Apollo Science and Sites: The Sonett Report (1963)

Apollo 17 Lunar Module Pilot Harrison Schmitt, a geologist, was the only professional scientist to reach the Moon. Image credit: NASA.

The Apollo Program was driven by the perceived national need to decisively demonstrate American technological prowess in the face of early Soviet space victories. Scientific lunar exploration was a secondary concern. In fact, some engineers saw lunar science as a distraction from the already daunting task of landing a man on the Moon and returning him safely to Earth.

The community of lunar scientists was small in May 1961, when President John F. Kennedy put the U.S. on the road to the Moon. Nevertheless, lunar science had its energetic proponents. In early 1962, they saw to it that NASA's Office of Manned Space Flight (OMSF) asked NASA's Office of Space Science (OSS) to outline an Apollo science program. OSS appointed NASA physicist Charles Sonett to head up an ad hoc working group and OMSF provided the group with guidelines for its deliberations.

The Sonett group's 12 members and nine consultants included U.S. Geological Survey geologist (and aspiring astronaut) Eugene Shoemaker, astronomers Gerard Kuiper and Thomas Gold, NASA geophysicist Paul Lowman, and chemist (and Nobel Laureate) Harold Urey. They circulated their July 1962 draft report at the National Academy of Science's 10-week Iowa City meeting (17 June-31 August 1962) and within NASA, receiving, they reported, "general endorsement" for their recommendations.

The final version of the Sonett report, published in December 1963 and labeled "for internal NASA use only," was the first in a series of influential Apollo planning documents that called for ambitious scientific exploration of the Moon. Its recommendations touched on many aspects of Apollo mission planning.

The Sonett group called for all proposed Apollo landing sites to be photographed by automated Lunar Orbiter spacecraft before final site selection. Lunar Orbiter photographs would be used to make detailed geological maps of planned landing sites. This, the Sonett group's members argued, would save precious time during Apollo landing missions, because it would enable astronauts to begin geological field work without first mapping their landing site.

They urged that every two-person Apollo landing crew include a scientist-astronaut with a Ph.D. in geology and from five to 10 years of field experience. Geologists on Earth would explore the Moon vicariously through his descriptions and through real-time television transmitted from a camera mounted on his space suit.

They acknowledged that Kennedy's end-of-decade deadline for reaching the Moon meant that Apollo scientist-astronauts would probably be drawn from the community of scientists already at work in 1962-1963. They assumed, however, that Apollo would be merely the first U.S. program of piloted lunar exploration, so urged that "graduate students and young post graduate scientists. . .be brought into the field of lunar science as potential astronauts as soon as possible."

OMSF had advised the Sonett group that the Apollo lunar surface space suit would "limit the crew's ability to act, particularly in performing precise manipulations." In their final report, the group's members, undaunted by anticipated technological limitations, urged early development of surface suits that would "permit a close approximation to unsuited limb, arm, and digital [finger] movements."

Sonett working group member Eugene Shoemaker models a pressure suit proposed for advanced Apollo Extension System lunar exploration missions. He stands outside the hatch of a mockup long-range lunar rover. Image credit: U.S. Geological Survey.

OMSF also told the group that a space-suited Apollo astronaut would probably be unable to walk more than a half-mile from his lunar lander, but raised the possibility of a rover or other mobility aids. The Sonett group declared that

. . .reconnaissance beyond a one-half mile radius of the spacecraft will be a necessity. . .For example, a lunar ray, a feature of great interest, is probably a poor place to land, yet the capability of traveling to a ray area is clearly indicated. . .For scientific purposes, therefore, there should be the capability of reaching areas some 50 miles from a landing site.

In 1962-1963, OMSF considered development of an automated lander capable of delivering to the Moon up to 15 tons of equipment and supplies. In addition to a beacon for guiding an Apollo Lunar Excursion Module (LEM) piloted lander to a safe touchdown nearby, it would carry one or more rovers and expendables — for example, liquid and gaseous oxygen — for extending LEM electricity-generation and life-support capabilities. The Sonett group urged OMSF to proceed with cargo lander development, noting that the LEM as planned would carry supplies and equipment inadequate to accomplish "even the modest scientific program recommended."

The Apollo LEM lander and lunar surface space suit as envisioned in 1964. Image credit: NASA.

OMSF informed the Sonett working group that the first Apollo lunar surface mission would probably spend only four hours on the Moon. The group urged OMSF to double that stay time so the astronauts could budget four hours for operational activities (for example, checking out their LEM before departing the Moon) and four hours for exploring the lunar surface. During their lunar traverses, they would take turns moving beyond the immediate vicinity of the LEM, collect up to 100 pounds of rocks, test soil strength, and study whether solar heating caused Moon dust to flow like a highly viscous liquid, as hypothesized by Sonett group member Thomas Gold.

The group acknowledged that "an accident" might limit surface exploration during the first Apollo landing mission to one hour. In that case, a single moonwalker would hurriedly collect about 50 pounds of geological samples near the LEM.

The group's members envisioned a five-day Apollo mission with four days of uninterrupted exploration, during which the two astronauts would drive a rover up to 10 miles from their landing site. They would also drill a hole up to 20 feet deep and insert a heat probe, collect samples "for biological purposes," and emplace a seismometer, a micrometeorite detector, and other instrument packages. They expected that the instruments would be linked by cables to a "central station" containing a radio transmitter. This would use a nuclear source to generate electricity so that it could relay data from the instruments to Earth for months or years.

OMSF asked the Sonett working group to assume "more than one but less than ten" Apollo landings. Apollo landings would, OMSF explained, be limited to sites near the equator on the side of the Moon that faces Earth. The Sonett group recommended that the first Apollo piloted lander set down near Copernicus crater.

Sonett group member Eugene Shoemaker was probably behind the Copernicus site choice; he had spent a great deal of time studying the crater starting in the late 1950s as part of his effort to resolve the debate over whether lunar craters were primarily the result of volcanism or of asteroid impacts and to establish the stratigraphic sequence of the Moon's geologic units. The latter was a requirement if the history of the lunar surface would be deciphered.

Copernicus, a leading Sonett group Apollo landing site candidate, as portrayed in an early 1960s map. Moon maps in this series, based on photos from Earth-based telescopes, were the best available at the time the Sonett Group wrote its report. Image credit: Lunar and Planetary Institute. 

In keeping with their conviction that lunar exploration should continue beyond Apollo, the Sonett group scientists offered two lists with a total of 28 candidate landing sites. All sites were selected using photographs taken using Earth-based telescopes.

The first list of 15 sites, compiled in June 1962 by Eugene Shoemaker and R. E. Eggleton, another U.S. Geological Survey geologist, took into account "possible landing conditions and trafficability, and prospects of discovering natural shelter and potential water supplies."

• 9.8° North (N), 20.1° West (W), near the Copernicus central peaks
• 13.1° N, 31° W, on a "typical lunar dome" near the crater Tobias Mayer
• 20.4° N, 3° W, on the southeast edge of Mare Imbrium, near Mt. Huyghens in the Apennine Mountains
• 12.6° N, 2° W, in Alphonsus crater, site of suspected on-going lunar volcanism
• 7.7° N, 6.3° East (E), within four-mile-wide Hyginus ("one of the largest craters of likely volcanic origin"), located at a potentially significant bend in Hyginus Rille
• 37.9° N, 16.4° W, near a "possible flow" in Mare Imbrium
• 40.9° South (S), 11.1° W, on the "rubbly" north flank of the great ray crater Tycho
• 50.6° S, 60.8° W, in Wargentin, an odd lava-filled crater
• 85° S, 45° E, in the south polar crater Amundsen, where, it was believed, permanently shadowed areas might preserve ice deposits
• 12.7° S, 49.8° W, on a "very bright" plateau north of the crater Billy
• 41.7° N, 57.5° W, on Oceanus Procellarum north of the Rumker Hills
• 5.6° S, 26.6° W, near a "small irregular depression" 35 miles southeast of the crater Hortensius
• 5.1° N, 14.2° W, on dark material about 140 miles southeast of the center of Copernicus
• 35.3° N, 5.5° W, on Mare Imbrium near the "mountainous block" Spitzbergen
• 9.1° S, 16.1° W, on the north flank of crater Parry A, a natural drill hole exposing ancient dark material

The Sonett working group's second list was compiled by geochemist Duane Dugan of NASA's Ames Research Center.

• 3° S, 44° W, in the middle of the Flamsteed Ring, a mostly submerged crater north of Flamsteed crater
• 13° S, 2.3° W, in Alphonsus
• 23.4° N, 43.3° W, near bright Aristarchus crater, flat-floored Herodotus crater, and sinuous Schröter's Rille (a region of suspected on-going lunar volcanism and many apparent volcanic features)
• 23° N, 51.45° W, inside Herodotus
• 20.3° N, 3.4° W, on Mare Imbrium west of Mt. Huyghens
• 28° N, 12° E, on Mare Serenitatis near the unusual crater Linne, site of suspected on-going lunar volcanism
• 19.3° S, 40.2° W, on safe, flat ground in Mare Humorum near the south wall of dark-floored Gassendi crater
• 5.5° N, 14.3° W, in a "black" surface area east of Fauth crater
• 5° S, 28.1° W, in the Ural and Riphaeus Mountains, near "old ghost rings" (submerged craters)
• 9° S, 2° W, on the floor of Ptolemaeus crater, site of ridges, "craterlets," and a "crater cone" of "remarkable" whiteness
• 15° N, 22° E, between crater Plinius and the Haemus Mountains, a place "with access to the color discontinuity between Mare Tranquillitatis and Mare Serenitatis"
• 24.3° S, 43.4° W, in Mare Humorum east of the crater Liebig (site of "an interesting scarp" that cuts through craters)
• 4.5° S, 25.5° E, in southern Mare Tranquillitatis, at the base of Theophilus crater rim west of Torricelli crater (a "very complex" region with "shading" reminiscent of "one of the terrestrial continental shelves")

That the Shoemaker-Eggleton and Dugan lists had in common only Alphonsus, the dark region near 5.5° N, 14.3° W, and Huyghens-Appenine reflected the wide range of attractive candidate lunar landing sites. Some of the proposed sites, such as Amundsen, lay beyond the equatorial zone OMSF had said Apollo could reach. The working group asserted that "there is no question that sites of the greatest scientific interest lie outside the equatorial belt," and urged that NASA develop the "capability of landing in the equatorial belt, at the poles, and elsewhere."

