A DARING PLAN

Robert Seamans resigned as NASA’s Deputy Administrator on 2 October 1967, and departed 3 months later. On 5 February 1968 the Senate accepted the nomination of Thomas O. Paine, a senior manager of the General Electric Corporation, and he was sworn in as Deputy Administrator on 25 March.

AS-502 was the second in the series of ‘A’ missions designed to ‘man rate’ the Saturn V launch vehicle. The payload was LTA-2R and CSM-020, a Block I with some Block II modifications for certification, including a heat shield with an actual unified crew hatch to be tested in lunar return conditions. In view of the fact that the mission would be unmanned, certain systems had been deleted from the command module in order to accommodate an electromechanical control sequencer.

The countdown proceeded without unplanned holds, and Apollo 6 lifted off from Pad 39A at 12:00:01 GMT on 4 April 1968. It contrast to the perfect performance of the first Saturn V, this one suffered a number of problems.

Firstly, between T+110 and T+140 seconds it underwent a ‘pogo’ oscillation, as a longitudinal structural mode frequency coupled with the resonant frequency of the oxidiser lines feeding the S-IC’s engines. The greatest disturbance was in the range 5.2 to 5.5 hertz. The oscillations in the engine chamber pressures built up to a peak – to-peak maximum of 8 to 10 psia at T+ 125, and the condition was reinforced by the consequent variation in thrust. The +0.6-g oscillation measured in the spacecraft exceeded the design criteria, and would have given astronauts a very rough ride. The emergency detection system cast one ‘vote’ for terminating the mission. Had it gone on to cast a second vote, an abort would have become mandatory and the command module would have been drawn clear by the launch escape system.

Ground-based and airborne cameras noted three small pieces and five or six large pieces separating from the vicinity of the SLA between T + 133.31 and T + 133.68, at which time strain, vibration and acceleration sensors in the S-IVB, IU, SLA, LTA and CSM reported abrupt changes. Subsequent analysis determined that one of the SLA panels had suffered structural failure and shed some of its skin. Fortunately, the supporting elements were able to sustain the loads for the remainder of the powered flight.

The S-IC shut down at T+ 148.21 and separated cleanly. The five J-2 engines of the S-II ignited at T+150 and performed satisfactorily for 169 seconds, but at T+319 the hydrogen flow rate to engine no. 2 suddenly increased and its thrust declined by 23 psi. The engine ran at this level until T + 412.92, whereupon the temperature in the engine bay suddenly rose and the engine shut down. Engine no. 3, which had shown no sign of distress, cut off 1.26 seconds later.

Despite the loss of 40 per cent of its power, the S-II was able to gimbal the three remaining engines to hold itself stable. However, the controller in the Instrument Unit had been configured to react only with a single-engine-failure contingency and was unable to take into account the loss of the second engine. It naively attempted to recover its trajectory as if it had four good engines. When the IU started to adjust the propellant mixture ratio to optimise consumption leading up to S-II shutdown, it also adopted a mode designed to stabilise the vehicle for separation. If all had been going to plan, at that time the S-II would have been within 5 seconds of cutoff but the loss of two engines reduced the rate of propellant consumption and the other engines had to burn for much longer than planned to trigger the fuel-depletion cutoff. In fact, the burn was 57.81 seconds longer than usual, and because the vehicle held its attitude fixed during this time it climbed higher than intended and the space – fixed velocity at cutoff was 335.52 ft/sec less than nominal.

The inherited trajectory anomaly presented the S-IVB with a serious challenge. It ignited at T + 577.28 and burned for 166.52 seconds, some 28.95 seconds longer than nominal. On finding itself high, slow and short, it pitched down 50 degrees in order to lose altitude, accelerate and gain range. On achieving the desired altitude it raised its nose above the local horizon to overcome the negative radial velocity acquired in descending, whilst simultaneously minimising further increasing its horizontal rate. On activating terminal guidance at T + 712.3, the system set the altitude constraints to zero and focused on achieving the desired velocity. Although it ordered the vehicle to pitch up beyond vertical and travel backwards, the 1 deg/sec rotation rate meant that when the space-fixed velocity exceeded the objective and the stage shut down at T+747.04 the angle had reached only 65 degrees. The velocity was 160 ft/sec greater than nominal, the surface range was 269.15 nautical miles longer than nominal and the flight path angle was slightly negative. A circular orbit at 100 nautical miles had been planned, but the actual orbit of 93.49 x 194.63 nautical miles did not preclude continuing with the mission.[50]

