1968: First Half

NASA officials faced 1968 with some satisfaction and a little trepidation. Apollo 4 the previous November had been a triumph, but the Apollo team might have to do just as well six times in 1968 and five in 1969. That string of successes seemed to be a necessary prelude to a timely lunar landing.¹ Against this backdrop of mounting schedule pressures, a spate of technical problems cropped up. The most worrisome were those connected with the lunar module. It had grown too fat again and still had problems with metal cracking and with the ascent engine during test firings. Combined, these faults played havoc with delivery schedules and posed a definite threat to achieving Apollo’s mission within the decade.

The command module also had some unresolved worries, although North American had made good progress in its redefinition and qualification. Flammability testing and the question of cabin atmosphere on the pad and at launch carried over into the new year, as did the difficulties in getting systems to the spacecraft production line at Downey.²

Worries and Watchdogs

Tardy deliveries by subcontractors were among the bigger stumbling blocks that North American faced in putting the command and service modules together. Eberhard Rees, an expert in manufacturing management from Marshall Space Flight Center, was lent to George Low, Apollo program manager at the Manned Spacecraft Center, to solve fabrication problems. In the later months of 1967, Rees visited North American and soon realized that cooperation between the prime contractor and the subsystem suppliers was not close enough. North American engineers, he said, should spend more time at the subcontractors’ plants while subsystem assemblies were in critical stages of fabrication. He also recommended that North American borrow some inspectors from General Electric to help conduct vendor surveys, specification reviews, and test failure assessments.³

The subsystem situation came to the attention of George Mueller, Associate Administrator for Manned Space Flight at Headquarters, when he visited Downey late in 1967. Mueller on his return to Washington asked Edgar M. Cortright, his deputy, to go to the major companies, review the status of hardware, and see if the condition could be improved.⁴

During January and February 1968, Cortright traveled to nine Apollo subcontractors. He was impressed with people, equipment, and facilities but not at all pleased with hardware or schedules. Cortright found that neither North American nor Grumman knew enough about the status of their subcontractors’ work to be able to forecast deliveries with any degree of accuracy. The subcontractors, Cortright also said, should be more aware of the importance of their systems in the total program - they should not just deliver their products to the dock in Downey or Bethpage and walk away. He was upset about failures in electronic parts, especially when he found that the subcontractors were doing their best to solve their problems by themselves by trial and error. Low asked the Houston subsystem managers to look into these deficiencies and correct them.⁵

Just the barest hint of something wrong with electrical parts, anything that might be a fire hazard, captured the immediate attention of special guardian groups. Spacecraft wiring and materials, cabin atmospheres, and crew safety were the subjects of many meetings. Third-party groups, such as a Senior Flammability Board, a Materials Selection Review Board, and a Crew Safety Review Board, were set up to ensure extra safeguards.

Late in 1967, Houston Director Robert Gilruth led a contingent of NASA officials to a meeting with William Bergen and his staff at North American^* to discuss flammability problems of the coaxial cable in the command module. Under particular scrutiny was spacecraft 101, slated for the first manned Apollo mission. After visually inspecting the vehicle and watching motion picture films of tests, the group concluded that 23 meters of the coaxial cable might be flammable. There were several options on what to do about it - replace it, wrap it with aluminum tape, partially wrap it to provide fire breaks, or leave it alone. Since other spacecraft wiring and electrical equipment might be damaged during replacement, even with extreme care, they decided it would be safer to fly 101 essentially as it was, with the exception of one bundle that would be wrapped.^{** 6}

No sooner had one NASA group acted than another demanded a defense of what had been done. Aleck C. Bond, speaking for the Houston Materials Selection Review Board, queried Low about the cable. Low pointed out that the decision had been made at the highest Apollo management level of both North American and NASA. He also reminded Bond that, in the NASA system of checks and balances, the board did not approve changes. It only recommended approval or disapproval. Low then required that all deviations be assessed by his Configuration Control Board and forwarded to Apollo Program Manager Phillips in Washington for final review.⁷

Most of the Flammability Board’s attention focused on cabin atmosphere at the launch site, which also affected materials selection. Established in September 1967, with Gilruth as chairman, the board directed several series of tests under a variety of atmospheric mixtures and pressures for pad operations. Thirty-eight tests had been completed by 7 January 1968. In the middle of the month, a second series began, using principally a 60-per-cent-oxygen and 40-percent-nitrogen mix (normal atmosphere is 21 percent oxygen and 78 percent nitrogen, with traces of other gases). This series ended on 25 January, and evaluations began.

