NASA, DOD, and the European Launcher Development Organization (ELDO) have studied a broad spectrum of Space Tug configuration candidates and operational modes in recent years. These studies established the feasibility and desirability of high performance, low operating cost cryogenic or storable propellant upper stages. The ELDO Tug investigations were discontinued at midyear 1972 by the European Space Conference (ESC) following the U.S. decision to withdraw the Tug system from consideration as a candidate for European post-Apollo development effort. As a consequence, NASA has initiated a significant effort in this area to generate system, technology support, and cost and operational data for planning purposes. This spring NASA and DOD have undertaken a cooperative project to evaluate likely alternatives for providing desired upper stage capability. This set of studies will analyze alternative concepts for achieving the required system characteristics within projected schedule and budgetary constraints. Alternatives of interest include:

1. Use of existing expendable stages modified for operational use with the Shuttle, to be followed by a Space Tug developed for a later operational date; 2. Use of existing stages, modified to provide for increased propellants and limited reuse capability, to be followed by a Space Tug with the desired capability, developed for a later operational date; and

3. Development and use of a low development cost, reusable, interim Space Tug, available at Shuttle initial operations that could evolve to a system with greater capabilities at a later date. (Phased development as available resources permit.)

Figure 184 (see p. 458) illustrates key milestones for the basic candidate program options under evaluation. Numerous program and configurational variations are being considered in the total effort. The NASA and DOD fiscal year 1973 Tug systems study effort is directed toward a joint comprehensive assessment of these alternative Tug program options that span the national range of interest, considering mission requirements and configuration capabilities as well as the re

CANDIDATE TUG PROGRAM OPTIONS

CALENDAR YEARS

1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983

sources and schedule constraints. Among the major tasks being undertaken are: analyses of mission abilities and requirements; subsystem, configuration and operational analyses; development plans, technology implications; interface ground and flight support systems requirements; cost relationships; and identifications of Space Tug development program definition options. A significant inhouse effort that is, engineering systems analyses, development program planning and supporting technology studies-is also underway at the Marshall Space Flight Center.

In fiscal year 1974 supporting engine design/performance studies will be conducted with a detailed examination of the interim Tug system requirements. Major areas to be considered include performance improvements to existing engines and an understanding of the implications of refurbishment and feasibility. Also in the fiscal year 1974 program further programmatic data on low cost development programs will be generated considering various approaches to the design, fabrication, and testing of development program hardware as well as facility requirements. Tug configuration definition and user requirements analysis will continue to support the generation of systems requirements and technology information to the depth necessary for development program planning. This effort will directly support the MSFO inhouse Tug effort in fiscal year 1974.

SUMMARY

Current study efforts will serve to refine the understanding and evaluation of the development options and technology requirements for the interim and the later, greater capability, Space Tug systems. The feasibility of achieving, at low cost, an acceptable interim Tug system that could evolve to a system with the desired capabilities at a later date is the principal object of these study efforts.

SPACE LIFE SCIENCES

INTRODUCTION

Now, at the conclusion of the Apollo program, we have an excellent opportunity to review what we have learned from space flight so far. We are vastly

wiser in many medical and technical areas for our decade in space. Much has been learned about the effects of the space flight environment upon man. We have found that some body systems respond to space flight factors, perhaps to weightlessness itself, with changes sufficiently marked to be observable in the period immediately following space flight. Occasionally changes have been noticeable during the inflight period of the mission. None of these changes has been of such a severity as to cause any real concern for man's safety in space, but all changes are, nonetheless, being watched closely lest they have implications for long-duration flight.

Cardiovascular system changes were the first to be observed and have exhibited the most noticeable alterations. Cardiovascular deconditioning, or reduced tolerance on return to Earth's gravity, has been the most consistently observed effect. The condition is reversible and appears to have no serious implications. The decrements in work capacity seen after space flight may be another reflection of the cardiovascular and hemodynamic changes which occur. Rare irregularities in heart beat have been noted, but these seem to be controllable. A decrease in heart size has been noted in both U.S. and Soviet crews. Bone density may be minimally reduced after space flight, and some Soviet crewmen have experienced muscular difficulties postflight. Both astronauts and cosmonauts have also reported sensations resembling sea sickness during spaceflight. On the whole, however, U.S. astronauts do not appear to be excessively plagued by motion sickness symptoms. The growth of opportunistic microorganisms appears to be favored in the space environment.

It should be stressed that none of the physiological changes noted have caused any severe or lasting difficulty to the individuals exhibiting these changes. Nevertheless, because we do not know whether these alterations will become more marked with increased duration of space flight exposure, countermeasures are being sought. Fortunately, cardiovascular system responses which, as we have noted, show the most marked change also appear to be the most amenable to regulation by the application of inflight countermeasures, such as the use of lower body negative pressure. Medication, in our experience, has not proved to be of value in treating either the cardiovascular deconditioning or the loss of exercise capacity noted postflight. Countermeasures are also being investigated for the small bone density losses noted. There is some early indication from bedrest studies that combinations of calcium and phosphate help to forestall the loss of calcium from the bones.

