for steps that NASA and the research community could take to maximize the research potential of the ISS.
When a major redesign of the ISS was announced in the spring of 2001, the new ISS configuration was initially referred to as the Rev. G design (the previous design had been Rev. F). Many aspects of the Rev. G design,6 which is now called “Core Complete,” are still highly fluid, and NASA has left open the possibility that it might eventually be able to restore some of the deleted elements of the Rev. F design in the eventuality that cost and schedule problems are resolved and money becomes available. Despite this possibility of restoration, in the past year NASA has moved forward rapidly with plans to adopt the Core Complete design, including extensive changes in shuttle schedules and facility funding. Tables 1.1 and 1.2 illustrate the task group’s understanding of many of the current differences between the Rev. F and Core Complete designs for ISS.
The most critical difference between the Rev. F design and the Core Complete design resulted from the deletion of the crew return vehicle, which reduced the number of crew that could live aboard the completed ISS, from six or seven to three. Since NASA has estimated that 2.5 crew members will be needed to maintain and operate the ISS, the number of crew available to perform scientific research drops from 3.5 or 4.5, to 0.5, a decrease of at least 85 percent. Of this remaining research time, the U.S. share is currently 50 percent7 and will drop to 38 percent once the laboratories of the international partners are brought into orbit.8 Based on NASA’s planned work week of 40 hours per crew member, a total of 20 hours would be devoted to research each week, with about 7.5 hours of this going to U.S. research. NASA data indicate that early ISS crews have chosen to work considerably longer than 40 hours per week, and some of that time has been devoted to performing additional experiment runs and procedures. However, this additional effort is unplanned and so the amount of supplementary science that can be obtained in this way is likely to be modest. NASA guidelines require that payload planning must be based on the assumption of a 40 hour week as this most accurately describes what can be accomplished on orbit. This assumption is further supported by the fact that NASA anticipates that crew time required for ISS maintenance and repair will rise on future missions as more elements are added to the ISS and the original elements accumulate hours of operation.
Since the release of the phase I report, NASA has reduced the number of planned shuttle flights for ISS to four flights per year. This may be an even more serious constraint on ISS science than the reduction in crew size. The task group has learned that NASA’s current analysis predicts that by the time the centrifuge accommodations module is launched,9 the entire upmass capacity of the four flights per year will be needed for the ISS logistics and maintenance hardware, leaving only limited capability for research outfitting and resupply. NASA is currently studying this issue, and few details are available at this time.
Also affecting the science capabilities of the completed ISS is the elimination of a number of research facilities from Rev. F, as shown in Table 1.2. Note that the loss of racks shown here does not capture the additional impact of deleted experiment modules, which are the functional experiment units that go into these racks. Most of these facilities and modules supported research in specific scientific fields and, as noted in the phase I report and discussed in detail in the chapters that follow, the impact of their elimination will vary by discipline. While the centrifuge, a key facility for life sciences research, is