Max Faget, whose engineers in Houston ran many tests for Gilruth’s board, said they used pure oxygen at a higher than normal pressure on the pad to check for air leaks from the cabin. After the Apollo 204 fire, everyone was aware that this was dangerous. They then ran pure oxygen tests at one-third the pressure (which simulated orbital conditions). With cabin fans off and no other means of spreading the flames, they found that fire would not propagate as rapidly in space. So Faget’s group agreed that if they could make the spacecraft safe on the ground, it would be safe during flight.

But there was no way to put 100-percent-fireproof materials in the spacecraft, especially in the electrical system. Many persons began campaigning for a two-gas atmosphere, with a higher concentration of nitrogen than oxygen. Use of this mixture would have required completely rebuilding the spacecraft to withstand the pressures of a sea-level atmosphere. The command module could withstand only about half that pressure in space, and the lunar module even less. Moreover, a mixed atmosphere in space would complicate the environmental system - Faget said the system “would get confused and would put too much nitrogen in the cabin, a very insidious thing because there was no way to detect [it].” The astronauts would just get sleepy - and die. Another complication was that a switch back and forth from the two-gas system in the cabin and the 100 percent oxygen in the hoses connected to the suits might give the crew aeroembolism, or the bends.

So the question was twofold: How much nitrogen was needed on the pad to prevent fire? And how much oxygen was needed during launch while the cabin pressure relief valve was venting? Tests revealed that a 60-percent-oxygen and 40-percent-nitrogen mixture at a pressure of 11.2 newtons per square centimeter (16.2 pounds per square inch) on the pad would result in 1.4 newtons (2 psi) in orbit after venting, which would give a partial pressure of oxygen compatible with the oxygen atmosphere and pressure in the suits. The cabin pressure would be lower at first, but the mixture would be breathable and it would sustain life. In fact, by the time the craft reached orbit, Faget said, the cabin mixture would actually be about 80 percent oxygen. And there was a bonus in this arrangement beyond the safety factor: no structural changes were needed in the spacecraft to accommodate this combination of oxygen and nitrogen.⁸

Low promised Phillips a decision on the prelaunch atmosphere in time for spacecraft 101’s Design Certification Review. A third set of tests, using boilerplate 1224, confirmed conclusions drawn from the second series. Gilruth’s Flammability Board met on 4 March and recommended the 60/40 mixture for the launch pad. On 7 March, Mueller’s Certification Board accepted this recommendation. In April, NASA’s medical group, expressed “enthusiastic approval of the . . . decision to adopt the 60/40 atmosphere.”⁹

For a while there was a good deal of discussion about the lunar module cabin atmosphere on the launch pad. Low recommended 100 percent oxygen for the LM, since there was no crew and little electrical power in the vehicle during launch. Moreover, the spacecraft-lunar module adapter, which held the lander, was filled with nitrogen, reducing flammability hazards to almost nothing. This procedure, Low pointed out, would save some of the lander’s oxygen supply, as well as minimizing crew procedures in changing the mixture to pure oxygen after launch. Marshall, however, objected, because any oxygen escaping from the lander during the launch phase might come in contact with hydrogen leaking from the S-IVB into the adapter and start a fire. Houston conceded that the advantages of launching the lunar module with pure oxygen had to give way to Huntsville’s concerns; the atmosphere in the lander’s cabin at launch would not exceed 20 percent oxygen.¹⁰

Another set of watchdogs, formed to consider manned operation of the machines, was the Apollo Crew Safety Review Board. Since Gilruth’s team mas investigating “spacecraft fire safety and air-on-the-pad,” the new group, at its first meeting in March 1968, began looking for problems that might be missed by other specialized committees. Led by John Hodge in Houston, the board concentrated on operations - all activities from the time the crew boarded the spacecraft through the launch phase - searching for weak links and hazards. One big worry that had to be faced was the possibility of a Saturn engine shutting down on the pad or during the launch trajectory.¹¹

