28 October 2016

George Landwehr von Pragenau's Quest for a Stronger, Safer Space Shuttle

The Space Shuttle Challenger and its booster system moments before they were destroyed. The plume of flame from its malfunctioning SRB is clearly visible. Image credit: NASA
The Space Shuttle Orbiter Challenger was minding its own business on 28 January 1986, working hard to get its seven-member crew and its large satellite payload to low-Earth orbit, when its booster stack betrayed it and everything began to go badly wrong. First, hot gas within its right Solid Rocket Booster (SRB) began to burn through a seal meant to contain it. Soon, a fiery plume gushed from the side of the SRB, robbing it of thrust, and reached out menacingly toward the side of the brown External Tank (ET) and the strut linking the lower end of the SRB to the ET (image at top of post). The plume broke though the ET's foam insulation and aluminum skin, then the strut pulled free of the weakened ET.

Challenger fought back as the ET began to leak liquid hydrogen fuel. It swiveled (the aerospace term is "gimballed") the three Space Shuttle Main Engines (SSMEs) in its tail as it struggled to stay on course. The plume from the SRB, meanwhile, glowed brighter as it began to burn hydrogen leaking from the ET. At the same time, the SRB began to rotate around the single strut left holding it to the ET. That strut was located not far from the Orbiter's gray nose, near the conical top of the errant SRB.

Throughout these events, Challenger's last crew remained oblivious to the technological drama taking place around them. This was just as well, since they had no way to escape what was about to happen to them.

When Challenger at last lost its struggle against its own booster stack, significant events were separated by tenths or hundredths of seconds. Immediately after the right SRB's lower strut came free, the entire Shuttle stack lurched right. Mike Smith, in Challenger's pilot seat, had time for a startled "Uh-oh" less than a second after the lurch. The ET's dome-shaped bottom then fell away, freeing all the hydrogen fuel it contained. The right SRB's pointed nose slammed into and crushed the top of the ET, freeing liquid oxygen oxidizer. The escaped hydrogen blossomed into a fireball that encompassed Orbiter, rapidly disintegrating ET, and SRBs.

Yet the Orbiter Challenger did not explode. Instead, it broke free of what was left of the ET and began a tumble. The aerodynamic pressures the Orbiter experienced as its nose pointed away from its direction of flight were more than sufficient to snap it into several large pieces: the crew cabin, the satellite payload, the wings, the SSME cluster. They emerged from the fireball more or less intact. The SRBs, still firing, flew out of the fireball, tracing random trails across the blue Florida sky until a range safety officer commanded them to self-destruct. The Orbiter's wreckage, meanwhile, plummeted into the Atlantic within sight of the Florida coast.

NASA recovered the bodies of the crew and portions of the wreckage, including the section of the right SRB that had leaked hot gas. The wreckage was turned over to accident investigators.

This 1975 NASA illustration depicts the basic components of the Space Shuttle system. The Orbiter includes three Space Shuttle Main Engines (left) and two Solid Rocket Boosters, one of which is mostly hidden behind the External Tank. The tank comprises (from right to left) a small tank for dense liquid oxygen, a drum-shaped structural support ring/tank separator below the Orbiter's nose, and a large tank for low-density liquid hydrogen.
During a Shuttle launch, the three SSMEs ignited first. This caused the twin SRBs, the bases of which were mounted to the launch pad by explosive bolts, to flex along their entire length away from the SSMEs, then straighten out again just as they ignited. O-ring seals between the cylindrical segments making up the SRBs often became unseated during flexure, then had to reseat to contain hot gases after SRB ignition. Accident investigators concluded that failure of one of those seals doomed Challenger. Even more damning, they found that partial seal failures followed by hot exhaust leaks had occurred on pre-Challenger flights – and had been disregarded by NASA managers.

After Challenger, NASA and its contractors redesigned the SRB joints and seals, added crew pressure suits and a limited crew escape capability, and banned potentially unsafe practices and payloads from Shuttle missions. Yet the U.S. civilian space agency might have gone much farther when it sought to enhance Space Shuttle safety after Challenger.

Even before the accident, NASA had at its disposal redesign proposals that could have made the Shuttle stack stronger and safer. In 1982, for example, George Landwehr von Pragenau, a veteran engineer at NASA's Marshall Space Flight Center, filed a patent application – granted in 1984 – for a Shuttle stack design that would have made the Challenger accident impossible.

Born and educated in Austria, von Pragenau joined the von Braun rocket team in Huntsville, Alabama, in 1957. He became a U.S. citizen in 1963. He specialized in rocket stability and flight effects on rocket behavior. He had, for example, been part of the team that found the cause of the "pogo" oscillations that crippled Apollo 6, the second unmanned Saturn V-launched Apollo test mission (4 April 1968).

