16 January 2017

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. These were designed to be launched in one piece into low-Earth orbit atop a two-stage Saturn V rocket. Both companies 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.

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 the Apollo moon program - 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 from 150 to 200 "caretaker" personnel. The industry publication Aviation Week & Space Technology explained in its 9 February 1970 issue that, if NASA proceeded with these 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 first Saturn V after the last Apollo Saturn V - the sixteenth - would not launch before July 1975.

On 4 May 1970, the Space Station Task Force asked MSFC and MSC to direct MDAC and NAR to devote some attention during their Phase B studies - which were set to conclude in two months - to assessing a new method of launching the Space Station: specifically, by boosting it into Earth orbit in pieces in the payload bays 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 research 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 fully reconciled themselves to these payload bay dimensions. Some sought a shorter - and sometimes wider - payload bay.

The modules they considered for their Space Station during 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.

MSC's four "second-pass" circular floor plan Shuttle-launched Space Station Modules. Image credit: NASA with stick figures by DSFPortree
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 floors 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 Shuttle Orbiter payload bay as short as 30 feet long. MSC assumed that the module would weigh about 8000 pounds empty and about 20,000 pounds fully outfitted.

MSC then used the selected module concept to create six modular Space Station configurations (shown below). Five of the six would provide their crews with a weightless living and working environment. All six would feature one Solar Power Boom with a pair of two-part solar arrays, one or two Central Assembly Element (CAE) core modules, eight Basic Structural Element (BSE) main modules, and two Expendables Storage Element (ESE) logistics and crew carriers. MSC calculated that all six module combinations would provide roughly the same workspace as the NAR monolithic Station design.

Illustrations of four configurations MSC considered and then put aside are labeled 1 through 4 below. X, Y, and Z axes and ground tracks are indicated. The designs are of two classes: the Configuration 1 and 2 BSE modules form arms and the Configuration 3 and 4 BSE modules form bundles. In Configurations 3 and 4, a single nadir-facing +Z BSE module is provided for Earth-observation experiments.

On 15 July 1970, MSC engineers briefed the Space Station Task Group on its progress at NASA Headquarters. They included in their presentation - which, being an interim product, contains its share of internal inconsistencies - the four designs they had put aside plus a preliminary revolving 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).

The baseline configuration illustration includes no ESE, though the modular Station would always operate with at least one - and more often two - attached to its CAE -Y or +Y "side" ports. Though its length was not given, the ESE was described as shorter than the CAE, BSE, and stowed Solar Power Boom modules.

The ESE was a temporary module - it would ride into space inside a Shuttle Orbiter payload bay, would transfer to the Station under its own propulsion bearing supplies, equipment, spare parts, and astronauts, then would remain docked with the Station after the Orbiter departed. While attached to the Station, it would serve as a "pantry" or "warehouse." It would later move under its own propulsion to another Shuttle payload bay bearing experiment results and astronauts for return to Earth.

The ESE was the only module intended to dock with the Station under its own power. During flight to the Station, the Solar Power Boom and BSE and CAE modules would be pivoted from the Shuttle 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. When time came to return to Earth, the Orbiter would undock from the module, leaving it attached to the Station.

MSC estimated that 14 Shuttle flights would be needed to launch and assemble its baseline modular Station. The first flight would place into Earth orbit 20,412-pound CAE 1 (labeled 1 on the drawing) with 10 ports. A pair of robot arms on the CAEs would subsequently aid Shuttle astronauts in safely attaching closely spaced modules. CAE 1 would have nothing yet with which to dock, so would be released directly from the Orbiter payload bay. It would include electricity and propulsion systems that would keep it operational until Shuttle flight 2.

The second Shuttle flight would see a 19,351-pound ESE dock with one of the two +Y side ports of the CAE, forming an "L" configuration. It would provide electricity and propulsion for the CAE-ESE combination, and would lay in a supply of food sufficient for 12 men for 90 days. It would, however, carry no astronauts.

Shuttle flight 3 would see the 19,154-pound Solar Power Boom (3) joined to the CAE +X end port (the CAE end port nearest the docked ESE). The Boom would include a docking port at either end. Its solar arrays would unfurl after the Shuttle Orbiter moved away, blocking the Boom's +X port and more than doubling the Station's length.

Shuttle flight 4 would place into space the first BSE, a 17,209-pound module containing the Station's main control & data processing facilities. It would be attached to the CAE 1 -Y port nearest the Solar Power Boom. It is not shown in the baseline configuration illustration above; an arrow, however, marks the port to which it would be docked. Except for the Solar Power Boom and CAEs, the Shuttle flight 4 BSE would be the only permanent module not docked to a CAE Z-axis port.

Shuttle flights 5 through 8 would also deliver BSE modules. Module placement would alternate between -Z and +Z CAE 1 ports.

Shuttle flight 5 would place in orbit a 20,605-pound BSE containing mainly life support and personal hygiene equipment (5). This would bring total Station mass to 96,731 pounds.

Shuttle flight 6 would deliver a 20,302-pound BSE outfitted with crew staterooms and communications equipment (6). Shuttle flight 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 Shuttle flight 8 module, a BSE dedicated to crew health (8), would also 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 would at that point be equivalent to two decks, an equipment bay, and the Solar Power Boom of the NAR monolithic Station. Station mass would total 143,724 pounds.

Launches 9 through 14 would boost into space the Station's second redundant, independent volume. This would be equivalent to another NAR monolithic Station equipment bay and two more decks.

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 would provide repair assistance or rescue. The modular Station would not be permanently staffed until both volumes were completed.

Shuttle flight 9 would place into space the 18,645-pound second CAE (9), the +X end port of which would be attached to the -X port of CAE 1. This would enable attachment of four more -Z and +Z BSEs. Shuttle flight 10's 16,395-pound BSE would include a maintenance shop and laboratory space (10), while Shuttle flight 11's 19,024-pound BSE would contain a general-purpose lab (11).

The Shuttle flight 12 BSE would provide backup control & data processing (12); like its twin delivered during Shuttle flight 4, it would weigh 17,209 pounds. The payload for Shuttle flight 13 would be a 15,756-pound BSE containing crew quarters (13).

Shuttle flight 14 would complete MSC's baseline modular Station. An Orbiter would release from its payload bay a 20,551-pound ESE 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 -Y CAE 2 port marked on the drawing by 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 scheduled for operations in the 1980s. It would include at least five more BSEs than the baseline configuration. Four would link to the Z-axis ports of a third CAE attached to the CAE 2 -X port.

In the painting, an ESE makes an appearance: it includes a pair of robot arms. One of the four BSE modules attached to CAE 3 is a dedicated Earth-observation module (an open round end-hatch and extended instruments are visible below the ESE arms).

Two BSEs are attached to Y-axis CAE ports; one is the BSE delivered during Shuttle flight 4 (it is displayed attached to the CAE 1 +Y port nearest the Solar Power Boom rather than the -Y port), while the other, attached to a CAE 2 -Y port, is probably a temporarily 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; such experiments could be adversely affected by vibrations caused by crew movement within the Station.

The approaching Shuttle Orbiter 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. It bears a BSE module - probably another freeflyer, or perhaps a temporary lab - bound for a CAE Y-axis port.

After its 15 July presentation at NASA Headquarters, the MSC team apparently halted its activities. The artificial-gravity baseline design, for example, seems not to have been developed further. I have found no evidence that briefings scheduled for 1 August and 7 September at MSC and 15 September at NASA Headquarters 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 Station designs in favor of Shuttle-launched modular designs. When unveiled in 1971, the NAR modular design resembled the baseline design from MSC's May-July 1970 in-house study.


Shuttle-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 Information

A 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 Presentation

05 January 2017

Early Apollo Mission to a Lunar Wrinkle Ridge (1968)

A network of sinuous wrinkle ridges as imaged from lunar orbit during the Apollo 15 mission. The low Sun angle causes the ridges to cast shadows so that they stand out; under high Sun they become be very difficult to see. Image credit: NASA
The 27 January 1967 AS-204/Apollo 1 fire undermined confidence in NASA's ability to put a man on the moon by 1970. The unmanned Apollo 4 (11 November 1967) and Apollo 5 (22 January 1968) missions, respectively the successful first test of the giant Saturn V rocket and the successful Saturn IB-launched unpiloted first test of the Lunar Module (LM), did much to restore faith in the U.S. civilian space agency.

