Chronology: Apollo-Shuttle Transition 1.0

Image credit: NASA.

Blogging history can be awkward — at least the way I do it. I tend to blog about whatever catches my interest as I sift through my files or locate new documents. The result is nothing like chronological, and chronology — the order in which things happened — is obviously essential for understanding history.

Because of this, I've decided to occasionally compile posts on a theme — posts that tell parts of one story — as a "chronological presentation." The posts listed below all can stand alone, but when placed together in chronological order they tell a more comprehensive story. As future posts fill in more gaps, the story will become more complete. Eventually, I'll post a 2.0 version of the link list below (and perhaps a 3.0 version after that).

Series Development: A 1969 Plan to Merge Shuttle and Saturn V to Spread Out Space Program Cost (December 1969)

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

McDonnell Douglas Phase B Space Station (June 1970)

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

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

The Last Days of the Nuclear Shuttle (February 1971)

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

Where to Launch and Land the Space Shuttle? (April 1972)

What If a Space Shuttle Orbiter Had to Ditch? (1975)

Final approach: the inner and outer wing flaps and body flap are visible at the aft end of the descending Orbiter. Image credit: NASA.

High on any pilot's list of things not to do with an aircraft is to ditch — that is, to make an emergency landing in water. Planes that nimbly slip through air become about as graceful as a brick when they touch an ocean swell. Anyone who has flubbed a dive and belly-flopped knows how painfully hard water can be.

Aircraft ditching behavior became of great interest in the United States during the Second World War, when B-24 Liberator bombers damaged by enemy fighters and flak — or simply lost and low on fuel — ended otherwise successful bombing runs over Nazi Germany by ditching in the English Channel or North Sea. Even in calm seas, the B-24 did not fare well. More often than not the plane broke apart and sank within minutes.

The Arsenal of Democracy: Workers assemble B-24 Liberator aircraft in the Consolidated Vultee plant in Fort Worth, Texas. More than 18,000 B-24s flew a wide range of missions in all Second World War operational theaters. Image credit: Wikipedia.

Because of this, on 20 September 1944, four months past the beginning of the D-Day invasion of Europe, a B-24 Liberator with two brave airmen on board intentionally ditched in the calm waters of Virginia's James River. Close by in a small boat was a team of engineers from the National Advisory Committee for Aeronautics (NACA) Langley Aeronautical Laboratory in nearby Hampton, Virginia. As the 44,100-pound, four-engine, straight-wing aircraft skimmed the water's surface at 97 miles per hour with its landing gear up, instruments inside the fuselage collected data on motion and deceleration.

The B-24's belly touched water at a point just behind the wing trailing edges. The plane began to skip, its nose rising and dipping to the left; then the water seemed to grab the bomber hard. Inside, the crew felt deceleration equal to 2.6 times the force of Earth's gravity. It threw them forward against their safety harnesses. Propellers still whirling, the plane nosed down and pieces flew out of an enormous cloud of spray that momentarily hid it from view. Rescuers moved in quickly; meanwhile, both pilots climbed atop the aircraft.

The men were in good shape, but their plane, a veteran of several European bombing missions, would never fly again. Even under the relatively benign conditions of the test, its fuselage had cracked, nearly breaking in two. The crack acted as a hinge, so the plane floated, rapidly filling with water, with both its tail and its nose in the air. The right inboard motor was gone, sheared away upon contact with the water.

When the NACA engineers lowered themselves inside to recover their instruments, they were in for a shock. Almost every piece of equipment bolted to the interior of the B-24 had torn loose and been flung forward, forming a nearly impassable heap just behind the cockpit. They found their instruments, secure in water-tight containers; meanwhile, a U.S. Navy salvage boat with a crane moved in fast to hoist the plane out of the water before it joined its missing engine 30 feet down on the muddy bottom of the James River. Smaller boats collected floating pieces.

On the salvage boat's deck, the plane looked even worse than it had in the river. A large dent marked where its belly first touched the water at a descent rate of 1.8 feet per second. Though they had been reinforced for the ditching test, the bomb bay doors had been pressed inward. The bomber's thin skin was rumpled over large areas; where it wasn't creased and puckered, it was ripped.

The 20 September 1944 ditching test became a pivotal event in aerospace history. It brought home to engineers as never before the powerful forces that ditching brought to bear on aircraft. It led NACA Langley to study ditching behavior in many types of aircraft. Because ditching full-size planes was both costly and dangerous, the lab developed techniques for testing scale-model airplanes in a water trough in what became known as the Langley Impacting Structures Facility (LISF). Above all, their experiments showed that ditching was actually crashing.

Fast forward 30 years to 1975. The era of scale-model experiments was gradually drawing to a close — computer models of complex phenomena, though still crude and costly, had made their debut in aviation and other fields. When NASA had formed in 1958, Langley had become one of its research centers. With the splashdown of the Apollo-Soyuz Test Project Apollo Command Module in the Pacific Ocean in July 1975, the first era of U.S. space capsules was over. The era of wings in Earth orbit was about the begin.

The Space Shuttle stack as envisioned in 1975 with major components indicated. Image credit: NASA.

NASA and its contractors envisioned several plausible scenarios which might lead a Space Shuttle Orbiter to ditch. The Orbiter was a glider, so it could not try again if it missed its runway at Kennedy Space Center (KSC), Florida. If the Orbiter crew realized the problem in time, they might ditch in the Banana or Indian Rivers or in the Atlantic Ocean off Cape Canaveral.

In the event that two of the Orbiter's three Space Shuttle Main Engines (SSMEs) failed early in its ascent to space, the Orbiter would need to return to KSC; however, depending on when the engines failed, it might not have enough altitude and energy to turn around, line up with the Shuttle runway, and stretch out its descent. In that case, it would probably fall short of the coast.

In October 1975, William Thomas, a former Langley engineer who had taken a job with Grumman Aerospace Corporation in Bethpage, New York, published results of 67 tests of a 1/20-scale model of the Space Shuttle Orbiter. The tests took place in the LISF starting in 1974. The actual Orbiter was planned to be 37.2 meters (122 feet) long, so the tests saw a 1.86-meter (6.1-foot) fiberglass and balsa-wood Orbiter launched into a broad trough of water using a ceiling-mounted "catapult" device. The trough could simulate smooth seas or seas with swells and waves.

The model included a replaceable balsa insert designed to give some sense of the belly damage a ditching Orbiter could expect. Removable weights enabled Thomas to simulate either 32,000-pound or 65,000-pound cargoes in its cargo bay. With the lighter cargo, the full-scale Orbiter would weigh 85,464 kilograms (188,247 pounds); with the heavier, 103,200 kilograms (227,313 pounds). The corresponding model weights were 10.68 kilograms (23.53 pounds) and 12.9 kilograms (28.41 pounds). Small lead weights permitted tests at intermediate Orbiter weights and allowed Thomas to trim the model so that it would, for example, dip one wing as it approached the water.

The model also included adjustable flaps and landing gear which could be installed to simulate gear-down ditching or left off to simulate ditching with landing gear doors closed. Flaps and landing gear were designed to break away at scale stresses — for example, on a full-sized Orbiter, the main landing gear would fail under a load of 356,270 pounds. The 1/20-scale landing gear would break if subjected to a torque of 6.41 pounds.

In the first of the 67 tests, the model Orbiter's nose was pitched up 16°, its aft-mounted body flap — located below the SSME engine bells — was tilted down 11.7°, and its wing flaps (inner and outer) were tilted up 4°. The water in the LISF trough was calm.

The 1/20-scale Orbiter, with a simulated mass of 93,000 kilograms and a simulated speed of 53.5 meters per second (just 120 miles per hour — slow for a Shuttle landing), contacted the water with its landing gear up. It skipped, then sank deeper on the next contact. The model decelerated very rapidly — it stopped four fuselage lengths from where it first touched the water. For the full-size Orbiter, this would have amounted to about 160 meters (490 feet). It was, Thomas commented, a "very stable run."

Beginning with Test 4, the model Orbiter was fitted with instruments for recording normal (fore-aft) and longitudinal (left-right) deceleration. These revealed that even a perfect ditching would likely harm the Orbiter crew. Apart from the instrumentation, the Test 4 Orbiter model was configured exactly like the Test 1 model. It touched calm water with its nose pitched up 12° moving at a scale speed of 72 meters per second (161 miles per hour).

Had it been a full-scale Orbiter carrying a crew, they would, after the initial skip, have been thrown forward against their straps with a force equal to 8.3 times the pull of Earth's gravity. As the Orbiter swerved to a stop, they would have felt a longitudinal jolt of 4.5 gravities. Test 4 was, it would turn out, only a little more arduous than average.

For Test 5, conditions were virtually identical to those of Test 4. Landing speed was slightly higher at 75.1 meters per second (168 miles per hour). Yet had the model been a full-scale Orbiter, it would have subjected its crew to 19.4 gravities of deceleration when it made its second contact with the water. The model's inner wing flaps broke free; this hinted that structural damage to the full-scale Orbiter was likely.

