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Apollo 13 was the third manned mission by NASAmarker that was intended to land on the moon, but a mid-mission technical malfunction forced the lunar landing to be aborted. The crew members were commander James A. Lovell, command module pilot John L. "Jack" Swigert, and lunar module pilot Fred W. Haise.

The mission launched on April 11, 1970 at 13:13 CST. Two days later, while the mission was en route to the moon, a fault in the electrical system of one of the Service Module's oxygen tanks produced an explosion which caused a loss of electrical power and failure of both oxygen tanks. The command module remained functional on its own batteries and oxygen tank, which were only designed to support the vehicle during the last hours of flight. The crew shut down the Command Module and used the Lunar Module as a "lifeboat" during the return trip to earth. Despite great hardship caused by limited power, loss of cabin heat, and a shortage of potable water, the crew returned safely to Earth, and the mission was termed a "successful failure." A misquotation of a radio transmission by Swigert has become widely quoted in popular culture: Houston, we have a problem.


Ken Mattingly was originally slated to be the command module pilot. After being exposed to rubella contracted by backup Lunar Module pilot Charles Duke—a disease to which Mattingly was not immune—he was replaced by Swigert three days before launch. Mattingly never contracted rubella, and he later flew as command module pilot of Apollo 16, which was the 5th mission to land on the moon.

Backup crew

John L. Swigert, the backup command module pilot, was moved to the prime crew three days before launch, and no replacement backup was assigned.

Support crew

Flight directors

Mission parameters

Oxygen tank rupture

  • April 14, 1970, 03:07:53 UTC {April 13, 21:07:53 CST}

Closest approach to Moon

  • April 15, 1970, 00:21:00 UTC

Mission highlights

The Apollo 13 mission was to explore the Fra Mauro formation, or Fra Mauro highlands, named after the 80-kilometer-diameter Fra Mauro cratermarker located within it. It is a widespread, hilly geological (or selenological) area thought to be composed of ejecta from the impact that formed Mare Imbriummarker.The cost of the mission was $4.4 billion. The next Apollo mission, Apollo 14, eventually made a successful flight to Fra Mauro.

The mission began with a lesser-known malfunction: during second-stage boost, the center (inboard) engine shut down two minutes early due to dangerous pogo oscillations that might have torn the second stage apart. The engine experienced 68g vibrations at 16 hertz, flexing the thrust frame by . The four outboard engines burned longer to compensate. Thrust chamber pressure fluctuations caused a sensor to trigger an engine shutdown. Smaller pogo oscillations had been seen on previous Titan and Saturn flights, but on Apollo 13 they were amplified by an unexpected interaction with turbopump cavitation. Later missions implemented anti-pogo modifications that had already been under development. They added a helium gas reservoir to the center engine liquid oxygen line to dampen pressure oscillations and an automatic cutoff as a backup. The propellant valves of all five second-stage engines were simplified.


Apollo 13's damaged Service Module, as photographed from the Command Module after being jettisoned.

En route to the moon, at a distance of 321,860 kilometers (200,000 mi) from Earth, the number two oxygen tank, one of two in the Service Module (SM), exploded. Mission Controlmarker had asked the crew to stir the hydrogen and oxygen tanks, destratifying the contents and increasing the accuracy of their quantity readings. Damaged Teflon insulation on the wires to the stirrer motor in oxygen tank 2 allowed them to short and ignite the insulation. The resulting fire rapidly increased pressure beyond its nominal 1,000 PSI (7 MPa) limit and either the tank or the tank dome failed. The cause was unknown at the time and the crew initially thought that a meteoroid might have struck the Lunar Module (LM).

The failure also damaged either the number one oxygen tank or its plumbing. Its contents leaked over the next several hours, entirely depleting the SM supply. Because the service module fuel cells combined hydrogen and oxygen to generate electricity and water, they shut down and left the command module (CM) on limited battery power. The crew was forced to shut down the CM completely and to use the LM, still attached to the Command/Service Module (CSM), as a "lifeboat". This 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.

