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{{Short description|Cancelled 2005–2010 NASA human spaceflight program}}
{{Infobox space program
| name         = Constellation program
| image        = [[File:Constellation logo white.svg|frameless|upright]]
| alt          = A red arrow-like shape resembling an element of the NASA logo, printed on top of three crescents
| country      = [[United States]]
| organization = [[NASA]]
| purpose      = {{Unbulleted list|Crewed orbital flight|Crewed lunar exploration|Crewed Mars exploration}}
| status       = Cancelled
| cost         = $230 billion (2004)
| duration     = 2004<ref name=georgewbush-whitehouse.archives.gov>{{cite web|title=A Renewed Spirit of Discovery|url=https://georgewbush-whitehouse.archives.gov/infocus/space/|publisher=NASA Constellation Program Office|access-date=13 October 2021}}</ref>–2010<ref>{{cite news|title=NASA grieves over canceled program
|author=Tariq Malik|date=February 2, 2010|url=https://www.nbcnews.com/id/wbna35209628|publisher=NBC News|access-date=May 6, 2023}}</ref>
| firstflight  = {{Unbulleted list|[[MLAS]]|{{Start date|2009|06|08}}}}
| lastflight   = {{Unbulleted list|[[Ares I-X]]|{{Start date|2009|10|28}}}}
| successes    = 2
| launchsite   = {{Unbulleted list|[[Kennedy Space Center Launch Complex 39]]|[[White Sands Missile Range|White Sands]]}}
| crewvehicle  = {{Hlist|[[Altair (spacecraft)|''Altair'']]|[[Orion (spacecraft)|''Orion'']]}}
| launcher     = {{Hlist|[[Ares I]]|[[Ares V]]}}
}}
{{United States space program sidebar}}

The '''Constellation program''' (abbreviated '''CxP''') was a [[crewed spaceflight]] program developed by [[NASA]], the [[space]] agency of the [[United States]], from 2005 to 2009. The major goals of the program were "completion of the [[International Space Station]]" and a "return to the [[Moon]] no later than 2020" with a crewed flight to the planet [[Mars]] as the ultimate goal. The program's [[logo]] reflected the three stages of the program: the Earth (ISS), the Moon, and finally Mars—while the Mars goal also found expression in the name given to the program's booster rockets: [[Ares V|Ares]] (the Greek equivalent of the Roman god [[Mars (mythology)|Mars]]).<ref name=nasa.gov>{{cite web|last1=Connolly|first1=John F.|title=Constellation Program Overview|url=http://www.nasa.gov/pdf/163092main_constellation_program_overview.pdf|publisher=NASA Constellation Program Office|access-date=23 October 2014|date=October 2006|archive-date=July 10, 2007|archive-url=https://web.archive.org/web/20070710060512/http://www.nasa.gov/pdf/163092main_constellation_program_overview.pdf|url-status=dead}}</ref><ref name="NASA">{{cite web|url=http://www.nasa.gov/mission_pages/constellation/orion/index.html |title=Constellation News and Media Archive |date=June 15, 2011 |access-date=August 7, 2011|archive-url=https://web.archive.org/web/20070711034325/http://www.nasa.gov/mission_pages/constellation/orion/index.html|archive-date=July 11, 2007}}</ref> The technological aims of the program included the regaining of significant [[astronaut]] experience beyond [[low Earth orbit]] and the development of technologies necessary to enable sustained human presence on other planetary bodies.<ref>{{cite web|url=http://www.nasa.gov/pdf/163092main_constellation_program_overview.pdf|title=Constellation Program Overview|last=Connolly|first=John F.|date=October 2006|publisher=Constellation Program Office|access-date=July 6, 2009|archive-url=https://web.archive.org/web/20070710060512/http://www.nasa.gov/pdf/163092main_constellation_program_overview.pdf|archive-date=July 10, 2007}}</ref>

Constellation began in response to the goals laid out in the [[Vision for Space Exploration]] under NASA Administrator [[Sean O'Keefe]] and President [[George W. Bush]].<ref>{{cite web|url=http://www.nasa.gov/missions/solarsystem/vision_concepts.html | title=Taking the Vision to the Next Step |publisher=NASA | date=October 5, 2004| access-date=August 16, 2011|archive-url=https://web.archive.org/web/20041101205026/http://www.nasa.gov/missions/solarsystem/vision_concepts.html|archive-date=November 1, 2004}}</ref><ref>{{cite web|url=http://www.nasa.gov/audience/formedia/speeches/okeefe_house_testimony_042104.html|title=Administrator O'Keefe's House Testimony|publisher=NASA|date=April 21, 2004|access-date=August 16, 2011|archive-url=https://web.archive.org/web/20040826054609/http://www.nasa.gov/audience/formedia/speeches/okeefe_house_testimony_042104.html|archive-date=August 26, 2004}}</ref> O'Keefe's successor, [[Michael D. Griffin]], ordered a complete review, termed the [[Exploration Systems Architecture Study]], which reshaped how NASA would pursue the goals laid out in the Vision for Space Exploration, and its findings were formalized by the [[NASA Authorization Act of 2005]]. The Act directed NASA to "develop a sustained human presence on the Moon, including a robust precursor program to promote exploration, science, commerce and US preeminence in space, and as a stepping stone to future exploration of Mars and other destinations."<ref name="nasa.gov"/> Work began on this revised Constellation Program, to send astronauts first to the [[International Space Station]], then to the [[Moon]], and then to [[Mars]] and beyond.<ref name="NASA"/>

