Constellation program

The Constellation program 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, in which no crewed missions flew before its cancellation, 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, the Moon, and finally Mars—while the Mars goal also found expression in the name given to the program's booster rockets: Ares. 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.
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. 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." 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.
Subsequent to the findings of the 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 U.S. 2011 fiscal year budget. He then revised administration statements in a major space policy speech at Kennedy Space Center on April 15, 2010. On October 11, the signing of the NASA Authorization Act of 2010 shelved the program, with Constellation contracts remaining in place until Congress would act to overturn the previous mandate. In 2011, NASA adopted the design of its new Space Launch System.

Designs

One of the main goals of Constellation was the development of spacecraft and 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 crew capsule, the Earth Departure Stage secondary booster, and the Altair lunar lander.

Vehicles

Orion

The 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, and Boeing was selected to build its primary heat shield on September 15, 2006. 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 similar to the Apollo command module, but capable of sustaining four to six crew members; a cylindrical service module containing the primary propulsion systems and consumable supplies; and the Launch Abort System, 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 the Orion spacecraft 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

Altair 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 compared with the Apollo lander's. It was to stand tall and span 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 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. 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 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, thus allowing the use of Altair for both the lunar orbit insertion 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/CH₄–fueled engines on board the Block II Orion CSM and Altair ascent stage would have been adopted.

Propulsion

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 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

The Orion spacecraft would have been launched into a low Earth orbit by the Ares I rocket, developed by Alliant Techsystems, Rocketdyne, and Boeing. Formerly referred to as the Crew Launch Vehicle, the Ares I consisted of a single Solid Rocket Booster 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.
NASA began developing the Ares I low Earth orbit launch vehicle, returning to a development philosophy used for the original Saturn I, test-launching one stage at a time, which 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

Ares V would have had a maximum lift capacity of about to low Earth orbit, compared to the Space Shuttle's capacity of, and the Saturn V's. The Ares V would have carried about to the Moon, versus the Saturn V's lunar payload.
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 regeneratively-cooled.

Earth Departure Stage

The Earth Departure Stage 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

NASA planned to use the first vehicles developed in the Constellation Program for Earth-orbit tasks formerly undertaken by the Space Shuttle. But unlike the X-33 and other programs intended to replace the Shuttle, Constellation reused concepts from the Apollo and Space Shuttle programs.
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. 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 engine intended for use on the Ares V booster rocket was originally to be similar to the 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." 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.
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, 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.