Space Sunday: Apollo 13, 50 years on

The Apollo 13 crew: Fred Haise, Jack Swigert and Jim Lovell. Credit: NASA

It is hard to believe fifty years after the fact, that with only two missions to surface of the Moon, America was ready to end its love affair with NASA by the time Apollo 13 lifted-off from Kennedy Space Centre’s Pad 39A at 19:13 UTC (14:13 EST) on Saturday, April 11th, 1970.

Already by that date, the Saturn V construction programme had been cancelled, leaving NASA with enough vehicles for seven more flights, and one of those (formerly Apollo 20) had been re-assigned to fly what would become the Skylab orbital laboratory (Apollo mission 18 and 19 would be later be cancelled completely their launch vehicles relegated to museum pieces).

Even Apollo 13 itself had something of a rocky path to the launch pad. Under the prevailing NASA crew rotation protocols, the prime crew for the mission was to have been Gordon Cooper, Edgar Mitchell, and Donn F.Eisele, but NASA’s Director of Flight Crew Operations Donald “Deke” Slayton vetoed any participation in a prime crew by Cooper, who had a lax attitude towards training, and by Eisle as a result of incidents that occurred in the Apollo 7 flight and for bringing the agency’s public image into disrepute as a result of an extramarital affair.

Up until two days before launch, Ken Mattingly had been Apollo 13’s Command Module Pilot

Instead, Slayton placed the crew due to fly Apollo 14 forward to take the prime slots for Apollo 13, with US Navy captain and veteran of three previous space flights, James Arthur “Jim” Lovell Jr., as commander and fellow test pilots Fred Haise (USAF) Thomas Kenneth “Ken” Mattingly II (USN) as the lunar module pilot (LMP) and command module pilot (CMP) respectively.  Their back-up crew were John Young, Charles Duke and John Leonard “Jack” Swigert Jr, with whom they shared time in training and simulation work for the mission.

Seven days prior to launch, Charles Duke was diagnosed with rubella, and Mattingly was the only man in the two crews not immune through prior exposure. Because of this, flight surgeons insisted he be removed from the prime crew in case he developed symptoms during the mission, and two days before launch, he was replaced by Swigert from the back-up crew (Mattingly subsequently never developed symptoms, and would eventually fly to the Moon on Apollo 16).

Even during the launch, the mission suffered what at the time appeared to be a relatively minor issue. Shortly after the separation of the Saturn V’s first stage the centre-most of the S-II second stage’s five engines was abruptly shut down automatically just 4 minutes into a planned 6.4 minute burn. The remaining four engines performed flawlessly, and no more thought was given to the issue at the time. Two and half hours later, the S-IVB upper stage motor was re-lit and Apollo 13 started its journey to the Moon.

Except for the launch, the three major TV networks showed little interest in Apollo 13. Planned broadcasts by the crew were not transmitted live, and America and the world carried on as if Apollo 13 wasn’t there.

After six successful Apollo flights, including two lunar landings, people were getting bored.

– Apollo 13 commander Jim Lovell reflecting on the lack of public
interest in the Apollo13 flight

All that changed on the night of April 13th/14th 1970, when the flight was almost 56 hours old and Apollo 13 was 330,00 km from Earth and less than a day from the Moon. The crew had just completed yet another televised transmission that had been ignored by the networks (and which included Richard Strauss’ Also Sprach Zarathustra, used as the iconic theme for Stanley Kubrick’s 2001 A Space Odyssey –  the latter being the command module’s (CM) call-sign), when mission control requested the crew carry out a number of tasks minor tasks, including one for Swigert, as CMP, to “stir” both of service module’s (SM) oxygen tanks.

The television broadcast that took place just before the Apollo 13 accident, and at least watched by mission control. Fred Haise can be seen in on the large screen while in the centre foreground, lead flight director Gene Kranz looks on. Credit: NASA

These two tanks supplied oxygen both to the CM’s cabin and to the three fuel cells alongside them that provided electrical power to the entire command and service module (CSM) combination. Due to solar heating the oxygen in the tanks would “stratify”, so each day fans in to the tanks would be turned on to normalise the temperature and pressure readings. However, an extra stir had been requested in the hope of eliminating an incorrect pressure reading.

Swigert duly turned on the fans in both tanks as requested, and 90 seconds later, Apollo 13 was rocked by a “pretty large bang” that caused the attitude control system (ACS) to automatically fire to stabilise the vehicle, and the CM’s instruments to register sudden power fluctuations within the Main Bus B, one of the two electrical power distribution systems delivering electrical power to the CM.

The bang and fluctuations prompted Swigert and Lovell to both report to Earth that the vehicle had had a problem – but as instrument readings returned to normal, astronauts and engineers were momentarily confused. Lovell actually thought Haise had opened the LM’s cabin repressurisation valve (which also caused a bang) in an attempt to startle his crew mates. But Haise’s expression as he came up through the docking tunnel from the LM indicated he was as equally confused by the noise. Then the electrical output from both the power distribution systems started falling.

“OK Houston, we’ve had a problem here…” Swigert and Lovell in turn report Apollo 13 could be in difficulties

Checking the status of the three SM fuel cells, Haise found two completely dead and the third dangerously low. Swigert, engaged in checking the slowly decreasing pressure in oxygen tank 1 flipped the displays to check tank 2, only to find it completely depleted. Moving to the CM’s windows, Lovell reported the SM appeared to be venting “a gas of some sort” and the vehicle as being surrounded by a cloud of fine debris – clearly, something was seriously wrong.

Worse, struggling to maintain power levels, the surviving cell  was drawing on oxygen from the CM’s surge tank. This was a reserve of oxygen intended to supply the crew with a breathable atmosphere at the end of a mission, between the CM detaching from the SM and splashing down on Earth. Were that supply to be depleted, the crew would face certain death.

Realising the significance of the surge tank situation, veteran flight controller and White Team leader Eugene Francis “Gene” Kranz, ordered the fuel cell immediately isolated from the surge tank’s oxygen supply. This left the crew with an estimated 2 hours of oxygen to in tank 1 to power the remaining fuel cell before it was also depleted, killing the command module – and the crew. With that realisation, Apollo 13 switched from being a lunar landing mission to a rescue mission.

My concern was increasing all the time. It went from, “I wonder what this is going to do to the landing?” To “I wonder if we can get back home again?”

– Apollo 13 commander Jim Lovell at a post-flight press conference,
May 1970.

Two options were available for bringing the crew home: a direct abort or a free return. The first involved turning the CSM / LM combination through 180° and then using the big service propulsion system (SPS) on the SM to reverse course and fly back to Earth, which would take about 2 days.

The free return option involved continuing on around the Moon and using its gravity, combined with an engine burn, to return to Earth in about 4 days. Both approaches would require the crew to power down the CM and use the LM as a lifeboat – something that NASA had actually planned for just after the first Apollo flight to the Moon (Apollo 8, which also had Jim Lovell as a member of the crew).

Gee, I think back in Apollo 9 we first started looking at the LEM [Lunar Excursion Module, NASA’s original official title for the lunar module] as more-or-less a lifeboat and fortunately, although the exact procedures do not tailor the exact case we’ve got, we looked at the utilisation of the LEM for an awfully long time. So we knew what the limitations were and we developed workaround procedures wherever it was possible. I think the LEM spacecraft is in excellent shape and it’s fully capable of getting the crew back.

– Lead Flight Director, Apollo 13, Gene Kranz during a press conference,
April 14th, 1970

A crowd Vilnius, Soviet Latvia, watch Russian coverage of Apollo 13 through a store window. Credit: