NASA Johnson Space Center's Shuttle II (1988)

Image credit: NASA.

Although the fact is mostly forgotten today, NASA launched plans to augment or replace the Space Shuttle even before the first Shuttle reached orbit on 12 April 1981. Much — though by no means all — of this planning occurred as part of joint Department of Energy/NASA Solar Power Satellite studies.

In 1985, U.S. President Ronald Reagan signed a directive ordering the U.S. civilian space agency to develop a Space Shuttle successor. Notably, this occurred before the 28 January 1986 Challenger accident laid bare the Shuttle system's many frailties.

One proposed Shuttle successor was called Shuttle II. Most Shuttle II design work took place at NASA Langley Research Center (LaRC) in Hampton, Virginia. Shuttle II first achieved prominence in 1986 in the high-level National Commission On Space report Pioneering the Space Frontier.

LaRC's Shuttle II design evolved — for a time it was to have been a single-stage-to-orbit vehicle. The favored design included a winged manned Orbiter and a winged unmanned Booster, both of which would take off vertically and land horizontally on runways. Both the Booster and the Orbiter would be entirely reusable. LaRC's Shuttle II Orbiter fuselage was meant to be crammed full of propellant tanks, so would tote cargo in a sizable hump on its back.

NASA Langley Research Center's dumpy Shuttle II, 1987. Image credit: NASA.

Shuttle II was intended mainly as a crew transport complementing a "mixed fleet" of launchers that would have included unmanned heavy-lift rockets capable of placing from 50 to 100 tons into space. LaRC envisioned that its Shuttle II would transport a small amount of cargo — perhaps 10 tons — and up to 25 astronauts, of whom only three would be considered Shuttle II crew members. The remainder would be passengers bound for a large advanced Space Station or a Transportation Node station. There they would board Moon or Mars spacecraft.

Although a good case can be made for calling LaRC's Shuttle II the Shuttle II, it was in fact not the only proposed Shuttle II design. The Advanced Programs Office at NASA Johnson Space Center (JSC) in Houston, Texas, put forward the sleek Shuttle II design depicted in the last seven images of this post. They portray JSC's Shuttle II as it would appear over the course of a typical mission.

The LaRC design was favored by NASA Headquarters and is relatively well documented. Neither can be said for JSC's design.

In flight: the Evolved Shuttle climbs toward space, probably sometime in the 1990s. Image credit: Eagle Engineering/NASA.

Model of proposed Evolved Shuttle showing major components. Image credit: NASA.

Engineers in Houston envisioned that their Shuttle II might develop from an Evolved Space Shuttle. In the Evolved Shuttle, Liquid Replacement Boosters stood in for the Shuttle's twin Solid Rocket Boosters. The Evolved Shuttle would retain the Shuttle's expendable External Tank and, with minor modifications, the Shuttle Orbiter's Space Shuttle Main Engines (SSMEs). Like the Space Shuttle, the Evolved Shuttle stack would ride to its Launch Complex 39 pad atop a creeping crawler-transporter with its nose aimed at the sky.

Winglets on the tips of the Evolved Shuttle's modified delta wings would replace the Shuttle's single vertical tail fin. Redesigned Orbital Maneuvering System (OMS) engines based on the venerable RL-10 engine would draw liquid hydrogen/liquid oxygen propellants from insulated tanks built into the Evolved Shuttle Orbiter wings.

The most dramatic changes would, however, be reserved for the Evolved Shuttle crew compartment. JSC engineers designed it so that it could separate from the Evolved Shuttle in the event of catastrophic failure and operate as an independent spacecraft. Canard winglets meant to improve the Evolved Shuttle's aerodynamic characteristics would separate with the crew compartment and become its wings.

JSC gave no timeline for the evolution of Shuttle to Evolved Shuttle. If, however, JSC's Shuttle II was to become operational in the same timeframe as LaRC's Shuttle II (the early 21st century), then one may assume that the Evolved Shuttle would have made its debut in the 1990s.

Shuttle II ready for a tow to its launch pad. A round panel covering an extendable docking adapter is visible just above the American flag on the fuselage. Image credit: NASA.

The JSC Shuttle II was meant to be towed horizontally on its tricycle landing gear from a hangar to its launch pad just four hours before planned launch. Unlike the Space Shuttle and Evolved Shuttle, JSC's Shuttle II would have no need of the Vehicle Assembly Building, the massive cuboid structure built at Kennedy Space Center in the 1960s for the assembly of Apollo Saturn V heavy-lift rockets.

Nor would it use the twin Launch Complex 39 pads, which were built in the 1960s to launch Saturn V rockets and rebuilt in the 1970s to launch the Space Shuttle. Shuttle II would instead lift off from a new-design pad, and Complex 39 would be given over once again to heavy-lift rocket launches. In fact, the JSC Shuttle II would make a complete break from the massive-scale Apollo-era infrastructure upon which the Space Shuttle relied.

JSC's Shuttle II in launch configuration. The round panel covering the extendible docking adapter is again visible; it leads to a crew access tunnel that runs the length of the spacecraft. Image credit: NASA.

At the launch pad, crew and passengers would board JSC's Shuttle II, then it would be tipped up to point its nose at the sky. Its landing gear doors would be closed, then its ground crew — small compared with the army of personnel that serviced the Space Shuttle — would load it with three kinds of propellants: liquid hydrogen fuel, liquid hydrocarbon (kerosene or propane) fuel, and liquid oxygen oxidizer.

For safety, most of the volatile fuels would be pumped into Shuttle II's four expendable over-wing tanks, while an integral, reusable tank within the spacecraft would carry most of the dense liquid oxygen. Fully loaded with propellants and payload, Shuttle II would weigh about 550 tons, or a little more than a quarter of the Shuttle's weight at SSME ignition.

