page_title: Altair (spacecraft)
section_title: Engines
hierarchical_section_title: Altair (spacecraft) / Description / Engines
caption_attribution_description: English: None.
context_page_description: The Altair spacecraft, previously known as the Lunar Surface Access Module or LSAM, was the planned lander spacecraft component of NASA's cancelled Constellation program. Astronauts would have used the spacecraft for landings on the Moon, which was intended to begin around 2019. The Altair spacecraft was planned to be used both for lunar sortie and lunar outpost missions. On February 1, 2010, U.S. President Barack Obama announced a proposal to cancel the Constellation program, to be replaced with a re-scoped program, effective with the U.S. 2011 fiscal year budget.
context_section_description: Altair intended to utilize current cryogenic technologies for the descent stages and hypergolic technologies for the ascent stage. The Apollo LM, as advanced in both computer and engineering technology in its day, used hypergolic fuels in both of its stages, chemicals that combust on contact with each other, requiring no ignition mechanism and allowing an indefinite storage period. Both the cryogenic and hypergolic systems, like that of the Apollo LM, would be force-fed using high-pressure helium, eliminating the need for malfunction-prone pumps utilized in most rocket technology.
  Mission requirements obliged the vehicle to be able to descend from an equatorial or high-inclination lunar orbit to a polar landing site, along with bringing it and the Orion spacecraft into lunar orbit, as the Orion spacecraft's onboard Aerojet AJ-10 rocket engine and the amount of fuel it carried would have been insufficient to brake the Orion/Altair stack into lunar orbit (also necessary if flown without Orion for cargo-only missions). The new lander would have been powered by a modified RL-10 engine (currently in use on the upper stage of the Delta IV rocket and Centaur upper stage of the Atlas V rocket), burning liquid hydrogen (LH₂) and liquid oxygen (LOX) for the descent phase. A single AJ-10 rocket engine, like that on the Orion, was intended to power the ascent stage.
  Originally, NASA wanted to power the ascent stage using LOX and liquid methane (LCH₄), RS-18, as future missions to Mars would require the astronauts to live on the planet. The Sabatier Reactor could be used to convert the carbon dioxide (CO₂) found on Mars into methane, using either found or transported hydrogen, a catalyst, and a source of heat. Cost overruns and immature LOX/LCH₄ rocket technology forced NASA to stick with cryogenic and hypergolic systems, although later variants of Altair were meant to serve as testbeds for methane rockets and Sabatier reactors after a permanent lunar base was established.
caption: Cargo variant of Altair
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