As the world faces arguably its greatest crisis since the Spanish ‘Flu of 1918-1920 and NASA gears up steadily for the first of its three, planned Artemis flights, which will take man (and almost certainly at least one woman) back to the Moon, there is a certain irony in the fact that Artemis 2, the first crewed Artemis flight and the first return to the Moon, will aim to carry out a watered-down version of the Apollo 8 mission, launched 54 years previously. However, Artemis 2 will replicate most exactly a flight – Apollo 13 – that launched exactly 50 years ago today, which is often regarded, even more than the first Moon landing, as NASA’s finest achievement.
Apollo 13 clears the tower after launch.
There was one man in common between these two missions that beat the odds, albeit in different ways: Jim Lovell, arguably the greatest astronaut to have flown.
What was not known at the time that Apollo 8 launched was that it was a desperate gamble. The American Moon programme was faltering. After the loss of Apollo 1’s crew and the subsequent painful investigation, the second test flight of the Saturn V – Apollo 6 – was an unmitigated disaster. The Saturn V rocket that was intended to take three men to the Moon little more than a year later, proved to be dangerous and unreliable. The First Stage suffered from such great combustion instability, creating violent thrust fluctuations that turned into pogo, that two of the five engines of the Second Stage were damaged. Pieces fell off the upper part of the rocket, which did not make trans-lunar injection because the motor of the Saturn IVb Third Stage was damaged also and failed to re-start. Had it been a crewed mission, there must be some question as to whether or not the crew would have survived.
Apollo 7 at least proved the Command Module ready for flight, although the near mutiny on-board ensured that none of the astronauts would ever fly again. However, the Lunar Module that was due to fly on Apollo 8 was giving severe problems, was delayed and was not going to be ready on time. And, with issues mounting for the programme, the et tu brute was the news that the Soviet Union planned to launch a single cosmonaut on a figure-of-eight trajectory around the Moon before the end of 1968. Even if the Soviet programme was not ready to land a man on the Moon, the mere fact of flying round the Moon first would take the gloss off the planned American landing with Apollo 12, late in 1969.
NASA decided on a Hail Mary play. The engineers thought that they had fixed the problems with the Saturn V – they had not, but that is part of the narrative later on in this story – so they decided to switch Apollo 8 and Apollo 9 and accelerate the Apollo 8 launch schedule. More dramatically, instead of being a Lunar Module test flight in a medium-high Earth orbit, Apollo 8 would fly to the Moon and go into lunar orbit.
Frank Borman, Michael Collins and Bill Anders had been training since November 1967 for an Earth orbit flight with the Lunar Module. In July 1968, one month before their mission was changed, the crew lost their Command Module pilot as Michael Collins suffered a herniated disk that required surgery. In quick and bewildering succession, Jim Lovell had to tell his wife, Marilyn, first that he had been moved on to the Prime Crew of Apollo 9 and then, just weeks later, ask her if she fancied travelling over Christmas.
“Where?” asked Marilyn innocently.
“How about the Moon?” replied her husband, in the matter or fact way that was to become his trademark.
That was how Jim Lovell announced to his family that he would be on the first crew to leave Earth orbit.
It also radically changed the direction of Jim Lovell’s astronaut career. Had Michael Collins not needed to be replaced and had the crew flown, as intended, Apollo 9, Lovell would most likely have flown as Command Module Pilot on Apollo 12 (then, intended to be the first Moon landing) before, presumably, commanding Apollo 18 [the standard crew rotation for a Command Module pilot was to be back-up crew for a mission (Apollo 9) then, three flights later, to fly as prime Command Module Pilot (Apollo 12) and then, six flights later, to command a flight (Apollo 18). Of course, there were many exceptions and the rotation was not always followed, but this was the likely scenario]. Instead, he jumped the queue and, as Command Module pilot for Apollo 8, was given command of Apollo 14.
Had Marilyn Lovell known that her husband was set to fly what were undoubtedly the two most dangerous flights that NASA had launched since John Glenn’s first orbital flight in the dangerously unreliable Atlas rocket, she would have felt a lot less happy for him.