JSC designers hoped to minimize Shuttle II weight in part by building it from advanced materials. The Space Shuttle Orbiter, with an empty mass of about 85 tons, had a more-or-less conventional load-bearing aluminum-titanium airframe clad in aluminum and lightweight thermal-protection materials. These included thousands of uniquely shaped ceramic tiles and Reinforced Carbon-Carbon (RCC) wing leading edges. Shuttle II, with an empty mass of 50 to 75 tons, would also rely on RCC, "but in larger, load-bearing, monolithic panels." The over-wing tanks would be made from lightweight welded aluminum-lithium alloy.

At launch, Shuttle II's single Space Transportation Main Engine (STME) and twin Space Transportation Boost Engines (STBEs) would ignite simultaneously. The former, designed to burn liquid hydrogen and liquid oxygen, was envisioned as a second-generation SSME. The latter, located between the STME and the Shuttle II body flap, would burn hydrocarbon fuel and liquid oxygen and employ liquid hydrogen as engine coolant. The STME and STBEs would together generate about 30% more thrust than the Space Shuttle's three SSMEs — between 1.3 and 1.6 million pounds.

Climb to orbit: JSC's Shuttle II following detachment of its outboard tanks and its twin STBEs. Image credit: NASA.

When it reached a velocity of between two and three kilometers per second, JSC's Shuttle II would shed its depleted outboard over-wing tanks and the STBEs. Dropping the STBEs would improve Shuttle II's flight performance by shifting its center of gravity forward. The tanks would break up and fall into the sea, but NASA would recover the twin engines for reuse. JSC engineers envisioned that they would descend in reentry shells, deploy maneuvering parachutes, and land in arresting nets aboard recovery ships.

The STME, meanwhile, would extend its telescoping exhaust nozzle to its full length and diameter to improve its performance in vacuum. Following separation of the outboard tanks and STBEs, the spacecraft would burn only liquid hydrogen/liquid oxygen propellants.

Immediately following STME cutoff, the engine's nozzle would retract and the inboard over-wing tanks would be cast off. Upon reaching apogee (the highest point in its orbit about the Earth), Shuttle II's twin OMS engines would ignite to raise its perigee (the lowest point in its orbit) out of the atmosphere. This would place it into a circular "Space Station rendezvous orbit" 485 kilometers high and inclined 28.5° relative to Earth's equator. The inboard tanks, meanwhile, would intersect Earth's atmosphere as they reached perigee and be destroyed.

The Shuttle II OMS would comprise a pair of new-design Advanced Space Engines or RL-10-derived engines. RL-10 had the advantage of a long flight history; derivatives of that engine have propelled upper stages and spacecraft since the 1960s. Liquid hydrogen and liquid oxygen for Shuttle II's OMS and the Reaction Control System (RCS) thrusters would be stored in double-walled, heavily insulated tanks in its tail section. Some propellants from the tail section would be combined in next-generation fuel cells to generate electricity and water for the spacecraft.

A crew access tunnel would run aft from the forward crew compartment for most of the length of the fuselage. Midway along the tunnel, on its left side, Shuttle II's docking adapter for linking up with the Space Station would be stowed behind a streamlined panel. The round panel is visible near the American flag in images that display the left side of the Shuttle II model. Prior to rendezvous with the Space Station, the panel would hinge out of the way, then the crew would extend the cylindrical docking adapter.

The image above shows Shuttle II in its orbital configuration with inboard tanks in place; this is apparently a photographer's error, since image captions make plain that the inboard tanks would separate immediately after STME cutoff, before the crew opened the payload bay. Image credit: NASA.

JSC engineers chose a novel method for exposing Shuttle II payloads to space: the crew would disable the OMS engines, vent and disconnect hoses that had linked the over-wing tanks to the STME, disengage locks, and hinge the tail section downward using electric motors. RCS thrusters in the tail would continue to operate; to minimize flexible wiring links between the main fuselage and the tail section, engineers proposed that the astronauts control the RCS thrusters via a short-range radio link.

Hinging the tail section down would expose a large round window and the open aft end of the 15-foot-wide-by-30-foot-long cylindrical payload bay. Astronauts at an aft workstation would look out through the window as they extended the cradle bearing their mission's payload. The photo captions do not name specific Shuttle II payloads, but it is logical to assume that these would include experiment packages for mounting on the Space Station and reusable Station logistics modules packed full of supplies and equipment. The payload bay would include an airlock for spacewalks and a pair of robot arms.

Unlike the Space Shuttle and Evolved Shuttle payload bays, the Shuttle II bay would normally not include radiators for dissipating heat generated by onboard equipment and astronaut exertions. Instead, Shuttle II's radiators would be built into the top surface of its wings. Supplemental radiators would be mounted on the payload cradle before flight only if "special purpose, high heat load conditions" were expected.

Before return to Earth, the astronauts would retract the payload cradle, then hinge shut the tail section. Shuttle II would include triple-redundant electric motors and a mechanical backup system for closing the payload bay "to assure that the vehicle configuration for entry [would] not have paths for hot plasma to enter the vehicle interior." During the first few Shuttle II flights, an astronaut would exit through the docking adapter and clamber over the fuselage to inspect the hinge area and seam between the tail section and the rest of the spacecraft. He or she might carry a repair kit "to fill any voids."

Reentry would occur as in the Space Shuttle Program; that is, Shuttle II would turn so that its aft end pointed in its direction of flight, then its OMS engines would ignite to reduce its orbital velocity. The spacecraft would then flip to point its nose forward as it fell toward the atmosphere. Following reentry, Shuttle II would glide to a runway landing.

JSC's Shuttle II in landing configuration. Image credit: NASA.

Unlike the Space Shuttle, which even after the Challenger accident included few realistic options for crew escape in the event of catastrophic failure, Shuttle II could in theory protect its crew through all phases of its mission. Like the Evolved Shuttle, Shuttle II would include a separable crew compartment; after separation, Shuttle II's canard fins — proportionately larger than those of the Evolved Shuttle — would become the crew compartment's wings.

