View source for Delta II

{{Short description|American space launch system (1989–2018)}}
{{about|the rocket|the submarine|Delta-class submarine|the airplane|Fairey Delta 2}}
{{Use American English|date=November 2020}}
{{Use dmy dates|date=August 2019}}
{{Infobox rocket
| logo           = Delta II logo.svg
| logo_upright   = 0.3
| image          = Delta II Dawn liftoff 1.jpg
| caption        = A Delta II rocket launches from [[Cape Canaveral Air Force Station|Cape Canaveral]] carrying the [[Dawn (spacecraft)|Dawn]] spacecraft.

| name           = Delta II
| function       = [[Launch vehicle]]
| manufacturer   = {{Ubli
   | [[McDonnell Douglas]]<br/>(1989–1997)
   | [[Boeing Defense, Space & Security]] (1997–2006)
   | [[United Launch Alliance]] (2006–2018)
}}
| country-origin = [[United States]]

| cpl            = {{Unbulleted list
   | US$51 million in 1987{{efn|(7920-10 model)}}<ref>{{cite web |url=http://www.spaceflight101.com/delta-ii-7920h-10.html |title=Delta II 7920H-10 |access-date=13 August 2024 |url-status=dead |archive-url=https://web.archive.org/web/20140714122955/http://www.spaceflight101.com/delta-ii-7920h-10.html |archive-date=14 July 2014}}</ref>
   | US$137 million in 2018<ref>{{cite web |url=https://www.faa.gov/about/office_org/headquarters_offices/ast/media/2018_ast_compendium.pdf |title=The Annual Compendium of Commercial Space Transportation: 2018 |date=January 2018 |access-date=13 August 2024 |website=Federal Aviation Administration's Office of Commercial Space Transportation |publisher=Bryce Space and Technology}} {{PD-notice}}</ref>
}}

| height         = {{cvt|38.9|m}}<ref name="data sheet"/>
| diameter       = {{cvt|2.44|m|ft|0}}
| mass           = {{cvt|152000-286100|kg}}<ref name="data sheet"/><ref name ="Guide"/>
| capacities     =

{{Infobox rocket/payload
  | location     = [[Low Earth orbit|LEO]]
  | inclination  = 28.7°
  | kilos        = {{cvt|2776-6107|kg}}<ref name ="Guide">{{cite report |last1=Isakowitz |first1=Steven J. |last2=Hopkins |first2=Joshua B. |last3=Hopkins |first3=Joseph R. Jr. |year=2004 |title=International Reference Guide to Space Launch Systems |publisher=American Institute of Aeronautics and Astronautics |edition=Fourth}}</ref>
}}

{{Infobox rocket/payload
  | location     = [[Geostationary transfer orbit|GTO]]
  | inclination  = 28.7°
  | kilos        = {{cvt|929-2180|kg}}<ref name ="Guide"/>
}}
{{Infobox rocket/payload
  | location     = [[Sun-synchronous orbit|SSO]]
  | inclination  = 98.7°
  | kilos        = {{cvt|1652-3182|kg}}<ref name ="Guide"/>
}}

| status         = Retired
| sites          = {{Unbulleted list
   | [[Cape Canaveral Space Force Station|Cape Canaveral]], [[Cape Canaveral Space Launch Complex 17|SLC-17]]
   | [[Vandenberg Space Force Base|Vandenberg]], [[Vandenberg Space Launch Complex 2|SLC-2W]]
}}
| launches       = {{Unbulleted list
   | 155:
   | {{in5|3}}'''Delta 6000:''' 17
   | {{in5|3}}'''Delta 7000:''' 132
   | {{in5|3}}'''Delta 7000 Heavy:''' 6
}}
| success        = {{Unbulleted list
   | 153:
   | {{in5|3}}'''Delta 6000:''' 17
   | {{in5|3}}'''Delta 7000:''' 130
   | {{in5|3}}'''Delta 7000 Heavy:''' 6
}}
| fail           = 1 (Delta 7000)
| partial        = 1 (Delta 7000)

| first          = {{plainlist|
* '''Delta 6000:''' 14 February 1989 ([[USA-35]])
* '''Delta 7000:''' 26 November 1990 ([[USA-66]])
* '''Delta 7000 Heavy:''' 7 July 2003 ([[Opportunity rover]])
}}
| last           = {{plainlist|
* '''Delta 6000:''' 24 July 1992 ([[Geotail]])
* '''Delta 7000:''' 15 September 2018 ([[ICESat-2]])
* '''Delta 7000 Heavy:''' 10 September 2011 ([[GRAIL]])
}}

| stagedata      = 
{{Infobox rocket/stage
  | type         = booster
  | diff         = Delta 6000
  | name         = [[Castor 4A]]
  | number       = 9
  | length       = {{cvt|9.2|m}}<ref name="Castor4A"/>
  | diameter     = {{cvt|1.02|m}}
  | empty        = {{cvt|1457|kg}}
  | gross        = {{cvt|11578|kg}}
  | propmass     = <!--propellant mass carried by a single booster in kilograms, use {{cvt}}, optional--> 
  | engines      = Solid
  | solid        = yes
  | thrust       = {{cvt|478.3|kN}}
  | total        = <!--total thrust for all boosters in kN, use {{convert}}, optional-->
  | SI           = {{cvt|266|isp}}
  | burntime     = 56 seconds
  | fuel         = [[Hydroxyl-terminated polybutadiene|HTPB]]
}}