Fortunately, Apollo 8 turned out to be a brilliant success and set the Moon-landing programme back on track, setting-up Jim Lovell to be the first of just four astronauts to make two trips to the Moon. In fact, it was so successful that it made it possible for NASA to start thinking of landing Apollo 11 on the Moon instead of Apollo 12 and even to offer the chance to Tom Stafford to land Apollo 10. What no one outside a very tight circle that included the astronauts, senior engineers and management was that the astronauts of Apollo 8 had been given no more than a 50-50 chance of returning from their mission.
In order to stay ahead of the Soviet Moon programme, there could be no test flight of the Saturn V, modified after the April 1968 launch of Apollo 6. In fact, many modifications had been made to the Saturn V to try to fix the problems that Apollo 6 had revealed and the Saturn V itself had also been upgraded for its mission, with the SA-503 more powerful than either of its predecessors. Apollo 8 would depend on the successful re-lighting of the Saturn IVb and on the ability of the motor of the Service Module to make multiple, long firings. And, not least of the issues, the failure of Apollo 6 to go into a translunar trajectory meant that the re-entry manoeuvre had not been tested at Lunar return velocity but, instead, only at the much lower velocity of re-entry from Earth orbit. All in all, there were a lot of untested components that would have to work perfectly, first time: the 50-50 odds were no exaggeration.
Apollo 8 was a unique flight in many senses. The elevation of Jim Lovell to prime crew made it unique in another, less commented way. Invariably, the mission commander was the most experienced astronaut on board. Michael Collins had spent 11 days in space on Gemini 10. Frank Borman had spent 14 days in space as Mission Commander in Gemini 7. And Bill Anders had not flown, so Borman clearly had seniority. When Lovell was bumped-up to the prime crew, not only did he have the experience of flying Gemini 7 with Frank Borman, but had also commanded a 4 day flight with Gemini 12, making him the most experienced NASA astronaut, in terms of time in space, after Walter Schirra and clearly senior to Borman, but only second-in-command on Apollo 8. For Lovell, though, the chance to make a second moonflight as commander and to walk on the Moon would have overridden any sense of broken command protocol.
After the PR success of Apollo 11 and the PR disaster of Apollo 12, with its TV camera burnt out within minutes of the first moonwalk starting, NASA desperately needed Apollo 13 to work well. Apollo 12 should have offered spectacular colour images of the moonwalk to Surveyor crater. Instead, frustrated networks had used puppeteers and other visual aids to try to make up for the lack of any images from the Moon. Patience had worn thin, public interest was waning and the networks no longer had an insatiable appetite for spaceflight. In response, NASA had picked the Fra Mauro Hills as the landing site, after the billiard-table smoothness of Mare Tranquilitatis and Oceanus Procelarum, in the hope of having some spectacular colour images of lunar hills to reawaken public interest. It was also going to be the first mission in which science would take priority over Public Relations. Like Apollo 12, it would carry out two moonwalks, but each would be nearly an hour longer than Apollo 12’s, taking the endurance of the backpacks on their spacesuits almost to its limit. NASA wanted to offer a good show. They got a show, but not the one that was intended. Apollo 13 launched on April 11th 1970. And, even before it launched, things started to go wrong.
Originally, Apollo 13 was to have been commanded by Alan Shepherd, the first American in space. He had been grounded by an inner ear disorder that caused him severe issues of balance and orientation. Finally, it had been cured by a new and risky procedure, allowing NASA once again to put a Mercury astronaut on the rotation for Moon flights. However, eight years inactive, most of it spent in the astronaut office, meant that he had missed both Gemini and the chance to back-up one of the early Apollo missions, either of which would have helped him to get up to speed again. As a result, training for their flight was going slowly and management decided, wisely, to give Shepherd and his crew more time to train by swapping Apollo 14 (originally intended to land in Littrow crater in Mare Serenitatis) and Apollo 13 (to land in Fra Mauro). So, Jim Lovell’s crew moved up one flight.