Subsequent to the findings of the [[Review of United States Human Space Flight Plans Committee|Augustine Committee]] in 2009 that the Constellation Program could not be executed without substantial increases in funding, on February 1, 2010, President [[Barack Obama]] proposed to cancel the program, effective with the passage of the [[2010 United States federal budget|U.S. 2011 fiscal year budget]].<ref name="BBC cancels Moon return"/><ref name=FY2011_budget/><ref name="WashPost eliminates funds"/><ref>{{cite web|url=http://www.nasa.gov/pdf/420990main_FY_201_%20Budget_Overview_1_Feb_2010.pdf|access-date=March 7, 2010|title=Fiscal Year 2011 Budget Estimates|archive-url=https://web.archive.org/web/20100201191410/http://www.nasa.gov/pdf/420990main_FY_201_%20Budget_Overview_1_Feb_2010.pdf|archive-date=February 1, 2010}}</ref> He then revised administration statements in a [[Space policy of the Barack Obama administration#Space policy speech at Kennedy Space Center|major space policy speech]] at [[Kennedy Space Center]] on April 15, 2010.<ref>{{cite news|title=Press Release: Remarks of President Barack Obama at the Kennedy Space Center - As Prepared for Delivery|date=April 15, 2010|url=https://www.presidency.ucsb.edu/documents/press-release-remarks-president-barack-obama-the-kennedy-space-center-prepared-for|website=ucsb.edu|access-date=May 6, 2023}}</ref> On October 11, the signing of the [[NASA Authorization Act of 2010]] shelved the program,<ref>{{cite news| url=https://www.bbc.co.uk/news/science-environment-11518049 |work=BBC News |title=Obama signs Nasa up to new future |date=October 11, 2010}}</ref> with Constellation contracts remaining in place until Congress would act to overturn the previous mandate.<ref>Testimony of Charles Bolden before the Senate Appropriations subcommittee, April 11, 2011</ref><ref name="space1">[http://www.space.com/9712-nasa-stuck-limbo-congress-takes.html "NASA Stuck in Limbo as New Congress Takes Over"]. Space.com, January 7, 2011.</ref> In 2011, NASA adopted the design of its new [[Space Launch System]].<ref name=New_Heavy-lift_Rocket>{{cite web |url=http://www.nasa.gov/home/hqnews/2011/sep/HQ_11-301_SLS_Decision.html |title= NASA Announces Design For New Deep Space Exploration System|publisher=NASA |date=September 14, 2011 |access-date=September 14, 2011|archive-url=https://web.archive.org/web/20110921160158/http://www.nasa.gov/home/hqnews/2011/sep/HQ_11-301_SLS_Decision.html|archive-date=September 21, 2011}}</ref>

==Designs==
One of the main goals of Constellation was the development of [[spacecraft]] and [[launch vehicle|booster vehicles]] to replace the [[Space Shuttle]]. NASA had already begun designing two boosters, the [[Ares I]] and [[Ares V]], when the program was created. Ares I was designed for the sole purpose of launching mission crews into orbit, while Ares V would have been used to launch other hardware which required a heavier lift capacity than the Ares I booster provided. In addition to these two boosters, NASA designed other spacecraft for use during Constellation, including the [[Orion (Constellation program)|Orion]] crew capsule, the [[Earth Departure Stage]] secondary booster, and the [[Altair (spacecraft)|Altair]] lunar lander.<ref>{{cite web|url=http://www.nasa.gov/pdf/140649main_ESAS_full.pdf|title=Exploration Systems Architecture Study – Final Report |publisher=[[NASA]] |date=November 2005|id=NASA-TM-2005-214062 |access-date=July 6, 2009|archive-url=https://web.archive.org/web/20061013112649/http://www.nasa.gov/pdf/140649main_ESAS_full.pdf|archive-date=October 13, 2006}}</ref>

===Vehicles===

====Orion====
{{Main|Orion (spacecraft)}}
[[File:Orion Spacecraft ArtemisI DEC2019 PBS.jpg|thumb|Orion spacecraft {{asof|December 2019|lc=y}}]]
The [[Orion (spacecraft)|Orion spacecraft]] was designed for the Constellation program as a crew compartment for use in [[low Earth orbit]]. [[Lockheed Martin]] was selected as the prime contractor for the Orion project on August 31, 2006,<ref>{{Cite press release|url=http://www.nasa.gov/home/hqnews/2006/aug/HQ_06305_Orion_contract.html|title=NASA Selects Orion Crew Exploration Vehicle Prime Contractor|publisher=[[NASA]]|date=August 31, 2006|access-date=July 6, 2009|archive-date=December 3, 2017|archive-url=https://web.archive.org/web/20171203132609/https://www.nasa.gov/home/hqnews/2006/aug/HQ_06305_Orion_contract.html|url-status=dead}}</ref> and [[Boeing]] was selected to build its primary heat shield on September 15, 2006.<ref>{{Cite press release|url=http://www.nasa.gov/home/hqnews/2006/sep/HQ_C06047_tps.html|title=NASA Awards Thermal Protection Contract for Orion Spacecraft|publisher=[[NASA]]|date=September 15, 2006|access-date=July 6, 2009|archive-date=July 7, 2017|archive-url=https://web.archive.org/web/20170707190531/https://www.nasa.gov/home/hqnews/2006/sep/HQ_C06047_tps.html|url-status=dead}}</ref> NASA initially planned to develop different Orion capsules tailored for specific missions. The Block I Orion was to be used for [[International Space Station]] missions and other Earth orbit missions, while the Block II and III variants were designed for deep-space exploration.

Orion's design consists of three main parts: a crew module (CM) similar to the [[Apollo command module]], but capable of sustaining four to six crew members; a cylindrical service module (SM) containing the primary propulsion systems and consumable supplies; and the Launch Abort System (LAS), which provides capability for the astronauts and Crew Module to escape from the launch vehicle should problems arise during launch ascent. The Orion Crew Module is designed to be reusable, allowing NASA to construct a fleet of Orion crew modules.

Despite the cancellation of the Constellation program, development of <!-- a variant of --> the Orion spacecraft <!-- , the Orion Multi-Purpose Crew Vehicle (MPCV), --> continues, with a test launch performed on December 5, 2014. Orion flew aboard [[Artemis I]] in 2022 and is planned to fly aboard [[Artemis II]] in 2026 and on several subsequent missions.

====Altair====
{{Main|Altair (spacecraft)}}
[[File:New Altair design.PNG|thumb|Design for Altair]]
Altair (formerly known as the Lunar Surface Access Module, LSAM) was designed to be the main transport vehicle for astronauts on lunar missions. The Altair design was much larger than its predecessor, the [[Apollo Lunar Module]], at almost five times the volume, occupying a total of {{Convert|1120|ft3}} compared with the Apollo lander's {{Convert|235|ft3}}. It was to stand {{Convert|32|ft}} tall and span {{Convert|49|ft}} wide from tip to tip of the landing gear.