{{Infobox rocket/stage
  | type         = booster
  | diff         = Delta 7000
  | name         = [[Graphite-Epoxy Motor|GEM 40]]
  | number       = 3, 4, or 9
  | length       = {{cvt|13.0|m}}<ref name ="Guide"/>
  | diameter     = {{cvt|1.02|m}}
  | empty        = {{cvt|1315|kg}}
  | gross        = {{cvt|13080|kg}}
  | propmass     = <!--propellant mass carried by a single booster in kilograms, use {{cvt}}, optional--> 
  | engines      = Solid
  | solid        = yes
  | thrust       = {{plainlist|
* '''Ground-lit''': {{cvt|499.2|kN}}
* '''Air-lit''': {{cvt|516.2|kN}}
}}
  | total        = <!--total thrust for all boosters in kN, use {{cvt}}, optional-->
  | SI           = {{plainlist|
* '''Ground-lit''': {{cvt|274.0|isp}}
* '''Air-lit''': {{cvt|283.4|isp}}
}}
  | burntime     = 64 seconds
  | fuel         = [[Ammonium perchlorate composite propellant|AP]] / [[Hydroxyl-terminated polybutadiene|HTPB]] / [[Aluminium|Al]]
}}

{{Infobox rocket/stage
  | type         = booster
  | diff         = Delta 7000 Heavy
  | name         = [[Graphite-Epoxy Motor|GEM 46]]
  | number       = 9
  | length       = {{cvt|14.7|m}}<ref name ="Guide"/>
  | diameter     = {{cvt|1.17|m}}
  | empty        = {{cvt|2035|kg}}
  | gross        = {{cvt|19040|kg}}
  | propmass     = <!--propellant mass carried by a single booster in kilograms, use {{cvt}}, optional--> 
  | engines      = Solid
  | solid        = yes
  | thrust       = {{plainlist|
* '''Ground-lit''': {{cvt|608.1|kN}}
* '''Air-lit''': {{cvt|628.5|kN}}
}}
  | total        = <!--total thrust for all boosters in kN, use {{convert}}, optional-->
  | SI           = {{plainlist|
* '''Ground-lit''': {{cvt|224.0|isp}}
* '''Air-lit''': {{cvt|284.0|isp}}
}}
  | burntime     = 76 seconds or 178.03 seconds after liftoff
  | fuel         = [[Ammonium perchlorate composite propellant|APCP]] / [[Hydroxyl-terminated polybutadiene|HTPB]] / [[Aluminium|Al]]
}} 
{{Infobox rocket/stage
  | type         = stage
  | stageno      = First
  | name         = Thor/Delta XLT(-C)
  | length       = {{cvt|26.1|m}}<ref name ="Guide"/>
  | diameter     = {{cvt|2.44|m}}
  | empty        = {{cvt|5680|kg}}
  | gross        = {{cvt|101800|kg}}
  | engines      = 1 × [[RS-27]] (6000 series) or [[RS-27A]] (7000 series) <ref>{{cite web |url=http://www.boeing.com/defense-space/space/delta/delta2/delta2.htm |title=Boeing: Integrated Defense Systems – Delta – Delta II Launch Vehicle Family |access-date=13 August 2024 |url-status=dead |archive-url=https://web.archive.org/web/20061103194958/http://www.boeing.com/defense-space/space/delta/delta2/delta2.htm |archive-date=November 3, 2006}}</ref>
  | thrust       = {{cvt|1054|kN}}
  | SI           = {{cvt|302|isp}}
  | burntime     = 260.5 seconds
  | fuel         = [[RP-1]] / [[LOX]]
}}

{{Infobox rocket/stage
  | type         = stage
  | stageno      = Second
  | name         = [[Delta K]]
  | length       = {{cvt|6|m}}<ref name ="Guide"/>
  | diameter     = {{cvt|2.44|m}}
  | empty        = {{cvt|950|kg}}
  | gross        = {{cvt|6954|kg}}
  | engines      = 1 × [[AJ-10|AJ10-118K]]
  | thrust       = {{cvt|43.6|kN}}
  | SI           = {{cvt|319|isp}}
  | burntime     = 431 seconds
  | fuel         = [[Dinitrogen tetroxide|N<sub>2</sub>O<sub>4</sub>]] / [[Aerozine 50]]
}}

{{Infobox rocket/stage
  | type         = stage
  | stageno      = Third
  | name         = [[Payload Assist Module|PAM-D]] (optional)
  | length       = <!--length of a single stage in metres, use {{cvt}}, optional-->
  | diameter     = <!--diameter of a single stage in metres, use {{cvt}}, optional-->
  | empty        = <!--empty mass of a single stage in kilograms, use {{cvt}}, optional-->
  | gross        = <!--gross (fuelled) mass of a single stage, use {{cvt}}, optional--> 
  | propmass     = <!--propellant mass carried by a single stage in kilograms, use {{cvt}}, optional--> 
  | engines      = 1 × [[Star 48B]]
  | solid        = yes
  | thrust       = {{cvt|66|kN}}
  | SI           = {{cvt|286|isp}}
  | burntime     = 87 seconds
  | fuel         = [[Hydroxyl-terminated polybutadiene|HTPB]]  
}}
}}

'''Delta II''' was an [[expendable launch system]] designed and built by [[McDonnell Douglas]], sometimes known as the Thorad Delta 1. Delta II was part of the [[Delta rocket]] family, derived from the [[Delta 3000]], and entered service in 1989. There were two main variants, the Delta 6000 and Delta 7000, with the latter also having "Light" and "Heavy" subvariants. During its career, Delta II flew several payloads, including 24 [[Global Positioning System]] (GPS) [[GPS satellite blocks|Block II]] satellites, several dozen NASA payloads, and 60 Iridium communication satellites. The rocket flew its final mission, [[ICESat-2]], on 15 September 2018, earning  a streak of 100 consecutive successful missions, with the last failure being [[GPS IIR-1]] in 1997.<ref name="data sheet">{{cite web |url=http://www.spacelaunchreport.com/delta2.html |title=Delta II Data Sheet |first=Ed |last=Kyle |website=spacelaunchreport.com |access-date=2014-07-28 |archive-url=https://web.archive.org/web/20140728024436/http://www.spacelaunchreport.com/delta2.html |archive-date=2014-07-28}}</ref> In the late 1990s, Delta II was developed into the unsuccessful [[Delta III]], which was in turn developed into the more capable and successful [[Delta IV]], though the latter shares little heritage with the original Thor and Delta rockets.