In the light of events, NASA must have thanked their lucky stars that when things went to pieces in space, the most experienced astronaut in the whole astronaut corps was in command and not someone who had made a single, 15 minute sub-orbital hop and who was supported by a rookie crew. No one has, to my knowledge, ever said it, but Jim Lovell may just have been the difference between just about making it back alive and failing to survive. However, we get ahead of ourselves…
The Apollo 13 crew, the day before launch, with a smiling Jack Swigert (centre), who probably could not believe his luck in getting an unexpected chance to walk on the Moon, flanked by Jim Lovell (right) and Fred Haise (left).
Things continued to go wrong from Apollo 13 a week before launch. Backup Lunar Module Pilot, Charlie Duke, later to fly on Apollo 16, caught German measles from a friend of his son. Both prime and back-up crews had been in close contact with him and could, potentially have come down with the illness in transit to the Moon. Jim Lovell and Fred Haise were found to be immune, Ken Mattingley, Command Module Pilot, was not. Mattingley could not be risked.
In these circumstances, NASA had two normal courses of action:
- The normal course was to swap the entire crew and have back-ups, John Young, Jack Swigert and Charlie Duke fly in their place. This, obviously was a non-starter as Charlie Duke was ill himself.
- Failing this, normally they would replace Ken Mattingley with the back-up Command Module Pilot, retaining the rest of the prime crew. Again, this was impossible because Mattingley’s back-up was Duke.
The remaining options were both undesirable: postpone the launch for a month, or make the highly unusual step of replacing Ken Mattingley at the last moment with the back-up Lunar Module Pilot, Jack Swigert, who would have to do a job that he had not trained for. Just two days before launch, a slightly bewildered Jack Swigert got the news that he would replace Mattingley.
Initially, after launch, all went well, however, all the Apollo astronauts were nervous about the fragile Saturn II Second Stage and none of them really trusted it. Jim Lovell had more reason than most to be concerned, as his Apollo 8 flight had, unexpectedly, experienced some serious pogo (violent back and forth oscillations due to uneven burning) from the Second Stage. It has not felt severe to Lovell and was not seen as a real issue, but had put the support of the central engine under severe strain. A fix had been designed, but the engineers had not had the time to install on Apollo 13 and relied, from Apollo 9, on the simple expedient of shutting off the central J-2 engine around a minute before the others to avoid the peak pogo effect in it.
Five minutes and thirty seconds into its flight, unknown to the astronauts and to mission control, Apollo 13 faced disaster, as the Second Stage came close to catastrophic failure. Responding to three seconds of severe and increasing oscillations caused by pogo, the centre engine shut down two minutes earlier than it should have. The pressure in the liquid oxygen feed to the combustion chamber went out of limits and the transducer that reported the pressure of liquid oxygen being fed into the combustion chamber broke, fortunately triggering the low pressure warning that shut down the engine.
At the time, it seemed like a minor inconvenience to the flight: the other four engines burned for extra time to compensate, using the fuel that the centre engine had not burnt and the correct Earth orbit was achieved with only a minor deviation from optimum. Crew communications, reported in the flight log, of which extensive extracts are reproduced throughout this article, reveal a calm call from Jim Lovell, followed an acknowledgement from CapCom, Joe Kerwin and then by some degree of concern from Lovell and Swigert, with the inserts from the Public Affairs Officer (in green) who was obviously unaware that this incident was an important anomaly:
(PA Officer) And at 5 minutes 30 seconds into the launch, we continue to look very good on the second stage. [NB: Famous last words here]
000:05:32 Lovell: Inboard.
(PA Officer) Jim Lovell just reported the inboard engine has shut down as scheduled.
000:05:32 Swigert (onboard): Inboard.
000:05:36 Kerwin: Rog. We confirm inboard out. [Pause.]
000:05:38 Lovell (onboard): That shouldn’t have happened.
