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What If an Apollo Saturn Rocket Exploded on the Launch Pad? (1965)
02 August 2015 David S. F. Portree

Abort Mode One-Alpha. Image credit: NASA

No member of the Saturn rocket family ever killed an astronaut. Two Saturn rocket designs were rated as safe enough to launch humans into space: the two-stage Saturn IB, which flew nine times between February 1966 and July 1975, and the giant Saturn V, which flew 12 times with three stages between November 1967 and December 1972, and once with two stages in May 1973. The 200-foot-tall Saturn IB flew five times with astronauts on board (Apollo 7, Skylab missions 2, 3, and 4, and the Apollo-Soyuz Test Project), while the 363-foot-tall Saturn V launched astronauts 10 times (Apollo missions 8 through 17).

Although man-rated, Saturn V rockets experienced four close calls. The first occurred on 4 April 1968, during the unmanned Apollo 6 test flight, when instability in the rocket’s fiery exhaust produced violent fore-and-aft shaking known as "pogo." Two of the five J-2 engines in the rocket’s S-II second stage shut down and pieces broke away from the streamlined shroud linking the Apollo Command and Service Module (CSM) to its S-IVB third stage. The CSM comprised the conical Command Module (CM), which carried the crew, and the Service Module (SM) which included electricity-generating fuel cells and the CSM's main engine, the Service Propulsion System (SPS). The Apollo 6 S-IVB's single J-2 engine under-performed, placing the stage and CSM into a lopsided orbit, then refused to restart.

Had the Apollo 6 CSM carried astronauts, pogo might have injured them; even if they had reached orbit unscathed, the S-IVB engine failure would have scrubbed their moon mission. As it was, flight controllers separated the unmanned CSM from the crippled S-IVB stage and used its SPS as a backup engine for completing the mission's Earth-atmosphere reentry test.

Apollo 12 experienced an even more perilous ascent. Following launch in a rainstorm on 14 November 1969, lightning struck its Saturn V 36.5 seconds and 52 seconds after liftoff. The lightning strikes knocked the Apollo 12 CSM Yankee Clipper's three electricity-generating fuel cells offline, along with its Apollo Guidance Computer and most other electrical systems.

The Saturn V's IBM-built Instrument Unit – its ring-shaped electronic brain, located atop its S-IVB third stage – soldiered on without a hiccup, however, safely guiding the giant rocket into Earth parking orbit. The Apollo 12 crew of Charles Conrad, Alan Bean, and Richard Gordon carried out a successful lunar landing mission and returned to Earth on 24 November. As they cast off their CSM's drum-shaped SM prior to reentry, they saw that it bore scorch marks from the lightning strikes it endured during launch.

NASA would rename the "Uprated Saturn I" (right) depicted in this 1966 illustration the Saturn IB. Image credit: NASA

Image credit: NASA

The third Saturn V close call saw the unexpected return of pogo. During ascent to orbit on 11 April 1970, the middle engine of the Apollo 13 S-II stage began to rapidly oscillate fore and aft, then shut down two minutes early. The four remaining J-2 engines burned for longer than planned to compensate. Apollo 13 astronauts Jim Lovell, Fred Haise, and Jack Swigert subsequently left Earth orbit for the moon, but an oxygen tank explosion in their CSM, the Odyssey, scrubbed their moon landing. They used their Lunar Module (LM) moon lander, the Aquarius, as a lifeboat and returned safely to Earth on 17 April.

The final Saturn V to fly, intended originally for Apollo 20 but launched unmanned with the Skylab Orbital Workshop (OWS) on top in place of an S-IVB stage and the Apollo CSM and LM spacecraft, survived a close call on 14 May 1973. A design flaw caused Skylab's meteoroid shield to tear loose 63 seconds into the flight. As the disintegrating shield tumbled down the length of the accelerating rocket, it tore at least one hole in the interstage adapter that linked the OWS to the S-II second stage and apparently damaged the system for separating the ring-shaped interstage adapter that linked the S-II with the S-IC first stage. This meant that the 18-foot-long adapter did not separate from the S-II three minutes and 11 seconds into the flight as planned. The S-II stage had excess capacity, however, so dutifully hauled its unplanned five-ton cargo into Earth orbit.

Apollo 12 might easily have ended in a Launch Escape System (LES) abort. The image at the top of this post shows the LES in action during Pad Abort Test-2 on 29 June 1965. The LES was a 33-foot-tall tower containing three solid-fueled rocket motors. The largest was the Launch Escape Motor, which had four exhaust nozzles. The tower stood atop the Boost Protective Cover (BPC), a conical shell that covered the CM.

There were four successive abort modes during Saturn V ascent to Earth orbit. Abort Mode One was in effect on the launch pad, during S-IC first-stage operation, and during the 30 seconds following S-IC separation, by which time the Saturn V would have reached an altitude of about 56 miles. As the Saturn V climbed toward space, the aerodynamic environment around it changed - the air grew thinner, the rocket moved faster, and increasingly it tilted so that it flew parallel to Earth's surface. As the environment changed, the abort modes changed to compensate.

Had it occurred, the Apollo 12 abort would have taken place during the first part of Abort Mode One. Known as Abort Mode One-Alpha, it began 45 minutes before scheduled launch and continued until about 42 seconds after liftoff, by which time the rocket would have climbed nearly vertically to an altitude of 3000 meters (9800 feet).

In the event of a catastrophic Saturn V failure while Abort Mode One-Alpha was in effect, the 155,000-pound-thrust Launch Escape Motor would have pulled the BPC and CM free of the SM, which would have remained mounted on the doomed rocket. Meanwhile, the small side-mounted solid-propellant rocket motor near the LES's nose, the Pitch Control Motor, would have ignited to push the LES-BPC-CM combination eastward, toward the Atlantic, so that it would be well clear of the Saturn V. The CM would then have dropped free of the BPC and deployed its three large parachutes to descend gently into the Atlantic within sight of Kennedy Space Center.