== History ==
[[Image:Delta rocket evolution.png|thumb|320px|left|Evolution of the modern Delta rockets]]

In the early 1980s, all United States [[expendable launch vehicles]] were planned to be phased out in favor of the [[Space Shuttle]], which would be responsible for all government and commercial launches. Production of Delta, [[Atlas-Centaur]], and [[Titan 34D]] had ended.<ref>{{cite book |title=Taming Liquid Hydrogen - The Centaur Upper Stage Rocket (1958-2002) |last1=Dawson |first1=Virginia P. |last2=Bowles |first2=Mark D. |year=2004 |page=308 |publisher=NASA |url=https://www.nasa.gov/wp-content/uploads/2023/04/sp-4230.pdf |access-date=13 August 2024}} {{PD-notice}}</ref> The [[Space Shuttle Challenger disaster|''Challenger'' disaster]] of 1986 and the subsequent halt of Shuttle operations changed this policy, and President [[Ronald Reagan]] announced in December 1986 that the Space Shuttle would no longer launch commercial payloads, and [[NASA]] would seek to purchase launches on expendable vehicles for missions that did not require crew or Shuttle support.<ref>{{cite news |url=https://apnews.com/7e6b76c27ec65f93f14fd7913cf95c48 |first1=Harry F. |last1=Rosenthal |title=Reagan Orders NASA To Halt Launch of Commercial Payloads |date=August 16, 1986 |work=Associated Press News Archive |access-date=13 August 2024 |archive-url=https://web.archive.org/web/20140306111634/http://www.apnewsarchive.com/1986/Reagan-Orders-NASA-To-Halt-Launch-of-Commercial-Payloads/id-7e6b76c27ec65f93f14fd7913cf95c48 |archive-date=March 6, 2014 |url-status=live}}</ref>

McDonnell Douglas, at that time the manufacturer of the Delta family, signed a contract with the [[U.S. Air Force]] in 1987 to provide seven Delta II. These were intended to launch a series of [[Global Positioning System]] (GPS) [[GPS satellite blocks|Block II]] satellites, which had previously been manifested for the Space Shuttle. The Air Force exercised additional contract options in 1988, expanding this order to 20 vehicles, and NASA purchased its first Delta II in 1990 for the launch of three Earth-observing satellites.<ref name=":0">{{cite book |title=NASA Historical Data Book, Vol. VII: NASA Launch Systems, Space Transportation, Human Spaceflight, and Space Science, 1989–1998 |last=Rumerman |first=Judy A. |publisher=NASA |year=2009 |id=NASA SP-4012 |pages=49–51 (73–75) |url=https://www.nasa.gov/wp-content/uploads/2023/04/sp-4012v7.pdf |access-date=13 August 2024}} {{PD-notice}}</ref><ref>{{cite web |url=https://www.losangeles.spaceforce.mil/ |title=Delta II, Atlas II, and Atlas III |date=26 April 2013 |archive-url=https://web.archive.org/web/20160414125341/http://www.losangeles.af.mil/shared/media/document/AFD-130426-024.pdf |publisher=Los Angeles Air Force Base |archive-date=14 April 2016 |url-status=live |access-date=13 August 2024}} {{PD-notice}}</ref> The first Delta II launch occurred on 14 February 1989, with a Delta 6925 boosting the first GPS Block II satellite ([[USA-35]]) from [[Cape Canaveral Space Launch Complex 17|Launch Complex 17A]] (SLC-17A) at [[Cape Canaveral Space Force Station|Cape Canaveral]] into a {{cvt|20000|km|mi}} high [[medium Earth orbit]].<ref>{{cite web |url=http://planet4589.org/space/log/launchlog.txt |title=Launch Log |publisher=Jonathan's Space Report |first=Jonathan |last=McDowell |archive-url=https://web.archive.org/web/20091113093423/http://planet4589.org/space/log/launchlog.txt |archive-date=13 November 2009 |access-date=13 August 2024 |url-status=live}}</ref>

The first Delta II 7000-series flew on 26 November 1990, replacing the [[RS-27]] engine of the 6000-series with the more powerful [[RS-27A]] engine. Additionally, the steel-cased [[Castor (rocket stage)|Castor 4A]] solid boosters of the 6000 series were replaced with the composite-cased [[Graphite-Epoxy Motor|GEM 40]]. All further Delta II launches except three were of this upgraded configuration, and the 6000-series was retired in 1992 with the last launch being on July 24.<ref>{{cite web |url=https://www.nasaspaceflight.com/2014/07/delta-ii-oco-2-launch-vandenberg/ |first=William |last=Graham |title=ULA Delta II successfully lofts OCO-2 to orbit |date=July 2, 2014 |access-date=13 August 2024 |website=nasaspaceflight.com}}</ref>

McDonnell Douglas began [[Delta III]] development in the mid-1990s as increasing satellite mass required more powerful launch vehicles.<ref name=":0"/> Delta III, with its liquid hydrogen second stage and more powerful [[Graphite-Epoxy Motor|GEM 46]] boosters, could bring twice as much mass as Delta II to [[geostationary transfer orbit]], but a string of two failures and one partial failure, along with the development of the much more powerful [[Delta IV]], led to the cancellation of the Delta III program.<ref>{{cite web |url=http://www.spacelaunchreport.com/delta3.html |title=Delta III Data Sheet |publisher=Space Launch Report |website=spacelaunchreport.com |date=2 November 2014 |access-date=13 August 2024}}</ref> The upgraded boosters would still find use on the Delta II, leading to the Delta II Heavy.