The Hodge Board was not the only group worrying about a Saturn V engine malfunction. Major General David M. Jones, Commander of the Eastern Test Range, reminded KSC Director Kurt Debus that the launch vehicle would remain over the Cape area for almost two minutes. Jones wanted the vehicle to move out over water as quickly as possible. Debus told Phillips what Jones had asked, adding that the launch azimuth should not be tampered with, since a wide range would be needed for a lunar launch. Phillips turned to Marshall for an answer, and the launch vehicle engineers modified the pitch program so the vehicle would head eastward sooner after launch than originally planned.¹²

Although the Saturn V may have been the key vehicle for escaping the earth’s gravity for the lunar trip, the keystone in the arch leading to the surface of the moon itself was the lunar module. At least, that was the way the Flight Operations Division in Houston viewed LM-1’s upcoming trial in earth orbit.¹³ And the path to the launch pad for that craft had been a long and arduous one.

Apollo 5: The Lunar Module’s Debut

A 1966 schedule called for LM-1 to be delivered to Cape Kennedy on 16 November of that year, but the craft ran into difficulties in manufacturing (see Chapter 8) and the months slipped by. Changes after the command module fire (see Chapter 9) caused further delays, and LM-1 did not arrive in Florida until 27 June 1967 (three months beyond its original launch date). John J. Williams, a veteran of both Mercury and Gemini, headed a 400-man spacecraft operations activity at Kennedy Space Center. When the spacecraft arrived, Williams’ men made sure that it met specifications and then watched the contractor during test, maintenance, and modifications to see that systems and equipment worked.¹⁴

The launch vehicle for the LM-1 mission was the one that would have boosted the ill-fated Grissom crew into orbit. Saturn IB 204 had been at the Cape since August 1966. When it was taken down from Launch Complex 34 in March 1967, the launch preparation crew, under the direction of Rocco Petrone, inspected the booster for corrosion or any other damage it might have sustained during its long stay on the pad and then erected it on Launch Complex 37, getting it in place on 12 April.¹⁵

The Apollo stack for this mission was 55 meters high, but it looked stubby, since the launch escape tower and the command and service modules mere missing. LM-1 - legless, because it would burn up on reentry (it had no heatshield) and therefore needed no landing gear - rested inside the spacecraft-lunar module adapter.¹⁶

Twenty-five priorities, monitored by 17 specialists, would put the vehicle through its paces to make sure that it was safe for crew operations. Three items at the top of the list pertained to fire-in-the-hole (FITH) requirements, or tests to check structural effects, staging dynamics, and stability during a simulated lunar abort. (FITH simply meant firing the ascent stage engine while it was still attached to the descent stage.) Other objectives included operating the descent and ascent propulsion systems, starting and stopping each to simulate phases of the lunar landing mission.¹⁷

By late fall and early winter of 1967, most of the mission documents were ready. Mission Director William C. Schneider, who had played this same role in the Gemini program, issued the mission rules on 28 November, ladling out responsibilities and spelling out what would be done in almost every eventuality. As the final testing on the vehicles progressed toward launch, flight readiness reviews were held at the Cape and in Washington. In the first few days of the new year, Mueller wrote Administrator James Webb that the launch would take place “no earlier than” 18 January 1968.¹⁸

Rocco Petrone’s launch team had difficulty loading the propellants, mainly because of procedural troubles, and small irritants such as clogged filters and ground support equipment problems further hampered the start of the mission. A simulated launch demonstration ended on 19 January, and the 22-hour countdown to launch began on 21 January. Back in Houston, lead flight director John Hodge and his chief assistant, Eugene F. Kranz, listened from the mission control center to the activities at the Cape launch center and waited patiently to take over direction of the flight once Apollo 5 cleared the pad.¹⁹

Just before dark, at 5:48 on the afternoon of 22 January, after several hours’ delay because of equipment problems, Apollo 5 lifted off. The powered phase of booster flight was uneventful, and LM-1, still attached to the S-IVB stage, went into orbit about 10 minutes into the flight. In less than 45 minutes, its attitude control engines pulled LM-1 away from the S-IVB. After checking out the spacecraft for two revolutions, ground control signaled the descent engine to fire for 38 seconds. Four seconds later, LM-1’s guidance system sensed that the vehicle was not going fast enough and stopped the engine. The cutoff was a planned feature - in a manned flight, it would give the crew time to analyze the situation and decide whether the engine should be restarted to continue the mission. Under normal conditions, the burn would have started with full tank pressurization and would have reached the proper velocity within four seconds. For this mission, however, the tank was only partially pressurized and it would have taken six seconds to reach the required speed. Because of the premature cutoff, the flight controllers moved to a planned alternate mission.

