tainty in terms of risk estimates, reported confidence intervals, or narrative discussion.

Heuristic solutions result from an informed set of principles or rules that an individual or group uses for decision making. Although such rules may rely on an empirically derived knowledge base, it is important to understand that experience, judgment, personal philosophies, and external pressure can affect a heuristic, causing different groups to reach different conclusions. Given that it is formulated from a set of risks derived from discussions among different teams of disciplinary experts, the BR is not immune to such effects. However, ongoing discussions among the Bioastronautics Science Management Team, the Office of the Chief Health and Medical Officer, the Astronaut Office, flight surgeons, and research management have led to views of the risks of space flight that are generally similar, but not identical, within and outside NASA.

For example, the Institute of Medicine (IOM, 2001) panel that authored Safe Passage: Astronaut Care for Exploration Missions selected four risks that earned the panel’s highest rating of “severe” for a flight to Mars:

1. Trauma and acute medical problems

2. Carcinogenesis caused by radiation

3. Human performance failure because of poor psychosocial adaptation

4. Acceleration of age-related osteoporosis

The version of the BR originally supplied to the IOM for review (NASA, 2004) used similar language, listing the most serious risks for a Mars mission as the following:

1. Addressing the requirements for autonomous medical care

2. Providing radiation protection

3. Maintaining behavioral health and performance

4. Bone loss–related issues

5. Advanced human support technology

Flight surgeons and astronauts provided the BR review panel with a narrower, operationally focused set of priorities for exploration (Baker et