Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan

 24 July 1969: Richard Nixon and Thomas Paine (left), NASA's third Administrator, wait on board the aircraft carrier Hornet for splashdown of the Command Module Columbia at the end of the Apollo 11, the first mission to land men on the Moon. At the time, Paine was lobbying hard for Nixon's acceptance of the IPP. Image credit: NASA.

When one reads of NASA's 1969 Integrated Program Plan (IPP), it is often difficult to know whether to laugh or cry. The IPP, a product of George Mueller's NASA Headquarters Office of Manned Space Flight, began to evolve as early as 1965, but not until May 1969 did it take on the grandiose form NASA Administrator Thomas Paine stubbornly advocated to President Richard Nixon.

Paine, a Washington neophyte who had replaced the politically wily James Webb in late 1968, expected that the IPP would be NASA's reward for vanquishing the Soviet Union in the race to the Moon. He urged his Center directors across the country to "think big" in their plans for post-Apollo space projects.

Had NASA gained approval for its Integrated Program Plan in 1969, a vast network of space transportation systems, space stations, and surface bases might have been in place by 1984. Image credit: NASA.

In its various versions, the IPP included space stations in low-Earth orbit (LEO), geosynchronous orbit (GEO), and near-polar lunar orbit; Saturn V and Saturn V-derived rockets for launching them; a fully reusable Earth-to-LEO Space Shuttle for launching astronauts, cargo, and propellants; a reusable modular Space Tug that could operate with or without a crew and do double-duty as a Lunar Module-B (LM-B) Moon lander; a reusable Nuclear Shuttle for LEO-GEO and LEO-lunar orbit transportation; and lunar and Mars surface bases. All of this complex and expensive infrastructure was meant to become operational by the mid-1980s at the latest.

The IPP is sometimes wrongly attributed to Wernher von Braun, director of NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama. Von Braun was in fact skeptical about the IPP. He did not expect an Apollo-level commitment to spaceflight following Apollo's culmination, let alone one several times larger. He had spent the 1960s seeking opportunities to expand U.S. piloted spaceflight using his Saturn rocket family. By the time Apollo 11 Commander Neil Armstrong set foot on the Moon (20 July 1969), however, it was abundantly clear to the pragmatic German-born rocketeer that this would not happen.

Nevertheless, with his position rapidly eroding in the new political climate, von Braun at Paine's request tasked MSFC's artists with pumping out IPP illustrations and its advance planners with grafting a piloted Mars mission onto the up-to-then cislunar IPP. He then touted the Mars plan to Nixon's high-level Space Task Group (STG) on 4 August 1969. Paine called von Braun NASA's "Big Gun" and expected the STG to be bowled over by anything he put before them. The first NASA piloted Mars mission could leave Earth as early as 1981, von Braun told the STG in a 30-minute presentation.

Nixon had appointed the STG in February 1969 to provide him with alternatives for NASA's future. Paine, a member of the STG, had won over Vice President Spiro Agnew, the STG's chairman, enabling him to put forward the IPP as the only choice for NASA's future. The STG's September 1969 report offered Nixon three schedules for accomplishing the IPP, but that was not the same as providing the three program alternatives Nixon had requested. Paine might have offered Nixon a choice between an LEO space station, a lunar base, or a man on Mars. Instead, he insisted on a package containing all three.

This was, of course, an ill-considered move. Nixon's Office of Management and Budget had made it clear that NASA should expect rapidly declining annual budgets, not rapidly increasing ones. Nixon interpreted Paine's stubborn advocacy of the ambitious IPP as a clumsy effort at bureaucratic empire-building, not as a sincere proposal for a bold ("swashbuckling" was a term Paine used) American space program.

Paine's inflexibility created a vacuum that the Nixon Administration filled. NASA had supplied a single plan for its future that was unacceptable, so the White House made its own plan that served the President's political ends.

First, before accepting the STG report in September 1969, the White House added a fourth IPP schedule with no fixed dates. Nixon then adopted the line that IPP development would proceed as funding became available with the goal of a man on Mars by the year 2000, a date so far in the future as to be meaningless.

