Guidelines and Capabilities for Designing Human Missions

App ro a che s to Avoid:
Although some activities are inherently dangerous, no human endeavor is completely free of risk. Space exploration is arguably dangerous; because human space exploration may threaten the lives of many people at taxpayers’ expense, NASA is expected to take every possible measure to reduce risk. Despite this, reducing the crewmembers’ risk to zero is nearly impossible, and any reduction often comes at significant cost. Occasionally, the following solutions have been advanced to circumvent the more difficult decisions in mission design and risk management. These solutions can be deceptively simple and unrealistic if they are not examined carefully. We thus provide, below, a brief discussion of each to discourage this kind of thinking in future mission
design and planning.

Accepting current risk: Just because a relatively large number of candidates, despite the danger and personal risk, are willing to journey to Mars or beyond does not mean that mission, programmatic, and personal risks can be ignored.
! Crew selection: Carefully selecting a crew for extraordinary resistance to the dangers and difficulties of the space environment is not feasible. Statistics refute this for at least two reasons: (1) if the top 10% of individuals are selected by a series of 20 independent scales, at least 1020 individuals must be tested to find one person who would rate in the top 10% of all 20 scales; and (2) variability in the human population is not sufficient to provide significant protection against the many challenges of exploration missions. This is because we—from geniuses to religious leaders to sports starsshare many of the same traits and are subject to many of the same weaknesses.