Alphonsus crater made both the Shoemaker-Eggleton and Dugan lists of candidate Apollo landing sites. Image credit: Lunar and Planetary Institute.

NASA paid attention to the Sonett report and other advice it received from scientists as it planned Apollo missions, but the complex interplay of competing technical, political, and scientific requirements meant that the space agency could give scientists no more than a small fraction of what they desired. Most notably, only one scientist-astronaut reached the Moon: geologist Harrison Schmitt (image at top of post), who explored the Taurus-Littrow valley east of Mare Serenitatis with Eugene Cernan during the Apollo 17 mission (7-19 December 1972).

Schmitt and Cernan spent three days on the Moon. They wore A7LB space suits which restricted their movements, but which were an improvement over the A7L suits worn by Apollo 11, 12, and 14 moonwalkers. They collected drill cores, deployed instruments and a heat-flow probe attached by cables to a nuclear-powered central station, and drove 35.9 kilometers using a jeep-like Lunar Roving Vehicle. All of their equipment arrived stowed on board the Apollo 17 Lunar Module Challenger; NASA developed no automated cargo lander. Apollo 17 returned 110.5 kilograms of geologic samples to researchers on Earth.

Astronauts explored few of the sites Shoemaker, Eggleton, and Dugan selected. The reasons for this were manifold: the U.S. flew only six successful Apollo lunar landing missions; NASA never became capable of landing men very far beyond the Nearside equatorial belt; new knowledge of the Moon from robotic missions and orbiting Apollos made some of the sites appear less scientifically significant than had been believed or less attractive than newly found candidate sites; and no follow-on lunar landing program materialized.

The first Apollo lunar landing mission, Apollo 11 (16-24 July 1969), spent about 21 hours on Mare Tranquillitatis, not in Copernicus; in fact, Copernicus remains unvisited today. Huyghens-Apennine became Hadley-Apennine; visited by Apollo 15 (26 July-7 August 1971), it is widely considered to be the most scientifically significant Apollo site.

Robots explored Alphonsus (Ranger 9, March 1965), the Flamsteed Ring (Surveyor 1, May-July 1966), and Tycho (Surveyor 7, January 1968). The lunar south pole and Aristarchus, as yet unvisited, are frequently mentioned as candidate landing sites for NASA's eventual return to the Moon.

Source

Report of the Ad Hoc Working Group on Apollo Experiments and Training on the Scientific Aspects of the Apollo Program, 15 December 1963. 

More Information

Plush Bug, Economy Bug, Shoestring Bug (1961)

Harold Urey and the Moon (1961)

Apollo Extension System Flight Mission Assignment Plan (1965)

Apollo Extension System Flight Mission Assignment Plan (1965)

NASA piloted spacecraft as conceived in 1964. The rockets at left are the Apollo-Saturn V, the Gemini-Titan, and the Mercury-Atlas. The spacecraft at right are the Apollo CSM/Apollo LEM, Gemini, and Mercury. At the time this was painted, only the one-man Mercury (lower right) had carried an astronaut into orbit. Note the round hatch on the front of the LEM ascent stage (upper right); a square hatch replaced this late in the year. Image credit: D. Meltzer, National Geographic Society/NASA.

On 30 January 1964, President Lyndon Baines Johnson asked NASA Administrator James Webb for a comprehensive list of candidate post-Apollo piloted space programs. At the time, NASA was between Project Mercury, its first piloted program, and Project Gemini, its second. The longest U.S. piloted mission at the time was Mercury-Atlas 9 (15-16 May 1963), which had lasted for 34 hours and 19 minutes. The space agency's top priority was to achieve the goal of a man on the Moon by the end of the 1960s decade.

Webb's response might have included a large Earth-orbiting space station, a lunar base, and a Mars expedition. NASA and its contractors had studied all three by 1964. Instead, his list included just one item: modification of Apollo Command and Service Module (CSM) and Lunar Excursion Module (LEM) spacecraft to provide Earth-orbital and lunar capabilities beyond those planned in the Apollo Program. Because its aim was to extend planned CSM and LEM capabilities, the proposed program was dubbed the Apollo Extension System (AES).

Using spacecraft derived from existing spacecraft to accomplish new missions was, of course, not a new idea. Gemini prime contractor McDonnell proposed a steady stream of Gemini-derived spacecraft beginning in 1962. Gemini had, in fact, started out as a Mercury derivative called "Mercury Mark II."

In 1963, CSM prime contractor North American Aviation (NAA) studied a six-man CSM derivative for delivering space station cargo and changing out station crews. That same year, LEM prime contractor Grumman studied a two-man LEM-derived reconnaissance spacecraft that could fly free of the CSM in lunar orbit, turn cameras toward the lunar surface, and dispense small landing probes.

NASA managers expected that, if all went well, they would have Apollo CSM and LEM spacecraft left over after they achieved Apollo's goal. Surplus Apollo lunar spacecraft would become available for AES missions.

At a press conference, Webb told reporters that he expected NASA's annual budget to climb to about $5.25 billion during Apollo and subsequently remain close to that amount. Funding freed up as Gemini and Apollo wound down would, like the surplus Apollo spacecraft, be shifted to AES, making no new infusion of funds necessary.

Though AES was generally ignored in the rush to develop approved programs like Gemini and Apollo, the proposed post-Apollo program had its critics. Some felt that it was not ambitious enough. The fact was, though, that NASA had enough to do in 1964-1965 without starting a new ambitious program.

Others believed that AES would do nothing in space that needed to be done. In testimony on the Fiscal Year 1966 NASA budget before the House Committee on Space and Astronautics on 18 February 1964, Associate Administrator for Manned Space Flight George Mueller sought to assure legislators that AES was not a "make-work" program. He explained that the Apollo-based program would enable NASA "to perform a number of useful missions. . .in an earlier time frame than might otherwise be expected."

On 29 January 1965, eighteen planners with Bellcomm, NASA's Washington, DC-based Apollo planning contractor, completed an interim report on their study of AES spacecraft and missions. Their eight-part report included a tentative Flight Mission Assignment Plan (FMAP).

In the FMAP, missions were assigned to specific months for planning purposes with the proviso that they would eventually be given precise dates determined by mission objectives, launch constraints, target lighting, and other factors. A chronological list of missions in the January 1965 AES FMAP can be found at the end of this post.

NASA had provided Bellcomm with a preliminary (hence vague) list of AES planning "ground rules" for its study. The first two ground rules taken together were clear: AES should not interfere with or compete with the Apollo Program.

NASA ground rules aimed to contain AES costs by placing restrictions on Apollo spacecraft modification. For example, they specified that CSMs and LEMs manufactured for AES missions were to be delivered to NASA configured for Apollo missions. Spacecraft modification and experiment installation for AES missions would occur outside the NAA and Grumman plants where the CSMs and LEMs were manufactured. In addition, no major facility construction or modification would be allowed; Apollo spacecraft would be converted into AES spacecraft inside buildings where Apollo spacecraft processing occurred.

NASA assured Bellcomm that eight Apollo spacecraft, along with six Saturn IB rockets and six Saturn V rockets, would be available for AES flights each year in the 1969-1971 period. The two-stage Saturn IB was designed for Apollo test missions in low-Earth orbit; the three-stage Saturn V, for boosting Apollo spacecraft to the Moon.

Bellcomm developed additional "guidelines" which it considered "not as firm" as the NASA-provided ground rules. For example, the Bellcomm team decided that all eighteen AES Saturn Vs launched in 1969-1971 should carry astronauts. Of the eighteen, six would launch crews to geosynchronous or polar Earth orbit and the rest would launch crews to the Moon.

The FMAP described 23 AES missions of three types — Earth orbital, lunar orbital, and lunar surface — spanning the period from March 1968 through December 1971. The team proposed eight mission classes within the framework of the three types. Earth-orbital missions included Earth-Oriented, Astronomy, Biomedical/Behavioral, and Operations/Technology classes. Lunar-orbital missions included Equatorial, Inclined, and Polar classes. Lunar-surface missions were of just one class: 14-Day Stays.

Mission difficulty would increase gradually and enough time would be allotted to enable data from one mission of a given class to be used to "optimize" the next mission of that class. Bellcomm cautioned that its list was not meant to include all possible classes, adding that the "catalog of suggested areas of investigation is expanding almost daily."

The Bellcomm engineers expected that, when AES began to fly modified Apollo spacecraft, the program would need one derivative of the Apollo CSM and three Apollo LEM derivatives. The CSM derivative was the Extended CSM (XCSM), the AES workhorse spacecraft. The XCSM would be capable of operating for up to 45 days in space without resupply. Bellcomm saw the XCSM as a "general purpose spacecraft" able to support any AES mission without additional modifications.

Bellcomm noted that design of workable LEM derivatives was problematic. The LEM was evolving rapidly in 1964-1965. In addition, the LEM was inherently more specialized and had more limited design margins than the CSM. Bellcomm described a LEM-Lab, LEM-Shelter, and LEM-Taxi in its January 1965 report, but cautioned that all three derivatives needed more study. Though they put a brave face on it, the Bellcomm engineers were clearly not confident that LEM hardware could be adapted to support all the missions they described.

LEM-Lab with legless descent stage from an October 1965 Grumman study document. The two large structures on either side of the ascent stage are components of a large-format stereo camera. The image at left depicts the LEM-Lab within the segmented Spacecraft Lunar Module Adapter (SLA) shroud. The position of the CSM engine bell within the SLA relative to the top of the LEM-Lab is indicated as an outline. Image credit: Grumman Aircraft Engineering Company.

LEM-Lab without descent stage as depicted in the 1965 Grumman study document. Image credit: Grumman Aircraft Engineering Company. 