On 28 March 2003, the Air Force Space Command began the process of deactivating the Delta II launch facilities and infrastructure at Cape Canaveral once the last of the second-generation GPS satellites were launched. However, in 2008, it instead announced that it would transfer all the Delta II facilities and infrastructure to NASA to support the launch of the [[GRAIL|Gravity Recovery and Interior Laboratory]] (GRAIL) in 2011.<ref>{{cite web |last=Cleary |first=Mark |title=Delta II and III Space Operations at Cape Canaveral 1989–2009 |url=http://www.afspacemuseum.org/library/histories/Delta.pdf |website=afspacemuseum.org |archive-url=https://web.archive.org/web/20150530135122/http://www.afspacemuseum.org/library/histories/Delta.pdf |access-date=13 August 2024 |archive-date=30 May 2015 |url-status=live}} {{PD-notice}}</ref>

On 14 December 2006, with the launch of [[USA-193]], was the first launch of the Delta II operated by [[United Launch Alliance]].<ref>{{cite web |title=United Launch Alliance Joint Venture Completes First Launch - ULA Demonstrates Commitment to Mission Assurance With Delta II West Coast Liftoff for NRO Customer|url=https://www.ulalaunch.com/missions/missions-details/2006/12/14/united-launch-alliance-joint-venture-completes-first-launch |website=ulalaunch.com |date=14 December 2006 |access-date=13 August 2024}}</ref>

The last GPS launch aboard a Delta II and the final launch from SLC-17A at Cape Canaveral occurred in 2009. The GRAIL Launch in 2011 marked the last Delta II Heavy launch and the last from Florida. The final five launches would all be from [[Vandenberg Space Force Base|Vandenberg Air Force Base]] in [[California]].<ref>{{cite web |title=The Hangar/Delta II |url=http://www.spaceflightinsider.com/hangar/delta-ii/ |website=spaceflightinsider.com |archive-url=https://web.archive.org/web/20171117170205/http://www.spaceflightinsider.com/hangar/delta-ii/#ELuwclvxe8H5Cdu1.99 |archive-date=17 November 2017 |access-date=13 August 2024 |url-status=live}}</ref>

On 16 July 2012, NASA selected the Delta II to support the [[Orbiting Carbon Observatory]] (OCO-2), [[Soil Moisture Active Passive]] (SMAP), and [[Joint Polar Satellite System]] (JPSS-1 – NOAA-20) missions. This marked the final purchase of Delta II. OCO-2 was launched on 2 July 2014, [[Soil Moisture Active Passive]] (SMAP) was launched on 31 January 2015, and [[NOAA-20|JPSS-1]] was launched on 18 November 2017. All three of these launches were placed into orbit from [[Vandenberg Space Launch Complex 2|SLC-2]] at Vandenberg.<ref>{{cite web |url=http://www.nasa.gov/home/hqnews/2012/jul/HQ_C12-028_RSLP-19_Launch_Services.html |date=16 July 2012 |title=NASA Selects Launch Services Contract for Three Missions |publisher=NASA |archive-url=https://web.archive.org/web/20130510160219/http://www.nasa.gov/home/hqnews/2012/jul/HQ_C12-028_RSLP-19_Launch_Services.html |archive-date=10 May 2013 |access-date=13 August 2024 |url-status=live}} {{PD-notice}}</ref>

The Delta II family launched 155 times. Its only unsuccessful launches were [[Koreasat 1]] in 1995, and [[GPS IIR-1]] in 1997. The Koreasat 1 launch was a partial failure caused by one booster not separating from the first stage, which resulted in the satellite being placed in a lower-than-intended orbit. By using reserve fuel, it was able to achieve its proper [[geosynchronous orbit]] and operated for 10 years.<ref>{{cite web |url=https://space.skyrocket.de/doc_sdat/koreasat-1.htm |title=Koreasat 1, 2 (Mugungwha 1, 2) / Europe*Star B / ABS-1A |last=Krebs |first=Gunter Dirk |date=14 January 2023 |access-date=13 August 2024}}</ref> The GPS IIR-1 was a total loss as the Delta II exploded 13 seconds after launch. The explosion occurred when a damaged [[solid rocket booster]] casing ruptured and triggered the vehicle's flight termination system.<ref>{{Cite web |url=http://www.gizmodo.com.au/2008/09/the_deadly_aftermath_of_a_rocket_explosion_seconds_after_launch-2.html |archive-url=https://web.archive.org/web/20090212062143/http://www.gizmodo.com.au/2008/09/the_deadly_aftermath_of_a_rocket_explosion_seconds_after_launch-2.html |title=Science & Health Archives |archive-date=12 February 2009 |website=gizmodo.com.au |access-date=13 August 2024}}</ref> No one was injured, and the launch pad itself was not seriously impacted, though several cars were destroyed and a few buildings were damaged.<ref>{{cite news |url=http://www.cnn.com/TECH/9701/17/rocket.explosion/index.html |title=Unmanned rocket explodes after liftoff |website=cnn.com |date=1997-01-17 |access-date=14 August 2024 |archive-url=https://web.archive.org/web/20090423212616/http://www.cnn.com/TECH/9701/17/rocket.explosion/index.html |archive-date=2009-04-23 |url-status=live}}</ref>

In 2007, Delta II completed its 75th consecutive successful launch, surpassing the 74 consecutive successful launches of the [[Ariane 4]].<ref>{{cite web |url=http://media.digitalglobe.com/index.php?s=press_release_popup&item=135 |title=DigitalGlobe Successfully Launches Worldview-1 |publisher=DigitalGlobe |access-date=2009-03-03 |archive-url=https://web.archive.org/web/20090302000726/http://media.digitalglobe.com/index.php?s=press_release_popup&item=135 |archive-date=2009-03-02 |url-status=dead}}</ref><ref>{{cite web |url=http://www.spacedaily.com/reports/Ariane_5s_impressive_75_in_a_row_launch_record_999.html |title=Ariane 5's impressive 75 in-a-row launch record |publisher=SpaceDaily |access-date=14 August 2024 |archive-url=https://web.archive.org/web/20171201080916/http://www.spacedaily.com/reports/Ariane_5s_impressive_75_in_a_row_launch_record_999.html |archive-date=2017-12-01 |url-status=live}}</ref> With the launch of [[ICESat-2]] in 2018, Delta II reached 100 consecutive successful launches.

