The Headquarters announcement, the first high-level step on the road to the Apollo Applications Program (AAP), undermined planetary exploration planning. Even before the announcement, however, die-hard Mars planners had begun to study how Saturn/Apollo hardware could be applied to planetary voyages. In February 1965, just three months after the Headquarters announcement, NASA Marshall Space Flight Center's Future Projects Office completed the first study of Apollo-based piloted Mars and Venus flyby missions.
In February 1967, Jack Funk and James Taylor, engineers in the Advanced Mission Design Branch at NASA's Manned Spacecraft Center (MSC) in Houston, Texas, proposed as AAP's "final goal" a series of three Apollo-based piloted Venus flybys. The missions would depart Earth during 30-day launch periods beginning on 4 April 1972, 14 November 1973, and 7 June 1975. Each would require a single unmodified three-stage Saturn V rocket of the type used to launch Apollo missions to the Moon, a lightly modified Apollo Command and Service Module (CSM), and a Mission Module (MM) based, perhaps, on the Apollo Orbital Research Laboratory (AORL) under study at the time.
MSC's piloted Venus flyby missions were intended to replace the piloted Mars and Mars/Venus flybys under study by the intercenter NASA Planetary Joint Action Group (JAG). MSC favored a piloted Venus flyby mission followed by a Venus orbiter because they would be of shorter duration and would need less propulsive energy than the Planetary JAG's missions. In MSC's plan, piloted Mars orbiter and piloted Mars landing missions in the late 1970s would follow successful piloted Venus flyby and Venus orbiter missions.
Funk and Taylor's 1972 AAP Venus flyby mission would begin with launch from Cape Kennedy on 2 April 1972. The Saturn V's S-IVB third stage would inject a 66,308-pound CSM with three astronauts on board and a 27,783-pound MM into a 100-nautical-mile circular parking orbit.
The stage would be restarted a few hours later to place itself and its payload into an elliptical orbit with a 70,000-mile apogee (high point above the Earth) and a 48-hour period. Payload injected into the elliptical orbit would total 107,578 pounds, or about 263 pounds beyond expected Apollo Saturn V capacity; Funk and Taylor shrugged off the shortfall, however, saying that it was so small as to be "in the noise level" of their calculations.
|Venus or bust. A = J-2 rocket motor; B = Saturn V S-IVB third stage; C = Spacecraft Launch Adapter (contains Mission Module); D = Apollo Command and Service Module spacecraft. Image credit: NASA.|
The next day, the astronauts would return to their couches in the CSM as the flyby spacecraft neared apogee. They would then fire the Service Propulsion System (SPS) main engine in the CSM's Service Module (SM) to raise the perigee (low point above Earth) of their spacecraft's orbit and tilt its orbital plane relative to Earth's equator. The drum-shaped SM would contain 40,000 pounds of propellants, enabling a total velocity change of 4800 feet per second.
In addition to refining the flyby spacecraft's trajectory for the Venus injection burn, which would occur at perigee, the apogee maneuver would test the SPS. If the engine failed, the astronauts would abort the mission by discarding the MM and lowering the CSM's perigee into Earth's atmosphere by firing special aft-mounted auxiliary attitude control thrusters near apogee. When the CSM approached perigee 24 hours later, they would cast off the SM and reenter in the conical Command Module (CM).
|Trans-Venus Injection scenario. See text for explanation. Image credit: NASA.|
Immediately after the Trans-Venus Injection burn, the astronauts would shut down the CSM to extend its lifetime and move back to the MM. They would reactivate the CSM three times during the 109-day flight to Venus so that they could perform small course correction burns using the SPS. Course correction navigation would be by Earth-based radar backed up by a hand-held sextant and a navigational computer in the MM.
Funk and Taylor calculated that the CSM would need 2000 pounds of extra meteoroid shielding for a Venus mission. Shielding — probably in the form of a Whipple Bumper (a thin layer of metal or plastic sheeting suspended a few inches from the hull that would break up meteoroids, reducing the damage they could inflict on the spacecraft) — would cover the entire CM and the SM tanks and SPS.