The LEM-Lab would have two forms: "ascent-stage-alone" and "ascent-stage-with-descent-stage." Both would depend entirely on the docked XCSM for life support and electricity. In the ascent-stage-with-descent-stage case, the LEM descent engine would augment XCSM propulsion but not attitude control; ascent-stage-alone would rely entirely on the XCSM for propulsion and attitude control. In the text that follows, LEM-Labs are ascent-stage-alone unless otherwise indicated.

At the time the Bellcomm engineers completed their interim study, the LEM ascent stage was expected to include 180 cubic feet of free pressurized volume. To form the LEM-Lab, most LEM ascent stage systems would be stripped out to free up an additional 60 cubic feet of pressurized volume for instruments and experiments in the LEM pressure vessel.

The LEM-Shelter would reach lunar orbit docked to a piloted Apollo CSM, land on the Moon automatically, hibernate on the surface for several months, then provide a two-man crew arriving in a LEM-Taxi with living quarters and exploration equipment for a 14-day lunar surface stay. The LEM-Taxi would be outwardly almost identical to the Apollo LEM, but could be placed in hibernation on the lunar surface for 14 days.

In an attempt to avoid interference with Apollo missions, the Bellcomm engineers built its AES FMAP around an "unofficial" Apollo schedule that saw the first unpiloted Apollo Saturn IB rocket test in January 1966. Bellcomm designated the test SA-201. Two additional Saturn IB test flights would occur, then astronauts would ride to Earth orbit in an Apollo CSM  for the first time atop a Saturn IB in October 1966. Bellcomm called the flight SA-204.

The FMAP also included nine "unassigned" missions for which Saturn rockets were expected to be manufactured, but which would, based on NASA's ground rules, have no Apollo spacecraft to launch. These brought the potential AES mission total to 32.

The first unassigned flight, SA-208, might occur as early as November 1967. Bellcomm explained that the SA-208 Saturn IB might remain in the Apollo Program or might be used to launch a "cislunar" version of the Pegasus micrometeoroid-detection satellite in the AES Program. At the time Bellcomm conducted its study, NASA had on its launch docket for 1965 three Pegasus launches. The first reached orbit less than a month (16 February 1965) after the Bellcomm team completed its AES report.

The next unassigned flight was SA-212 in December 1968. The Bellcomm engineers saw it as another candidate cislunar Pegasus mission. It would be the first cislunar Pegasus mission if SA-208 stayed in the Apollo Program. Other unassigned missions were SA-216 (July 1969), SA-217 (September 1969), SA-220 (April 1970), SA-222 (July 1970), SA-223 (September 1970), SA-224 (November 1970), SA-225 (January 1971), and SA-226 (March 1971).

The original Apollo "buy" included 12 Saturn IB rockets and 15 Saturn V rockets, which meant that SA-212 would be the last flight of an Apollo Saturn IB rocket. NASA would need to order new rockets in 1966 if six Saturn IBs and six Saturn Vs were to be available per year in 1969, 1970, and 1971.

The Bellcomm engineers included five Saturn IB-Centaur upper stage missions in the AES FMAP because Saturn IB-Centaur was nominally under AES management at the time they completed their study. They did not, however, see them as AES missions; they were included for planning purposes. All would carry as payloads automated Voyager Mars/Venus exploration spacecraft (see "More Information" below).

The first Saturn IB-Centaur mission, designated SA-210, would be a Voyager test. It would depart Cape Kennedy in June 1968. The first operational Voyager missions (SA-213/SA-214) would launch to Mars in February/March 1969. A second Voyager pair (SA-227/SA-228) was scheduled for Mars launch in May/June 1971.

The first piloted flight of the AES program would be SA-209 in March 1968. The mission to near-equatorial low-Earth orbit would include two or three astronauts, an unmodified Apollo CSM, and an unmodified Apollo LEM ascent stage with no descent stage. The mission would last from 10 to 14 days. Its crew would focus on engineering experiments, such as pumping propellants in weightlessness and performing spacewalks to test new tools. SA-209 was the first mission in the AES Operations/Technology class.

The first unpiloted Saturn V test (SA-501) would take place as part of the Apollo Program in January 1967. On its third flight (SA-503) in October 1967, the Saturn V would launch its first Apollo crew to Earth orbit.

The first Apollo lunar landing attempt would occur during mission SA-506 in August 1968. If it was successful, then its backup mission (SA-507) might become the first Saturn V-launched AES mission in November 1968. The AES SA-507 mission would see unmodified Apollo CSM and Apollo LEM spacecraft launched to geosynchronous or polar Earth orbit for from 10 to 14 days. Because SA-507 reassignment was tentative, Bellcomm did not specify the mission's class.

If SA-507 stayed within the Apollo Program, then the first AES Saturn V flight (SA-509) would take place in April 1969. Two or three men, an unmodified Apollo CSM, and an unmodified Apollo LEM ascent stage would be launched to geosynchronous Earth orbit for a 10-to-14-day "subsystems development" (Operations/Technology class) mission in preparation for SA-211.

SA-211 in September 1968 would see the first flight of the XCSM and LEM-Lab. The three-man flight in near-equatorial low-Earth orbit, scheduled to last for from 30 to 45 days, would emphasize biomedical/behavioral experiments and would test lunar survey instruments ahead of mission SA-511.

Bellcomm explained that all AES missions would include a biomedical/behavioral component, and all Biomedical/Behavioral-class missions would include at least one other activity. It noted also that AES missions that studied the effects of long-duration spaceflight on astronauts were the most important for future NASA piloted programs.

The Bellcomm engineers might have transferred all Apollo hardware to AES after SA-506 or SA-507 — whichever mission became the first successful Apollo lunar landing mission — but they opted instead to schedule SA-508, SA-510, and SA-512 as Apollo lunar landing missions in February, June, and October 1969. Sandwiched between the February and June Apollo flights, the team scheduled SA-215, an Earth-orbital Apollo CSM/Apollo LEM ascent stage mission intended to test Earth survey instruments (Earth-Oriented class). Between the June and October flights, it scheduled SA-511 (August 1969), the first AES Lunar Orbital Survey mission.

During SA-511, three astronauts would image the Moon from near-equatorial lunar orbit using instruments mounted in a LEM-Lab with a descent stage. The descent stage would help the SA-511 XCSM/LEM-Lab stack maneuver so that it could pass over important lunar surface targets. Bellcomm envisioned that the SA-511 LEM-Lab might release small lunar probes derived from planned Surveyor robotic landers. The mission would last about 35 days, of which about 30 days would be spent in lunar orbit.

In December 1969, a pair of AES missions would lift off, but only one would conclude. SA-513 (Apollo CSM/Apollo LEM ascent stage) was an Operations/Technology-class subsystems development mission like SA-509. It would include three astronauts and operate for from 10 to 14 days in polar Earth orbit. SA-218, on the other hand, would continue — and greatly extend — the biomedical research SA-211 began.

The SA-218 crew would attempt to remain in space for from 60 to 90 days on board an XCSM/LEM-Lab in near-equatorial Earth orbit. They would take an occasional break from gathering data on their own reactions to long-duration spaceflight by testing a "zero-g lab."

In January 1970, NASA would launch SA-219, a three-man XCSM/LEM-Lab mission meant to rendezvous with and resupply SA-218. The Bellcomm team provided little information on how resupply would take place. The SA-218 crew would not return to Earth until March (for the 60-day mission) or April (for the 90-day mission).

Just as SA-218/SA-219 would support a giant leap in space biomedical knowledge, so would SA-514/SA-515 support a giant leap in lunar knowledge. Launched in February 1970 with a crew of two or three, it would see an Apollo CSM transport a LEM-Shelter to the Moon. After insertion into lunar orbit, the LEM-Shelter would separate from the CSM without a crew on board, land automatically at a complex exploration site, and put itself into hibernation.

LEM-Shelter as depicted in the 1965 Grumman study document. Note the rover at right shown in stowed and deployment positions. To the left of the descent stage engine bell, a deep drill is shown in deployed position. Image credit; Grumman Aircraft Engineering Company.

Stylized depiction of the LEM as envisioned in 1964. This image can stand in for the 1964 LEM-Taxi; outwardly, the Apollo LEM and the LEM-Taxi designs were very similar. Image credit: NASA.

In April 1970, SA-515 would reach lunar orbit. The mission would use the last of the 15 Saturn V rockets ordered for Project Apollo. Its payload would comprise an XCSM, LEM-Taxi, and a crew of three.

Two men would descend to a landing near the LEM-Shelter in the LEM-Taxi, then would put the LEM-Taxi in hibernation and transfer to the LEM-Shelter. The LEM-Shelter would carry a small rover, enabling longer geologic traverses than could be achieved during Apollo missions (at the time Bellcomm performed its study, no Apollo mission was expected to carry a rover).

The LEM Shelter would include analysis equipment to enable the astronauts to decide which geologic samples should be returned to Earth (Bellcomm assumed that the astronauts would collect more samples than the LEM-Taxi could carry to lunar orbit, so some form of "discrimination" would be required). After 14 days on the Moon, they would abandon the LEM-Shelter, revive the LEM-Taxi, and return to the XCSM in lunar orbit in the LEM-Taxi ascent stage. Mission duration would total about 20 days.

Bellcomm noted that astronauts living in the LEM-Shelter for 14 days stood a 28% chance of exceeding their allowed mission radiation dose. Passing the limit would force them to terminate their surface mission early. Beefing up radiation protection would dramatically increase LEM-Shelter weight. They determined that, combined with other modifications required for months-long hibernation and a 14-day surface stay — for example, replacement of Apollo LEM batteries with fuel cells and insulated tanks containing cryogenic liquid oxygen/liquid hydrogen fuel cell reactants — the LEM-Shelter might put on so much weight that its landing legs would collapse (unless, of course, they were also modified).

SA-221 (May 1970) was a three-man, 30-to-45-day XCSM/LEM-Lab mission in near-equatorial low-Earth orbit dedicated to meteorology, agricultural remote sensing, and oceanography, placing it in the Earth-Oriented mission class. The Bellcomm engineers stressed that astronauts on board would serve as "trained observers" and "data filters," functions that automated satellites were unable to perform. The following month, SA-516 (XCSM/LEM Lab, 30-45 days, geosynchronous orbit) would test an astronomy payload.