In the conventional Shuttle stack, von Pragenau explained, SRB thrust was transmitted through the forward SRB attachment points to a reinforced intertank ring between the ET's top-mounted liquid oxygen tank and its liquid hydrogen tank.  He considered this "indirect routing" of thrust loads to be perilously complex. SSME thrust loads, for their part, passed through the Orbiter to its twin aft ET attachment points on the large fragile hydrogen tank.

By the time he filed his 1982 patent application, von Pragenau had spent almost a decade thinking about how the Shuttle stack might be rearranged to reduce weight and aerodynamic drag, increase stability, simplify paths through which the force of rocket thrust was transmitted, and provide greater structural strength. His 1984 patent was, in fact, not his first aimed at Shuttle improvement.

Von Pragenau's 1974 alternative Shuttle stack. Image credit: U.S. Patent Office

In 1974, von Pragenau had filed a patent – granted the following year – in which he proposed a more slender, more vertically oriented Shuttle stack; that is, one that would mimic conventional rocket designs in which stages are stacked one atop the other. He linked the twin SRBs side by side. Moving the tank for dense liquid oxygen from the ET's nose to its tail placed its concentrated mass nearer the base of the stack, improving in-flight stability. He then mounted the SRBs to the Orbiter's belly and perched the ET atop the SRB/Orbiter combination. SRB and SSME thrust loads were conveyed through struts to meet at the ET's flat, reinforced base.

Von Pragenau's 1982 Shuttle stack design was in some ways a less radical departure from the existing Shuttle design than was his 1974 design. He left the SRBs, ET, and Orbiter in their normal positions relative to each other, but made other significant changes. As in his 1975 patent, he moved the liquid oxygen tank from the ET's nose to its tail and brought the SRBs closer together to improve stability. The liquid oxygen tank became skinny, cylindrical, and almost as long as the Orbiter and SRBs attached to it. The liquid hydrogen tank, fat with low-density fuel, von Pragenau mounted atop the oxygen tank, partially overhanging the Orbiter and SRBs.

Von Pragenau's 1982 Shuttle stack redesign. The numeral "15" points to the rigid thrust structure framework. "34," "35," "36" are Solid Rocket Booster attachment fixtures. These would link to slide rails ("31" and "32") that would run the length of the liquid oxygen tank ("20"). "19" is the liquid hydrogen tank. Image credit: U.S. Patent Office 
Von Pragenau could not tolerate flexing SRBs. He proposed to mount a slide rail on either side of the liquid oxygen tank. Three attachment fixtures on each SRB would link to the slide rails, helping to ensure rigidity. When the SRBs depleted their propellant, pyrotechnic bolts would fire, freeing them to slide backwards down the rails and fall neatly away from the Orbiter/ET stack.

The most important feature of von Pragenau's redesign was a rigid framework – a thrust structure – that would link the bottom of the SRBs just above their rocket nozzles. In addition to holding the SRBs rigidly in place, the thrust structure would transmit SRB thrust loads to the bottom of the ET oxygen tank, which would rest atop the center of the thrust structure. When the spent SRBs slid away from the Orbiter/ET stack, they would take the thrust structure with them.

Side view of Von Pragenau's 1982 Shuttle stack concept. Image credit: U.S. Patent Office
Von Pragenau's concepts apparently exerted little influence on NASA's post-Challenger recovery effort. A likely explanation is that neither of his proposals – if they were known to decision-makers at all – was deemed affordable. In addition to extensive changes in manufacturing tooling, both proposals would have required modifications to the Vehicle Assembly Building, the twin Complex 39 Shuttle pads at Kennedy Space Center (KSC), and even the barge that delivers ETs to KSC. Instead of beefing up the existing Shuttle, NASA studied designs for new shuttles which, for lack of funding, remained firmly in the low-cost realm of CAD drawings, conference papers, and conceptual artwork.

On 1 February 2003, the Space Shuttle claimed another crew. The oldest Orbiter, Columbia, was heavier than her sisters Atlantis, Discovery, and Endeavour, which limited the amount of cargo she could deliver to the International Space Station (ISS). For this reason, NASA largely relegated to Columbia the few remaining non-ISS missions - for example, Hubble Space Telescope servicing.

As they began Earth-atmosphere reentry at 8:44 a.m. Eastern Standard Time after a nearly 16-day life sciences mission, the seven STS-107 astronauts on board Columbia were unaware that, during ascent, a piece of ice-impregnated insulating foam nearly a meter wide had broken free from the ET and impacted their spacecraft's left wing. Ice and foam had broken free from ETs before, but the damage they caused was, after cursory examination, deemed acceptable by Shuttle Program managers. This time, however, the impact opened a hole up to 10 inches wide in the Orbiter's left wing leading edge.