Two weeks after the fire's solemn first anniversary, M. T. Yates, an engineer with Bellcomm, NASA's Apollo planning contractor, completed a memorandum which demonstrated that renewed confidence. In it, he proposed a surface exploration plan for the third Apollo manned moon landing mission.

In keeping with the lunar mission nomenclature proposed in Bellcomm's January 1968 Lunar Exploration Program Plan (see link below), Yates designated the mission Lunar Landing Mission-3 (LLM-3). An "early Apollo" mission, LLM-3 would include a 35-hour stay on the moon, three three-hour moonwalks by two astronauts, and surface exploration on foot no farther than one kilometer from the LM.

Critical for detailed geologic traverse planning would be the LLM-3 LM's ability to set down within a 200-meter-diameter circle centered on a pre-selected landing point. LLM-1 and LLM-2 would be counted as successful if they managed to touch down anywhere on a smooth mare (Latin for "sea") within an ellipse with a total area of 235 square kilometers; LLM-3's landing area would total just 0.25 square kilometers.

Artist concept of an early Apollo landing site atop a rugged ridge. Image credit: NASA
Yates selected as his LLM-3 landing site an area photographed by the Lunar Orbiter III spacecraft between February and October 1967. Located at 36° west, 3° south, it lay in Oceanus Procellarum directly south of the prominent ray crater Kepler. Specifically, he aimed the LLM-3 LM at a half-kilometer-wide mare "wrinkle ridge" with a fresh, 200-meter-wide crater on top.

Mare ridges are common features on the dark-hued lunar maria; some mare ridges are faults, where the mare's basaltic crust has shifted, cracked, and rumpled, while others might indicate magma movement just beneath the lunar surface in the past. Yates expected that the crater on the mare ridge would act as a natural drill hole, enabling the astronauts to collect geologic samples from deep inside the ridge which they could not obtain otherwise.

The first moonwalk of the LLM-3 mission would see the two astronauts, in Yates' plan designated A and B, working together to set up an Apollo Lunar Scientific Experiment Package (ALSEP) north of their LM. The LLM-3 ALSEP would include a hand-held drill for collecting subsurface core samples and heat-flow probes for installation in the resulting empty drill holes.

The astronauts would then move south past the LM to the rim of the Fresh crater. During the second moonwalk, astronaut B would descend into the crater while astronaut A monitored his activities from its rim. In addition to keeping an eye on his colleague, A would relay radio signals from B's space suit backpack radio to the LM for transmission to Earth. This would be necessary, Yates wrote, because the crater rim would block astronaut B's radio signals.

In the third and final LLM-3 moonwalk, astronaut B would move westward down a short canyon to the mare floor, then would walk south along the ridge-mare contact. Astronaut A, meanwhile, would walk along the mare ridge crest to keep B in sight and again relay his radio signals to the LM. The astronauts would then meet up and return to the LM via the east rim of the crater.

No Apollo mission explored a mare ridge, and Yates's proposed radio-relay technique was never used. The second Apollo lunar landing mission, Apollo 12, amply demonstrated the pinpoint landing capability Yates rightly deemed crucial to geologic traverse planning by setting down near the derelict Surveyor III lander in November 1969. Apollo 14, the third successful Apollo lunar landing mission, used this capability to land near Cone Crater, a naturally occurring drill hole that permitted astronauts Alan Shepard and Edgar Mitchell to collect samples from within the Fra Mauro Formation in February 1971.


"A Lunar Landing Mission to a Mare Ridge – Case 340," M. T. Yates, Bellcomm, 14 February 1968

More Information

"A Continuing Aspect of Human Endeavor": Bellcomm's January 1968 Lunar Exploration Program

Robot Rendezvous at Hadley Rille (1968)

An Apollo Landing Near The Great Ray Crater Tycho (1969)

01 January 2017

Robot Rendezvous at Hadley Rille (1968)

Image credit: Bendix/NASA
In May 1968, Bellcomm planners Noel Hinners, Farouk El-Baz, and A. Goetz described a unique post-Apollo mission to the Apennine Front-Hadley Rille region of the moon. The mission would see a melding of manned and automated lunar exploration, potentially yielding results greater than either astronauts or exploring machines could achieve on their own.

Hinners, El-Baz, and Goetz invoked an Extended Lunar Module (ELM) capable of bearing 750 pounds of payload to the moon's surface. During the crew's first venture outside the ELM, they would rendezvous with a waiting Unmanned Lunar Roving Vehicle (ULRV).

The wheeled ULRV, with a mass of between 1,500 and 3,000 pounds, would have landed some 500 kilometers from the Apennine Front-Hadley Rille ELM site some time earlier. Under guidance from controllers on Earth, it would then have made its way to meet the astronauts, all the while beaming TV images of its surroundings to Earth, charting the moon's gravity and magnetic fields, leaving behind Remote Geophysical Monitor instrument packages, and collecting rock samples. The ELM astronauts would retrieve the ULRV rock samples for return to Earth.

Image credit: Aeronautical Chart and Information Center
The Bellcomm planners proposed four candidate traverse routes for the ULRV (map above). For route 1, the automated rover would land in the Sulpicius Gallus region of southwest Mare Serenitatis and strike north through an area of north/south-trending rilles (canyons) and dark, thus possibly volcanic and young, surface material. The lunar Apennine Mountains would dominate the western horizon as the ULRV rolled northward, gradually entering a region with lighter and older surface materials.

At the contact between Mare Serenitatis and Mare Imbrium, the rover would turn west, then south, so the Apennines would dominate its eastern horizon. The ULRV would pass through hills made up of rocks of the Fra Mauro Formation, which was widely interpreted as ejecta from the immense ancient impact that excavated Mare Imbrium.

Finally, the route 1 rover would carefully pick its way across steep-sided Hadley Rille (also known as Rima Hadley) and park close to the planned post-Apollo ELM landing site south of the crater Hadley C. The Bellcomm researchers declared 10-kilometer-wide Hadley C to be a "probable maar" - that is, a surface feature produced when rising magma comes into contact with subsurface ice or water, generating a steam explosion.

Route 2 would see the ULRV land south of the crater Alexander in northern Mare Serenitatis. The rover would strike southwest toward the Mare Serenitatis-Mare Imbrium contact through a region of hummocky Highland rock units, including probable examples of the Fra Mauro Formation. The route would cross dark materials (possible young volcanics) and light materials (possible rays from young impact craters) before it turned south to follow the same path to the ELM site as the Route 1 ULRV.

The ULRV for traverse route 3 would land in southern Mare Imbrium west of the "ghost" crater Wallace, an ancient impact crater mostly submerged by flowing lava in the distant past. The rover would trundle eastward across a bright ray from the young large crater Copernicus, than pass through a crater chain to reach Wallace's subdued, ancient rim. Once there, it would strike out northeastward across eastern Mare Imbrium, then over the Apennine Bench (a possible volcanic ash or flow deposit), before crossing Palus Putredinis to Hadley C and the planned ELM site.

Route 4 would begin at a ULRV landing site in central Mare Imbrium, in an area with many fresh-looking wrinkle ridges. The ULRV would surmount one such ridge on its way to the north rim of the large smooth-floored crater Archimedes. After cautiously picking its way through the boulders and crevasses near Archimedes' rim, the ULRV would turn southwest through a region of exposed bedrock, then would cross hummocky Fra Mauro Formation hills and Palus Putredinis before parking near the ELM site.

The Bellcomm planners identified routes 1 and 2 as having the greatest potential for increasing geophysical understanding of the moon. In addition, route 1 would pass through terrain similar to that observed at Littrow, another candidate post-Apollo landing site, possibly freeing the proposed Littrow ELM mission to explore elsewhere on the moon. The Littrow is located on the eastern side of Mare Serenitatis.

Hadley C landing site and traverses. Image credit: Defense Mapping Agency Topographic Center/NASA/DSFPortree
Hinners, El-Baz, and Goetz noted that, in addition to collecting a diverse suite of samples along its 500-kilometer traverse path, the ULRV might be used to survey the ELM landing site, which would be located on the Hadley Rille rim at 26° 52′ North, 3° 00′ East (marked by the red star on the Hadley C landing site map above). The ULRV survey might eliminate the need for high-resolution orbital photography of the area. The rover might also act as a landing beacon for the ELM and serve as a radio relay for the astronauts exploring the site, which would contain many places where they might pass behind hills and into trenches, out of line-of-sight radio contact with the antennas on the ELM.

