Apollo 13

Prime and backup crew

According to the standard crew rotation in place during the Apollo program, the prime crew for Apollo 13 would have been the backup crew for Apollo 10 with Mercury and Gemini veteran L. Gordon Cooper in command. That crew was composed of

Deke Slayton, NASA's Director of Flight Crew Operations, never intended to rotate Cooper and Eisele to another mission, as both were out of favor with NASA management for various reasons (Cooper for his lax attitude towards training, and Eisele for incidents aboard Apollo 7 and an extra-marital affair). He assigned them to the backup crew simply because of a lack of flight-qualified manpower in the Astronaut Office at the time the assignment needed to be made. Slayton felt Cooper had no more than a very small chance of receiving the Apollo 13 command, if he did an outstanding job with the assignment, which he did not. Despite Eisele's issues with management, Slayton always intended to assign him to a future Apollo Applications Program mission rather than a lunar mission, but this program was eventually cut down to only the Skylab component.

Thus, the original assignment Slayton submitted to his superiors for this flight was:

For the first time ever, Slayton's recommendation was rejected by management, who felt that Shepard needed more time to train properly for a lunar flight, as he had only recently benefited from experimental surgery to correct an inner ear disorder which had kept him grounded since his first Mercury flight in 1961. Thus, Lovell's crew, backup for the historic Apollo 11 mission and therefore slated for Apollo 14, was swapped with Shepard's crew and the original crew selection for the mission became:

Prime crew:

Backup crew:

Ken Mattingly was originally intended as the Command Module Pilot. Seven days before launch, the Backup Lunar Module Pilot, Charlie Duke, contracted rubella from one of his children. This exposed both the prime and backup crews, who trained together. Mattingly was found to be the only one of the other five who had not had rubella as a child and thus was not immune. Three days before launch, at the insistence of the Flight Surgeon, Swigert was moved to the prime crew.

Mattingly never contracted rubella and was assigned after the mission as Command Module Pilot to Young's crew, which later flew Apollo 16, the fifth mission to land on the Moon.

Support crew

Flight directors

Mission insignia

The astronauts' mission insignia was sculpted as a medallion titled Steeds of Apollo by Lumen Martin Winter and was struck by the Franklin Mint.

Mission parameters

Objective

The Apollo 13 mission was to explore the Fra Mauro formation, or Fra Mauro highlands, named after the 80-kilometer (50 mi) diameter Fra Mauro crater located within it. It is a widespread, hilly selenological area thought to be composed of ejecta from the impact that formed Mare Imbrium.

The next Apollo mission, Apollo 14, eventually made a successful flight to Fra Mauro.

Abort

April 14, 1970 UTC (April 13, 21:07:53 CST)

Closest approach to Moon

April 15, 1970, 00:21:00 UTC; 137 nmi (253.7 km)

Splashdown

April 17, 1970, 18:07:41 UTC (142:54:47 Ground Elapsed Time). Crew was on board the USS Iwo Jima 45 minutes later.

Launch and translunar injection

The mission was launched at the planned time, 02:13:00 PM EST (19:13:00 UTC) on April 11. An anomaly occurred when the second-stage, center (inboard) engine shut down about two minutes early. The four outboard engines and the third-stage engine burned longer to compensate, and the vehicle achieved very close to the planned circular 100 nautical miles (190 km) parking orbit, followed by a normal translunar injection about two hours later. The engine shutdown was determined to be caused by severe pogo oscillations measured at a strength of 68 g and a frequency of 16 hertz, flexing the thrust frame by 3 inches (76 mm). The vehicle's guidance system shut the engine down in response to sensed thrust chamber pressure fluctuations. Pogo oscillations had been seen on previous Titan rockets, and also on the Saturn V during Apollo 6, but on Apollo 13, they were amplified by an unexpected interaction with turbopump cavitation. Later missions implemented anti-pogo modifications that had been under development. These included addition of a helium-gas reservoir to the center engine liquid oxygen line to damp pressure oscillations, an automatic cutoff as a backup, and simplification of the propellant valves of all five second-stage engines.