The astronauts would perform solar, space environmental, and astronomical observations during the Earth-Venus transfer and would begin deploying automated probes a few days before the 23 August 1972 Venus flyby. Closest approach to the planet would occur over the day side.
Using the SPS, the astronauts would perform three small course corrections during the 250-day voyage to Earth. As the homeworld grew in their viewports, the astronauts would transfer to the CSM and undock from the MM. On 30 March 1973, just 359 days after Earth launch, they would carry out a final course correction, then would detach the CM from the SM and re-enter Earth's atmosphere. A beefed-up heat shield would permit the CM to withstand atmosphere reentry at up to 45,000 feet per second (that is, about 9000 feet per second faster than Apollo lunar return speed).
|Trajectory and key dates for the Venus flyby mission departing Earth on 5 April 1972. Venus flyby occurs on 23 August 1972; Earth return on 30 March 1973. Image credit: NASA.|
The 1973 mission Venus flyby spacecraft would need the most propulsive energy to depart Earth orbit for Venus — a total of 12,150 feet per second, or about 70 feet per second more than the 1972 spacecraft and 300 feet per second more than the 1975 spacecraft. The 1972 CM would have the fastest Earth-atmosphere reentry speed (45,000 feet per second), while the 1973 CM would reenter moving at 44,500 feet per second and the 1975 CM at 44,000 feet per second.
Funk and Taylor's AAP Venus flyby plan stands out from the many 1960s plans for piloted flybys because it has been brought to life as fiction. In his 2017 alternate history Island of Clouds: The Great 1972 Venus Flyby, author Gerald Brennan puts narrative meat on the technical skeleton Funk and Taylor presented in their MSC Internal Note.
Told in the first person by a believable fictional Buzz Aldrin, Brennan's tale owes much to the Apollo 11 moonwalker's autobiography Return to Earth (1973). Its focus on exploration far from rescue puts Island of Clouds in a class with Hank Searls' classic 1964 adventure The Pilgrim Project (described elsewhere in this blog — click on the last link under "More Information" below).
Six months after Funk and Taylor completed their study, AAP bore the brunt of more than $500 million in Congressional cuts to NASA's Fiscal Year 1968 budget. The program, which for a time in 1966 had been planned to include some 40 Earth-orbital and lunar missions, shrank rapidly during 1968-1969. It was officially renamed the Skylab Program in February 1970. Between May 1973 and February 1974, three three-man crews occupied the Skylab Orbital Workshop in Earth orbit for a total of 173 days.
Robot probes, not astronauts, explored Venus in the 1970s. The Soviet Union's Venera 8 took advantage of the 1972 launch opportunity, leaving Baikonur Cosmodrome in Central Asia on 27 March 1972. The armored probe landed on Venus and transmitted data on its brutal surface conditions for 50 minutes. The U.S. Mariner 10 probe (launched 3 November 1973) flew past Venus en route to Mercury on 5 February 1974.
After skipping the 1973 Venus opportunity to launch Mars probes, the Soviets launched Venera 9 and Venera 10 on 8 and 14 June 1975, respectively. Each consisted of an orbiter and a lander. The Venera 9 lander transmitted the first picture of the Venusian surface on 22 October. Venera 10's lander set a new endurance record on 23 October, returning data from the surface for 65 minutes before its orbiter passed out of radio range.
The first, fourth, and fifth images in this post are Copyright 2017 by William Black (http://william-black.deviantart.com/) and are used by special arrangement with the artist.
Preliminary Mission Study of a Single-Launch Manned Venus Flyby with Extended Apollo Hardware, MSC Internal Note No. 67-FM-25, J. Funk & J. Taylor, Advanced Mission Design Branch, Mission Planning and Analysis Division, NASA Manned Spacecraft Center, Houston, Texas, 13 February 1967.
After EMPIRE: Using Apollo Technology to Explore Mars and Venus (1965)
Triple Flyby: Venus-Mars-Venus Piloted Missions in the Late 1970s/Early 1980s (1967)
Space Race: The Notorious 1962 Proposal to Launch an Astronaut on a One-Way Trip to the Moon