The crew compartment aft end would include launch escape/deorbit rocket engines, a crew hatch, and a deployable aerodynamic flap. Following separation in orbit, the crew compartment could support 11 astronauts for up to 24 hours. This endurance was meant to ensure that Earth's rotation could bring into range a suitable landing site on U.S. soil. The crew compartment would touch down and slide to a halt on extendable skids.

Crew cabin separation on the launch pad or during ascent. Image credit: NASA.

Crew cabin separation in orbit or during reentry. Image credit: NASA.

JSC engineers acknowledged that wind-tunnel testing might show that the Shuttle II crew compartment shape was not flight-worthy in all abort situations. They proposed that inflatable or extendable structures "be employed to obtain an acceptable configuration for hypersonic, supersonic, and subsonic controlled flight."

They also proposed that the Shuttle II crew compartment become the Space Station's Crew Emergency Rescue Vehicle (CERV). The CERV was conceived as a "lifeboat" for use if the Space Station had to be evacuated rapidly, if a crew member became seriously ill or injured and needed hospital treatment on Earth, or if Shuttle II became grounded due to malfunction or accident and could not retrieve a Space Station crew.

The JSC engineers noted that the Shuttle II crew compartment/CERV, like Shuttle II itself, would subject its occupants to no more than three gravities of acceleration or deceleration. This would help to ensure that, during return to Earth, it would not inflict additional harm on a sick or injured Space Station crewmember.

NASA continued to attempt to develop a Shuttle successor — a winged spacecraft that would enable it to apply the lessons learned from the Shuttle Program. Some proposed complex new vehicles employing scramjets; others, vehicles smaller and less capable than the Shuttle tailored mainly for Space Station crew rotation and crew escape. Unfortunately, the space agency's budget was not expanded to permit simultaneous ongoing Shuttle operations, Space Station development and assembly, and development of a Shuttle successor.

By the mid-1990s, many in the Shuttle Program had changed their tactics; they declared that the Shuttle should continue to fly at least until 2010. In 2001, Boeing proposed that the Shuttle should fly until 2030.

The 2003 Columbia accident ended such plans. When the Shuttle was retired in 2011, a new NASA Shuttle design was as far away as it had been during Shuttle II planning in the late 1980s.

Sources

Caption Sheet, NASA Photo S88 29029, Shuttle II Candidate Configuration, 1988.

Caption Sheet, NASA Photo S88 29035, Shuttle II Launch Configuration, 1988.

Caption Sheet, NASA Photo S88 29032, Shuttle II Post-Boost Flight Configuration, 1988.

Caption Sheet, NASA Photo S88 29028, Shuttle II Orbital Flight Configuration, 1988.

Caption Sheet, NASA Photo S88 29026, Shuttle II Entry and Landing Configuration, 1988.

Caption Sheet, NASA Photo S88 29024, Shuttle II Pad Abort Crew Escape, 1988.

Caption Sheet, NASA Photo S88 29030, Shuttle II Crew Escape System, 1988.

Caption Sheet, NASA Photo S89 34837, Evolved Shuttle, 1989.

"Shuttle II Progress Report," T. Talay, NASA Langley Research Center; paper presented at the 24th Space Congress, 21-24 April 1987, Cocoa Beach, Florida.

Pioneering the Space Frontier: the Report of the National Commission on Space, Bantam Books, 1986.

"At 15, A Safer, Cheaper Shuttle," J. Asker, Aviation Week & Space Technology, 8 April 1996, pp. 48-51.

"Boeing upgrade would keep Space Shuttle flying to 2030," G. Warwick, Flight International, 8-14 May 2001, p. 37.

More Information

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

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

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

As Gemini Was to an Apollo Lunar Landing by 1970, So Apollo Would Be to a Permanent Lunar Base in 1980 (1968)

Cutaway of the Apollo Lunar Module (LM) showing its Ascent Stage (top) and Descent Stage (bottom). A total of six descent stages were left on the lunar surface at six separate sites between July 1969 and December 1972. Image credit: NASA.

When we look back at the Apollo Program, those of us who think of any part of it beyond Neil Armstrong's historic first footfall recall a series of increasingly ambitious missions to a variety of landing sites. Apollo 12's 19 November 1969 landing on the Ocean of Storms, close by the derelict Surveyor III lander, demonstrated the pinpoint landing capability that would enable detailed pre-mission geologic traverse planning for subsequent flights. Apollo 13 (11-17 April 1970) failed to land, but Apollo 14 (31 January-9 February 1971) safely set down at Apollo 13's intended landing site on the geologically significant Fra Mauro Formation.

NASA then ramped up Apollo exploration by stretching lunar surface stay time to three days, upgrading the Apollo lunar suits to permit moonwalks of about seven hours, and providing the astronauts with a Boeing-built lunar "jeep" — the Lunar Roving Vehicle (LRV) — to extend their exploration range. Apollo 15 (26 July-7 August 1971) exploited these new capabilities to survey Hadley-Apennine, a complex site between mountains and a winding rille (canyon). Apollo 16 (16-27 April 1972) was the only mission to land in the heavily-cratered lunar highlands. Apollo 17 (7-19 December 1972) concluded the Apollo Program with a visit to Taurus-Littrow, where Harrison Schmitt, the only professional geologist to explore the Moon, found tiny orange glass beads — remnants of ancient volcanic fire fountains — with his feet.

The Apollo 11 landing site imaged in 2011 by the Lunar Reconnaissance Orbiter (LRO) spacecraft. Clearly visible are dark astronaut trackways and the light-colored area disturbed by the LM Eagle's Descent Stage and Ascent Stage engines. LRRR = Lunar Ranging Retro-Reflector; PSEP = Passive Seismic Experiment Package. Image credit: NASA.

Not widely known is that in 1968, as it prepared its first piloted Apollo flight — Apollo 7, which flew in September 1968 — and its Fiscal Year (FY) 1970 submission to the Bureau of the Budget, NASA briefly considered an alternate approach to Apollo. Had it been pursued, it might have laid the technological foundation for a permanent lunar base in 1980. After perhaps three Apollo exploration missions to different landing sites, NASA would have dispatched a series of Apollo missions to a single site.