Next, in July 1970, a year after Apollo 11, Nixon accepted Paine's resignation effective on the first anniversary of the STG report's public release (15 September 1970), and replaced him with the much more pliant James Fletcher. Finally, on 5 January 1972, Nixon made the Space Shuttle the sum total of NASA's post-Apollo piloted program. He touted the aerospace jobs it would create in California, a state vital to his 1972 reelection bid.

5 January 1972: President Richard Nixon and NASA's fourth Administrator, James Fletcher, in California with a model of the Space Shuttle. The Space Shuttle was the only element of the IPP to fly, and then only in a partially reusable form. It first reached orbit on 12 April 1981. Image credit: NASA.

Before that fateful announcement, however, NASA expended considerable effort on planning the IPP's execution. Paine's resignation did not stop the study efforts immediately. The LEO Station and Shuttle received more attention than the other elements because they were viewed together as the IPP's first step, but planners continued to look at all elements of the IPP well into 1971.

In June 1970, E. Grenning, an engineer with Bellcomm, NASA's Washington, DC-based advance planning contractor, developed a "traffic model" (basically, a flight schedule) based on a modified version of Paine's IPP Option I (the so-called "Maximum Program"). Grenning's model spanned the years 1970 through 1984.

Grenning explained that the IPP was based on two fundamental principles. These were "the systematic establishment of semi-permanent manned bases in various locations in cislunar space and eventually in interplanetary space" and the "parallel introduction of low cost transportation systems. . . for the purpose of economically moving cargo and personnel to and from the bases."

A major change from the IPP as submitted to Nixon was that the piloted Mars program, which would span seven years, was not tied to any specific dates. Grenning explained, however, that, when the decision was taken to proceed with the piloted Mars program, its seven-year schedule would need to be tied to existing Earth-Mars minimum-energy transfer opportunities, which occur every 26 months.

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

In addition, Grenning stretched the pre-Mars IPP over a slightly longer period, so that its elements would not all be in place until 1984. Combined with not providing a specific date for its man-on-Mars program, this made Grenning's traffic model for Option I somewhat more conservative than the one in the STG report. It was, however, more conservative only relative to the grandiose Option I Paine championed.

Until 1975, Grenning's model was based wholly on Apollo spacecraft and Saturn rockets, none of which were reusable. Because it used no reusable vehicles and established no permanent bases, it was simple in execution compared with the traffic model that began to take hold 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 lunar landing missions that had begun with Apollo 11. It is interesting to note here that Grenning's model, dated June 1970, seemed to exist in a parallel universe; after the Apollo 13 accident in April 1970, Apollo was grounded until January 1971.

The year 1971 would see the first two Extended Apollo missions. An uprated Saturn VB rocket would launch three astronauts, an Extended CSM (XCSM) capable of 16 days of flight, and an Extended LM (XLM) capable supporting two astronauts for three days. The XLM would have a landed payload capacity of 1000 pounds. NASA would fly two Extended Apollo missions per year from 1971 through 1974, plus one in 1975, for a total of nine missions and 54 man-days on the Moon.

Once again, Grenning's model did not match up with reality. In January 1970, Paine had announced that, far from being uprated, Saturn V production would go on standby. He had also cancelled Apollo 20, at the time the last planned Moon-landing mission.

The IPP would have seen two-stage Saturn V rockets (designated Int-21) launch many payloads. Int-21 would have remained operational as late as the mid-1980s. This image shows the only two-stage Saturn V; it launched the Skylab space station in May 1973. Image credit: NASA.

In Grenning's traffic model, 1972 would see the first two-stage Int-21 Saturn V derivative launch the first Apollo Applications Program (AAP) Orbital Workshop (OWS). The AAP OWS was a 22-foot-diameter Saturn V S-IVB third stage converted into a temporary space station. The Int-21, of which a whopping total of 41 were meant to fly between 1972 and 1984, would be capable of placing up to 250,000 pounds into LEO.

Saturn IB rockets would launch three CSMs, each bearing a three-man crew, to the first AAP OWS between mid-1972 and early 1973. NASA would launch a second AAP OWS at the beginning of 1974. A total of nine CSMs would deliver crews to the the second AAP OWS by early 1976.