Once the S-IVB had realigned its axis with the horizon it initiated a sequence of manoeuvres to be undertaken on the first revolution. First, it rolled 180 degrees and pitched down 20 degrees, and then it pitched up 20 degrees and rolled to resume its original attitude. The only appreciable effect was the sloshing of liquid oxygen at the onset of each change in pitch, but this was rapidly damped out. This qualified such manoeuvres to orient the vehicle to enable astronauts to perform landmark tracking while in parking orbit.

The Apollo 6 plan was to reignite the S-IVB at the end of the second revolution to simulate the translunar injection. Although this was to achieve lunar distance, the apogee was to be away from the Moon in order not to complicate the evaluation of the guidance system in deep space. Immediately after cutoff, the S-IVB was to pitch through 155 degrees and release the CSM in an attitude appropriate for a retrograde burn. A 254-second burn by the service propulsion system would put the spacecraft into an ellipse with an apogee reduced to about 12,000 nautical miles and with an atmosphere-intercepting perigee. The vehicle was to coast in an attitude that would ‘cold soak’ the heat shield to approximate lunar return thermal conditions. Late in the descending portion of the ellipse, the spacecraft would fire its engine again to accelerate to 36,500 ft/sec with a flight path angle of-6.5 degrees to simulate lunar return, jettison the service module and orient itself for atmospheric entry leading to splashdown in the Pacific.

Despite the additional propellant consumed in attaining orbit, the S-IVB was still capable of performing the planned program. However, the restart system failed to produce hydraulic pressure. On noting this failure, the IU cancelled the ignition command at 003:13:50.33 and advanced to the next programmed item – just as if it had achieved the burn. At 003:14:10.33 it initiated the 155-degree pitch manoeuvre, and 15 seconds later was still rotating when the ground commanded the spacecraft to separate. The hinges had been designed to rotate the SLA panels to 45 degrees from the vehicle’s longitudinal axis within 1.3 seconds, but in this case the S-IVB was still in the process of pitching and the fact that the spacecraft suffered a disturbance in pitch of 1.5 deg/sec during separation implied that one of the panels had nudged the spacecraft. A preplanned alternative mission was selected in which the service propulsion system would fire to obtain the desired apogee of 12,000 nautical miles, although the propellant required to achieve this would rule out the follow-on burn to accelerate to lunar return velocity. As planned, the spacecraft adopted an attitude to ‘cold soak’ its heat shield for 6 hours. At high altitude, a 70-mm camera snapped 370 colour pictures of Earth in daylight, and instruments monitored how efficiently the command module’s wall blocked the charged-particle radiation circulating in the van Allen belts.

On jettisoning the service module, the command module oriented itself for entry, making contact at 009:38:29 at an inertial velocity of 32,830 ft/sec (10 per cent less than intended) on a flight path angle of-5.85 degrees. It splashed down 49 nautical miles short of USS Okinawa, on station at the recovery point for the simulated lunar return. For the first time, a capsule adopted the apex-down flotation attitude, but was promptly righted by a set of airbags that inflated on its nose. It was recovered when the ship arrived 6 hours later.

Even while CSM-020 was coasting in space, NASA set up a meeting at the Cape with the contractors to investigate the problems suffered by the upper stages. Within 24 hours a review of the recorded telemetry established that:

• 70 seconds after S-II ignition, sensors in the engine compartment began to report chilling and the flow of liquid hydrogen to engine no. 2 increased;

• at +110 seconds the thrust of this engine began to decline gradually, and then dropped sharply at +169 seconds, at which time the load on the mechanism that gimballed the engine suddenly increased to counter a lateral component of thrust;

• at +263 seconds the thrust fell sharply again, there was a sudden increase in temperature in the engine compartment, the automatic system to shut down an engine if its thrust fell below a specific value intervened; and

• one second later engine no. 3, which had shown no anomalous behaviour, suddenly cut off!