During its career, Delta II achieved a peak launch rate of 12 launches in a single year, although its infrastructure was capable of supporting up to 15 launches per year.<ref name ="Guide"/>

While all completed Delta II rockets were launched, many flight-qualified spare parts remained in inventory. These spare parts were assembled, alongside a few structural simulators, to create a nearly complete Delta II for exhibition in its 7320-10C configuration. The rocket is displayed vertically at the [[Kennedy Space Center Visitor Complex]], and bears its popular "shark teeth" livery on its fairing, which was painted on past Delta II rockets for the GPS launches.<ref>{{cite web |url=https://spaceflightnow.com/2018/09/15/leftover-delta-2-rocket-to-go-on-display-at-kennedy-space-center/ |title=Leftover Delta 2 rocket to go on display at Kennedy Space Center |publisher=Spaceflight Now |website=spaceflightnow.com |date=15 September 2018 |access-date=14 August 2024 |archive-url=https://web.archive.org/web/20190129220657/https://spaceflightnow.com/2018/09/15/leftover-delta-2-rocket-to-go-on-display-at-kennedy-space-center/ |archive-date=2019-01-29 |url-status=live}}</ref>

== Vehicle description ==
[[Image:Foguete Delta II 7425 - Corte esquematico.jpg|thumb|270px|left|Delta II 7425 diagram]]
[[File:Delta II second stage.jpg|thumb|270px|right|A Delta-K stage]]

=== First stage ===
The first stage of the Delta II was propelled by a Rocketdyne [[RS-27]] or [[RS-27A]] main engine burning [[RP-1]] and [[liquid oxygen]]. This stage was technically referred to as the "Extra-Extended Long Tank Thor", a derivative of the [[PGM-17 Thor|Thor]] ballistic missile <ref>{{cite web |url=http://www.spacelaunchreport.com/thorh12.html |title=Space Launch Report |archive-url=https://web.archive.org/web/20120418063513/http://www.spacelaunchreport.com/thorh12.html |website=spacelaunchreport.com |archive-date=2012-04-18 |access-date=14 August 2024}}</ref> as were all Delta rockets until the [[Delta IV]]. The RS-27 used on the 6000-series Delta II produced {{cvt|915|kN|lbf}} of thrust,<ref>{{cite web |url=http://www.astronautix.com/r/rs-27.html |title=RS-27 |website=astronautix.com |access-date=14 August 2024}}</ref> while the upgraded RS-27A used by the 7000-series produced {{cvt|1054|kN|lbf}}.<ref>{{cite web |url=http://www.astronautix.com/engines/rs27a.htm |title=RS-27A |access-date=14 August 2024 |website=astronautix.com}}</ref> The stage was {{convert|26.1|m|ft|sp=us}} long and {{convert|2.44|m|ft|sp=us}} wide, had a mass of {{convert|101.8|t|lb}} when fueled, and burned for 260 seconds.<ref name="data sheet"/> The main engine, which could not throttle, provided pitch and yaw control for the vehicle during ascent using hydraulic gimballing. In addition, two [[Rocketdyne LR-101-NA-11]] vernier engines provided roll control for the first stage during ascent and continued firing after the main engine shut down to stabilize the vehicle before stage separation.<ref name="D2PG"/><ref name ="Guide"/>

The two first-stage tanks were constructed from aluminum isogrid panels, providing high strength at a lower mass. Nitrogen gas was used to pressurize the tanks. These tanks were stretched a total of {{convert|148|in|m}} from those of the Extended Long Tank Thor that flew on older Delta rockets, providing more propellant. Between the two tanks was the "center body", where first-stage avionics and communications equipment were housed. The solid rocket booster attachment points were located on the outside of the liquid oxygen tank and the aft skirt, the latter of which also contained a [[gyroscope]] for vehicle stability.<ref name ="Guide"/>

=== Solid rocket boosters ===
For additional thrust during launch, the Delta II used solid boosters. For the 6000-series, Delta II used Castor 4A boosters (sometimes stylized as "Castor IVA"), while the 7000-series used GEM 40 [[Graphite-Epoxy Motor]]s manufactured by [[Alliant Techsystems]] (ATK). Like its predecessors, the Delta II 6000-series was only offered in nine-booster configurations. However, with the arrival of the 7000-series, variants with three and four boosters were introduced to allow Delta II to fly small payloads for cheaper.<ref name ="Guide"/> When three or four boosters were used, all ignited on the ground at launch, while models that used nine boosters would ignite six on the ground, then the remaining three would ignite in flight after the burnout and jettison of the first six.<ref name="data sheet"/>

The Castor 4A boosters were an improvement over the Castor 4 motors flown on the earlier [[Delta 3000]] rocket, replacing the propellant with more modern [[Hydroxyl-terminated polybutadiene|HTPB]]-based propellant and providing an 11% increase in performance.<ref name="Castor4A">{{cite web |url=http://www.astronautix.com/c/castor4aengine.html |title=Castor 4A engine |first=Mark |last=Wade |website=Encyclopedia Astronautica |access-date=2024-02-27 |archive-url=https://web.archive.org/web/20221220153857/http://www.astronautix.com/c/castor4aengine.html |archive-date=2022-12-20}}</ref> The GEM 40 boosters on the 7000 series further improved Delta II's performance by each featuring {{convert|2.5|t|lb}} of extra propellant than the Castor 4A thanks to a lengthening of {{convert|3|m|ft|sp=us}}. In addition, the GEM boosters also boasted a lower dry mass than the Castors due to the former's carbon composite construction.<ref name="gem40">{{cite web |url=http://www.astronautix.com/g/gem40.html |title=GEM 40 |first=Mark |last=Wade |website=Encyclopedia Astronautica |access-date=2024-02-27 |archive-url=https://web.archive.org/web/20221223211757/http://www.astronautix.com/g/gem40.html |archive-date=2022-12-23}}</ref>