The first test of an Orbiter model with a simulated 65,000-pound payload (Test 17) saw a scale deceleration of nearly 11 gravities. In all, 14 of the 67 tests subjected the model Orbiter to greater than 10 gravities of scale deceleration.

Tests 9 and 62 were without question the most dramatic. In both, the model Orbiter stalled following release and hit the water tail first.

Other tests saw the 1/20-scale Orbiter model skip along simulated 2.1-meter (seven-foot) wave crests, plow through waves with a series of sharp jolts, dive under the water and bob to the surface, and lose both its inner and outer wing flaps. Tests with landing gear down never went well; the gear always broke away. In a full-scale Orbiter, tearing away the landing gear would likely have permitted water to enter through the damaged wheel wells.

Thomas's interpretation of the results of the 67 tests was notable: "a fairly smooth runout is expected but considerable fuselage tearing and leaking or flooding will occur." He was confident, however, that a full-scale Orbiter would remain afloat if its wings, which contained hollow spaces, remained intact. The more damage the wings suffered, the faster the Orbiter would sink.

The LISF 1/20-scale Orbiter tests were, of course, simplistic. They did not reflect the fact that Space Shuttle Orbiters were not designed to withstand the deceleration loads most of the model tests indicated. The average ditching deceleration ranged between five and eight gravities; this would have been sufficient to cause significant structural damage. In other words, in almost all cases, the Orbiter would have snapped apart.

Moments before the end: the plume from the Solid Rocket Booster leak that doomed Challenger is clearly visible. Image credit: NASA.

A little more than a decade later (28 January 1986), the Challenger accident made obvious the Space Shuttle Orbiter's fracture lines. The Orbiter Challenger did not explode; rather, the brown External Tank (ET) upon which it rode and from which it drew liquid hydrogen/liquid oxygen propellants for its SSMEs was destroyed by a malfunctioning Solid Rocket Booster (severe wind shear might also have played a role).

The fuel and oxidizer the ET contained came together and ignited, producing an explosion, but it was aerodynamic forces that tore the Orbiter apart. Basically, as its ET disintegrated, Challenger's nose stopped pointing in the right direction. This subjected it to drag and deceleration.

The crew compartment broke free, trailing behind it a comet's tail of cables. Some of the crew inside remained conscious long enough to take prescribed — though futile — emergency measures. The compartment remained mostly intact until it hit the water about two minutes later.

The Payload Bay disintegrated, but Challenger's main payload, a Tracking and Data Relay Satellite with an attached Inertial Upper Stage, remained more or less intact as it flew free of the fireball and fell toward the Atlantic. Challenger's wings separated, partly disintegrating. Each, however, remained recognizable in images and video captured from the ground. The aft compartment containing the SSMEs also emerged from the fireball mostly intact.

After Challenger, the Space Shuttle Program came under intense scrutiny. The Report to the President by the Presidential Commission on the Space Shuttle Challenger Accident cited Thomas's 1975 report when it stated that the probability was high that a Shuttle Orbiter would break up and sink after a ditching. Even if the Orbiter remained intact, the Commission report continued, cargoes mounted in the Payload Bay would break loose from their supports, slide forward, and smash into the back of the crew cabin. Though Thomas's report did not in fact say these things, they were logical conclusions based on the results of the 67 1/20-scale model Orbiter test runs.

Sources

YouTube - "Ditching of a B-24 Airplane into the James River" (https://youtu.be/WjadMxpXprk — uploaded by Jeff Quitney — accessed 16 January 2016).

YouTube - "Space Shuttle Orbiter Ditching Investigation of a 1/20-Scale Model" (https://www.youtube.com/watch?v=dlG-HcZIDl0 — uploaded by Jeff Quitney — accessed 16 January 2016).

Ditching Investigations of Dynamic Models and Effects of Design Parameters on Ditching Characteristics, Report 1347, L. Fisher and E. Hoffman, Langley Aeronautical Laboratory, National Advisory Committee for Aeronautics, 1958.

Ditching Investigation of a 1/20-Scale Model of the Space Shuttle Orbiter, NASA Contractor Report 2593, W. Thomas, NASA, October 1975.

Report to the President by the Presidential Commission on the Space Shuttle Challenger Accident, Presidential Commission on the Space Shuttle Challenger Accident, Volume I, pp. 182-183, June 1986.

"A Plane Crash in 1944 Is Saving Lives Today," Peter Frost, Daily Press, 22 February 2009 (http://articles.dailypress.com/2009-02-22/news/0902210116_1_b-24-successful-emergency-landing-hudson-river - accessed 16 January 2016).

More Information

What If an Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

What If a Lunar Module Ran Low on Fuel and Aborted Its Landing? (1966)

Where to Launch and Land the Space Shuttle? (1971-1972)

What Shuttle Should Have Been: NASA's October 1977 Space Shuttle Flight Manifest

One Space Shuttle, Two Cargo Volumes: Martin Marietta's Aft Cargo Carrier (1982)

Series Development: A 1969 Plan to Merge Shuttle and Saturn V to Spread Out Space Program Cost

Apollo 4, the first Saturn V rocket to fly, departs the Vertical Assembly Building bound for Pad 39A, 26 August 1967. LUT 1 rides beside the rocket on a crawler-transporter; a second LUT in the background awaits its first launch. Image credit: NASA.

A red-painted Launch Umbilical Tower (LUT) was the Saturn V's constant companion from the moment technicians lowered the rocket's 138-foot-tall S-IC first stage into place beside it within a Vertical Assembly Building (VAB) high bay until shortly after the S-IC's engines ignited on one of the twin Launch Complex (LC) 39 pads. At the moment of liftoff, the nine servicing arms linking the 398-foot-tall LUT to the 363-foot-tall Saturn V would retract or swing out of the way; then, between 1.4 and 9.4 seconds after liftoff, the rocket would perform a LUT clearance yaw maneuver, its five F-1 engines bathing the launch pad in flame. After that, the LUT would stand alone, awaiting transport back to the VAB atop one of Kennedy Space Center's two enormous crawler-transporters and assembly of a new Saturn V.

By late 1969, with the Apollo 11 and 12 lunar landing missions successfully accomplished, it had become clear that only a few more Saturn V rockets would depart LC 39 for the Moon. The $25-billion Apollo Program had achieved its goal of humbling the Soviet Union, and many outside of space industry and the fledgling planetary science community saw little cause to continue it.

Meanwhile, NASA Administrator Thomas Paine aspired to replace the Moon program with a large Earth-orbiting Space Station serviced by a fully reusable crew rotation and logistics resupply spacecraft (a "Space Shuttle"). A fully functional 6-man or 12-man core station would reach Earth orbit on a Saturn V rocket; later, Saturn V rockets would launch multiple large Space Station modules which would be brought together to form a 50- or 100-man "Space Base." By the beginning of the 1980s these would, it was hoped, become elements in an Integrated Program Plan that would lead to a piloted lunar surface base and humans on Mars by 1990.

The Nixon White House and the Congress would have none of it, however. By the time Congress passed the $3.75-billion Fiscal Year 1970 NASA budget — the lowest since 1962, the first year of the Apollo Program build-up — space planners had begun to seek tactics that they could use to achieve ambitious goals while spreading out costs. One of those tactics was "series development."

Booster-first development: in this artist concept, a reusable Space Shuttle Booster carries an expendable Saturn S-IVB stage and payload to the edge of space. Image credit: NASA.

As applied to the Space Shuttle, series development could take either of two forms. In the first, the Space Shuttle's fully reusable piloted Booster would be developed and brought into service, then development work would begin on its fully reusable piloted Orbiter.

Until the Orbiter became available, the suborbital Booster would lift off from Cape Kennedy, Florida, carrying on its back an unmanned payload attached to an expendable upper stage based on an existing stage design — the Saturn V S-IVB third stage was one attractive candidate. The upper stage would ignite high over the Atlantic, boosting the payload to Earth orbit — or beyond. The astronauts, meanwhile, would pilot the Booster back to a runway at Cape Kennedy, where it would be refurbished, mated with a new upper stage and payload, and flown again.

Three-stage Saturn V rocket with Apollo spacecraft payload on top, Orbiter with Saturn S-IC first stage, and LUT with nine Apollo Saturn V servicing arms. Image credit: Bellcomm/NASA.

More attractive to space planners eager to see astronauts continue to fly into orbit (that is, almost all of them) was development of the Shuttle Orbiter followed by development of the Booster. In this "Orbiter-first" scenario, an expendable Saturn V S-IC would stand in for the Booster during the first few years of Shuttle flights.

On the last day of 1969, C. Eley, an engineer with Bellcomm, NASA's Washington, DC-based planning contractor, published a memorandum in which he examined how the Orbiter/S-IC combination might be serviced and launched using a LUT "without extensive [and expensive] modifications." Eley assumed that the S-IC would fly virtually unmodified (apart from a 10-foot-long streamlined shroud linking its dome-shaped top to the Orbiter's tail) and that the Orbiter would measure 183 feet long. This would make the combination 331 feet tall, or 32 feet shorter than the Apollo Saturn V.