Hot plasma generated during reentry entered the hole and began to destroy Columbia's left wing from the inside out. Observers along the Orbiter's flight path, which cut across the southern tier of U.S. states, reported unusual flashes. Meanwhile, members of the STS-107 crew on Columbia's Flight Deck observed and recorded on video flashes visible outside their windows. In the recovered video, the astronauts appear to realize that the flashes were unusual but show no signs of panic.

Much as Challenger had before it, Columbia fought bravely against the forces destroying it. Onboard computers took account of increased drag on the left side of the Orbiter and sought to compensate to keep it on the flight path. At 8:59 a.m. Eastern Standard Time, however, Columbia tumbled and disintegrated over northeast Texas.

Both of von Pragenau's design concepts placed all or part of the ET above the Orbiter, so one might argue that they would not have prevented a failure resembling that which killed the STS-107 crew. On the other hand, one can be forgiven for speculating that a U.S. civilian space agency provided with the means after Challenger to rebuild the Shuttle system to make it safer might also have evolved an organizational culture more prone to investigating and less prone to tolerating recurring flight anomalies.

Von Pragenau retired from NASA in 1991 after more than 30 years of service. He remained involved in engineering efforts at NASA Marshall Space Flight Center during his retirement. He died two years after the Space Shuttle's final flight (STS-135, 8-24 July 2011), on 11 July 2013, at the age of 86.


Patent No. 4,452,412, Space Shuttle with Rail System and Aft Thrust Structure Securing Solid Rocket Boosters to External Tank, George L. von Pragenau, NASA Marshall Space Flight Center, 15 September 1982 (filed), 5 June 1984 (granted)

Patent No. 3,866,863, Space Vehicle, George L. von Pragenau, NASA Marshall Space Flight Center, 21 March 1974 (filed), 18 February 1975 (granted)

Hampton Cove Funeral Home Obituaries: George Landwehr von Pragenau - http://www.hamptoncovefuneralhome.com/fh/obituaries/obituary.cfm?o_id=2150841&fh_id=13813 (accessed 27 October 2016)

NASA History: Columbia Accident Investigation Board - http://history.nasa.gov/columbia/CAIB.html (accessed 29 October 2016)

NASA History: Challenger STS 51-L Accident - https://www.hq.nasa.gov/office/pao/History/sts51l.html (accessed 29 October 2016)

More Information

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

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

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

What If Galileo Had Fallen to Earth? (1988)

Dreaming a Different Apollo, Part Two

24 October 2016

Talking to the Farside: A 1963 Proposal to Use the Apollo Saturn V S-IVB Stage as a Radio Relay

The moon's Farside hemisphere: a mosaic of Lunar Reconnaissance Orbiter images. Image credit: NASA 
A Saturn S-IVB stage awaits shipment from the Douglas Aircraft plant in California. Various red protective covers would be removed before flight. Image credit: NASA
The S-IVB rocket stage played several important roles in NASA's 1960s and 1970s piloted space programs. The 58.4-foot-long, 21.7-foot-wide stage, which comprised a single restartable J-2 rocket engine, a forward liquid hydrogen tank, and an aft liquid oxygen tank, served as the second stage of the two-stage Apollo Saturn IB rocket and the third stage of the three-stage Apollo Saturn V.

The Saturn IB S-IVB's J-2 engine would ignite at an altitude of about 42 miles and burn until it placed a roughly 23-ton payload into low-Earth orbit. After that, it would shut down and the spent stage would separate. The Saturn V S-IVB's J-2, on the other hand, would ignite twice to accelerate the stage and its payload: once for 2.5 minutes at an altitude of about 109 miles and again for six minutes about two and a half hours later. The first burn would place the S-IVB and payload into a low parking orbit between 93 and 120 miles above the Earth; the second would place the S-IVB and payload onto a path that would intersect the moon, about 238,000 miles away, about three days after Earth launch. Departure for the moon was called Translunar Injection (TLI).

During Apollo moon landing missions, the payload was a three-man Command and Service Module (CSM) and a Lunar Module (LM) moon lander. The astronauts would separate the CSM from the four-segment shroud linking it to the S-IVB about 40 minutes after TLI. They would then maneuver it clear of the S-IVB and turn it end-for-end so that its nose pointed back at the top of the stage. The shroud segments, meanwhile, would hinge back and separate to reveal the LM spacecraft mounted atop the S-IVB. The crew would guide the CSM to a docking with the LM; then, about 50 minutes after docking, the joined CSM and LM would move away from the S-IVB. The stage would then vent residual propellants and ignite auxiliary rocket motors to place itself on a course away from the CSM-LM combination.

Schematic representation of Apollo 8 mission events (not to scale). Apollo 8 was the first mission to inject the Saturn V S-IVB stage into orbit around the Sun. Image credit: NASA 
Roughly 60 hours after launch from Earth, the docked CSM and LM would enter the moon's gravitational sphere of influence. About 12 hours later, they would pass behind the moon over the Farside, the lunar hemisphere that is turned always away from Earth. There, out of visual, radar, and radio contact with Earth, the astronauts would ignite the CSM's Service Propulsion System (SPS) main engine to slow the CSM and LM so that the moon's gravity could capture them into lunar orbit. This critical maneuver was called Lunar Orbit Insertion (LOI). Orbital mechanics dictated that LOI should occur more or less over the center of the Farside.