SA-517 (August 1970), the second Lunar Orbital Survey mission, would see an XCSM/LEM-Lab/descent stage stack enter an orbit inclined steeply relative to the lunar equator, enabling it to pass over a larger portion of the lunar surface than its predecessor SA-511. SA-518 in October 1970, an XCSM/LEM-Lab, would survey the Earth from polar orbit using instruments tested during SA-215. SA-519 (December 1970) would round out the year by delivering a LEM-Shelter to a new complex landing site on the Moon.

The first mission of the AES program's last year would be the February 1971 SA-520 LEM-Taxi mission to the LEM-Shelter delivered during SA-519. Next up would be Earth-Oriented SA-521 (April 1971), which would see three astronauts in an XCSM/LEM-Lab study meteorology and oceanography from geosynchronous orbit for up to 45 days. Bellcomm noted that AES meteorological studies might lead to an "economical" weather satellite system or even "eventual control of the weather."

In June 1971, NASA would launch to lunar polar orbit SA-522 (XCSM/LEM-Lab/descent stage), the third and final AES Lunar Orbital Survey Mission. In polar orbit, the spacecraft would pass over the lunar polars on every orbit and fly over the entire lunar surface in daylight over a period of about a month.

SA-523 (XCSM/LEM-Lab) would be a long-duration Earth-orbital astronomy mission with a substantial biomedical/behavioral component (August 1971). SA-229 (XCSM/LEM-Lab) would rendezvous with and resupply SA-523 in September 1971.

SA-524 (October 1971) would deliver to the Moon the third and last LEM-Shelter of Bellcomm's AES FMAP. The same month, SA-230 (XCSM/LEM-Lab) would rendezvous with and resupply the ongoing SA-523 mission in Earth orbit. The final scheduled AES FMAP mission, SA-525 in December 1971, would see astronauts in a LEM-Taxi descend from an XCSM in lunar orbit to land near the SA-524 LEM-Shelter for 14 days of exploration.

The Bellcomm engineers argued that AES could accomplish many more types of missions if NASA's ground rules were relaxed. They suggested, for example, that another LEM derivative, the LEM-Truck, be developed to deliver large lunar surface payloads, such as more capable rovers, to the surface of the Moon in the period after 1971. The LEM-Truck would enable planners to abandon entirely the restrictive confines of the LEM ascent stage, permitting maximum exploitation of descent stage payload capacity. Grumman had studied the LEM-Truck since 1962.

The LEM-Truck was a LEM descent stage that included ascent stage systems required for landing on the Moon. Cargo would replace the LEM ascent stage. The image shows cargo volume available atop the LEM-Truck. Image credit: Grumman Aircraft Engineering Company.

In March 1965, against a backdrop of budget hearings in Congress, President Johnson made a surprise visit to NASA Headquarters. He received a briefing on Mariner IV, which had left Earth for Mars on 28 November 1964. Along with Vice President Hubert Humphrey's visit to Cape Kennedy a few days earlier, this was widely seen as a show of support for programs in the Fiscal Year 1966 NASA budget, including AES.

In August 1965, with the Fiscal Year 1966 budget in effect since 1 July, George Mueller established the Saturn/Apollo Applications Office at NASA Headquarters. The following month, AES became the Apollo Applications Program (AAP). The name changes signalled that NASA managers had learned an important lesson during the Fiscal Year 1966 budget cycle; that extending Apollo had less appeal than applying Apollo to new tasks with benefits for people on Earth.

Webb and Mueller remained outwardly enthusiastic about minimally modified Apollo spacecraft and long-duration missions; during August 1965 visits to the NASA Manned Spacecraft Center (MSC) in Houston, Texas, for example, Webb reiterated that AAP should use "off-the-shelf" spacecraft with minimal modifications. Mueller, for his part, raised the possibility of a 135-day XCSM/LEM-Lab AES Earth-orbital mission in a 27 August 1965 letter to MSC director Robert Gilruth.

Bellcomm, Grumman, and NASA in-house studies had, however, by August 1965 raised questions about the practicality of using modified Apollo spacecraft for long-duration flights. On 20 August 1965, NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama, home of the Saturn rocket family, began an in-depth in-house study of an orbital "workshop" based on the 21.7-foot-diameter S-IVB stage. The S-IVB was the second stage of the Saturn IB and the third stage of the Saturn V.

At the end of November, MSFC planners briefed Mueller on their results as part of the lead-up to NASA's Fiscal Year 1967 budget request. On 1 December 1965, Mueller gave MSFC director Wernher von Braun authority to establish the S-IVB Workshop Project Office.

Apollo and AES Flights in the January 1965 AES FMAP (includes Voyager)

1. 1/66 - SA-201 - Apollo
2. 4/66 - SA-202 - Apollo
3. 7/66 - SA-203 - Apollo
4. 10/66 - SA-204 - Apollo, CSM test
5. 1/67 - SA-205 - Apollo, CSM/LEM test
6. 1/67 - SA-501 - Apollo
7. 4/67 - SA-206 - Apollo
8. 5/67 - SA-502 - Apollo
9. 7/67 - SA-207 - Apollo
10. 10/67 - SA-503 - Apollo
11. 11/67 - SA-208 - Apollo or AES, unassigned
12. 2/68 - SA-504 - Apollo
13. 3/68 - SA-209 - AES, Apollo CSM/Apollo LEM ascent stage
14. 5/68 - SA-505 - Apollo
15. 6/68 - SA-210 - Voyager, Saturn IB/Centaur
16. 8/68 - SA-506 - Apollo, lunar landing 1
17. 9/68 - SA-211 - AES, XCSM/LEM-Lab
18. 11/68 - SA-507 - Apollo, lunar landing (SA-506 backup), or AES, Apollo CSM/Apollo LEM
19. 12/68 - SA-212 - AES, unassigned
20. 1/69 - SA-213 - Voyager, Saturn IB/Centaur
21. 2/69 - SA-508 - Apollo, lunar landing 2
22. 2/69 - SA-214 - Voyager, Saturn IB/Centaur
23. 4/69 - SA-509 - AES, Apollo CSM/Apollo LEM ascent stage
24. 5/69 - SA-215 - AES, Apollo CSM/Apollo LEM ascent stage
25. 6/69 - SA-510 - Apollo, lunar landing 3
26. 7/69 - SA-216 - AES, unassigned
27. 8/69 - SA-511 - AES, XCSM/LEM-Lab/descent stage
28. 9/69 - SA-217 - AES, unassigned
29. 10/69 - SA-512 - Apollo, lunar landing 4
30. 12/69 - SA-513 - AES, Apollo CSM/Apollo LEM ascent stage
31. 12/69 - SA-218 - AES, XCSM/LEM-Lab
32. 1/70 - SA-219 - AES, XCSM/LEM-Lab
33. 2/70 - SA-514 - AES, Apollo CSM/LEM-Shelter
34. 4/70 - SA-220 - AES, unassigned
35. 4/70 - SA-515 - AES, XCSM/LEM-Taxi
36. 5/70 - SA-221 - AES, XCSM/LEM-Lab
37. 6/70 - SA-516 - AES, XCSM/LEM-Lab
38. 7/70 - SA-222 - AES, unassigned
39. 8/70 - SA-517 - AES, XCSM/LEM-Lab/descent stage
40. 9/70 - SA-223 - AES, unassigned
41. 10/70 - SA-518 - AES, XCSM/LEM-Lab
42. 11/70 - SA-224 - AES, unassigned
43. 12/70 - SA-519 - AES, Apollo CSM/LEM-Shelter
44. 1/71 - SA-225 - AES, unassigned
45. 2/71 - SA-520 - AES, XCSM/LEM-Taxi
46. 3/71 - SA-226 - AES, unassigned
47. 4/71 - SA-521 - AES, XCSM/LEM-Lab
48. 5/71 - SA-227 - Voyager, Saturn IB-Centaur
49. 6/71 - SA-228 - Voyager, Saturn IB-Centaur
50. 6/71 - SA-522 - AES, XCSM/LEM-Lab/descent stage
51. 8/71 - SA-523 - AES, XCSM/LEM-Lab
52. 9/71 - SA-229 - AES, XCSM/LEM-Lab
53. 10/71 - SA-524 - AES, Apollo CSM/LEM-Shelter
54. 10/71 - SA-230 - AES, XCSM/LEM-Lab
55. 12/71 - SA-525 - AES, XCSM/LEM-Taxi

Sources

Final Technical Presentation: Modified Apollo Logistics Spacecraft, Contract NAS 9-1506, North American Aviation, Inc., Space and Information Systems Division, November 1963.

Study of LEM for Lunar Orbital Reconnaissance, ASR 323D-1, Grumman Aircraft Engineering Company, 23 September 1963.

"LBJ Wants Post-Apollo Plans," H. Taylor, Missiles and Rockets, 4 May 1964, p. 12.

"Interim Report for AES Flight Mission Assignment Plan — Part I: Summary," Bellcomm TM-65-1011-7, T. Powers, 29 January 1965.

"Interim Report for AES Flight Mission Assignment Plan — Part III: Extended CSM Spacecraft," Bellcomm TM-65-1011-2, K. Martersteck, 29 January 1965.

"Interim Report for AES Flight Mission Assignment Plan — Part IV: LEM Derivatives," Bellcomm TM-65-1011-3, J. Waldo, 29 January 1965.

"Interim Report for AES Flight Mission Assignment Plan — Part VII: Scheduling Constraints and Alternative Schedules," Bellcomm TM-65-1011-6, P. Gunther, 29 January 1965.

"Top-Level Space Support," W. Coughlin, Missiles and Rockets, 8 March 1965, p. 46.

"NASA to Decide Key AES Issues in June," W. Normyle, Aviation Week & Space Technology, 24 May 1965, pp. 16-17.

LEM Utilization Study for Apollo Extension System Missions, Final Report - Volume I: Summary, Design 378, Grumman Aircraft Engineering Company, 15 October 1965.

Skylab: A Chronology, R. Newkirk and Ivan Ertel with Courtney Brooks, NASA, 1977, pp. pp. 28-29, 35-43, 47-55.

More Information

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

The First Voyager (1967)

Gemini on the Moon (1962)

Retrograde Module separation. Image credit: Jeff Bateman/David S. F. Portree.