Paine had cancelled Apollo 20 so that its 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 that Grenning did not use in his June 1970 traffic model document.

Reusable IPP spacecraft and semi-permanent bases would make their debut in 1975, overlapping with missions using Apollo-Saturn systems and helping to ensure that there would be no gap in U.S. piloted spaceflight. As already indicated, these would increase the complexity of NASA piloted space operations. Spacecraft and bases would need to be assembled, refueled, and resupplied using other spacecraft and bases that would themselves need to be assembled, refueled, and resupplied.

Cutaway of a Saturn Int-21-launched Space Station Module with docked and docking research modules and, at its far end, a transfer module for transporting Station crews and supplies from a Space Shuttle Orbiter payload bay to the Station. Image credit: NASA.

In 1975, NASA would launch on an Int-21 its first LEO Space Station Module (SSM), the prototype for all subsequent SSMs. Grenning wrote that the LEO SSM, which would orbit between 200 and 300 nautical miles above the Earth, would be used to conduct science, applications, and technology research. It would also serve as a depot for cargo bound for GEO and the Moon, a satellite repair base, and an assembly and launch control center for automated and piloted planetary missions.

Soon after the LEO SSM reached space, the fully reusable Space Shuttle would take wing for the first time. In the LEO SSM's first year, winged Shuttle Orbiters would visit it three times. The 12-man Shuttle Orbiter would lift off vertically on the back of a winged, piloted booster larger than a 707 airliner, then would separate and ignite its own cluster of engines to complete the climb to LEO. It would carry up to 50,000 pounds of payload in its 15-by-60-foot payload bay. A Shuttle Orbiter would be good for 100 flights before it would need to be replaced.

The cislunar portion of the IPP architecture. Space Station Modules, color-coded blue, appear in low-Earth orbit, in synchronous Earth orbit, in lunar orbit, and on the lunar surface. The Shuttle is depicted as the only Earth-to-orbit transportation system, though the Saturn V would have remained in service into the 1980s. Image credit: NASA.

In 1975, NASA would also conduct a test flight of the Saturn VC, a beefed-up three-stage Saturn V with a Space Tug/LM-B fourth stage. The Saturn VC, an "interim system" for bridging the gap between Apollo and more advanced IPP lunar systems, would be capable of placing 100,000 pounds into lunar orbit. The LM-B, a Space Tug with landing legs, could operate on the lunar surface for up to 14 days at a stretch.

Early in 1976, a Saturn VC would launch a 50,000-pound SSM and a fully fueled Space Tug/LM-B to near-polar lunar orbit. During 1976, 1977, and 1978, nine Saturn VCs would launch four Space Tug/LM-Bs and five four-man "QCSMs" to the lunar-orbit SSM, enabling a continuous lunar population of four astronauts. The QCSM, which Grenning did not describe, would be an interim system like the Saturn VC. Two-person crews would land on the Moon in Space Tug/LM-Bs four times in 1976, five times in 1977, and four times in 1978. Each trip to the lunar surface and back would expend 50,000 pounds of liquid hydrogen/liquid oxygen (LH2/LOX) propellants.

One design concept for the Space Tug/LM-B. Image credit: NASA.

A slightly different design concept for the Space Tug/LM-B. Both the Tug/LM-B in this illustration and the one shown above it would have had similar capabilities. Image credit: NASA.

The Space Tug would have an important "Space Shuttle Augmentation" function. Among augmentation missions considered was satellite servicing beyond Space Shuttle/Space Station operational altitude. Image credit: NASA.

The American Bicentennial year of 1976 would see an Int-21 boost a stack of five fully fueled Space Tug/LM-Bs into LEO. With a full load of LH2 fuel and LOX oxidizer, each Tug/LM-B would have a mass of about 50,000 pounds. Space Tug/LM-Bs would be designed for a one-year in-space lifetime. Beginning in 1976, one Space Tug/LM-B would be based at the LEO SSM at all times for use in satellite servicing, spacecraft assembly, Earth-orbital rescue, and other missions.