The damage to the service module made a lunar landing impossible. Instead, the moon's gravity was used to return to Earth. Apollo 13 had initially been on a free return trajectory that would have automatically resulted in a return to Earth with no additional engine firings, but landing at Fra Mauro required leaving the free return trajectory early in the mission. Returning to the free return trajectory required a significant change that would have been a small burn with the SM Service Propulsion System engine but its condition was unknown. After extensive discussion, the return to a free return trajectory was performed with the LM descent propulsion system within hours of the accident. The descent engine was fired again two hours after pericynthion (closest approach to the moon) for a PC+2 burn to speed the return. One more descent engine burn was later required for a minor course correction.

Considerable ingenuity under extreme pressure was required from the crew, flight controllers and support personnel for the safe return. Much of the world watched the developing drama 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 even made voice communications difficult.

The LM "lifeboat" consumables were intended only to sustain two people for two days, not three people for four days. However, oxygen was the least critical consumable because the LM carried enough to repressurize the LM after each surface EVA. Unlike the 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 especially water 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.

Another serious limitation was lithium hydroxide (LiOH) for removing carbon dioxide. The LM's internal stock ofLiOH canisters would not 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 that were incompatible with those used by the LM. Ground controllers improvised a way to use the cube-shaped CM canisters on the LM's circular canister-sockets by drawing air through them with a suit return hose. The astronauts called the jury-rigged device "the mailbox."

The thermal design of the spacecraft assumed normal operating power levels, so the survival power level caused internal temperatures to drop considerably. Water condensed in the CM, causing concern this might damage electrical systems when it was reactivated. This turned out not to be a problem, partly because of the extensive CM safeguards instituted after the Apollo 1 fire.

As Apollo 13 neared Earth, the crew first jettisoned the Service Module so pictures could be taken for later analysis. The crew reported that the Sector 3 panel enclosing the fuel cells, hydrogen, and oxygen tanks was missing for the entire length of the SM.

After jettisoning the lunar module Aquarius, command module Odyssey splashed down safely in the Pacific. 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.

Although the explosion aborted the mission, it fortunately happened on the way to the moon when the LM was still available with its full complement of consumables. Had the explosion occurred after the landing or on the return to earth after the LM had been jettisoned, the crew would not have survived.

The crew's lives may have been saved by the same malfunction. At around 46h 40m into the mission, the oxygen tank 2 quantity gauge went "off-scale high" (reading over 100%) and stayed there, possibly due to the damaged internal insulation. To assist in determining the cause, the crew was asked to perform cryo-tank stirs more often than originally planned. In the original mission plan, the stir that ruptured the tank would not have been done until after the lunar landing.

Cause of the accident

The explosion on Apollo 13 led to a lengthy investigation which, based on detailed manufacturing records and logs, determined the cause of the tank failure 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. 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 weight of oxygen, which was used for breathable air and the production of electricity and water. However, the construction of the tank made internal inspection of the tank impossible.

The tank contained several components relevant to the accident:
  • a quantity sensor;
  • a fan to stir the tank contents for more accurate quantity measurements;
  • a heater to vaporize liquid oxygen as needed;
  • a thermostat to protect the heater;
  • a temperature sensor;
  • fill and drain valves and piping.

The heater and protection thermostat 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 temperature sensor could not read above the highest operational temperature of the heater, which was approximately . This was not normally a problem due to the fact that the thermostat was designed to open at .

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 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 . However, when the thermostat opened, the 65-volt supply fused its contacts closed and the heater remained powered.

This raised the temperature of the heater to an estimated . 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 could not read higher than , the monitoring equipment did not register the true temperature inside the tank. The gas evaporated 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.

The other oxygen tank or its piping, located near the failed tank, was damaged, allowing it to leak as well. Design fixes included moving the tanks farther apart and adding a third tank and an emergency battery to another sector in the service module.