In addition to intensively exploring the selected site, the astronauts would have performed engineering and life sciences experiments, assessed the lunar environment for radio and optical astronomy, and experimented with resource exploitation. The single site revisit missions would have played the role for a permanent lunar base that Project Gemini played for Apollo; that is, it would have enabled NASA to acquire operational skills needed for its next step forward in space.

LRO image of the Apollo 12 site in Oceanus Procellarum. Astronauts Charles Conrad and Alan Bean succeeded in landing the LM Intrepid about 100 meters from the derelict Surveyor 3 robotic soft-lander, proving the pinpoint landing capability necessary for planning geologic traverses. This capability would also have been required if the Single Site missions had been carried out; as many as four LMs or LM derivatives would have needed to land within walking distance of each other. Image credit: NASA.

The single site revisit concept — sometimes called the "lunar station" concept — got its start some time before 30 April 1968, when the NASA-appointed Lunar Exploration Working Group (LEWG) presented it to the Apollo Planning Steering Group. The exact date is not known. Lee Scherer, director of the Apollo Lunar Exploration Office at NASA Headquarters, asked mission planner Rodney Johnson on 7 May to chair a 10-man Single Site Working Sub-Group of the LEWG. He directed Johnson to present a progress report at the LEWG meeting scheduled for the third week of May. The Sub-Group held a two-day meeting on 12-13 May and presented results of its brief study at the 22 May LEWG meeting. It issued a revised final report on 4 June 1968.

The Sub-Group's efforts were probably intended to replace lunar missions originally planned for the Apollo Applications Program (AAP), which had begun officially in August 1965. AAP aimed to put Saturn rockets and Apollo spacecraft developed to achieve President John F. Kennedy's goal of a man on the Moon by 1970 to new uses that would be beneficial to people on Earth.

As originally conceived, AAP would have included both Earth-orbital and advanced lunar missions. Congress had not seen fit to fully fund AAP, so by the time the Single Site Working Sub-Group began its work, AAP lunar missions had been largely abandoned. In fact, AAP had increasingly come to be seen as the lead-in to the new NASA goal of a permanent Earth-orbital space station by 1980.

The Sub-Group's report began by declaring that a 12-man "International Lunar Scientific Observatory" in 1980 could become the new "Major Agency Goal" for NASA following Apollo. The single site revisit missions, it continued, would pave the way to the new lunar goal by demonstrating the value of a permanent base on the Moon. The Sub-Group then examined four options for carrying out its single site revisit program, which it labeled 0, A, B, and C. All would employ spacecraft and standard Saturn V launch vehicles the space agency had already ordered for Apollo.

The first of the four options, Option 0, would employ the basic Apollo Lunar Module (LM), which could support two men on the Moon for 24 hours and deliver 300 pounds of cargo to the lunar surface. Three Option 0 missions would visit the single site, where their crews would perform a total of six moonwalks on foot and minimal exploration and technology experimentation. The Sub-Group rejected this option out of hand because it would provide NASA with insufficient experience ahead of the 1980 lunar base.

The Apollo 14 landing site near Cone Crater, a natural drill hole in the Fra Mauro Formation, as imaged by LRO. The small arrows point to the faintly visible trackways astronauts Alan Shepard and Edgar Mitchell left during their moonwalks. ALSEP = Apollo Lunar Science Experiment Package. Image credit: NASA.

Option A, which the Sub-Group called the "bare minimum" single site revisit option, would use an Extended Lunar Module (ELM) with a lunar surface stay time of three days and a 450-pound cargo capacity. In their report, the Sub-Group referred to this uprated version of the Apollo LM as ELM-A. Three Option A crews would land at the single site over 18 months, amassing a total of nine days of surface stay-time and carrying out a total of up to 18 moonwalks.

The first Option A mission, scheduled for the fourth quarter of 1971, would see two astronauts conduct from four to six moonwalks and up to four traverses using a rocket-propelled Lunar Flying Unit (LFU) fueled using residual propellants in the ELM-A Descent Stage. In addition to exploring the single site's geology, the astronauts would set up a "technology package" to assess the lunar "optical environment" for astronomy. They would also deploy exposure samples to test the effects of the lunar environment on materials and coatings that might be used to build the 1980 Moon base. When they left the single site in the ELM-A Ascent Stage to rejoin their lone comrade on board the orbiting Apollo Command and Service Module (CSM), they would leave behind for the next crew tools, the LFU, the exposure samples, and the optical environment package.

The second Option A mission would take place in the second quarter of 1972. The astronauts would carry out six moonwalks and, after servicing the LFU, up to four flying traverses. The LFU would amount to a exposure experiment; it would need to work reliably after being parked at the single site for six months (that is, through six lunar day-night cycles). The astronauts would also set up an "advanced" Apollo Lunar Scientific Experiment Package (ALSEP) and a technology package to assess the lunar environment's suitability for radio astronomy. Between moonwalks, they would perform unspecified biology experiments in the ELM-A cabin. Finally, they would retrieve for return to Earth some of the exposure samples left behind by the first Option A crew.

The third and final Option A mission would reach the single site in the fourth quarter of 1972, six months after the second. Its crew would perform six moonwalks, fly the LFU three or four times on geologic traverses, and observe the Sun using a small telescope they would bring with them to the site. They would also retrieve for return to Earth the remaining exposure samples left behind by the first Option A crew. If necessary, they would service the advanced ALSEP instruments deployed by the second Option A crew.

LRO image of the Apollo 15 landing site at Hadley-Apennine. Black arrows point to tracks left by the Lunar Roving Vehicle (LRV), the "lunar jeep" David Scott and James Irwin used to explore the complex geology within a few kilometers of their base of operations, the LM Falcon. Image credit: NASA.