000:05:40 Swigert (onboard): No. That’s 7:42. That’s 2 minutes early
What no one knew at the time was that the pogo had been so severe that the forces on the engine support structure had gone way over the design limits and the structure itself had started to deform, albeit only by a few centimetres so far: the peak was estimated at 34g (34 times the force of gravity), more than double the design limit of 15g and almost ten times more than any other flight had suffered in normal circumstances. Had the centre engine not shut down, the entire structure would, almost inevitably, have failed, potentially at about 4 minutes into the Second Stage burn, sending fragments exploding into the rocket. It would have been similar to the Challenger disaster.
Above: the force on the centre engine support. The engine was oscillating backwards and forwards, 17 times per second with a maximum force that according to post-flight estimates, reached ±33.7 times the force of gravity.
Below: Liquid oxygen feed pressure into the combustion chamber. About 330.7 seconds into the flight there was a pressure surge so large that it broke the transducer that measured the pressure, triggering the shutdown of the engine.
After the issues with Apollo 13, the fix was added for Apollo 14 and, finally, cured the pogo problems of the Second Stage for once and for all. In the aftermath of what happened later, the incident during the ride to orbit got little attention, but it was a huge wake-up call for the engineers and is still used by NASA as an object lesson in how dangerous the pogo effect can be. Catastrophe was barely avoided and only because it was a non-critical component that broke first and triggered the engine shutdown.
Once in orbit, all seemed plain sailing to the extent that US networks lost interest totally in the flight. The news from Vietnam seemed much more important and immediate than the news from space. The Apollo 13 film recounts the families of the crew going to Mission Control to watch the broadcast from the capsule but, in reality, they had no choice, as no network chose to show it, so the families were fully aware of the complete lack of interest from the media. A consequence of this was that when, suddenly and unexpectedly, the mission became interesting, it was foreign media such as the BBC who were better placed to ramp-up coverage quickly. The BBC’s Apollo 13 studio was (almost) constantly manned, with its stream of updates and inserts into news bulletins; in contrast, most US media had dispersed their teams and shut down their studios until the moonwalks.
Fifty-five hours and fifty-two minutes into the mission came the fateful exchange between CapCom Jack Lousma and Command Module Pilot, Jack Swigert:
055:52:58 Lousma: 13, we’ve got one more item for you, when you get a chance. We’d like you to stir up your cryo tanks. In addition, I have shaft and trunnion… [Pause.]
055:53:06 Swigert: Okay.
055:53:07 Lousma: …for looking at the Comet Bennett, if you need it.
055:53:12 Swigert: Okay. Stand by.
Normally, the cryotank stir would be done just once a day but, the previous day, the sensor of Oxygen Tank 2 had failed. EECOM, Sy Libergot, another of the legendary figures of the Apollo missions, was concerned that with one tank in an unknown state, it was vital to get a good measure on the other. To do this they would stir both tanks with a fan to mix up the slurry of semi-frozen and liquid gas and get a good reading of content. Seeing how much oxygen had been used from #1 Tank would give an idea of the amount used also in #2.
Jack Swigert was in the left-hand seat and flicked the two switches marked “O2 FANS ON” on the panel in front of him.
The cryocontrol panel in front of Jack Swigert. The oxygen tank fan switch that triggered the explosion is marked in red. Above are the gauges that show the pressure in the hydrogen and the oxygen tank and the fill level (here, just over 60%) as Swigert saw it at that moment. Within minutes, the oxygen tank #1 level would start to fall rapidly. Tank #2’s sensors started to work again, momentarily, with the jolt of the explosion, although giving false readings.
At 055:54:53 Ground Elapsed Time – 03:07:53GMT on April 14th 1970 – Number 2 Oxygen Tank exploded with a force of about 3.7kg of TNT, blowing out a panel of the Command Module and crippling the mission.
Initially, the astronauts did not realise that something serious had happened. In his book “Lost Moon“, Jim Lovell explains what happened (I recommend listening to his reading in the audiobook edition to hear his calm reaction and dry wit describing events). Fred Haise was floating up in the Lunar Module. A standard joke that was played by him was to hit the tunnel re-pressurisation button, which equalised pressure between the Command Module and the Lunar Module: this produced a rather satisfactory bang of released pressure and made the tunnel between the two craft shake and, which was the reason for playing the joke, the noise gave his fellow astronauts a violent start. Hearing the bang and feeling the shake, Jack Swigert and Jim Lovell started to curse Fred Haise, as they felt that the re-press valve joke was wearing thin.