In 2003, the Delta II Heavy debuted, featuring larger GEM 46 motors from the abandoned [[Delta III]] program. These new motors allowed the vehicle to carry over {{cvt|1,000|kg}} of extra payload into low-Earth orbit. Only Cape Canaveral Space Launch Complex 17B was capable of flying the Heavy configuration, as it was previously reinforced to handle the Delta III.<ref name ="Guide"/>

The Castor motor nozzles were angled 11° from vertical to aim their thrust into the vehicle's center of gravity, while the GEM motors had a slightly lower 10° tilt.<ref name="Castor4A"/> On the nine-engine configuration, the three air-lit motors featured longer nozzles to allow the boosters to perform better in the upper atmosphere.<ref name="D2PG"/> All solid motors that flew on the Delta II featured fixed nozzles, meaning the first stage was solely responsible for vehicle control during the initial portions of the flight.<ref name ="Guide"/>

=== Delta-K second stage ===
The second stage of Delta II was the [[Delta-K]], powered by a restartable (up to six restarts) [[Aerojet]] [[AJ10]]-118K engine burning [[hypergolic]] [[Aerozine-50]] and {{N2O4|link=https://en.wikipedia.org/wiki/Dinitrogen_tetroxide}}. These propellants are highly toxic and corrosive, and once loaded the launch had to occur within approximately 37 days or the stage would have to be refurbished or replaced.<ref>{{cite web |url=http://dawn.jpl.nasa.gov/mission/journal_7_15_07.asp |title=DAWN Journal |access-date=2008-09-06 |author=Dr. Marc D. Rayman |date=2007-07-15 |publisher=JPL NASA |archive-url=https://web.archive.org/web/20081012160553/http://dawn.jpl.nasa.gov/mission/journal_7_15_07.asp |archive-date=2008-10-12 |url-status=live}} {{PD-notice}}</ref> This stage also contained a combined [[inertial platform]] and [[guidance system]] that controlled all flight events.<ref name="data sheet"/>

The Delta-K consisted of stainless steel tanks and a lightweight aluminum structure. The tanks were pressurized with helium gas, and the stage featured nitrogen thrusters for roll control during burns and for complete attitude control during coasts. The stage had a mass of {{cvt|950|kg}} when empty, and {{cvt|6954|kg}} when fully fueled.<ref name ="Guide"/>

=== Third stage ===
For low Earth orbit missions, Delta II was not equipped with a third stage. Payloads bound for higher energy orbits such as [[geostationary transfer orbit|GTO]] or to reach Earth escape velocity for [[trans-Mars injection]] or other destinations beyond Earth used an [[HTPB]] solid propellant third stage, situated inside the fairing during launch. This stage was [[spin-stabilized]] and depended on the second stage for proper orientation prior to stage separation, but was sometimes equipped with a hydrazine nutation control system to maintain proper spin axis.<ref name="D2PG"/> The third stage would be spun up using small rocket motors and then released by the second stage to perform its burn. The third stage also included a yo-weight system to induce tumbling in the stage after payload separation to prevent recontact, or a [[yo-yo de-spin]] mechanism to slow the rotation before payload release.<ref name="D2PG">{{cite web |title=Delta II Payload Planner's Guide 2007 |url=http://www.ulalaunch.com/uploads/docs/DeltaIIPayloadPlannersGuide2007.pdf |website=ulalaunch.com |access-date=24 July 2014 |archive-url=https://web.archive.org/web/20110919175556/http://www.ulalaunch.com/site/docs/product_cards/guides/DeltaIIPayloadPlannersGuide2007.pdf |archive-date=19 September 2011 |url-status=live}}</ref> The stage would also contain an S-band transmitter, batteries, and a sequencer to command the stage events.

Two third-stage options were available, both consisting of a single solid rocket motor. The most common by far was [[Star 48]], flying on over 70 missions. The Star 48, also referred to as the Payload Assist Module-Delta (PAM-D, PAM-Delta), was the more, powerful of the two options, producing an average thrust of about {{cvt|66.4|kN}} during its 87.1 seconds of burn time. The stage would end up flying primarily on the more powerful Delta variants and never flew on the three-booster configuration.

The other third-stage option was [[Star 37FM]]. This stage flew four times, and only on three- and four-booster configurations of Delta. Star 37FM produced about {{cvt|45.8|kN}} of thrust during its 66.4-second burn.<ref name ="Guide"/>

== Naming system ==
The Delta II family used a four-digit system to generate its technical names:<ref>{{cite web |url=http://kevinforsyth.net/delta/vehicle.htm |title=Vehicle Description and Designations |last=Forsyth |first=Kevin S. |access-date=2008-03-15 |date=2007-08-10 |work=History of the Delta Launch Vehicle |archive-url=https://web.archive.org/web/20110808102239/http://kevinforsyth.net/delta/vehicle.htm |archive-date=2011-08-08 |url-status=live}}</ref>
* The '''first digit''' was either 6 or 7, denoting the 6000- or 7000-series Delta;
* The '''second digit''' indicated the number of boosters. Most Delta II rockets flew with 9 boosters, but some flew with 3 or 4;
* The '''third digit''' was always 2, denoting a second stage with an Aerojet AJ10 engine. Only Deltas prior to the 6000-series used a different engine, the [[TR-201]];
* The '''last digit''' denoted the third stage. 0 denoted no third stage, 5 indicated a [[Payload Assist Module]] (PAM) stage with Star 48B being used, and 6 indicated it used the Star 37FM motor for a [[Payload Assist Module|PAM]].
* An '''H''' following the four digits denoted that the vehicle used larger [[Delta III]] [[GEM 46]] boosters. The [[Delta IV Heavy|Heavy]] variant could be launched only from [[Cape Canaveral]] (as [[Vandenberg Space Force Base|Vandenberg]]'s pad wasn't modified to handle the larger SRBs) and was retired with the closure of that launch site in 2011;<ref name="nsfoco">{{cite web |last1=Graham |first1=William |title=ULA Delta II successfully lofts OCO-2 to orbit |url=http://www.nasaspaceflight.com/2014/07/delta-ii-oco-2-launch-vandenberg/ |website=NASASpaceflight.com |access-date=July 23, 2014 |date=July 2, 2014 |archive-url=https://web.archive.org/web/20140714130852/http://www.nasaspaceflight.com/2014/07/delta-ii-oco-2-launch-vandenberg/ |archive-date=July 14, 2014 |url-status=live}}</ref>
* Numbers and letters following those indicate the type of fairing. -9.5 means that the vehicle had a {{cvt|9.5|ft}} diameter fairing, -10 means an aluminum {{cvt|10|ft}} diameter fairing, -10C means a composite {{cvt|10|ft}} diameter fairing, and -10L indicates a lengthened {{cvt|10|ft}} diameter composite fairing. In some early Delta II flights, a fairing, about 8-feet in diameter (from older Delta rockets) was flown, and those vehicles had the -8 designation.