The lunar-orbit SSM would have on hand two fully fueled Space Tug/LM-Bs at all times. One would land on the Moon and the other would stand by to rescue the surface astronauts in the event that their Space Tug/LM-B malfunctioned. After a year of operations, Space Tug/LM-Bs based at the lunar-orbit SSM would be stripped down and turned into tankage for a propellant depot in lunar orbit.

Also in 1976, the Space Shuttle would fly eight times. Six Shuttle missions would deliver astronauts, supplies, and cargoes, including two automated planetary spacecraft, to the LEO SSM. The remaining two missions would see the Shuttle orbiter serve in a "tanker" role. Each Shuttle Orbiter would carry 50,000 pounds of LH2/LOX propellants, enough to refuel one Space Tug/LM-B.

The Space Shuttle Orbiter in one of its chief IPP roles: that of tanker supplying propellants to other IPP spacecraft. Image credit: NASA.

A piloted Space Tug removes a cargo module from the Shuttle payload bay using robot arms, stacks it on its top (center left), performs rendezvous with a waiting Moon-bound Nuclear Shuttle (upper right), and transfers the cargo module. Image credit: NASA.

The first two missions of the Balanced Base planetary program, the Venus Explorer Orbiter and the Comet d'Arrest flyby, would depart Earth in 1976. Automated planetary missions would each need two fully-fueled Space Tug/LM-Bs. When the planetary launch window opened, Space Tug/LM-B #1 would ignite its rocket engines to accelerate Space Tug/LM-B #2 and the planetary probe, then would shut down its engines, undock from Space Tug/LM-B #2, turn end for end, and fire its engines again to return to LEO for refueling and reuse.

Space Tug/LM-B #2 would fire its engines to further accelerate the planetary probe, then would shut down its engines and release the probe onto its interplanetary trajectory. Space Tug/LM-B #2 would then turn end for end and fire its engines to slow itself and return to LEO.

Grenning's IPP included many Space Tug-launched robotic probes. The probe above resembles the Voyager Mars/Venus orbiter/lander design cancelled in 1967. Image credit: NASA.

In 1977, the Space Shuttle would fly 10 times and the Int-21 would fly twice. The Space Tug/LM-B could not carry enough propellants to change from near-equatorial LEO SSM orbit to polar Earth orbit, so two Shuttle Orbiters would launch directly from Earth's surface into polar orbit to perform sortie (non-Space Station) missions. Polar sorties would occur at a rate of two per year through 1984.

Eight Shuttle missions would transport crews and cargoes bound for the LEO SSM. One of those would deliver to 50,000 pounds of LH2 propellant for the first NERVA nuclear-thermal rocket engine-equipped Nuclear Shuttle, and four would deliver 50,000 pounds of Space Tug/LM-B propellants each.

The Nuclear Shuttle would extend the IPP's reach to the Moon and Mars, enabling establishment of Moon and Mars bases. Note the crew cabin (upper right). Image credit: NASA.

One Int-21 would launch the first Nuclear Shuttle and another would launch five fully fueled Space Tug/LM-Bs (four for the robotic planetary program and one for the LEO SSM). The Int-21 would not have the lift capacity to launch the Nuclear Shuttle to LEO fully fueled, so it would reach space with room in its tank for an additional 50,000 pounds of LH2. Before a newly launched Nuclear Shuttle departed LEO for the first time, a Shuttle Orbiter tanker would rendezvous with it to top off its tank.

Nuclear Shuttles would each be good for 10 missions from LEO to GEO or lunar orbit and back, then would be launched into disposal orbit around the Sun. Some would carry a cargo of worn-out Space Tug/LM-Bs into solar orbit with them.

Each Nuclear Shuttle mission would expend 240,000 pounds of LH2. Six Space Shuttle tanker flights would be required to refuel the Nuclear Shuttle once. The Nuclear Shuttle would transport to the lunar-orbit SSM six astronauts and 90,000 pounds of cargo, or 100,000 pounds of cargo in automated mode. It could return 10,000 pounds of cargo and six astronauts from the Moon to the LEO SSM.

