"Still Under Active Consideration": Five Proposed Earth-Orbital Apollo Missions for the 1970s (1971)

The Skylab 2 Apollo CSM and Saturn IB launcher stand ready atop the "milk stool" on Pad 39B at NASA's Kennedy Space Center, May 1973. Image credit: NASA.
From its conception in 1959 until President John F. Kennedy's 25 May 1961 call to put a man on the Moon, Apollo was seen mainly as an Earth-orbital spacecraft. NASA intended to use Apollo in the second and third phases of its planned 1960s piloted space program. The first phase, characterized by suborbital flights lasting minutes and sorties into Earth orbit lasting at most a few days, would be accomplished by brave pioneers in missile-launched single-seater Mercury capsules.

In the second phase, three astronauts would live and work on board Apollo spacecraft for ever-longer periods. They would use a pressurized Mission Module (MM) launched attached to their spacecraft as a small space station. The third phase would see Apollo spacecraft transport crews to and from an Earth-orbiting space station. Cargo bound for the station would ride in the MM. An Apollo circumlunar mission — a flight around the Moon without capture into lunar orbit — was an option, but was considered unlikely before 1970.

Simplified cutaway of the General Electric D-2 Apollo, perhaps the best known of the pre-Moon program Apollo designs. Colored lines represent separation planes: orange is the spacecraft/launch vehicle separation plane; red is the abort separation plane (two "pusher" solid-propellant abort rockets are visible on the outside of the Service Module); green is the shroud/Service Module separation plane; and blue is the Mission Module/Command Module separation plane. In the event of a launch abort, the part of the Service Module to the right of the red line would remain attached to the launch vehicle. During reentry, the spacecraft would first split along the green line, then the Command Module would separate from the Mission Module along the blue line. The shroud covering the Command Module during flight would remain with the Mission Module. The Command Module would lower on parachutes and perform a land landing while the Service Module and Mission Module/shroud would both burn up. Image credit: General Electric/DSFPortree.
Following studies that lasted six months, in mid-May 1961 General Electric (GE), The Martin Company, and Convair submitted Apollo spacecraft designs suited to NASA's three-phase plan. In the event, none of the designs left the drawing board; after Apollo became NASA's lunar landing mission spacecraft, the agency funded new studies and selected North American Aviation (NAA) as its Apollo spacecraft contractor.

Initially, NASA intended to land NAA's Apollo on the Moon atop a descent stage with landing legs. In July 1962, however, after more than a year of sometimes acrimonious debate, the space agency selected Lunar Orbit Rendezvous (LOR) as its lunar landing mission mode. NAA's Command and Service Module (CSM) spacecraft became the LOR mission's Moon-orbiting mother ship, and to Grumman's bug-like Lunar Module (LM) went the honor of landing on the Moon.

Before the Lunar Module. Image credit: NASA.
As flown, 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 MM of the May 1961 GE, Martin, and Convair designs was judged unnecessary for lunar landing missions. In fact, at first some sources perceived the LM to be the MM's replacement.

The CM's nose carried a probe docking unit, and at the aft end of the SM was mounted the Service Propulsion System (SPS) main engine. The SPS remained sized for CSM launches from the lunar surface, which meant that it was more powerful than necessary for CSM insertion into and escape from lunar orbit.

Technical details of the Apollo Command and Service Module (CSM) spacecraft configured for lunar missions. Image credit: NASA.
The CM also included a pressurized crew compartment, crew couches, flight controls, a compact guidance computer, rendezvous aids, a bowl-shaped heat shield for Earth atmosphere reentry, reentry batteries, and parachutes for descent to a gentle splashdown at sea.

The SM, which was discarded before atmosphere reentry, included propellant tanks, fuel cells for making electricity and water, fuel cell reactants (liquid oxygen and liquid hydrogen), four attitude-control thruster quads, radiators for discarding excess heat generated by on board systems, a high-gain radio antenna, and room for a Scientific Instrument Module (SIM) Bay. An umbilical beneath a streamlined housing linked CM and SM.

