceflight}}
* {{annotated link|Ground segment}}
* {{annotated link|Launch vehicle}}
* [[List of rocket launch sites]]
* [[Missile launch facility]]
* [[Non-rocket spacelaunch]]
* {{annotated link|Pad abort test}}
* [[Rocket launch]]
* {{annotated link|Service structure}}
* [[Spaceport]]
* {{annotated link|Stratolaunch Systems}}
* {{annotated link|Transporter erector launcher}}

== References ==
{{reflist}}

== External links ==
* [https://patents.google.com/patent/US2592873A/en?oq=US2592873 Apparatus for landing rockets and rocket ships]

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{{Baikonur Cosmodrome launch sites}}
{{CSG launch sites}}
{{Merritt Island}}
{{Plesetsk Cosmodrome launch sites}}
{{Point Arguello launch sites}}
{{Satish Dhawan Space Centre}}
{{Vandenberg Air Force Base launch sites}}
{{Wallops Island}}}}
{{Spaceflight}}

[[Category:Rocket launchers]]