Orion is a spacecraft design currently under development by the National Aeronautics and Space Administration (NASA). Each Orion spacecraft will carry a crew of four to six astronauts, and will be launched by the new Ares I launch vehicle. Both Orion and Ares I are elements of NASA's Project Constellation, which plans to send human explorers back to the Moon by 2020, and then onward to Mars and other destinations in the solar system.
Orion will launch from the same launch complex at Kennedy Space Center that currently launches the Space Shuttle. NASA will use Orion spacecraft for its human spaceflight missions after the last Shuttle orbiter is retired in 2010. Orion will initially handle logistic flights to the International Space Station starting at the end of 2014 or beginning of 2015, and after that it will become a key component of missions to the Moon and Mars.

Origin
The Orion Crew and Service Module (CSM) stack consists of two main parts: a conical Crew Module (CM), and a cylindrical Service Module (SM) which will hold the spacecraft's propulsion system and expendable onboard supplies. Both are based heavily on the Apollo Command and Service Modules (Apollo CSM) flown between 1967 and 1975, but include advances derived from the Space Shuttle program. "Going with known technology and known solutions lowers the risk," according to Neil Woodward, director of the integration office in the Exploration Systems Mission Directorate.

Design
The shape of the Orion Crew Module (CM) is a 70° cone, similar to that of the Apollo Command Module. The Orion CM will hold four to six crew members, compared to a maximum of three in the smaller Apollo CM. Despite its conceptual resemblance to the 1960s-era Apollo, Orion's CM will use several improved technologies, including:
An important planned feature that would have been introduced in the Orion CM was a new system employing a combination of parachutes and either retrorockets or airbags for capsule recovery. This would have allowed retrieval of the Orion CM on land, like the Russian Soyuz descent module and its derivatives, and eliminated the expensive naval recovery fleet employed on all Mercury, Gemini, and Apollo flights. However, NASA removed this feature in August 2007.
An "autodock" feature, like those of Russian Progress spacecraft and the European Automated Transfer Vehicle, with provision for the flight crew taking manual control of the vehicle in an emergency (Gemini, Apollo, and Shuttle required a pilot to manually control the spacecraft for docking).
Improved waste-management facilities, consisting of a miniature camping-style toilet and unisex "relief tube" used on the Space Shuttle (whose system was based on that used on Skylab) and the International Space Station (based on the Soyuz, Salyut, and Mir systems). This eliminates the use of the much-hated plastic "Apollo bags" used by the Apollo crews.
A nitrogen/oxygen (N₂/O₂) mixed atmosphere at either sea level (101.3 kPa; 14.7 psi) or slightly reduced (55.2 to 70.3 kPa; 8.0 to 10.2 psi) pressure. Crew Module
Like its Apollo predecessor, the Orion Service Module (SM) has a cylindrical shape, but the new Orion SM will be larger, shorter, and lighter. It too will be constructed from the same Al-Li alloy as the Orion CM, and will feature a pair of deployable circular or rectangular solar panels (a final decision on their design has not yet been made), eliminating the need to carry fuel cells and the associated hardware—mainly tanks containing liquid hydrogen [LH₂]—needed for their operation. The spacecraft's main propulsion system is a Delta II upper stage engine using hypergolic propellants (nitrogen tetroxide and monomethyl hydrazine) drawn from spherical, helium-pressurized titanium tanks. The SM Reaction Control System (RCS — the spacecraft's maneuvering thrusters) will also be pressure-fed, and will use the same propellants. NASA believes the SM RCS would be able to act as a backup for a trans-Earth injection (TEI) burn in case the main SM engine fails. The SM's twin spherical "slush" LOX tanks and a single tank of liquid nitrogen (LN₂) will provide the crew with breathing air during the majority of the mission, while a "surge tank" located in the Orion CM itself will provide the crew with 2 to 4 hours (depending upon the number of crew members) of the same breathing air after SM jettison. Lithium hydroxide (LiOH) cartridges will recycle the spacecraft's environmental system by "scrubbing" the carbon dioxide (CO₂) exhaled by the astronauts from ship's air and adding fresh oxygen and nitrogen, which is then cycled back out into the system loop. Because of the elimination of the fuel cells and LH₂ tanks, a large tank of potable water will be carried in both the CM and SM that will both provide drinking water for the astronauts and (mixed with glycol) cooling water for the electronics. A system identical to that used in the ISS will allow the astronauts to recycle both waste water and urine into glycol-mixed cooling water for the electronics.
The SM also mounts the spacecraft's waste heat management system (its radiators) and the aforementioned solar panels. These panels, along with backup batteries located in the Orion CM, will provide a total of 28 V (dc) in-flight power to the ship's systems. This is similar to the voltage used on the Apollo spacecraft during flight.

Service Module
See also: Orion abort modes
In the event of an emergency on the launch pad or during ascent, a launch escape system called the Launch Abort System (LAS) will separate the Crew Module from the launch vehicle using a rocket-powered launch abort motor. On July 10, 2007, Orbital Sciences -- the contractor for the LAS -- awarded Alliant Techsystems (ATK) a $62.5 million sub-contract to, "design, develop, produce, test and deliver the launch abort motor." ATK intends to use an innovative "reverse flow" design for the motor.

