The most challenging radiation in space consists of fully ionized atomic elements with high energy for which only the few lowest energy ions can be stopped in shielding materials. The health risk from exposure to these ions and their secondary radiations generated in shield materials is poorly understood since there are few human data and a systematic study in relevant animal model systems has not been made. The accuracy of risk prediction is described as the major limiting factor in the management of space radiation risk. The expected impact of systematic studies is examined using the limited available biological data and models. Given the limitations of current predictions, models must be developed that are able to incorporate the required fundamental scientific data into accurate risk estimates. The important radiation components that can be provided for laboratory testing are identified. The use of ground-based accelerator beams to simulate space radiation is explained and quantitative scientific constraints on such facilities are derived. Three facilities, one each in the United States, in Germany and in Japan, currently have the partial capability to satisfy these constraints. A facility has been proposed using the Brookhaven National Laboratory Booster Synchrotron in the United States; in conjuction with other on-site accelerators, it will be able to provide the full range of heavy ion beams and energies required.