The Single Site Working Sub-Group called its Option B "a substantial improvement" over Option A. The ELM, designated ELM-B, would be uprated to permit a lunar surface stay of up to six days with 450 pounds of cargo or three days with 750 pounds of cargo. Upgrades would include solar cells for recharging the ELM's batteries, a radiator to replace the water-evaporation system used for cooling basic LM and ELM-A avionics, and breathing oxygen stored as dense supercooled liquid instead of as gas. ELM upgrades and new scientific equipment development would require time; for this reason, the first Option B mission would not leave Earth until the second quarter of 1972.

Option B mission 1 would last six days, during which time its crew would carry out from six to 10 moonwalks and up to four LFU geologic traverses. In addition to twin LFUs, the ELM-B would deliver an advanced ALSEP, geology tools, unspecified "biological colonies," and environment and technology exposure samples. As with the Option A missions, lunar environment experiments would focus on optics and radio.

Option B mission 2 would land in the fourth quarter of 1972 for a three-day stay. Its crew would perform six moonwalks and up to four LFU traverses. The three-day stay time would mean that the ELM-B could carry 750 pounds of cargo; this would include a solar telescope, plant and animal packages, and bioscience supplies. The crew would also examine the exposure samples left by the first Option B crew and service any equipment at the site that needed it.

The third Option B mission would land in the second quarter of 1973 and last for either three or six days depending on the results obtained during missions 1 and 2. Its crew would perform from six to 10 moonwalks and three or four LFU traverses. In addition to technology and astronomy experiments, the astronauts would retrieve and prepare technology and biology packages and exposure samples for return to Earth.

The Apollo 16 landing site at Descartes imaged by LRO. Trackways left by astronauts John Young and Charles Duke stand out plainly in the light-colored area disturbed by the LM Orion's descent and ascent engines. The "geophone line" is a part of the Active Seismic Experiment; similar experiments, which recorded seismic waves generated by explosive charges, were deployed during Apollo 14 and Apollo 17. Image credit: NASA.

The Single Site Working Sub-Group called Option C its "most productive option," in part because its hardware could form the "nucleus" of the proposed 1980 lunar base. It would, however, require a large new funding commitment in Fiscal Year 1970. A "one-of-a-kind spacecraft," the automated Lunar Payload Module (LPM), would account for much of the extra cost. The Sub-Group expected that the LPM, which would land a whopping 7000 pounds of cargo on the Moon, would take the form of an LM Descent Stage with no Ascent Stage. Systems needed for descent that normally would be installed in the LM Ascent Stage would be relocated to the Descent Stage.

A 2000-pound cylindrical shelter capable of supporting two men on the lunar surface for from 12 to 14 days would constitute the heaviest LPM cargo item. In addition, the LPM would carry a pair of LFUs, tanks of LFU propellants, a "dual-mode" Lunar Roving Vehicle (LRV) capable of being driven by either astronauts on the Moon or flight controllers on Earth, a solar furnace for technology and lunar resource exploitation experiments, a 12-inch reflecting telescope, laboratory equipment, bioscience packages, lunar environment exposure sample packages, and an advanced ALSEP.

Though the Single Site Working Sub-Group called their automated LM an LPM, in fact it closely resembled an LM derivative Grumman, the LM prime contractor, called an LM Truck. Grumman proposed two LM Truck types — one would carry only cargo atop a Descent Stage, while the other would carry cargo and a cylindrical shelter. Grumman's version of the LPM would include an LM Ascent Stage to house the astronauts on the lunar surface, not a cylindrical shelter. Despite this, I will in this post continue to refer to the Sub-Group's LM derivative for Option C as an LPM.

The first of four Option C missions would see a piloted CSM deliver the LPM to lunar orbit at the beginning of 1973. The Single Site Working Sub-Group wrote that, in general, little CSM orbital science would occur in the single site revisit program. This was because much CSM orbital science was meant to support selection of multiple Apollo landing sites, which the single site revisit missions would make unnecessary. The LPM-delivery CSM would, however, remain in lunar orbit for some unspecified period after the LPM undocked. During that time, its crew would turn a suite of remote sensors toward the lunar surface and deploy a science subsatellite.

Option C mission 2, launched just one month after the LPM delivery mission, would employ a modified ELM designed to remain "quiescent" on the lunar surface while its crew lived in the LPM shelter. Grumman called the quiescent ELM the LM Taxi. Because most of its systems would be made dormant after landing, it would need fewer expendables than an ELM-B, permitting it to carry up to 750 pounds of cargo despite its 12-to-14-day lunar surface stay time. Cargo would include an LFU for transporting the two-man crew to and from the LPM in the event that navigational error caused them to land beyond walking distance.

The Option C mission 2 crew would perform many tests and experiments over the course of from 12 to 20 moonwalks, up to 14 LFU flights, and up to eight LRV traverses during their 12 to 14 days on the Moon. Basically, they would accomplish all of the tasks planned for the three Option B missions and more; they would, for example, not only collect rock samples for return to Earth, they would also analyze them in the manner astronauts would at the 1980 Moon base. Before returning to the quiescent ELM and blasting off in the Ascent Stage to rejoin the CSM Pilot in lunar orbit, they would reconfigure the LRV for remote-controlled operation and turn it loose under guidance from controllers on Earth to travel tens or hundreds of miles across the lunar surface in a loop that would end back at the single site.

Option C mission 3, in the third quarter of 1973, would see an ELM-B land near the LPM with 750 pounds of cargo. The astronauts, who would live in the ELM-B would conduct from six to 10 moonwalks, four LFU flights, and up to four LRV traverses. In their most notable experiment, they would attempt to extract water from lunar dust and rocks using the solar furnace; if successful, this could lead to production of life support consumables and rocket propellants on the Moon, slashing the cost of lunar base resupply. Before they left the Moon, they would reconfigure the dual-mode LRV for remote-control operation.