A few hours later, two astronauts would separate from the CSM in the LM. They would fire the moon lander's throttleable descent stage engine - again over Farside, as dictated by orbital mechanics - to begin their descent toward their pre-selected landing site on Nearside, the lunar hemisphere that is turned always toward Earth. Following a safe landing and a period of surface exploration (about one Earth day for the earliest Apollo landing missions), the LM ascent stage would lift off.

About two hours later - again over the moon’s hidden hemisphere – the CSM would rendezvous and dock with the LM. The lunar landing crew would rejoin the CSM pilot, the astronauts would cast off the LM ascent stage, and preparations would begin to ignite the SPS to depart lunar orbit for Earth. The critical lunar-orbit departure maneuver, also carried out over Farside, was called Trans-Earth Injection (TEI).

The S-IVB stage would, meanwhile, swing past the moon and enter orbit around the Sun. Although it would travel to the moon and beyond, as of early 1963 no one had identified any further role for the S-IVB after the CSM and LM separated from it.

The silhouette at left shows the position of the S-IVB third stage in the Saturn V stack. The cutaway illustration (right) shows the interstage faring that linked the S-IVB to the Saturn V S-II second stage and the relative sizes of the liquid oxygen and liquid hydrogen propellant tanks. Helium stored in spherical tanks push propellants into the J-2 engine. Image credit: NASA
For six months in 1963, engineers at The Bissett-Berman Corporation in Santa Monica, California, working on contract to NASA Headquarters, studied another use for the Apollo-Saturn V S-IVB stage. In a series of "Apollo Notes" prepared beginning in March of that year, they identified a need for a relay satellite to enable Earth-based radar tracking of the Apollo CSM and LM while they carried out crucial maneuvers over the Farside. They then proposed that the spent S-IVB be outfitted to serve as a relay.

The first note, authored by H. Epstein and based on a concept suggested by L. Lustick, proposed a radar relay satellite for tracking the Apollo CSM during LOI and CSM rendezvous and docking with the LM ascent stage. Epstein and Lustick's satellite would include an omnidirectional antenna for near-lunar operations and, for "deeper phase operation," a steerable four-foot parabolic dish antenna.

The relay satellite, Epstein wrote, would separate from S-IVB stage along with the Apollo LM and CSM after TEI, then separate from the CSM-LM combination before LOI. It would fly past the moon on a path that would keep both Earth and most of the Farside in view during LOI and CSM-LM rendezvous and docking. The omni antenna would relay radar from Earth until the satellite was 40,000 kilometers beyond the moon, then the dish would take over.

The second Bissett-Berman Apollo Note, dated 16 April 1963, raised the possibility of placing a "special purpose relay package" on the S-IVB stage. The package would either remain attached to the stage or would eject from it when activated. The Apollo Note's author, L. Lustick, attributed the S-IVB relay concept to one Dr. Yarymovych, whose organizational affiliation was not stated.

For his analysis, Lustick assumed that the S-IVB would retain enough propellants for its J-2 engine to restart a third time shortly after CSM-LM separation, raising its speed by 160 feet per second. He calculated that, at the time of CSM-LM LOI, the S-IVB or ejected relay package would have in view simultaneously both Earth and more than three-quarters of the Farside hemisphere. At the time of CSM docking with the LM ascent stage, about 100 hours after Earth launch, the relay would have in view Earth and a little more than two-thirds of the Farside. Throughout the approximately 28-hour period between LOI and CSM rendezvous with the LM ascent stage, the S-IVB or ejected relay package would remain within 143,000 miles of the moon.

The S-IVB would rely for attitude control guidance on the ring-shaped Instrument Unit (IU), the Saturn V's "electronic brain." The IU, located on top of the S-IVB during launch, encircled the LM descent stage and provided attachment points for the four separable shroud segments. It was not intended to operate for more than a few hours, so would need modifications to ensure that it could reliably stabilize the S-IVB throughout the relay period.

The ring-shaped Instrument Unit (IU) rode atop the S-IVB stage on both Saturn IB and Saturn V rockets. Image credit: NASA
The Instrument Unit assembly line at the IBM plant in Huntsville, Alabama. Image credit: NASA
In an addendum to Lustick's 16 April Apollo Note dated 18 April, engineer H. Epstein looked at simplifying the S-IVB Farside Relay concept by assuming that the stage would lack attitude control while it acted as a data relay. Replacing steerable dish antennas – one for Earth-S-IVB communication and one for S-IVB-Apollo CSM communication – with two passive omnidirectional antennas would permit data relay no matter how the S-IVB stage became oriented, he wrote.

