Integrated program plan “Maximum rate” traffic model (1970)

A major change from the IPP as submitted to Nixon was that the Manned Mars program, which would run for seven years, was not tied to any specific date. Grenning explained, however, that when the decision was made to continue the manned program on Mars, its seven-year schedule should be tied to existing opportunities for minimal Earth-Mars energy transfer.

Another change was that Grenning listed the proposed automated planetary exploration missions. It was a response to protests from scientists, who were understandably eager to explore the many body types in the solar system. The planetary “Balanced Base” program would include 21 missions, all of which would leave Earth between 1976 and 1984.

In addition, Grenning extended the PPI over a longer period of time, so that not all of its elements would be in place until 1984. Combined with not providing a specific date for his Man on Mars program, this made the slightly more conservative Grenning traffic model for Option I. than that of the STG report. he was, however, no longer conservative except in relation to the grandiose option that Paine was defending.

Until 1975, Grenning’s traffic model was based entirely on Apollo spacecraft and Saturn rockets, neither of which were reusable. Because it did not use reusable vehicles and did not establish permanent bases, its execution was straightforward compared to the circulation model that began to take effect in 1975.

The year 1970 would see three Apollo moon landing missions, Grenning wrote, each with three astronauts, a command and service module (CSM) and a lunar module (LM) launched on a three-stage Saturn V rocket. They would constitute the continuation of the Apollo moon landing missions which had started with Apollo 11. It is interesting to note that the Grenning model, dated June 1970, seemed to exist in a parallel universe; after the Apollo 13 crash in April 1970, Apollo was grounded until January 1971.

The year 1971 will see the first two extended Apollo missions. An improved Saturn VB rocket would launch three astronauts, an extended CSM (XCSM) capable of 16 days of flight, and an extended LM (XLM) capable of supporting two astronauts for three days. The XLM would have a disembarked payload capacity of 1,000 pounds. NASA would conduct two extended Apollo missions per year from 1971 to 1974, plus one in 1975, for a total of nine missions and 54 man-days on the moon.

Again, Grenning’s model did not match reality. In January 1970, Paine announced that, far from being upgraded, Saturn V would cease production. He also canceled Apollo 20, around the time of the last scheduled moon landing mission, leaving no more than seven landings after Apollo 12. Apollo 13 then reduced that number to six.

In Grenning’s traffic model, 1972 would see the first two-stage derivative Int-21 Saturn V launch the first Orbital Workshop (OWS) of the Apollo Applications Program (AAP). The AAP OWS was a 22-foot-diameter Saturn V S-IVB third stage converted into a temporary space station. The Int-21, 41 of which in total would fly between 1972 and 1984, would be capable of placing up to 250,000 pounds in LEO. Saturn IB rockets would launch three CSMs, each carrying a three-man crew, to the first AAP OWS between mid-1972 and early 1973. NASA would launch a second AAP OWS in early 1974. A total of nine CSMs would provide crews at the second AAP OWS in early 1976.

Paine had canceled Apollo 20 so his Saturn V could be used to launch the first AAP OWS. In February 1970, NASA announced that the AAP OWS program would be called the Skylab program, a name Grenning did not use in his June 1970 traffic model document.


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