Ground control sent a switch-off signal to the guidance computer and cut in a mission programmer to command the lander’s maneuvers. The descent engine was fired twice more (once for a full 33 seconds). There were two ascent engine firings, one for the fire-in-the-hole abort maneuver. Mueller reported to Webb that all primary objectives had been achieved. LM-1 reentered the atmosphere, and its fiery remains plunged into the Pacific several hundred kilometers southwest of Guam on 12 February.²⁰

The LM: Some Questions, Some Answers

Following Apollo 5, it appeared likely that one of the six flights planned for 1968 might be canceled. Fewer flights should mean a better chance of landing a crew on the moon within the decade. After reading a preliminary version of the mission report, Phillips wired the three manned space flight centers not to plan a second unmanned lunar module mission. Shipment of LM-2 and its Saturn IB booster to the Cape was delayed, pending an assessment by George Mueller’s Certification Board. On 6 and 7 March, the board agreed there was no reason for another unmanned lunar module flight. The first lunar module to carry men would be launched by a Saturn V later in 1968.²¹

The lander still had hurdles to clear, however, before anyone would be allowed to ride it in space. Ascent engine instability, for example, had been a matter of concern from August 1967 to June 1968. When Mueller and Phillips visited the builder of the engine in the summer of 1967, they agreed that Bell had a good chance of solving fuel-injector problems and getting a stable engine ready for the first manned lander. Nevertheless, NASA had hired Rocketdyne to develop an alternate injector, sending Cecil R. Gibson from the Houston center to work with Bill Wilson at Rocketdyne. This contract lasted for about a year, and Gibson and Wilson successfully stayed on schedule, held down costs, and got the job done.²²

One question that arose was whether a new and improved injector should be flown in a manned lander without a thorough revalidation test program. Joseph G. Thibodaux (Gibson’s boss and chief of the Propulsion and Power Division in Houston, who had been asked to head a team to evaluate the injector) believed that it would be safe, so long as fuel did not enter the firing chamber before oxidizer. An Agena engine that had allowed the fuel to go first in the Gemini program had exploded during 1965.²³

Grumman and NASA officials met on 29 April to discuss the status of the injector. They were not happy with what they had discovered during visits to the subcontractor plants. Bell had been lax in configuration control, and Rocketdyne was having trouble getting engines to start and then to run smoothly. For some time, NASA Headquarters had considered asking Rocketdyne and Bell, even though they were competitors, to pool their knowledge to get the best possible injector. Rocketdyne might send its injector and some of its personnel to the Bell test cell for checkout. Although hesitant at first, because this might slow down Bell’s work, Houston told Grumman to coordinate this combined testing, calling on specialists from both subcontractors for help.²⁴

As time passed, Phillips and Low began to worry more and more about what would happen if the Rocketdyne injector were picked. How much testing would have to be done to make certain that a Rocketdyne engine was safe enough for a crew to fly on LM-3? And how long would it take?²⁵

Numerous trips were made to Bell by NASA officials, trying to get a grip on the problem. In May, after one visit, Low wrote: “If stability were the only criterion for acceptance, then a decision to select the Rocketdyne engine would have been clear. However, the Rocketdyne engine has also some short-comings, which are not yet completely understood.” Low also believed that, if Rocketdyne were picked, it would take some “extraordinary efforts to integrate the new engine into the LM.” That same month, a group led by Phillips of NASA and Joseph Gavin of Grumman met to discuss the alternatives they faced: (1) to use the Bell engine and Bell injector, (2) to ship Bell engines to Rocketdyne for fitting with Rocketdyne injectors, or (3) to send Rocketdyne injectors to Bell for installation in the Bell engine. Low finally decided to use a Bell engine and a Rocketdyne injector, with the entire assembly being put together and furnished by Rocketdyne.²⁶

At 17 and 19 June program reviews at Rocketdyne and Bell, respectively, Low learned that qualification tests were progressing with such excellent results (the engine had gone through 53 good tests) that an end to qualification by mid-August seemed possible.²⁷ Success now appeared certain, but the race with the decade was becoming very close.