The crew performed the separation and transposition maneuver to dock the Command Module Odyssey to the Lunar Module (LM) Aquarius, and pulled away from the spent third stage, which ground controllers then sent on a course to impact the Moon in range of a seismometer placed on surface by Apollo 12. They then settled in for the three-day trip to Fra Mauro.

Accident

Approaching 56 hours into the mission, Apollo 13 was approximately 205,000 miles (330,000 km) from Earth en route to the Moon. Approximately six and a half minutes after the end of a live TV broadcast from the spacecraft, Haise was in the process of powering down the LM, while Lovell was stowing the TV camera, and Houston flight controllers asked Swigert to turn on the hydrogen and oxygen tank stirring fans in the Service Module, which were designed to destratify the cryogenic contents and increase the accuracy of their quantity readings. Two minutes later, the astronauts heard a "loud bang," accompanied by fluctuations in electrical power and the firing of the attitude control thrusters. The crew initially thought that a meteoroid might have struck the Lunar Module. Communications and telemetry to Earth were lost for 1.8 seconds, until the system automatically corrected by switching the high-gain S-band antenna used for translunar communications from narrow-beam to wide-beam mode.

Immediately after the bang Swigert reported a "problem", which Lovell repeated and clarified as a "main B bus undervolt", a temporary loss of operating voltage on the second of the spacecraft's main electrical circuits. Oxygen tank 2 immediately read quantity zero. About three minutes later, the number 1 and number 3 fuel cells failed. Lovell reported seeing out the window that the craft was venting "a gas of some sort" into space. The number 1 oxygen tank quantity gradually reduced to zero over the next 130 minutes, entirely depleting the SM's oxygen supply.

Because the fuel cells generated the Command/Service Module's electrical power by combining hydrogen and oxygen into water, when oxygen tank 1 ran dry, the remaining fuel cell finally shut down, leaving the craft on the Command Module's limited-duration battery power and water. The crew was forced to shut down the CM completely to save this for re-entry, and to power up the LM to use as a "lifeboat." This situation had been suggested during an earlier training simulation, but had not been considered a likely scenario. Without the LM, the accident would certainly have been fatal.

Crew survival and return journey

The damage to the Service Module made safe return from a lunar landing impossible, so Lead Flight Director Gene Kranz ordered an abort of the mission. The existing abort plans, first drawn up in 1966, were evaluated; the quickest was a Direct Abort trajectory, which required using the Service Module Propulsion System (SPS) engine to achieve a 6,079-foot-per-second (1,853 m/s) delta-v.^p. III-14 Although a successful SPS firing at 60 hours ground elapsed time (GET) would land the crew one day earlier (at 118 hours GET, or 58 hours later), the large delta-v was possible only if the LM were jettisoned first,^p. II-1 and since crew survival depended on the LM's presence during the coast back to Earth, that option was "out of the question."^p. III-17 An alternative would have been to burn the SPS fuel to depletion, then jettison the Service Module and make a second burn with the LM Descent Propulsion System (DPS) engine. It was desired to keep the Service Module attached for as long as possible because of the thermal protection it afforded the Command Module's heat shield. Apollo 13 was close to entering the lunar sphere of gravitational influence (at 61 hours GET), which was the break-even point between direct and circumlunar aborts, and the latter allowed more time for evaluation and planning before a major rocket burn.^{p. B-5} There also was concern about "the structural integrity of the Service Module,"^p. III‑23 so mission planners were instructed that the SPS engine would not be used "except as a last-ditch effort."^p. III-14

For these reasons, Kranz chose the alternative circumlunar option, using the Moon's gravity to return the ship to Earth. Apollo 13 had left its initial free-return trajectory earlier in the mission, as required for the lunar landing at Fra Mauro. Therefore, the first order of business was to re-establish the free-return trajectory with a 30.7-second burn of the DPS. The descent engine was used again two hours after pericynthion, the closest approach to the Moon ("PC+2 burn"), to speed the return to Earth by 10 hours and move the landing spot from the Indian Ocean to the Pacific Ocean. A more aggressive burn could have been performed at PC+2 by first jettisoning the Service Module, returning the crew in about the same amount of time as a direct abort,^p. III-20 but this was deemed unnecessary given the rates at which consumables were being used. The 4-minute, 24-second burn was so accurate that only two more small course corrections were subsequently needed.