The Apollo 8 Saturn V rocket - the first Saturn V to carry a precious human cargo - stands on Launch Pad 39A at Kennedy Space Center, Florida. A Saturn V explosion before or during liftoff would have destroyed most of the structures visible in this image. Image credit: NASA

27 April 1972: The Apollo 16 CM descends to a splashdown in the Pacific Ocean after an 11-day voyage to the moon. A CM descending into the Atlantic after an LES abort would have appeared very similar. Image credit: NASA

In August 1965, R. High and R. Fletcher, engineers at NASA's Manned Spacecraft Center in Houston, Texas, calculated the characteristics of Saturn IB and Saturn V launch pad explosions to aid LES development. Of particular concern, they explained, was the damage an explosion fireball's heat might do to the CM's nylon main parachutes. In their report they did not, however, reach specific conclusions about parachute heat damage.

High and Fletcher found that calculating the characteristics of launch pad failures was not an exact science, in large part because there were so many variables to be taken into account, and also because no rocket as large as the Saturn V had ever exploded. They explained that "many of the [fireball] parameters may defy an accurate theoretical treatment."

For their analysis, they assumed that all propellants in the exploding rocket would contribute to forming a fireball. This would occur, they explained, because "large overpressures from detonations and the intense heat from both detonations and burning would cause failure of any propellant tanks not initially involved." If a Saturn V exploded on the pad at launch, 5,492,000 pounds of RP-1 refined kerosene, liquid oxygen (LOX), and liquid hydrogen would contribute to its fireball. For a Saturn IB pad explosion, 1,110,000 pounds of RP-1, LOX, and liquid hydrogen would fuel its fireball.

High and Fletcher wrote that the fireball from a Saturn rocket launch pad failure would expand in a "nearly fixed location." For the Saturn V, the fireball would expand to a diameter of 1408 feet. The Saturn IB fireball would expand to 844 feet. The fireballs would thus completely engulf the Saturn launch pads. For both rockets, fireball surface temperature would attain 2500° Fahrenheit, and heat would be felt up to a mile from the launch pad.

A fireball would begin to rise when it reached its maximum diameter. Fireball ascent would commence about 20 seconds after a Saturn V launch pad explosion and about 10 seconds after a Saturn IB explosion, High and Fletcher calculated. The Saturn V fireball would reach an altitude of about 300 feet in 15 seconds, while the Saturn IB fireball would climb 300 feet in 11 seconds. The Saturn V fireball would persist at its maximum diameter for 34 seconds, while the Saturn IB fireball would last for 20 seconds. The fireball would then begin to cool and dissipate.

Though they assumed for their calculations that all propellants in an exploding Saturn rocket would contribute to its fireball, High and Fletcher wrote that some would likely be "spilled on the ground, creating residual pools which [would] burn for relatively long periods of time." This was, they judged, especially likely if a launch pad failure began with the rupture of the fuel tank in the Saturn V's S-IC first stage. The ruptured tank would spill RP-1 onto the pad, then the oxidizer tank located above it would rupture and mix liquid oxygen with the burning fuel, triggering an explosion. They added that "the residual fire and extreme heat of the fireball [would] prevent approach to the ground area enveloped by the fireball for an unknown period."


Estimation of Fireball from Saturn Vehicles Following Failure on Launch Pad, NASA Program Apollo Working Paper No. 1181, R. High and R. Fletcher, NASA Manned Spacecraft Center, Houston, Texas, 3 August 1965

Skylab 1 Investigation Report, Hearing Before the Subcommittee on Manned Space Flight of the Committee on Science and Astronautics, U.S. House of Representatives, Ninety-Third Congress, First Session, 1 August 1973, U.S. Government Printing Office, 1973

Apollo Experience Report - Launch Escape Propulsion Subsystem, NASA Technical Note D-7083, N. Townsend, NASA, March 1973, pp. 1-7

Where No Man Has Gone Before: A History of Apollo Lunar Exploration Missions, W. David Compton, NASA SP-4214, 1989, pp. 177-178

How Apollo Flew to the Moon, W. David Woods, Springer-Praxis, 2008, pp. 69-73

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Source: What If an Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

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What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)
19 August 2015 David S. F. Portree

238,000 miles from home - Earth as viewed by the Apollo 8 astronauts in lunar orbit, Christmas Eve 1968. Image credit: NASA

The three-man crew of Apollo 8 – Commander Frank Borman, Command Module Pilot James Lovell, and Lunar Module Pilot William Anders – was the first to leave Earth on a Saturn V rocket. They departed Cape Kennedy, Florida, on 21 December 1968, and left Earth orbit for the moon about two and a half hours later.

Though its target was the moon, the Apollo 8 mission included no Lunar Module (LM). The manned lunar lander had suffered production delays; this was understandable, given that no one had ever before built a vehicle for landing humans on another world. NASA's planned mission sequence for manned Apollo missions had begun with a low-Earth orbit (LEO) test of the Command and Service Module (CSM) on Apollo 7 (11-22 October 1968). This was to have been followed in short order by an LEO test of the CSM and LM, then a CSM/LM test flight in higher Earth orbit. During the next mission in the sequence, astronauts would test the CSM and LM in lunar orbit, then the first Apollo lunar landing attempt would take place. NASA designated these five increasingly ambitious missions C, D, E, F, and G.

Putting off the next Apollo flight - the D mission - until the LM was ready might have placed in jeopardy attainment of Apollo's goal of landing a man on the moon ahead of the Soviet Union and before the end of the 1960s. Because of this, in late summer 1968, NASA began to look at a modified mission sequence. The C-prime mission, which would see the Apollo 8 CSM orbit the moon without an LM, was made public on 12 November 1968, three weeks after Apollo 7 successfully accomplished the C mission. The mission would test many CSM elements of the lunar landing mission and the world-wide system of radio dishes and transceivers NASA had created for Apollo lunar mission communications and tracking.