Eley found that LUT servicing arms 1, 2, 4, 8, and 9 would remain useful for Orbiter/S-IC pre-launch servicing. He recommended that arms 3, 5, 6, and 7 be removed and stored to prevent them from becoming damaged (implying, perhaps, that the LUT might be restored to its original form and purpose — that is, launching Saturn V rockets — at some point). Arms 1 and 2, which would service the S-IC stage, would remain completely unchanged in form and function.

Orbiter-first development: a reusable Shuttle Orbiter with an expendable Saturn S-IC first stage stands beside a modified LUT. Image credit: Bellcomm/NASA.

All Orbiter servicing — for example, propellants loading — would employ arm 4, close by the Orbiter's tail. Arm 8 would provide services — for example, cooling — to the payload in the Orbiter payload bay, but would not enable access to the payload because the Orbiter's top side, where its payload bay doors would be located, would face away from the LUT on the pad. Eley assumed that the Mobile Servicing Structure used during Apollo to reach parts of the Saturn V located out of reach of the LUT arms would not be used with the Orbiter/S-IC. He suggested that a special arm be added to the LUT if payload access on the launch pad were judged to be necessary. Arm 9 would reach out from the LUT to cap the Orbiter's nose, permitting access to its crew cabin.

Eley then examined the probable launch rate of the Orbiter/S-IC stage Space Shuttle. He made three assumptions about the Orbiter and the LUT: that the Orbiter would include an "autonomous checkout capability" that would help to reduce to from five to 10 days the time spent on the launch pad prior to launch; that all three Apollo LUTs would be modified for Orbiter/S-IC launches; and that experience would prove that a LUT could be fully refurbished within 15 days of taking part in a launch.

If these assumptions were shown to be correct, Eley found, then more than 40 Orbiter/S-IC launches could take place in a year. If, on the other hand, only a single modified LUT, a 30-day LUT refurbishment period, and an on-pad preparation time no less than 30 days were assumed, then only six or seven Orbiter/S-IC flights could occur per year.

A little more than two years after Eley completed his memorandum, budget shortfalls forced NASA to postpone Space Station development until after the Shuttle flew — another example of series development. Shuttle Orbiters, not Saturn V rockets, would launch NASA's future Space Station. The Station would be launched in pieces in the Shuttle Orbiter payload bay and assembled in Earth orbit.

Two of the Apollo LUTs were put to use in the Space Shuttle Program, though not as Eley envisioned. NASA partially dismantled them, reducing their height to 247 feet (not counting a new 80-foot-tall lightning mast), then permanently mounted them on the two LC 39 pads. The third LUT was dismantled sometime after 1982 and scrapped in 2004 after its peeling red paint was judged to be an environmental hazard.

Sources

"Feasibility of Shuttle (Orbiter)/S-IC Launches at LC-39 — Case 320," C. Eley, Bellcomm, Inc., 31 December 1969.

Welcome to the Save the LUT Campaign (http://www.savethelut.org/ — accessed 19 November 2015)

More Information

What if an Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

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

McDonnell Douglas Phase B Space Station (1970)

Where to Launch and Land the Space Shuttle? (1971-1972)

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

The Skylab Orbital Workshop as seen by the Skylab 4 crew, the last astronauts to live on the station. Image credit: NASA.

On 14 May 1973, the last Saturn V rocket to fly, designated SA-513, launched the Skylab space station into a 435-kilometer-high orbit about the Earth. Flight controllers soon realized that the 85-ton space laboratory was in trouble. Although they did not know it at the time — Skylab climbed rapidly into dense clouds, so could not be imaged during most of its ascent — 63 seconds after liftoff a design flaw caused its meteoroid shield to rip away. Shield debris jammed one of the workshop's two main electricity-producing solar arrays. The other array remained attached to Skylab's side only at its hinge (forward) end.

Shield debris also pummeled SA-513, tearing at least one hole in the tapered interstage adapter that linked its S-II second stage with the Skylab station. Debris also apparently damaged the system for separating the cylindrical adapter that linked the S-II to the S-IC first stage. The adapter, meant to separate shortly after the spent S-IC, remained stubbornly attached to the S-II all the way to orbit.

Skylab 1 launch, 14 May 1973. Image credit: NASA.

After the S-II's five J-2 engines shut down, forward-facing solid-propellant rockets ignited to push the spent stage away from Skylab. Their plumes blasted open and tore away the loose solar array. Ironically, the jammed array probably survived because it was tied down by meteoroid shield debris.

Without the protection of the reflective meteoroid shield, temperatures within Skylab's 11,303-cubic-foot pressurized volume soon soared, raising fears that its air would become tainted by outgassing from materials on board, film would be ruined, and food and medicines spoiled. Flight controllers soon found to their dismay that maneuvers designed to cool Skylab's interior tended to starve it of electricity, for they turned away from the Sun the four "windmill" solar arrays on the Apollo Telescope Mount (ATM), the beleaguered space laboratory's only functioning sources of power.

NASA immediately began a Skylab salvage effort. Engineers developed deployable sunshields and tools for freeing the stuck main solar array, flight controllers carefully maneuvered Skylab to maximize the amount of electricity the ATM arrays could produce while reducing temperatures on board as much as possible, and the first crew meant to board Skylab (their mission was designated Skylab 2) hurriedly trained to become the world's first orbital repairmen.

Skylab 2 astronauts Joseph Kerwin, Charles "Pete" Conrad, and Paul Weitz. Image credit: NASA.

On 25 May, the Skylab 2 crew of Pete Conrad, Paul Weitz, and Joe Kerwin lifted off in an Apollo Command and Service Module (CSM) atop a Saturn IB rocket. After a failed attempt to pull open the one remaining main solar array with a hook extended from the open CSM hatch, they docked with and entered Skylab, then deployed a sunshield through an experiment airlock. Temperatures began to fall, but the station remained starved for electricity. On 7 June, Conrad and Kerwin succeeded in forcing open the surviving main solar array, saving not only their own 28-day mission but also the planned Skylab 3 and Skylab 4 missions.

The Skylab 3 crew of Alan Bean, Jack Lousma, and Owen Garriott lifted off on 28 July. During their 6 August spacewalk, Lousma and Garriott deployed an improved sunshield. They lived and worked on board the station for 59 days.

The Skylab 4 crew of Jerry Carr, William Pogue, and Ed Gibson boarded the station on 16 November. Carr and Gibson mounted a meteoroid collector on an ATM strut during their spacewalk on 3 February 1974, in the hope that a Space Shuttle crew might retrieve it as early as 1979. When the Skylab 4 crew undocked on 8 February 1974 after a record-breaking 84 days in space, Skylab was expected to remain aloft until 1983, when atmospheric drag would cause it to re-enter Earth's atmosphere. They left Skylab's airlock hatch closed but not latched so that it could provide entry for future visitors.

This pre-launch cutaway illustration of Skylab shows the station as it would have appeared if it had reached Earth orbit undamaged. In addition to two large main solar arrays, it includes the micrometeoroid shield which tore free during Skylab's ascent through the atmosphere. Skylab was the largest single-launch space station ever; astronauts, dressed in brown, look very small inside it. Image credit: NASA.

During the solar-minimum years of the mid-1970s, the Sun was more active than had been anticipated at the time of Skylab's launch. Solar activity heated and expanded Earth's upper atmosphere, subjecting the first U.S. space station to more aerodynamic drag than expected. In March 1977, the NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama, asked NASA Headquarters to grant it permission by mid-1977 to begin work on a mission to raise Skylab's orbital altitude so that its lifespan could be extended, giving NASA time to consider future uses for the space station.

That MSFC maintained a strong proprietary interest in Skylab should not be surprising. In November 1965, the Huntsville center had proposed that a space laboratory based on a spent Saturn V S-IVB stage be added to the Apollo Applications Program (AAP), at the time NASA's main post-Apollo piloted program. The spent-stage AAP workshop, a low-cost space station, had much greater potential for supporting long-duration astronaut stays in orbit than did modified Apollo CSM and Lunar Module (LM) spacecraft. NASA Headquarters quickly approved MSFC's plan.

For its first three-and-a-half years, the AAP Workshop was the S-IVB second stage of a Saturn IB rocket and, on its top, a small pressurized module with multiple docking ports. During ascent to Earth orbit, it would act as a normal Saturn IB stage. After its single J-2 rocket motor shut down, the four segments of its streamlined launch shroud would open like the petals of a flower, revealing the docking module. Controllers would then command vents in the stage to open so that residual liquid oxygen/liquid hydrogen propellants could escape into space. Meanwhile, solar arrays would unfold from the inside of two of the four shroud segments to generate electricity.

The AAP spent-stage workshop. At left an AAP CSM docks with one of the docking modules four radial ports through the intermediary of an add-on module. Image credit: NASA.

