Editing Mars Direct (section)

==Revisions==
Since Mars Direct was initially conceived, it has undergone regular review and development by Zubrin himself, the [[Mars Society]], [[NASA]], [[Stanford University]] and others.

===Mars Semi-Direct===

[[File:Mars design reference mission 3.jpg|thumb|350px|Artist's rendering of Mars Semi-Direct/DRA 1.0: The Manned Habitat Unit is "docked" alongside a pre placed habitat that was sent ahead of the Earth Return Vehicle.]]

Zubrin and Weaver developed a modified version of Mars Direct, called Mars Semi-Direct, in response to some specific criticisms.<ref>{{cite conference | first1 = Robert M. | last1 = Zubrin | first2 = David B. | last2 = Weaver | title = Practical methods for near-term piloted Mars missions | citeseerx = 10.1.1.23.1915 | conference = AIAA93-2089,29th AIAA/ASME Joint Propulsion Conference | location = Monterey CA, United States | date = June 28–30, 1993 | doi = 10.2514/6.1993-2089 }}</ref> This mission consists of three spacecraft and includes a "Mars Ascent Vehicle" (MAV). The ERV remains in Mars orbit for the return journey, while the uncrewed MAV lands and manufactures propellants for the ascent back up to Mars orbit. The Mars Semi-Direct architecture has been used as the basis of a number of studies, including the NASA Design Reference Missions.

When subjected to the same cost-analysis as the [[NASA 90 Day Study|90-day report]], Mars Semi-Direct was predicted to cost 55 billion dollars over 10 years, capable of fitting into the existing NASA budget.

Mars Semi-Direct became the basis of the [[Design Reference Mission]] 1.0 of NASA, replacing the [[Space Exploration Initiative]].

===Design Reference Mission===
The NASA model, referred to as the [[Design Reference Mission]], on version 5.0 as of September 1, 2012, calls for a significant upgrade in hardware (at least three launches per mission, rather than two), and sends the ERV to Mars fully fueled, parking it in orbit above the planet for subsequent rendezvous with the MAV.

===Mars Direct and SpaceX===

With the potentially imminent advent of low-cost [[Heavy Lift Launch Vehicle|heavy lift capability]], Zubrin has posited a dramatically lower cost human Mars mission using hardware developed by [[space transport]] company [[SpaceX]].  In this simpler plan, a crew of two would be sent to Mars by a single [[Falcon Heavy]] launch, the [[Dragon spacecraft]] acting as their interplanetary cruise habitat.  Additional living space for the journey would be enabled through the use of inflatable add-on modules if required.  The problems associated with long-term weightlessness would be addressed in the same manner as the baseline Mars Direct plan, a tether between the Dragon habitat and the TMI (Trans-Mars Injection) stage acting to allow rotation of the craft.

The Dragon's heatshield characteristics could allow for a safe descent if landing rockets of sufficient power were made available.  Research at NASA's [[Ames Research Center]] has demonstrated that a robotic Dragon would be capable of a fully propulsive landing on the Martian surface.<ref>{{cite journal |last1=Gonzales |first1=Andrew A. |last2=Stoker |first2=Carol R. |title=An efficient approach for Mars Sample Return using emerging commercial capabilities |journal=Acta Astronautica |date=June 2016 |volume=123 |pages=16–25 |doi=10.1016/j.actaastro.2016.02.013|pmid=27642199 |pmc=5023017 }}</ref> On the surface, the crew would have at their disposal two Dragon spacecraft with inflatable modules as habitats, two ERVs, two Mars ascent vehicles and 8 tonnes of cargo.

===Other Studies===

The Mars Society and Stanford studies retain the original two-vehicle mission profile of Mars Direct, but increase the crew size to six.

[[Mars Society Australia]] developed their own four-person ''Mars Oz'' reference mission, based on Mars Semi-Direct. This study uses horizontally landing, bent biconic shaped modules, and relies on solar power and chemical propulsion throughout,<ref>{{cite conference |first1=D. |last1=Willson  |first2=J.D.A. |last2=Clarke |title=A Practical Architecture for Exploration-Focused Manned Mars Missions Using Chemical Propulsion, Solar Power Generation and In-Situ Resource Utilisation |conference=Proceedings of the 6th Australian Space Science Conference |conference-url=http://www.nssa.com.au/6assc/downloads/6assc%20proceedings.pdf |pages=186–211 |location=Canberra |date=19–21 July 2006 |url=https://marssociety.org.au/sites/default/files/library/willson-et-al.pdf}}</ref> where Mars Direct and the DRMs used nuclear reactors for surface power and, in the case of the DRMs for propulsion as well. The Mars Oz reference mission also differs in assuming, based on space station experience, that spin gravity will not be required.