From Monolithic to Modular: NASA Establishes a Baseline Configuration for a Shuttle-Launched Space Station (1970) |
| Modular Shuttle-launched Station in the 1980s. Image credit: NASA |
On 22 July 1969, two days after Apollo 11's triumphant landing on the moon's Sea of Tranquillity, NASA issued a pair of Phase B Space Station study contracts. One, under the direction of NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, went to McDonnell Douglas (MDAC), while the other, under the direction of the Manned Spacecraft Center (MSC) in Houston, Texas, went to North American Rockwell (NAR).
Both companies looked at 33-foot-diameter, barrel-shaped "monolithic" stations meant to be launched in one piece into low-Earth orbit atop a two-stage Saturn V rocket, and both assumed that a logistics vehicle - commonly called a Space Shuttle - would resupply the Station, rotate its six-to-12-man crews, deliver experiment equipment and small experiment modules, and return experiment results and experiment modules to Earth.
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| Plan drawing of NAR's Phase B "monolithic" Space Station design. Image credit: NAR/NASA/DSFPortree |
Elsewhere in this blog (see "More Information" at the bottom of this post) I have described the monolithic Space Stations and efforts in the early 1970s to preserve a Space Station Program in the face of rapidly shrinking NASA budgets and rapidly changing national priorities. In this post, I will describe a little-known study performed in-house by NASA personnel at MSC for the NASA Headquarters Space Station Task Force. The study helped to pave the way for a sea-change in Station planning in late July 1970.
In January 1970, as negotiations toward the Fiscal Year (FY) 1971 NASA budget got under way between NASA, President Richard Nixon's White House, and the Congress, NASA Administrator Thomas Paine announced that, to accommodate proposed funding cuts, NASA's Saturn V rocket test and assembly facilities would be mothballed. He was not specific about when this would happen, stating only that it would occur after the last Saturn V ordered for Apollo - the fifteenth - was completed and tested. That was expected to occur before the end of 1971.
The Mississippi Test Facility at Bay St. Louis, home of test stands for Saturn V engines and rocket stages, would be hardest hit; from about 2000 its staff would shrink to 150-200 "caretaker" personnel. The industry publication
Aviation Week & Space Technology explained in its 9 February 1970 issue that, if NASA proceeded with its Saturn V plans and then received funding for new Saturn Vs in its FY 1972 budget, it would need four years to restore its assembly and test capabilities. The next Saturn V would not launch before July 1975.
On 4 May 1970, the Space Station Task Force asked MSFC and MSC to direct McDonnell Douglas and North American Rockwell to devote some attention during their Phase B studies - which were set to conclude in two months - to assessing a new method for launching the Space Station: specifically, by boosting it into Earth orbit in pieces in the payload bays of a succession of Space Shuttle Orbiters. At about the same time, MSC began to organize its Shuttle-launched modular Station study, which commenced officially on 1 June 1970.
One ground rule of the MSC study was that the modular Station should be able to accomplish the same objectives as its monolithic counterpart. Another was that MSC should seek to "exploit the unique capabilities of multiple Shuttle launches."
By June 1970, NASA had, in exchange for U.S. Air Force political support, largely settled on a 15-foot-by-60-foot payload bay for its winged Shuttle Orbiter design. Engineers at its Houston center had, however, not yet fully reconciled themselves to these payload bay dimensions. Led mainly by Maxime Faget, co-designer of the Mercury capsule, they sought a shorter - and sometimes wider - payload bay.
The modules they considered for their Space Station in June 1970 reflected this. They looked at five modules; then, in a second round of analysis, they emphasized four. The initial five measured 12 feet in diameter by 39.5 feet long; 12 feet in diameter by 29 feet long; 14 feet in diameter by 29 feet long; 16 feet in diameter by 22.2 feet long; and 18 feet in diameter by 17.4 feet long. The four "second-pass" modules measured 12.5 feet in diameter by 30 or 40.5 feet long; 14.5 feet in diameter by 30 feet long; 16.5 feet in diameter by 23.2 feet long; and 18.5 feet in diameter by 18.4 feet long.