Launch Abort System
In late July of 2006 NASA's second design review resulted in major changes to the spacecraft design.

Design revisions and updates
See also: Exploration Systems Architecture Study#Criticism

Criticism
The Space Frontier Foundation has asserted that the $3.9 billion initial phase of the Orion contract essentially duplicates the functionality of NASA's $500 million Commercial Orbital Transportation Services program.

Acquisition strategy

Main article: Exploration Systems Architecture Study Exploration Systems Architecture Study

Main article: Crew Exploration Vehicle Competition and proposals

Testing
NASA will perform environmental testing of Orion from 2007 to 2011 at the Glenn Research Center Plum Brook Station in Sandusky, Ohio. The Center's Space Power Facility is the world's largest thermal vacuum chamber.

Environmental testing
NASA will perform a series of six Abort Flight Tests between the fall of 2008 and the end of 2011 at the United States Army's White Sands Missile Range (WSMR), New Mexico. The Orion AFT subproject includes two pad abort tests and four ascent abort tests. The four ascent aborts are planned to be flown from a special test launch vehicle, the Orion Abort Test Booster. The Orion Abort Flight Tests are similar in nature to the Little Joe II tests performed at WSMR between September 1963 and January 1966 in support of the development of the Apollo program's Launch Escape System.

Abort Flight Test (AFT)
NASA hopes to follow this schedule in development of the Orion:
NASA initially established that it would initiate a phased retirement of the Space Shuttle, which would have begun with the retirement of one orbiter, Atlantis, in 2008. This decision was later changed; all three remaining shuttles would keep flying until 2010. In the meantime, NASA engineers would work to upgrade the current launch facilities to work with the next generation shuttle-derived launch vehicles.
2014 (September) — First manned flight of Orion in Earth orbit.
2015–2018 — First unmanned flight of Lunar Surface Access Module (LSAM).
2016–2018 — First manned flight of LSAM.
2019 — First manned lunar landing with Orion/LSAM system.
2020 — Start of planning for Mars missions Schedule
After the replacement of Sean O'Keefe, NASA's procurement schedule and strategy has completely changed, as described above. In July 2004, before he was named NASA administrator, Michael Griffin participated in a study called "Extending Human Presence Into the Solar System" Possibilities for future CEV development
Rather than designing a CEV solely for the earliest lunar landing possible, the report recommends developing the CEV in two Blocks. The Block I CEV would be suitable for LEO missions only and would be developed as quickly as possible to avoid the gap between the currently scheduled Shuttle retirement in 2010 and CEV flights starting in 2014. It would carry a crew of 4–6 astronauts. The report recommends the development of a shuttle-derived CEV launch vehicle based on the "Shuttle Solid Rocket Motor with a new liquid propellant upper stage" The report suggests the use of expendable launchers, either foreign vehicles such as the Ariane and Proton, or a new Shuttle-derived, heavy-lift launch vehicle to complete the ISS after Shuttle retirement. The Block I CEV could also act as an ISS Crew Return Vehicle, allowing crews of more than three to be supported. Stage I is to be implemented by 2010.

Stage II
In Stage III, human-rated landers are developed to allow landings on both the Moon and Mars. Since the Block II CEV should be capable of flights to both these destinations, lunar and Mars landings could begin simultaneously, with the experience gained from exploring the four destinations referenced in Stage II. These landings would begin in 2020.

Stage III
Although Orion development is in an early stage and it remains to be seen what form it will finally take, NASA is apparently taking exactly the steps recommended for the implementation of Stage I of the report. Therefore, it is likely that the three-stage plan suggested in this report will be the plan for the actual Project Constellation. Although it appears that the plan will not be followed exactly, it is possible that elements of it will still be used as a baseline for Constellation exploration strategies (for example, Stage I appears to have become a NASA strategy). The plan does not allow for lunar landings as early as 2015, as suggested in the Bush vision, but does permit an early Mars landing in 2020, contemporaneous with lunar landings by that date.
Building 9 at the Johnson Space Center in Houston, Texas contains a full-scale mock-up simulator of the Orion "capsule". As of July 26, 2006, internal components were being fitted.

Summary
President Bush's budget request for Fiscal Year 2005 included "$428 million for Project Constellation ($6.6 billion over five years) to develop a new crew exploration vehicle". The budget for FY2005 was confirmed by the Congress in November 2004 with full funding for the CEV.
The FY2006 budget request includes $753 million for continuing development of the CEV. As of 2005 the total development costs of the CEV are estimated at $15 billion.

Funding
In June 2006 the NASA assigned two "notional" names, Altair and Artemis, to the CSM and LSAM spacecraft. However, on 20 July 2006, it was reported In October 2006 NASA announced the official name "Artemis" for the LSAM spacecraft.
Further revisions in nomenclature by NASA are possible before the launch of the first Orion mission.

Orion nomenclature (October 2006)

Cleon Lacefield, Orion program manager for LM
Kliper, Russian concept for replacement of the Soyuz Spacecraft
Crew Space Transportation System, European-Russian counterpart of the CEV
Orbital Space Plane
Shuttle Derived Launch Vehicle, Current front-runner launch vehicle for the CEV
Exploration Systems Architecture Study
Atmospheric reentry
Colonization of the Moon
Colonization of Mars