Almost all piloted Apollo Earth-orbital missions were launched atop two-stage Saturn IB rockets. The sole exception was Apollo 9 (3-13 May 1969), which used NASA's fourth Saturn V. All Apollo lunar missions left Earth on three-stage Saturn V rockets.

Apollo 7 and Apollo 9 were test flights, so their CSMs operated exclusively in low-Earth orbit. This image shows the CM of the Apollo 9 CSM Gumdrop as viewed from the LM Spider in May 1969. Apart from thruster quads and antennas, very little of Gumdrop's SM is visible. No other Apollo spacecraft would operate only in low-Earth orbit until the Skylab 2 CSM flew in May 1973. Image credit: NASA.
The United States began to abandon the technology of piloted lunar exploration by late 1967, nearly a year before the first astronauts reached Earth orbit in an Apollo CSM (Apollo 7, 11-22 October 1968). Abandonment of the Moon began with deep cuts in the Apollo Applications Program (AAP), the planned successor to the Apollo lunar program. Ambitious two-week stays on the Moon were among the first AAP missions to feel the budget-cutters' blades.

In early 1970, NASA brought together the parts of AAP that survived — several space station-related Earth-orbital missions — to form the Skylab Program, which was expected to include at least one and possibly two temporary Skylab Orbital Workshops. The first, Skylab A, was meant to receive at least three Apollo CSMs, each bearing a three-man crew, over a period of about nine months.

By late 1970, with just two Apollo Moon landings (Apollo 11 and Apollo 12) and the Apollo 13 accident under its belt, NASA cancelled three lunar landing missions. Apollo 20, the planned final Apollo lunar mission, was cancelled in early 1970 to free up its Saturn V rocket to launch Skylab A. Apollo 15, the planned fourth and last walking mission, was cancelled in September 1970, as was Apollo 19. NASA Administrator Thomas Paine dropped the missions at least partly in an attempt to to gain President Richard Nixon's support for a large permanent space station. The space agency renumbered the surviving missions so that Apollo lunar exploration would end with Apollo 17.

On 27 August 1971, Philip Culbertson, director of the Advanced Manned Missions Program Office 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 it, he outlined five Earth-orbital CSM missions for the 1970s 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 19 August. Based on his letter, Culbertson had phoned Berglund in an effort to impress on him the seriousness of NASA's budget situation.

Space Base: a large permanent Space Station, c. 1980. The nuclear-powered station, shown here passing over Australia and New Guinea, would have had a crew of from 50 to 100 persons. Image credit: NASA.
Berglund and his predecessor at MSC, Edward Olling, had throughout the 1960s remained staunch advocates of a large permanent Earth-orbiting space station. MSC Director Robert Gilruth was also a station supporter. They regarded AAP as at best a not-too-necessary rehearsal for a space station; they saw it at worst as a waste of time and money. They anticipated that before the mid-1970s AAP would draw to a close, freeing up funds for a real space station.

By mid-1971, however, it was increasingly obvious that a permanent space station was of interest neither to Nixon's White House nor the Congress. In fact, a reusable space station logistics resupply and crew rotation vehicle — a Space Shuttle — was by then emerging as the preferred post-Apollo program. The space station — if it were built at all — would have to wait until the Shuttle could launch its modules and bring them together in Earth orbit.

Culbertson referred to an unspecified new contract MSC had awarded CSM contractor North American. 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 options until the end of the [Fiscal Year] 1973 budget cycle." Fiscal Year 1973 would conclude on 1 October 1973.

Culbertson's five missions were all to some degree station-related. The first and simplest was an "independent CSM mission for earth observations." Earth observation by astronauts was often mentioned as a space station justification. The mission's CSM would probably include 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.

A SIM Bay was part of the final three Apollo lunar CSMs. The image above shows the Apollo 15 CSM Endeavour in lunar orbit with its rectangular SIM Bay (upper center) open to space. Image credit: NASA.
The second mission on Culbertson's list was an Apollo space station flight that would have been almost unimaginable at the time Kennedy diverted Apollo to the Moon. It would see a CSM dock in Earth orbit with a Soviet Salyut station.