A crew launched on a second Saturn IB would rendezvous and dock with the spent stage in an AAP CSM, enter the docking module, then enter the cavernous liquid hydrogen tank, the largest of the two S-IVB stage tanks. They would pressurize the tank with gaseous oxygen and nitrogen from tanks in the docking module, then install in the tank furnishings, fabric floors and walls, lights, and experiments transferred from the CSM and docking module. Subsequent AAP Saturn IB/CSM flights would deliver Earth-looking and space-looking science modules for attachment to the docking module, including an array of solar telescopes based on the Apollo LM design.

In July 1969, NASA Administrator Thomas Paine approved plans to shift from the Saturn IB-launched "wet workshop" (as it was colloquially known) to a Saturn V-launched "dry workshop." The latter, more capable than the former, would include neither propellants nor an engine and would reach Earth orbit fully outfitted. In February 1970, the AAP workshop (and, indeed, AAP as a whole) was renamed Skylab. NASA Headquarters made MSFC responsible for Skylab Saturn V and Saturn IB rockets, overall Skylab systems engineering and integration, and most onboard experiment apparatus.

On 10 June 1977, former Skylab Deputy Director John Disher, by then NASA's Director of Advanced Programs, requested that MSFC conduct a preliminary in-house study of the feasibility of reusing Skylab in the Space Shuttle era. At about the same time, NASA Headquarters directed NASA Johnson Space Center (JSC), lead center for the Space Shuttle, to study an early Shuttle mission to either boost Skylab to a higher, longer-lived orbit or cause it to safely reenter over an unpopulated area.

In September 1977, JSC informed NASA Headquarters and MSFC that the earliest it could reboost or deboost Skylab was September 1979, as part of the fifth Orbital Flight Test (OFT) Shuttle mission. At the time, NASA envisioned a total of six OFT missions before the Shuttle was declared operational. NASA Headquarters then gave the go-ahead for MSFC and JSC to begin work toward a September 1979 Skylab reboost/deboost mission.

On 16 November 1977, MSFC engineers J. Murphy, B. Chubb, and H. Gierow presented to NASA Associate Administrator for Space Flight John Yardley results of the study they had begun in June. They were addressing a Skylab expert: before coming to NASA in 1974, Yardley had managed Skylab work at McDonnell Douglas, the prime contractor for the OWS.

The MSFC engineers first described Skylab's condition. They reported that when the Skylab 4 crew returned to Earth, the Orbital Workshop's water system contained 1930 pounds of water (enough to supply three men for 60 days). The water, they said, probably remained potable, but might have developed a bad taste. If it was no longer potable, then it might be used for bathing. In any case, the Skylab water system included resupply points, so a Space Shuttle crew could refill it with fresh water if water transfer equipment were developed.

The oxygen/nitrogen supply remaining on Skylab was probably sufficient to supply three men for 140 days at Skylab's standard operating pressure of five pounds per square inch, the MSFC engineers estimated. The station's ventilation and carbon dioxide-removal systems were almost certainly functional. Even if they were not, their most important components were designed to be replaceable in space.

The MSFC engineers also assessed Skylab's electrical power system. They estimated that the main solar array Conrad and Kerwin had freed could still generate between 1.5 and 2.5 kilowatts of electricity, and that the batteries it had charged, located in Skylab's Airlock Module, were probably still usable. The batteries for the four ATM arrays, located inside the ATM, were, on the other hand, almost certainly frozen. The team recommended that controllers reactivate the main array electrical system from the ground before the first Shuttle visit, and that any effort to revive the ATM electrical system be left for a later time.

More problematic than the electrical system was Skylab's attitude control system, which relied on a trio of Control Moment Gyros (CMGs) to turn Skylab so that, among other things, it could reliably point its solar arrays at the Sun. At the time the Skylab 4 crew departed, one CMG had already failed and another showed signs of impending failure. In addition, Skylab's guidance computer was probably dead after being subjected to "extreme thermal cycling" as Skylab passed between daylight and night. The Orbital Workshop's thruster system, on the other hand, was probably operational with about 30 days of propellant remaining.

Finally, the MSFC team looked at Skylab's cooling system, which had leaked while the astronauts were on board and had probably frozen and ruptured since the last crew returned to Earth. They called "serviceability of [the] cooling system. . .the most questionable area" as far as Skylab's reusability was concerned, but added that "any inflight 'fixes' should be well within the scope of crew capability."

The MSFC engineers then proposed a four-phase plan for reactivating and reusing Skylab. The target date for their first Phase I milestone had already passed by the time they briefed Yardley: though it was already mid-November, they made a point of calling for an October 1977 decision on whether Skylab should be reboosted to a higher orbit, extending its orbital lifetime until about 1990, or deboosted so that it could reenter safely over an unpopulated area.

Assuming that NASA decided to reboost Skylab, then a ground-controlled Skylab reactivation test would occur between June 1978 and March 1979. If the test was successful, then the fifth OFT Space Shuttle mission would rendezvous with Skylab. As already mentioned, in September 1977 JSC estimated that the fifth OFT would fly in September 1979. Two months later, when the MSFC team briefed Yardley, the mission had already slipped to February 1980.

Artist concept of Teleoperator spacecraft. Image credit: NASA.

The MSFC team anticipated that the Space Shuttle crew would conduct an inspection fly-around of Skylab, then would deploy an unmanned Teleoperator spacecraft from the Shuttle Orbiter payload bay. Using a control panel on the Orbiter flight deck, the astronauts would guide the Teleoperator, which would carry an Apollo probe-type docking unit, to a docking with the drogue-type docking unit on the front of Skylab's Multiple Docking Adapter. The Teleoperator would fire its thrusters to raise Skylab's orbit; then, its work completed, it would detach, freeing up Skylab's front docking port for Phase II of MSFC's plan.

Astronauts in a nearby Space Shuttle Orbiter stand by as the Teleoperator ignites its thrusters to raise Skylab's orbit and extend its orbital lifetime. Image credit: NASA.

Phase II would begin in March 1980, when NASA would initiate development of Skylab refurbishment kits, a 10-foot-long Docking Adapter (DA) module, and a 25-kilowatt Power Module (PM). The DA would include at one end an Apollo-type probe docking unit for attaching it to Skylab's front port and at the other end an Apollo-Soyuz-type androgynous unit with which Shuttle Orbiters and the PM could dock.

The first refurbishment kit and the DA would reach Skylab on board a Shuttle Orbiter in January 1982, almost two years after the reboost mission. During the 1982 mission, spacewalking astronauts would fold two of the four ATM solar arrays out of the way to improve clearance for visiting Orbiters and would retrieve the meteoroid experiment the Skylab 4 astronauts had left on the ATM. As time allowed, this and other Phase II crews would perform unspecified "simple passive experiments" on board Skylab and would collect samples of its structure for engineering analysis on Earth.

The third Shuttle visit to Skylab would not take place until August 1983. The astronauts would install additional refurbishment kits and would tackle the daunting job of repairing Skylab's damaged cooling system.

The refurbished Skylab station after the start of Phase III of the NASA MSFC reactivation program. The Power Module, Docking Adapter, and Shuttle-carried Spacelab are clearly visible. Image credit: Junior Miranda.

The MSFC engineers told Yardley that Phase III of the Skylab reactivation program would begin in March 1984 with delivery of the PM and any remaining refurbishment kits. Using the Shuttle Remote Manipulator System robot arm, astronauts would lift the PM from the Orbiter payload bay and turn it 180° so that it protruded forward well beyond the Orbiter's nose. They would then dock one of the PM's three androgynous docking units to an identical unit at the front of the Orbiter payload bay. The Shuttle would use another of the PM's docking units to dock with the DA on Skylab.

Following docking with Skylab, the astronauts would deploy the PM's twin solar arrays and thermal radiators, link the PM to Skylab's systems using cables extended through open hatchways or installed on the hull during spacewalks, and power up the PM's three CMGs to replace Skylab's crippled attitude control system. The Orbiter would then undock from the PM, leaving it attached permanently to Skylab. Shortly thereafter, NASA would declare the revived and expanded Orbital Workshop to be fully habitable.

Phase III would continue with the first in a series of 30-to-90-day missions aboard Skylab. During these, a Shuttle Orbiter carrying a Spacelab module in its cargo bay would remain docked with the Orbital Workshop. The astronauts would work in the Spacelab module, take advantage of Skylab's large pressurized volume to perform "simple experiments" requiring more room than Shuttle and Spacelab could provide (for example, preliminary trials of space construction methods), and begin building up stockpiles of food, film, clothing, and other supplies on the revived station.

Another 30-to-90-day mission would see the astronauts refurbish and use selected Skylab science equipment, install new experiments based on Spacelab experiment designs, and stockpile more supplies. Between these missions, the new and improved Skylab would fly unmanned under control from the ground.

The view from the Sun: all of the solar arrays deployed for Phase III of the Skylab reactivation program are visible in this image by Junior Miranda.

