Editing Mars Direct (section)

==Mission scenario==

===First launch===

The first flight of the Ares rocket (not to be confused with the similarly named rocket of the now defunct [[Constellation program]]) would take an uncrewed '''Earth Return Vehicle''' to Mars after a 6-month cruise phase, with a supply of hydrogen, a chemical plant and a small [[nuclear reactor]]. Once there, a series of chemical reactions (the [[Sabatier reaction]] coupled with [[electrolysis]]) would be used to combine a small amount of hydrogen (8 tons) carried by the ''Earth Return Vehicle'' with the [[carbon dioxide]] of the Martian atmosphere to create up to 112 tonnes of methane and oxygen. This relatively simple chemical-engineering procedure was used regularly in the 19th and 20th centuries,<ref>{{cite web |url= https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1912/press.html |title= The Nobel Prize in Chemistry 1912 |author= Professor H.G. Söderbaum |date= 2 Sep 2012  |access-date= 2 September 2012}}</ref> and would ensure that only 7% of the return propellant would need to be carried to the surface of Mars.

96 tonnes of methane and oxygen would be needed to send the ''Earth Return Vehicle'' on a trajectory back home at the conclusion of the surface stay; the rest would be available for Mars rovers. The process of generating fuel is expected to require approximately ten months to complete.

===Second launch===

Some 26 months after the ''Earth Return Vehicle'' is originally launched from Earth, a second vehicle, the '''Mars Habitat Unit''', would be launched on a 6-month long [[low-energy transfer]] trajectory to Mars, and would carry a crew of four astronauts (the minimum number required so that the team can be split in two without leaving anyone alone). The Habitat Unit would not be launched until the automated factory aboard the ERV had signaled the successful production of chemicals required for operation on the planet and the return trip to Earth. During the trip, [[artificial gravity]] would be generated by tethering the Habitat Unit to the spent upper stage of the booster, and setting them rotating about a common axis. This rotation would produce a comfortable 1&nbsp;''g'' working environment for the astronauts, freeing them of the debilitating effects of long-term exposure to [[weightlessness]].<ref name = "Mars Underground" />

====Landing and surface operations====

Upon reaching Mars, the upper stage would be jettisoned, with the Habitat Unit [[aerobraking]] into Mars orbit before soft-landing in proximity to the ''Earth Return Vehicle''. Precise landing would be supported by a radar beacon started by the first lander. Once on Mars, the crew would spend 18 months on the surface, carrying out a range of scientific research, aided by a small rover vehicle carried aboard their Mars Habitat Unit, and powered by the methane produced by the Earth Return Vehicle.

====Return and follow-up missions====

To return, the crew would use the ''Earth Return Vehicle'', leaving the Mars Habitat Unit for the possible use of subsequent explorers. On the return trip to Earth, the propulsion stage of the Earth Return Vehicle would be used as a [[counterweight]] to generate artificial gravity for the trip back.

Follow-up missions would be dispatched at 2 year intervals to Mars to ensure that a redundant ERV would be on the surface at all times, waiting to be used by the next crewed mission or the current crew in an emergency. In such an emergency scenario, the crew would trek hundreds of kilometers to the other ERV in their long-range vehicle.