LONG-TERM SPACE MISSION REQUIREMENTS

 

CLAYTON S. HUBER

 

Technology Incorporated

[145] Spaceflights for the Mercury, Gemini, and Apollo programs (table D, are extremely brief compared with flights for future programs now in the planning stages. Apollo Applications Program (AAP) missions have been designed to last 28 or 56 days, the minimum time being twice the length of present accomplishments. The missions for AAP, however, are only intermediate in length.

[146] The purpose of this paper is to discuss space missions beyond the AAP, which are classified as long term. It should be emphasized that these concepts are only possibilities at the present time. No definite programs have been implemented, although considerable effort has been expended during initial planning stages. Attention will be focused on three concepts of space exploration. They are designated as the Earth-Orbit Program, the Lunar Program, and the Planetary Program. These three programs will be discussed individually.

Future Earth-orbit programs will begin with the AAP. Subsequent Earth-orbit missions will increase both in crew size and mission time. ln the next decade the launching of an Earth-orbiting space station manned by a crew of 8 to 12 individuals is a distinct possibility. The duration of such a flight would be about 180 days. (This is about 13 times longer than any previous flight). Flights within this time frame and longer ones must be classified as long-term space missions.

Near the latter part of the decade a space-station facility which will support men and equipment on a permanent basis will be assembled in space. Such a station could have the capability of housing 50 to 100 individuals in an Earth-like artificial-gravity environment. The space station would be equipped with a hangar and docking area. Space shuttle vehicles traveling between the station and the Earth would provide logistical support, thereby resupplying expendable materials. Resupply would probably be reserved for expendables and subsystems which require openloop operation. This space station could also serve as a centralized storage facility for expendables and equipment which could be utilized for subsequent planetary missions.

Lunar landings during Apollo and post Apollo lunar exploration will utilize small vehicle and crews will be confined to the immediate area of the spacecraft. Future exploration will require multiman vehicles and additional supporting systems for increased stay times. Concepts for the establishment of a lunar base are being developed. Such a structure would be somewhat permanent. Conceivably, a lunar base could be resupplied with expendable materials and crew members could be rotated periodically.

Another category of long-term space missions is that of planetary exploration. For such missions a spacecraft could be launched from Earth or from a permanent base such as a space station. Present plans call for a Mars-Venus manned fly-by during the latter part of the next decade and a Mars orbital mission or landing by the year 1984. These flights would be extended nonresupply missions which would require 420 to 540 days for completion.

The requirements for a feeding system may not be identical for all of the long-term missions categorized earlier. Unique features associated with each program will need to be satisfied. Missions will vary with respect to crew size, extent of activity, and environmental conditions. The extreme conditions on the lunar surface are quite different from the artificial-gravity environment in a large space station. There is one common denominator, however; as the length of [147] manned spaceflights and exploration increases, the problems associated with life support multiply and become more complex and much more speculative.

As previously noted, the space station could be resupplied periodically with expendables, including food. The requirements for a feeding system will be quite flexible and not so restrictive as those for past and present systems. It is anticipated that conventional methods of food preparation and eating will be compatible with the environment within the space station. Hardware and equipment will be provided which will heat and cool foods prior to consumption. It is also conceivable that the technique of resupply for the lunar exploration programs could also be applicable for a portion of the nutritional requirements. Because of the factors of space and weight, which will not be restricted, recycling methods may be quite feasible on the lunar surface.

Extended planetary missions with no resupply will require a highly reliable feeding system. Such reliability may result in some redundancy. A nominal system might be designed to include several food sources, with provisions for complete failure of one or more sources. With this approach, failure of a single food source would compromise overall food acceptance but not the available nutrients required to maintain crew health and performance.

At some point a closed life-support system must be integrated into the program. The objective of closing loops is to reduce the weight of expendable supplies, life-support equipment, and supporting equipment for electric power. At some point the penalties for resupply or for an adequate supply for the duration of the mission will exceed those for regeneration. This point was illustrated in a study by the Convair Division of the General Dynamics Co. (ref. 1). Closed-loop systems for the regeneration of water and the recovery of oxygen will probably be used first (100 to 1000 man days). The feasibility of regenerating food from wastes in a closed system is more distant, but such a concept could be integrated into the feeding systems during the next decade. In fact, systems could be qualified on missions for which resupply is the core of a feeding system.

Recently the Soviet Union conducted a 1-year test of life-support systems. Three human subjects spent 1 year in a sealed chamber. Air and water were regenerated; food consisted of vacuum-dried products and fresh vegetables from a "cosmic" greenhouse. Dehydrated foods include such items as salmon, chocolate, cottage cheese, and prune paste. To provide variety, a repeatable 5-day menu was devised. During the second and third stages this diet was augmented by fresh vegetables (which included cabbage, cress, cucumber, greens, and dill) from the greenhouse (refs. 2 to 6).