Although the ascent engine was the most serious lander problem, there were others that created worries. For example, a window blew out of LM-5 during a test. On another occasion, a window fractured during a 72-hour high-temperature test. Corning Glass Works immediately began improving the panes, producing what Mueller called the strongest windows ever put in a spacecraft. And Grumman instigated a series of pressure tests to qualify the new windows.²⁸ All this took time.

Still another area that raised a red flag of concern was the discovery of stress corrosion cracks in the lander’s aluminum structural members. This meant replacements and still more lost time, which angered George Mueller. He reminded Gilruth that these aluminum tubes (made of an alloy called “7075 T6”) had caused problems in the past. Mueller could not understand why the cracks had not been noticed earlier. He wanted a “stress corrosion team” to find out why detection had failed and to figure out how to prevent a recurrence. Gilruth replied that there was no need for a special team. Stress corrosion surveys had been conducted in 1964, but the job simply “was not handled properly on the last go-round.” Low then asked Joseph Kotanchik, a Houston structures expert, to investigate the overall stress corrosion problem and to look into all equipment furnished by suppliers to the prime contractors to make sure no problems were lurking in any of these systems.²⁹

By mid-February 1968, Grumman had inspected six landers (LM-3 through LM-8), examining more than 1,400 different components. Some parts were buried so deeply in the structure that they could not be reached. When no major cracks were found in the accessible areas, Grumman assumed that the problem was not as bad as NASA thought. Grumman did strengthen any parts not yet assembled by replacing the 7075 T6 tubes with 7075 T73, a heavier alloy. By the end of the month, Mueller told Webb he was no longer worried about stress corrosion.³⁰

Another nagging problem in the lander was broken wiring. Brigadier General Carroll H. Bolender, Manned Spacecraft Center’s lunar module manager, received the impression when visiting the Cape that the wiring was in poor shape in LM-2 and not much better in LM-3. Bolender told his resident Apollo spacecraft representative at the Grumman plant in New York to emphasize to Grumman’s engineering team the need to assist manufacturing in the wiring of the spacecraft. Some improvement came from this move, but not much. During an inspection of LM-3, several broken wires were discovered, apparently caused by carelessness during rework after testing. Toward the end of April 1968, fixtures were installed to protect vulnerable wire bundles and technicians were ordered to be more careful when working in the confined spacecraft areas, easing the problem to a certain extent. But the lander’s schedule was getting tighter and tighter.³¹

And the vehicle was steadily getting fatter. Reductions were urged, but reducing diets in 1968 were nothing like those in 1965, when 1,100 kilograms were shaved from the lander. NASA used the incentive contract as a lever to get Grumman moving on weight reduction, starting the second quarter of 1968 with the goal of cutting 22 kilograms off the ascent stage and 68 off the descent stage.³²

All in all, the chances for launching a manned lunar module during 1968 seemed very slim in June of that year. And Saturn V, the launcher, was still giving program officials some anxious moments.

Apollo 6: Saturn V’s Shaky Dress Rehearsal

The success of Apollo 4 gave good reason to believe that the Saturn V could be trusted to propel men into space. But NASA pushed on with its plans for a second unmanned booster flight, primarily to give the Pad 39 launch team another rehearsal before sending men into deep space on the Saturn V.

Getting Apollo 6 to the launch pad was a lengthy process. The S-IC first stage of the Saturn V arrived at Kennedy Space Center^* on 13 March 1967. Four days later it was on a mobile launcher in the cavernous assembly building, awaiting the S-II second stage - which did not get to Kennedy until May. On 6 February 1968, a Tuesday morning, a crawler carrying the whole Apollo stack on its platform edged out of the building into a wind-driven rain and headed slowly down a track to the launch complex, five kilometers away. En route, trouble with communications circuits forced a two-hour wait. When communications were restored, the crawler resumed its snail’s pace. At 5:00 that afternoon, the rain stopped, and the Apollo stack arrived at the launch area an hour later.³³