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| MSC's four "second-pass" circular floor plan Shuttle-launched Space Station Modules. Image credit: NASA with stick figures by DSFPortree |
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| MSC's four "second-pass" horizontal floor plan Shuttle-launched Space Station Modules. In this image and the image above, the stick figures indicate the positions of the floors in the modules, not necessarily the presence of artificial gravity. Image credit: NASA with stick figures by DSFPortree |
MSC looked at both "horizontal" and "circular" module floor plans for the four second-pass modules. The former yielded a rectangular floor and ceiling aligned with the long axis of the module. Space above the ceiling and below the floor could hold supplies, spare parts, and equipment. The latter, a stack of floors, each as wide as the module's maximum diameter, tended to have more decks and less equipment space.
Module design Concept Selection took place on 1 July. MSC chose a horizontal module 14 feet in diameter by 29 feet long, which could launch in a 15-foot-diameter Orbiter payload bay as short as 30 feet long.
MSC combined these modules to create six modular Space Station configurations (shown below). Five of the six would see the crew living and working in weightlessness. All featured one Solar Power Boom with a pair of two-part solar arrays, one or two Central Assembly Elements (CAEs), eight Basic Structural Elements (BSEs), and two Expendables Storage Elements (ESEs). These module combinations would provide roughly the same workspace as the four 33-foot-wide circular decks and the upper and lower equipment bays of the NAR monolithic Station design, MSC calculated.
Four configurations MSC considered and then put aside are labeled 1 through 4 below. None includes an ESE, though the Shuttle-launched Station would not operate without one attached. The station designs are in two classes: the BSE modules in Configurations 1 and 2 form arms and in 3 and 4 they form bundles. In Configurations 3 and 4, a single nadir-facing (Earth-facing) BSE module is provided for Earth observation experiments.
On 15 July 1970, MSC engineers traveled to NASA Headquarters to brief the Space Station Task Group on its progress. They included in their presentation - which, being an interim product, contained its share of internal inconsistencies - the four designs they had put aside plus a preliminary artificial-gravity baseline design with a specialized telescoping CAE (fifth image above). Most of their presentation was, however, devoted to a preliminary assembly sequence for their baseline Shuttle-launched Station configuration (bottom image above - click to enlarge).
MSC expected that 14 Space Shuttle launches would be required to place their baseline modular Space Station into Earth orbit; that is, that NASA would need 14 Shuttle launches to replace a single two-stage Saturn V launch. Launch 1 of the Station Program would place into orbit a 20,412-pound CAE (
1 on the drawing above) with nine ports (one on each end and seven on its four sides) and a pair of robot arms to facilitate module manipulation and attachment. Launch 2 would attach a 19,351-pound ESE (not shown) to one of the CAE "side" ports, forming an "L"-shaped configuration. Though its length was not given, the ESE was meant to be shorter than the other module types. It would carry enough food to supply 12 men for 90 days.
Launch 3 would see a Shuttle Orbiter join the 19,154-pound Solar Power Boom (
3) to one end of the CAE. After the Orbiter moved away, the Boom's solar arrays would unfurl. Launch 4 would place into space the first BSE, a 17,209-pound module containing a stateroom for the Station Commander and the Station's main control and data processing facilities. It would be attached to the CAE port on the side opposite the ESE. It is not shown in the baseline configuration illustration above; an outline of an arrow marks the port where it would be attached.
Launches 5 through 8 would attach BSE modules to ports perpendicular to the long axis of the ESE module. Their placement would alternate between zenith (space-facing) and naidr ports. Launch 5 would deliver a 20,605-pound BSE containing mainly life support and personal hygiene equipment (
5). This would bring total Station mass to 96,731 pounds. Launch 6 would deliver a 20,302-pound BSE outfitted with crew staterooms and communications equipment (
6). Launch 7, midway through the assembly sequence, would attach to the Station a lightweight 13,367-pound BSE containing crew recreation and dining facilities and a galley (
7).
The Launch 8 module, a BSE dedicated to crew health (
8), also would be a lightweight (13,324 pounds). Its arrival at the Station would mark completion of one of the modular Station's two redundant, independently pressurized volumes. MSC's modular Station at that point would be equivalent to two decks, an equipment bay, and the Solar Power Boom of the NAR monolithic Station design. Station mass would total 143,724 pounds with completion of the eighth assembly flight.
Redundant, independent volumes reflected the Station's crew safety philosophy. If one volume became uninhabitable, the entire crew could retreat to the second volume to await an Orbiter that could provide repair assistance or rescue. The modular Station would not be permanently staffed until both volumes were completed.
Launches 9 through 14 would assemble the Station's second redundant, independent volume. This would be equivalent to an NAR monolithic Station equipment bay and two decks.