Option C mission 4, a near-carbon copy of mission 3, would land in the first quarter of 1974. The crew would complete any ongoing experiments at the LPM, observe the Sun, and retrieve biological colonies and exposure samples. They would also dispatch the dual-mode LRV on its longest remote-controlled traverse yet; because it would not again be driven by astronauts, it would not need to return to the LPM site and thus might wander for hundreds of miles across the lunar surface under the direction of controllers on Earth.

LRO image of the Apollo 17 landing site at Taurus-Littrow. Side-by-side tracks left by LRV-3 — parked at right — stand out against the light-colored area disturbed by the LM Challenger's Descent Stage and Ascent Stage engines. Eugene Cernan and Harrison Schmitt spent three days at the site. Image credit: NASA.

The Single Site Working Sub-Group provided "rough" estimates of Option A, B, and C costs. Option A would add $725 million to the Apollo Program’s projected cost; Option B, $745 million; and Option C, $1.090 billion.

The Sub-Group then summed up "Major Conclusions" of its brief study. Only a few are noted here. The Sub-Group confided that the single site revisit missions could be portrayed as a part of the Apollo Program, not as a costly new program, thus avoiding possible political roadblocks. It also claimed that the single site revisit program would be "strongly identifiable with the public interest," though it did not specify how. Finally, the Sub-Group explained that the program would meaningfully exploit uniquely human capabilities: these included on-the-spot judgement; skilled observation (for example, rapid recognition of significant geological relations); and complex tool-using skills.

The ascent engine on the Apollo 16 LM Orion ignites, blasting pieces of reflective insulating foil in all directions. This image is a frame from video captured by the steerable TV camera on Apollo 16's parked LRV and transmitted to Earth by the LRV's high-gain antenna. Image credit: NASA.

Shortly after liftoff: the Descent Stage of the Apollo 17 LM Challenger abandoned in the Taurus-Littrow valley. Image credit: NASA.

The 10 members of the Sub-Group ended their report by raising issues which they felt would need further examination. They explored the matter, for example, of whether astronauts should work at the single site during lunar day and night or instead continue the Apollo policy of operating on the Moon only by day.

They also contemplated where NASA might establish its 1980 Moon base; the only specific sites they mentioned, however, were the two lunar poles. This was in keeping with the main body of their report, which provided no candidate sites for the single site revisit program. Finally, they sought guidance as to how they should proceed if the single site revisit option received no funding in NASA's FY 1970 budget.

Some small movement toward including the single site revisit concept in the FY 1970 NASA budget took place; however, most work on the concept ended with the Sub-Group's 4 June 1968 revised report to the LEWG. In retrospect, it seems likely that the concept would have split the lunar science community between those eager for data from as many landing sites as possible as soon as possible and those prepared to wait (perhaps in vain) for enhanced exploration capabilities available after the 1980 lunar base was established. In any case, it appears unlikely that an Apollo planning option that laid the groundwork for a long-term lunar presence could have gained much traction in Washington in 1968; by the time the Single Site Working Sub-Group began its deliberations, Congress had already displayed a marked lack of enthusiasm for expansive post-Apollo space goals.

Sources

Report of the Lunar Exploration Working Group to the Planning Steering Group, revised 30 April 1968.

Report of the Single Site Working Sub-Group to the Lunar Exploration Working Group, 22 May 1968 (revised 4 June 1968).

Memorandum with attachment, MTX/Chairman, Lunar Station Subgroup, to Distribution, "Meeting of the Lunar Station Subgroup," 7 May 1968.

Memorandum with attachment, MAL/Director, Apollo Lunar Exploration Office to MTX/Rodney W. Johnson, "Lunar Single Site Working Subgroup," 7 May 1968.

Apollo News Reference, Public Affairs Office, Grumman, 1969, pp. LMD-4, LMD-6-8.

Conversations with Paul D. Lowman, NASA geophysicist and participant in the Single Site Working Sub-Group, at and around NASA Goddard Space Flight Center, Greenbelt, Maryland, Summer 2000.

More Information

Early Apollo Mission to a Lunar Wrinkle Ridge (1968)

Robot Rendezvous At Hadley Rille (1968)

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

Rocket Belts and Rocket Chairs: Lunar Flying Units

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

Footsteps to Mars (1993)

The ungainly contraption pictured above is a piloted Mars lander based partly on planned Space Station Freedom hardware. Boeing proposed the design in 1990 as part of President George H. W. Bush's failed Space Exploration Initiative. Image: Boeing/NASA.

The Space Exploration Initiative (SEI), launched by President George H. W. Bush amid great fanfare on the steps of the National Air and Space Museum on the 20th anniversary of the Apollo 11 Moon landing (20 July 1989), was seen by many space supporters as a new Apollo Program. Nothing, however, could have been farther from the truth.

Apollo fulfilled a perceived national need: specifically, to assert U.S. technological primacy in the Cold War with the Soviet Union. SEI, by contrast, seemed to fulfill no purpose commensurate with its projected cost. President John F. Kennedy called for Apollo at the Cold War's height; Bush proposed SEI as the Eastern Bloc disintegrated. Though Bush, a Republican, apparently felt genuine enthusiasm for space exploration, he distanced himself from SEI by the beginning of 1991, when it had become an obvious political liability.

The initiative continued with minimal funding until Democratic President William Jefferson Clinton took office in January 1993. By May of that year, when the Case for Mars V conference convened in Boulder, Colorado, NASA's Moon and Mars exploration planning apparatus was in the process of being dismantled. The Case for Mars V became SEI's wake.

Geoffrey Landis, a NASA Lewis Research Center (now NASA Glenn Research Center) engineer and award-winning science-fiction author, presented a plan for recovery from SEI at The Case for Mars V. He subsequently published it in The Journal of the British Interplanetary Society. He began his paper by declaring that SEI was "politically dead" — it had, he wrote, come to be "viewed as an expensive Republican program with no place in the current era of deficit reduction." Landis then asked, "how can we advocate Mars exploration without appearing to be attempting to revive SEI?"