For example, a Delta 7925H-10L used the RS-27A, nine [[GEM 46]] boosters, a [[Payload Assist Module|PAM]] third stage, and a lengthened {{cvt|10|ft}} diameter fairing. A Delta 6320–9.5 is a two-stage vehicle with an RS-27 first-stage engine, three Castor 4A boosters, a {{cvt|9.5|ft}} diameter fairing, and no third stage.

== Launch profile ==
; Launch vehicle build-up: A Delta II [[launch vehicle]] was assembled vertically on the launch pad. Assembly started by hoisting the first stage into position. The solid rocket boosters were then hoisted into position and mated with the first stage. Launch vehicle build-up then continued with the second stage being hoisted atop the first stage.<ref>{{cite web |url=http://www.nasa.gov/centers/kennedy/launchingrockets/status/2007/elvstatus-20070606.html |title=Expendable Launch Vehicle Status Report |date=June 6, 2007 |publisher=NASA |access-date=June 8, 2007 |archive-url=https://web.archive.org/web/20070608140719/http://www.nasa.gov/centers/kennedy/launchingrockets/status/2007/elvstatus-20070606.html |archive-date=June 8, 2007 |url-status=live}} {{PD-notice}}</ref>

; Fueling: It took approximately 20 minutes to load the first stage with {{cvt|10000|USgal|L|-2|order=flip|sp=us}} of fuel.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/swift/launch/pad.html |title=Swift Launch Pad Activities |date=2004-11-18 |access-date=2007-12-20 |archive-url=https://web.archive.org/web/20070808154914/http://www.nasa.gov/mission_pages/swift/launch/pad.html |archive-date=2007-08-08 |url-status=live}} {{PD-notice}}</ref>

: At T-45 minutes, fueling completion was confirmed. At T-20 minutes, the [[Flight termination|FTS]] pyros were armed. At T-20 minutes and T-4 minutes, two built-in holds occurred. During these holds, final launch checkouts were performed. At T-11 seconds SRB igniters were armed. Ignition of the main engine was at T-0.4 seconds. The ascent profile varies between missions.

; SRB staging: If nine solid rocket boosters were used, only six were ignited at launch. After about a minute, once the first six were depleted, three air-start motors would ignite for another minute and the ground-start motors would separate.<ref>{{Cite book |last=Squyres |first=Steve |title=Roving Mars: Spirit, Opportunity, and the Exploration of the Red Planet |publisher=Hachette Books |year=2005 |isbn=9781401308513}}</ref> The air-start motors had nozzles optimized for high-altitude as they operated mostly in a near-vacuum during the flight.

: If only three or four boosters were used, all were ignited on the ground and jettisoned at the same time.

== Delta II launches ==
{{Main|List of Delta II launches}}
[[File:Lancement Spirit fusee Delta IIs 10062003.jpg|thumb|270px|right|Delta II lifting off with MER-A on 10 June 2003]]
[[File:Mer-b-final-launch.jpg|right|thumb|270px|Delta II Heavy (7925H-9.5) lifting off from pad 17-B carrying [[Opportunity (rover)|MER-B]]]]

=== Notable payloads ===
Earth-orbiting
{{div col|colwidth=15em}}
* [[Fermi Gamma-ray Space Telescope|GLAST]]
* [[Gravity Probe B]]
* 24 GPS satellites
* 60 [[Iridium satellite constellation|Iridium]] satellites
* [[ICESat-2]]
* [[Kepler space telescope]]
* [[OSTM/Jason-2]]
* [[Radarsat-1]]
* [[ELFIN]]
* [[Polar (satellite)]]
* [[ROSAT]]
* [[USA 205|STSS-ATRR]]
* [[Swift Gamma-Ray Burst Mission|Swift]]
* [[THEMIS]]
* [[USA 193|USA 193 (NROL-21)]]
* [[WIND (spacecraft)|WIND]]
* [[Wide-field Infrared Survey Explorer|WISE]]
* [[Wilkinson Microwave Anisotropy Probe|WMAP]]
{{div col end}}

Interplanetary
{{div col|colwidth=15em}}
* [[2001 Mars Odyssey]]
* [[CONTOUR]]
* [[Dawn (spacecraft)|Dawn]]
* ''[[Deep Impact (spacecraft)|Deep Impact]]''
* [[Deep Space 1]]
* [[Genesis (spacecraft)|Genesis]]
* [[GRAIL]]
* [[Mars Climate Orbiter]]
* [[Mars Exploration Rover]]s
* [[Mars Global Surveyor]]
* [[Mars Pathfinder]]
* [[Phoenix (spacecraft)|Mars Phoenix]]
* [[Mars Polar Lander]]
* [[MESSENGER]]
* [[NEAR Shoemaker|NEAR]]
* [[Spitzer Space Telescope|Spitzer Space Telescope (SIRTF)]]
* [[STEREO]]
{{div col end}}