Although the spacecraft itself had no primary objectives to accomplish, a Block I version (CSM-020) with many Block II improvements (such as the new hatch) was allocated to the mission. Kleinknecht, the command and service modules manager in Houston, was pleased with the machine that North American sent to Kennedy, although he was upset when he learned that the protective Mylar film that covered the spacecraft during shipment was flammable. In engineering terms, it was a clean spacecraft. Only 23 engineering orders were outstanding (as opposed to the hundreds listed for spacecraft 012 only a year and a half earlier), and most of these were the kind that the spacecraft operations people at Kennedy normally handled anyway.³⁴ The spacecraft had no last-minute problems, but the mission planners did.

In November 1967, the idea of putting a camera in the window of the spacecraft to take some earth resources photographs had been explored in a review for Mueller at North American. John Mayer’s MSC mission planners were hit hard by the late inclusion of the camera. Because Apollo 6 was unmanned, all the flight trajectory data had to be correlated with the photographic aims and a computer program had to be developed and fed into the onboard computer. After many careful checks, the mission planners decided that there might be a chance during the first orbit and part of the second to get some pictures of the area from Baja California to Texas.³⁵

Apollo 6 had been scheduled for the first quarter of 1968, but several brief postponements slipped it past that date. On 15 January, Mueller wrote Webb that the tank skirt of service module 008 had split during structural testing. The skirt on spacecraft 020 was strengthened to prevent a similar mishap. Then, after the stack had been trundled down the path to the launch area on a rainy day, water seepage was found in the Saturn’s S-II stage, and some parts had to be replaced. And, finally, the countdown-to-launch practice did not end until 29 March.³⁶

At 7:00 a.m. on 4 April 1968, Saturn V 502 rose thunderously from its Florida launch pad to boost Apollo 6 (AS-502) into orbit, but that was nearly the last normal thing the big rocket did. For the first two minutes, the five huge engines in the first stage roared, shook the ground, and belched fire evenly. Then there were thrust fluctuations that caused the vehicle to bounce like a giant pogo stick for about 30 seconds. Low-frequency modulations (known as the pogo effect) as high as +/-0.6 g were recorded in the command module, which exceeded design criteria (0.25 g was the upper limit permitted for manned flight in Gemini). Except for the bouncing and the loss of a piece of the panel in the adapter, the first stage did its job, however.

Very shortly after the second stage ignited, two of its five J-2 engines stopped. The other three engines had to fire longer to compensate for this loss of power. The second stage did not reach the desired altitude and velocity before its fuel gave out and it dropped away. To reach the required speed, the S-IVB third stage also had to burn longer than planned, putting the spacecraft into an orbit of 178 by 367 kilometers, instead of a 160-kilometer circular orbit.

Mission Director Schneider and Flight Director Clifford E. Charlesworth left the vehicles in a parking orbit for two circuits of the earth while system checks were performed, operational tests were conducted, and several attitude maneuvers were carried out. Then flight control tried to restart the S-IVB, to simulate translunar injection, but the third stage refused to answer the call. The next step was to separate the command and service modules from the now useless S-IVB.

While Apollo 6 had been whirling around the earth, the spacecraft’s special 70-millimeter camera had been clicking away, getting some spectacular color stereo photographs.^** These were later found to be excellent for cartographic, topographic, and geographic studies of continental areas, coastal regions, and shallow waters.

Following the system checks and the photography, controllers turned to an alternate mission. The service module engine was fired for 442 seconds,^*** which exceeded lunar mission requirements, to produce the simulated translunar injection maneuver. Apollo 6 shot out to 22,200 kilometers. Although the spacecraft had enough altitude for a good simulation of an Apollo spacecraft returning to the earth from the moon, the service module engine no longer had sufficient fuel to give it the correct speed for its dive. The command module reached a velocity of 10,000 meters per second, about 1,270 less than planned, and splashed down in the Pacific, missing its predicted impact point by 80 kilometers. The spacecraft was hauled aboard the U.S.S. Okinawa to complete its 10-hour mission.³⁷

On 9 April 1968, a NASA news release declared that preliminary data on Apollo 6 indicated that the spacecraft had done its job well. Mueller and Phillips, however, concluded that the overall flight had not been a success.