Salyut 1, the world's first space station, had reached Earth orbit on 19 April 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 Patseyev, and Vladislav Volkov had undocked on 29 June 1971, after nearly 24 days in space (at the time, a new world record for human space endurance). The three cosmonauts had suffocated during reentry when a malfunctioning valve caused their capsule to lose pressure, so the Soviet Union halted all piloted missions while the Soyuz spacecraft was put through a significant redesign.

The third Earth-orbital CSM mission on Culbertson's list combined the first two missions. 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 CSM-119 dock first with a Salyut for a brief time, then undock and rendezvous with the dormant Skylab A Orbital Workshop. After docking with and reviving Skylab A, CSM-119's crew would live and work on board for an unspecified period.

Image credit: NASA.
NASA planned that, during the three CSM 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). The Salyut-Skylab A mission, which would include no rescue CSM, was planned to begin 18 months after Skylab A reached orbit, or about nine months after the third Skylab A mission returned to Earth.

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 CSM modified to carry five astronauts stood by. NASA had funded partial assembly of Skylab B so that it would have a backup in the pipeline in case Skylab A failed. Reflecting uncertainty about the availability of Saturn rockets and CSMs, Culbertson gave no date for the Skylab B launch.

Of the five missions Culbertson declared to be on the table in August 1971, none flew. In January 1972, Nixon called on Congress to fund Space Shuttle development, and Congress agreed. Shuttle costs and continued NASA budget cuts pushed even the least complex and cheapest of Culbertson's five missions off the table.

For a short time, his second mission looked to be within reach. Formal joint U.S./U.S.S.R. planning for an Apollo docking with a Salyut was under way when Culbertson wrote his letter. In early April 1972, however, 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.

NASA was disappointed to lose an opportunity for an early post-Skylab space station visit; the Nixon White House, on the other hand, saw the mission as a poster child for its policy of detente with the Soviet Union, so any sort of piloted docking mission would do. At the superpower summit in Moscow on 24 May 1972, Nixon and Soviet Premier Alexei Kosygin signed the agreement creating the Apollo-Soyuz Test Project (ASTP).

Skylab A, re-designated Skylab 1 (but more commonly called simply Skylab), reached orbit on 14 May 1973 on a two-stage Saturn V. It suffered damage during ascent, but NASA and its contractors pulled it back from the brink.

Skylab in a photograph taken by the second crew to live on board. Signs of damage the Orbital Workshop suffered during ascent to low-Earth orbit are obvious: one solar array wing is missing (left) and a hastily improvised solar shield stands in for the reflective meteoroid shield that would have protected Skylab's crew volume from the Sun. Image credit: NASA.
The three CSM missions to Skylab spanned 25 May-22 June 1973, 28 July-25 September 1973, and 16 November 1973-8 February 1974, respectively. Leaks in attitude control thrusters on the second CSM to dock with Skylab caused NASA to ready CSM-119 for flight, going so far as to roll it and its Saturn IB rocket out to the launch pad; the leaks stopped by themselves, however, so the rescue CSM remained earthbound.

In August 1973, with Skylab functioning well in Earth-orbit, NASA began to mothball its backup. Several plans were floated for putting Skylab B to use in Earth orbit. In December 1976, however, NASA turned the second Skylab over to the newly opened Smithsonian National Air and Space Museum on the National Mall in Washington, DC.

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, officially designated "Apollo" (but sometimes informally called Apollo 18), docked with Soyuz 19 on 17 July 1975. CSM-111 did not include a SIM Bay. The last CSM to reach space undocked on 19 July and, after a period during which its crew performed experiments in the CM, splashed down in the Pacific Ocean near Hawaii on 24 July 1975, six years to the day after Apollo 11, the first Moon landing mission, returned to Earth.