The C-prime mission had been the subject of intense debate at the highest levels of NASA, for it meant traveling to the moon without the backup life support and propulsion systems the LM could provide. Those in favor of launching the C-prime mission were helped by intelligence reports that the Soviet Union might launch a man around the moon during December 1968. Such a mission might steal Apollo's thunder; though it would merely swing around the moon and fall back to Earth, it would enable the Soviets to claim that they had launched a man to the moon first.

Eleven hours after launch, the Apollo 8 crew carried out a course correction. This required that they ignite the CSM's Service Propulsion System (SPS) main engine for the first time. Had the SPS not functioned as planned, the crew could have adjusted their course using the CSM's cluster of four Reaction Control System (RCS) thruster quads. The CSM would then have swung around the moon without entering orbit and fallen back to Earth.

Partial cutaway of Apollo CSM spacecraft. Image credit: NASA

The 20,500-pound-thrust SPS, an AJ-10-137 rocket engine manufactured by Aerojet, was located at the aft end of the CSM. Other AJ-10 variants had propelled Vanguard, Atlas-Able, and Thor-Able launch vehicles. The SPS burned hydrazine/UDMH fuel and nitrogen tetroxide oxidizer. Chemically inert helium gas pushed the propellants into the engine's ignition chamber. Hydrazine/UDMH and nitrogen tetroxide are hypergolic propellants; that is, they ignite on contact with each other. The resulting hot gas then vented through a large engine bell, which swiveled to help steer the CSM.

The Apollo 8 SPS performed almost perfectly during the 21 December course correction burn and during a second burn 61 hours after launch designed to help ensure that the Apollo 8 CSM would enter the orbit about the moon planned for it. Three hours later, Apollo 8 was given a "go" to enter lunar orbit. The spacecraft passed behind the moon, out of radio contact with Earth, and the crew ignited the SPS for the third time. It burned for a little more than four minutes, slowing the Apollo 8 CSM enough for the moon's gravity to capture it into orbit.

The Apollo 8 CSM orbited the moon 10 times over the next 20 hours. Then, on 25 December 1968, about 89 hours after launch, the crew ignited the SPS behind the moon to begin the journey home to Earth. The rocket motor performed flawlessly during this critically important burn, which NASA dubbed Trans-Earth Injection (TEI).

Two and a half days later, on 27 December, the CSM split into two parts. The Service Module (SM), which contained the SPS, separated from the Command Module (CM), which held the crew. The former burned up in Earth's atmosphere as planned, while the latter, protected by a heat shield, maneuvered in the upper atmosphere to reduce heating and deceleration, deployed parachutes, and splashed safely into the Pacific Ocean.

Four days after Apollo 8's triumphant return, A. Haron and R. Raymond, engineers with Bellcomm, NASA's Washington, DC-based planning contractor, completed a brief study of what might have happened had the SPS not ignited for the TEI burn. Specifically, they looked at how long a crew might survive in lunar orbit following a TEI failure.

Haron and Raymond found that the "first constraint" on the crew's endurance would be depletion of the CSM's supply of lithium hydroxide (LiOH) canisters. The square canisters were used in pairs to remove carbon dioxide exhaled by the crew from the CSM's pure oxygen atmosphere. During Apollo 8, the crew had traded a saturated LiOH canister for a fresh one every 12 hours, thus expending two per day.

The Bellcomm engineers calculated that, at that rate, the crew would use up the last of the 16 LiOH canisters launched on board the CSM 96 hours after TEI failure. They would then grow drowsy and become unconscious as carbon dioxide built up in the crew cabin. Had TEI failed on Apollo 8, Borman, Lovell, and Anders would probably have suffocated on 29 December.

Haron and Raymond noted, however, that LiOH canisters might be changed less often without harming the crew. They cited a November 1968 Manned Spacecraft Center study that had shown that LiOH canisters could absorb carbon dioxide for up to 37 hours. If a stranded Apollo CSM crew began to ration its LiOH canisters immediately after TEI failure, they would be able to stretch their survival time to 148 hours. In that case, the Apollo 8 crew would have survived until New Year's Eve – the day Haron and Raymond completed their study.

If NASA elected to include 10 additional LiOH canisters on CSMs bound for the moon, and if immediately after TEI failure the astronauts powered down the CSM so that its three fuel cells remained just barely operational, then endurance might be stretched to about two weeks, the Bellcomm team estimated. The fuel cells, manufactured by Allis Chalmers, operated by combining liquid hydrogen and liquid oxygen reactants to produce electricity and water. Electricity from the fuel cells powered the CSM through most of the mission. The crew drank the water; it was used also for cooling in the CSM's Environmental Control System (ECS) and electronics. Excess water could be dumped overboard.

Haron and Raymond looked briefly at the possibility of switching off two fuel cells to conserve reactants. If this were done, then the remaining fuel cell might operate for up to three weeks after TEI failure. However, a single fuel cell would probably not produce enough electricity to operate all CSM systems vital to the crew's continued survival, some of which were not immediately obvious. As an example, Bellcomm cited the RCS quads: the astronauts would need to use them to maneuver the CSM to keep its ECS radiators in shadow to conserve cooling water. In addition, the LiOH canister shortage would remain. "The feasibility of extending survival time to as much as three weeks cannot be confirmed at this time," Haron and Raymond wrote.

The Bellcomm study was mainly of academic interest, since a crew stranded in orbit around the moon, 238,000 miles from Earth, could not have been rescued even if they did survive for two or three weeks. NASA did not have the ability to maintain a rescue Saturn V rocket and CSM on standby.

The space agency would have cause to recall the brief Bellcomm study twice during subsequent Apollo missions. During Apollo 13 (11-17 April 1970), an oxygen tank exploded in the CSM Odyssey, badly damaging its SM. Because the explosion happened while the mission was en route to the moon, its crew, commanded by Apollo 8 astronaut James Lovell, was able to use the LM Aquarius as a lifeboat. They employed its descent engine in place of the SPS. The docked spacecraft flew behind the moon, where the crew fired the LM descent engine to adjust their course and speed their return to Earth.