The use of relatively low-power omni antennas would produce few problems as far as Earth-S-IVB communication was concerned, for NASA could call into play large antennas on Earth to ensure reception of the weak signal. Epstein proposed increasing from four feet to five feet the planned diameter of the dish antenna on the CSM to enable it to receive data from Earth relayed through the S-IVB-CSM omni antenna. He noted, however, that, even with a larger CSM dish antenna, radio interference from the Sun might stymie the omni antenna relay concept.

An undated Apollo Note by Lustick and C. Siska explored the S-IVB Farside Relay concept in yet greater detail, and included evidence of NASA interest in the scheme: for the first time, the authors cited NASA Headquarters-imposed study requirements. The space agency told Bissett-Berman to assume that the S-IVB could increase its speed by up to 1000 feet per second for up to about seven hours after TLI, and that the maximum range between the S-IVB Farside Relay and the CSM should not exceed 40,000 nautical miles throughout the relay period.

NASA, Lustick and Ciska explained, sought to learn whether relay of voice (not only data or radar) would be possible using an S-IVB Farside Relay during the roughly 30-hour period between LOI (a "particularly important" time to have voice relay capability, NASA asserted) and CSM-LM ascent stage rendezvous and docking. The authors found that boosting the S-IVB's speed by 1000 feet per second 7.6 hours after TLI would place it on a path to relay voice between Earth and Farside from 72 hours after Earth launch until 102 hours after Earth launch, at which time the S-IVB would reach NASA's 40,000-nautical-mile operational limit. In fact, they found that the S-IVB would have Farside in view as early as 60 hours after Earth launch (this was of purely academic interest, however, because the Apollo spacecraft would not be orbiting over the Farside at that time).

Lustick and Ciska also noted that the S-IVB would pass out of sight behind the moon (that is, become occulted by the moon) as viewed from Earth 102 hours after Earth launch. They added, however, that slight adjustments in S-IVB boost direction would postpone loss of Earth contact with the S-IVB Farside Relay for long enough to ensure that voice communication could continue during CSM rendezvous with the LM ascent stage.

In Bissett-Berman's penultimate examination of the S-IVB Farside Relay concept, author Ciska noted that a 1000-foot-per-second boost could be planned for as early as TLI. This would, however, leave no propellant margin for later correction of S-IVB boost aim errors. On the other hand, S-IVB attitude control was expected to "drift" over time, making accurate boost pointing later than TLI increasingly unlikely. Furthermore, boil-off of liquid hydrogen from the S-IVB stage would rapidly reduce the amount available to fuel a later boost. Both of these factors favored an "all-or-nothing” early boost.

Ciska noted also that, regardless of the S-IVB boost aim point selected, the stage would pass out of sight behind the moon as viewed from Earth for roughly half an hour at some point along its curved path during the voice relay period. For a 1000-foot-per-second boost applied 7.6 hours after TLI with an aim point slanted 100° relative to a line linking the Earth and moon, for example, the half-hour occultation would occur about 99 hours after Earth launch.

The last Bissett-Berman Apollo Note devoted to the S-IVB Farside Relay concept, also by Ciska and dated 20 August 1963, was an extension of his earlier note. In it, he examined an S-IVB boost 4.15 hours after TLI and considered further the impact of boost direction. Ciska did not attempt to plot S-IVB attitude drift or liquid hydrogen boiloff rates; nevertheless, he proposed as realistic a 700-foot-per-second boost 4.15 hours after TLI with an aim point slanted 100° relative to the Earth-moon line. Following this maneuver, the S-IVB Farside Relay would pass out of view of Earth for about 30 minutes a little more than 83 hours after Earth launch and would pass beyond NASA’s 40,000-nautical-mile limit about 103 hours after launch.

The S-IVB stage converted into the Skylab Orbital Workshop retained its IU and liquid oxygen tank - the latter launched dry and used as a dumpster - but lost its J-2 engine and saw its liquid hydrogen tank converted into a large habitable volume (note astronaut on lower deck for scale). Image credit: NASA
Though the Bissett-Berman S-IVB relay proposal was not taken up, S-IVB stages did play key non-propulsive roles in NASA's manned space program. NASA converted Saturn IB S-IVB 212 into the Skylab 1 Orbital Workshop. Skylab was launched into low-Earth orbit on the last Saturn V to fly and staffed by three three-man crews in 1973-1974. Saturn V S-IVB 515, originally intended to boost the Apollo 20 mission to the moon, was converted into the Skylab B workshop, but was not launched and became a walk-through display in the National Air and Space Museum in Washington, DC.