Like its predecessor, the Altair design consists of two parts: an ascent stage which houses the four-person crew; and a descent stage consisting of the landing gear, and storage for the majority of the crew's consumables (oxygen and water) and for scientific equipment. Unlike the Lunar Module, Altair was designed to land in the lunar polar regions favored by NASA for future lunar base construction.<ref>{{cite news|url=http://www.space.com/businesstechnology/080929-nasa50-orion-apollo.html|year=2008|author=Jim Banke|title=Orion vs. Apollo: NASA's 21st Century Moonshot|work=[[Space.com]]|access-date=December 11, 2008 }}</ref> Altair, like the Lunar Module, was not designed to be reusable, and the ascent stage would be discarded after use.

The Altair descent stage was to be powered by four [[RL-10]] rocket engines, which are also those used in the [[Centaur (rocket stage)|Centaur upper stage]] of the [[Atlas V]] rocket. Unlike the current RL-10 engines in use, these newer RL-10s were to have the ability to throttle down to as low as 10% rated thrust (the older specifications allow for 20%), thus allowing the use of Altair for both the lunar orbit insertion (LOI) and landing stages of lunar missions. The ascent stage was designed to be powered by a single engine, likely a [[hypergolic]] engine similar or identical to the main engine of the Orion CSM, which would use the descent stage as both a launchpad and a platform for future base construction. Alternately, there was a small possibility that the original plan of using LOX/CH<sub>4</sub>–fueled engines on board the Block II (lunar) Orion CSM and Altair ascent stage would have been adopted.

===Propulsion===
[[File:Maximum payload.PNG|thumb|right|upright=1.9|Comparison of maximum payload to [[low Earth orbit]].<br />1. [[Space Shuttle]] payload includes crew and cargo.
2. [[Ares I]] payload includes only crew and inherent craft.
3. [[Saturn V]] payload includes crew, inherent craft and cargo.
4. [[Ares V]] payload includes only cargo and inherent craft.]]

NASA planned to use two separate boosters for the Constellation Program missions – the [[Ares I]] for crew and the [[Ares V]] for cargo. This would have allowed the two launch vehicles to be optimized for their respective missions, and allowed a much higher total lift for the Ares V without being cost-prohibitive. The Constellation Program thus combined the [[Lunar Orbit Rendezvous]] method adopted by the [[Apollo program]]'s lunar missions with the [[Earth Orbit Rendezvous]] method which had also been considered.

The name [[Ares]] (the Greek god called Mars in Roman mythology) was chosen for the boosters as a reference to the project's goal of landing on Mars. The numbers I and V were chosen to pay homage to the Saturn rockets of the 1960s.

====Ares I====
{{Main|Ares I}}
[[File:Ares I-X launch 08.jpg|thumb|right|The launch of Ares I prototype, [[Ares I-X]]
on October 28, 2009]]
The Orion spacecraft would have been launched into a [[low Earth orbit]] by the Ares I rocket (the "Stick"), developed by [[Alliant Techsystems]], [[Rocketdyne]], and [[Boeing]].<ref name="Ares1stStage">{{cite web|url=http://www.nasa.gov/pdf/230922main_1stStage_FS.pdf|title=NASA's Ares I First Stage, Powering the Ares I Rocket for liftoff|publisher=[[Marshall Space Flight Center]]|date=April 29, 2009|access-date=August 5, 2009}}</ref><ref name="Rocketdyne">{{Cite press release|title=NASA Awards Upper Stage Engine Contract for Ares Rockets|publisher=[[NASA]]|date=July 16, 2007|url=http://www.nasa.gov/home/hqnews/2007/jul/HQ_C07030_J2X_Contract_prt.htm|access-date=July 17, 2007|archive-date=August 1, 2020|archive-url=https://web.archive.org/web/20200801040403/https://www.nasa.gov/home/hqnews/2007/jul/HQ_C07030_J2X_Contract_prt.htm|url-status=dead}}</ref><ref>{{Cite press release|url=http://www.nasa.gov/home/hqnews/2007/dec/HQ_C07060_Ares_1_Avionics.html|title=NASA Selects Prime Contractor For Ares I Rocket Avionics|publisher=[[NASA]]|date=December 12, 2007|access-date=August 5, 2009}}</ref> Formerly referred to as the Crew Launch Vehicle (CLV), the Ares I consisted of a single [[Solid Rocket Booster]] (SRB) derived in part from the primary boosters used in the [[Space Shuttle]] system, connected at its upper end by an interstage support assembly to a new liquid-fueled second stage powered by a [[J-2X]] rocket engine. NASA selected the Ares designs for their anticipated overall safety, reliability and cost-efficiency.<ref name="SafetyDesign">{{cite web|url=http://www.nasa.gov/mission_pages/constellation/ares/aresl/index.html|title=NASA – Ares I Crew Launch Vehicle|access-date=May 13, 2009|publisher=[[NASA]]|date=April 29, 2009}}</ref>

NASA began developing the [[Ares I]] low Earth orbit launch vehicle (analogous to Apollo's [[Saturn IB]]), returning to a development philosophy used for the original [[Saturn I]], test-launching one stage at a time, which [[George Mueller (NASA)|George Mueller]] had firmly opposed and abandoned in favor of "all-up" testing for the [[Saturn V]]. As of May 2010, the program got as far as launching the first [[Ares I-X]] first-stage flight on October 28, 2009 and testing the Orion launch abort system before its cancellation.

====Ares V====
{{Main|Ares V}}
<!-- Deleted image removed: [[File:Ares V View.png|thumb|upright|left|Exploded view of Ares V showing where Altair would be]] -->
Ares V would have had a maximum lift capacity of about {{convert|188|MT|lb}} to [[low Earth orbit]] (LEO), compared to the [[Space Shuttle]]'s capacity of {{convert|24.4|MT|lb}}, and the [[Saturn V]]'s {{convert|118|MT|lb}}. The Ares V would have carried about {{convert|71|MT|lb}} to the [[Moon]], versus the [[Saturn V]]'s {{convert|45|MT|lb}} lunar payload.<ref name="AresV_overview">[http://www.nasa.gov/mission_pages/constellation/ares/aresV/index.html Overview: Ares V Cargo Launch Vehicle] {{Webarchive|url=https://web.archive.org/web/20120412004044/http://www.nasa.gov/mission_pages/constellation/ares/aresV/index.html |date=April 12, 2012 }}, NASA. Retrieved September 30, 2008.</ref><ref>Steve Creech, Steve and Phil Sumrall. [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080036820_2008036005.pdf "Ares V: Refining a New Heavy Lift Capability"]. NASA.</ref>