The following statement was made in a report issued by the Space Science Board (ref. 7): "Very long duration missions may require production of food in the spacecraft. Further study of the production of the nutritionally important substances and their conversion into edible food is necessary before the practicality of such procedures can be assured. "

Several life-support systems have been proposed whereby food is produced from biological wastes. Biological systems which have been investigated include algae, bacteria, higher plants (hydroponics), herbivorous invertebrate animals, fungi, and plant cultures. The Space Science Board in 1966 (ref. 8) suggested that: "Consideration should also be given to the production of [148] higher plants or animals that may be more palatable to humans. It has been shown, for example, that sweet potatoes grow well in hydroponic culture utilizing the end products of the stabilization of human wastes. " Chemical synthesis, including the synthesis of carbohydrates, lipids, and amino acids, has also been suggested as a possible alternative to biological systems.

Inherent advantages and disadvantages are associated with each biological and chemical system. Each system must be evaluated in terms of purifying and converting the material into an edible form, food acceptability and palatability, nutritional adequacy, efficiency, compatibility with the total life-support system, logistical support, mission duration, and the number of individuals involved.

In reference 9 several statements were made on this subject: "There are two significant areas with a high probability of future research and development effort. These pertain to the nutritional aspects of the food-waste loop and the ultimate acceptance or rejection of the produced food by the crew. The crew acceptance of the synthesized food may well prove to be the major restraint in this method of closing the ecology. "

Feeding systems for long-term aerospace missions must provide adequate nutrients which will maintain the original health of the flight crews and maintain a high level of crew performance, behavior, and morale. It was stated in a report by the Space Science Board (ref. 10) "As flights become longer, the attitudes of the astronauts will increasingly affect the success of missions. It will be necessary to have an intensive and extensive knowledge of the dynamics of man's behavior in respect to food and to be able to predict man's performance."

Long-term studies similar to the one conducted by the Soviet Union could provide important data in the development of future concepts for long-term missions. Studies conducted in the United States have been of less than 60 days' duration. More long-term research needs to be conducted. Possible areas of research as outlined by the Space Science Board (ref. 11) might include:

(1) The analysis from a storage stability standpoint of the presently available take-along foods

 

(2) The study of changes in dietary appeal due to long confinement

 

(3) The toxicological properties in foods which may be used

 

(4) The effect of dietary regimens on waste production

 

(5) The investigation of continued long-term consumption of unconventional food materials on intestinal flora and motility

 

(6) The effect of diet on flatus

 

(7) The investigation of changes in metabolic balance under the stresses of flight

In summary, each program - Earth orbital, lunar exploration, and planetary - has unique concepts associated with it. An all-inclusive approach will not completely satisfy the requirements for these long-term space missions. Life-support systems will probably be integrated into long-term feeding systems. It is doubtful, however, that a feeding system designed for any long-term mission will be completely dependent upon food production within the spacecraft as the sole source of nutrients.

1. Drake, G. L.: Regenerable Life Support Systems. General Convair Rept., Biomedical and Engineering Symp., Gen. Dynamics Co., 1966.

2. Izvestiya, Dec. 24, 1968, p. 5, cols. 1-6.

3. Garodinskaya, V.; and Repin, L.: Komsomol' skaya pravda, Dec. 25, 1968, p. 4, cols. 1-3.

4. Tass, Krasnaya Zvezda, Dec. 25, 1968, p. 3, cols. 1-5.

5. Tass, Izvestiya, Dec. 26, 1968, p. 6, cols. 2-5.

6.Vason, M. Pravda, Dec. 26, 1968, p. 6, cols. 3-6.

7. Space Science Board: Summary Report of Working Group on Nutrition and Feeding Problems. Man in Space Comm., Natl. Acad. Sci., Natl. Res. Council (Washington, D. C.), 1963.

8. Space Science Board: Report of the Panel on Space Nutrition of the Committee on Life Sciences. Natl. Acad. Sci., Natl. Res. Council (Washington, D.C.), 1966.

9. Drake, G. L.; King, C. D.; Johnson, W. A.; and Zuraw, E. A.: The Closed Life Support System. NASA SP-134, 1967.

10. Life Sciences Committee, Space Science Board: Summary Report. Symp. on Acceptability and Palatability of Food for Manned Space Missions, Natl. Acad. Sci., Natl. Res. Council (Washing ton, D.C.), 1966.

11. Space Science Board: Report of the Panel on Space Nutrition of the Committee on Life Sciences. Natl. Acad. Sci.,Natl. Res. Council (Washington, D.C.), 1966.

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