Apollo was not top international or even national news in April 1968, even though this flight was a major step in the program to land men on the moon. President Johnson had announced 31 March that he did not intend to seek reelection, hoping that this action would expedite the ending of the war in Southeast Asia. And on 4 April, the day of the flight, Martin Luther King, Jr., a civil rights leader of international stature, was assassinated in Memphis, Tennessee. About the only explaining that NASA had to do, therefore, was to the congressional committees on space activities, who seemed satisfied with what they heard.³⁸

But the Apollo team did not need a round of public criticism in April 1968. With the decade nearing its end, pressures were already exceedingly heavy. In the alphabet game of reaching the “G” (or lunar landing) mission, NASA had flown only two “A” missions (Saturn V unmanned) and one “B” (Saturn IB with an unmanned lunar module). Now Huntsville had to find out why the Saturn V’s S-IC first stage bounced, why the S-II second stage turned off two of its engines, and why the S-IVB third stage refused to fire a second time. Meanwhile, Houston had to determine exactly how much shaking the lander could stand and why a large piece of the spacecraft-lunar module adapter had blown out during launch. Without satisfactory answers, the Saturn V might have to make a third unmanned flight.

Pogo and Other Problems

The pogo bounce had been observed (although to a much smaller degree) on Apollo 4, so its appearance during Apollo 6 did not come as a complete surprise. Also, five years earlier, in 1963, pogo had threatened to end the Gemini program when the Titan II suffered this phenomenon on launch after launch. Its apparent cause was a partial vacuum created in the fuel and oxidizer suction lines by the pumping rocket engines. This condition produced a hydraulic resonance - more simply, the engine skipped when the bubbles caused by the partial vacuum reached the firing chamber. Sheldon Rubin of the Aerospace Corporation had finally suggested installing fuel accumulators and oxidizer standpipes, to ensure a steady flow of propellants through the lines. This had solved the Gemini launch vehicle problems, and NASA had this background experience to draw on when the Saturn V began having pogo troubles.^{* 39}

Pogo on Apollo 4 had been measured at one-tenth g, much less than the one-fourth g set as the upper limit in Gemini. The lower oscillation was probably the result of carrying just “a hunk of junk,” to simulate lunar module weight, on the earlier flight. But a test article flown on Apollo 6 had the shape and weight of a real lander in the adapter. This change in mass distribution coupled back into the fuel system problem and increased the pogo oscillations. The mission analysts later discovered that two of the Saturn engines had been inadvertently tuned to the same frequency, probably aggravating the problem. (Engines in the Saturn V cluster were to be tuned to different frequencies to prevent any two or more of them from pulling the booster off balance and changing its trajectory during powered flight.)

The rocketeers at Huntsville first wanted to know from Houston whether a crew could have withstood the vibration levels on Apollo 6. If so, the next Saturn V flight could be manned, even without a pogo cure. Low informed Saturn V Program Manager Arthur Rudolph that these levels could not be tolerated. Marshall also asked whether the emergency detection system could be used to abort the mission automatically if such high vibrations again occurred. During Apollo 6, the system had cast one vote for ending the mission. Had it cast a second vote, abort would have been mandatory. Low and chief astronaut Donald Slayton did not want to use the system in an automatic pogo abort mode. Low met with George H. Hage, Phillips’ deputy, and they decided on the immediate development of a “pogo abort sensor,” a self-contained unit that would monitor and display spacecraft oscillations. From what the sensor told him, a spacecraft commander could decide whether to continue or stop the mission.⁴⁰

Marshall Space Flight Center pulled an S-IC stage out of Michoud Assembly Facility, brought it to Huntsville, and erected it in a test stand. By May, Huntsville, Houston, and Washington Apollo officials were ready to attack the pogo problem. Hage agreed to head the activity until Eberhard Rees could finish his task on the command module at Downey and take over. At one time during the pogo studies, Lee B. James (who had replaced Rudolph as the Huntsville Saturn V manager) said, 1,000 engineers from government and industry were working on the problem.⁴¹