The Ares V design consisted of six [[RS-68]] engines with assistance from a pair of 5.5-segment SRBs. Five [[RS-25]] engines were originally planned for the Ares V, but the RS-68 engines are more powerful and less complex and therefore less expensive than the SSMEs. The Ares V would have flown for the first eight minutes of powered flight, then the Earth Departure Stage would have placed itself and the Altair spacecraft into low Earth orbit while awaiting the arrival of the Orion.  Toward the end of the program, it became apparent that the ablatively-cooled RS-68B engines would not withstand the heat from the solid rocket boosters at launch, and NASA began again to consider using RS-25 engines instead of upgrading the RS-68 to be [[Regenerative cooling|regeneratively-cooled]].<ref>{{cite web|url=http://www.nasaspaceflight.com/2008/12/ssme-ares-v-undergoes-evaluation-potential-switch/|title=Return to SSME – Ares V undergoes evaluation into potential switch|date=26 December 2008}}</ref>

====Earth Departure Stage====
[[File:EDP and CEV leaving orbit.jpg|thumb|right|[[Earth Departure Stage]]]]
{{Main|Earth Departure Stage}}

The Earth Departure Stage (EDS) was the propulsion system designed to put the Altair upper stage on a lunar trajectory from within low Earth orbit. It was designed as the second liquid-fueled stage of the Ares V rocket. The Orion spacecraft would have been launched separately by Ares I, and then met and docked with the Ares V-launched EDS/Altair combination, delivering the crew and configuring the spacecraft for its journey to the Moon in a process known as [[Earth orbit rendezvous]].

===Comparison to Apollo and Space Shuttle designs===
{{Main|Apollo program|Space Shuttle program}}

NASA planned to use the first vehicles developed in the Constellation Program for Earth-orbit tasks formerly undertaken by the [[Space Shuttle]].<ref name="NASAhq">{{cite web |url=http://www.hq.nasa.gov/office/hqlibrary/pathfinders/constellation.htm |title=Constellation Program |work=NASA Headquarters Library |publisher=NASA |archive-url=https://web.archive.org/web/20110209100037/http://www.hq.nasa.gov/office/hqlibrary/pathfinders/constellation.htm |archive-date=February 9, 2011 |url-status=dead |access-date=July 4, 2013}}</ref>  But unlike the [[X-33]] and other programs intended to replace the Shuttle, Constellation reused concepts from the [[Apollo program|Apollo]] and [[Space Shuttle program]]s.<ref name="NASAhq" />

The shape of the Orion command module closely resembles the aerodynamic shape of the [[Apollo command and service module]]. However, in other areas Orion employs updated technology.<ref>{{cite magazine|last=Roush |first=Wade |url=http://www.technologyreview.com/printer_friendly_article.aspx?id=17482 |title=Part Apollo, Part Boeing 787 |magazine=Technology Review |date=September 11, 2006 |access-date=August 7, 2011}}</ref>  The design of the launch vehicle taking Orion into orbit, the [[Ares I]], employs many concepts from the Apollo program.

The design of the [[J-2X|J-2X engine]] intended for use on the Ares V booster rocket was originally to be similar to the [[J-2 (rocket engine)|J-2]] engine of the Apollo-era Saturn V and Saturn IB rockets. In designing the J-2X, NASA engineers visited museums, searched for Apollo-era documentation and consulted with engineers who worked on the Apollo program. "The mechanics of landing on the Moon and getting off the Moon to a large extent have been solved," said Constellation program manager Jeff Hanley. "That is the legacy that Apollo gave us."<ref>{{Cite news| url=https://www.usatoday.com/tech/science/space/2006-08-14-nasa-apollo_x.htm?csp=34 | work=USA Today | title=NASA is borrowing ideas from the Apollo | date=August 14, 2006 | access-date=April 30, 2010 | first=Jay | last=Reeves}}</ref>  However, as the J-2X program progressed, it became apparent that, because of revised safety requirements and the growing mass of the upper stage, it was necessary to scrap the original J-2 design completely and use a completely new design for the J-2X.<ref>{{cite web|date=4 June 2012|title=J-2X Extra: What's in a Name?|url=http://blogs.nasa.gov/cm/newui/blog/viewpostlist.jsp?blogname=J2X|publisher=NASA|author=William D Greene|access-date=November 26, 2014|archive-url=https://web.archive.org/web/20101109091510/http://blogs.nasa.gov/cm/newui/blog/viewpostlist.jsp?blogname=J2X|archive-date=November 9, 2010|url-status=dead}}</ref>

Like Apollo, Constellation would have flown a [[lunar orbit rendezvous]] mission profile, but unlike Apollo, Constellation would have also employed [[Earth orbit rendezvous]], conveying the crew to the vehicle. The lander, known as [[Altair (spacecraft)|Altair]], would have been launched separately on the [[Ares V]] rocket, a rocket based on both Space Shuttle and Apollo technologies. Orion would have been launched separately and would have linked up with Altair in low Earth orbit. Also, unlike Apollo, Orion would have remained uncrewed in lunar orbit while the entire crew landed on the lunar surface. Toward the end of the mission, the Altair spacecraft would have launched into lunar orbit to link up with the Orion spacecraft in lunar orbit rendezvous.  Like Apollo, the Orion capsule would then have returned to Earth, re-entering the atmosphere and landing in water.

==Missions==
{{Main|List of Constellation missions}}

Like those of the Apollo Program, Constellation program missions would involve its main vehicle, the Orion spacecraft, flying missions in [[Low Earth Orbit|low Earth orbit]] to service the International Space Station, and in conjunction with the [[Altair (spacecraft)|Altair]] and [[Earth Departure Stage]] vehicles, on crewed flights to the polar regions of the Moon. There were no well-defined plans at the time of cancelation for a crewed flight to [[Mars]], the ultimate goal of the project, but a [[Orion Asteroid Mission|mission to a Near-Earth asteroid]] was in the initial planning phase as of 2008.

===International Space Station and low-Earth orbit flights===
{{See also|Low Earth orbit}}

After being manufactured at private plants, the parts of the Ares I/Orion stack would be tested and assembled at the [[Vehicle Assembly Building]] at the [[Kennedy Space Center]]. Once assembly was completed and a launch date was set, the [[crawler-transporter]] would transport the completed stack, along with the launch support tower and the [[mobile launcher platform#Space Launch System|Mobile Launcher-1]], out to [[LC-39B]]. Once the crawler-transporter reached the pad, the stack and the Launcher Platform would be left in place and the crawler-transporter removed to a safe distance.