In June 1962, a little more than a year after President John F. Kennedy put the U.S. on course for the Moon, NASA's piloted spaceflight organizations agreed that Lunar Orbit Rendezvous (LOR) should be the Apollo lunar landing mission mode. LOR would employ two spacecraft: a Command and Service Module (CSM) for carrying three astronauts from Earth to lunar orbit and back again; and a Lunar Excursion Module (LEM) for landing two astronauts on the Moon and returning them to the CSM in lunar orbit. Both the CSM and the LEM would include two modules: the Command Module (CM) and Service Module (SM) in the case of the CSM, and the Descent Module and Ascent Module in the case of the LEM.

On 11 July 1962, NASA Administrator James Webb made public NASA's mode choice. He told a press conference that LOR Apollo would leave Earth on a Saturn C-5 (as the Saturn V rocket was known at the time) capable of launching 45 tons to the Moon, and that the agency would also study a two-man Direct Ascent Apollo lunar landing mission launched on a Saturn C-5. In Direct Ascent, a single spacecraft would carry the astronauts from Earth to the lunar surface and back again.

NASA Administrator James Webb (left) explains NASA's decision to adopt LOR at a NASA Headquarters press conference on 11 July 1962. Seated beside Webb are (L to R) NASA human spaceflight officials Robert Seamans, Brainerd Holmes, and Joseph Shea. Image credit: NASA.

Webb did not provide a justification for the two-man Direct Ascent study, though it soon became clear that it was a concession to Jerome Wiesner, chairman of the President's Science Advisory Council (PSAC). Wiesner, a Massachusetts Institute of Technology professor who had also served as PSAC chair for President Kennedy's predecessor, President Dwight Eisenhower, was not comfortable with LOR's complexity.

While NASA moved ahead with LOR, it also hired McDonnell Aircraft Company and TRW Space Technology Laboratories to study Wiesner's preferred mode. For McDonnell, manufacturer of the one-man Mercury and two-man Gemini spacecraft, the study had three aims.

McDonnell would develop a conceptual Direct Ascent Moonship design incorporating a two-man CM similar to the three-man North American Aviation (NAA) Apollo CM. When NAA contracted with NASA to build the Apollo CSM in November 1961, it had assumed that Apollo would use either Direct Ascent or Earth-Orbit Rendezvous. In both of those mission modes, the CSM would have had the honor of landing on the Moon. NAA did not welcome NASA's choice of LOR.

McDonnell would also look at using Gemini for the Direct Ascent Moon landing mission. At the time it conducted its study, Gemini's maiden flight was scheduled for launch in 1964. Known initially as "Mercury Mark II," the spacecraft, which was meant to reach Earth orbit atop a Titan II rocket, was meant to provide NASA with experience with spacewalks and rendezvous and docking ahead of Apollo.

From aft to front, the Gemini spacecraft consisted of the Adapter Module, the Service Module, and the CM. The Gemini CM, which measured 8.7 feet across its heatshield and weighed 5775 pounds, had two hatches (one per astronaut) with one forward-facing window each. Gemini could carry enough life support consumables and fuel cell reactants for a 14-day Earth-orbital mission.

Cutaway of a Gemini spacecraft. Image credit: NASA.

Finally, McDonnell would determine modifications the two-man Apollo and Lunar Gemini spacecraft would need to serve as unpiloted "rescue" vehicles. NASA expected that a rescue lander, if one flew, would be landed without a crew at the target landing site ahead of the Direct Ascent mission crew's arrival.

The company proposed four two-man Direct Ascent Command Module designs. The company's conical two-man Apollo would measure 8.8 feet tall and 10.4 feet across its heat shield. (For comparison, the three-man Apollo was 10.6 feet tall and 12.8 feet across.) Interior volume would total 185 cubic feet, of which 73 cubic feet would be available for the crew.

The astronauts would enter and leave the module through a hatch with two windows located above the pilot's couch. A blow-out hatch with one window located above the co-pilot's couch would provide emergency egress. During Earth launch and reentry, lunar liftoff, and while sleeping on the Moon, the astronauts would recline in their couches facing the nose and main control panel. This would place the windows above and behind their heads.

During lunar landing, they would sit upright on their couch backs facing landing controls and view the Moon's surface through the windows. Following Earth atmosphere reentry, the two-man Apollo CM would lower to a gentle land landing on three 71-foot-diameter parachutes.

Lunar Gemini I modifications would include a beefed-up heat shield so that it could withstand reentry at lunar-return speed, improved radio systems for communication between Moon and Earth, lunar landing controls, and life support consumables stocks sufficient to support an eight-day lunar mission. The spacecraft would also include two systems for viewing of the lunar surface during landing. The right-side astronaut would recline in his couch normally (back toward heat shield and lunar surface) and deploy an external mirror for an "over-the-shoulder" surface view. The left-side astronaut would roll over in his couch and view the lunar surface directly through a transparent "viewing dome" built into his hatch. The Lunar Gemini I Command Module would weigh 6802 pounds.

Except for its Earth-landing system, Lunar Gemini II would closely resemble Lunar Gemini I. Until June 1964, NASA planned a land landing for its Earth-orbital Gemini spacecraft. The Gemini CM would deploy an steerable delta-winged paraglider during descent to Earth and glide to a touchdown on skids or wheels. McDonnell retained this system in its Lunar Gemini I design, but decided to trim weight from Lunar Gemini II by substituting a single 84-foot-diameter parachute and splashdown at sea.

Land landing in the Lunar Gemini II capsule would be not survivable; if emergency land landing became necessary, the astronauts would eject from the falling capsule after reentry and descend on personal parachutes. The Lunar Gemini II Command Module would weigh 6376 pounds.

Lunar Gemini II spacecraft configurations. Clockwise from lower left: Lunar Gemini II Command Module; Lunar Gemini II Command Module with Service Module, Terminal Landing Module, and Retrograde Module; top view of Lunar Gemini II Command Module with Service and Terminal Landing Modules; Lunar Gemini II Command, Service, and Terminal Descent Modules; and Lunar Gemini II Command and Service Modules. Image credit: Jeff Bateman/David S. F. Portree.

Earth-orbital Gemini astronauts would rely on ejection seats for escape if their Titan II booster rocket malfunctioned. Lunar Gemini I and II would retain this system.

For its Lunar Gemini III design, McDonnell opted for a launch-escape tower similar to the one used on the Mercury capsule. In the event of a Titan II malfunction, the tower's solid-rocket motor would blast the Lunar Gemini III CM to safety. Couches with shock absorbers would replace the ejection seats, and three 71-foot-diameter parachutes would provide a slower, gentler descent than Lunar Gemini II's single parachute. These modifications would restore the land landing capability lost in Lunar Gemini II. All three Lunar Gemini versions could return up to 85 pounds of scientific equipment and lunar samples to Earth.

The Lunar Gemini III couches could be configured so that the astronauts could sit upright (feet toward heat shield) relative to the Moon's surface during lunar landing. New hatch windows would provide direct views of the lunar surface for both astronauts. The Lunar Gemini III CM would weigh 6453 pounds minus its launch escape tower.

McDonnell proposed that both the two-man Apollo and the Lunar Gemini CMs reach the Moon atop a stack of three propulsion/service modules. The cylindrical, 21.6-foot-diameter, 16.4-foot-tall Retrograde Module would weigh 26.9 tons with a full load (23.8 tons) of liquid hydrogen/liquid oxygen propellants. It would rest atop the Saturn C-5 rocket and its top would attach to the bottom of the Terminal Landing Module. The Retrograde Module would perform course corrections during flight to the Moon, lunar orbit insertion, de-orbit, and descent to 6000 feet above the Moon, then would detach from the Terminal Landing Module and tumble away to crash on the surface (image at top of post).

Lunar Gemini II on the Moon. Image credit: Jeff Bateman/David S. F. Portree. 

The Terminal Landing Module, which would perform descent to the lunar surface following Retrograde Module separation, would weigh three tons with a full load (1.7 tons) of ignite-on-contact hydrazine/nitrogen tetroxide propellants. It would measure 21.6 feet across its base, which would attach to the top of the Retrograde Module, and 19.3 feet across its top, which would attach to the bottom of the Service Module. It would measure only 6.5 feet tall; this low profile would keep the Direct Ascent lander's center of gravity near the surface, helping to ensure that it would not tip during landing on its four spindly legs.

The legs would fold against the Retrograde Module's sides under ejectable streamlined fairings during ascent through Earth's atmosphere. A compartment in the module's underside would hold 165 pounds of scientific gear for exploring the lunar surface.

The top of the Service Module would measure 10.4 feet across if attached to a two-man Apollo CM and 8.7 feet across if joined to a Lunar Gemini CM. It would stand 8.5 feet tall and measure 19.3 feet across its base, where it would attach to the top of the Terminal Landing Module. The Service Module would perform lunar liftoff and course corrections during the flight home to Earth. It would weigh 11.7 tons with a full load (9.7 tons) of hydrazine/nitrogen tetroxide propellants.

In addition to propulsion systems, the Service Module would carry 1148 pounds of CM support equipment, including Gemini fuel cells to provide electricity and drinking water, a surface-mounted radiator for cooling, life-support oxygen tanks, and two boom-mounted radio dish antennas.

The Lunar Gemini II Service Module rocket motor ignites, boosting the Command Module off the Moon. Image credit: Jeff Bateman/David S. F. Portree.

McDonnell found that both the two-man Apollo and the Lunar Gemini could serve a rescue function. The automated rescue spacecraft might home in on a radio beacon mounted on a pre-landed automated Surveyor lander. It could remain dormant on the lunar surface for up to 30 days awaiting arrival of the crew. If the piloted Direct Ascent spacecraft became damaged during landing or malfunctioned after touchdown, the astronauts would walk to the rescue spacecraft and use it to return to Earth.

Rescue modifications would include a guidance system similar to that under development for the automated Surveyor lunar soft-lander; additional liquid oxygen/liquid hydrogen fuel cell reactants (5.7 pounds per day) for powering electric heaters in the Command Module during the 14-day lunar night; additional water (6.5 pounds per day) for evaporative cooling during the 14-day lunar day; and a propellant-saving Surveyor-type "direct descent" landing profile with no stop in lunar orbit before descent to the lunar surface.