The Nuclear Shuttle could deliver 90,000 pounds of cargo and six astronauts to GEO and return six astronauts from GEO to the LEO SSM. After the GEO SSM was established in 1980, all Nuclear Shuttles would perform a shakedown cruise to GEO before traveling to lunar orbit for the first time. If it malfunctioned during its maiden flight to GEO, a Space Tug/LM-B could rendezvous with it to make repairs or return it to the LEO SSM.

The first Nuclear Shuttle would operate only in automated mode; its 10 missions would serve as an extended flight test. The first piloted Nuclear Shuttle, the second launched, would reach LEO on an Int-21 in early 1979. Four piloted and six automated Nuclear Shuttle flights would occur each year beginning in 1981, by which time one new Nuclear Shuttle would reach LEO and one old Nuclear Shuttle would be disposed of in solar orbit each year.

In 1977, four Tug/LM-B pairs would launch the Mars Explorer Orbiter, the Mars High Data Orbiter, and two Jupiter-Saturn-Pluto Mariner-class flyby spacecraft. The Tug/LM-Bs would burn the propellants with which they were launched to send the two Mars missions on their way, then would be refueled to launch the twin Jupiter-Saturn-Pluto missions. Grenning noted that dispatching automated spacecraft to destinations beyond the Main Asteroid Belt would need so much energy that the second Tug/LM-B could spare no propellants to return to LEO. It would, therefore, be expended.

The year 1978 would see a Mercury-Venus Mariner flyby, a Venus Mariner Orbiter, and a Solar-Electric Asteroid Belt Survey depart the LEO SSM. All Space Tug/LM-Bs used to launch these missions would be recovered. In 1979, NASA would launch the 6,000-pound Mars Soft Lander/Rover and two more Jupiter-Saturn-Pluto Mariner-class flybys, expending two Tug/LM-Bs.

In 1980, a second Venus Explorer Orbiter would leave Earth, as would two Jupiter Flyby/Atmosphere Probe spacecraft. The latter would expend two Tug/LM-Bs. The year 1981 would see a second Mars Explorer Orbiter, two Saturn Mariner-class Orbiter/Atmosphere Probes, and two more expended Tug/LM-Bs.

NASA would launch only one automated planetary mission, the 8,000-pound Mercury Solar Electric Orbiter, in 1982. Venus would get another Venus Explorer Orbiter and a Venus Mariner Orbiter/Rough Lander in 1983. NASA would also launch its second comet mission, a Mariner rendezvous with Comet Kopff. With a mass of 8500 pounds, it would be the heaviest of the 21 automated probes in the Balanced Base program. Mars would get a second High Data Orbiter and a second Soft Lander/Rover in 1984.

Back in NASA's piloted program, between 1979 and 1981 Int-21s would launch three more LEO SSMs. These would be combined with the first LEO SSM to form a "Space Base" with a permanent crew of from 50 to 100 astronauts. In 1980, an Int-21 would launch into LEO an SSM that would be mated to a Nuclear Shuttle and boosted to GEO. Early in 1979, Space Shuttle missions would begin to fly at a rate of 30 per year; by mid-1980, Grenning had the number of flights ramping up to 90 per year.

One proposed Space Base configuration. This three-armed design, which would have a permanent crew complement of 50 astronauts and scientists, would spin about its axis to produce acceleration in the habitat arm (left). The crew would feel the acceleration as gravity. The other two arms would each hold a nuclear reactor at a safe distance from the crew in the habitat module and core section. Also visible to the right of the Space Base is a small free-flying science module; these would dock with the non-spinning core section for servicing. Image credit: NASA.

As indicated earlier, Grenning tied piloted Mars missions to no particular year. Probably the piloted Mars program would not begin until NASA had ample experience with long-duration spaceflight, orbital assembly, and Nuclear Shuttle operations. The Bellcomm planner did, however, lay out a seven-year plan encompassing two complete piloted Mars missions and the first half of a third. The first and second missions and second and third missions would overlap.