Hinners, El-Baz, and Goetz noted other operational challenges of the Apennine Front-Hadley Rille ELM site. The most important involved lighting. The ELM would approach the site from the east with the Sun behind it, pass over the Apennine Mountains, then descend almost vertically on the west side of the range. As it descended, it would plunge suddenly into shadow cast by the mountains. On some landing dates, the astronauts might touch down in darkness lit only by sunlight reflected off the Hadley C rim and other features beyond the shadow; in others, they would emerge from shadow into dazzling sunlight just before touchdown.

The scientists were convinced, however, that the scientific benefits of their ELM site would outweigh these difficulties. They wrote that
This site is important among those proposed in that it may provide access to a major portion of lunar history. . .Such access comes from over 1 km of vertical relief resulting from the combination of the Apennines Mountains scarp, the rim of the Imbrium Basin[,] and the rille…. This historical sequence may run from materials that constitute original lunar crust to relatively young materials derived from that crust. The oldest crustal materials in the area, possibly exposed in the lower part of the Apennine Front to the east of the proposed landing area, should provide data bearing directly on the problems of the primary physical and chemical composition of the Moon and thus, indirectly, of the Earth.
The scientists noted that the Manned Spacecraft Center in Houston, Texas, had established as a ground rule that only a single Extravehicular Activity (EVA) could take place on the first and last days of a lunar landing mission. The first three-hour EVA (purple on Hadley C site map) of the Apennine Front-Hadley Rille mission, on landing day, would see the astronauts walk to the parked ULRV to retrieve the samples it had gathered during its traverse. They would also work together to assemble and point at Earth the umbrella-like S-band antenna, inspect the ELM's exterior for any damage incurred during descent and landing, deploy "staytime extension equipment" (for example, a small solar array for generating supplemental electricity), and unstow the mission's twin 180-pound Lunar Flying Units (LFUs).

Lunar Flying Unit concept art. Image credit: North American Aviation/NASA
NASA and its contractors had studied the concept of the LFU, a small, rocket-powered hopper, for several years by the time Hinners, El-Baz, and Goetz made it a critical part of their Apennine Front-Hadley Rille mission (see "More Information" below). If all went as planned, the ELM would land with close to 1,000 pounds of propellants remaining in its descent stage tanks. At the start of the first EVA of day 2 (green on Hadley C site map), the astronauts would spend 30 minutes pumping into each LFU 300 pounds of propellants from the ELM. They would also load LFU #1 with cameras and film, geologic tools including a 25-pound hand drill for collecting sample cores, and sample containers.

Astronaut #1 would then fly LFU #1 3.3 kilometers to his first stop, the Apennine Front-mare contact, where he would spend one hour collecting up to 25 pounds of samples, including cores drilled to a depth of 10 feet. He would then fly two kilometers to the top of the Apennine ridge, about 500 meters above the ELM. He would spend an hour there collecting another 25 pounds of samples. The Bellcomm planners explained that materials blasted from "depths of several tens of kilometers in the moon" by the Imbrium impact might be draped over the sites he visited. These would, they argued, "offer our best chances to examine 'primitive' planetary materials which have not been affected by later planetary differentiation processes."

Astronaut #2, meanwhile, would deploy the 280-pound Apollo Lunar Scientific Experiment Package (ALSEP) near the ELM. He would also stand by LFU #2 to rescue Astronaut #1 in the event that LFU #1 failed on top of the ridge, which would lie just beyond the five-kilometer “walk-back limit” of the Apollo space suits. Assuming, however, that LFU #1 gave no trouble, Astronaut #1 would fly it 5.2 kilometers back to the landing site and join Astronaut #2 inside the ELM for lunch and rest.

To begin the second EVA of mission day 2 (blue on the Hadley C site map), Astronaut #1 would board LFU #2 and fly 3.2 kilometers west of the ELM to the bottom of Hadley Rille. Astronaut #2, meanwhile, would walk to a point on the Rille rim within sight of both Astronaut #1 and the ELM. He would collect up to 25 pounds of samples and serve as a radio relay linking Astronaut #1 to the ELM and, through the ELM, to Earth. After 1.5 hours of sampling the shadowed floor of Hadley Rille, Astronaut #1 would fly LFU #2 4.8 kilometers to the Hadley C rim. He would spend 30 minutes sampling, then would fly back to the ELM. At no point would Astronaut #1 pass beyond the Apollo suit walk-back limit, so Astronaut #2 would have no need to stand by LFU #1 to mount a rescue.

The fourth and final EVA of the Apennine Front-Hadley Rille mission (yellow on the Hadley C site map) would occur on departure day. After loading LFU #1 with propellants, Astronaut #1 would fly 2.5 kilometers west of the ELM to two sets of crater pairs. After 30 minutes of sample collection, he would fly 1.5 kilometers to a crater on Hadley Rille’s rim, where he would again sample for 30 minutes. Finally, he would fly three kilometers to a “promontory” on the Rille rim, sample for 30 minutes, and fly 1.4 kilometers back to the ELM.

Astronaut #2, meanwhile, would "conduct local investigations" close by the ELM, "adjust ALSEP experiments," and prepare samples for return to Earth. After returning to the ELM, Astronaut #1 would assist Astronaut #2. After packing up about 100 pounds of samples, they would lift off in the ELM ascent stage, leaving behind the LFUs and other equipment.

They would also leave behind many of the samples they had collected. Hinners, El-Baz, and Goetz noted that, while the ULRV would collect some unspecified (but probably large) quantity of unique samples during its 500-kilometer traverse and the astronauts might collect about 200 pounds of samples, the ELM ascent stage could carry only 100 pounds of payload into lunar orbit. This meant that the sample packing process would mostly involve hurried screening, with the majority of the samples collected during the mission being thrown away. They also noted that their EVA schedule was very tight, so that mission success would depend "on everything going with clockwork precision during the crowded EVA periods."

To solve these problems, they proposed that the ELM for the Apennine Front-Hadley Rille mission be upgraded to permit a 1,000-pound science payload, a four-day surface stay, and 200 pounds of returned samples. This would, among other things, enable addition of a walking traverse to the Apennine Front-mare contact and introduction of a 400-pound Advanced ALSEP. Additional stay-time would permit more care to be taken in selecting samples for return to Earth; at the same time, doubling the returned sample weight would make sample screening less critical.

Apollo 15 Lunar Roving Vehicle. Image credit: NASA
Apollo 15, the first of three advanced J-mission Apollos NASA flew in 1971-1972, landed at 26° 8′ North, 3° 38′ East, about 30 kilometers northeast of the Hinners, El-Baz, and Goetz ELM landing site, on 30 July 1971. The site, close to where Hadley Rille turns sharply toward the northwest, is farther from the mountains than the Hadley C site, eliminating lighting problems. The LM Falcon remained on the surface for nearly three days. Astronauts David Scott and James Irwin had at their disposal no LFU; the concept, though much studied, had gained little traction, in large part because of Astronaut Office opposition.

In place of the LFU, Scott and Irwin traversed their landing site using a 460-pound four-wheeled Lunar Roving Vehicle (LRV). They drove almost 50 kilometers during three periods of space-suited surface activity, the longest of which lasted seven hours and 13 minutes. Falcon's ascent stage lifted off from Hadley-Apennine on August 2 with a cargo of about 170 pounds of lunar samples.

Apollo 15 was the fourth of six successful manned lunar landings. By the time it flew, budget cuts and policy changes had caused NASA to truncate Apollo and abandon plans for post-Apollo lunar exploration. In an editorial published the day after Falcon's ascent stage left the moon, The New York Times pointed to the mission's many achievements and reminded its readers that manned lunar exploration was set to end with Apollo 17. A "vast and complex technology developed at a cost of billions of dollars over the last decade is being abandoned even as its vast potentialities are being demonstrated," the paper lamented.