It was soon realised that engine no. 3 had cut off because it received the command intended for its ailing sibling. It was inferred that the control wires for the solenoids of the liquid oxygen prevalves of engines 2 and 3 must have been erroneously cross­connected. A check of the records showed that the wiring had been modified several months previously. Thus the intervention had shut down engine no. 2 by cutting off its fuel supply and shut down engine no. 3 by cutting off its oxidiser.

The telemetry from the S-IVB showed that its J-2 had also behaved anomalously by starting to chill at +68 seconds, the thrust starting to decline at +107 seconds, the rate of decline increasing at +115 seconds, and then the engine compartment temperature increasing at +119 seconds. However, in this case the engine continued until it was shut down nominally at +170 seconds.

Thus two engines on different stages had misbehaved in a strikingly similar way: namely, the onset of chilling in the engine compartment about 70 seconds into the burn, the thrust starting to decay about 40 seconds later, and then a sudden increase in temperature – although at different times.

The chilling implied a propellant leak – and the fact that a temperature colder than liquid oxygen was measured indicated a leak of hydrogen somewhere in the feed to the engine. The way in which the engine compartment of the S-II had been chilled supported the case for a hydrogen leak – that is, it had affected engine no. 5, which was in the centre of the cluster, but the engine on the opposite side of the cluster was unaffected. The structure of the engine and its orientation within the cluster implied that the leak was associated with a stainless steel pipe about 1 inch in diameter that wound its way ‘upwards’ from the middle of the assembly. This pipe carried liquid hydrogen to the ignition system, a small chamber in the middle of the injector plate in the roof of the combustion chamber. Another pipe delivered liquid oxygen. Spark plugs ignited this mix and issued a jet of flame into the chamber to start and sustain main combustion. The hydrogen pipe incorporated three flexible bellows to permit movement, with one bellows located precisely where the leak was inferred to have occurred. Evidently, the leaking pipe sprayed liquid hydrogen into the engine bay, chilling it. This flow created the lateral component of the thrust which the gimbal counteracted. The reduced flow of hydrogen to the igniter made the flame from the igniter oxygen-rich and turned it into a ‘torch’ which so eroded the structure as to let blazing gases enter the engine compartment, heating it. Rocketdyne rigged an engine at the Santa Susanna Test Laboratory in California to replicate the leak, and within a month was able to reproduce the behaviour of engine no. 2.

In the case of the S-IVB it was concluded that when the feed pipe broke, it did so completely, and with no hydrogen reaching the igniter there was no ‘torch’ to erode the structure. However, gas was able to pass from the combustion chamber through the igniter and out of the severed pipe to cause external heating. The cryogenic leak froze the hydraulic fluid, with the result that during the restart attempt both the main and auxiliary hydraulic pumps cavitated and yielded essentially no system pressure. In any case, with no hydrogen reaching the igniter there was no way that the engine could have been ignited even if everything else had worked.

Within a month, therefore, the investigators knew what had happened to the J-2s, but not why. To discover why the pipe was vulnerable, the telemetry from AS-501

was compared with that from AS-502. It was noted that on AS-502 the power of the engines was greater, and that the liquid hydrogen pressures in the pipes would have been marginally greater. Tests by Rocketdyne established that the bellows section vibrated at the increased flow rate, but even on a prolonged firing remained intact. The entire engine was vibrated prior to ignition to simulate the pogo of the S-IC in case this had been a factor, but the engine fired as before with the bellows vibrating. After several weeks, it was decided to vibrate the engine while passing fluid at the increased rate – but for safety using gaseous nitrogen at room temperature instead of liquid hydrogen. As the flow rate was being adjusted to the value desired, and prior to the vibration being introduced, the bellows failed. The same thing happened to a replacement. An inspection indicated metal fatigue arising from vibration induced by the flow.