LIFE SCIENCES IN SKYLAB

During the Skylab program for the first time, inflight measurements will be made of orthostatic tolerance to reveal the status of the cardiovascular system in weightlessness. These will be made with a device which duplicates the physiological effect of gravity while the astronaut is experiencing, and becoming adapted to, weightlessness. The apparatus, known as the lower body negative pressure (LBNP) device, is illustrated in figure 185 (see p. 460). The study subject is placed in the device and a mild, fully controllable negative pressure is applied from the waist down. Although the subject—and the device-remain in the horizontal position, the negative pressure creates a force on the circulatory blood volume, tissues of the lower extremities, and viscera, producing the same reflexes as would gravity in the upright position. As the negative pressure is applied, a time profile is obtained for various physiological measurements, such as EKG and blood pressure, the same measurements made during the tilt table studies conducted on the ground to test for orthostatic tolerance pre- and postflight. Besides being independent of gravity, the LBNP device is more precise than the tilt table for correlating cardiovascular responses with the degree of circulatory stress.

Typical results of orthostatic testing during the Apollo program are shown at the left side of figure 185. The higher heart rates, lower blood pressures, and increased leg volumes are indicative of pooling of blood in the extremities during postflight LBNP tests. In ground studies with subjects at bed rest, used as an analog of weightlessness, we are evaluating the possibility of employing LBNP with longer exposure and different pressures as a countermeasure to orthostatic intolerance.

The LBNP experiment is just one of 16 medical experiments to be conducted during Skylab missions. Another important experiment will investigate metabolic activity, or work capacity, inflight. Reduced work capacity has been a consistent postflight finding. While this reduction is fairly quickly restored and preflight levels are ultimately reached, even temporarily reduced performance capability engenders some concern since it may be an indication of deconditioning of the cardiovascular and musculoskeletal systems. To learn more about the nature and extent of the effects of space flight on metabolic processes, a metabolic experiment is included in the Skylab payloads. The basic objectives of the Skylab metabolic experiment will be: to determine the difference in metalolic cost (energy expenditure) in performing identical tasks of equal workload on Earth and in the weightlessness of space; to determine if man's metabolic effectiveness in doing mechanical work is progressively impaired by exposure to the space environment; and to provide inflight data reflecting the physiological status of the crewmembers. This will be accomplished by measuring respiratory gases and selected physiological variables during rest and calibrated exercise during the flight.

PREPARATION FOR SPACE SHUTTLE MISSIONS

Much of our work in the areas of life support system development, manmachine technology, and space life research is geared toward the Space Shuttle missions of the future. We are continuing to emphasize life support systems that regenerate vital supplies and are sufficiently lightweight to be used in the Space Shuttle Earth-orbiting vehicle and the Shuttle itself. Refinement in teleoperator technology will expedite satellite servicing, cargo handling, and other space Shuttle operations. Space life research will establish the most effective and efficient techniques for the prevention and correction of the undesirable effects of space flight on man. Parallel development of bioinstrumentation will insure accurate measurement and monitoring of any changes of a physiological nature that do occur.

With the introduction of the Space Shuttle in the 1980's space travel will be relatively economical and practical for scientists, technicians, and people in many relevant professional disciplines. NASA is developing appropriate medical standards for use in screening and evaluationg nonastronaut personnel who may par

ticipate in these missions. Since some of these individuals, notably scientists, may be advanced in years, cardiovascular system integrity and its tolerance to postweightlessness, reentry acceleration forces take on increased importance. The NASA Ames Research Center has begun a program to investigate this problem. Scientists at Ames have completed two studies so far, exposing healthy males to 14 days of bed rest to simulate weightlessness and then to head-to-foot accelerations in the order of 2, 3, and 4 G, typical of Space Shuttle accelerations. In the most recent study, as shown schematically in figure 186, various remedial

measures (isotonic exercise, isometric exercise, and rehydration) were examined. The Johnson Space Center has conducted a similar study in which 7 days of bed rest were followed by Shuttle acceleration profile runs. Observations on a wider segment of the population, in terms of both age and sex, are planned.

Shuttle Life Support and Protective Equipment

We have several efforts in life support equipment development under way for the Space Shuttle. The most important is the Representative Shuttle Environmental Control System (RSEC) (figure 187) (see p. 462). It is a test-bed to evaluate and compare the baseline environmental control system design approach with alternate advanced techniques. These advanced techniques include a regenerable desiccant for humidity and carbon dioxide control in lieu of replaceable carbon dioxide absorber canisters. Figure 187 depicts the atmospheric revitalization section of this system.

The RSEC program will also verify maintenance, checkout, and turn-around procedures to enhance flight systems design. Specialized component development and testing necessary for this task will be conducted. An example is the maintenance disconnect valve (figure 188) (see p. 462), for integrating the various life support subsystems. To accomplish the reliability goals of the program, it was necessary to design and develop a value concept which would allow components to be removed and replaced and allow the valve itself to be repaired without depressurizing the system, without introducing gas into the system liquid loop, and without significant loss of liquid. The selected concept was a cartridge valve which can be applied to nearly all liquid and gas line components.