There was a 26 second delay as the astronauts realised that, this time, Fred Haise was innocent. Then, the calls started to come in:
055:55:19 Swigert: Okay, Houston…
055:55:19 Lovell: …Houston…
055:55:20 Swigert: …we’ve had a problem here. [Pause.]
055:55:26 Fenner (GUIDO): FLIGHT, GUIDANCE.
055:55:27 Kranz (FLIGHT): Go GUIDANCE.
055:55:28 Lousma: This is Houston. Say again, please.
Contrary to popular belief, no one said “Houston, we have a problem”, least of all Jim Lovell. There is momentary confusion as both Swigert and Lovell start to speak and Swigert makes the famous call. At the same time, the White Team Flight Guidance Office, Bill Fenner, alerted Gene Kranz that he had seen a problem and Gene Kranz asks him to report. Jack Lousma, the CapCom, was disconcerted by the word “problem” and, after a few seconds hesitation, asked the crew to confirm their call.
By this time, the crew knew that they had a serious issue and Lovell took over, repeating Swigert’s words and adding information, while Bill Fenner reported what he had seen:
055:55:28 Fenner (GUIDO): We’ve had a Hardware Restart. I don’t know what it was.
055:55:30 Kranz (FLIGHT): Okay. GNC, you want to take a look at it? See if you see any problems?
055:55:35 Lovell: [Garble.] Ah, Houston, we’ve had a problem. We’ve had a Main B Bus Undervolt.
Over the next few minutes the problems multiplied until it became obvious that a major catastrophe had overtaken the mission. However, it took more than an hour before the astronauts finally gave up on the Moon landing.
The initial problem call came at 055:55:20 (just about 2 days and 8 hours) into the mission. Just under fourteen minutes later, at 056:08:57, Jim Lovell reported that #2 Oxygen Tank was reading empty. Ten seconds later, as he next reported on attempts to restore AC power on-board, he noted calmly that something was venting into space from the spacecraft. At this point, Mission Control and crew were still thinking that there had been an instrument problem and were trying to safeguard the Moon landing. However, to see something venting out of the side of the spacecraft did not square with an instrument issue. Finally, the penny started to drop that it was their precious oxygen that was escaping into space.
A puzzled Gene Kranz watching the telemetry from the spacecraft and listening to the multiple problems being reported. This is a still from internal NASA filming of Mission Control at the moment of the crisis.
Fifteen and a half minutes after Jack Swigert’s initial call, Gene Kranz made the first suggestion that the Lunar Module might need to be used as a lifeboat:
056:10:46 Kranz (FLIGHT): Okay now, let’s everybody keep cool, we got the LM still attached, the LM spacecraft’s good so if we need, uh, to get back home we’ve got a LM to do a good portion of it with. Okay, let’s make sure that we don’t do anything that’s going to blow our CSM electrical power with the batteries or that will cause us to lose the main or the fuel cell number 2. Okay, we want to keep the O2 and that kind of stuff working. We’d like to have RCS, but we got the Command Module system, so we’re in good shape if we need to get home. Let’s solve the problem but let’s not make it any worse by guessing.
Finally, at 56:50:10 into the flight, fifty-five minutes after the explosion, after a definitive and terminal report from Sy Libergot that, at the rate of loss, the remaining oxygen would last less than two hours, Gene Kranz made the call to get the astronauts back as fast as possible using the Lunar Module.
Even so, for the next 25 minutes, Mission Control and the astronauts made some final, desperate efforts to stop the oxygen tank leak as Glynn Lunney’s Black Team took over from Gene Kranz’s White Team at shift change. Finally, CapCom, Jack Lousma, tells the astronauts that they are now thinking of using the Lunar Module as a lifeboat and, after a short delay, Jack Swigert confirms that the astronauts have come to the same conclusion. The Moon landing was cancelled.