All three would follow a conjunction-class mission profile; that is, they would reach Mars in about six months, remain there for about 18 months, and return to Earth in about six months. For safety, two identical six-person Mars spacecraft would travel as a convoy. At launch from the Space Base, each would comprise three Nuclear Shuttles, a mission module housing the crew, a payload module bearing unmanned probes and supplies, and a two-stage piloted Mars Excursion Module (MEM) lander. Both Mars spacecraft would be capable of supporting the entire 12-person mission complement in case one failed catastrophically.

Nuclear Shuttle IPP mission applications would culminate with Mars missions in the 1980s. Each Mars expedition would include two piloted Mars spacecraft and each piloted Mars spacecraft would include one Nuclear Shuttle with strap-on tanks (as shown here) or a cluster of three Nuclear Shuttles (as shown in the next image). Image credit: NASA.

The IPP Mars mission would have seen two Nuclear Shuttles used as interplanetary boosters. After they set a third Nuclear Shuttle, a Space Station Module-based crew module, and a piloted Mars Excursion Module lander on their way, each would have separated, turned end-for-end, and fired its NERVA engine to slow down and return to low-Earth orbit for reuse. Image credit: NASA.

A pair of IPP interplanetary spacecraft en route to Mars. The bulbous forward section (right) would have housed sample-returner probes and the Mars Excursion Module piloted Mars lander. Image credit: NASA.

Eighteen months before the first mission was set to depart the Space Base, NASA would launch four Nuclear Shuttles on Int-21 rockets and then launch four Space Shuttles to top off their tanks. The following year, the space agency would launch two more Nuclear Shuttles. These would each have a half-load of LH2 propellant because the Int-21s that launched them would also carry one MEM each. Topping off the Nuclear Shuttle tanks would need three Space Shuttle flights. Six Shuttle flights would fuel Space Tug/LM-Bs used for Mars spacecraft assembly. A final pair of Int-21s would launch the twin SSM-derived Mars spacecraft mission modules; a final Space Shuttle would launch the Mars spacecraft crews.

As the countdown clock reached zero, the NERVA engines in the two outboard Nuclear Shuttles on each spacecraft would fire to place the third Nuclear Shuttle, mission module, payload module, and MEM on course for Mars. They would then shut down, separate, turn end for end, and fire their engines again to slow themselves and return to LEO. The center Nuclear Shuttle on each spacecraft would perform course corrections and slow the spacecraft so that martian gravity could capture them into orbit.

The Apollo Command Module-shaped MEM was designed to descend through the thin martian atmosphere found by the 1960s flyby Mars Mariners. It would have comprised two main parts: the descent module with Mars surface living accommodations and an airlock/garage with Mars surface rover; and the cramped ascent module, where the crew would ride during descent, landing, and ascent after the surface mission was complete. Image credit: NASA.

MEM ascent stage liftoff. The ascent stage was a stage-and-a-half design with a cluster of approximately conical expendable propellant tanks and integral tanks in its cylindrical core feeding a single engine. Image credit: NASA.

After 18 months at Mars, during which at least one MEM would land on the planet for about a month (the second might be held in reserve in Mars orbit as a rescue vehicle), the twin center Nuclear Shuttles would fire again to put the mission modules on course for Earth. They would be used to perform course corrections; then, as the Mars spacecraft neared Earth, they would fire for the last time to slow the mission modules for capture into Earth orbit. Space Tug/LM-Bs would retrieve the Mars crews and the center Nuclear Shuttles.

The second and third Mars missions would be carried out in much the same way. The four outboard Nuclear Shuttles from the first mission would be reused for the second and third missions and the two center Nuclear Shuttles from the first mission would be reused for the third mission. The second mission would leave LEO before the first mission returned, so would need two new center Nuclear Shuttles. Grenning wrote that the third mission, preparations for which would begin in the fifth year of the seven-year program, might establish the first semi-permanent Mars surface base.

Grenning forecast that the seven-year piloted Mars program would need four Space Shuttle flights and four Int-21 flights in its first year to place Mars spacecraft components and (especially) propellants into LEO. Year 2, toward the end of which the first two piloted Mars spacecraft would depart from Earth orbit, would need four Int-21s and 13 Shuttles.

