Chapter
Apr 26, 2012

The Distinction between an Interplanetary Vehicle and a Mars Surface Habitat

Publication: Engineering, Construction, and Operations in Space V

Abstract

This essay attempts to clear up a persistent confusion about the character of planetary surface exploration habitats and what they have and do not have in common with interplanetary vehicles. This essay argues that a Trans Mars Injection Vehicle (TMIV) or Trans Earth Injection Vehicle (TEIV) and a Mars Surface Habitat are so fundamentally different in functional and architectural character that no single design can serve both purposes. This confusion between interplanetary vehicles and surface habitats probably springs from the romantic sources of science fiction in which the Buck Rogers type pilot lands his space ship on the surface of the planet. The intrepid explorer descends a ladder in a pressure suit, and proceeds forthwith to the business of exploring. A recent incarnation of this tradition appears in Weaver & Duke's Mars Exploration Strategies, which describes a NASA "1993 Reference Mission" that depends extensively upon "commonality" between the TMIV habitat and the Mars surface habitat. In Weaver & Duke's vision, the crew launches direct to Mars à la Robert Zubrin's Mars Direct concept in a habitat and then "fly it down" to the Mars surface. The romantic paradigm of exploration from the landed spaceship—surface base carries many unexamined assumptions with it that appear even today in serious proposals for planetary exploration. Chief among these assumptions are: 1) that it makes sense to design a living environment that serves equally well in zero gravity and in a gravity field, 2) that it is economical and sensible to drag the mass of radiation shielding and zero-G countermeasures down to the surface after having paid a high price to place it in Low Earth Orbit and given it sufficient Δν to reach Mars, and 3) that the extravehicular exploration systems, including pressure suits, airlocks, and rovers require no design features specialized for the planetary surface and that they are essentially similar to zero-gravity EVA systems. Beyond these assumptions are a number of misunderstandings of the specific characteristics of an interplanetary vehicle. TABLE 1 summarizes these characteristics, showing the corresponding design solutions for both interplanetary vehicles and surface habitats. The Apollo Lunar Module (LM) had all the characteristics of an ascent/descent vehicle ensemble, but it also served as the surface habitat while the crew was on the lunar surface. The Apollo paradigm sometimes serves as an example of combining the lander with the surface habitat but it is an incorrect example because of the tremendous differences in surface stay times, as well as the transit times. Apollo astronauts typically spent less than 48 hours on the moon, with the total trip time less than a week. A First Mars Outpost crew will spend about 500 to 600 days on the surface, with a total trip time of 1000 to 1200 days. This much greater timeline creates not only a quantitative difference, but also a qualitative difference. There was no way that the LM could support the crew for even a few weeks, let alone nearly two years on the surface An expedition of almost two years requires a specialized habitat to support the crew in their necessary living and working activities. A generic or general purpose habitat will not serve this purpose on the surface nor on the interplanetary vehicle. The LM was a specialized vehicle, not intended to support a crew between the earth and the Moon. It's success during Apollo 13 was the exception that proves the rule. NASA needed to improvise several extraordinary procedures to enable the LM to serve as an interplanetary rescue vehicle. The Mars transit vehicle and the Mars surface habitat should be separate systems, optimized to their primary functions. This essay questions whether habitat commonality as a key to cost and risk reduction is really possible. It questions how the 1993 NASA Reference Mission and other variations of "Mars Direct" trade this reduction of potential risk for acceptance of known, actual and quantifiable danger, particularly in terms of radiation exposure on the Mars and Earth legs. Nor does the 1993 NASA Reference Mission provide for effective counter-measures against the debilitating effects of prolonged exposure to weightlessness. Yet, at the same time, they propose to bring down to the Mars surface all the accommodations within the habitat that presumably should provide protections from the interplanetary environment.

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Go to Engineering, Construction, and Operations in Space V
Engineering, Construction, and Operations in Space V
Pages: 984 - 996

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Published online: Apr 26, 2012

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Marc M. Cohen [email protected]
Arch.D., Architect, Advanced Projects Branch, Space Projects Division, Mail Stop 244.14, NASA.Ames Research Center, Moffett Field, CA 94035-1000.E-mail: [email protected]

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