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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Constellation program | 2/6 | https://en.wikipedia.org/wiki/Constellation_program | reference | science, encyclopedia | 2026-05-05T12:41:43.933180+00:00 | kb-cron |
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 1,120 cubic feet (32 m3) compared with the Apollo lander's 235 cubic feet (6.7 m3). It was to stand 32 feet (9.8 m) tall and span 49 feet (15 m) 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. 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 (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/CH4–fueled engines on board the Block II (lunar) 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 (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 ====
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. 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. 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 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 188 metric tons (414,000 lb) to low Earth orbit (LEO), compared to the Space Shuttle's capacity of 24.4 metric tons (54,000 lb), and the Saturn V's 118 metric tons (260,000 lb). The Ares V would have carried about 71 metric tons (157,000 lb) to the Moon, versus the Saturn V's 45 metric tons (99,000 lb) 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 (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 ===