by connecting the cell science experiments to the ISS cooling loop to take advantage of ISS-wide efficiencies.⁵ For the protein crystal growth experiments, minimal vibration is important and can be obtained by installing an active rack isolation system (ARIS), which cushions the rack from ISS motion and the effects of surrounding equipment. ARIS and the cooling loop cannot be installed on the same rack. The cell science experiments require frequent exchanges of samples, which would also negatively affect the vibrational quiet of the protein crystal growth modules. If cell science and protein crystal growth equipment are housed within one rack, one or both of the disciplines will be forced to operate under suboptimal conditions. Another technical consideration is coordination with other related equipment on the ISS. It would be more efficient for the cell science work to be located near associated analytical equipment or storage facilities, while the importance of the monitoring, mounting, and freezing capabilities of the XCF means that the protein crystal growth experiments need to be closely coordinated with this facility.

The task group also carefully considered the needs of the various research communities expected to use the biotechnology facilities on the ISS. For cell science, there was concern that the amount of data and results generated from half a rack would not be substantial enough to maintain interest within the scientific community, whereas a full rack's worth of instrumentation could raise the program to a critical threshold. For protein crystal growth, the research community is still uncertain about the benefits of growing crystals in a microgravity environment, so the guest investigator program is undersubscribed and commercial interest is low. By focusing the protein crystal growth research efforts on biologically challenging problems and by emphasizing hardware capable of monitoring and preserving samples (the XCF, for instance), NASA could direct its resources to validating the program. The current volume commitment of half a rack of general macromolecular research is insufficient to establish the value of the crystal growth program, but a full rack, filled with peer-reviewed experiments that employ all types of available hardware and have access to the capabilities of the XCF, should be adequate to give the program a fair chance of success. If after several years the results from the protein crystal growth work have provided sufficient proof of microgravity's benefits and the academic and commercial demand for facilities on the ISS increases, then high-throughput hardware should be developed and the allotment of space on the ISS reconsidered based not only on the demand for macromolecular crystallography research volume but also on the results to that point from the cell science program. Alternatively, if the work done through the augmented commitment suggested here fails to clearly demonstrate the value of microgravity for work in structural biology, then the protein crystal growth program can justifiably be terminated.

Recommendation: The volume allotment for biotechnology work on the ISS should be redistributed as follows:

• The mounting, freezing, and diffracting equipment of the X-ray Crystallography Facility (XCF) should occupy one rack (as currently planned).

• The cell science work should occupy the entirety of what is currently designated the Biotechnology Facility.

• The rack currently assigned to the XCF growth equipment and managed by NASA Space Product Development should be officially dedicated to the peer-reviewed macromolecular research run out of the NASA Microgravity Research Division.