Of the 10 Apollo Saturn V S-IVBs that departed low-Earth orbit between 1968 and 1972, half reached orbit about the Sun and half were intentionally crashed into the moon. The Apollo 8, Apollo 9, Apollo 10, Apollo 11, and Apollo 12 S-IVBs departed the Earth-moon system, while those that boosted Apollo 13, 14, 15, 16, and 17 out of low-Earth orbit toward the moon were intentionally impacted on the moon's Nearside. The impacts were part of a science experiment: the seismic waves their impacts generated registered for hours on seismometers left behind on the lunar surface by earlier Apollo crews, helping to reveal to scientists the structure of the moon's deep interior.

The irregular ray crater blasted out by the impact of the Apollo 13 S-IVB stage in 1970 as imaged by NASA's Lunar Reconnaissance Orbiter in 2010. Image credit: NASA
The Apollo 12 S-IVB, launched on 14 November 1969, flew past the moon too fast to receive a gravity-assist boost into orbit about the Sun, so circled the Earth in a loosely bound distant orbit until 1971, when, through gravitational perturbations from Earth, Sun, and moon, it finally escaped into solar orbit. It orbited the Earth again for about a year in 2002-2003, during which time it was observed and mistakenly identified as a near-Earth asteroid. Spectral analysis revealed the presence of titanium-based paint, however, confirming the object's identity as Apollo 12's errant S-IVB.


Apollo Note No. 35, Lunar Far Side Relay Technique – Some Basic Radar Considerations, H. Epstein, The Bissett-Berman Corporation, 21 March 1963

Apollo Note No. 44, Back of Moon Relay Trajectories, L. Lustick, The Bissett-Berman Corporation, 16 April 1963

Addendum to Apollo Note No. 44, Communications Capability of Unstabilized S-4-B Satellite Relay System, H. Epstein, The Bissett-Berman Corporation, 18 April 1963

Apollo Note No. 87, Section 7, Far-Side Relay, L. Lustick and C. Ciska, The Bissett-Berman Corporation, no date

Apollo Note No. 90, Further Examination of Far-Side Relay Trajectories, C. Ciska, The Bissett-Berman Corporation, 6 August 1963

Apollo Note No. 97, Minimum Boost Velocity Requirement for Far-Side Relay, C. Ciska, The Bissett-Berman Corporation, 20 August 1963

More Information

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

What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)

Solar Flares and Moondust: The 1962 Proposal for an Interdisciplinary Science Satellite at Earth-moon L4

15 October 2016

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

Lunar Exploration Program candidate landing sites. Of these, the Apollo Program would reach only Fra Mauro; Apollo astronauts would, however, visit five other sites not labeled here. Please click on image to enlarge. Image credit: NASA/Arizona State University/DSFPortree
Bellcomm, Inc., based near NASA Headquarters in Washington, DC, was carved out of Bell Labs in 1962 to provide technical advice to NASA's Apollo Program Director. NASA rapidly expanded Bellcomm's bailiwick to take in nearly all NASA Office of Manned Space Flight planning.

In a January 1968 report, Bellcomm planners N. Hinners, D. James, and F. Schmidt proposed a lunar mission series designed to bridge a gap in NASA plans they believed existed between the first piloted "Early Apollo" moon flights and sophisticated Apollo Applications Program (AAP) lunar expeditions. They declared that their Lunar Exploration Program was "based upon a reasonable set of assumptions regarding hardware capability and evolution, an increase in scientific endeavor, launch rates, budgetary constraints, operational learning, lead times, and interaction with other space programs," as well as "the assumption that lunar exploration will be a continuing aspect of human endeavor."

Hinners, James, and Schmidt envisioned a series of 14 lunar missions in four phases. Phase 1 would span the period from 1969 through 1971. The five Phase 1 missions were approximately equivalent to the Early Apollos. They would launch at least six months apart to give engineers and scientists adequate time to learn from each mission's successes and failures and enable them to apply their new knowledge to subsequent missions. Phase 1 would begin with Lunar Landing Mission (LLM)-1, the historic first Apollo moon landing.

The LLM-1 Lunar Module (LM) would alight on one of the moon's flat, relatively smooth basaltic plains. Called since the 17th century "maria" (Latin for "seas" - the singular is "mare"), they appear as mottled gray areas on the moon's white face. They cover about 20% of the moon's Earth-facing Nearside hemisphere, but are scarce on the hemisphere the moon turns always away from Earth (its Farside). LLM-1 and the other Phase 1 missions would each have several back-up near-equatorial Nearside mare landing sites, enabling them to land in safe places regardless of how their planned launch dates might slip.

Almost any mare would do for LLM-1, Hinners, James, and Schmidt argued, because the first piloted landing mission would emphasize engineering, not science. LLM-1 would test the LM, lunar space suits, and other Apollo systems ahead of more ambitious Phase 1 missions. If all went as planned, the LLM-1 crew would stay on the moon for 22 hours and carry out two short moonwalks.