After final safety checks, the ground crew would fill up the second stage with liquid hydrogen (LH<sub>2</sub>) and liquid oxygen (LOX) fuel, and the crew, wearing [[Constellation Space Suit|all-purpose spacesuits]], would enter the spacecraft three hours before liftoff. Once they were locked in, and after all systems were cleared by controllers at both the Cape and [[Mission Control]] in Houston, the Ares I would then launch.

After a two-day orbital chase, the [[Orion (spacecraft)|Orion spacecraft]], having jettisoned much of the initial stack during takeoff, would meet with the [[International Space Station]]. After getting the go ahead from Houston, Orion would then dock with the ISS. The six-man crew (at a maximum) would then enter the station in order to perform numerous tasks and activities for the duration of their flight, usually lasting six months, but possibly shortened to four or lengthened to eight, depending upon NASA's goals for that particular mission. Once completed, the crew would then reenter the Orion, seal itself off from the ISS, and then undock from the station.

Once the Orion reached a safe distance from the ISS, the Command Module (after having jettisoned the disposable service module) would re-enter in the same manner as all NASA spacecraft prior to the Shuttle, using the ablative heat shield to both deflect heat from the spacecraft and to slow it down from a speed of {{cvt|17500|mph}} to {{cvt|300|mph}}. After reentry was completed, the forward assembly would be jettisoned, and two drogue parachutes released, followed at {{convert|20000|ft|m}} by three main parachutes and airbags filled with nitrogen (N<sub>2</sub>), which does not combust when exposed to heat, allowing the spacecraft to splashdown.<ref>{{cite web|title=Orion landings to be splashdowns – KSC buildings to be demolished|first=Chris|last=Bergin|publisher=NASASpaceFlight.com|year=2007|url=http://www.nasaspaceflight.com/2007/08/orion-landings-to-be-splashdowns-ksc-buildings-to-be-demolished/|access-date=August 5, 2007}}</ref> The Command Module would then be returned to Kennedy Space Center for refurbishment for a later flight. Unlike the Apollo CM, which was used only for one flight, an Orion CM could theoretically be used up to ten times under normal operating conditions.

===Lunar sortie flights===
[[File:Orion lunar orbit (Sept 2006).jpg|thumbnail|right|Artist's conception of the [[Orion spacecraft]] in lunar orbit]]
{{See also|Lunar sortie|NASA lunar outpost concepts}}

Unlike the Apollo missions, where both the [[Apollo command and service module]] and the [[Apollo Lunar Module]] were launched together on the [[Saturn V]] rocket, the crewed Orion spacecraft would be launched separately from the uncrewed [[Earth Departure Stage|EDS]] and lunar lander. The Ares&nbsp;V/Altair stack would be assembled at the [[Vehicle Assembly Building]] and then transported to [[LC-39A]], and the Ares&nbsp;M/Orion stack would be transported to the adjacent Pad 39B. The Ares V/EDS/Altair stack would be launched first, into a {{Convert|360|km|order=flip}} high circular orbit. Approximately 90 minutes later, the Ares&nbsp;I/Orion would then launch with the crew into a nearly identical orbit.

The Orion would then [[Earth orbit rendezvous|rendezvous]] and dock with the Altair/EDS combination already in low-Earth orbit. After the necessary preparations for lunar flight, the EDS would fire for 390 seconds in a [[translunar injection]] (TLI) maneuver, accelerating the spacecraft to {{Convert|40,200|km/h|order=flip}}. After this burn, the EDS would be jettisoned.

During the three-day trans-lunar coast, the four-man crew would monitor the Orion's systems, inspect their Altair spacecraft and its support equipment, and correct their flight path as necessary to allow the Altair to land at a near-polar landing site suitable for a future lunar base. Approaching the lunar far side, the Orion/Altair combination would orient the Altair's engines forward and make the [[lunar orbit insertion]] (LOI) burn.

Once in lunar orbit, the crew would refine the trajectory and configure the Orion spacecraft for uncrewed flight, allowing all four crew members to transfer to the Altair vehicle and land on the Moon, while the Orion waits for their return. Upon receiving clearance from Mission Control, the Altair would undock from the Orion and perform an inspection maneuver, allowing ground controllers to inspect the spacecraft via live TV mounted on Orion for any visible problems that would prevent landing (on Apollo this was done by the Command Module Pilot). After receiving approval from ground controllers, the two craft would separate to a safe distance and the Altair's descent engines would fire again for powered descent to a pre-determined landing spot previously selected by [[uncrewed spacecraft]].

Upon landing, the crew would put on their [[extravehicular activity]] (EVA) spacesuits and commence the first of five to seven lunar EVAs, collecting samples and deploying experiments. After completing their Lunar Sortie operations, the crew would then enter the Altair and fire the ascent stage engine to lift off from the surface, using the descent stage as a launchpad (and leaving it as a platform for future base construction). Upon entering orbit, the Altair would rendezvous and dock with the waiting Orion spacecraft, and the crew would then transfer, along with samples collected on the Moon, back to the Orion. After jettisoning the Altair, the crew would perform the [[Trans Earth Injection]] (TEI) burn for the return trip to Earth.

After a two-and-a-half-day coast, the crew would jettison the Service Module (allowing it to burn up in the atmosphere) and the CM would reenter the Earth's atmosphere using a special reentry trajectory designed to slow the vehicle from its speed of {{Convert|40,200|km/h|order=flip}} to {{Convert|480|km/h|order=flip}} and thus allow a Pacific Ocean splashdown. The Crew Module would then be flown back to Kennedy Space Center for refurbishment, while lunar samples would be routed to the [[Johnson Space Center]]'s (JSC) [[Lunar Receiving Laboratory]] for analysis.