When the crew started to activate the Lunar Module, they had an estimated 15 minutes left to carry out a procedure that would normally take several hours and that occupied 59 pages of instructions. Once the oxygen tank pressure dropped below 100 pounds per square inch (about 7 times atmospheric pressure), the final fuel cell would fail and there would be no power left for the critical Lunar Module activation.
The cryocontrol panels readings that Sy Libergot would have seen, which made Gene Kranz make the call to get the astronauts back home as fast as possible in the Lunar Module. In the right hand circle, Oxygen Tank 2 is showing zero pressure; in the left, Oxygen Tank 1, which should have shown a pressure of 870 pounds per square inch, is showing just 300 and dropping fast.
What had happened? It seems that the issue originated with Apollo 10. Before that flight, the oxygen tank was taken out of the Apollo 10 Service Module to be modified and a different tank substituted. In this process, the original tank was dropped. Although it fell only about 5cm, it seems that the fall must have damaged the valve that allowed the tank to be drained of its contents, although this issue was not detected and the tank was cleared for re-use in Apollo 13.
Here, Apollo 13’s problems started.
The company that fitted the tank thermostat built it for 28 volts. The ground test equipment at the launch pad had been changed to use 65 volts. The thermostat was then, accidentally, welded shut in ground tests by having the higher voltage run through it for prolonged periods.
Due to the damage to the valve, the liquid oxygen in the tank could not be emptied properly, so the engineers, unaware that the thermostat that controlled the temperature of the tank was not working, used the heaters to boil out the remaining liquid oxygen. The maximum temperature allowed by the thermostat inside the tank should have been 26⁰C; in reality, the temperature reached 500⁰C for several hours and damaged the Teflon insulation on the wiring. Three days later, a second test completed the damage.
When Jack Swigert threw the switch for the fans of Oxygen Tank #2, the insulation failed and an arc formed between two wires in a tank of high-pressure oxygen. The explosion was inevitable and could have happened at any point in the mission when an oxygen tank stir was requested. Fortunately, it occurred while the Lunar Module was attached to the Command Module, allowing the Lunar Module to be used as a lifeboat.
Lost Moon: although the low angle of illumination exaggerates the roughness of the terrain, the green spot shows the planned landing site and makes it clear that NASA was starting to be a little less cautious in selecting its landing sites, picking a spot in the middle of the hills formed by debris from the Imbrium Basin impact.
Most of the rest of the story is well-known and nicely re-told in the film “Apollo 13”, although there are two details that are less well known. The first is that, in his four years with NASA, Jack Swigert’s expert role had been to develop emergency on-board procedures. The film gives the impression that, as a late substitute, the crew somehow blamed him for the explosion, assuming that he had done something wrong; reality is that his emergency manual became the basis of crew survival and his presence undoubtedly was a factor in getting the crew back alive. Another detail is the way that both Jim and Marilyn Lovell appear in the film. Marilyn Lovell’s appearance is a fleeting one in a crowd scene before launch. Jim Lovell’s appearance is much higher profile. The Director of the film offered him the role of Admiral of the recovery carrier fleet – with its associated dialogue – a role that Jim Lovell rejected. As he explained later, he told the Director:
“I was a Captain in the Navy, being a Captain is good enough for me now.”
So, he was re-cast as the recovery carrier Captain and greeted his fictional self on the hanger deck.
Apollo 13 was a triumph of resourcefulness and brilliant problem solving. It was also a tribute to a crew who never gave up. Of course, the film glosses-over many details. One of the worst problems faced by the astronauts was a severe lack of water. As a by-product of the fuel cells in the Service Module it was never expected to be an issue, so there was only a very limited supply of drinking water on board, which also had to be used for instrument cooling.
The astronauts rationed themselves so severely that they became badly dehydrated and Fred Haise became seriously ill with a kidney infection. At the same time, as portrayed, the temperature in the cabin dropped as low as 2⁰C, making sleep extremely hard to obtain for the lightly-clad astronauts who did not dare put on their EVA suits and risk making things even worse by sweating inside them.