On Apollo 16 (16-27 April 1972), as the CSM Casper orbited the moon, it suffered a malfunction in the system used to swivel the SPS engine bell. The LM Orion, which had already undocked in preparation for landing, stood by in lunar orbit until the SPS problem was understood, then landed several hours behind schedule.

Had it been judged necessary, NASA could have scrubbed the Apollo 16 landing. Orion would then have redocked with Casper. The astronauts could have used Orion's descent engine and (if necessary) Casper's RCS quads to perform TEI. Going ahead with the landing eliminated that option; the descent engine used most of its propellants to land on the moon, then was left behind on the surface with the rest of the LM descent stage. The LM ascent stage, with its smaller engine, returned to lunar orbit with virtually dry tanks. This left only the SPS available for TEI.

As a precaution, NASA moved up Apollo 16's TEI burn by a day in the hope that, should the SPS misbehave, the crew and engineers on Earth would have adequate time to find a solution and ensure a safe, if delayed, return to Earth. As it turned out, the Apollo 16 SPS performed a flawless TEI burn.


NASA News Press Kit, Project: Apollo 8, 15 December 1968

"Consumables Affecting Extended CSM Lifetime in Lunar Orbit," Case 320, A. Haron and R. Raymond, Bellcomm, Inc., 31 December 1968

Apollo 8: "A Most Fantastic Voyage," Lt. Gen. Sam C. Phillips, National Geographic, May 1969, pp. 593-631

Apollo 13: "Houston, We've Had a Problem," NASA EP-76, 1970

NASA Mission Report: Apollo 13, A Successful Failure, 20 May 1970

How Apollo Flew to the Moon, W. David Woods, Springer Praxis, 2008, pp. 236-238

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Source: What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)
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What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)
24 August 2015 David S. F. Portree

Image credit: NASA

George Mueller left private industry to become NASA's new Associate Administrator for Manned Space Flight in September 1963. He immediately asked John Disher and Adelbert Tischler, two veteran NASA engineers not directly involved in Apollo, for an independent assessment of the moon program. On 28 September, they told Mueller that it could not achieve President Kennedy's goal of a man on the moon by 1970. They estimated that NASA might be able to carry out its first manned moon landing in late 1971.

Mueller took drastic action. When he joined NASA, the Apollo flight-test plan was based on the philosophy of incremental testing, which meant that untried rocket stages would launch only dummy stages and dummy spacecraft. On 29 October 1963, Mueller informed his senior managers that Apollo test flights would henceforth use complete systems. Mueller's directive meant that, when the Saturn V S-IC first stage flew for the first time, it would be as part of a complete 363-foot-tall three-stage Saturn V. The new "all-up" approach would, it was hoped, slash the number of test flights needed before the Saturn V could launch astronauts to the moon.

George Mueller. Image credit: NASA

All-up Saturn V testing, today hailed as a visionary and heroic step, made many Apollo engineers nervous. The Saturn V was the largest rocket ever developed. It had engines of unprecedented scale and power: the F-1 engines in the 33-foot-diameter S-IC first stage, which burned RP-1 kerosene fuel and liquid oxygen, remain today the largest ever flown. The J-2 engines in the top two stages, the 33-foot-diameter S-II second stage and the 22-foot-diameter S-IVB stage, gulped down temperamental liquid hydrogen and liquid oxygen propellants. Cautious engineers could see many opportunities for trouble, and they were aware that problems they could not foresee might be the most difficult to solve. Many believed that NASA should have in place backup plans in case the Saturn V suffered development delays.

Eighteen months after Mueller's announcement, E. Harris and J. Brom, engineers with The RAND Corporation think tank, proposed one such back-up plan. Their brief report, originally classified "Secret," looked at how NASA might accomplish a manned moon landing by 1970 if the Saturn V could not be certified as safe enough to launch astronauts.

Harris and Brom's backup plan would see the Apollo Saturn V lift off without astronauts on board. It would expend its S-IC first stage and S-II second stage in turn, then its S-IVB third stage would place itself plus unmanned Apollo Command and Service Module (CSM) and Lunar Module (LM) spacecraft into parking orbit about the Earth. Because it would carry no crew, the CSM would need no Launch Escape System (LES) tower on its nose.

The astronauts would reach Earth orbit separately in a ferry CSM launched atop a two-stage Saturn IB rocket. The ferry CSM would carry a special drogue docking unit on its nose for linking up with the unmanned CSM's nose-mounted probe docking unit. The special drogue, the only new system required for RAND's backup plan, would need about one year and "perhaps several million dollars" to develop.

The top of the Apollo 13 Lunar Module Aquarius. The red arrow points to the concave drogue docking unit. Image credit: NASA

The astronauts would dock with and transfer to the lunar mission CSM in Earth orbit, then would cast off the ferry CSM. The remainder of their mission would occur as in NASA's Apollo plan (image at top of post). The astronauts would restart the S-IVB stage to perform Trans-Lunar Injection (that is, to leave Earth orbit for the moon). After S-IVB stage shutdown, they would detach the CSM from the Spacecraft Launch Adapter (SLA) shroud that linked the bottom of the CSM to the top of the S-IVB. The SLA, made up of four segments, would peel back and separate, revealing the LM. The CSM would then dock with the drogue docking unit on top of the LM and pull the moon lander free of the spent S-IVB stage.

The RAND engineers declined to recommend whether the unmanned Saturn V or the manned Saturn IB should be launched first. They noted that liquid hydrogen fuel in the Saturn V's S-IVB stage would boil and escape at a rate of 700 pounds per hour; the stage would thus need to be restarted within 4.5 hours of reaching parking orbit if it were to retain enough propellants for Trans-Lunar Injection. They noted that deletion of the 2900-pound LES would make the unmanned Saturn V that much lighter, so its S-IVB stage could be loaded with an extra 2900 pounds of liquid hydrogen; that is, enough to permit it to loiter in low-Earth orbit for nearly 10 hours. Extending the loiter time further would demand a complex and costly S-IVB stage redesign.

