control and life support. In concept III, the laboratory module would again be housed in the LEM adapter but in this case would carry all the necessary expendables and would depend on the command and service modules only for communications, guidance and navigation. Of course, either of these latter alternatives would be such a major undertaking that this could no longer be considered a minimum concept solely designed for the "zero g. decision." The basic advantage of the extended APOLLO minimal concept is its simplicity and relatively early availability, achieved at the expense of nonoptimum design. Six-man orbital research laboratory Another concept whose feasibility has been recently examined is a SATURN IB boosted laboratory having a volume of about 4,000 cubic feet and the capability to support six men in orbit. Figure 85 shows one of the concepts proposed by the Douglas Aircraft Co. Essentially an extension of the S-IVB stage of the SATURN IB, the laboratory would consist of a pressurized spherical interior providing for living space and experimentation by the crew. At the forward end of the laboratory, a hangar would be provided for the docking of logistics vehicles bringing up supplies or rotating the crews. Like the extended APOLLO concepts, the six-man orbital research laboratory (ORL) is basically a zero gravity station, but could be conceived in such a way that it could provide an artificial gravity field for the crew in the laboratory by rotating the laboratory and the expended upper stage of the launch vehicle about their common center, MANNED ORBITAL RESEARCH LABORATORY FIGURE 85 utilizing a connecting system of cables or some form of rigidized structure. For the Earth orbital mission, the ORL and the last booster stage would be injected unmanned from Cape Kennedy into a 160 to 200 nautical-mile circular orbit having an inclination somewhat less than 30°. Provisions would be onboard to support for a month or so the ORL and the crew, which would arrive after the unmanned laboratory has been checked out in orbit. Regardless of the method of ORL launch, ferry and resupply operations would be required for any extended duration mission to replace the crew, provide life support and stabilization expendables, replace experiments and provide fuels or possibly propulsion units for orbit keeping or changing. As indicated, crew replacement could be accomplished by a ferry spacecraft using launch, rendezvous, reentry, landing procedures, operations, and landing sites currently planned and being developed for the GEMINI program. The application of an APOLLOSATURN ferry vehicle which has the additional capability of carrying supplies with the crew is also being considered. The choice between GEMINI, modified GEMINI B/MOL, APOLLO, and high L/D lifting-body type ferry/logistics vehicles and their respective boosters is presently unresolved and will depend on the operational requirements for crew replacement and resupply. Twenty-four man orbital laboratory The concept of a large orbital research facility having a crew of up to 24 people has been investigated. It would be launched on a SATURN V booster. The laboratory's size could range from 150 to 200 feet in diameter and the internal volume could range up to 50,000 cubic feet. The large station concepts studies have ranged from inflatable toroidal concepts to huge stations assembled in orbit. The major feature of most large ORL concepts is that they provide for continuous rotation, thus creating an artificial gravity field. Nonrotating central hubs could be utilized as zero gravity laboratories. Radial spokes would provide areas of varying gravity fields as one proceeds toward or away from the rim of the station. The size of the station, the large crew and the varying gravity fields would allow the large ORL to function as a versatile space laboratory, and it could possibly be adaptable to operational growth into an elaborate orbital launch facility. These features, of course, are acquired at greater expense in development costs and time and in operational costs. One of the large rotating ORL configuration designs, which is now being studied in greater detail, is the three-radial module type shown in figure 86. It is comprised of a hangar type hub area and three radially-deployed modules. The diameter of this station would be approximately 150 feet, and it would rotate about its axis of symmetry at three to four revolutions per minute. The station would generally be oriented to point its axis of rotation in the direction of the Sun so as to best utilize the solar cell powerplant deployed outboard of each radial module. The hub of the station would contain an environmentally controlled area for service and checkout of logistics spacecraft, and a zero gravity laboratory would be located in a circular area below the hangar. The zero gravity laboratory would not be rotated but would be mounted on bearings to allow for the relative motion between it and the rest of the station. During launch the radial modules would be folded down so that the axis of their cylindrical areas would be parallel to the axis of the hub. The space vehicle is launched with the space station unmanned and with a crew of six in a modified APOLLO logistics spacecraft atop the space station. After injection into orbit, deployment of the radial modules is initiated. On completion of deployment, the ferry spacecraft is separated, performs a turnaround maneuver and docks with the station. The ferry is then towed into the hangar area, and the crew transfers into the space station to activate the onboard systems. In this concept, no extravehicular operations are required. Once the systems are activated the station is then spun up to the required angular velocity. MANNED PLANETARY MISSIONS Expeditions to the planets of our solar system, the ultimate goal of manned space flight, will be an undertaking of immense significance. To date, efforts have been concentrated on studies to define the objectives of planetary exploration and the required means, methods, and resources. Both detailed and broad conceptual studies are being made. The broad conceptual studies will aid in the definition of an overall program, provide direction to advanced technology programs, and delineate information required from the unmanned interplanetary program. The more detailed studies are to assure mission feasibility, determine the utility of existing or planned hardware, and define the technological, economic and schedule aspects of manned planetary exploration. Based on current study results, the first manned planetary expedition will be a trip to Mars or Venus. The less hostile environment which appears to exist on Mars (fig. 87) and the apparent technical feasibility of landing on that planet make it the most likely candidate for a landing mission. Although initial study efforts have concentrated on Mars missions, missions to Venus have also been considered. Factors affecting missions The following are a few facts about the planets which strongly affect planetary missions. 1. Oppositions of Mars (fig. 88) occur when the Earth passes between Mars and the Sun. They happen approximately every 25 months. The time between oppositions is termed a "Synodic period." 2. At times of opposition, Earth and Mars are closest to each other. However, because of the eccentricity of the Martian orbit, this distance varies from approximately 34 million miles during a favorable opposition, such as in 1971, to as much as 64 million miles during an unfavorable opposition, such as that of 1980. The cycle of oppositions repeats at 15- and 17-year intervals. This is termed a "Synodic cycle." (The orbits of Earth and Venus for our purposes can be considered circular.) 3. A fly-by mission (fig. 89) is one which passes near one or more |