A Preliminary ELM/Unmanned LRV Mission Plan for the Apennine Front-Hadley Rille Area – Case 340, N. Hinners, F. El-Baz, and A. Goetz, Bellcomm, Inc., 31 May 1968

Astronautics & Aeronautics 1971, NASA SP-4016, NASA, pp. 217-218

More Information

"A Continuing Aspect of Human Endeavor": Bellcomm's January 1968 Lunar Exploration Program

Rocket Belts and Rocket Chairs: Lunar Flying Units

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

The Spacewalks That Never Were: Gemini Extravehicular Planning Working Group (1965)

25 December 2016

Electricity from Space: The 1970s DOE/NASA Solar Power Satellite Studies

Image 1 (see callout in text). Image credit: NASA
Of all the many spaceflight concepts NASA has studied, probably the most enormous was the Solar Power Satellite (SPS) fleet. Czech-born physicist/engineer Peter Glaser outlined the concept in a brief article in the esteemed journal Science in November 1968, and was awarded a patent for his invention on Christmas Day 1973.

Glaser had noticed that a satellite in geosynchronous Earth orbit (GEO), 35,786 kilometers above the equator, would pass through Earth's shadow for only a few minutes each year. It was well known that a satellite in equatorial GEO moves at the same speed the Earth rotates at the equator (1609 kilometer per hour). This means that, for people on Earth's surface, the satellite appears to hang motionless over one spot on the equator. Glaser also understood that electricity did not have to travel through wires; it could be beamed from a transmitter to a receiver.

Glaser mixed these three ingredients and came up with a satellite in equatorial GEO that would use solar cells to convert sunlight into electricity, convert the electricity into microwaves, and beam the microwaves at a receiving antenna (rectenna) on Earth. The rectenna would turn the microwaves back into electricity, then wires would carry it to the electric utility grid.

The great advantage an SPS enjoyed over a solar array on Earth's surface was, as mentioned, that it would spend almost no time in Earth's shadow. Earth's rotation meant that an Earth-surface solar array could make electricity at most about half the time. The rest of the time it would sit dormant under the night sky.

NASA and its contractors displayed low-level interest in the SPS concept as early as 1972. Early work took place at the Jet Propulsion Laboratory and NASA Lewis Research Center (now NASA Glenn), as well as at Arthur D. Little, a Cambridge, Massachusetts-based engineering firm of which Glaser was a Vice President. The level of effort increased in 1973, after the Organization of Petroleum Exporting Countries imposed an oil embargo to punish the U.S. and other industrialized nations for their support of Israel in the 1973 Yom Kippur War. By 1976, NASA's Johnson Space Center in Houston, Texas, and Marshall Spaceflight Center in Huntsville, Alabama, led SPS studies within the space agency.

In June 1975, NASA and the Energy Research and Development Administration (ERDA) signed a Memorandum of Understanding calling for joint SPS research. ERDA began to plan a joint SPS study with NASA at the beginning of Federal Fiscal Year 1977 (October 1976), in the waning days of Gerald Ford's caretaker Presidency. The three-phase study began in July 1977. Total cost of the joint SPS studies, which were meant to last for three years, was $15.6 million, of which the DOE paid 60%.

Energy shortages coupled with the Three-Mile Island nuclear accident (March 1979), made the mid-to-late 1970s a fertile environment for alternative energy research. A month after the ERDA/NASA studies began, President James Carter made ERDA a part of the new Department of Energy (DOE). Creation of the DOE was part of a policy package aimed at U.S. energy independence and "clean energy."

After Apollo, NASA had, despite its best efforts, found itself without a clearly defined mission for its piloted program other than development of the Space Shuttle. SPS supporters in the aerospace community saw in the concept an irresistible opportunity for NASA to contribute to the solution of a pressing national problem.

Development, deployment, and operation of SPSs would confront NASA with engineering problems far beyond any it had tackled before. If an SPS was to contribute a meaningful amount of electricity to the interlinked U.S. utility grids - and, by DOE's reckoning, "meaningful" meant gigawatts - then it would have to be colossal by normal aerospace engineering standards. The SPS silhouetted against the Sun in the NASA artwork at the top of this post (Image 1) is typical: it would have measured 10.5 kilometers long by 5.2 kilometers wide and had a mass of 50,000 tons.

Paired with a rectenna a couple of kilometers across, such an SPS would contribute five gigawatts to the U.S. electricity supply. DOE estimated that 60 such satellites with a total generating capacity of 300 gigawatts could contribute meaningfully to satisfying projected U.S. electricity demand in the 2000-2030 period.

Image 2. Image credit: Boeing/NASA
There was, of course, no way that NASA could launch such huge satellites intact, or even in a few modular parts. It would need to construct the SPS fleet in space, most likely in GEO, from many parts. This called for an armada of highly capable space transport vehicles and an army of astronauts and automated assembly machines.

The red, white, and blue "Space Freighter" pictured in the Boeing painting above (Image 2) was, as its name implies, meant to serve as the main cargo launcher for SPS construction. Fully reusable to cut costs, it would have comprised at launch an automated, delta-winged Booster with a piloted, delta-winged Orbiter on its nose. After separating from the Orbiter, the Booster would have either landed downrange (if it were launched from a site in California, Arizona, New Mexico, or western Texas) or would have deployed turbofan engines and flown back to its launch site.

Image 3. Image credit: NASA
Had it been built, the Space Freighter would have utterly outclassed all other launchers. Its Orbiter would have delivered up to 420 metric tons of cargo to a staging base in low-Earth orbit (LEO). For comparison, the largest single-launch U.S. payload ever put into LEO, the Skylab Orbital Workshop, weighed 77 metric tons. Skylab was launched on a two-stage Saturn V rocket.

Engineers speak of "gross liftoff weight" (GLOW) when they describe large launchers. The Space Shuttle had a GLOW of about 2040 metric tons and the three-stage Apollo Saturn V, about 3000 metric tons. Estimated GLOW for the Space Freighter was a whopping 11,000 metric tons.

Alert readers will notice discrepancies in the paintings that illustrate this post. These occur because the images are based on design concepts developed by different engineers in different phases of the multi-year SPS study. The delta-winged Boeing Space Freighter design, for example, is different from the NASA Space Freighter design depicted in the illustration above (Image 3).

The NASA Space Freighter has a Booster with some resemblance to a Saturn V S-IC stage; both the Booster and the Orbiter have skinny main wings and forward canard fins. The Orbiter payload bay is located near its front; not, as in the Boeing design, at mid-fuselage. Despite these differences, the NASA Space Freighter would have had the same capabilities as the Boeing Space Freighter.

Image 4. Image credit: NASA
The NASA painting above (Image 4) depicts a hexagonal LEO staging base with a central "control tower." Access tubes link the control tower to docking modules at the hexagon’s six vertices. Between the access tubes are color-coded triangular “marshaling yards” with socket-like bays for storing standardized NASA Space Freighter cargo containers.

The staging base control tower has mounted on its roof a "space crane" descended from the much smaller Space Shuttle Canadarm, which was under development at the time DOE and NASA conducted their joint SPS study. The control tower space crane is positioning a cargo container so that an automated chemical-propulsion Orbital Transfer Vehicle (OTV) can dock with it. After docking and space crane release, the OTV would automatically transport the container to a construction base in GEO.

Another, smaller space crane rides a track around the edge of the hexagon. It is shown unloading a cargo container from the newly docked Space Freighter Orbiter.

The painting includes many other details. It shows, for example, what appears to be a conventional Space Shuttle Orbiter approaching the staging base in the background. Rockwell, prime contractor for the Space Shuttle, proposed that second-generation Space Shuttle Orbiters serve as dedicated crew transports for the SPS program. The company envisioned that replacing the Orbiter’s payload bay with a pressurized crew module would enable it to transport up to 75 astronauts at a time.

Next to the crew transport is a cluster of cylindrical modules for housing the staging base crew and astronauts in transit between Earth and GEO. A piloted OTV for transporting astronauts to and from the GEO SPS work-site – identical to the automated OTV, except for the presence of a pressurized crew module – is shown docked with the LEO staging base at lower right.

Image 5. Image credit: NASA
Image 6. Image credit: NASA
In the SPS study, NASA sought to balance automation and astronauts. Automation was, its engineers noted, good for repetitive actions such as fabricating the tens of kilometers of trusses needed to support SPS solar cell blankets.