LLM-1 would follow a "free-return" flight path that would guarantee that the Apollo Command and Service Module (CSM) could loop around the moon and return to Earth without propulsion in the event that its Service Propulsion System (SPS) main engine failed en route to the moon. The SPS was meant to adjust the CSM/LM combination's course during flight to and from the moon, slow the CSM and LM so that the moon's gravity could capture them into lunar orbit, and boost the CSM out of lunar orbit to return to Earth. The Bellcomm planners noted that use of the free-return trajectory would greatly limit the percentage of the moon's surface a lunar mission could reach.

The LMs constructed for Phase 1 missions would each be capable of delivering two astronauts. their space suits, and up to 300 pounds of payload to the lunar surface. This would include geologic tools for collecting up to 50 pounds of lunar rock and dust samples for return to Earth. Missions LLM-2 through LLM-5 would, in addition, each include an Apollo Lunar Scientific Experiment Package (ALSEP) – a cluster of geophysical experiments – for deployment on the moon. The ALSEPs would monitor the moon and return data after the astronauts returned to Earth.

LLM-2 through LLM-5 would see astronauts perform geological traverses on foot to spots up to several kilometers from the LM. Meanwhile, the CSM Pilot, alone in lunar orbit, would photograph the moon's surface through the CSM's small windows.

LLM-2, like LLM-1, would follow a free-return trajectory and remain for 22 hours at a mare landing site. It would, however, add a third moonwalk.

LLM-3 would abandon the free-return trajectory so that it could reach a fresh crater on a mare. The crater, the Bellcomm planners explained, would serve as a natural "drill hole." Studies of both natural and human-made craters on Earth had shown that the LLM-3 astronauts would find the oldest rocks – those excavated from deepest beneath the surface – on the crater's rim. The astronauts would explore the lunar surface for longer than 22 hours but less than 36 hours.

LLM-4 would be similar to LLM-3, but would be targeted to land at one of the many widely scattered mare "wrinkle ridges." In 1968, some scientists (notably, Nobel Laureate Harold Urey) still attributed these sinuous raised features to salty water escaping from reservoirs beneath the moon's surface, but today we know that they formed when lava that filled the mare nearly 4 billion years ago buckled as it cooled. Some may link or follow traces of ancient landscape drowned when the lava welled up from within the moon.

LLM-5, the final Phase 1 flight, would see an LM land at a mare site bordering a Highlands region. The Highlands of the moon, the light-colored areas on the moon's disk, are ancient cratered terrain. The LLM-5 astronauts would squeeze four moonwalks into their 36-hour mission.

The Bellcomm planners' four Lunar Exploration Program Phase 2 missions would commence about two years after LLM-5 and span 1972-1973. Upgrades to Apollo hardware and operations in Phase 2 would permit in-depth exploration of specific unique landing sites selected primarily for scientific interest. Among the upgrades that Hinners, James, and Schmidt proposed was variable Earth-to-moon flight time or time spent in lunar orbit prior to landing. This operational flexibility was intended to permit an Extended LM (ELM) spacecraft to reach its pre-planned target site even if launch from Earth were delayed for several days.

The Phase 2 lunar-surface astronauts would perform six moonwalks at each landing site. The ELM would land 1300 pounds of payload. Phase 2 CSMs would carry prototype remote sensors to test their feasibility ahead of their operational use in Phases 3 and 4.

The first Phase 2 mission, LLM-6, would see an ELM spend three days at Tobias Mayer in the extensive Oceanus Procellarum ("Ocean of Storms") mare region. Its crew would deploy an ALSEP and explore on foot a sinuous rille (canyon), a dome (possible volcano), and a fresh crater with a surrounding dark halo (possible volcanic vent). LLM-7 would be similar to LLM-6, but would land at a linear rille site designated I-P1.

LLM-8 would see the introduction of the Lunar Flying Unit (LFU), a one-person rocket flyer. Bellcomm targeted LLM-8 to the Flamsteed Ring, an ancient crater mostly submerged by lava during the formation of Oceanus Procellarum. At the time Hinners, James, and Schmidt selected it, the Flamsteed Ring was suspected of being an extrusive volcanic feature called a "ring dike."

LLM-9, similar to LLM-8, would visit Fra Mauro, a site known for its domes and rilles, which geologists interpreted as signs of recent volcanism. Fra Mauro would later come to be seen (correctly) as a large geologic unit made up of ejecta from the enormous impact that blasted out Mare Imbrium, the right "eye" of the "Man in the Moon." Cone crater, a natural drill hole in the Fra Mauro Formation, would become the target of Apollo 13 (and, after that mission failed to land on the moon, Apollo 14).