Launching the crew first would avoid the S-IVB stage loiter-time constraint. Harris and Brom noted that, though the Apollo lunar mission was scheduled to last only from seven to 10 days, NASA planned a 14-day Earth-orbital Gemini mission by the end of 1965 to certify that astronauts could withstand long space flights. Assuming that the Gemini flight confirmed that humans could endure 14 days in weightlessness, then the ferry CSM crew could in theory wait for from four to seven days for the unmanned Saturn V to join them in Earth orbit. Harris and Brom recommended that, if the unmanned Saturn V became delayed so that the astronauts waiting in orbit could not accomplish a lunar mission and return to Earth within 14 days of first reaching space, then they should carry out an unspecified backup Earth-orbital mission in the ferry CSM so that their flight would not be wasted.

NASA officials did not take up the Harris and Brom proposal, though for a time in 1968 they might have wished that they had. The first unmanned Saturn V test flight, Apollo 4, lifted off on 9 November 1967. In keeping with Mueller's 1963 directive, it included complete S-IC, S-II, and S-IVB stages, plus a CSM with LES. Because LM development had hit snags, a dummy LM rode inside its SLA. The eight-hour Earth-orbital mission was an unqualified success.

Troubled flight: Apollo 6 unmanned Saturn V test, 4 April 1968. Image credit: NASA

Apollo 6 was, however, another story. On 4 April 1968, two minutes into its unmanned flight, the second Saturn V to fly began to shake back and forth along its long axis. Dubbed "pogo" by engineers, the violent oscillations tore pieces off the SLA and damaged one of the S-II's five J-2 engines. Following S-II ignition, the engine under-performed and shut down prematurely, then a control logic flaw caused a healthy S-II engine to shut down. The remaining three S-II engines burned for a minute longer than planned to compensate for the two failed engines. The S-IVB's single J-2 engine then burned for 30 seconds longer than planned to reach a lopsided Earth orbit. Two orbits later, the engine refused to restart.

The pogo oscillations might have injured astronauts; the S-IVB failure would certainly have scrubbed their flight to the moon. Post-flight analysis showed, however, that the pogo and engine failures had relatively simple fixes. After intense internal debate, NASA decided in October 1968 that the third Saturn V should launch Apollo 8 astronauts Frank Borman, James Lovell, and William Anders to the moon. The giant rocket performed flawlessly, placing the Apollo 8 CSM on course for lunar orbit on 21 December 1968.


"Apollo Launch-Vehicle Man-Rating: Some Considerations and an Alternative Contingency Plan (U)," Memorandum RM-4489-NASA, E. D. Harris and J. R. Brom, The RAND Corporation, May 1965

The Apollo Spacecraft: A Chronology, Volume II, NASA SP-4009,  Mary Louise Morse & Jean Kernahan Bays, NASA Scientific and Technical Information Office, 1973, pp. 104-106

Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles, NASA SP-4206, Roger Bilstein, NASA, 1980, pp. 347-363

Apollo: The Race to the Moon, Charles Murray & Catherine Bly Cox, Simon & Schuster, 1989, pp. 153-162

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

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If an Apollo Lunar Module Crashed on the Moon, Could NASA Investigate the Cause? (1967)
04 October 2015 David S. F. Portree

All alone in the gray: the Apollo 17 Lunar Module Challenger photographed by its crew from a distance of about two miles. Image credit: NASA

The early piloted Apollo missions were a rapid series of test flights. Apollo 7 (11-22 October 1968), the first manned Apollo, saw a Command and Service Module (CSM) spacecraft and its three-man crew put through their paces in low-Earth orbit. Apollo 8 (21-27 December 1968), originally planned as a test of the CSM and the Lunar Module (LM) in high-Earth orbit, might have been postponed because the LM was not yet ready; instead, Apollo 7’s success and the perceived threat to American prestige of a Soviet manned circumlunar mission induced NASA managers to make it a lunar-orbital CSM test and a trial run for the Apollo tracking and communications network.

Apollo 9 tested the CSM, LM, and the Apollo space suit in low-Earth orbit (3-13 March 1969). Apollo 10 (18-26 May 1969) tested the CSM and LM in lunar orbit and rehearsed the Apollo lunar descent procedure down to an altitude of 50,000 feet.

Apollo 11 (16-24 July 1969), the first lunar landing attempt, was also a test flight, though it is seldom seen that way today. In an effort to make that first landing as easy as possible, engineers directed the Apollo 11 LM Eagle to the northern Sea of Tranquility, one of the flattest stretches of lunar equatorial terrain scientists could find. It was, however, also a U.S. victory in the Cold War with the Soviet Union and the first time humans had explored an alien world first-hand. Scientists and engineers fought a running battle over the degree to which scientific exploration should play a role in Apollo 11, and President Richard Nixon telephoned moonwalkers Neil Armstrong and Edwin "Buzz" Aldrin to read a celebratory speech as they stood next to the U.S. flag.

Eagle landed downrange of its planned landing site. Its overworked computer might have flown it into boulder-filled West Crater had it not been for the quick thinking of former X-15 rocket plane test-pilot Armstrong. Apollo 12 (14-24 November 1969) thus became a test of the Apollo system’s ability to make a pinpoint landing. The ability to reach a pre-determined spot on the moon was important to scientists planning Apollo geologic traverses, as well as to ensure safety. The Apollo 12 LM Intrepid landed on the Ocean of Storms, another flat plain, just 600 feet from its target, the derelict Surveyor 3 lander, which had preceded it to the site on 20 April 1967.

Any Apollo mission might have failed catastrophically far from Earth, a point driven home by the explosion on board the CSM Odyssey during Apollo 13 (11-17 April 1970). Hollywood scriptwriters notwithstanding, failure was an option during Apollo missions. Apollo pushed the limits of 1960s technology to do extraordinary things.