The basic "beambuilder" depicted in the upper image above (Image 5) would turn tight rolls of thin aluminum sheeting into sturdy single trusses. The more complex multiple beambuilder system in the lower image (Image 6) would combine and link together single trusses to make the major structural members of the satellite.

Astronauts would supervise and maintain the beambuilder robots and join together the trusses they fabricated. Automated OTVs would deliver thousands of aluminum rolls to the GEO work-site, which the astronauts would then load into the beambuilders.

DOE and NASA expected to added two SPSs to the "fleet" in GEO each year starting in 2000. Each SPS would need about 200 Space Freighter launches and hundreds of OTV transfers between the LEO staging base and GEO. Propellants for the OTVs, as well as 50 metric tons of orbit trim propellants for each SPS per year, would demand even more Space Freighter launches.

Image 7. Image credit: NASA
Despite extensive reliance on automation, the 30-year SPS project would require the presence of nearly 1000 astronauts in space at all times. Most would be based in GEO (Image 7).

In addition to construction workers, personnel needed in space would include physicians, administrators, OTV pilots, life support engineers, general maintenance workers ("janitors"), cooks, space suit tailors, and computer technicians. Personnel needed on the ground - at the launch/landing site, at the rectennas, and at widely scattered factories for manufacturing SPS parts, OTVs, spares, foodstuffs, and propellants - would outnumber astronauts by at least 10 to 1, NASA and DOE estimated. Building and operating the SPSs could become a major new U.S. industry.

Image 8. Image credit: NASA
As beambuilders and astronauts completed trusswork sections, automated OTVs would begin to deliver rolls of solar cell "blankets" to the SPS work-site. The NASA painting above (Image 8) shows in the background an automated OTV laden with bluish rolls of solar cell blankets (upper right).

Meanwhile, an automated system feeds blanket sections to a piloted "cherry picker" at the end of a small space crane. The cherry picker's "pilot" - who wears only shirt-sleeves in his pressurized cab - uses manipulator arms to link one end of a solar cell blanket to a truss.

More than 50 square kilometers of solar cell blankets would be spread over the trusswork of each SPS in this way. The end result of this intensive human and machine labor is depicted in idealized form immediately below (Image 9).

Image 9. Image credit: NASA
Image 10. Image credit: NASA
The lower painting above (Image 10) shows Glaser's invention at work. The intense sunlight of space strikes solar cells, which are hidden from view (the image does, however, provide a good look at the backside of a completed SPS). Millions of silicon or gallium arsenide cells efficiently convert the sunlight into electricity.

The kilometer-wide steerable microwave transmission antenna at the lower end of the SPS converts the electricity into microwaves and focuses the microwave beam on a rectenna on Earth, nearly 36,000 kilometers away. The beam appears in the illustration as a ghostly cone; in reality, the microwaves would of course be invisible.

DOE and NASA envisioned building the 60 rectennas (Image 11) required for the SPS system from coast to coast along the 35° latitude line. Cities on or near that line include Bakersfield, California; Flagstaff, Arizona; Albuquerque, New Mexico; Amarillo, Texas; Oklahoma City, Oklahoma; Little Rock, Arkansas; Memphis and Chattanooga, Tennessee; and Charlotte, North Carolina. If one flew between these cities, one would overfly rectennas on the ground in different settings - forest, farm fields, mountains, swamp, desert - every 50 kilometers or so.

The 1970s saw growing awareness of environmental problems and the dangers of terrorism. DOE and NASA took pains to seek public input so that they could attempt to calm public fears. Most people polled worried about the microwave beams linking the SPSs with their rectennas on Earth. Some expressed concern about the environmental impact of the beams, while others feared that terrorists might seize control of an SPS and turn its beam on a city.

Image 11. Image credit: NASA
NASA pointed out that the beam would be de-focused to reduce risk to the Earth's upper atmosphere, aircraft, and people working at the rectennas. As depicted in the painting above, limited agriculture could take place under the rectennas, directly in the path of the microwave beams. In addition, the microwave transmitter on the SPS could be designed to shut off if its beam drifted. DOE and NASA expected that each rectenna would have around it a "buffer" zone of uninhabited land so that if the beam drifted a small distance before it turned off automatically, only the ring-shaped buffer would be affected.

In this final image of this post (Image 12), we see the SPS fleet near the end of 2015; that is, halfway through the 30-year construction program, when 30 satellites would form a bright line across the southern night sky as viewed from the contiguous United States. A DOE document explained that each satellite would shine a little brighter than Venus. The satellites would appear about as far apart as the stars making up Orion's belt. Widely available 7 x 50 binoculars would reveal each satellite's rectangular shape to Earth-bound observers.

Image 12. Image credit: NASA
The string of satellites would remain still against a background of moving stars and planets. In reality, of course, the stars and planets would remain still relative to the rotating Earth and the SPSs would keep up with Earth's rotation.

Every six months, at the time of the spring and autumn equinoxes, each SPS would pass through Earth's shadow near midnight for several days in succession. During its brief shadow passage, a satellite would not produce electricity. One by one, starting with the eastern satellites, the SPSs would redden and grow dark. After about 10 minutes in eclipse, each would return to its full brightness.

The DOE/NASA SPS studies continued into the Administration of President Ronald Reagan, who took office in January 1981. In August 1981, the Congressional Office of Technology Assessment (OTA) published a review of SPS work performed since 1976. The OTA's assessment of the viability of the concept was generally favorable. The Reagan Administration was, however, not enthusiastic about electricity from space or, indeed, from any but conventional sources.

The DOE/NASA SPS studies constituted only a tiny, low-priority portion of the space agency's total activities. The first Space Shuttle test flight in April 1981, the first American piloted space mission since July 1975, was, of course, of far greater consequence. With the first Shuttle flight under its belt, NASA redoubled its efforts to build support for a Shuttle-launched Earth-orbital space station. The agency portrayed the station as a space shipyard, a marshalling yard for space tugs and payloads, and a laboratory for exploitation of the unique qualities of space.


"Power from the Sun: Its Future," Peter Glaser, Science, Vol. 162, 22 November 1968

Feasibility Study of a Satellite Solar Power Station, NASA Contractor Report 2357, P. Glaser, O. Maynard, J. Mackovciak, and E. Ralph, February 1974

Memorandum of Understanding Between the Energy Research and Development Administration and the National Aeronautics and Space Administration, 23 June 1975

The Solar Power Satellite Concept: The Past Decade and the Next Decade, JSC-14898, July 1979

Some Questions and Answers About the Satellite Power System (SPS), DOE/ER-0049/1, U.S. Department of Energy, Office of Energy Research, Satellite Power System Project Office, January 1980

Satellite Power System Concept Development and Evaluation Program, Volume I: Technical Assessment Summary Report, NASA Technical Memorandum 58232, NASA Lyndon B. Johnson Space Center, November 1980

Solar Power Satellites, Office of Technology Assessment, U.S. Congress, August 1981

More Information

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

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

18 December 2016

NASA Marshall's 1966 NERVA-Electric Piloted Mars Mission

Image credit: NASA
Through most of 1966, it was still reasonable to assume that NASA and the United States might enjoy an expansive post-Apollo future off the Earth. Manned missions beyond the moon were expected to evolve from programs already in place; namely, the Apollo lunar landing program, the joint NASA/Atomic Energy Commission NERVA nuclear-thermal rocket program, and the Apollo Applications Program of advanced lunar missions and Earth-orbiting space stations.

With these programs in mind, in March 1966 the American Institute of Astronautics and Aeronautics and the American Astronautical Society jointly convened the Stepping Stones to Mars conference in Baltimore, Maryland. As it turned out, it would be the last major Mars-focused engineering meeting until the 1980s.

Attendees heard a team of engineers from NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, describe a piloted Mars mission based on both high-thrust NERVA-II nuclear-thermal rockets and low-thrust nuclear-electric (ion) propulsion. The study team's leader was veteran German-born rocketeer Ernst Stuhlinger, the director of MSFC's Research Projects Laboratory.

Stuhlinger had begun his work on electric propulsion in the 1930s. He earned a Ph.D. at age 23, then worked for Hitler's nuclear program. In spite of his science training, in 1941 he was drafted into the Wehrmacht and sent to the Russian front. After suffering wounds in the Battle of Moscow and surviving the Battle of Stalingrad, he was reassigned to Wernher von Braun's rocket team at the Baltic Sea rocket base of Peenemünde in 1943. There he worked on the guidance system for the V-2 missile.