===Orion asteroid mission===

{{For|the asteroid visit mission superseding the corresponding Constellation program mission|Asteroid Redirect Mission}}

The ''Orion Asteroid Mission'' was a proposed NASA mission to a [[Near-Earth object|near-Earth asteroid]] (NEA) which would use the standard [[Orion (spacecraft)|Orion spacecraft]], and a landing module based on a modified [[Altair (spacecraft)|Altair]] lunar lander. Most of its specific details are now deprecated by the cancellation of the Constellation Program and related designs. Such a mission could assess the potential value of water, iron, nickel, platinum and other resources on the asteroid; test possible ways to extract them; and possibly examine or develop techniques which could be used to protect the Earth from [[asteroid impact]]s. This would be the first crewed mission to any extraterrestrial body besides the Moon, and would represent a step towards a [[human mission to Mars]].

The mission would start in a similar fashion to the [[#Lunar sortie flights|lunar landing mission]] described above, using an Ares V to launch the landing module into [[Low Earth orbit]], followed by the launch of an Orion spacecraft, with a two- or three-person crew (as opposed to a four-person crew for lunar missions) on an Ares I rocket. Once the Orion spacecraft docked with the landing module and the [[Earth Departure Stage]] (EDS), the EDS would then fire again and propel the Orion spacecraft to a nearby near-Earth asteroid where the crew would then land and explore its surface.

Once the task was completed, the Orion spacecraft would then depart from the asteroid and, upon reaching the vicinity of Earth, would jettison both the [[service module]] and the landing module in a manner similar to that of [[Apollo 13]] before entering the atmosphere for a Pacific Ocean splashdown.<ref>{{cite magazine|url=http://www6.lexisnexis.com/publisher/EndUser?Action=UserDisplayFullDocument&orgId=574&topicId=100017159&docId=l:681629004&start=6|title=NASA's New Target|last=Stover|first=Dawn|magazine=[[Popular Science]]|date=November 2007|access-date=December 5, 2007|archive-url=https://web.archive.org/web/20120224065639/http://www6.lexisnexis.com/publisher/EndUser?Action=UserDisplayFullDocument&orgId=574&topicId=100017159&docId=l:681629004&start=6|archive-date=February 24, 2012|url-status=dead}}</ref>

===Orion Mars mission===
The ultimate goal of NASA's Constellation program was a crewed mission landing humans on [[Mars]] in the 2030s as a spiritual successor to the [[Apollo Applications Program]] in the 1960s. The mission would utilize the hardware of the Constellation Project, primarily the Orion spacecraft (or a variation based on the Orion), and the Ares V cargo-launch vehicle.<ref name="NASAMoonMars">[https://web.archive.org/web/19990903204757/http://www.spaceflight.nasa.gov/mars/ The Vision for Space Exploration]. NASA</ref>

A design study utilizing Constellation launch vehicles, known as [[Mars Design Reference Mission|Design Reference Architecture]] 5.0, was completed in 2009. In DRA 5.0, a Mars mission would have involved multiple launches of an Ares V rocket, as well as an Ares I to launch the crew. In the first Mars [[launch window]], two cargo payloads would be launched into Earth orbit, as well as a [[nuclear thermal rocket]] stage for each payload, in order to boost them to Mars. Alternatively, chemical (specifically liquid hydrogen/liquid oxygen) propellant stages could have been used, although this would have required more launches. One cargo payload would include a Mars Ascent Vehicle (MAV), as well as [[In-situ resource utilization]] equipment to generate propellant for the MAV. The second cargo payload would be a habitat that the astronauts would live in during the stay on the surface. In the next launch window, 26 months after the first, the crew would go to Mars in an interplanetary transfer vehicle with nuclear thermal rocket and propellant modules assembled in Earth orbit. Once at Mars, the crew would rendezvous with the Mars habitat in orbit, land on Mars, and explore for 500 days. The crew would use the MAV to return to their interplanetary vehicle in Mars orbit, which would then be used to return to Earth. The mission would conclude with the re-entry and landing of the Orion capsule.<ref name="DRA5">[http://www.nasa.gov/pdf/373665main_NASA-SP-2009-566.pdf Human Exploration of Mars Design Reference Architecture 5.0]. NASA</ref>

===Justification for a return to the Moon===
NASA lists a number of reasons for a human return to the Moon on its website:<ref>"[http://www.nasa.gov/mission_pages/exploration/mmb/why_moon.html Why The Moon?] {{Webarchive|url=https://web.archive.org/web/20100130021624/http://www.nasa.gov/mission_pages/exploration/mmb/why_moon.html |date=January 30, 2010 }}". December 4, 2006</ref>
#to extend human [[Colonization of the Moon|colonization]],
#to further pursue [[Moon science|scientific activities intrinsic to the Moon]],
#to test new technologies, systems, flight operations and techniques to serve future [[space exploration]] missions,
#to provide a challenging, shared and peaceful activity to unite nations in pursuit of common objectives,
#to expand the economic sphere while conducting research activities that benefit our home planet,
#to engage the public and students to help develop the high-technology workforce that will be required to address the challenges of tomorrow.

In the words of former NASA Administrator, [[Michael D. Griffin]],<ref>{{Cite news|url=https://www.washingtonpost.com/wp-dyn/content/article/2005/09/23/AR2005092301691.html|title=NASA's Griffin: 'Humans Will Colonize the Solar System'|date=September 25, 2005|newspaper=Washington Post|pages=B07}}</ref> "The goal isn't just scientific exploration.... It's also about extending the range of human habitat out from Earth into the [[Solar System]] as we go forward in time.... In the long run a single-planet species will not survive.... If we humans want to survive for hundreds of thousands or millions of years, we must ultimately populate other planets ... colonize the Solar System and one day go beyond."

A report published in June 2014 by the [[US National Academy of Sciences]] called for clear long-term space goals at NASA. The report said that the agency's current course invited "failure, disillusionment, and [loss of] the longstanding international perception that human space-flight is something that the United States does best." The report recommended that Mars be the next major goal of human space flight. Several possible paths for reaching the planet by 2037 were explored in the report, which noted that returning to the Moon would offer "significant advantages" as an intermediate step in the process.<ref>{{cite news|url=http://www.scientificamerican.com/article/humans-on-mars-as-soon-as-2037-should-be-nasas-goal-panel/|title=Humans on Mars as Soon as 2037 Should Be NASA's Goal: Panel|author=Lauren Morello, Nature magazine|website=[[Scientific American]]|access-date=October 23, 2014}}</ref>

