The United States began to abandon the technology of manned lunar exploration by late 1967, a year before astronauts first reached space on board Apollo spacecraft. By early 1971, NASA was hard at work returning Apollo to its roots.
For more than a year before President John F. Kennedy's May 25, 1961 call for a man on the moon, Apollo had been seen primarily as an Earth-orbital spacecraft capable of both independent manned missions and crew ferry flights to Earth-orbiting space stations. A decade after Kennedy's call, NASA was preparing for Skylab A, its first Earth-orbiting space station, which would receive at least three three-man crews on board Apollo Command and Service Module (CSM) spacecraft (images above). The agency also studied independent CSM missions in Earth orbit and CSM missions to Earth-orbiting stations other than Skylab A.
The CSM, which measured a little more than 11 meters long, comprised the conical Command Module (CM) and the drum-shaped Service Module (SM). The CM's nose carried a probe docking unit, and at the aft end of the SM was mounted the Service Propulsion System main engine. The CM also included the pressurized crew compartment, flight controls, a bowl-shaped heat shield for Earth atmosphere reentry, and parachutes, while the SM included hydrogen-oxygen fuel cells for making electricity and water, propellant tanks, four attitude-control thruster quads, and room for a Scientific Instrument Module (SIM) Bay.
On August 27, 1971, Philip Culbertson, director of the Advanced Manned Missions Program at NASA Headquarters in Washington, DC, dispatched a letter to Rene Berglund, Manager of the Space Station Project Office at NASA's Manned Spacecraft Center (MSC) in Houston, Texas, in which he outlined five Earth-orbital CSM missions that were "still under active consideration" at NASA Headquarters. Culbertson explained that his letter was meant to "emphasize the importance" of statements he had made in a telephone conversation with Berglund on August 19.
Culbertson referred to an unspecified new contract MSC had awarded to North American, prime contractor for the CSM. He told Berglund that, in "the early stages of your contract. . .you should concentrate on defining the CSM modifications required to support each of the [five] missions and possibly more important defining the effort at North American which would hold open as many as possible of the [five] options until the end of the [Fiscal Year] 1973 budget cycle." U.S. Federal Fiscal Year 1973 would end on October 1, 1973.
The first and simplest of the five missions was an "independent CSM mission for earth observations." The mission would probably use a CSM with a SIM Bay fitted out with remote-sensing instruments and cameras. At the end of the mission, an astronaut would spacewalk to the SIM Bay to retrieve film for return to Earth in the CM.
The second mission on Culbertson's list was an Apollo space station flight unlike any envisioned in the year before Kennedy diverted Apollo to the moon. It would have seen a CSM dock in Earth orbit with a Soviet Salyut space station.
Salyut 1, the world's first space station, had reached Earth orbit on April 19, 1971. The 15.8-meter-long station remained aloft as Culbertson wrote his letter, but had not been manned since the Soyuz 11 crew of Georgi Dobrovolski, Viktor Patsayev, and Vladislav Volkov had undocked on June 29, 1971, after nearly 24 days in space (a new world record). The three cosmonauts had suffocated during reentry when their capsule lost pressure, so the Soviet Union had halted manned missions while the Soyuz spacecraft underwent a significant redesign.
The third Earth-orbital CSM mission on Culbertson's list combined the first two missions into a single mission. The CSM crew would turn SIM Bay instruments toward Earth before or after a visit to a Salyut.
Culbertson's fourth CSM mission would see the Skylab A backup CSM (CSM-119) with a crew of three dock first with a Salyut for a brief time, then with Skylab A. CSM-119's crew would remain on board 26-meter-long Skylab A for an unspecified period. NASA planned that, during the three missions to Skylab A in the basic Skylab Program, CSM-119 would stand by as a rescue vehicle capable of carrying five astronauts (Commander, Pilot, and the three rescued Skylab A crewmen). It would thus need to be refitted for the Salyut-Skylab A mission. Culbertson added that the Salyut-Skylab A mission would begin 18 months after Skylab A reached orbit.
The fifth and final Earth-orbital CSM mission was really two (or, possibly, three) CSM missions. A pair of "90 day" CSMs would dock with the Skylab B station while a rescue vehicle modified to carry five astronauts stood by. Beginning in 1969 (that is, at the same time it started Skylab A funding), NASA had funded assembly of Skylab B as a backup in case Skylab A failed. Culbertson gave no date for the Skylab B launch, which would have required one of the two Apollo Saturn V rockets made surplus by the September 1970 cancellation of the Apollo 15 and 19 missions (the Apollo 20 mission had been cancelled in January 1970 to make its Saturn V available to launch Skylab A).
Of the five missions Culbertson declared to be on the table in August 1971, not one flew. Skylab A, re-designated Skylab I (but more commonly called Skylab), reached orbit on May 14, 1973. It suffered damage during ascent, but NASA and its contractors pulled it back from the brink. In August 1973, with Skylab I functioning well in Earth-orbit, NASA began to mothball its backup. Several plans for putting Skylab B to use were floated in the 1973-1976 timeframe, but Space Shuttle development had funding priority, so NASA's second space station wound up in the National Air and Space Museum.
The three CSM missions to Skylab spanned May 25-June 22, 1973, July 28-September 25, 1973, and November 16, 1973-February 8, 1974, respectively. Leaks in attitude control thrusters on the second CSM to dock with Skylab caused NASA to ready CSM-119 for flight; the leaks stopped of their own accord, however, so the rescue CSM remained earthbound.
In early April 1972, shortly before finalizing its agreement with NASA to conduct a joint Apollo-Salyut mission, the Soviet Union declared the concept to be impractical and offered instead a docking with a Soyuz. At the superpower summit in Moscow on May 24, 1972, U.S. President Richard Nixon and Soviet Premier Alexei Kosygin signed the agreement creating the Apollo-Soyuz Test Project (ASTP).
Apollo CSM-111 was the ASTP prime spacecraft, while CSM-119 was refitted to serve as its backup. In the event, the backup was not needed. CSM-111, designated simply Apollo, docked with Soyuz 19 on July 17, 1975. The last CSM to fly undocked on July 19 and returned from Earth orbit on July 24, 1975.