Stuhlinger arrived in the United States in 1945 courtesy of the U.S. Army with von Braun, 124 other German rocketeers, and a trainload of captured V-2 missiles. Stuhlinger resumed his electric propulsion work in Huntsville in the early 1950s, while von Braun's team was part of the Army Ballistic Missile Agency at Redstone Arsenal. Under von Braun's leadership, the Peenemünde rocketeers became the nucleus around which NASA MSFC coalesced in July 1960.

Ernst Stuhlinger (left, holding slide rule) and Wernher von Braun during filming of the classic Walt Disney-produced documentary Mars and Beyond. The model Mars spacecraft shown, based on a Stuhlinger design, includes a disk-shaped thermal radiator, a bomb-shaped piloted Mars lander, and, at the end of a downward-pointing stalk, a nuclear reactor. The reactor would power thrusters mounted on the stalk opposite the lander. Crew quarters are near von Braun's hand. Image credit: NASA
In the years before the Stepping Stones to Mars meeting, Stuhlinger had put forward several electric-propulsion spacecraft designs. His 1954 Sun Ship would have relied on concentrated sunlight for electrical power to drive its ion thrusters, but his other electric-propulsion designs - the 1957 Mars and Beyond crew and 1959 lunar freighter disc ships and his 1962 lunar freighter and spinning Mars crew spacecraft - would have employed large nuclear reactors.

The hybrid NERVA/nuclear-electric approach would, the MSFC engineers explained, magnify the benefits and mitigate the drawbacks of both propulsion methods. Efficient electric propulsion would slash the amount of the propellant required to reach and return from Mars. This would in turn reduce the number of costly rockets required to place a hybrid Mars spacecraft into Earth orbit for assembly. Five uprated two-stage Saturn V rockets would be sufficient to launch all the components making up a hybrid spacecraft into Earth orbit - about half as many as required to launch a Mars spacecraft propelled by NERVA nuclear-thermal rocket engines alone.

Nuclear-thermal rockets, for their part, would trim trip time and reduce crew radiation exposure. Nuclear-electric spacecraft could escape from Earth orbit only after spiraling outward for weeks or months. Because of this, they would linger in the Van Allen radiation belts for days or weeks. Nuclear-thermal spacecraft, on the other hand, could escape from Earth orbit in hours and race through the Earth-girdling radiation belts in minutes.

Stuhlinger and his colleagues scheduled their NERVA/nuclear-electric Mars expedition for launch in 1986, 20 years after they presented their paper, because in that year the amount of energy needed to travel from Earth to Mars and back would be relatively small and solar activity would be at an ebb. The MSFC team assumed (rather naively) that their expedition would encounter no solar flares, so they skimped on radiation shielding to reduce spacecraft weight.

They also anticipated that electric propulsion would be applied first to Earth-orbital satellite station-keeping in the late 1960s, and that enough electric propulsion research would be completed by 1974 to justify government approval of the NERVA/nuclear-electric Mars expedition. That would leave 12 years for spacecraft development and testing.

The hybrid Mars expedition would occur in three phases. Phase 1 would see nuclear-electric spacecraft components and propellant launched from Earth's surface. To enhance safety, four identical manned spacecraft would undertake the Mars voyage. If one failed, its crew could find refuge on board the remaining three spacecraft. Each spacecraft would in fact be capable of returning all 16 crew members to Earth in cramped conditions.

For each Mars spacecraft, three uprated two-stage Saturn V rockets would launch a total of 388 tons of components and propellant into 485-kilometer-high assembly orbit. For the four-spacecraft expedition, 12 uprated Saturn Vs would launch a total of 1552 tons.

Ernst Stuhlinger displays models of the MSFC 1966 NERVA/nuclear-electric Mars spacecraft, an Apollo Saturn V rocket, and, at right, a Saturn V-launched payload module containing NERVA/nuclear-electric spacecraft truss components. The NERVA-II stage/propellant tank combination is not shown. The payload module, nuclear-electric spacecraft, and Saturn V are the same scale. On the wall in the background is an illustration of the 1962 diamond-shaped Mars spacecraft design developed with MSFC engineer Joseph King, a member of the 1966 Mars spacecraft study team. Image credit: NASA
The spacecraft would each include a central module containing the nuclear-electric propulsion system, a four-person, 57-ton Mars Excursion Module (MEM) lander, and space "taxis" for crew transport between the four spacecraft. The 123-ton propulsion system would include a 20-megawatt nuclear reactor, an electricity-generating turbine-generator, electric thrusters, and a cylindrical tank holding 153 tons of xenon or cesium propellant. Twin telescoping truss-like arms extending from either side of the central module would each carry four rectangular reactor radiator panels and, at its end, one two-deck drum-shaped pressurized crew module.

Phase 2 would see launch of four nuclear-thermal rocket stages and the Mars expedition's departure from Earth orbit. Shortly before the scheduled launch date, four uprated Saturn Vs would launch one NERVA-II nuclear-thermal propulsion module each, then four more uprated Saturn Vs would launch one liquid hydrogen tank module each. The NERVA-IIs and tank modules would dock in orbit to form four 54-meter-long, 10-meter-diameter nuclear-thermal stages, each with a mass of 309 tons. Of this mass, liquid hydrogen propellant would account for 226 tons. The nuclear-thermal stages would then each maneuver to dock with a nuclear-electric spacecraft's central module.

On 1 May 1986, the four NERVA-II engines would power up and operate for nearly 30 minutes. The spacecraft crews would, meanwhile, shelter in their MEMs. In the event of NERVA-II trouble, the MEM would serve as the crew's abort-to-Earth vehicle.

About 17 minutes after start-up, each NERVA-II engine would vent hot gas from its turbopump to spin its spacecraft once per minute, producing acceleration equal to 20 percent of Earth's surface gravity in the crew modules at the ends of the twin telescoping arms. Artificial gravity would ensure, among other things, that toilets and showers would operate much as they did on Earth.

The MSFC team noted, however, that "available evidence from the Gemini flight missions suggests that artificial gravity for long space missions may not be required physiologically." The longest two-man Gemini mission, Gemini VII, had lasted for just 14 days in December 1965, so the MSFC team in fact had very little basis for its opinion.

The NERVA-IIs would deplete their propellant at an altitude of 3450 kilometers, then Phase 3, the actual Mars expedition, would commence. The crews would leave their MEMs, climb down pressurized tunnels in the telescoping arms to their cabins, discard the spent NERVA rocket stages, and activate the nuclear-electric thrusters to complete spacecraft injection onto a trans-Mars trajectory. The astronauts would switch off the thrusters after an unspecified short period and the fleet would then coast around the Sun along a curving Mars-bound path.

One-hundred-and-forty-five days out from Earth, the four ships would re-activate their nuclear-electric thrusters to begin deceleration. Then, on 23 September 1986, Mars's gravity would capture them into a high orbit. Their nuclear-electric thrusters would continue to operate for 23.5 days so that they would spiral down to a 1000-kilometer circular Mars orbit.

During the spiral-down period, the four MEMs would undock and land on Mars, leaving the four ships unmanned. Relieved of the weight of the MEMs, the nuclear-electric ships could spiral inward toward Mars more rapidly.

The MSFC team cited data from the Mariner IV Mars probe when they proposed an "Apollo-shaped" conical MEM design. Mariner IV had flown past Mars in July 1965, returning data that indicated that the planet's atmosphere was about 10 times thinner than expected. Because of this, winged and lifting-body Mars landers, which would rely on aerodynamic lift to reduce the amount of landing and liftoff propellants they would need, were no longer considered feasible. The Apollo-shaped MEM design had been the subject of special study by Gordon Woodcock, a member of the MSFC study team.

Atmospheric drag would slow the 10-meter-wide MEM, then its heat shield would eject to expose chemical-propellant landing retrorockets. These would slow the MEM to a halt 400 meters above Mars; the MEM pilot would then have 60 seconds to select a landing spot before he exhausted the MEM's descent propellants.

