crew would be dependent on hardware used in surface operations for a longer period of time on a long-stay mission.
Once the astronauts are on the Martian surface, there are a variety of operational scenarios that could be conducted by NASA. The simplest would be that astronauts land and never leave a stationary habitat. The most complex scenario could include astronauts using large, pressurized rovers to travel long distances from a base habitat to conduct extravehicular activities (EVAs). The committee anticipates that a long-stay mission would probably involve the following:
The use of unpressurized rovers similar to the lunar rover from the Apollo program;
Walking EVAs of several kilometers (round-trip) from the base camp; and
Pressurized rovers for transporting the astronauts greater distances. These could allow walking EVAs from the rover to take place, extending human presence even farther from the base camp.
The committee determined that it might best assist NASA by assuming that a long-stay mission to Mars will take place, as such a mission would levy the more stringent demand for the safety of astronauts while in the Martian environment. The reader should not conclude that this assumption implies an endorsement of the long-stay mission as a baseline mission, nor that the committee concluded that the long-stay mission is, in total, the least hazardous option.
As dictated by the statement of task (Appendix A), this report examines only those hazards to which astronauts will be exposed while on the surface of Mars. For instance, the committee did not address the need for so-called pinpoint landing on Mars, nor did it look at what technologies must be developed to accomplish pinpoint landing. However, the committee does address the terrain issues associated with setting down on the Martian surface.
Also, in accordance with the statement of task the committee considered only indigenous risks on Mars&— that is, those hazards presented by the Martian environment itself, not risks based on engineering design. For instance, the committee did not examine the reliability of habitat control systems or the likelihood of their failure, but it did consider the effects acidic airborne dust or soil might have on such control circuits.
This report does not examine the hazard of forward contamination, that is, transporting Earth life to Mars from a contaminated spacecraft. There are risks associated with forward contamination of Mars by life from Earth, including the possibility of generating false positive tests in life-detection experiments (NRC, 1992a, 2002). This could certainly be a critical issue when astronauts on the surface of Mars are looking for life. A false positive result could inadvertently require a long-term astronaut quarantine. While this is a topic for continued study and debate, it is beyond the scope of this committee 's charge.
Similarly, this report does not address technologies associated with in situ resource utilization (ISRU) or deep drilling. ISRU is the use of indigenous materials to produce consumables (e.g., breathable oxygen, propellant), thus reducing the tonnage of materials that must be transported to Mars. As such, ISRU does not deal directly with the “management of environmental, chemical, and biological risks, ” as set forth in the statement of task. Drilling systems might be used on human missions to Mars to explore the subsurface of Mars for scientific purposes. However, these systems are not critical to human survival. In fact, by using a drill, astronauts might become exposed to other indigenous Martian hazards. The hazards of subsurface probing by astronauts are discussed in detail in this report.
Other potential hazards the committee did not address involve the effects on astronaut health of a long-duration mission to Mars. A recent Institute of Medicine report states that the three most important health issues that have been identified for long-duration missions are radiation, loss of bone mineral density, and behavioral adaptation (IOM, 2001). The committee acknowledges that these issues are important, as is the need to ensure a benign social environment during a multiyear voyage, but again such considerations fall outside the scope of this report.
Even though there is no baseline mission defined for human missions to Mars, it is likely that rovers of some form will be used to perform functions critical to the safety of the astronauts. For example, human assistant rovers may carry life support equipment, while others robots, such as slow-moving scientific rovers, will likely perform mission-critical functions.