Year 3, during which preparation for the second Mars expedition would begin, would need just one Int-21 and 13 Shuttle flights. NASA would launch 20 Space Shuttle flights and three Int-21s in the Mars program's fourth year, 10 Shuttle flights and no Int-21s in its fifth, and 24 Shuttle flights and four Int-21s in its sixth. The final year of the program would see no Int-21s and 13 Shuttle flights.

Grenning also summed up the number of flights required to carry out the Maximum Rate cislunar program from 1975, when IPP stations and spacecraft began to replace Apollo-based stations and spacecraft, to 1984. The Space Shuttle fleet would accomplish 518 missions to LEO. The Saturn VC would fly 11 times between 1975 and 1979, when it would be phased out in favor of piloted lunar flights via the Space Shuttle, LEO SSM, Nuclear Shuttle, lunar-orbit SSM, and LM-B. The Int-21 would fly 25 times in the cislunar IPP, with a peak annual launch rate of five in 1981.

Was the Mueller/Paine IPP in any sense realistic? It depends on the judgement criteria one uses. Certainly, it was not a realistic option for 1970 America due to domestic political and economic considerations, the opposition of the Nixon White House and the Congress, and public disinterest.

In addition, one might take issue with its confident assertion that its network of reusable space systems and permanent and semi-permanent bases would save money. Complex reusable space systems require either costly development or costly maintenance and refurbishment. A single failure can take down an entire network of interdependent complex systems, and pioneering systems are more prone to failure than well-established ones. If, for example, a Space Shuttle had exploded, then crew and propellant transport would have ground to a halt throughout the IPP infrastructure for an indeterminate period of time.

One might, on the other hand, argue that the IPP's scale was not adequate for the challenges of piloted space exploration. Even the IPP would have permitted astronaut access only to cislunar space, the Moon, and Mars. Perhaps we find the IPP grandiose in part because we have been conditioned to "think small" about space exploration. If our plans took in our entire local neighborhood — the Solar System — and sought to be realistic, then they would of necessity demand a scale orders of magnitude beyond that of the IPP.

Sources

"Integrated Manned Space Flight Program Traffic Model Case 105-4," E. M. Grenning, Bellcomm, 4 June 1970.

The Next Decade in Space: A Report of the Space Science and Technology Panel of the President's Science Advisory Committee, Executive Office of the President, Office of Science and Technology, March 1970.

"Statement About the Future of the United States Space Program," Richard M. Nixon, 7 March 1970.

"An Integrated Space Program for the Next Generation," George Mueller, Astronautics &  Aeronautics, January 1970, pp. 30-51.

"Integrated Space Program - 1970-1990," Internal Note-PD-SA-69-4, Terry Sharpe & Georg von Tiesenhausen, Advanced Systems Analysis Office, Program Development, NASA Marshall Space Flight Center, 10 December 1969.

America's Next Decades in Space: A Report for the Space Task Group, NASA, September 1969.

The Post-Apollo Space Program: Directions for the Future, Space Task Group Report to the President, September 1969.

"Manned Mars Landing Presentation to the Space Task Group," Wernher von Braun, 4 August 1969.

"Integrated Manned Space Flight Program: 1970-1980," NASA Office of Manned Space Flight, NASA Headquarters, 12 May 1969.

Astronautics and Aeronautics, 1970, NASA SP-4015, 1972, pp. 77-79, 82-84.

Astronautics and Aeronautics, 1969, NASA SP-4014, 1970, pp. 266-269, 304-305, 308.

After Apollo? Richard Nixon and the American Space Program, John M. Logsdon, Palgrave MacMillan, 2015.

More Information

Triple-Flyby: Venus-Mars-Venus Piloted Missions in the Late 1970s/Early 1980s (1967)

An Alternate Station/Shuttle Evolution: The Spirit of '76 (1970)

McDonnell-Douglas Phase B Space Station (1970)

Space Station Resupply: The 1963 Plan to Turn the Apollo Spacecraft Into a Space Freighter