Open Questions And Outlook

In spite of more than 30 years of research on the biological effects of radiation in space, there are still experimental data are lacking for several essential issues as follows:

a. Concerning sparsely ionizing radiation:

• To what extent do the factors of the spaceflight environment interact with the induction and/or expression of late effects, especially during long-duration missions?

b Concerning densely ionizing radiation:

• To what extent do the factors of the spaceflight environment interact with the early effects of this radiation component?

• To what extent differ late effects produced by the densely ionizing component from those of sparsely ionizing radiation with respect to severity and/or kinetics of expression?

• To what extent are these late effects modified by the factors of the spaceflight environment?

• To what extent are the effects of nuclear reaction stars comparable to those produced by HZE particles, and if not, in which of the above three cases do they differ?

c. For all radiation components in space:

• If interactions of the space radiation environment and the other factors of the spaceflight environment do exist, what are the relative contributions of these factors?

None of these questions can be adequately resolved by spaceflight experiments alone. Neither in spaceflight experiments nor in terrestrial experiments can these challenges be attacked by experiments with human subjects. Their solution therefore must rely on results from either animal experiments, tissue culture in vitro experiments, or experiments with other biological test organisms suitable for investigations on specific fundamental questions. On this empirical basis, theoretical models are to be established in order to render extrapolation to radiation effects in humans. Until these radiation mechanisms are satisfactorily well understood, comprehensive dosimetry of the radiation in space should be a sine qua non for all human spaceflights.

As a consequence, substantial research and development activities are required in order to provide the basic information for appropriate integrated risk managements, including efficient countermeasures. These activities include but are not limited to:

a. Research during long-duration orbital spaceflights, with emphasis on the ISS or other human missions in LEO;

b. Research on robotic precursors missions to the Moon and Mars, including orbiters and landing vehicles;

c. Research during ground-based simulation studies using heavy ion accelerators (Figure 7-20).

Research Area

Task

Approach

Risk assessment

Determine depth dose distribution inside habitats and human body

Human phantoms inside and outside of ISS, e.g., MATROSHKA

Determine interactions of space radiation and other space factors, e.g., microgravity

Cell and animal experiments with artificial radiation source

Surveillance

Determine individual biological significant radiation dose

Develop:

(a) personal dosimeters (passive and active)

(b) biodosimetry concepts, e.g,. chromosome aberration

(c) biodiagnostic systems, e.g., cellular biosensors

Countermeasures

Determine role of diet in radiation responses

Interact with nutrition to develop dietary concepts for minimizing oxidative stress

Table 7-03. Research required in LEO in preparation of future human exploration missions in the field of radiation biology and radiation health (Horneck et al. 2003a).

Table 7-03. Research required in LEO in preparation of future human exploration missions in the field of radiation biology and radiation health (Horneck et al. 2003a).

As outlined in Table 7-03, substantial information can be gained from studies in LEO to obtain a solid base when approaching the next frontier, namely human missions beyond the Earth orbit to the Moon or Mars. This information will be useful to optimize risk assessment, surveillance, and countermeasures for the crew. Robotic precursor missions to the Moon and Mars are required to improve and validate transport codes for prediction of solar particle and cosmic heavy ion radiation doses inside a given shielding distribution at a given position in interplanetary space at a given time within the solar cycle. Robotic lander missions will provide data on the radiation climate on the surface, and modes and efficiency of natural (e.g., regolith) and artificial (e.g., habitat) shielding.

Whereas radiobiological research on board the ISS is an inevitable condition for all questions concerning the possible impact of microgravity, hypogravity, radiation, other space specific factors, and potential interactions between them, several basic questions can be more appropriately addressed by ground-based studies using heavy ion accelerators. These studies include improving and validating transport codes, determining the effects of single heavy ions by applying microbeams, and determining the interaction of radiation and microgravity by installing facilities providing simulated functional microgravity at heavy ion accelerators.

Lander.s

Radiation

Tele med ici ne CELSS Autonomous systems

Ground simulations

Radiation Gravity Psychology CÉI.SS

Radial ion Gravity Psychology CHLSS

Figure 7-20. Roadmap in human health issues for ESA's exploration program, as recommended in the HUMEXstudy (Horneck et ai 2003a).

Lander.s

Radiation

Tele med ici ne CELSS Autonomous systems

Ground simulations

Radiation Gravity Psychology CÉI.SS

Radial ion Gravity Psychology CHLSS

Figure 7-20. Roadmap in human health issues for ESA's exploration program, as recommended in the HUMEXstudy (Horneck et ai 2003a).

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