Attention then turned to the environmental factors. The flight engine had been in near-vacuum in the upper atmosphere. The firing tests had been at sea level where, with liquid hydrogen at -253°C, a coating of ice would have formed on the bellows and tended to dampen out the vibration induced by the flow. Rocketdyne put an engine into an altitude chamber and pumped liquid hydrogen through the pipe, and the bellows failed after 100 seconds. In retrospect, the mystery was not that failures had occurred in flight; it was that the other engines had not succumbed to the same problem! Regardless, the fix was to use pipes which incorporated bends capable of absorbing the movements that the flexible bellows had been intended to counter.

Meanwhile, the pogo had been overcome by modifying the prevalves in the liquid oxygen ducts of the S-IC engines to incorporate a cavity containing helium which, by compressing, would dampen pressure fluctuations and thereby maintain a smooth combustion.

An analysis of the structural failure of one of the SLA panels found that this was unrelated to the pogo. Aerodynamic heating had increased the pressure of moisture inside the aluminium honeycomb material sufficiently for part of the facing sheet to puncture and tear off in the slipstream. It was decided to apply a layer of cork to the exterior of the adapter to absorb moisture, and to drill holes to prevent a build up of pressure within the underlying honeycomb.

Sam Phillips said this post-flight investigation was “one of the most aggressive, thorough and determined engineering test and analysis programs I have ever seen”.

In fact, AS-502 was a successful test flight precisely because it revealed problems which were then fixed.

Notwithstanding the problems suffered by AS-502, on 23 April George Mueller called for AS-503 to be manned. Although Sam Phillips directed the next day that this launch vehicle be prepared with CSM-103 and LM-3 for a manned mission, he also instituted contingency planning to reconfigure it with BP-30 and LTA-B in the event of the decision to undertake a third unmanned test. The Kennedy Space Center replied that, given sufficient notice of the configuration, the ‘boilerplates’ would be able to be launched in mid-October but the manned mission would not be ready until late November at the earliest. On 26 April James Webb approved this planning for a manned mission, subject to a resolution of the anomalies which afflicted AS-502. In seeking to overcome the pogo, the Marshall Space Flight Center asked whether the

would damp out pressure fluctuations.

emergency detection system could be configured to trigger an abort automatically. When Deke Slayton argued against doing so, George Low ordered the development of a ‘pogo abort sensor’ with a display in the command module to enable the crew to judge whether to initiate an abort. On 17 August, by which time it was clear that the pogo would be able to be eliminated, Low recommended that work on this sensor be terminated and a week later Phillips concurred.

Meanwhile, when the fuel injector of the ascent propulsion system developed by the Bell Aerospace Company for the LM continued to suffer combustion instability into the summer of 1967, NASA hired Rocketdyne to develop an alternative injector as a contingency measure. In April 1968 Grumman was instructed to coordinate the testing of Rocketdyne’s injector in Bell’s engine. In May George Low decided that this hybrid should be used, and told Rocketdyne to perform the integration work. By mid-August it was clear from qualification testing that the modified engine was free of instabilities, and there would be no need to mount another test flight. On 13 May Low met Chris Kraft, Deke Slayton and Maxime Faget to consider whether the ‘fire in the hole’ staging demonstration should be on the ‘D’ or ‘E’ mission. A key factor was that LM-3 would be the last to have the development flight instrumentation for monitoring the systems. Faget argued that whilst such data was desirable, it was not essential – it would be sufficient to take photographs of the base of the ascent engine following the rendezvous. In view of this line of argument, and the fact that the ‘fire in the hole’ staging demonstration would increase the complexity of the ‘D’ mission, Low postponed making a decision on whether to do it on the ‘E’ mission until the performance of the engine on LM-1 had been thoroughly analysed. On 17 May Kraft advised Low that the ‘E’ mission was already a complex affair, and that as further objectives were added the probability of achieving them diminished. In fact, Kraft saw little need for a ‘fire in the hole’ test. He understood the engineers’ desire to test all the systems in space in both normal and backup modes, but the first ‘fire in

the hole’ test at the White Sands Test Facility on 22 December 1967 had achieved all its objectives and further ground testing would provide the data needed to calculate the pressure and temperature transients pertaining to lunar lift off.5 In parallel with these discussions, the Manned Spacecraft Center was studying extending the apogee of the ‘E’ mission to almost lunar distance to investigate navigation, communica­tions and thermal control issues in the event of the lunar orbital ‘F’ mission being deleted, and this alternative mission was labelled ‘E-prime’.