Artist concept of the Apollo-Soyuz docking in Earth orbit, 17 July 1975. Image credit: NASA.

A Summary of NASA Manned Spacecraft Center Advanced Earth Orbital Missions Space Station Activity from 1962 to 1969, Maxime Faget and Edward Olling, NASA Manned Spacecraft Center, February 1969.

Letter, Philip E. Culbertson to Rene A. Berglund, 27 August 1971.

Skylab News Reference, NASA Office of Public Affairs, March 1973, pp. IV-6 - IV-8.

Living and Working in Space: A History of Skylab, NASA SP-4298, W. David Compton and Charles Benson, NASA, 1983.

Thirty Years Together: A Chronology of U.S.-Soviet Space Cooperation, NASA CR 185707, David S. F. Portree, February 1993, pp. 9-26 (http://ntrs.nasa.gov/search.jsp?R=19930010786 — accessed 10 May 2017).

Mir Hardware Heritage, NASA RP 1357, David S. F. Portree, March 1995, pp. 33-35, 65-72 (http://history.nasa.gov/SP-4225/documentation/mhh/mhh.htm — accessed 10 May 2017).

"Skylab B: Unflown Missions, Lost Opportunities," Thomas Frieling, Quest, Volume 5, Number 4, 1996.

More Information

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

"Assuming That Everything Goes Perfectly Well In the Apollo Program. . ." (1967)

Apollo's End: NASA Cancels Apollo 15 & Apollo 19 to Save Station/Shuttle (1970)

A Bridge from Skylab to Station/Shuttle: Interim Space Station Program (1971)

Skylab-Salyut Space Laboratory (1972)

What If a Crew Became Stranded On Board the Skylab Space Station? (1972)

Reviving & Reusing Skylab in the Shuttle Era: NASA Marshall's November 1977 Pitch to NASA Headquarters


  1. Paragraph 12: "Apollo 15 and Apollo 19" should read "Apollo 18 and Apollo 19."

    1. 15 and 19 is correct. In September 1970, NASA canceled the last H-class mission (Apollo 15) and the last J-class (Apollo 19); then, as I state, renumbered the surviving missions to make Apollo 17 the last Apollo lunar mission. 16, intended as the first J-class mission and first LRV mission, became 15, 17 became 16, and 18 became 17.


  2. In the end the only earth observation space shuttle mission that produced a significant dataset still used to this day is SRTM. As a Remote Sensing Scientist the human spaceflight program has really not given that significant a contribution, SRTM has seen huge applications, the ISS has proven a good albeit data limited destination for sensors, especially those in the testing / space qualifying phase and some astronaut photography has value in that before Landsat 1 there were few EO sensors in space. It is nice to read about LEO applications of Apollo, even though with the benefit of hindsight only the ferry to Skylab seems worthy.

    1. If the US/Soviet Apollo-Salyut missions had come off, they might have been interesting, if only for the insights they would have provided into Soviet space technology and methods. Skylab B would have been pretty nifty - a nice gap-filler between ASTP and Shuttle, and Skylab B would certainly have remained in orbit long enough for a Shuttle visit and perhaps even reused in the Shuttle era.

      Agreed about the Earth observation missions, however. A question for you - did the Earth obs instrument package on Skylab contribute anything to the field?


    2. Your comment is the first time I have heard of the Skylab Earth observation instrument package, and I have a PhD in GIS & Remote Sensing. The start of operational remote sensing is considered to be Landsat 1 in 1972, perhaps a topic of a future post? Landsat 1 had two sensors, Return Beam Vidicon (RBV) and the USDA lobbied Multi Spectral Sensor (MSS). If you want today to look back in the 1970s you just download MSS imagery, despite that data's peculiarities (e.g. MSS pixels are not square) knowing how to treat and interpret it is part of the modern Remote Sensing student skillset. I started looking both at USGS Earth Explorer and REVERB Echo to see what Skylab data looks like. Nowadays we do not use film imagery so much. Reading the description of the datasets I would say that Skylab imagery does not have direct descendants in modern civilian remote sensing. Considering that the NRO used film well into the 1980s, I would not be surprised if it contributed to that side, but you should better ask someone familiar with military photoreconnaisance satellites.