The [[National Space Society]] (NSS), a private nonprofit, regards a return to the Moon as a high priority for the US space program, in order to develop the body of scientific knowledge of the Moon, particularly in regards to its potential for the creation of new industries, in order to provide further funding for further space exploration.<ref name=thirteen>{{cite web|last1=Tumlinson|first1=Rick|url=http://commerce.senate.gov/pdf/tumlinson102903.doc|title=Testimony to United States Senate|date=October 29, 2003|access-date=February 14, 2010|archive-url=https://web.archive.org/web/20160303172327/http://www.commerce.senate.gov/pdf/tumlinson102903.doc|archive-date=March 3, 2016|url-status=dead}}</ref>

==Budget and cancellation==

===Bush administration===
On January 14, 2004 President [[George W. Bush]] requested that NASA develop a proposal for continued crewed space exploration after the completion of the [[International Space Station]] and the planned retirement of the [[Space Shuttle]] program in 2010. This proposal<ref name="NASAaddress">{{cite web|url=https://history.nasa.gov/Bush%20SEP.htm|title=President Bush Announces New Vision for Space Exploration Program|access-date=June 17, 2009|publisher=[[NASA]]|date=January 14, 2004|archive-url=https://web.archive.org/web/20041018053912/https://history.nasa.gov/Bush%20SEP.htm|archive-date=October 18, 2004}}</ref> was to be a way to "establish an extended human presence on the Moon" to "vastly reduce the costs of further space exploration." Included in this would be the "harvesting and processing of [[lunar soil]] into rocket fuel or breathable air." According to Bush, experience gained could help "develop and test new approaches and technologies and systems"<ref name="NASAaddress" /> to begin a "sustainable course of long-term exploration."<ref name="BushView">{{cite news|title=FAQ: Bush's New Space Vision|url=http://www.space.com/news/bush_plan_faq_040115.html|work=space.com|access-date=February 7, 2008}}</ref>

NASA estimated that the original policy would cost $230 billion (in 2004 dollars) through 2025, including the Commercial Crew and Cargo program, which is separate from the Constellation program.<ref name="accountability1">{{Cite report|url=http://www.gao.gov/new.items/d09844.pdf|author=GAO|title=Constellation Program Cost and Schedule Will Remain Uncertain Until a Sound Business Case Is Established|publisher=Government Accountability Office|access-date=February 3, 2010}}</ref>  However, unsolved technical and design challenges made it impossible for NASA to provide a conclusive estimate.<ref name="accountability1"/>

===Obama administration===

Upon taking office, [[Barack Obama|President Obama]] declared Constellation to be "over budget, behind schedule, and lacking in innovation."<ref name="BBC cancels Moon return"/><ref name=FY2011_budget/><ref name="WashPost eliminates funds"/><ref>[http://www.bbc.co.uk/worldservice/news/2010/02/100201_obama_moon_wup_sl.shtml Obama scraps funding for Nasa's American Moon base mission]. BBC</ref>  A review concluded that it would cost on the order of $150 billion for Constellation to reach its objective if adhering to the original schedule.<ref>Kenneth Chang (27 January 2012), [https://www.nytimes.com/2012/01/28/science/space/for-a-moon-colony-technology-is-the-easy-part.html "For a Moon Colony, Technology Is the Easy Part"] ''[[The New York Times]]''</ref> Another review in 2009, ordered by President Obama, indicated that neither a return to the Moon nor a crewed flight to Mars was within NASA's current budget.<ref>{{Cite news|url=https://www.voanews.com/a/a-13-2009-08-26-voa54-68820852/413483.html|author=Art Chimes|title=Expert Group Says NASA Budget Too Small for Big Space Plans|publisher=VOA News|access-date=April 19, 2011}}</ref> The [[Augustine panel]] proposed various options, that included two primary destination points (the Moon and deep space), three different types of [[Comparison of super heavy lift launch systems|Super Heavy Launch vehicles]], and a robust research and development program that would include work on [[propellant depot]]s.<ref name="Augustine Report">{{cite web|last1=Augustine|first1=Norman R.|author-link1=Norman R. Augustine|title=Seeking a Human Spaceflight Program Worthy of a Great Nation|url=http://www.nasa.gov/pdf/396093main_HSF_Cmte_FinalReport.pdf|publisher=Review of U.S. Human Spaceflight Plans Committee|access-date=23 October 2014|date=October 2009|display-authors=etal|archive-date=February 16, 2019|archive-url=https://web.archive.org/web/20190216063908/https://www.nasa.gov/pdf/396093main_HSF_Cmte_FinalReport.pdf|url-status=dead}}</ref>

After reviewing the report, and following congressional testimony,<ref name="SBorenstein">{{Cite news|url=http://usatoday30.usatoday.com/tech/science/space/2009-09-15-return-to-moon_N.htm|author=Seth Borenstein|title=Return-to-moon plan gets boost on Capitol Hill|work=USA Today|access-date=September 17, 2009}}</ref> the [[Obama administration]] decided to exclude Constellation from the [[2011 United States federal budget]].<ref>[http://www.orlandosentinel.com/news/space/os-no-moon-for-nasa-20100126,0,2770904.story "Obama aims to ax Moon mission"] {{Webarchive|url=https://web.archive.org/web/20100129153048/http://www.orlandosentinel.com/news/space/os-no-moon-for-nasa-20100126,0,2770904.story |date=January 29, 2010 }}. Orlando Sentinel, January 27, 2010.</ref><ref>{{cite news|last=Santini |first=Jean-Louis |title=Obama trims US space ambitions |agency=[[Agence France-Presse|AFP]] |date=January 31, 2010 |url=https://news.yahoo.com/s/afp/20100131/ts_alt_afp/usspacepolitics |access-date=January 31, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100204201200/http://news.yahoo.com/s/afp/20100131/ts_alt_afp/usspacepolitics |archive-date=February 4, 2010 }}</ref> On February 1, 2010, the President's proposed budget was released, which included no funding for the project, and it became law on April 15, 2011.<ref name="BBC cancels Moon return">{{Cite news|url=http://news.bbc.co.uk/1/hi/sci/tech/8489097.stm|access-date=March 7, 2010|title=Obama cancels Moon return project |work=BBC News  | date=February 1, 2010 | first=Jonathan | last=Amos}}</ref><ref name=FY2011_budget>{{cite web|url=https://obamawhitehouse.archives.gov/sites/default/files/omb/budget/fy2011/assets/trs.pdf|access-date=March 7, 2010|work=[[Office of Management and Budget]]|title=Terminations, Reductions, and Savings|via=[[NARA|National Archives]]|df=mdy-all}}</ref><ref name="WashPost eliminates funds">{{Cite news|url=https://www.washingtonpost.com/wp-dyn/content/article/2010/01/31/AR2010013101058.html|title=NASA budget for 2011 eliminates funds for crewed lunar missions|newspaper=Washington Post|date=February 1, 2010|access-date=February 1, 2010 | first=Joel | last=Achenbach}}</ref>