Out on the West Coast, at the rocket engine test site at Edwards Air Force Base, Rocketdyne started testing its F-1 engine in late May. In the first six tests, helium was injected into the liquid-oxygen feed lines in an attempt to interrupt the resonating frequencies that had caused the unacceptable vibration levels. In four of the six tests, the cure was worse than the disease, producing even more pronounced oscillations. The Saturn V people at Marshall also tried helium injection, but their results were decidedly different. No oscillations whatsover were observed. Tests using the S-IC stage’s prevalves as helium accumulators were then conducted at both Edwards and Marshall. The prevalves were in the liquid-oxygen ducts just above the firing chambers of the five engines and were used to hold up the flow of oxygen in the fuel lines until late in the countdown, when the fluid was admitted to the main liquid-oxygen valves in preparation for engine ignition. The prevalves were modified to allow the injection of helium into the cavity about 10 minutes before liftoff; the helium would then serve as a shock absorber against any liquid-oxygen pressure surges.

What had happened to the S-II and S-IVB stages, with two of the five J-2 engines shutting down in one case and the single J-2 engine refusing to start in the other, was more of a mystery than pogo. During tests at Arnold Engineering Development Center, at Tullahoma, Tennessee, engineers discovered that frost forming on propellant lines when the engines were fired at ground temperatures served as an extra protection against lines burning through. But frosting did not take place in the vacuum of space; the lines could have failed because of this. Also, in the line leading to each of the engines was an augmented spark igniter. Next to the igniter was a bellows. During ground tests, liquid air, sprayed over the exterior to cool it, damped out any vibrations. Vacuum testing revealed that the bellows vibrated furiously and failed immediately after peak-fuel-flow rates began. These lines were strengthened and modified to eliminate the bellows.⁴²

Another item noticed by the flight control monitors during the boosted flight of Apollo 6 (and later confirmed by photographs) was that a panel section of the adapter that housed the lander had fallen away just after the Saturn V started bouncing. The controllers had been amazed that the structural integrity was sufficient to carry the payload into orbit. James Chamberlin in Houston discovered that thermal pressure (and therefore moisture) had built up in the honeycomb panels during launch; with no venting to allow the extra pressure to escape, the panel had blown out. A layer of cork was applied to the exterior of the adapter to keep it cooler and to absorb the moisture, and holes were drilled in the adapter panels to relieve the internal pressure if heat did build up inside on future launches.⁴³

Although Marshall was responsible for stability and dynamic structural integrity throughout the boost phase, the Manned Spacecraft Center could not afford to sit on the sidelines and watch while its sister center wrestled with these problems. Houston had to get an Apollo payload stack together for structural testing. On 16 May 1968, Low and James decided to use a “short stack” (the S-IC stage would be left out at this time but could be incorporated later).^** Astronaut Charles Duke was sent to Huntsville to keep information flowing between the centers, and Rolf Lanzkron was assigned by Low to manage the spacecraft dynamic integrity testing, which was satisfactorily completed on 27 August with no major hardware changes found necessary.⁴⁴

The Outlook

At midyear 1968, chances for landing on the moon within the decade were still touch-and-go. It did seem likely that NASA would have to fly only five, instead of six, preparatory flights that year, but one of these might have to be another unmanned Saturn V. Not knowing exactly what would follow the third mission of the year (a manned Saturn IB launch) caused some extra planning. For example, the Kennedy spacecraft preparation team had to prepare both a boilerplate and a qualified production command module for the next Saturn V shot, since the choice for launch depended on the outcome of the pogo investigations. Mission planners in Washington also revived the plan for launching two Saturn IB missions to give both the North American and the Grumman spacecraft a workout in earth orbit, if another unmanned Saturn V had to be flown.⁴⁵ Even this plan was tentative, however, as the delivery date for LM-3 was still not firm.

On the brighter side of the ledger at mid-year was North American’s work in getting CSM-101 ready for the first manned Apollo mission. Although the contractor was late in shipping the craft from its California factory to the Florida launch site, improvements in the fabrication of this machine indicated that future spacecraft should be on time. After a traumatic and pressure-packed 18 months, North American was finally delivering satisfactory, flight-ready hardware. When 101 arrived at the Cape on 30 May, the receiving inspectors found fewer discrepancies than on any spacecraft previously delivered to Kennedy.⁴⁶

Mueller had told the Senate space committee in February 1968 that the first manned Apollo mission would be flown in the last quarter of the year.⁴⁷ In June, this still seemed feasible.