In these conditions, rest could only be obtained by floating in the cabin and allowing a bubble of warm air to form around their bodies (in microgravity there was no convection to carry the warmed air away) but, as soon as the astronaut moved, the bubble of warm air over their skin was broken and the icy chill returned. Jim Lovell slept a total of just 11 hours and Jack Swigert 12 in the five days after the explosion; even Fred Haise managed just 19 hours sleep. By the time that they re-entered the Earth’s atmosphere, the entire crew was utterly exhausted and making errors just when they needed to be most alert to carry out the delicate process of transferring navigational alignment back to the crippled Command Module and powering-up systems using a long and complex checklist that had been dictated to the astronauts and written on every scrap of blank paper on board.
As history recalls, the astronauts were stunned when they discarded the Service Module and saw the extent of the damage to it as it floated away. That such a crippled ship could be brought home safely was utterly incredible.
138:04:46 Lovell: And there’s one whole side of that spacecraft missing.
138:04:50 Kerwin: Is that right? [Pause]
138:04:57 Lovell: Right by the – Look out there, will you? Right by the high gain antenna, the whole panel is blown out, almost from the base to the engine.
138:05:09 Kerwin: Copy that. [Long pause]
138:05:22 Haise: Yes, it looks like it got to the SPS bell, too, Houston.
138:05:28 Kerwin: Think it zinged the SPS engine bell, huh?
138:05:31 Haise: That’s the way it looks; unless that’s just a dark brown streak. It’s really a mess. [Long pause]
This, spectacular image, taken as the Service Module starts to drift away, shows graphically the extent of the damage better than the close-ups . Half of the base of the Command Module by the engine bell has been ripped away and the whole side panel is missing.
There can be little doubt that Apollo 13 was NASA’s finest hour and getting the crew back alive, their greatest achievement. For a few days the whole world united. People followed the mission with an attention that surpassed even that of Apollo 11. The Soviet Union helped cover potential back-up splashdown sites in case the crew could not make it to their specified Pacific landing area. Then, after an agonising delay in communications that was around two minutes, with enormous concern that the explosion had damaged the heat shield, finally, the crew answered the increasingly anxious calls from the CapCom.
Strangely, the incredibly detailed Apollo 13 flight journal lacks timing information at this point. There were several calls from the Public Affairs Officer that have no timing information and the multiple unanswered calls from the CapCom, Joe Kerwin, to the astronauts are not recorded in the journal. For the last few minutes before re-entry Jack Swigert, as the Command Module Pilot, is the only voice heard. His last message came at a Ground Elapsed Time of 142:38:45 (i.e. 142 hours 38 minutes and 45 seconds into the mission). The log then simply reports a very long communications break (7 minutes and 23 seconds) until finally:
142:46:03 Kerwin: Odyssey, Houston standing by. Over.
142:46:08 Swigert: Okay, Joe.
142:46:12 Kerwin: Okay. We read you, Jack. [Long pause.]
Why did the crew take so long to respond? The favourite theory was that because the Command Module’s re-entry angle was flatter than expected, the radio blackout lasted much longer than predicted (6 minutes, rather than 4) but, even the official flight journal expresses surprise that no information exists on this point other than speculation and, surprisingly, the issue was not addressed in the post-mission de-brief. Curiously too, if the flatter entry angle was the cause of a much longer re-entry, why did the landing not overshoot, with Apollo 13 splashing down just 6.5km away from the Iwo Jima?
When the astronauts answered calls from the CapCom and the TV images showed the parachutes deployed, the tension burst, Mission Control relaxed, the crew relaxed (Jim Lovell reported in the Mission de-brief that Fred Haise even fell asleep before recovery) and the public switched off.
It would not be until February 5th 1971 that Apollo 14 would land in the Fra Mauro Hills. Apart from the brief interlude of television images at the start of the first Apollo 12 moonwalk, more than eighteen months had passed without pictures of astronauts walking on the Moon. In the meantime, the huge interest generated by Apollo 11 and the good will of Apollo 13 evaporated: it was all too easy. Been there! Done that! Saw the fuzzy pictures. The later Apollo missions sent high-quality TV pictures of spectacular landscapes, but the viewing figures for them had plummeted.