Landis's solution was a new piloted Mars program that would take into account lessons taught by Apollo ("If you accomplish your goal, your budget will be cut") and the Space Shuttle ("if you do the same thing over and over, the public will focus on your failures and forget your successes"). The Landis program was a 14-year series of incremental "footsteps" which, he said, would be in keeping with NASA Administrator Dan Goldin's "faster, better, cheaper" philosophy of spaceflight (at the time of The Case for Mars V, this philosophy was still in its infancy). The footsteps would, he argued, provide a series of interesting milestones that would maintain public enthusiasm for the program at least until a piloted Mars landing took place.

Landis's first footstep, which he optimistically asserted could occur "immediately," was a piloted Mars flyby mission based on existing U.S. and Russian launch vehicles and space station hardware. The 18-month mission would test a potential design for a piloted Mars transfer vehicle and demonstrate long-duration interplanetary flight and high-speed Earth-atmosphere reentry.

While close to Mars, the astronauts would take advantage of short radio signal travel time to teleoperate a rover on the planet. The rover would be launched to Mars on a separate launch vehicle ahead of the piloted flyby spacecraft. Teleoperations would enable planetary quarantine to be maintained until the debate over whether life exists on Mars could be resolved.

The second footstep in the Landis plan would be a piloted landing on Deimos. Landis noted that, with the possible exception of a few near-Earth asteroids, Mars's outer moon was the most accessible object beyond Earth orbit in terms of the amount of energy required to reach it. The mission would demonstrate Mars orbit insertion, Mars orbital operations, and Mars orbit departure. Deimos, Landis added, might contain water that could be split using electricity into hydrogen and oxygen, which could serve as chemical rocket propellants.

The third footstep was a piloted landing on Phobos, Mars's inner moon. "From Phobos," Landis declared, "the view of Mars will be spectacular." He proposed that an unmanned version of the piloted Mars lander be test-landed on Mars during the Phobos expedition. The lander might be used to collect a Mars surface sample and blast it back to Phobos for recovery by the astronauts and return to Earth laboratories for analysis.

Boeing design for a nuclear-thermal-propulsion piloted Mars spacecraft based on Space Station Freedom hardware heritage. The large round bowl at left is the heat shield for one of the mission's two piloted Mars landers, which nestles in the bowl. The lander is depicted on the surface of Mars in the image at the top of this post. An ascent stage from another Mars lander is about to dock. The ascent stage is shown in more detail in the image near the bottom of this post. Boeing proposed this inelegant design during 1990 for President George H. W. Bush's abortive Space Exploration Initiative. Image: Boeing/NASA.

Landis's fourth footstep would encompass several piloted Mars lander tests in Earth orbit and on the Moon (incidentally returning Americans to the Moon for the first time since Apollo 17 in December 1972). This would set the stage for the fifth footstep, a piloted landing during summer on one of Mars's polar ice caps.

Landis wrote that the martian ice caps contained readily accessible water that could be melted and split into hydrogen and oxygen propellants. In addition, the summer pole would receive continuous sunlight. Landis, a space power system engineer, noted that this would make highly efficient the use of electricity-generating solar arrays. Because the Sun would not set, the expedition would need neither batteries nor the extra solar arrays required to charge them for periods when the Sun was below the horizon.

The Mars temperate landing, the sixth footstep, would mark the culmination of Landis's program. Successfully accomplishing a landing in the martian mid-latitudes would, Landis predicted, result in budget cuts and Mars program cancellation within two years.

His seventh footstep was, thus, designed to postpone the inevitable. He argued that a landing in Valles Marineris, the equatorial "Grand Canyon" of Mars, would provide a spectacular coda exciting enough to forestall program cancellation.

Liftoff from Mars — time to slash the Mars program budget. Painted by Pat Rawlings for NASA, this image depicts the ascent stage of the Boeing-designed piloted Mars lander shown at the top of this post. Though Geoffrey Landis expected that Americans would support only two or three piloted Mars landing missions before they lost interest, this optimistic Space Exploration Initiative-era painting hints at an on-going piloted Mars program: shown on the surface are habitats, solar arrays, a tethered research balloon, and a nuclear plant.

Landis wrote that finding easily exploitable resources on Deimos, Phobos, and Mars might lower costs, enabling piloted Mars exploration to continue on "a shuttle-scale budget." He echoed science popularizer and planetary scientist Carl Sagan when he proposed that Mars replace the Cold War as a driver for Western aerospace, adding that the Soviet Union's collapse in 1991 had made available Russia — with its Energia heavy-lift rocket, Mir space station modules, and long-duration spaceflight experience — as a cooperative partner. Landis concluded by urging an immediate start to his Mars program, arguing that "despite indications, there is no better time to act."

Source

"Footsteps to Mars: An Incremental Approach to Mars Exploration," Geoffrey Landis, Journal of the British Interplanetary Society, Vol. 48, September 1995, pp. 367-372; paper presented at The Case for Mars V conference in Boulder, Colorado, 26-29 May 1993.

More Information

After EMPIRE: Using Apollo Technology to Explore Mars and Venus (1965)

Making Rocket Propellants from Martian Air (1978)

Bridging the Gap Between Space Station and Mars: The IMUSE Strategy (1985)

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 Corporation (MDC), 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 MDC 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 in-house 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 habitat 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 dancing 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/DSFPortree.

MSC looked at both "horizontal" and "circular" floor plans for the four second-pass habitat 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 internal diameter, tended to have more floors and less equipment space.

Module design Concept Selection took place on 1 July. MSC chose a horizontal habitat 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 — which it called a Basic Structural Element (BSE) — would weigh about 8000 pounds empty and about 20,000 pounds fully outfitted.

MSC then included the selected habitat module concept in 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 with 10 docking ports each, eight BSE modules, and two Expendables Storage Element (ESE) logistics and crew carriers. MSC calculated that all six modular configurations 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 Station 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 plus-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 often two — attached to CAE Y-axis ports. Though its length was not given, the ESE was described as shorter than the CAE, BSE, and Solar Power Boom modules.