The last Delta II launch was the [[ICESat-2]] satellite in September 2018.<ref name="nsfoco"/><ref>{{cite web |url=http://www.marketwatch.com/story/nasa-selects-launch-services-contract-for-three-missions-2012-07-16 |archive-url=https://archive.today/20130129044229/http://www.marketwatch.com/story/nasa-selects-launch-services-contract-for-three-missions-2012-07-16 |url-status=dead |archive-date=29 January 2013 |title=NASA Selects Launch Services Contract For Three Missions |date=16 July 2012 |access-date=16 July 2012 |publisher=MarketWatch}}</ref><ref>{{cite web |url=http://www.nasa.gov/centers/kennedy/news/releases/2013/release-20130222b.html |title=NASA Selects Launch Services for ICESat-2 Mission |date=22 February 2013 |access-date=15 March 2013 |publisher=NASA [[Kennedy Space Center]] |archive-url=https://web.archive.org/web/20130708083045/http://www.nasa.gov/centers/kennedy/news/releases/2013/release-20130222b.html |archive-date=8 July 2013 |url-status=live}}</ref>

In 2008, ULA indicated that it had "around half a dozen" unsold Delta II rockets on hand,<ref name=until2015>{{cite web |url=http://www.space.com/businesstechnology/080630-busmon-delta-2.html |title=Delta 2 Rockets to Remain Competitive Until 2015 |first=Brian |last=Berger |publisher=Space News |date=2008-06-30 |access-date=2008-07-03 |archive-url=https://web.archive.org/web/20080703100017/http://www.space.com/businesstechnology/080630-busmon-delta-2.html |archive-date=2008-07-03 |url-status=live}}</ref> and by October 2017, ULA CEO [[Tory Bruno]] stated that there were no complete Delta II rockets left in ULA inventory. 

There were some unused Delta II components, but not enough to build another vehicle.<ref>{{cite tweet |user=torybruno |author-link=Tory Bruno |number=920249741082062853 |title=Less than 1. Last 2 complete DIIs are ordered, JPSS is flying next. Most of a 3rd DII's parts remain in inventory |date=17 October 2017 |access-date=7 August 2019}}</ref> A Delta II, made of these leftover parts alongside some [[Simulation|simulated]] parts, is located at the [[Rocket garden|Kennedy Space Center rocket garden]].<ref>{{Cite web |url=https://www.space.com/delta2-rocket-garden-nasa-display |title=Last Delta II takes root in Kennedy Space Center rocket garden |author1=Robert Z. Pearlman |date=23 March 2021 |website=Space.com |access-date=11 March 2023}}</ref>

== Comparable rockets ==
* [[Antares (rocket)|Antares]]
* [[Ariane 4]] (retired)
* {{annotated link|Geosynchronous Satellite Launch Vehicle|GSLV}}
* [[Long March 4B]]
* {{annotated link|Polar Satellite Launch Vehicle|PSLV}}
* [[Soyuz (rocket family)|Soyuz]]
* {{annotated link|Tsyklon-3}} (retired)
* {{annotated link|Vega (rocket)|Vega}}

== Space debris (a.k.a. "Space junk") ==
The only person on record ever hit by [[space debris]], Mrs. Lottie Williams, was hit by a small, light piece of a Delta II rocket. Mrs. Williams was exercising in a park in [[Tulsa, Oklahoma]] on 22 January 1997 when she was hit in the shoulder by a {{convert|6|in|cm|adj=on|order=flip|sp=us}} piece of blackened metallic material. The [[United States Space Command|U.S. Space Command]] confirmed that a used Delta II rocket from the April 1996 launch of the [[Midcourse Space Experiment]] had crashed into the [[atmosphere]] 30 minutes earlier. The object tapped her on the shoulder and fell off harmlessly onto the ground. Williams collected the item and [[NASA]] tests later showed that the fragment was consistent with the materials of the [[rocket]], and Nicholas Johnson, the agency's chief scientist for [[orbital debris]], believes that she was, indeed hit by a piece of a recently launched Delta II.<ref>{{cite news |title=Space Junk Survivor |url=https://abcnews.go.com/Technology/story?id=98700&page=1 |access-date=2 January 2018 |date=3 March 2017 |archive-url=https://web.archive.org/web/20180103072647/http://abcnews.go.com/Technology/story?id=98700&page=1 |archive-date=3 January 2018 |url-status=live}}</ref><ref>{{cite news |last1=Long |first1=Tony |title=January 22, 1997: Heads Up, Lottie! It's Space Junk! |url=https://www.wired.com/2009/01/jan-22-1997-heads-up-lottie-its-space-junk/ |access-date=2 January 2018 |date=22 January 1997 |archive-url=https://web.archive.org/web/20180102224533/https://www.wired.com/2009/01/jan-22-1997-heads-up-lottie-its-space-junk/ |archive-date=2 January 2018 |url-status=live}}</ref>

Delta rockets have been involved in multiple fragmentation events as they were routinely left in orbit with enough fuel to explode. A large amount of current "[[Space debris|space junk]]" is Delta rocket debris.<ref>{{cite web |title=Micrometeoroids and Orbital Debris (MMOD) |date=14 June 2016 |url=https://www.nasa.gov/centers/wstf/site_tour/remote_hypervelocity_test_laboratory/micrometeoroid_and_orbital_debris.html |access-date=20 March 2023}}</ref>

== See also ==
* [[Comparison of orbital launchers families]]
* [[Comparison of orbital launch systems]]

== Notes ==
{{notelist}}

== References ==
{{reflist}}

== External links ==
{{Commons category-inline|Delta II}}
* [https://web.archive.org/web/20061103194958/http://www.boeing.com/defense-space/space/delta/delta2/delta2.htm Delta II page] at Boeing.com
* [https://web.archive.org/web/20110718145330/http://space.skyrocket.de/doc_lau/delta.htm Delta I, II und III launch data] at Skyrocket.de
* [http://kevinforsyth.net/delta/ History of the Delta launch vehicle]
* [http://www.nasa.gov/sites/default/files/633163main_delta-2-weather.pdf Delta II Launch Weather Commit Criteria]

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