After a month on Mars, each MEM's 27-ton ascent stage would blast its crew back to their orbiting nuclear-electric mothership. The crews would return to the cabin modules, then the ascent stages would be cast off. Because the Mars spacecraft would no longer carry the weight of the MEMs, outward spiral from Mars would last just 17.5 days, with Mars escape taking place on 12 November 1986.

Mars-Earth crossing would need 255 days; about halfway through, the spacecraft would begin deceleration. Earth-orbit capture would occur on 25 July 1987. A five-day inward spiral would place the fleet in 30,000-kilometer-high Earth parking orbit, where the electric thrusters would be turned off for the final time. A chemical-propulsion "commuter rocket" would then arrive to retrieve the Mars explorers and ferry them home to Earth. The Mars expedition ships would remain in distant Earth orbit as permanent monuments to the early days of space exploration.

The 1966 study was among the last to look in detail at nuclear-electric propulsion until the late 1980s. Just seven years earlier, Stuhlinger had concluded his 1959 nuclear-electric freighter paper by predicting that a nuclear-electric cargo ferry would serve a U.S. moon base "from 1965-70 on." When he retired from NASA in 1975, however, the U.S. had abandoned the moon and nuclear-electric propulsion was little closer to flight than it had been in 1959. The last survivor of the German rocketeers brought in 1945 to the United States, Stuhlinger died at age 94 in May 2008.


"Possibilities of Electrical Space Ship Propulsion," E. Stuhlinger, Bericht über den V Internationalen Astronautischen Kongreß, Frederich Hecht, editor, 1955, pp. 100-119; paper presented at the Fifth International Astronautical Congress in Innsbruck, Austria, 5-7 August 1954

"Lunar Ferry with Electric Propulsion System," Ernst Stuhlinger, First Symposium (International) on Rockets and Astronautics, Tokyo, 1959, Proceedings, M. Sanuki, editor, 1960, pp. 224-234

"Concept for a Manned Mars Expedition with Electrically Propelled Vehicles," Ernst Stuhlinger and Joseph C. King, Progress in Astronautics, Vol. 9, pp. 647-664, 1963; paper presented at the American Rocket Society Electric Propulsion Conference in Berkeley, California, 14-16 March 1962

"Study of a NERVA-Electric Manned Mars Vehicle," Ernst Stuhlinger, Joseph King, Russell Shelton, and Gordon Woodcock, A Volume of Technical Papers Presented at the AIAA/AAS Stepping Stones to Mars Meeting, pp. 288-301; paper presented in Baltimore, Maryland, 28-30 March 1966

"Ernst Stuhlinger: Rocket Scientist Crucial in Space Race, is Dead at 94," John Noble Wilford, New York Times, 28 May 2008 - http://www.nytimes.com/2008/05/28/us/28stuhlinger.html (accessed 18 December 2016)

More Information

The Challenge of the Planets, Part Two: High Energy

Gumdrops on Mars (1965)

The Last Days of the Nuclear Shuttle (1971)

17 December 2016

"A Vision of the Future": Military Uses of the Moon and Asteroids (1983)

Image credit: Department of Defense
On the evening of 23 March 1983, U.S. President Ronald Reagan addressed the people of the United States from the Oval Office. Citing aggressive moves on the part of the Soviet Union, he defended proposed increases in U.S. military spending and the introduction of new missiles and bombers. He then called for a revolution in U.S. strategic doctrine.

"Let me share with you a vision of the future," Reagan began. He then summed up his vision in a two-part question replete with the Cold War language of his Presidency: "What if free people could live secure in the knowledge that their security did not rest upon the threat of instant U.S. retaliation to deter a Soviet attack, that we could intercept and destroy strategic ballistic missiles before they reached our own soil or that of our allies?"

Reagan acknowledged that his vision represented "a formidable technical task, one that may not be accomplished before the end of this century." He then called on U.S. scientists – "those who gave us nuclear weapons" – to direct their talents "to the cause of Mankind and world peace, to give us the means of rendering these nuclear weapons impotent and obsolete."

President Ronald Reagan shares his missile-defense vision with the American people. The image on the easel is a declassified satellite view of Soviet MiG aircraft stationed in Cuba. Image credit: The Reagan Library
Thus was born the Strategic Defense Initiative (SDI), which is perhaps better known by its cinema-inspired nickname "Star Wars." This post is not meant to discuss the true origins, geopolitical ramifications, or technical feasibility of SDI. It will instead focus on one of the lesser-known aspects of SDI planning: the use of space resources.

The Reagan White House appointed James Fletcher, NASA Administrator from 1972 until 1977 under Presidents Nixon and Ford, to head up a panel to propose an SDI experimentation and development program. Fletcher tasked the California Space Institute (Calspace) at the University of California-San Diego (UCSD) with holding a workshop to consider whether exploiting the resources of the moon and asteroids might help to give substance to Reagan's vision. The Defense Applications of Near-Earth Resources Workshop took place in La Jolla, California, on 15-17 August 1983.

That Fletcher should have asked Calspace to assist with his SDI report is not too surprising. In February 1977, James Arnold, a UCSD chemistry professor, had spoken with NASA Administrator Fletcher about making the exploitation of near-Earth space resources a major new focus for NASA. He subsequently summed up his thoughts in a detailed two-page letter to Fletcher. Three years later, Arnold became the first director of Calspace, which had its origins in California Governor Jerry Brown's enthusiasm for technological development in his state.

Arnold's deputy in 1983-1984, young planetary scientist Stewart Nozette, organized the La Jolla workshop, which brought together 36 prominent scientists and engineers from aerospace companies, national laboratories, NASA centers, the Department of Defense, and defense think-tanks to weigh in on the potential use of moon and asteroid resources in SDI. Nozette also edited the workshop report, which Arnold submitted to Fletcher on 18 August 1983. A revised version of the workshop report was completed on 31 October 1983. This post is based upon the latter version.

In the cover letter to the La Jolla workshop report, Nozette described how, in the late 1970s, NASA, aerospace companies, and universities expended a great deal of time and effort on planning large structures - for example, Solar Power Satellites - which would be assembled in space. Some of these plans relied on space resources. Nozette explained that these studies, though conducted "in an unfocused and low priority vein," had laid the groundwork for SDI exploitation of moon and asteroid resources. The La Jolla workshop was, he added, the first to consider the defense implications of the 1970s concepts.

Lunar prospector: Apollo 16 astronaut Charles Duke collects geologic samples in the Descartes region of the Lunar Highlands in April 1972. The Lunar Roving Vehicle is just visible among rocks and boulders in the background. Image credit: NASA
At the time of the La Jolla workshop, relatively little was known of near-Earth space resources. Five Lunar Orbiter spacecraft had imaged much of the moon at modest resolution and selected areas of it – mostly corresponding to potential Apollo landing sites – at higher resolution. NASA had landed Apollo astronauts at six sites between 1969 and 1972 and scientists had analyzed many of the more than 2400 geologic samples they collected. In addition, Apollo astronauts had surveyed the moon from lunar orbit using remote sensors. These provided low-resolution data on the composition of perhaps 10% of the lunar surface.

Scientists had hypothesized since 1961 that permanently shadowed craters at the lunar poles might contain ice deposited by comet impacts. The lunar poles, far from the "Apollo Zone" – the near-equatorial region where orbital mechanics dictated the Apollo Lunar Modules could land – nevertheless remained unexplored.

In 1983, only 75 near-Earth asteroids (NEAs) had known orbital paths; the rate of discovery in the late 1970s/early 1980s suggested a population of sizable NEAs numbering many thousands, of which perhaps 20% would be readily accessible to prospecting spacecraft (these early gross estimates have been revised downward over the years). Meteorites collected on Earth were assumed (correctly) to have originated among the NEAs, but their relationship to specific asteroids remained unclear.

The La Jolla workshop report thus urged more resource exploration as an early step toward exploitation of near-Earth resources. An automated prospecting spacecraft that would pass over both lunar poles during each orbit - a Lunar Polar Orbiter (LPO) - topped the Workshop's list of "projects to be started immediately." The moon would revolve under such a spacecraft so that over the course of about two weeks it would present its entire surface to the LPO's instruments for scrutiny.

In addition, the La Jolla workshop report recommended that efforts to discover and perform initial analyses of NEAs using Earth-based telescopes should be stepped up dramatically. It noted that, in terms of NEAs accessible to spacecraft, "the most promising targets very likely have not, as yet, been detected." The workshop report then urged NASA to carry out a series of automated NEA rendezvous missions.