Considerable ingenuity under extreme pressure was required from the crew, flight controllers, and support personnel for the safe return. The developing drama was shown on television. Because electrical power was severely limited, no more live TV broadcasts were made; TV commentators used models and animated footage as illustrations. Low power levels made even voice communications difficult.

The Lunar Module consumables were intended to sustain two people for a day and a half, not three people for four days. Oxygen was the least critical consumable because the LM carried enough to repressurize the LM after each surface EVA. Unlike the Command/Service Module (CSM), which was powered by fuel cells that produced water as a byproduct, the LM was powered by silver-zinc batteries, so electrical power and water (used for equipment cooling as well as drinking) were critical consumables. To keep the LM life-support and communication systems operational until re-entry, the LM was powered down to the lowest levels possible. In particular, the LM's Abort Guidance System was used for most of the coast back to Earth instead of the primary guidance system, as it used less power and water.^{pp. III‑17,33,40}

Availability of lithium hydroxide (LiOH) for removing carbon dioxide presented a serious problem. The LM's internal stock of LiOH canisters was not sufficient to support the crew until return, and the remainder was stored in the descent stage, out of reach. The CM had an adequate supply of canisters, but these were incompatible with the LM. Engineers on the ground improvised a way to join the cube-shaped CM canisters to the LM's cylindrical canister-sockets by drawing air through them with a suit return hose. The astronauts called the improvised device "the mailbox."

Another problem to be solved for a safe return was accomplishing a complete power-up from scratch of the completely shut-down Command Module, something never intended to be done in-flight. Flight controller John Aaron, with the support of grounded astronaut Mattingly and many engineers and designers, had to invent a new procedure to do this with the ship's limited power supply and time factor. This was further complicated by the fact that the reduced power levels in the LM caused internal temperatures to drop to as low as 4 °C (39 °F). The unpowered CM got so cold that water began to condense on solid surfaces, causing concern that this might short out electrical systems when it was reactivated. This turned out not to be a problem, partly because of the extensive electrical insulation improvements instituted after the Apollo 1 fire.

The last problem to be solved was how to separate the Lunar Module a safe distance away from the Command Module just before re-entry. The normal procedure was to use the Service Module's reaction control system (RCS) to pull the CSM away after releasing the LM along with the Command Module's docking ring, but this RCS was inoperative because of the power failure, and the useless SM would be released before the LM. To solve the problem, Grumman called on the engineering expertise of the University of Toronto. A team of six UT engineers, led by senior scientist Bernard Etkin, was formed to solve the problem within a day. The team concluded that pressurizing the tunnel connecting the Lunar Module to the Command Module just before separation would provide the force necessary to push the two modules a safe distance away from each other just prior to re-entry. The team had 6 hours to compute the pressure required, using slide rules. They needed an accurate calculation, as too high a pressure might damage the hatch and its seal, causing the astronauts to burn up; too low a pressure would not provide enough separation distance of the LM. Grumman relayed their calculation to NASA, and from there in turn to the astronauts, who used it successfully.

Re-entry and splashdown

As Apollo 13 neared Earth, the crew first jettisoned the Service Module, using the LM's reaction control system to pull themselves a safe distance from it, instead of the normal procedure which used automatic firing of the SM's RCS. They photographed it for later analysis of the accident's cause. It was then that the crew were surprised to see for the first time that the entire Sector 4 panel had been blown off. According to the analysts, these pictures also showed the antenna damage and possibly an upward tilt to the fuel cell shelf above the oxygen tank compartment.