The Apollo Program had, in fact, claimed lives before the first Apollo spacecraft left Earth: the AS-204 (Apollo 1) fire killed Gus Grissom, Ed White, and Roger Chaffee during a launch pad training exercise on 27 January 1967, barely a month before their planned launch. Because the Apollo 1 fire occurred on the ground, engineers could take apart the AS-204 CSM piece by piece to try to trace the fire's cause. Even so, they never conclusively identified its ignition source.

A December 1964 report by R. Moore of the Project RAND think-tank anticipated that accidents that took place on the moon would be even more difficult to analyze. Moore proposed that NASA continue the Ranger lunar probe series to enable photography of lunar crash sites. The last four Rangers each carried a battery of six television cameras intended to return images to Earth as the spacecraft plummeted toward destructive impact.

If, for example, Eagle had crashed in West Crater, then NASA would have dispatched a Ranger to image the site. Ranger seemed well suited to aiding accident investigators: Ranger 7,  which struck the Ocean of Storms on 31 July 1964, had imaged features as small as 18 inches wide in its final seconds before impact.

Image credit: NASA

NASA did not act on Moore's proposal, but the concept of Apollo accident site investigations was not forgotten (or, just as likely, was discovered again). In November 1967, C. Byrne and W. Piotrowski of Bellcomm, NASA's Washington, DC-based Apollo planning contractor, wrote a memorandum in which they looked at whether a Command Module Pilot (CMP) whose moonwalking colleagues had suffered a fatal mishap on the moon might assist investigators by photographing the accident site from the CSM in lunar orbit before returning to Earth alone.

They began by acknowledging that telemetry could provide valuable accident data: they added, however, that "certain types of failure can be imagined which would not permit enough data to be transmitted to support a diagnosis." In those cases, they wrote, observation from lunar orbit might be the only way to collect data that could guide engineers in their efforts to redesign the Apollo system to avoid similar accidents.

Byrne and Piotrowski then looked at the image resolution necessary to make useful observations of an accident site on the moon. To locate and identify an intact LM, which measured a little more than 20 feet tall, images showing details as small as 10 feet across would be needed. Eight-foot resolution would be needed to determine the status of the LM's 12-foot-tall ascent stage; for example, if it had lifted off from the descent stage and then crashed on the surface. Four-foot resolution would suffice to determine whether the LM had tipped over.

The ability to resolve features as small as a yard across would enable engineers to assess landing site roughness and slope. Two-foot resolution would, they estimated, be adequate to discern astronaut bodies on the surface. One-foot resolution would reveal whether the LM landing gear had failed, "hazardous sinkage" had occurred, the LM ascent stage crew cabin lay open to vacuum, or an explosion in the LM had scattered "litter" around the landing site.

Byrne and Piotrowski then took stock of the cameras and telescopes expected to be on board the CSM during a normal lunar mission and their performance if the CSM were orbiting 80 nautical miles (n mi), 40 n mi, or 10 n mi above the accident site. They proposed that CSM propellants budgeted for rescue of astronauts on board an LM ascent stage that attained only a low orbit be used to lower the CSM's altitude for accident site observations.

The CSM's scanning telescope would, despite its name, not magnify objects, so would be of "no value" as a diagnostic tool, Byrne and Piotrowski judged. The sextant, on the other hand, could magnify objects 28 times. The Bellcomm engineers found that the sextant would offer 8.6-foot resolution at an orbital altitude of 80 n mi, 4.3-foot resolution at 40 n mi, and 1.1-foot resolution at 10 n mi. (Apollo CMPs did in fact use the sextant to spot LMs - or at least the shadows they cast - on the moon.)

The sextant was, however, designed to superimpose a pair of star images, could not be used to photograph objects, and, with a field of view only 1.8° wide, would require a highly skilled operator to spot an LM at all. This would be the case especially at lower altitudes, when the CSM would be moving fastest relative to the surface. Byrne and Piotrowski estimated that an astronaut searching the surface with the sextant at an altitude of 10 n mi would at best have 10 seconds in which to find and observe an accident site.

Apollo 12 Command Module Pilot Richard Gordon trains with cameras and lenses in a Command Module simulator before his November 1969 flight to the moon. Image credit: NASA

Byrne and Piotrowski wrote that NASA planned to include among the Apollo CSM experiments a Swedish-built Hasselblad 500EL camera with 80-millimeter (mm) f/2.8 and 250-mm f/5.6 lenses. Used with S0-243 film and the 250-mm lens, the Hasselblad 500EL could in theory take photos of the lunar surface with a resolution of 13 feet at 80 n mi of altitude, 6.5 feet at 40 n mi, and 1.6 feet at 10 n mi.

Other constraints would, however, conspire to reduce camera performance. In particular, there was the problem of image motion compensation. Experience gained through Earth photography during the Gemini V mission (21-29 August 1965) showed that astronaut movements were jerky, not smooth, when tracking and photographing targets. Jerky tracking would cause image "smear," reducing resolution.

Byrne and Piotrowski recommended that the CMP mount the Hasselblad 500EL securely in a new-design clamp or bracket at either the CSM hatch window or one of the side windows after he located the LM site. He would then fire the CSM's Reaction Control System thrusters to roll the spacecraft and keep the surface target in his camera's field of view as the CSM passed over it. This form of image motion compensation was unlikely to be perfect; for one thing, roll rate would be affected by factors beyond the CMP's control, such as the distribution and movement of liquid propellants in the CSM's tanks.

As with the sextant, time-over-target would pose a constraint. The Bellcomm engineers assumed that the CMP would need at least 30 seconds to locate the LM on the moon, 15 seconds to prepare the camera and roll the CSM, and 15 seconds for photography.

For a CSM at an altitude of 80 n mi, an LM on the lunar surface would remain in view for two minutes and 24 seconds. This was ample for photography, but at that altitude resolution would be inadequate - no better than 10 feet. At 40 n mi of altitude, the CMP could keep the LM in view for 90 seconds. At 30 n mi, he would have about 60 seconds - the minimum necessary - to find and photograph his target. Byrne and Pietrowski thus selected 40 n mi as the altitude for accident site photography.