The MSFC engineers told Yardley that the volume available to a crew on board a Shuttle Orbiter without a Spacelab module in its payload bay would total only 1110 cubic feet. Adding a Spacelab would increase that to about 5100 cubic feet. This would, however, amount to less than half the pressurized volume of Skylab. For a mission including a Shuttle Orbiter, Spacelab module, and Skylab, the total volume available to the crew would exceed 16,400 cubic feet.

They were not specific about what Skylab would be used for when Phase IV of their program began in mid-1986, though they did offer several intriguing possibilities. Shuttle Orbiters might, for example, attach modified Spacelab modules and experiment pallets to the third docking port on the PM.

A Shuttle External Tank might be joined to Skylab to serve as a strongback for large-scale space construction experiments using a mobile "space crane." These experiments might include construction of a large space solar power module or a multiple beam antenna.

A new "floor" might be assembled within Skylab, enabling it to house up to nine astronauts. As NASA developed confidence in the revived space laboratory's health, manned missions on board Skylab without a Shuttle Orbiter present might commence, leading to permanent manning and "support [of] major space operations."

The MSFC engineers did not estimate the cost of Phases I and IV of their plan, though they did provide (perhaps optimistic) cost estimates for Phases II and III. Their estimates did not include Space Shuttle transportation and contractor study costs.

In Fiscal Year (FY) 1980, NASA would spend $2 million each on Phases II and III. This would increase to $5 million for Phase II and $3.4 million for Phase III in FY 1981. FY 1982, their plan's peak funding year, would see $4.5 million spent on Phase II and $10.2 million spent on Phase III. In FY 1983, NASA would spend $2.5 million to close out Phase II and $12 million to continue Phase III. The following year it would spend $9.1 million on Phase III. Phase III closeout in FY 1985 would cost $4.5 million. Phase II would cost a total of $14 million, while the more ambitious Phase III would total $41.2 million.

In November 1977, the month the MSFC engineers briefed Yardley on their study, NASA awarded Martin Marietta Corporation a small ($1.75-million) contract to begin development of the Teleoperator. The remote-controlled spacecraft was envisioned as a small space tug made up of modular components.

No decision was taken at that time as to whether the Teleoperator would reboost Skylab to make it available for possible future use or would deorbit it in a controlled manner; that decision would await assessment of Skylab's condition and additional study of potential applications. McDonnell Douglas and Martin Marietta subsequently commenced more detailed and extensive Skylab reuse studies under MSFC supervision with inputs from JSC and NASA Headquarters.

Sources

Skylab 1 Investigation Report, Hearing Before the Subcommittee on Manned Space Flight of the Committee on Science and Astronautics, US House of Representatives, Ninety-Third Congress, First Session, 1 August 1973.

"Skylab Reuse Study Presented to Mr. Yardley by MSFC," 16 November 1977.

Living and Working in Space: A History of Skylab, NASA SP-4208, W. David Compton & Charles D. Benson, 1983, pp. 361-372.

More Information

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

Evolution vs. Revolution: The 1970s Battle for NASA's Future

What Shuttle Should Have Been: NASA's October 1977 Space Shuttle Flight Manifest

One Space Shuttle, Two Cargo Volumes: Martin Marietta's Aft Cargo Carrier (1982)

Image credit: Martin Marietta.

The destruction of the Orbiter Challenger on 28 January 1986, just 73 seconds into the 25th Space Shuttle mission, put an end to many proposals and plans for Shuttle improvement and augmentation. The powerful liquid hydrogen/liquid oxygen-propelled Centaur G' upper stage, routine satellite servicing and refueling in orbit, the nitrogen-gas-propelled Manned Maneuvering Unit, launches from the U.S. West Coast, launches to polar and retrograde orbits, frequent non-astronaut passengers, solar-powered long-duration Spacelab missions, and an eventual flight rate upwards of 50 per year — all of these were abandoned as NASA sometimes reluctantly acknowledged the Shuttle's frailties and foibles.

Among the proposed improvements permanently grounded after the Challenger accident was Martin Marietta's Aft Cargo Carrier (ACC), a cargo canister meant to be bolted over the dome-shaped aft end of the Space Shuttle External Tank (ET). Martin Marietta, prime contractor for the 154-foot-long ET, had begun in-house studies of the ACC at about the time the first Shuttle launched into orbit (STS-1, 12-14 April 1981).

Aft Cargo Carrier and Orbiter payload bay dimensions compared. The entire ACC is 31.9 feet long; the aft shroud is 20.8 feet long. Image credit: Martin Marietta.

By the middle of 1982, Martin Marietta aggressively pitched the ACC concept at aerospace conferences. NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama, soon took notice and contracted with the company for ACC engineering and economic feasibility studies. MSFC had since the mid-1970s sought out low-cost ways of incrementally improving the Space Shuttle and evolving NASA piloted programs toward a permanent Space Station (see "More Information" below).

The ACC's position adjacent to the Orbiter's three Space Shuttle Main Engines (SSMEs) and between the powerful twin Solid-Rocket Boosters (SRBs) meant that payloads it carried would be subjected to more heating and acoustic pounding than would those in the Orbiter payload bay. Martin Marietta proposed an ACC "environmental protection system" made up of 707 pounds of thermal insulation and a 2989-pound "acoustical barrier."

Adding these layers would make the ACC shell a little more than a foot thick, reducing the diameter of payloads it could carry to about 25 feet. Even so, this made the ACC payload volume about 10 feet wider than the 15-by-60-foot Orbiter payload bay.

Martin Marietta assumed that, with planned Shuttle performance upgrades, an Orbiter would be able to boost 36.9 tons of payload into a 160-nautical-mile-high orbit inclined 28.5° relative to Earth's equator. An empty ACC would add 8.3 tons to the Shuttle's mass at liftoff, potentially reducing the payload mass the Orbiter and ACC could inject into orbit. If the ACC remained attached until SSME cutoff, then the payload mass the Orbiter and ACC could place into orbit would total 28.7 tons.

Left to right: ACC shroud; ring for mounting cargoes; and ACC skirt with twin solid-propellant rocket motors. Image credit: Martin Marietta.

Martin Marietta had, however, found a way around this problem. The ACC would include an aft shroud and a forward skirt. Discarding the 3.7-ton aft shroud as early as possible during the Shuttle's eight-minute climb to orbit would reduce the payload mass penalty to only about four tons. This meant that the Orbiter payload bay and ACC skirt could together deliver to 160-nautical-mile orbit payloads with a total mass of 33 tons.

The twin SRBs would burn out and fall away from the ET 120 seconds after liftoff at an altitude of about 146,000 feet. The ACC shroud would then detach from the skirt and fall away 35 seconds after SRB separation.

During Orbiter-only Shuttle missions, the Orbiter would shut down its SSMEs and discard the ET before attaining orbital velocity. The ET would reenter the atmosphere and be destroyed over the Indian Ocean. This would, of course, deprive the SSMEs of their source of liquid hydrogen/liquid oxygen propellants: hence, after ET separation, the three engines would amount to "dead weight." The astronauts would then ignite the Orbiter's twin Orbital Maneuvering System (OMS) engines for the first of two orbit-insertion burns.

Orbiter/ACC missions would see Orbiter, ET, ACC skirt, and payloads in a 57-by-160-nautical-mile orbit at SSME cutoff, so that the first orbit-insertion OMS burn would be unnecessary. When the assemblage attained apogee (the highest point in its orbit around the Earth), the astronauts would ignite the OMS engines, increasing its velocity by 183 feet per second. This would raise its perigee (the low point in its orbit around the Earth) and circularize its orbit at an altitude of 160 nautical miles.

Martin Marietta proposed a host of potential ACC payloads. Many would ride on a mounting ring attached to the ACC skirt. "Catch tanks" might collect liquid hydrogen/liquid oxygen propellants left in the ET at SSME shutdown for later use in orbit. A turbine generator might burn leftover propellants to augment the electricity the Orbiter fuel cells would provide.

The ACC skirt might carry a 25-foot-diameter, 20-foot-long space station module. The module might be designed to remain attached to the ET, so that the big tank could become a strong-back for mounting large payloads or, with the addition of an access hatch linking the ET's hydrogen tank with the module, a large enclosed volume for experiments or habitation. Large folded structures — for example, an umbrella-like radio dish antenna more than 50 feet across — might also be deployed from the skirt.

Potential Aft Cargo Carrier payloads. Image credit: Martin Marietta.

Martin Marietta described three example Orbiter/ACC payload manifests and deployment scenarios. Flight 1, a mission with an initial circular 160-nautical-mile orbit at 28.5° of inclination, would see three satellites with identical solid-propellant upper stages launched in the ACC. These were the 4.4-ton Brazilsat/Payload Assist Module (PAM)-D; the 4.4-ton GOES/PAM-D; and the 4.7-ton Telsat/PAM-D. The Orbiter, meanwhile, would carry a 58-foot-long, 14-foot-diameter "large observatory" with a mass of 9.4 tons.