Apollo 20 had been cancelled three months before Apollo 13 launched.
In the aftermath of Apollo 13, less than six months after the flight’s triumphant return, Apollos 19 and 18 were cancelled too, as the Apollo programme was dismembered. Triumph had become tragedy for the project.
The lowest point of all was reached when, within weeks of Apollo 15 landing, President Nixon proposed to cancel even Apollos 16 and 17, demonstrating just how little political interest there was left in going to the Moon.
Fortunately, Nixon was persuaded to change his mind but, even if the Artemis programme stays on schedule, it will have taken NASA 54 years to get back to where they were in 1968.
 The unwritten rule was that, in normal circumstances, the back-up crew became prime crew in the same roles, three flights later. This would be the last flight for the Commander and the Lunar Module Pilot, but the Command Module pilot would Command a mission six flights later and get to walk on the Moon. Of course, Apollo 18 was cancelled and Apollo 14 switched with Apollo 13, so Jim Lovell would not have got to walk on the Moon in this alternative scenario either.
This rotation rule though gave Alan Shepherd his chance to walk on the Moon. Normally, command of Apollo 13 would have gone to Don Eisele, Command Module Pilot on Apollo 7, but the fall in disgrace of the crew opened a Mission Commander slot for Shepherd that he accepted eagerly.
 As of the end of 1968, of the Mercury seven: Gus Grissom had died in Apollo 1; Scott Carpenter, Alan Shepherd and Deke Slayton were grounded due to medical issues (while Shepherd and Slayton finally got to return to flight status, Carpenter had suffered such severe injuries in a 1964 motorcycle accident that he was forced to resign from NASA); John Glenn was regarded as too valuable to risk; and Wally Schirra and Gordon Cooper were in disgrace and, effectively, off flight status. Re-commissioning Alan Shepherd allowed NASA to take advantage of one of the icons of the space programme.
 This is not to talk down Alan Shepherd. His story is an amazing one of courage and determination to get back onto flight status. If I could meet any astronaut who has ever or will ever fly, my #1 choice would be Jim Lovell, #2 would be Alan Shepherd, well ahead, even, of John Glenn [the Apollo 11 crew would, actually, be well down my list].
 You may recall that Neil Armstrong had a similar call to make when Deke Slayton offered to replace Lunar Module Pilot, Buzz Aldrin, with back-up Command Module Pilot, Jim Lovell on Apollo 11, giving him two Command Module Pilots, one of whom would have to be demoted to the lower-ranking Lunar Module Pilot position.
 The graph on page 13 of the NASA report into pogo incidents in manned space flight by NASA during the Gemini and Apollo (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080018689.pdf) shows a first peak at 1g about 10 seconds into the burn, a second at 2g at around 70 seconds, a third at 34g at 160 seconds, at which point the engine shut down. Assuming, as the engineers who analysed the engine data did, that there would have been a further and even larger peak about 80 seconds after the third, it is likely that it would have marked the end of the mission and, potentially, of the crew. At this point, the launch escape tower had been jettisoned, so there was no chance of escape had the rocket gone out of control or, worse, exploded.
In the aftermath of Apollo 13, the fix was put in place that eliminated these issues by fitting a helium-bleed around the centre J-2 engine of the Second Stage.
 The Flight Operations Report after landing showed that, as off four days into the mission, the astronauts only had a predicted 24 hours margin on water, while battery power and oxygen both had several days margin (this allowed power consumption to be increased slightly on-board, which actually increased the water consumption on board). Ironically, they had an emergency water reserve in a tank in the Lunar Module, which lay untouched. By the time that they knew that it would not be required for instrument cooling and could be drunk, the water in the tank had frozen solid. The astronauts had limited themselves for almost a week to less than a litre of water per day for drinking, re-hydrating food and other uses.
 NASA’s C-135 “Hercules” chase aeroplane had spotted the Apollo 13 capsule well before the call from Jack Schmidt, which was, itself, almost three minutes before the small, drogue parachutes were deployed.