The Bellcomm engineers looked at adding a special cartridge of high-contrast film and a 500-mm f/8 lens to the Hasselblad 500EL, and at replacing the Hasselblad 500EL with the Zeiss Contarex Special 35-mm camera and 200-mm f/4 and 300-mm f/4 lenses. These had already reached space on board Gemini V. They noted that both cameras would yield a resolution of about one yard at an altitude of 40 n mi with a secure mounting bracket and adequate image motion compensation. In the end, they favored the Hasselblad 500EL with 500-mm f/8 lens and high-contrast film because it would be about eight pounds lighter than the Zeiss camera.

Byrne and Piotrowski noted that the camera system and techniques they proposed would have uses other than accident site investigation. They might, for example, be used to photograph the landing site after a successful LM landing. This would, among other things, enable scientists to precisely locate the post-deployment position of the Advanced Lunar Scientific Experiment Package, a suite of instruments the moonwalkers would deploy some distance away from the LM. Images of the landing site might also assist geologists in understanding the context of the samples the moonwalking astronauts would return to Earth.


"A Suggestion for Extension of the NASA Ranger Project in Support of Manned Space Flight," Memorandum RM-4353-NASA, R. C. Moore, The RAND Corporation, December 1964

"Diagnostic Observation of Lunar Surface Accidents – Case 340," C. Byrne & W. Piotrowski, Bellcomm, Inc., 7 November 1967

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Source: If an Apollo Lunar Module Crashed on the Moon, Could NASA Investigate the Cause? (1967)

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North American Aviation's 1965 Plan to Rescue Apollo Astronauts Stranded in Lunar Orbit
09 October 2015 David S. F. Portree

Apollo 15 Command and Service Module Endeavour in lunar orbit. The drum-shaped portion is the Service Module and the conical portion, the Command Module. Note the Service Propulsion System rocket engine bell at upper left and the extended probe docking unit at lower right. Image credit: NASA

North American Aviation (NAA) became the prime contractor for the Apollo Command and Service Module (CSM) spacecraft on 28 November 1961. In July of the following year, the company received the unwelcome news that its spacecraft would not land on the moon. NASA had favored the Lunar-Orbit Rendezvous (LOR) mode for carrying out Apollo moon landings over Direct-Ascent or Earth-Orbit Rendezvous, both of which would have seen the CSM reach the lunar surface.

LOR made the CSM a lunar orbiter and spawned a new spacecraft: the Lunar Excursion Module (LEM) moon lander. The LEM, later redesignated the Lunar Module (LM - pronounced "lem"), would transport two astronauts from the CSM in lunar orbit to a landing site on the lunar surface and back again. The LEM was a two-part vehicle: it consisted of a descent stage with landing legs and a throttleable rocket engine and an ascent stage with a pressurized crew cabin, flight controls, a rocket engine, and a concave drogue docking unit on its roof.

LOR meant that NASA needed to develop the technologies and techniques of rendezvous and docking in lunar orbit. The LEM ascent stage would use the descent stage as a launch pad and climb to a low lunar orbit. The CSM would then move in, extend the active probe docking unit on its nose, and dock with the passive drogue on the LEM. After the LEM crew transferred back to the CSM, the ascent stage would be cast off. The CSM would subsequently ignite its large Service Propulsion System (SPS) main engine to escape lunar orbit and begin the fall back to Earth.

This image of the Apollo 16 Lunar Module Orion shows clearly the separation plane between the descent and ascent stages. The former has legs, a ladder, and is covered with black paint and gold foil for thermal control; the latter is silver and black and has attitude-control thruster quads (two of four are visible), a crew hatch (square with rounded corners), and a pair of triangular windows. Image credit: NASA

In December 1965, NAA's engineers briefed the NASA Headuarters Office of Manned Space Flight (OMSF) and Bellcomm, Inc., NASA's Washington, DC-based Apollo planning contractor, on results of a preliminary feasibility study of a one-person CSM mission to rescue Apollo astronauts stranded in lunar orbit. The NAA engineers did not describe specific lunar-orbit rescue scenarios, though the CSM modifications they outlined offer clues about the types of rescue missions they envisioned.

The most important piece of rescue hardware would be a special docking adapter ring on the rescue CSM's nose. Either an active probe or an active drogue could be mounted on the ring, so the rescue CSM could dock with either a LEM or a CSM. The lone rescue CSM astronaut could reconfigure the docking unit during the flight from the Earth to the moon; this would permit adaptation to changing circumstances in lunar orbit.

NAA anticipated that a lunar-orbit rescue might require spacewalks, so provided the rescue CSM pilot with a tether and a life-support umbilical extension, a cold gas-propelled hand-held maneuvering device, and a protective "meteoroid garment" of the type Apollo moonwalkers would wear over their suits on the lunar surface. In addition, the rescue CSM would carry an Expandable Structures Space Rescue System (ESSRS) device. ESSRS was an inflatable "pole" meant to serve as a handrail for astronauts spacewalking between two spacecraft.

Other rescue CSM modifications would include new crew couches to accommodate up to four astronauts, a fourth umbilical so that all could link their suits to the rescue CSM's life support system, added breathing oxygen, a dish-shaped LEM docking radar on an extendable boom, and new rendezvous and docking computer software. Modifications and additions would add a total of 445 pounds to the rescue CSM's weight. Removal of science equipment and other systems not required to rescue and return to Earth a crew stranded in lunar orbit would, however, reduce the rescue CSM's mass by 415 pounds, for a net mass gain of only 30 pounds.

The rescue CSM would be an advanced Block II spacecraft akin to the Apollo lunar CSMs. In late 1965, NAA expected to build a total of six Block I and Block II CSMs per year beginning in late 1966. Block I CSMs would be used in Apollo testing and Apollo Extension System (AES) Earth-orbital missions. AES, a proposed program intended to apply Apollo hardware to new missions, became a predecessor to the Apollo Applications Program, which subsequently evolved into the Earth-orbital Skylab Program. In the event, only Block II CSMs carried astronauts; work on Block I CSMs ceased following the deadly AS-204 (Apollo 1) fire of 27 January 1967.