Phase 3 of Bellcomm's Lunar Exploration Program would comprise a single lunar-orbital survey mission in 1974. Because it would include no lunar landing, it received no LLM number. The mission would, for all practical purposes, mark the start of advanced AAP lunar flights. A solar-powered sensor module based on a planned AAP Earth-resources observation module design would replace the LM. By spending 28 days (one lunar day-night period) in lunar polar orbit, the mission's augmented CSM could pass over the entire lunar surface in daylight, enabling the crew to conduct global high-resolution film photography. When time came to return to Earth, the astronauts would load exposed film into their CSM, then undock from the sensor module and leave it behind in lunar orbit to function as an independent satellite.

Hinners, James, and Schmidt explained that Lunar Exploration Program Phases 1 and 2 missions would gather "ground truth" data on the composition and structure of the moon's surface. These data would enable scientists to interpret Phase 3 mission results in preparation for Lunar Exploration Program Phase 4, which would span 1975-1976.

Phase 4 would see two "Dual Launch" Lunar Surface Rendezvous and Exploration Missions. Each Dual Launch mission would require two Saturn V rockets, two augmented CSMs, an LM-derived unmanned Lunar Payload Module (LPM), and an augmented ELM bearing one LFU.

LLM-10 and LLM-11 together would make up the first Dual Launch mission. LLM-10 would deliver an unmanned LPM to either Hyginus Rille or the Davy crater chain. The LLM-10 crew, orbiting the moon in their augmented CSM, would remotely pilot the LPM's final approach to the landing site to help to ensure that it would set down within 100 meters of a predetermined target point. Before returning to Earth, the LLM-10 astronauts would "photo locate" the landed LPM from lunar orbit to aid the follow-on LLM-11 crew in finding it. They would also release a science subsatellite into lunar orbit.

LLM-11 would see two astronauts wearing advanced "hard" (mostly non-fabric) space suits land their augmented ELM near the pre-landed LPM for a two-week stay. They would draw on the LPM's 8000-pound payload to conduct in-depth exploration of their complex landing site.

The LPM payload would include lunar surface transportation systems: specifically, one LFU and a one-man, 2000-pound Local Scientific Survey Module (LSSM) moon rover. Other LPM cargo would include: a spare hard suit; a core drill attached to the LPM for obtaining a 100-foot drill core; an LSSM-transportable core drill for obtaining 10-foot cores at scattered sites; life support consumables for replenishing those on board LLM-11's ELM; and an advanced lunar-surface geophysical station with a 10-year design life.

Hinners, James, and Schmidt selected the Marius Hills as the landing site for LLM-12 and LLM-13, their second Dual Launch mission pair and the final missions of their Lunar Exploration Program. The Marius Hills were popular with planners for their many domes and other features of possible volcanic origin.

The Bellcomm planners anticipated that, after the LLM-13 crew returned to Earth, even more ambitious AAP moon missions would commence. These might lead to establishment of a lunar surface outpost. They were, of course, incorrect; it became clear soon after they completed their report that lunar exploration would not become "a continuing aspect of human endeavor."

This NASA map, published at the time of the Apollo 17 mission in December 1972, shows the six Apollo landing sites. All landings occurred within an area the size of the western United States between the Mississippi River and the Rocky Mountains (on a world with about as much surface area as Europe and North America combined). If Apollo 17 had landed in St. Louis, Missouri, Apollo 16 would have landed in northeastern Texas; Apollo 15 on the Kansas-Nebraska border; Apollo 14 and Apollo 12 in New Mexico; and Apollo 11 in Oklahoma.
The earliest Apollo landing missions (Apollo 11, Apollo 12, and Apollo 14) were roughly equivalent to Bellcomm's LLM-1, LLM-2, and LLM-3, though their crews performed fewer moonwalks. Apollos 15, 16, and 17, by contrast, were mainly shaped by the certain knowledge that Apollo lunar exploration would soon conclude. They became unlike any of Bellcomm's proposed missions as NASA sought to accomplish as much lunar exploration as possible at minimal cost before political support for the Apollo Program ran out.

The final Apollo lunar mission, Apollo 17 (December 1972), saw astronauts Eugene Cernan and Harrison Schmitt explore the Highlands-bordering Taurus-Littrow mare site for about three days. They drove an electric-powered Lunar Roving Vehicle (LRV). Meanwhile, Ron Evans, on board the Apollo 17 CSM in lunar orbit, used a suite of sensors to map a broad swath of the moon's surface and released a science subsatellite.


"A Lunar Exploration Program – Case 710," N. Hinners, D. James, and F. Schmidt, TM-68-1012-1, Bellcomm, 5 January 1968

To a Rocky Moon: A Geologist's History of Lunar Exploration, D. Wilhelms, University of Arizona Press, 1993

The Geologic History of the Moon, U.S. Geological Survey Paper 1348, D. Wilhelms, J. McCauley, and N. Trask, USGS, 1987

More Information

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

Rocket Belts and Rocket Chairs: Lunar Flying Units

"Assuming That Everything Goes Perfectly Well in the Apollo Program. . ." (1967)

Harold Urey and the Moon (1961)