  3. Fascinating that you have that GIS & Remote Sensing training and can place some of this in context for me. Thanks!

    Back in the good old days, when NASA put out big books summing up mission results for the public, they produced two pertinent volumes - SKYLAB EREP INVESTIGATIONS SUMMARY and SKYLAB EXPLORES THE EARTH. They are easily the fattest of the several Skylab summary books. The former is NASA SP-399 and the latter is NASA SP-380. EREP stood for Earth Resources Experiment Package. The book describes "thousands of photographs and miles of magnetic tape." My understanding is that the instrument package, which was located just below the forward docking port, operated pretty much automatically. Other experiments used the big wardroom window and (I think) The Earth-pointing science airlock. There's mention of Landsat-1 and Landsat-2 - the EREP package was meant to explore other parts of the spectrum. The EREP Program was begun in 1970.

    Most of this I'm drawing from memory - been a while since I looked at those books. Luckily, I have copies - I'll have to look at them again, maybe fold some new info into this post and (as you suggest) try to come up with a primary source document so I can cover early Landsat!


    1. The standard story of Landsat is that it is highly indebted to William T Pecora, USGS director. Back in the 1960s he was also president of the Century Club in DC and he convinced Congress to fund a civilian Remote Sensing Satellite program under USGS despite the objections of NASA and the unnameable agencies. The next thread in Remote Sensing is usually NOAA AVHRR and SPOT, the first private RS satellite, although private is subject to definition considering it was majority owned by CNES until 5 years ago. I will read the two reports you mentioned when I get the time. When we are talking about RS we usually mean a series of Vegetation Indices and other mathematical transformations of camera response to reflected radiation, plus a whole lot of literature on how to get a good number despite the soup of the atmosphere (land/ocean remote sensing) or on soup the atmosphere (meteorology) plus what the index corresponds to real world phenomena. Military remote sensing is more related to aerial photointerpretation, people in the loop looking for new building as opposed to algorithm trying to see if spring comes earlier than in 1972. Perhaps there were new bands in Skylab first tried there to pull out new methodologies, Hyperion (of EO-1 satellite) style. I'd have to look in the volumes but let's say the civilian side never really adopted film for various reasons.

  4. The EREP payload was never EVA serviced the way the ATM (which did use film) was, so I suspect the "thousands of feet of film" were generated on Earth from transmitted data and/or were a form of hyperbole meant to convey the volume of data involved. That was the main Earth obs payload. The smaller experiments seem to have used mainly hand-held cameras.

    The books I mentioned are heavily illustrated and nearly all the illustrations have informative captions. I suspect someone with your experience could glance through the images and get a lot out of it - you'd not need a lot of explanation to work out what they were doing all those years ago.


    1. My family's first computer was a PC XT with a 20 MB hard drive. A Landsat 4 TM image, contemporary of the time, has a size 450 MB, not to mention that a Hercules monitor was only black and white. At conference we were told that back in those days a single LANDSAT image arrived in 7 tapes, one per spectral band, so your comment makes sense. Now in the building across from where you are at Flagstaff there is an excellent Remote Sensing group, one of Prasad's postmaster students was a classmate of mine and he showed me your building a few months ago when I visited him, he took a picture of me in the rover at your entrance. I will gladly give you all the help you need but there are people physically closer to you that are able to answer some questions, not just me random guy on the web.

  5. USGS Astro has connections with the Remote Sensing gang through joint projects, and a good friend worked with them until recently. Our kiddos are in the same grade and we have made it a habit of taking them to the County Fair and trick-or-treating each year. The "space people" world is really quite small.

    I'm not actually after more Earth obs info at this time; I thought I was helping you with some Skylab Earth obs tips, not the other way around! But never mind - I appreciate your inputs and I'll keep in mind the folks across the parking lot if I need some help in the future.



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