NAA offered two plans for building the six rescue CSMs it expected would be needed for the Apollo Program. Rescue Vehicle Program "A" would see CSM-110 and CSM-113 converted into rescue CSMs; that is, diverted from lunar exploration missions. They would be flight-ready in early 1969 and mid-1969, respectively. (In actuality, CSM-110 became the Apollo 14 CSM Kitty Hawk, while CSM-113 was assigned to Apollo 16 and named Caspar.) Starting in mid-1970, one of the six CSMs NAA produced annually would be built as a rescue CSM; the first would be designated CSM-119. This, the company noted, would reduce the number of Block II CSMs available for lunar exploration.

Rescue Vehicle Program "B" would see NAA produce nine CSMs per year. The company's representatives told NASA that this would guarantee "non-interference with basic Apollo or AES." The first rescue CSM of Program "B," designated CSM R-1, would be ready for flight at the end of 1968, between AES CSM-109 and lunar CSM-110. Program "B" rescue CSM R-2, R-3, and R-4 would be completed in mid-1969, early 1970, and late 1970, respectively.

NAA assumed that during every Apollo lunar mission a rescue CSM would stand by atop a three-stage Saturn V rocket on one of the two Launch Complex (LC) 39 pads at Kennedy Space Center (KSC), Florida. The lunar mission would launch from the other LC 39 pad.

The rescue CSM Saturn V would be outwardly nearly identical to the lunar mission Saturn V. The rescue rocket would, however, carry no LEM in the tapered Spacecraft Launch Adapter shroud that would link the aft end of the rescue CSM to the ring-shaped Instrument Unit atop the Saturn V's S-IVB third stage. In addition, the Boost Protective Cover which protected the conical Command Module during the first part of ascent would need to be modified slightly to make room for the special docking ring.

On the launch pad, the Saturn V rocket bearing the rescue CSM would have appeared nearly identical to one bearing a lunar landing mission CSM Saturn V. The Boost Protective Cover, visible near the top of the image, would have had a slightly more bulbous nose. Internally, the most significant difference would have been the lack of a Lunar Module within the segmented Spacecraft Launch Adapter, the white tapered housing linking the bottom of the CSM to the ring-shaped Instrument Unit on top of the Saturn V's S-IVB third stage. Image credit: NASA

The rescue CSM and Saturn V would stand by on the launch pad until the Apollo lunar landing mission CSM safely departed lunar orbit and began the fall back to Earth, then would be rolled back to KSC's cavernous Vertical Assembly Building for storage until the next Apollo lunar mission. A single rescue CSM could be prepared for flight three times and and mothballed twice; this meant that it could stand by during three lunar missions, then would need to be replaced.

NAA did not explain what would be done with disused rescue CSMs; presumably they would be scrapped, though perhaps some systems could be salvaged for use in other CSMs. Neither did the company explain what would happen to the rescue Saturn V rockets.

The company assumed that in most cases the rescue CSM would launch immediately after NASA learned that a crew had become stranded in lunar orbit. Because it would not wait, in most cases it would not be able to rely on Earth launch geometry to help it to match orbits and carry out a rendezvous with the stranded spacecraft.

NAA determined that launching the rescue CSM immediately could create other complications. It might, for example, increase the rescue mission's duration. NAA calculated that the time needed to reach a stranded spacecraft and return to Earth could in fact exceed the Block II CSM's anticipated 240-hour (10-day) operational lifetime by up to 52 hours in the worst case. NAA recommended that NASA delay the rescue CSM's launch until its launch geometry would ensure that its mission duration would not exceed 10 days.

The company found that, once the rescue CSM reached the moon's vicinity, ignition of its SPS main engine could place it in an elliptical "catch up" orbit around the moon; then, at apolune (lunar orbit high point), the pilot could ignite the SPS again to line up the rescue spacecraft's orbital plane with that of the stranded spacecraft. At perilune (lunar orbit low point), the pilot would fire the SPS a third time to lower the rescue CSM's apolune, circularizing its orbit and placing it near the stranded spacecraft.

NAA estimated that its Rescue Vehicle Program "A" would add a total of $86 million to the cost of the Apollo Program per year. An 18-month program of development and testing would cost $50 million, $6 million would pay for modifications to two Apollo lunar CSMs, and four new rescue CSMs would cost $38 million each. The company provided no cost estimate for its Rescue Vehicle Program "B."

Program "A" rescue CSM 1 (CSM-110) would roll off the assembly line early in 1969, about three months after the first lunar CSM. Rescue CSM 2 (CSM-113) would become available in mid-1969, and rescue CSM 3 (CSM-119), would be ready in mid-1970.

The NAA engineers did not discuss how astronauts stranded in lunar orbit might eke out their limited supplies of consumables - for example, breathing oxygen - while they awaited rescue. This would be particularly worrisome in the case of a LEM stranded in lunar orbit by a catastrophic CSM failure: At the time of the NAA study, the LEM was expected to keep two astronauts alive for at most one or two days. Neither did they assess the enhanced risks of a one-person mission to lunar orbit, nor the technical problems of running two lunar missions concurrently.

Perhaps because of these difficulties, NASA chose not to prepare for astronaut rescues in lunar orbit. This did not stop Bellcomm from considering the problems of lunar orbit survival three years later, in December 1968, shortly after the Apollo 8 CSM became the first inhabited spacecraft to return from lunar orbit.


4-Man Apollo Rescue Mission, AS65-36, M. W. Jack Bell, et al., North American Aviation, November 1965; presentation at NASA Headquarters, 13 December 1965

More Information

Source: North American Aviation's 1965 Plan to Rescue Apollo Astronauts Stranded in Lunar Orbit