In 1983, NASA's piloted spaceflight focus was on working the bugs out of the Space Shuttle, which, despite a minimal flight record (the eighth Shuttle mission flew between the La Jolla workshop and completion of the Fletcher Report), already had an extensive manifest of planned missions. Many within the space community hoped that President Reagan would soon green-light a NASA Space Station that would be launched in pieces in the payload bays of Shuttle Orbiters and assembled in low-Earth orbit (LEO). They expected that auxiliary spacecraft, including piloted Orbital Transfer Vehicles (OTVs) for reaching beyond Shuttle/Station orbit, would be based permanently at the Station.

An Orbital Transfer Vehicle (left) with a disk-shaped reusable heat shield maneuvers in lunar orbit near a tank farm and a moon lander. This 1984 concept art by Pat Rawlings illustrates a lunar oxygen mining infrastructure: SDI-related facilities and vehicles in lunar orbit would no doubt have appeared very similar. Image credit: NASA
The La Jolla workshop participants saw in the OTVs the potential for carrying out piloted mining missions to the moon and NEAs. The key upgrade that would make such missions possible, the workshop report explained, was a reusable heat shield that would enable OTVs to use Earth's atmosphere to slow down and capture into LEO. The report also recommended a lunar base feasibility study and studies of lunar and NEA mining and raw materials processing techniques.

Participants in the La Jolla workshop proposed more than a dozen SDI applications for lunar and asteroid resources. What follows is a description of the top three applications in terms of the mass of lunar and asteroid materials required.

Much of the wide-ranging prospecting, mining, and processing the La Jolla workshop advocated would lead to in-space manufacture of spacecraft "armor" made of lunar aluminum, asteroid iron, and aluminum and iron alloys created by adding small amounts of metals launched from Earth. The workshop report noted that military space systems launched from Earth tended to be made as lightweight as possible to reduce launch costs; this made them fragile and thus vulnerable if attacked.

"On the other hand," the workshop report continued, "if a relatively inexpensive (500-1000 dollars per kilogram) supply of construction materials became available high above Earth, defensive systems would likely be designed very differently, with greater capabilities and greater survivability." Layered armor for an SDI missile-defense platform with a cross-sectional area of 20 square meters would have a mass of about 400 metric tons; 100 such platforms would thus require about 40,000 metric tons of armor.

Layered metal armor would blunt attacks by kinetic-energy weapons (that is, weapon systems that fired solid projectiles); for defense against particle beams or nuclear explosions, however, radiation shielding would be needed. The La Jolla workshop proposed using water from asteroids or (if any existed) from the lunar poles as neutron shielding for vulnerable electronic systems. Water would, of course, also have life support uses, and could be split into liquid oxygen and liquid hydrogen chemical rocket propellants.

After armor, the most important application of space resources in terms of mass was what the La Jolla workshop report dubbed "stabilizing inertia.” An enemy attack might cause a missile-defense platform to spin out of control even if its armor shielded it from damage. Mounting the platform on a chunk of raw asteroid would greatly increase its mass, making it much harder to shove around.

Third after armor and stabilizing inertia were heat sinks. The La Jolla workshop anticipated that missile-defense systems - for example, missile-destroying lasers powered by exploding nuclear bombs - would generate a great deal of waste heat very rapidly. Without places for the heat to go, they could easily destroy themselves. A heat sink might take the form of a large tank of water or large block of metal.

The Fletcher Panel submitted its hefty seven-volume final report to the Reagan White House on 4 November 1983. More than three decades later, most of the Fletcher Report remains classified, so the degree to which the La Jolla workshop influenced its findings is unclear.

Fifteen years into the 21st century, SDI has yet to match Reagan's vision, in no small part part because the Soviet Union - which Reagan had dubbed "the evil empire" - collapsed in 1991. Instead of leading to a shield against massive Soviet nuclear attack, SDI became the most important space technology development program since Apollo. Neither the ongoing Discovery Program of cheap, relatively frequent automated lunar and planetary missions nor the low-cost automated Mars missions of the 1996-2008 period would have been possible without the technology infusion from SDI.

Image credit: NASA/USGS
The pioneer for these missions was Clementine, a joint project of the SDI Organization (later renamed the Ballistic Missile Defense Organization - BMDO), the U.S. Air Force, Lawrence Livermore National Laboratory, the Naval Research Laboratory, and NASA. Stewart Nozette led the Clementine mission. The octagonal 227-kilogram Clementine spacecraft, intended mainly as a BMDO technology demonstrator, lifted off atop a repurposed Titan II missile from Vandenberg Air Force Base on 25 January 1994.

The Clementine spacecraft entered lunar polar orbit on 19 February 1994, where it carried out the first U.S. lunar exploration mission since Apollo 17 in December 1972. It surveyed almost the entire lunar surface for two months. In collaboration with Deep Space Network antennas on Earth, it prospected for ice in the permanently shadowed lunar polar craters. Clementine researchers interpreted data they collected as evidence of large deposits of water ice. This interpretation was questioned almost as soon as it was announced at a Department of Defense press conference on 4 December 1996. Subsequent lunar spacecraft (Lunar Prospector, Chandrayaan-1, LCROSS, and the currently operational Lunar Reconnaissance Orbiter) have, however, confirmed the existence of hundreds of millions of tons of water ice at the lunar poles.

Permanently shadowed areas at the moon's south pole stand out as a cluster of dark gray voids at the center of this Clementine image mosaic. Image credit: NASA/USGS
On 5 May 1994, Clementine departed lunar orbit bound for the near-Earth asteroid 1620 Geographos. Geographos, discovered in 1951, is an S-type asteroid, meaning that it is composed mainly of nickel-iron. Radar images of Geographos show it to be extremely elongated (5.1 kilometers long, 1.8 kilometers wide) with pointed ends.

Unfortunately, just two days into its four-month journey, the spacecraft suffered a computer malfunction that caused it to expend all of its attitude-control propellant. The flyby, incidentally, had been the mission's primary goal when spacecraft and mission design began in March 1992; Clementine had been named in reference to the song "Oh, My Darling Clementine" because it would be "lost and gone forever" after it flew past Geographos. The lunar phase of the Clementine mission was added later.

A Clementine 2 asteroid-flyby spacecraft was proposed and studied, but did not receive development funding. Clementine 2 would have flown past near-Earth asteroids 433 Eros and 4179 Toutatis. During the flybys, it would have released impactors, the design of which would have been based on proposed missile interceptors. Instruments on board Clementine 2 based on missile-detection sensors would have recorded the impacts to enable scientists to determine asteroid surface properties. Work on Clementine 2 ceased in 1997.

The fate of Stewart Nozette forms a strange denouement to this story. He was widely celebrated for his work on Clementine: among other awards, he received the NASA Exceptional Achievement Medal. He went on to play roles in the Lunar Reconnaissance Orbiter and Chandrayaan-1 missions. In 2006, 49-year-old Nozette left government service to head up the not-for-profit Alliance for Competitive Technology, which received NASA funding.

Nozette, who had "top secret" security clearance from 1989 to 2006, soon came under Justice Department scrutiny for misappropriation of NASA funds and tax evasion; he was then charged with espionage after attempting to sell classified information to an FBI agent posing as an Israeli spy. In 2011, he was sentenced to 13 years in Federal prison.


"Ex-White House Scientist Pleads Guilty in Spy Case Tied to Israel," S. Shane, The New York Times, 8 September 2011, p. A22

"The Clementine Satellite," Energy & Technology Review, Lawrence Livermore National Laboratory, June 1994

"Reagan is Urged to Increase Research on Exotic Defenses Against Missiles," C. Mohr, The New York Times, 5 November 1983, p. A32

Defense Applications of Near-Earth Resources, Workshop Held at the University of California, San Diego, Hosted by the California Space Institute, 15-17 August 1983, S. Nozette, editor/workshop organizer, 31 October 1983

Address to the Nation on Defense and National Security, President Ronald Reagan, 23 March 1983

More Information

Earth-Approaching Asteroids as Targets for Exploration (1978)

An Apollo Landing Near the Great Ray Crater Tycho (1968)

Starfish and Apollo (1962)