On 7 May 1968 CSM-101 passed its final customer acceptance review, and at the end of the month was delivered to the Cape. The inspectors were delighted to find fewer discrepancies than on any previous spacecraft. But Wally Schirra, who would be in command of flying the vehicle, did not accept it as flightworthy until after its altitude chamber tests in June. In contrast, when LM-3 was delivered on 14 June the inspectors found over 100 deficiencies, many of which were classified as major. In July, George White, the Chief of Reliability and Quality Assurance in the Office of Manned Space Flight, briefed George Mueller on the issues the Certification Review Board would require to consider.

On 7 August George Low advised the Manned Space Flight Management Council that the delivery of CSM-103 was imminent, but LM-3 was unlikely to be ready for launch until February 1969.

Low felt that for Apollo to have a chance of achieving a lunar landing in 1969, the first manned Saturn V must be flown in late 1968. By this point, the pogo problem was heading towards resolution and the other issues that marred AS-502 had been fixed. In April 1967 the Manned Spacecraft Center had outlined a contingency for a lunar mission involving only the CSM. On 8 August Low asked Kraft to consider sending CSM-103 to the Moon, and then he flew to the Cape with Carroll Bolender, ASPO’s LM Manager, Scott Simpkinson, Chief of ASPO’s Test Division, and Owen Morris, ASPO’s Chief of Reliability and Quality Assurance, to discuss AS-503 with Sam Phillips, Kurt Debus, Director of the Kennedy Space Center, Rocco Petrone, Director of Launch Operations and Roderick Middleton, the Apollo Manager at the Cape.

At 08:45 local time in Houston on 9 August, Low met Kraft and Robert Gilruth to discuss the CSM-only option. Kraft said that it was feasible and Gilruth was enthusiastic. At 09:30 Deke Slayton was called in, and offered his support. Low then telephoned Sam Phillips, who had remained in Florida, and a meeting was arranged at 14:30 in Huntsville. In attendance were Low, Gilruth, Kraft and Slayton from the Manned Spacecraft Center; Wernher von Braun, Eberhard Rees (his deputy), Lee James (his Saturn V Program Manager) and Ludie Richard from the Marshall Space Flight Center; Kurt Debus and Rocco Petrone from the Kennedy Space Center; and Phillips and George Hage (his deputy) from headquarters. Low opened by saying that if the Apollo 7 evaluation of CSM-101 went well, it would be technically possible to send CSM-103 out to the Moon in December. However, if CSM-101 had

In the event, no ‘fire in the hole’ separation was demonstrated in space.

problems then it would be necessary to confine CSM-103 to Earth orbit to continue the evaluation of the spacecraft’s systems. Kraft pointed out that a mere ‘loop’ around the far-side of the Moon and then back to Earth would be insufficient – the spacecraft would have to enter orbit in order to contribute significantly to the lunar landing mission (which, depending on whether the ‘F’ mission was undertaken, might be the next mission to venture to the Moon). There was general agreement to initiate the planning for this contingency in secret, pending the decision and public announcement. The meeting broke up at 17:00. On returning to Houston, at 20:30 Low briefed George Abbey (his technical assistant), Kenneth Kleinknecht (his CSM Manager), Carroll Bolender (his LM Manager) and Dale Myers (Apollo Program Director for North American Aviation).

On 10 August Slayton offered this ‘new’ mission to James McDivitt, who was earmarked to fly AS-503, but McDivitt opted to await LM-3 so as to keep the ‘D’ mission for which his crew had been training. In contrast, Frank Borman, who had eagerly followed the discussions to extend the apogee of his ‘E’ mission out to lunar distance, readily accepted, and thereby regained the first manned Saturn V mission.

Kraft told Low on 12 August that a daylight launch would be required to allow an Atlantic recovery after an abort, and this meant the lunar launch window would open on 20 December. Low selected LTA-B as a stand-in for the LM because it had been assigned to fly with BP-30 on the unmanned mission and was already in preparation.