Without the ACC, payload mass for Flight 1 would be limited to what could be carried in the Orbiter payload bay, or about a quarter of the 36.9-ton theoretical maximum for the flight. With the ACC, the Flight 1 payload could total 22.9 tons. Following deployment from the ACC skirt, the satellites would ride their PAM-D stages to their assigned slots in the geostationary orbit (GEO) belt, 22,236 miles above the equator.

The Orbiter crew would then cast off the ET and its attached ACC skirt. A two-ton pair of solid-propellant deorbit rocket motors on the ACC skirt would ignite over the western Pacific Ocean, causing the ET/ACC combination to tumble and reenter the atmosphere. Any parts that survived reentry would splash into the Pacific south of Hawaii.

The astronauts, meanwhile, would maneuver the Orbiter to a 190-nautical-mile-high orbit and deploy the large observatory from the payload bay. They would then ignite the OMS engines to slow the Orbiter and cause it to re-enter Earth's atmosphere. The delta-winged space plane would glide to a runway landing.

Flight 2 would launch the 1.7-ton Tiros-N satellite inside the ACC and the 8.2-ton Atmosphere Monitor satellite at the aft end of the Orbiter payload bay. Because the Orbiter/ET/ACC skirt/payloads assemblage would be required to ascend to an energetically challenging 160-nautical-mile-high, 98.2° near-polar retrograde orbit, Flight 2's payload mass could total at most 11.8 tons.

The Flight 2 crew would first guide their spacecraft to a rendezvous with a two-ton Thermosat payload, which they would captured and stow at the front of the Orbiter payload bay for return to Earth. They would then fire the OMS engines to climb to a 380-nautical-mile orbit, where they would deploy the Atmosphere Monitor.

Next, they would ignite the OMS engines again to climb to a 448-nautical-mile orbit inclined 98.8° to Earth's equator. There they would deploy Tiros-N from the ACC skirt. After discarding the ET/ACC skirt, they would ignite the OMS engines to return Orbiter, crew, and Thermosat to Earth.

Aft Cargo Carrier in flight. Image credit: Martin Marietta.

Flight 3, with an initial 100-nautical-mile orbit at 28.5° of inclination and a payload mass of 26.5 tons, would see the introduction of a new reusable hardware element made possible by the ACC's large-diameter payload envelope: the 15-foot-long, 25-foot-diameter, 17-ton Orbital Transfer Vehicle (OTV). The OTV would be based in space. Visiting Orbiters would supply it with propellants and service its systems as required.

Martin Marietta noted that, by providing a second payload volume, the ACC could enable secret Department of Defense (DOD) payloads to be carried separate from but on the same flight as NASA civilian payloads. The Orbiter payload bay would thus on Flight 3 carry two Department of Defense payloads: the NATO IV/PAM-D satellite and the 35-foot-long, 10-foot-wide, 6.5-ton Synchronous Observation Satellite (SOS).

The OTV would scavenge residual ET propellants to fill its tanks, then would detach from the ACC skirt. The Orbiter crew, meanwhile, would raise the SOS on a tilt-table mounted in the payload bay. The OTV would dock with the SOS, detach it from the tilt-table, boost it to its assigned slot in GEO, and release it. Mission accomplished, the OTV would fire its engines to return to low-Earth orbit for a new mission.

The Orbiter crew, meanwhile, would cast off the ET/ACC skirt and maneuver to a 160-nautical-mile orbit, where they would deploy NATO-IV/PAM-D from the payload bay. The PAM-D stage would boost the satellite to GEO. The astronauts, meanwhile, would fire the Orbiter's OMS engines to re-enter Earth's atmosphere.

Martin Marietta placed great emphasis on the cost savings that would accrue from making the ACC a Shuttle hardware element. First, however, it estimated the costs of developing and using the cargo canister. The company assumed that NASA would give a green light to begin ACC development in late 1983, and that the first ACC would lift off three years later.

The company calculated that ACC development would cost $113 million. Changes to the Shuttle design to accommodate ACCs would cost $78 million, and changes to Kennedy Space Center facilities would cost $35 million.

Martin Marietta quoted NASA when it placed the base cost of a Shuttle flight without an ACC at an optimistic $75 million. The base cost of a Shuttle flight would increase by about $5 million when it included an ACC, the company estimated.

For its cost-savings calculations, the company employed a Shuttle traffic model less optimistic than the one NASA touted. It assumed that 331 Shuttle flights would take place between 1988 and 2000, with 34 flights in 1988 and a steady decline to 20 flights per year in 2000. During the same 12-year period, NASA assumed 26 flights per year in 1988, an upward trend to nearly 60 flights per year by 2000, and a total of 581 flights.

Based on its "low" traffic model, Martin Marietta estimated that NASA might benefit from flying 71 civilian and 35 Department of Defense Shuttle/ACC missions. The company conservatively assumed, however, that NASA would be able to fund only a total of 75 civilian and Department of Defense Orbiter/ACC flights.

Martin Marietta determined that the added payload capacity the ACC could provide would permit the elimination of 40 Orbiter-only Shuttle missions. It placed the cost of 331 Orbiter-only missions at $24.8 billion and the cost of 216 Orbiter-only and 75 Orbiter/ACC missions at $22.2 billion. The ACC would thus save NASA $2.6 billion over 12 years.

Sources

Space Transportation System with Aft Cargo Carrier: A Natural Augmentation of System Capability, Martin Marietta, no date (late 1982).

"External Tank Aft Cargo Carrier," T. Mobley and J. Hughes; paper presented at the Twentieth Space Congress, Cocoa Beach, Florida, 26-28 April 1983.

ACC External Tank Aft Cargo Carrier, Martin Marietta, no date (late 1985).

More Information

Evolution vs. Revolution: The 1970s Battle for NASA's Future

Where to Launch and Land The Space Shuttle? (1971-1972)

Humans on Mars in 1995! (1980-1981)

The 1991 Plan to Turn Space Shuttle Columbia Into a Low-Cost Space Station

This NASA artwork from 1972 portrays the sheer volume of the Skylab Orbital Workshop, the first U.S. space station.

The first U.S. space station was Skylab, which NASA carefully dubbed an "Orbital Workshop" in order to distinguish it from the "real" space station it hoped to launch into low-Earth orbit by the mid-1970s. Skylab — a converted Saturn S-IVB rocket stage with a pressurized volume of more than 12,500 cubic feet — was launched on the last Saturn V heavy-lift rocket to fly. Three three-man crews lived and worked on board the 22-foot-diameter single-launch station for a total of 171 days between 26 May 1973 and 8 February 1974.

Nearly three years earlier, budget cuts had halted Saturn V production, so NASA had been forced to abandon plans for a single-launch, 33-foot-diameter core station. The Space Shuttle, originally intended as a cost-saving fully reusable space station crew and cargo transport, was subsequently tapped to serve also as the sole launch vehicle for a multi-modular space station built up over the course of many flights. This meant that the Shuttle Orbiter payload bay dimensions (15 feet in diameter by 60 feet long) and maximum payload mass (in theory, up to 32.5 tons) would dictate the size and mass of station modules and other components.

NASA's single-launch core station (left) would throughout its life receive independently maneuverable add-on modules delivered by fully reusable Shuttle Orbiters. This 1970 illustration depicts one such module outfitted to transport astronauts and cargo from the Shuttle payload bay to the core station main docking port and back. The modules would also be outfitted as special-purpose labs that would link up with round ports scattered over the station's hull. Image credit: McDonnell Douglas.

Launching the space station in the Shuttle payload bay meant also that NASA could not begin to assemble it until after Space Shuttle development and flight testing were completed. When the last crew left Skylab, the Shuttle's orbital maiden flight was officially set for early 1978. Operational flights were to start by 1980. Some hoped that an early Shuttle flight might boost Skylab to a higher orbit, postponing its eventual reentry and perhaps permitting it to be outfitted as a temporary interim space station in the early 1980s.

In the event, the first mission of the partially reusable Shuttle, STS-1, did not lift off until 12 April 1981, nearly two years after Skylab reentered and broke up over Australia (11 July 1979). The Orbiter Columbia remained aloft for two days before gliding to a landing on the dry lake-bed at Edwards Air Force Base (EAFB), California.

By then, engineers at NASA's Johnson Space Center had been at work for more than two years on a design for a Shuttle-launched station they dubbed the Space Operations Center (SOC). The SOC included a laboratory for experiments in microgravity, but was conceived mainly as a construction site for large structures, a servicing center for satellites, and a home port for a small fleet of space tugs. It was intended, in fact, to serve as a space shipyard, where would be assembled spacecraft for voyages beyond low-Earth orbit and large space structures such as Solar Power Satellites.

The 1982 Space Operations Center design became the point of departure for NASA station studies after the creation of the Space Station Task Force. Visible is a skeletal "false Shuttle payload bay" for satellite servicing and a hexagonal space tug hangar. Image credit: NASA.