NASA/PSAC differences over the Apollo mode choice became public midway through the two-man Direct Ascent study, when Wiesner and Webb argued in front of President Kennedy and reporters during a presidential tour of NASA Marshall Space Flight Center (11 September 1962). Soon after McDonnell submitted its report, NASA reaffirmed its decision to go with LOR (24 October 1962).

Webb threatened to resign if NASA's choice were overruled, and Wiesner, sensing that Kennedy would back his NASA Administrator, acquiesced. On 7 November, the agency finalized its LOR decision by awarding the contract to build the LEM to Grumman Aircraft Engineering Corporation in Bethpage, Long Island.

Source

Direct Flight Apollo Study, Volume I: Two-Man Apollo Spacecraft and Volume II: Gemini Spacecraft Applications, McDonnell Aircraft Corporation, 31 October 1962.

More Information

Plush Bug, Economy Bug, Shoestring Bug (1961)

Space Station Gemini (1962)

The First Voyager (1967)

Artist concept of a Voyager spacecraft. Although the spacecraft design is correctly depicted, some liberties are taken with the planets (Mars and Earth are never this close together). The robotic Voyager includes a main engine derived from the Apollo Lunar Module Descent Propulsion System; a body-mounted, ring-shaped solar array; a skeletal high-gain antenna (it points toward Earth); a cylindrical body with rectangular thermal-control louver ports; and a Mars landing capsule with a conical heat shield sealed inside a "sterilization canister." The spacecraft is larger than it might appear: at this point in its mission, it would weigh 10.25 tons and measure 6.1 meters in diameter. Image credit: NASA/Jet Propulsion Laboratory.

In 1961, the Pasadena, California-based Jet Propulsion Laboratory (JPL), a spaceflight engineering laboratory managed by California Institute of Technology on contract to NASA, began study of Voyager, a robotic spacecraft program for exploring Mars and Venus in the late 1960s and 1970s. NASA Headquarters formally approved Project Voyager in 1964. Cuts in NASA's space science budget and debate over how Voyager should be managed and launched delayed NASA's push for a formal "new start" until January 1967, when President Lyndon Johnson's Fiscal Year (FY) 1968 NASA budget called for $71.5 million for the new program.

In January 1967, NASA's Office of Space Science and Applications published a 26-page brochure as part of its efforts to move Voyager from planning to development. The brochure was an introduction (and sales pitch) aimed at members of Congress and other individuals who would need to support Voyager if it was to become part of NASA's approved planetary exploration program for the 1970s.

In the foreword to the brochure, Homer Newell, NASA Associate Administrator for Space Science and Applications, explained that Voyager's chosen launch vehicle was the "awe-inspiring" Saturn V. One three-stage Saturn V rocket would launch two 12-ton Voyager spacecraft to Mars. For comparison, the Mariner IV Mars flyby spacecraft, launched on an Atlas-Agena D rocket in November 1964, had weighed only 260.4 kilograms. Newell wrote that

[s]uccesses already achieved in the 1960s with unmanned spacecraft of limited weight and power. . .foretell the great work of exploration that lies ahead. . .With Voyager, the U.S. capability for planetary exploration will grow by several orders of magnitude. . .Voyager could well be the means by which man first learns of extraterrestrial life.

NASA, the brochure explained, favored Mars over Venus as Voyager's first exploration target because "the high surface temperatures on Venus make the existence of extraterrestrial life less likely than on Mars" and because "the thin, normally transparent Martian atmosphere is conducive to detailed scanning of its surface features from orbit." In addition, "manned landings on Mars will someday be possible. . .[but] they may not be possible on Venus."

The brochure placed Voyager within an evolutionary robotic exploration program designed to take advantage of low-energy Earth-Mars transfer opportunities that occur every 26 months. It retroactively made Mariner IV, which had flown by Mars on 14-15 July 1965, the first mission in its program. Inclusion of Mariner IV, the first successful Mars explorer, is somewhat ironic, for its discoveries had helped to undermine support for Voyager.

In addition to recording for slow playback 21 black-and-white images that took in about 1% of the martian surface, Mariner IV had enabled Earth-bound scientists to measure martian atmospheric pressure by transmitting its feeble radio signal through the atmosphere as it passed behind the planet as viewed from Earth. Based on the degree of refraction of the signal, scientists had determined that surface pressure on Mars is not, as expected, about 10% of Earth sea-level pressure; it is, in fact, less than 1% of Earth sea-level pressure.

The Saturn IB with Centaur third stage was the first planned Voyager launch vehicle. Never fully developed, this booster would have launched a single Voyager Orbiter/Lander combination with a mass of up to 5440 kilograms toward Mars or Venus. The third stage includes the cylindrical lower part of the Payload Shroud. The Interstage, linking the S-IB first stage and the S-IVB second stage and covering the S-IVB's single J-2 engine, is generally considered to be part of the S-IVB stage. The IU is the Instrument Unit, which houses the guidance system for the rocket's first two stages. Image credit: NASA/heroicrelics.org/DSFPortree.

The brochure acknowledged that the new atmosphere data had forced a redesign of the Voyager landing system. The new design replaced lightweight parachutes with heavier landing rockets. According to historians Edward Clinton Ezell and Linda Neumann Ezell, writing in their 1984 NASA-published history On Mars: Exploration of the Red Planet, 1958-1978, the redesign bumped Voyager's projected cost above the psychologically significant $1 billion mark. Adoption of the Saturn V launch vehicle in place of the Saturn IB with a Centaur upper stage — a move designed to justify continuation of the Saturn V assembly line after Apollo and to provide flexibility in the event that Voyager redesigns significantly boosted its mass and heat shield diameter — pushed the program's price-tag past $2 billion.

The brochure called for new Mariner Mars flybys in 1969 and 1971. In 1969, a Mariner spacecraft would photograph the entire visible disk of Mars during approach and return detailed images of 10% of the planet. During the 1971 flyby, a Mariner would release a small sterilized probe into the martian atmosphere to measure pressure, density, temperature, and composition as it plummeted toward surface impact and destruction. The flyby spacecraft would act as a relay for probe signals and would image 10% of Mars at high resolution.

The first Voyager missions would take place in 1973. A battery-powered Voyager Lander with a mass of up to 390 kilograms would seek life and observe changes at the landing site over several days, and a solar-powered Voyager Orbiter would observe seasonal changes on a planet-wide scale for months.

The Voyager 1975 orbiters and landers would rely on Radioisotope Thermoelectric Generators (RTGs) for electricity. This would allow the landers to survive on Mars for one martian year (about two Earth years); that is, long enough for them to observe seasonal changes at their landing sites. Voyager could land up to 499 kilograms on Mars in the 1975 opportunity. The 1977 and 1979 Voyager missions would see introduction of a lander-deployed Mars surface rover and biological experiments specially designed to study any living things found in 1973 and 1975. A Voyager lander could deliver up to 680.4 kilograms to the surface of Mars in 1977 and 1979.

The brochure then detailed the 1973 Voyager Mars mission, which it described as typical. Voyagers would lift off from the Kennedy Space Center Complex 39 launch pads NASA built for the Apollo Saturn V launches. The 1970s Mars launch windows would last at least 25 days and would include daily one-hour launch opportunities. Voyager Saturn V rockets would be identical to Apollo lunar Saturn Vs; that is, each would comprise an S-IC first stage with five F-1 engines, an S-II second stage with five J-2 engines, and an S-IVB third stage with one J-2.

Voyager Saturn V rockets would have included the three stages and ring-shaped Instrument Unit of the Apollo Saturn V rocket. A cylindrical segmented shroud with a conical top containing twin Voyager spacecraft would, however, have replaced the Apollo spacecraft, which included the  Command and Service Module (CSM) and Lunar Module (LM) spacecraft, the Spacecraft Launch Adapter shroud containing the LM, and the pencil-shaped Launch Escape System tower. Image credit: NASA. 

The twin Voyager lander/orbiter combinations would be stacked atop the S-IVB third stage within a protective launch shroud. The first stage would burn for 2.5 minutes and fall away at an altitude of 62.8 kilometers, then the second stage would burn for 6.5 minutes and fall away at an altitude of 182.5 kilometers. The third stage would fire briefly to place itself, the twin Voyagers, and their launch shroud into Earth parking orbit.

Voyager's launch shroud would measure 6.7 meters in diameter — the same diameter as the S-IVB stage — and would have a mass of 4.7 tons. Once in Earth orbit, the shroud's conical top section would jettison, exposing the upper Voyager to space. The S-IVB stage would then ignite a second time to push the Voyagers out of Earth orbit toward Mars. After S-IVB shutdown, the upper Voyager would separate. The shroud's cylindrical central portion would then jettison to expose the lower Voyager, which would separate from the S-IVB a short time later. In the 1973 opportunity, each Voyager would have a mass of 10.25 tons after separation.

A model made in 1967 displays how two Voyager spacecraft would be stacked within the shroud atop the Saturn V S-IVB third stage. The conical, streamlined nose cone at the top of this shroud/spacecraft stack is absent. Image credit: NASA.

During the months-long interplanetary cruise, the twin Voyagers would turn their ring-shaped body-mounted solar arrays toward the Sun. They would use course-correction engines based on the Minuteman missile second-stage engine to place themselves on precise paths to Mars. The S-IVB stage trailing them would make no course adjustments, so would miss the planet by a wide margin. Because the Voyagers would perform their course corrections at different times, they would arrive at Mars up to 10 days apart.

As each Voyager neared Mars, it would fire its main rocket engine to slow down so that the planet's gravity could capture it into an elliptical orbit. Initial orbit periapsis (low point) would be about 1127 kilometers above the planet, while apoapsis (high point) would occur beyond the orbit of Deimos, the outer martian moon, which orbits at a mean altitude of 22,660 kilometers. The brochure noted that the leading Voyager main engine candidate was a modified Apollo Lunar Module descent engine. The complete Voyager Orbiter propulsion system fully loaded with propellants would weigh 6.5 tons.