On 14 August the original twelve conferees, minus Rees, were joined at a meeting at NASA headquarters by Deputy Administrator Thomas Paine, Julian Bowman and William Schneider (the latter both of the Office of Manned Space Flight) to make a formal recommendation. With the discussion in progress, George Mueller telephoned from Vienna in Austria, where he and James Webb were at a United Nations Conference on the Exploration and Peaceful Uses of Outer Space. Mueller was sceptical of the proposal, and said he would not be able to discuss it until 22 August. Paine, playing the devil’s advocate, pointed out to the conferees that until recently there had been doubts about whether the Saturn V was safe for manned flight, and here they were considering having it send a spacecraft on an impromptu mission to orbit the Moon, then he invited comments. Von Braun pointed out that once it was decided to man AS-503, it did not matter how far the spacecraft went. Hage noted that there were a number of points in the mission where go/no-go decisions could be made, managing the risk. Slayton opined that not to pursue this option would significantly diminish the likelihood of achieving President Kennedy’s deadline. Debus had no technical reservations about the launch. Nor did Petrone. Bowman said it would be a ‘shot in the arm’ for the program. Lee James said it would enhance the safety of later flights. Ludie Richard said it would improve lunar capability. Schneider was fully in favour. Gilruth pointed out that although it was an impromptu mission, it would improve the chance of being able to achieve the overall goal of the program. Kraft reiterated that it should be a lunar orbital rather than a circumlunar mission. Low pointed out that if Apollo 7 succeeded, they could either fly this impromptu mission or await LM-3 and launch in February or March. In view of the deadline for the lunar landing, Low said the decision was obvious: they should send Apollo 8 to the Moon. Paine concurred. Phillips ordered planning to continue.

Phillips and Paine discussed the plan with Mueller and Webb on the telephone the next day. Mueller had warmed to the idea overnight. Webb was “fairly negative” (as Phillips later put it) but asked for information to be sent by telegram. On 16 August Webb called Paine and agreed to the mission planning, with the proviso that there be no public announcement. On 17 August Phillips told Low that although Webb had authorised a manned Saturn V launch in December, there must be no ‘leak’ that the spacecraft might venture to the Moon – that decision was contingent on the outcome of Apollo 7.

Meanwhile, CSM-103 had arrived at the Cape and a start had been made on the modifications required to send it to the Moon. On 19 August Phillips directed that if AS-503 was manned and did not carry a LM, irrespective of where the spacecraft went the mission was to be designated ‘C-prime’. Then McDivitt’s crew would fly the ‘D’ mission riding AS-504 with CSM-104 and LM-3. The ‘E’ mission had been deleted. That same day, Phillips told the press that if the mission of CSM-101 was a success, AS-503 would be manned and that because the LM would not be ready this would be a CSM-only mission; by not mentioning the option of leaving Earth orbit he readily conveyed the impression of an Earth orbit mission. On 3 September Low directed that if the ‘C-prime’ mission went to the Moon, it would make ten orbits over a period of 20 hours and then head home. If it was confined to Earth orbit, it would undertake the parking orbit preparations for translunar injection and then fly one of a number of alternative missions, each of which would involve simulating the transposition, docking and extraction of the LM. On 9 September Borman’s crew began to train in the simulator at the Cape for the lunar mission. Ten days later, with the AS-502 investigations finished and the remedies implemented, Mueller declared the Saturn V to be ‘man rated’. CSM-103 was mated with AS-503 on 7 October, the launch escape system was added on 8 October, and the next day the space vehicle was rolled out and installed on Pad 39A.

On 31 March 1968 Lyndon Johnson announced that he would not seek and would not accept his party’s nomination for the presidential election in November. The two main candidates were Hubert H. Humphrey and Richard M. Nixon. Perhaps because James Webb knew that neither would retained him as NASA Administrator, he informed Johnson on 16 September that he would stand down on 6 October, which was his 62nd birthday. Thomas Paine was promoted to Acting Administrator.

Meanwhile, on 20 September CSM-101 passed its flight readiness review, and later that day Wally Schirra announced to reporters that Apollo 7 would be his final mission because he intended to retire from NASA.