Launch 9 would see arrival of a 18,645-pound CAE (
9), which would be attached to the end of the first CAE opposite the Solar Power Boom. This would enable attachment of four more BSEs to the modular Station. Launch 10's 16,395-pound BSE would include a maintenance shop and room for experiments (
10), while Launch 11's 19,024-pound BSE would contain a general-purpose lab (
11).
The Launch 12 BSE would provide backup control & data processing and more staterooms (
12); like its twin delivered during the fourth assembly flight, it would weigh 17,209 pounds. The payload for Launch 13 would be a 15,756-pound BSE containing crew quarters (
13).
Launch 14 would complete the modular Space Station. An Orbiter would arrive with a 20,551-pound ESE module containing the Station's first six long-term resident astronauts and food for 12 men for 90 days. Like the first ESE, the second ESE is not shown in the drawing above; it would, however, be attached to the side CAE port marked on the drawing with the outline of a star. With the addition of the 14th Shuttle payload, Station mass would total 251,304 pounds.
The image at the top of this post (click to enlarge) shows an advanced version of MSC's modular Station. It is sometimes mistakenly attributed to McDonnell Douglas. The advanced configuration, scheduled for the 1980s, includes six more BSEs than the baseline configuration. Four are attached to a third CAE. An ESE makes an appearance: it includes a pair of robot arms. One of the four modules attached to a third CAE is a dedicated nadir-facing Earth-observation module (an open round end-hatch and extended instruments are visible below the ESE arms).
Two BSEs are attached to the "side" CAE ports; one, nearest the Solar Power Boom, is the Launch 4 BSE, while the other, on the same side as the ESE, might be a docked free-flyer with an independent propulsion system. This would detach from the Station periodically to provide a stable platform for materials science and astronomy experiments that would suffer from vibrations caused by crew movement.
The approaching Shuttle Orbiter bearing a BSE module - possible a second free-flyer - is an MSC design with straight wings a little more than 90 feet across, internal liquid oxygen and liquid hydrogen tanks, and a payload bay shorter than 60 feet. The module would be lifted from the payload bay and attached to a docking unit atop the Orbiter crew cabin. The Orbiter would move close to the Station, then dock with it through the intermediary of the module it carried. When time came to return to Earth, it would undock from the module, leaving it attached to the Station.
After its July 15 presentation at NASA Headquarters, the MSC team appears to have halted its activities. The artificial-gravity baseline design, for example, seems not to have been developed further. I could find no evidence that planned briefings at MSC and NASA Headquarters scheduled for 1 August, 7 September, and 15 September 1970 took place.
NASA extended the NAR and MDAC Space Station Phase B contracts by six months on 30 June 1970. On 29 July 1970, Charles Mathews, chair of the Space Shuttle Task Force, requested that MSC and MSFC instruct their respective Phase B Extension contractors to abandon all work on monolithic Saturn V-launched Space Station designs in favor of Shuttle-launched modular designs. When unveiled in 1971, the NAR design resembled the baseline design from MSC's May-July 1970 in-house Shuttle-launched Station study.
SourcesShuttle-Launched Space Station Study Interim Review, NASA Manned Spacecraft Center presentation to NASA Headquarters, 15 July 1970
"Curtailing Field Centers Limits Saturn 5 Options,"
Aviation Week & Space Technology, 9 February 1970, pp. 26-27
"Space Station and Space Platform Concepts: A Historical Overview," J. Logsdon and G. Butler,
History of Space Stations and Space Platforms - Concepts, Designs, Infrastructure, and Uses, I. Bekey and D. Herman, editors, Volume 99, Progress in Astronautics and Aeronautics, American Institute of Aeronautics and Astronautics, 1985, pp. 226-233
Space Shuttle: The History of the National Space Transportation System - The First 100 Flights, Third Edition, D. Jenkins, Specialty Press, 2008, pp. 101-108, 137
More InformationA Bridge from Skylab to Station/Shuttle: Interim Space Station Program (1971)An Alternate Station/Shuttle Evolution: The Spirit of '76 (1970)Apollo's End: NASA Cancels Apollo 15 & Apollo 19 to Save Station/Shuttle (1970)McDonnell Douglas Phase B Space Station (1970)Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan"A True Gateway": Robert Gilruth's June 1968 Space Station PresentationSource:
From Monolithic to Modular: NASA Establishes a Baseline Configuration for a Shuttle-Launched Space Station (1970)
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