Finally, the crew jettisoned the Lunar Module Aquarius using the above procedure worked out at the University of Toronto, leaving the Command Module Odyssey to begin its lone re-entry through the atmosphere. The re-entry on a lunar mission normally was accompanied by about four minutes of typical communications blackout caused by ionization of the air around the Command Module. The blackout in Apollo 13's reentry lasted six minutes, which was 87 seconds longer than had been expected. The possibility of heat-shield damage from the O
2 tank rupture heightened the tension of the blackout period.

Odyssey regained radio contact and splashed down safely in the South Pacific Ocean, 21°38′24″S 165°21′42″W, southeast of American Samoa and 6.5 km (3.5 nmi) from the recovery ship, USS Iwo Jima. The crew was in good condition except for Haise, who was suffering from a serious urinary tract infection because of insufficient water intake. To avoid altering the trajectory of the spacecraft, the crew had been instructed to temporarily stop urine dumps. A misunderstanding prompted the crew to store all urine for the rest of the flight.

Analysis and response

NASA Administrator Thomas Paine and Deputy Administrator George Low sent a memorandum to NASA Langley Research Center Director Edgar M. Cortright on April 17, 1970, (date of spacecraft splashdown) advising him of his appointment as chairman of an Apollo 13 Review Board to investigate the cause of the accident.

Review board

The second memorandum to Cortright from Paine and Low on April 21 established the board as follows:

Activities and report

The board exhaustively investigated and analyzed the history of the manufacture and testing of the oxygen tank, and its installation and testing in the spacecraft up to the Apollo 13 launch, as documented in detailed records and logs. They visited and consulted with engineers at the contractor's sites and the Kennedy Space Center. Once a theory of the cause was developed, elements of it were tested, including on a test rig simulation in a vacuum chamber, with a damaged tank installed in the fuel cell bay. This test confirmed the theory when a similar explosion was created, which blew off the outer panel exactly as happened in the flight. Cortright sent the final Report of Apollo 13 Review Board to Thomas Paine on June 15, 1970.

The failure started in the Service Module's number 2 oxygen tank. Damaged Teflon insulation on the wires to the stirring fan inside oxygen tank 2 allowed the wires to short-circuit and ignite this insulation. The resulting fire rapidly increased pressure beyond its 1,000-pound-per-square-inch (6.9 MPa) limit and the tank dome failed, filling the fuel cell bay (Sector 4) with rapidly expanding gaseous oxygen and combustion products. It is also possible some combustion occurred of the Mylar/Kapton thermal insulation material used to line the oxygen shelf compartment in this bay.

The resulting pressure inside the compartment popped the bolts attaching the 13-foot (4.0 m) Sector 4 outer aluminum skin panel, which as it blew off probably caused minor damage to the nearby S-band antenna.

Mechanical shock forced the oxygen valves closed on the number 1 and number 3 fuel cells, leaving them operating for only about three minutes on the oxygen in the feed lines. The shock also either partially ruptured a line from the number 1 oxygen tank, or caused its check or relief valve to leak, causing its contents to leak out into space over the next 130 minutes, entirely depleting the SM's oxygen supply.

The board determined the oxygen tank failure was caused by an unlikely chain of events. Tanks storing cryogens, such as liquid oxygen and liquid hydrogen, require either venting, extremely good insulation, or both, in order to avoid excessive pressure buildup due to vaporization of the tanks' contents. The Service Module oxygen tanks were so well insulated that they could safely contain supercritical hydrogen and oxygen for years. Each oxygen tank held several hundred pounds of oxygen, which was used for breathable air and the production of electricity and water. The construction of the tanks made internal inspection impossible.

The tank contained several components relevant to the accident:

The heater and protection thermostats were originally designed for the Command Module's 28-volt DC bus. The specifications for the heater and thermostat were later changed to allow a 65-volt ground supply, in order to pressurize the tanks more rapidly. Beechcraft, the tank subcontractor, did not upgrade the thermostat to handle the higher voltage.

The oxygen shelf carrying the oxygen tanks was originally installed in the Apollo 10 Service Module, but was removed to fix a potential electromagnetic interference problem. During removal, the shelf was accidentally dropped about 2 inches (5 cm) because a retaining bolt had not been removed. The tank appeared to be undamaged, but a loosely fitting filling tube was apparently damaged, and photographs suggested that the close-out cap on the top of the tank may have hit the fuel cell shelf. The report of the Apollo 13 review board considers the probability of tank damage during this incident to be "rather low." After the tank was filled for ground testing, it could not be emptied through the normal drain line. To avoid delaying the mission by replacing the tank, the heater was connected to 65-volt ground power to boil off the oxygen. Lovell signed off on this procedure. It should have taken a few days at the thermostatic opening temperature of 27 °C (81 °F). When the thermostat opened, the 65-volt supply fused its contacts closed and the heater remained powered. The board confirmed by testing that the thermostats welded themselves closed under the higher voltage. This raised the temperature of the heater to an estimated 540 °C (1,000 °F). A chart recorder on the heater current showed that the heater was not cycling on and off, as it should have been if the thermostat was functioning correctly, but no one noticed it at the time. Because the temperature sensor was not designed to read higher than the 27 °C (81 °F) thermostat opening temperature, the monitoring equipment did not register the true temperature inside the tank. The gas boiled off in hours rather than days.

The sustained high temperatures melted the Teflon insulation on the fan power supply wires and left them exposed. When the tank was refilled with oxygen, it became a bomb waiting to go off. During the "cryo stir" procedure, fan power passed through the bare wires which apparently shorted, producing sparks and igniting the Teflon. This in turn boiled liquid oxygen faster than the tank vent could remove it.

In June 1970, the Cortright Report provided an in-depth analysis of the mission in an extremely detailed five-chapter report with eight appendices. It included a copy of established NASA procedures for alleviating high pressure in a cryogenic oxygen tank, to include:

This procedure was designed to prevent hardware failure so that the lunar landing mission could be continued. The Mission Operations Report Apollo 13 recounts how the master caution and warning alarm had been turned off for a previous low-pressure reading on hydrogen tank 2, and so it did not trigger to call attention to the high oxygen pressure reading.

Oxygen tank 2 was not the only pressure vessel that failed during this mission. Prior to the accident, the crew had moved the scheduled entry into the Lunar Module forward by three hours. This was done to get an earlier look at the pressure reading of the supercritical helium (SHe) tank in the LM descent stage, which had been suspect since before launch. After the abort decision, the helium pressure continued to rise and Mission Control predicted the time that the burst disc would rupture. The helium tank burst disc ruptured at 108:54, after the lunar flyby. The expulsion reversed the direction of the passive thermal control (PTC) roll (nicknamed the "barbecue roll").

While the investigation board did recreate the oxygen tank failure, it did not report on any experiments that would show how effective the Cryogenic Malfunctions Procedures were to prevent the system failure by de-energizing the electrical heater and fan circuits.

Corrective actions

The oxygen tank was redesigned, with the thermostats upgraded to handle the proper voltage. The heaters were retained since they were necessary to maintain oxygen pressure. The stirring fans, with their unsealed motors, were removed, which meant the oxygen quantity gauge was no longer accurate. This required adding a third tank so that no tank would go below half full.

All electrical wiring in the power system bay was sheathed in stainless steel, and the oxygen quantity probes were changed from aluminum to stainless steel. The fuel cell oxygen supply valves were redesigned to isolate the Teflon-coated wiring from the oxygen. The spacecraft and Mission Control monitoring systems were modified to give more immediate and visible warnings of anomalies.

Spacecraft location

The Command Module shell was formerly at the Musée de l'Air et de l'Espace, in Paris. The interior components were removed during the investigation of the accident and reassembled into boilerplate BP-1102A, the water egress training module; and were subsequently on display at the Museum of Natural History and Science in Louisville, Kentucky, until 2000. The Command Module and the internal components were reassembled, and Odyssey is currently on display at the Cosmosphere in Hutchinson, Kansas.

The Lunar Module burned up in Earth's atmosphere on April 17, 1970, having been targeted to enter over the Pacific Ocean to reduce the possibility of contamination from a SNAP 27 radioisotope thermoelectric generator (RTG) on board. Intended to power the mission's ALSEP, the RTG survived re-entry (as designed) and landed in the Tonga Trench. While it will remain radioactive for several thousand years, it does not appear to be releasing any of its 3.9 kg of radioactive plutonium-238.

Lovell's lunar space suit helmet, one of his gloves, and the plaque that had been intended to be left on the Moon are on exhibit at the Adler Planetarium in Chicago, Illinois.

The Apollo 13 S-IVB with its Instrument Unit was guided to crash onto the lunar surface on April 14, providing a signal for the Apollo 12 Passive Seismic Experiment.

Popular culture and media

The 1974 movie Houston, We've Got a Problem, while set around the Apollo 13 incident, is a fictional drama about the crises faced by ground personnel when the emergency disrupts their work schedules and places additional stress on their lives; only a couple of news clips and a narrator's solemn voice deal with the actual problems. "Houston... We've Got a Problem" was also the title of an episode of the BBC documentary series A Life At Stake, broadcast in March 1978. This was an accurate, if simplified, reconstruction of the events.

Lovell was approached in 1991 by journalist Jeffrey Kluger about collaborating on a non-fiction account of the mission. The resultant book, Lost Moon: The Perilous Voyage of Apollo 13, was published in 1994. The next year, a film adaptation of the book, Apollo 13, was released, directed by Ron Howard and starring Tom Hanks as Lovell, Bill Paxton as Haise, Kevin Bacon as Swigert, Gary Sinise as Mattingly, Ed Harris as flight director Gene Kranz, and Kathleen Quinlan as Marilyn Lovell. James Lovell, Eugene Kranz, and other principals have stated that this film depicted the events of the mission with reasonable accuracy, given that some dramatic license was taken. For example, the film changes the tense of Lovell's famous follow-up to Swigert's original words from, "Houston, we've had a problem", to "Houston, we have a problem". The film was nominated for several Academy Awards, including Best Picture, Best Supporting Actor (Harris) and Best Supporting Actress (Quinlan).

In the 1998 miniseries From the Earth to the Moon, co-produced by Hanks and Howard, the mission is dramatized in the episode "We Interrupt This Program". Rather than showing the incident from the crew's perspective as in the Apollo 13 feature film, it is instead presented from an Earth-bound perspective of television reporters competing for coverage of the event.

In 2008, an interactive theatrical show titled Apollo 13: Mission Control premiered at BATS Theatre in Wellington, New Zealand. The production faithfully recreated the mission control consoles and audience members became part of the storyline. The show also featured a 'guest' astronaut each night: a member of the public who suited up and amongst other duties, stirred the oxygen tanks and said the line "Houston, we've had a problem." This 'replacement' astronaut was a nod to Jack Swigert, who replaced Ken Mattingly shortly before the launch in 1970. The production toured to other cities extensively in New Zealand and Australia in 2010–2011. The production was scheduled to travel to the US in 2012.

In November 2011, a notebook containing a checklist Lovell used to calculate a trajectory to get the damaged spacecraft, Apollo 13, back to Earth, and handwritten calculations by Lovell, was auctioned off by Heritage Auctions for $388,375. NASA made an email inquiry asking Heritage if Lovell had clear title to the notebook, stating that NASA had "nothing to indicate" the agency had ever transferred ownership of the checklist to Lovell. In January 2012, Heritage stated that the sale had been placed on hold after NASA launched an investigation into whether it was the astronaut’s property to sell.