After orbit insertion, the Orbiter's instruments would be turned toward Mars to image candidate sites for the first Voyager landing. After scientists and engineers on Earth settled on a site, the 2.5-ton Voyager landing capsule would eject its sterilization canister, separate from the Orbiter beyond Deimos, and fire a 188.2-kilogram solid-propellant deorbit rocket to change its path so that at periapsis it would intersect the martian atmosphere. The deorbit rocket would then detach.

The Voyager landing capsule would enter the martian atmosphere moving at between two and three miles per second. Aerodynamic braking using the 6.1-meter-diameter conical heat shield would cut speed to between 122 and 305 meters per second by the time the capsule fell to within 4570 meters of the surface. The heat shield would eject, then the Lander would fire its descent engines and deploy a supplemental parachute.

Voyager hardware heritage. Note the Voyager capsule and Lander configurations. Image credit: NASA.

During descent, the Lander would image the surface and collect atmospheric data. It would release the parachute, then slow to a hover three meters above Mars. Its descent engines would then shut off, allowing it to drop to a gentle touchdown on three legs.

The 1973 Lander would include 136.1 kilograms of science equipment. Over several days, it would search for water and life, measure cosmic and solar radiation, and study the atmosphere — it would, for example, measure the quantity of dust in the martian air.

The 1973 Orbiter, for its part, would include 181.4 kilograms of scientific instrumentation, which it would use to map Mars in detail and search for surface changes over time, determine surface composition, and measure solar and cosmic radiation. The Orbiter would also act as a martian weather satellite. It would, the brochure explained, use its main engine to change the altitude and inclination of its orbit several times during its two-year operational lifetime, allowing detailed study of much of Mars.

Congress refused to fund Voyager in FY 1968, in part because it had come to be seen as a lead-in to a costly post-Apollo piloted Mars/Venus flyby program, and also because the Apollo 1 fire (27 January 1967) undermined confidence in NASA. The U.S. civilian space agency formally abandoned its Voyager plans in September 1967.

In 1968, however, Congress agreed to fund the Viking program in FY 1969. Like Voyager, Viking would emphasize the search for life and would use twin spacecraft, each including a lander and an orbiter. Unlike its ill-starred progenitor, however, Viking made no claim to be a precursor for a piloted Mars mission. In addition, Viking would be managed by NASA's Langley Research Center, not JPL, though the later would build the Viking orbiters. Many interpreted assignment of Viking management to Langley as a congressional rebuke to JPL for its independent mindset; efforts to preserve NASA centers as Apollo spending began to wind down probably also played a role.

Twin flyby Mariners 6 and 7 flew by Mars in 1969, and Mariner 9 orbited the planet in 1971-1972. After skipping the 1973 Mars launch opportunity, NASA launched Viking 1 on a Titan-IIIE rocket with a Centaur upper stage on 20 August 1975. Viking 1's Mariner-based, solar-powered orbiter and RTG-powered lander together weighed about 2.56 tons at launch. After deploying the lander in Mars orbit, the Viking 1 orbiter weighed about 898.1 kilograms.

The Viking 1 lander became the first spacecraft to land successfully on Mars on 20 July 1976, seven years to the day after Apollo 11 became the first manned lunar lander. The lander had a mass of about 598.7 kilograms after touchdown; of this, about 42.2 kilograms comprised scientific instrumentation. Viking 2 launched from Earth on 9 September 1975, and its lander touched down on 3 September 1976. At about three meters wide, the Viking landers were about half the size of the planned Voyager landers.

NASA and JPL recycled the Voyager name in 1977, applying it to twin Mariner-derived Jupiter-Saturn flyby spacecraft (the mission was originally called Mariner Jupiter-Saturn 77). Voyager 2 left Earth first, on 20 August 1977, atop a Titan III-E/Centaur. Voyager 1 launched 16 days later, on 5 September. Voyager 1 passed Voyager 2 on 19 December 1977, as the twin spacecraft traversed the Asteroid Belt between Mars and Jupiter.

Beyond Mars: artist concept of the flight path of a Mariner Jupiter-Saturn 77 spacecraft. Image credit: NASA.

At each planet, the Voyagers performed a gravity-assist maneuver; that is, they used the target planet's gravity and orbital momentum to speed themselves onward to their next destination. Voyager 1 flew by Jupiter at a distance of 349,000 kilometers on 5 March 1979; Voyager 2 followed on 9 July 1979, passing the giant planet at a distance of 570,000 kilometers. Voyager 1 then flew by Saturn, its last planned target, at a distance of 124,000 kilometers on 12 November 1980. Voyager 2 passed Saturn at a distance of 101,000 kilometers on 25 August 1981.

By that time, the decision had been made to add Uranus and Neptune to Voyager 2's list of targets. The intrepid spacecraft flew by the former at a distance of 81,500 kilometers on 24 January 1986, and passed the latter at a distance of just 4951 kilometers on 25 August 1989.

The Voyagers continue to transmit data on space conditions beyond the planets. At this writing, Voyager 1 is 144.7 Astronomical Units (AU) from the Sun (one AU is defined as the mean distance from Earth to the Sun, or about 149.6 million kilometers - for comparison, the most distant planet in the Solar System, Neptune, is on average 30.1 AU from the Sun). Radio signals traveling at the speed of light (299,792 kilometers per second) need more than 20 hours to reach it. Voyager 2, which dove below the plane of the Solar System after departing Neptune, is 119.8 AU from the Sun; radio signals need about 16 hours, 42 minutes to reach it.

Voyager 1 became the first spacecraft to pass beyond the heliosphere, the bubble of space where solar particles and fields are dominant, in August 2012. Voyager 2 joined it at the edge of interstellar space in November 2018.

Sources

Summary of the Voyager Program, NASA Office of Space Science and Applications, January 1967.

On Mars: Exploration of the Red Planet 1958-1978, NASA SP-4212, Edward Clinton Ezell and Linda Neumann Ezell, NASA, 1984, pp. 85-86, 101-103, 117-118.

Voyager: Mission Status (https://voyager.jpl.nasa.gov/mission/status/#where_are_they_now - accessed 4 February 2019).

Saturn IB/Centaur (http://heroicrelics.org/info/saturn-i-and-ib/saturn-ib-centaur.html - accessed 6 February 2019).

More Information

Centaurs, Soviets, and Seltzer Seas: Mariner 2's Venusian Adventure (1962)

Things To Do During a Venus/Mars/Venus Piloted Flyby Mission (1968)

Lunar Viking (1970)

The Challenge of the Planets, Part Three: Gravity

Another Look at Staged Reentry: Janus (1962-1966)

The M2-F1 lifting-body glider (left) and its successor, the M2-F2. Of the experimental lifting bodies NASA built and flew, the Janus spacecraft would have most resembled these pioneering aircraft. Image credit: NASA.

In 2013, while spending a gleeful Sunday afternoon searching through old patent applications (don't judge me), I stumbled upon an intriguing design for a piloted spacecraft using "staged reentry." I wrote about it on my old Beyond Apollo blog on the WIRED website.

In 2017, I expanded that post with more context details on the history of lifting body research and better illustrations and posted it on this blog (see the link at the end of this post). At the time, the patent application, filed in January 1964 by TRW engineers C. Cohen, J. Schetzer, and J. Sellars and granted in December 1966, remained my only source of information on the staged reentry concept.

No longer. One benefit of working at a university is that journal articles formerly locked up behind paywalls, out of reach of independent scholars on a budget, are now readily accessible. Last month, while spending a gleeful Sunday afternoon searching through the 1965 volume of The Journal of Spacecraft & Rockets, I stumbled upon a staged reentry design named for Janus, the two-faced Roman god of endings and beginnings. Closer examination confirmed that the Janus spacecraft was indeed the unnamed spacecraft of the 1966 patent.

Janus is an apt name for the proposed spacecraft design, because its most unique features are related to launch and (especially) landing - that is, the beginning and ending of its mission. The name was first used in a confidential May 1962 TRW Space Technology Labs report by I. Spielberg and C. Cohen.

Spielberg, whose name does not appear on the patent application, presented the staged reentry concept at the first conference of the American Institute of Aeronautics and Astronautics in Washington, DC (29 June-2 July 1964) along with Cohen, whose name was the only one to appear on the 1962 report, the 1964 presentation, the 1965 Journal of Spacecraft & Rockets paper based on the presentation, and the 1966 patent. It seems likely, given his continuous involvement, that Cohen originated and championed the Janus staged reentry concept.

Patent applications are not engineering papers; or, perhaps, one may say that lousy is the engineering paper that reads like a patent application. In addition to being more readable, the 1965 Spielberg and Cohen paper provides considerably more detail than the patent application.

The TRW engineers explained the rationale behind the staged reentry concept:

A manned system should provide precision and flexibility in its landing characteristics. It should be capable of routine launch and routine return without a large recovery task force. Moreover, these criteria must be satisfied without curtailing payload volume or weight or reducing the reliability of reentry protection. In general, these requirements conflict, since efficient entry vehicles (e.g., blunt lifting bodies) have poor landing characteristics, whereas vehicles that land well (winged configurations) tend to have low volumetric efficiency and serious reentry design problems. The staged reentry concept. . . circumvents the difficult design compromises that otherwise must be made to ensure good landing qualities, high volumetric efficiency, and desirable reentry characteristics.

The Janus spacecraft comprised two parts that would separate in flight. The largest part was a 26.8-foot-long, 16-foot-wide, 10-foot-deep "pod." Designed to carry three astronauts, it was an 11,660-pound half-cone lifting body with flat aft and top surfaces and a curved, blunt nose.

The TRW engineers described the pod's double-walled structure. Its inner hull, the pressure vessel, would be manufactured from aluminum sheet. The outer hull would be made of aluminum honeycomb with aluminum alloy plates for added strength. Aluminum frames with "I" and "Z" cross-sections would link the two hulls. An ablative heat shield (that is, one that chars and erodes to carry away heat) would cover the aluminum honeycomb, and low-density insulation would fill the space between the inner and outer hulls.

Cutaway view of the Janus spacecraft. Image credit: U.S.Patent Office.

The other part of the Janus spacecraft was a 4000-pound delta-wing jet aircraft measuring 21 feet long, 13.3 feet across its wings, and 5.33 feet tall. It would include twin downward facing rudder fins and a belly-mounted air intake feeding a Continental 356-23 turbojet engine. The engine could be started at 18,000 feet of altitude using ambient air or at up to 45,000 feet with supplemental oxygen. Cruise speed at 30,000 feet was about Mach 0.6 (370 knots) and range with a full load of 77 gallons (500 pounds) of jet fuel was 200 nautical miles.

The flat top of the small jet would form the largest part of the top of the lifting body. The jet's underside would form the "ceiling" of the lifting body's 860-cubic-foot pressurized internal volume; that is, the plane's belly, including its air intake, would protrude into the main crew living and working space. Ceiling height, though variable, would measure no less than seven feet.

The jet would ride on three rod-like "pneumatic/explosive actuators" attached to the pod. Latches would link the actuators to holes in the plane's nose and on the underside of its wings. Other latches would anchor the jet's wing leading edges.

Spielberg and Cohen recognized that creating an air-tight seal between jet and pod would pose significant design challenges. They proposed an inflatable or "fluted" (grooved) gasket, presumably made of a rubberized fabric. They admitted that their seal system, though "feasible," was not yet "optimized."

Atop a booster on the launch pad, jet and lifting body would point their noses at the sky. Spielberg and Cohen envisioned that the flat aft surface of the pod would sit atop a launch vehicle adapter that would measure 10 feet in diameter where it linked to the pod. The bottom of the adapter would match the larger diameter of the launch vehicle upper stage.

Just before launch, the astronauts would pass through a hatch in the side of the adapter. Overhead they would see the flat aft surface of the pod, which would include a round hatchway. The hatchway would lead into a cylindrical airlock just large enough to hold one space-suited astronaut. A round hatch in the airlock would in turn lead into the pod. In the near-vacuum of low-Earth orbit, the airlock would permit astronauts to spacewalk without depressurizing the pod.

Forward-facing crew couches would be arranged single-file, one behind the other, in a line beneath the jet fuselage. This would place the astronauts one above the other on the launch pad.

The pod would contain the Janus spacecraft main control console. Intended for use in orbit, it would be mounted on the pod's aft interior wall next to the inner airlock hatch. This would place it out of reach of the reclining astronauts. Critically important controls would be mounted on couch arms.

The patent application said nothing about possible launch vehicles, but in their paper Spielberg and Cohen specified two candidates: Titan III (probably the Titan IIIC variant) and Saturn C-1 (otherwise known as Saturn I). The former could boost 28,000 pounds into the 140-nautical-mile orbit required to forestall orbital decay long enough to carry out a two-week Janus mission; the latter, 20,000 pounds. The total weight of the Janus spacecraft (crew, pod, and jet) was 15,660 pounds, so in theory it could transport 12,340 pounds of unspecified payload if launched on a Titan III and 4340 pounds if launched on a Saturn C-1.

It is worth noting that Janus included no docking mechanism, and that was it not designed to perform significant maneuvers in space (apart from a deorbit burn). This ran against the grain of NASA requirements in the first half of the 1960s, when both Gemini and Apollo were under development. Though it could carry a hefty payload, it could not deliver it anywhere. Presumably, this meant that its payload would always take the form of equipment that would remain inside the pod. It is conceivable, however, that small payloads could be tossed out its airlock and larger ones assembled outside by spacewalkers — Spielberg and Cohen did not, however, suggest these possibilities.

A successful mission would begin with launch from Cape Kennedy on Florida's east coast. The launch vehicle would ascend vertically, then roll toward the southeast on a course that would avoid Caribbean islands and South America. About 10 minutes after liftoff, Janus would reach its operational orbit and separate from the upper stage of its launch vehicle. The crew would then unstrap from their couches and begin work in the pod's large pressurized volume.

They would also work in the jet cockpit. The jet's glass canopy, which would stand higher than the rest of the Janus spacecraft's mostly flat top, would make the cockpit the prime spot for conducting Earth and astronomy observations.

Spielberg and Cohen proposed a novel method for entering and leaving the cockpit. The crew couches would each be mounted on a pair of rails, and the underside of the jet's fuselage would include automatic doors. Operating controls on the couch arms would cause the doors to open and the couch to ride the rails from pod to cockpit and vice versa. The TRW engineers explained that a single set of couches shared between the pod and the jet would save weight, though with the large Janus payload capability this would probably have been a minor concern.

The crew would breathe a 47% oxygen/53% nitrogen air mix at a pressure of 7.5 pounds per square inch. Water for crew needs would come from fuel cells, the primary task of which would be to generate 2.5 kilowatts of continuous electricity by combining liquid hydrogen and liquid oxygen. Fluid circulating in pipes in the pod walls would gather and carry waste heat from the pressurized volume and the fuel cells to a radiator mounted on the pod's aft surface.

For return to Earth, the astronauts would sit in their couches in the pod, turn the Janus spacecraft using small thrusters so that its aft end pointed in its direction of motion, and ignite its 1100-pound solid-propellant retrorocket. After burnout, the retrorocket casing would be cast off and Janus reoriented with its nose aimed forward. Descent toward 400,000-foot reentry altitude would last 14 minutes. At start of reentry, the Janus spacecraft would be moving at about 250 feet per second (fps).

Reentry would be a balancing act. The lifting-body pod would need trim flaps for stability and steering; however, four trim flaps attached in pairs to the bottom edge of its flat aft surface would tend to tip its nose down (that is, give it a negative angle of attack). This would permit hot reentry plasma to course over the pod's top surface, destroying the jet canopy. At the same time, the pod would be tail-heavy, raising its nose and making it aerodynamically unstable.

Spielberg and Cohen proposed a two-part solution: cautiously reshaping the pod's nose and packing its triangular nose volume with heavy subsystems (for example, the fuel cells and their reactants). The former would tend to level its angle of attack and the latter, they calculated, would shift its center of gravity forward to a point 54% of its length (about 11 feet) aft of the pod's nose, yielding a slightly "nose up" angle of attack. The pod's nose would thus bear the brunt of reentry heating, and no reentry plasma would reach the jet canopy.

The Janus spacecraft would reenter at a very shallow angle (just 2°). It would thus shed speed gradually in a low-density atmosphere, preventing maximum deceleration from exceeding 1.9 gravities. An automated attitude control system would operate the trim flaps and small thrusters to maintain stability as the pod descended.

During reentry, the outer hull, safe behind its heat shield, would maintain a temperature below 600° Fahrenheit (F). The inner hull would remain at 70° F throughout the mission. The hot outer hull would tend to expand. If the aluminum frames linking the inner and outer hulls were rigidly attached at both ends, differential expansion would tear them apart. To avoid this, Spielberg and Cohen proposed that the frames be attached to the outer hull by flexible connections and to the inner hull by rigid ones.

A little less than 12 minutes after reentry start, at an altitude of about 120,000 feet, the Janus spacecraft would slow to a velocity of about 50 fps. Deprived of lift, its angle of descent would increase in a little over a minute to about 55°.

At 50,000 feet of altitude, the Janus spacecraft would slow to subsonic speed and begin to lose stability. The mission commander would activate the motors that would raise the three couches into the jet cockpit. Beneath the astronauts' feet, the fuselage doors would close and seal. At 45,000 feet, the spacecraft would slow to Mach 0.9, and jet separation from the pod could occur.

Separation would begin with a command to fire explosive bolts. This would release the latches linking the jet to the pod so that the three rod-like pneumatic actuators could extend, pushing the jet away from the pod with a jolt. The pressure seal would be breached, exposing the pod's interior to the outside environment.

The commander would ignite the jet's engine and fly at a cruise altitude of 30,000 feet to a waiting airfield up to 200 nautical miles away. The jet would land on a nose wheel and skids attached to the ends of its rudder fins. The pod, meanwhile, would deploy parachutes from its aft surface and descend to a landing on its nose.

In the event of an abort on the launch pad or during first-stage operation, a pair of solid-propellant abort rocket motors mounted on the pod's aft surface outside the adapter linking it to the launch vehicle would ignite to boost the Janus spacecraft up and away. The motors would propel it to an altitude of 6600 feet in 19 seconds. If no first-stage abort took place, the abort motors would eject after second-stage ignition so that the launch vehicle would not need to carry their weight to orbit.

The deorbit rocket motor would play two possible abort roles: in an abort off the launch pad, it could be ignited after the twin abort rocket motors burned out to boost the Janus spacecraft higher and farther downrange, providing more time for successful jet separation; it would also become the primary abort rocket motor after the twin abort motors ejected.

An abort within 200 nautical miles of Cape Kennedy would see the commander separate the jet from the pod as during a normal descent, then fly back to the launch site. The jet could also remain attached to the pod throughout the abort, in which case the entire Janus spacecraft would descend nose down on parachutes to a landing or splashdown at 25 feet per second. Spielberg and Cohen included 1030 pounds of recovery gear in the Janus spacecraft mass budget.

Down-range aborts — for example, during second stage flight — would occur over open ocean, placing land — never mind suitable airports — outside the jet's 200-nautical-mile range. Spielberg and Cohen noted that the lifting body would during second-stage flight be high enough to use its trim flaps and steering thrusters to maneuver closer to land. This would, they judged, permit jet separation within 200 miles of airfields on Caribbean islands or in northeastern South America.

Here is the link to my staged reentry post based only on the Cohen, Schetzer, and Sellars patent of December 1966. In addition to a summary history of lifting body development in the United States, the post contains detailed labeled drawings from the patent application.

Sources

"Janus: A Manned Orbital Spacecraft with Staged Re-Entry," I. N. Spielberg and C. B. Cohen, The Journal of Spacecraft & Rockets, Volume 2, Number 4, July-August 1965, pp. 531-536.

Patent No. 3,289,974, "Manned Spacecraft With Staged Re-Entry," C. Cohen, J. Schetzer, and J. Sellars, TRW, 6 December 1966.

Related Links

X-15: Lessons for Reusable Winged Spaceflight (1966)

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

What if a Shuttle Orbiter Struck a Bird? (1988)

NASA Johnson Space Center's Shuttle II (1988)