On 20 May 1982, a little more than a year after STS-1 and a little more than a month before STS-4 (27 June-4 July 1982), NASA Administrator James Beggs established the NASA-wide Space Station Task Force. President Ronald Reagan was on hand at EAFB Runway 22 that U.S. Independence Day to welcome home the STS-4 crew. Some within NASA hoped that he would use the occasion to declare his support for a permanent Earth-orbiting space station, "the next logical step" after the Shuttle. Instead, Reagan declared that STS-4 was the final Shuttle test flight. With its next flight, STS-5, the Space Shuttle would be considered operational.

Reagan withheld his support for a further 18 months, until the beginning of the 1984 election year, when endorsing a space station — which was bound to create thousands of jobs — could provide maximum political advantage. During his 25 January 1984 State of the Union Address, he echoed President John F. Kennedy's May 1961 "Urgent National Needs" speech by calling on the U.S. civilian space agency "to develop a permanently manned space station and to do it within a decade." Reagan made mention only of the station's role as a laboratory. The station would, he said, "permit quantum leaps in our research in science, communications and in metals and life-saving medicines that can only be manufactured in space."

The Reagan White House disdained a space shipyard for two reasons. First, it was a relatively complicated design that could not be built for $8 billion spent over 10 years, the maximum price Administration budget watchdogs were willing to pay for a space station. The second reason was related to the first: a shipyard in space implied that things would be built there, and that in turn implied a commitment to new expenditures in the future.

Despite this clear message, NASA did not abandon its plans for a shipyard in orbit. In August 1984, the space agency released a "reference configuration" intended to guide aerospace companies bidding on Space Station Program contracts. Called the "Power Tower," it included a 400-foot-long single main truss where SOC-type space construction equipment might eventually be mounted. In NASA artwork depicting the station, featureless boxes stood in for unspecified large user payloads and hoped-for shipyard elements.

The August 1984 Power Tower station configuration was the Space Operations Center with trusses added. The small spacecraft with twin solar arrays at upper right is a self-propelled free-flyer bearing experiments likely to be interfered with by other station activities (for example, astronaut movement). Image credit: NASA.

NASA envisioned that spacewalking astronauts would bolt together the Power Tower truss in orbit piece by piece. During Shuttle mission STS-61B (26 November-3 December 1985), in fact, spacewalkers successfully tested two truss-assembly methods in the payload bay of the Orbiter Atlantis.

From the Power Tower evolved the "Dual Keel" in late 1985. In May 1986, NASA released its Space Station "Baseline Configuration," a Dual-Keel station measuring 503 feet wide and 361 feet tall. The new design included about twice as many truss elements as the Power Tower, providing ample room for both space-facing and Earth-facing user payloads and eventual addition of space construction facilities. Assembly in orbit was to begin in 1992 and to be completed by Reagan's 1994 deadline.

The Baseline Configuration was dead on arrival, however, because of the 28 January 1986 loss of the Shuttle Orbiter Challenger and its seven-member crew. By March 1986, NASA and its contractors had begun to scale back the station. At first it shrank but retained its Dual-Keel shape. After that, in the "revised baseline configuration" of 1987, it lost its keel trusses, becoming only a single truss with solar arrays at either end and laboratory and habitat modules at its center. NASA made sure, however, that the design included "hooks" and "scars" that would enable eventual expansion to the Dual-Keel design.

NASA's ambitious Dual-Keel Baseline Configuration of May 1986 was dead on arrival. Image credit: NASA.

President Reagan christened the Space Station Freedom in 1988; a gesture which for some rang hollow (they had hoped he might support a moon and Mars program that would give Freedom a long-term direction). The following year, with the Station expected to be over-budget, overweight, under-powered, and too demanding to build, NASA entirely abandoned the Dual Keel configuration. At the same time, planners proposed that NASA make plans to build an advanced "transportation node" space station in the early 21st century. This proposed separation of functions was an acknowledgment that the jolts and vibrations one could expect on board an orbital shipyard would wreak havoc with microgravity laboratory experiments.

The year 1990 saw new problems. Persistent hydrogen fuel leaks grounded the three-orbiter Shuttle fleet for nearly half the year, renewing doubts about the Shuttle's ability to reliably launch, assemble, resupply, and staff Freedom. Against this background, news emerged of a dispute within NASA over estimates of the number of spacewalks required to build and maintain the Space Station. The row triggered congressional hearings in May 1990.

In a report released on 20 July 1990, former astronaut and spacewalker William Fisher and JSC robotics engineer Charles Price, co-chairs of the Space Station Freedom External Maintenance Task Team, declared that Freedom would need four two-man spacewalks per week during its assembly and 6,000 hours of maintenance spacewalks per year after its completion. This amounted to 75% more spacewalks than the official NASA estimate, which was already considered excessive. Fisher called the spacewalk requirement "the greatest challenge facing the Space Station."

In November 1990, with new budget cuts in the offing, NASA began yet another Freedom redesign. At about the same time, Space Industries Incorporated (SII), a small engineering firm for which Maxime Faget, co-designer of the Mercury capsule, worked as Technical Advisor, began to examine a radical new approach to solving Freedom's persistent problems. SII performed its Orbiter-Derived Station (ODS) study on contract to Rockwell International, prime contractor for the Shuttle Orbiter.

SII noted that the U.S. House of Representatives Committee on Science, Space, and Technology wanted a "permanently manned Space Station, that meets our International Agreements, retains a capability for evolution, and has minimum annual and aggregate cost." At the same time, it explained, scientists and engineers of the space technology development and microgravity and life sciences research communities wanted NASA to provide an orbiting laboratory "without spending the entire available budget on the laboratory rather than on the experiments."

To satisfy these needs, SII proposed to draw upon Space Shuttle design heritage and operational experience. Specifically, the company proposed that NASA launch in 1996 an unmanned "stripped-down" Orbiter — one without wings, tail, landing gear, body flap, forward reaction control thrusters, and reentry thermal protection — to serve as Freedom's largest single element.

Orbiter Derived Station in Man Tended Configuration after Mission Build-1. Image credit: SII/NASA.

Removing systems with a total mass of 45,600 pounds would boost the Orbiter's payload capacity to 81,930 pounds, permitting it to transport a 56.5-foot-long pressurized module permanently mounted in its payload bay and four pairs of rolled-up 120-foot-long solar arrays under streamlined housings along its sides. The pressurized module would include a single docking port on top and a short tunnel linking it to the stripped-down Orbiter's two-deck crew compartment. In effect, SII's ODS launch approach would briefly restore the heavy-lift capability lost when the U.S. abandoned the Saturn V rocket.

What follows is a synthesis of information from two SII documents concerning the ODS. The first, a set of presentation slides, is not dated, though individual slides in the presentation carry July 1991 dates. The second document is SII's final report to Rockwell International dated September 1991. When the documents differ in significant ways, this is noted.

Copying NASA parlance, SII referred to the launch of the stripped-down Orbiter as Mission Build-1 (MB-1). Upon achieving a 220-nautical-mile-high orbit inclined 28.5° relative to Earth's equator, the ODS would turn its payload bay doors toward Earth, open them to expose the pressurized module and door-mounted radiators, and unroll its solar arrays to generate up to 120 kilowatts of electricity. At that point, the ODS would achieve Man-Tended Configuration (MTC). MTC meant that the station could be staffed while a Shuttle Orbiter was docked with it. According to SII, NASA's Freedom would not achieve MTC until MB-6, and its solar arrays would not generate 120 kilowatts of electrical power until MB-10.

Orbiter Derived Station (top) and Shuttle Orbital Maneuvering System propulsion pod design differences. Image credit: SII/NASA.

During a normal Space Shuttle mission, the twin 6,000-pound-thrust Orbital Maneuvering System (OMS) engines would ignite twice to complete orbital insertion after the Orbiter's three Space Shuttle Main Engines (SSMEs) shut down and and its External Tank separated. The OMS-1 burn would put the Orbiter into an elliptical orbit; then, at apogee (the high point of its orbit about the Earth), the OMS-2 burn would raise its perigee (the low point in its Earth orbit) to make its orbit circular. Subsequently, the OMS engines would be used to perform major maneuvers and would slow the Orbiter at the end of its mission so that it would reenter the atmosphere. The OMS engines would burn hypergolic (ignite-on-contact) hydrazine/nitric acid propellants.

SII proposed changes to the stripped-down Orbiter's OMS pods to increase reliability and enable long-duration use. A hydrazine monopropellant system would replace the baseline Orbiter bi-propellant system. The SSMEs would insert the stripped-down Orbiter directly into its initial elliptical orbit, then two sets of four 500-pound-thrust OMS engines — one set per OMS pod — would each draw on a pair of propellant tanks to perform the OMS-2 orbit-circularization burn at apogee. The roughly 13,000 pounds of propellant remaining after the OMS-2 burn would be sufficient to resist atmospheric drag and supply OMS pod attitude-control thrusters for two years.

SII suggested that the OMS tanks be refilled in orbit after they exhausted their initial load of hydrazine, but provided no details as to how this might be accomplished. Alternately, the company suggested, a new propulsion module might be docked with the ODS after the modified OMS pods ran out of propellant.