The ESE was intended as a temporary Station module — it would ride into space inside a Shuttle Orbiter payload bay, then would transfer to a Station Y-axis port under its own propulsion bearing supplies, equipment, spare parts, and astronauts. It 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 designed to dock with the Station under its own power.

Shuttle Orbiters would dock the Solar Power Boom, BSE, and CAE modules with the Station. All three module types would include a docking port at either end. After reaching orbit, the Orbiter crew would pivot the module out of the payload bay and, using one of its end ports, attach it to a docking port atop the Orbiter cabin. They would then rendezvous with the Station and dock with it using the port at the module's other end. 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). CAE 1 would have nothing yet with which to dock, so it would be released directly from the Orbiter payload bay without first linking to the docking port atop the Orbiter crew cabin. 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 plus-Y CAE 1 ports, giving the growing Station an "L" configuration. It would provide electricity and propulsion for the CAE 1-ESE combination, and would carry 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) join to the CAE 1 plus-X end port (the end port nearest the docked ESE). Its solar arrays (2) would unfurl after the Shuttle Orbiter that delivered it moved away, This would block the Boom's plus-X docking port (4) and double 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 & science data processing facilities. It would be attached to the CAE 1 minus-Y port nearest the Solar Power Boom; that is, to the Y-axis port on the opposite side of CAE 1 from the ESE. It is not shown in the baseline configuration illustration above; an arrow, however, marks the port to which the first BSE would be docked. Except for the Solar Power Boom and the one or two 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 minus-Z and plus-Z CAE 1 ports. A pair of robot arms on CAE 1 would aid Shuttle astronauts in safely docking the closely spaced BSEs.

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 and biomedical studies (8), would also be a lightweight (13,324 pounds). Its arrival at the Station would signal 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. It would weigh 143,724 pounds.

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 launches 9 through 14 would boost into space the Station's second redundant, independent volume. It would be equivalent to a monolithic Station equipment bay and two more decks.

Shuttle flight 9 would place into space the 18,645-pound second CAE (9), the plus-X end port of which would be attached to the CAE 1 minus-X port. This would enable attachment of four more Z-axis BSEs. The MSC team did not specify whether CAE 2 would include its own pair of robot arms or if it would use the pair launched on CAE 1. 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 Station 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 CAE 2 Y-axis port marked on the drawing by a star. With the addition of the 14th Shuttle payload, Station mass would total 251,304 pounds.

MSC Baseline Shuttle-Launched Station Assembly Sequence

1. Shuttle flight 1: CAE 1
2. Shuttle flight 2: ESE 1 (to CAE 1 +Y port)
3. Shuttle flight 3: Solar Power Boom (to CAE +X port)
4. Shuttle flight 4: BSE 1 (to CAE 1 -Y port)
5. Shuttle flight 5: BSE 2 (to CAE 1 -Z port)
6. Shuttle flight 6: BSE 3 (to CAE 1 +Z port)
7. Shuttle flight 7: BSE 4 (to CAE 1 -Z port)
8. Shuttle flight 8: BSE 5 (to CAE 1 +Z port)
9. Shuttle flight 9: CAE 2 (to CAE 1 -X port)
10. Shuttle flight 10: BSE 6 (to CAE 2 -Z port)
11. Shuttle flight 11: BSE 7 (to CAE 2 +Z port)
12. Shuttle flight 12: BSE 8 (to CAE 2 -Z port)
13. Shuttle flight 13: BSE 9 (to CAE 2 +Z port)
14. Shuttle flight 14: ESE 2 (to CAE 2 -Y port)

The image at the top of this post (click to enlarge) shows MSC's modular Station as it would appear by the mid-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 minus-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 shown attached to Y-axis CAE ports; one is the BSE delivered during Shuttle flight 4 (it is displayed here attached to the CAE 1 plus-Y port nearest the Solar Power Boom rather than the minus-Y port), while the other, attached to a CAE 2 minus-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 vibration 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, twin main engines, and a payload bay shorter than 60 feet. It bears atop its crew compartment, attached to its docking port, a BSE module - probably another freeflyer, or perhaps a temporary attached 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 actually took place.

NASA extended the NAR and MDC Space Station Phase B contracts by six months on 30 June 1970. On 29 July 1970, Charles Mathews, chair of the Space Station Task Force, requested that MSC and MSFC direct their respective Phase B contractors to expend more effort to study Shuttle-launched modular designs. This direction became formal on 1 February 1971, when NAR and MDC began Phase B Extension studies almost entirely focused on modular designs. When unveiled in late 1971, the NAR modular design resembled the baseline design from MSC's May-July 1970 in-house study.

Acronyms

BSE = Basic Structural Element
CAE = Central Assembly Element
ESE = Expendables Storage Element
MDC = McDonnell Douglas Corporation
MSC = Manned Spacecraft Center
MSFC = Marshall Space Flight Center
NAR = North American Rockwell

Sources

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

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 automated 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. 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 piloted Moon landing mission.

In keeping with the lunar mission nomenclature proposed in Bellcomm's January 1968 Lunar Exploration Program Plan (see "More Information" 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 preselected 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, astronaut 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' 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 for geologic traverse planning by setting down near the derelict Surveyor III lander in November 1969. Apollo 14 (February 1971), 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 deep within the Fra Mauro Formation.

Source

"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)

Robot Rendezvous at Hadley Rille (1968)

Unmanned Lunar Roving Vehicle (ULRV). 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. Had it flown, the mission would have seen 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.

Numbers are explained in the text. 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 landing 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 the crater's 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 site was located on the eastern side of Mare Serenitatis.

Hadley C landing site and traverses. Numbers and colors are explained in the text. 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 include 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; on other dates, 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 operational 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 (1 and 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 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 (2 and 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 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 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 (2 and 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 (4 and 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 the Hadley Rille 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 28 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.

Sources

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)