President Obama hosted a Space Conference on April 15, 2010, in Florida.<ref>{{cite web|url=https://www.nbcnews.com/id/wbna35751461 |title=Obama to unveil 'ambitious plan' for NASA |work=NBC News |date=March 7, 2010 |access-date=May 18, 2010}}</ref> This came at a time when the president's administration was being criticized considerably for leaving the Constellation Program out of the 2011 budget. At the conference, President Obama and top officials, as well as leaders in the field of spaceflight, discussed the future of U.S. efforts in human spaceflight and unveiled a plan for NASA that followed the Augustine Panel's "Flexible Path to Mars" option,<ref>{{cite web|url=http://www.nasa.gov/pdf/396093main_HSF_Cmte_FinalReport.pdf|title=Review of U.S. Plans Committee|publisher=Human Space Flights Committee|access-date=July 7, 2010|archive-date=February 16, 2019|archive-url=https://web.archive.org/web/20190216063908/https://www.nasa.gov/pdf/396093main_HSF_Cmte_FinalReport.pdf|url-status=dead}}</ref> modifying President Obama's prior proposal to include the continuing development of the Orion capsule as an auxiliary system to the ISS and setting the year 2015 as the deadline for the design of a new Super Heavy Launch Vehicle. In October 2010, the NASA authorization bill for 2010 was signed into law which canceled Constellation.<ref>[http://www.space.com/9305-president-obama-signs-vision-space-exploration-law.html "President Obama Signs New Vision for U.S. Space Exploration Into Law"]. Space.com, October 11, 2010.</ref>  However, previous legislation kept Constellation contracts in force until passage of a new funding bill for 2011.<ref>[https://web.archive.org/web/20110420033120/http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news%2Fawx%2F2010%2F10%2F22%2Fawx_10_22_2010_p0-264465.xml&headline=Constellation%20Is%20Dead%2C%20But%20Pieces%20Live%20On "Constellation Is Dead, But Pieces Live On"]. ''Aviation Week'', October 26, 2010.</ref><ref name="space1"/>

=== Commercial Crew Vehicles and the Artemis program ===
NASA continues the development of the [[Orion (spacecraft)|Orion spacecraft]] for deep space travel. In an effort to reduce costs, it has contracted for private development of vehicles for use in low Earth orbit. Since May 2020, the [[Commercial Crew Development]] program has used the SpaceX [[SpaceX Dragon 2|Crew Dragon]] spacecraft to bring people to and from the International Space Station,<ref>{{Cite web|title=May 2020 – Commercial Crew Program|url=https://blogs.nasa.gov/commercialcrew/2020/05/|access-date=2021-11-16|website=blogs.nasa.gov|date=May 31, 2020 |language=en-US}}</ref> while Boeing's [[Boeing Starliner|Starliner]] spacecraft started operating in 2024 for the same purpose.<ref>{{cite web | url=https://spaceflightnow.com/2022/08/25/nasa-boeing-target-february-for-first-crew-flight-on-starliner-spacecraft/ | title=NASA, Boeing target February for first crew flight on Starliner spacecraft – Spaceflight Now }}</ref> Furthermore, it seeks [[human-rating]] for the [[launch vehicle|launch vehicles]] in the [[United States Air Force]] [[National Security Space Launch|Evolved Expendable Launch Vehicles]] program. Private spacecraft are also operating under the [[Commercial Resupply Services]] program bringing cargo to ISS.

The Orion spacecraft and Ares V (also Jupiter DIRECT family of rockets) was modified and reauthorized in 2010/2011 as the main payload of the [[Space Launch System]], and ''the'' Space Launch System, and the program was partially revived as the [[Artemis program]] in 2017.

==See also==
{{Portal|Spaceflight}}
* [[Artemis program]], similar program by NASA
* [[Space Launch System]]
* [[List of Constellation missions]]
* [[Crew Space Transportation System]] (CSTS), European-Russian counterpart of the CEV and the Vision of Space Exploration
* [[Exploration Systems Architecture Study]]
* NASA's [[Vision for Space Exploration]]
* [[Soviet Moonshot]]
* [[SpaceX Dragon]], Space capsule built by SpaceX for NASA's [[Commercial Resupply Services]] program.

==References==
{{Include-NASA}}
{{Reflist}}

;Further reading
* {{Cite book |editor-last=Mari |editor-first=Christopher |title=The Next Space Age |url=https://archive.org/details/nextspaceage0000unse |access-date=July 4, 2013 |series=The Reference Shelf |volume=80 |issue=5 |year=2008 |publisher=[[H. W. Wilson Company]] |location=[[Bronx, New York|Bronx]], New York |isbn=978-0-8242-1082-3 |lccn=2008036936 |url-access=registration }}

==External links==
{{Commons}}
* [https://web.archive.org/web/20060702073701/http://www.nasa.gov/constellation/ Official Constellation NASA web page]
* [http://www.nasa.gov/orion/ Official Orion NASA web page]
* [http://www.nasa.gov/ares/ Official Ares web page] {{Webarchive|url=https://web.archive.org/web/20160131060951/http://www.nasa.gov/ares/ |date=January 31, 2016 }}
* [http://www.tallgeorge.com/projectconstellation.php A Visual History of Project Constellation on tallgeorge.com]
* [https://www.youtube.com/watch?v=uUBhn3_P3hU Video animation – crewed Mission to Mars concept]

{{Project Constellation}}
{{NASA planetary exploration programs}}
{{NASA navbox|state=collapsed}}
{{US human spaceflight programs}}
{{Human missions to Mars}}
{{Use mdy dates|date=August 2011}}

{{Use American English|date=January 2014}}

[[Category:Constellation program| ]]
[[Category:Exploration of the Moon]]
[[Category:NASA programs]]
[[Category:Human missions to Mars]]
[[Category:Cancelled projects]]
[[Category:2000s in the United States]]