With MB-1 complete, SII's ODS would provide 11,000 cubic feet of pressurized volume containing 58 standardized payload racks. NASA’s Freedom, by comparison, would have no pressurized volume at all until the addition of the U.S. Lab during MB-6, and would not exceed 10,000 cubic feet of pressurized volume until MB-13. The U.S. Hab and Lab modules would together hold only 48 racks.

In SII's July 1991 ODS design, the large module launched in the stripped-down Orbiter payload bay on MB-1 included only Hab module functions, and MB-2 in 1997 would see a piloted Shuttle Orbiter deliver the U.S. Lab module. In its September 1991 final report, SII combined Lab and Hab in the stripped-down Orbiter payload bay and substituted a 47.5-foot-long "core module" for the Lab on MB-2. The cylindrical core would include eight docking ports on its sides and one at either end.

One of the core module end ports would be docked permanently with the port on the Hab/Lab module. Visiting Shuttle Orbiters would dock with the Earth-facing port at the core module's other end. Addition of the core module would increase ODS pressurized volume to 15,000 cubic feet. NASA's Freedom station would not exceed 15,000 cubic feet of volume until MB-16.

SII envisioned that ODS assembly flights would be interspersed with utilization flights beginning immediately after MB-1. The first ODS utilization mission would occur in 1996, and three would take place in 1997.

In addition to permitting early research on board the ODS, some utilization flights after MB-2 would deliver supplies and equipment in a drum-shaped Logistics/Life Support Module (LLSM). Astronauts would dock the LLSM to a core module side port using the visiting Orbiter's Canada-built Remote Manipulator System (RMS). Spent LLSMs would be returned to Earth for refurbishment and reuse. SII placed the ODS toilet and shower in the LLSM, arguing that servicing waste and water systems on the ground would be preferable to doing so in orbit.

SII noted that its Station would need very few assembly and maintenance spacewalks. It would, nevertheless, include a modified Shuttle Orbiter airlock attached to one of its core module side ports. The airlock would reach the ODS during an unspecified utilization flight after MB-2. Because ODS assembly would be relatively simple and assembly spacewalks minimal, SII assumed that the Station could do without its own Canada-built RMS. The company did not address how deletion of the Station RMS would affect U.S.-Canada relations.

The second assembly mission of 1997, MB-3, would see arrival of an Orbiter bearing in its payload bay an eight-man Assured Crew Return Vehicle (ACRV), a space station lifeboat. With the docking of the ACRV at a core module side port, the ODS could be staffed by eight astronauts with no Orbiter present. NASA called the ability to maintain a full crew with no Orbiter present "Permanent Manned Configuration" (PMC). NASA's Freedom Station would not achieve PMC until MB-16.

Orbiter Derived Station in Assembly Complete configuration after Mission Build-6 in late 1998. The image displays an RMS robot arm, though SII stated that the stripped-down Orbiter would not carry one. Image credit: SII/NASA.

The year 1998 would see three assembly flights, all international in character. In his January 1984 State of the Union speech, Reagan had invited U.S. allies to lend a hand in building NASA's space station in exchange for opportunities to reap its rewards. In addition to Canada, Japan and Europe had answered the call.

MB-4 would see an Orbiter deliver the pressurized part of the Japanese Experiment Module (JEM). Astronauts would use the Orbiter's RMS to dock it to a core module side port. During MB-5, astronauts would use the visiting Orbiter RMS to add the European Space Agency's Columbus laboratory module. With that, the SII's ODS would achieve its maximum pressurized volume: 24,000 cubic feet, or about 8,000 cubic feet more than planned for NASA's Freedom Station. MB-6 would add Logistics and unpressurized Exposure components to complete the JEM.

SII recommended that the core module's Earth-facing port be designed to rotate so that visiting Orbiters could optimally position themselves for assembly missions. During MB-5, for example, the visiting Orbiter's nose would face in the ODS's direction of flight so that its RMS could place the Columbus module at its designated core module side port. During MB-4 and MB-6, it would face in the opposite direction so that JEM components could be added.

MB-6, which would take place near the end of 1998, would mark the end of ODS assembly. By then, SII's station would have hosted seven utilization flights. For comparison, NASA's Freedom Space Station would host no utilization flights until 1998, when three would take place. Freedom would not reach "Assembly Complete" until 2000.

SII proposed ways that the baseline ODS might be upgraded. The company noted that, beginning with MB-10, NASA's Freedom would provide experimenters with more electricity (180 kilowatts) than would the ODS. If this power level were judged to be necessary for ODS operations, then a 60-kilowatt "power kit" could be added during a utilization flight. The company suggested that the kit's rolled solar arrays be attached to a special port installed in the stripped-down Orbiter's nose behind a streamlined faring.

The ODS included no provision for space-facing experiments; all of its modules were expected to be mounted on its Earth-facing payload bay side. This reflected the science and technology community's desire for a microgravity lab and the fact that highly capable automated space-facing satellites (for example, the Hubble Space Telescope) were available. If, however, space-facing experiments were desired on board the ODS, then it could be launched with a docking port on the Orbiter's space-facing belly. A tunnel through the ODS payload bay floor would link the port to the Hab/Lab module.

Probably the company's most controversial proposal was to accelerate ODS assembly by stripping down Columbia, NASA's oldest Orbiter. SII noted that Columbia was the heaviest Orbiter, so had the least payload capacity. It assumed that NASA would want to replace Columbia with a new, less heavy Orbiter, thus increasing the Shuttle fleet's overall lift capacity. SII called this "disposing of the worst and and replacing it with the best." Some components stripped from Columbia could, it suggested, be reused in the new Orbiter to save money.

By the time SII submitted its final report, NASA's latest Freedom configuration had been public for three months. The new design included truss segments launched pre-assembled, smaller U.S. modules, and other changes meant to reduce the number of spacewalks and assembly flights required to build and maintain it. The station would, however, lose yet more capability (notably in the area of electrical power, which was reduced to about 60 kilowatts at PMC). The April 1991 redesign set the stage for Freedom's near-cancellation in June 1993 (it survived by a single vote in the U.S. House of Representatives) and, beginning later that year, its revival as the International Space Station.

This rendition of Space Station Freedom in its 1991 configuration contains several interesting features. The overall station design is obscured by shadows, denoting the uncertainty surrounding the station's future form. Only the international pressurized modules — the JEM and Columbus labs — are visible. Beginning with the the May 1986 Dual Keel, these modules changed very little in NASA artwork because the International Partners insisted that the U.S. adhere to its agreements. The U.S. modules, in the meantime, decreased in number and shrank to a fraction of their planned former size. A Shuttle Orbiter is displayed, but not attached to Freedom; placing it too close to the station would show plainly the 1991 station's small size relative to earlier designs. The moon and Mars are visible above Freedom; in 1991, NASA still paid lip-service to carrying out President George H. W. Bush's abortive Space Exploration Initiative (SEI), which aimed to launch humans to those worlds. Freedom was meant to play a role in furthering SEI's goals, though the precise nature of that role was not clear. Image credit: NASA.

Sources

The Space Shuttle at Work, NASA SP-432/EP-156, H. Allaway, NASA, 1979, pp. 64-72.

Aboard the Space Shuttle, NASA EP-169, F. Steinberg, NASA, 1980.

Space Station, NASA EP-211, D. Anderton, NASA, no date (1984).

Space Station: The Next Logical Step, NASA EP-213, W. Froehlich, NASA, no date (1985).

Space Station: Leadership for the Future, NASA PAM-509, F. Martin & T. Finn, NASA, August 1987.

Space Station: A Step Into the Future, NASA PAM-510, A. Stofan, NASA, November 1987.

Space Station Freedom Reference Guide, Boeing, 1988.

Space Station Freedom: A Foothold on the Future, NASA NP-107, L. David, NASA, October 1988.

"Freedom Spacewalks 'unacceptable': NASA," Flight International, 1-7 August 1990, p. 18.

"Freedom failure threatens NASA's future," T. Furniss, Flight International, 29 May-4 June 1991, p. 34.

"Operation Scale-Down," T. Furniss, Flight International, 29 May-4 June 1991, pp. 76-78.

Shuttle Derived Space Station Freedom, Space Industries International, Inc./Rockwell International Space Systems Division, presentation materials, n.d. (July 1991).

Expanded Orbiter Missions Final Report: Orbiter Derived Space Station Freedom Concept, prepared by Space Industries, Inc. (SII), Webster, Texas, for Rockwell International, Inc., Downey, California, September 1991.

"House Retains Space Station in a Close Vote," C. Krauss, International New York Times, 24 June 1993 (http://www.nytimes.com/1993/06/24/us/house-retains-space-station-in-a-close-vote.html - accessed 16 October 2015).

International Space Station, Boeing, May 1994.

More Information

McDonnell Douglas Phase B Space Station (1970)

Where to Launch and Land the Space Shuttle? (1971-1972)

Skylab-Salyut Space Laboratory (1972)

Evolution vs. Revolution: The 1970s Battle for NASA's Future

NASA's 1992 Plan to Land Soyuz Space Station Lifeboats in Australia