Mission notes

By the standard crew rotation in place during the Apollo program, the prime crew for Apollo 13 should have been the backup crew for Apollo 10 with Mercury and Gemini veteran L. Gordon Cooper in command. That crew was composed of the following astronauts:

However, Deke Slayton recollected in his memoirs that Cooper and Eisele were never intended to rotate 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) and were assigned 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. Cooper, Slayton noted, had a very small chance of receiving the Apollo 13 command if he did an outstanding job with the assignment, which he didn't. Eisele, despite his issues with management, was always intended for future assignment to the Apollo Applications Program (which was eventually cut down to only the Skylab component) and not a lunar mission.

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

However, for the first time ever, Slayton's recommendation was rejected by management because they felt that Shepard, who had only recently benefited from experimental surgery to correct an inner ear disorder and had not flown since 1961 needed more time to properly train for a lunar flight. Thus, Lovell's crew, backup for the historic Apollo 11 mission, which had been targeted for (by virtue of the rotation) Apollo 14, was swapped for Shepard's crew.

Eight days before the launch, Apollo 13 backup lunar module pilot Charlie Duke contracted German measles from one of his children. Although Lovell and Haise had rubella as children, command module pilot Ken Mattingly had not, and the flight surgeons replaced him with his backup, Jack Swigert. Mattingly never developed rubella, and later flew on Apollo 16, STS-4, and STS-51-C, retiring from both NASA and the U.S. Navy with the rank of Rear Admiral. During the emergency, Mattingly and flight controller John Aaron used the CSM simulator to work up a plan to revive Odyssey using the ship's limited power supply.
Plaque that was to be attached to Aquarius
Also, the original lunar plaque on Aquarius bore Mattingly’s name, so the crew was given a replacement with Swigert’s name on it. Aquarius never landed on the moon, however, so Lovell kept the plaque. In his book Lost Moon (later renamed Apollo 13), Lovell states that apart from the Apollo 13 plaque and a couple of other pieces, the only other memento he possesses is a letter from Charles Lindbergh.

Because Apollo 13 followed the free return trajectory, its altitude over the lunar far side was approximately greater than the orbital altitude on the remaining Apollo lunar missions. It made the all-time altitude record for human spaceflight. The variation in distance between Earth and the Moon, however, is much larger than , so it is not certain whether the actual distance from Earth was greater than that of other Apollo missions. The Guinness Book of Records lists this flight as holding the absolute altitude record for a manned spacecraft, thus Lovell and crew should have received a certificate attesting to this record.

The splashdown point was , SE of American Samoa and from the recovery ship, USS Iwo Jima.

The A7L spacesuit intended to be worn on the lunar surface by Lovell would have been the first to feature red bands on the arms, legs, lunar EVA helmet assembly, and the life-support backpack. This came about because Mission Control personnel watching the video feeds of Apollos 11 and 12 had trouble distinguishing the astronauts while both had their helmet sunshades down. The red bands were a feature for the remaining Apollo flights and are used on the Extravehicular Mobility Units worn by the astronauts of the Space Shuttle program and on the International Space Station (ISS).

The Apollo 13 mission has been called "a successful failure", because the astronauts were brought home safely notwithstanding the failure of the mission.

The crew and the Apollo 13 Mission Operations Team were awarded the Presidential Medal of Freedom for their actions during the mission.

The Cold Cathode Gauge Experiment (CCGE), which was part of the ALSEP on Apollo 13 was never flown again. It was a version of the Cold Cathode Ion Gauge (CCIG) which featured on Apollo 12, Apollo 14, and Apollo 15. The CCGE was designed as a standalone version of the CCIG. On other missions, the CCIG was connected as part of the Suprathermal Ion Detector (SIDE). Because of the aborted landing, this experiment was never actually deployed. Other experiments included on Apollo 13's ALSEP included the Heat Flow Experiment (HFE), the Passive Seismic Experiment (PSE), and the Charged Particle Lunar Environment Experiment (CPLEE).


The Apollo 13 crew patch featured three flying horses as Apollo's 'chariot' across space. Given Lovell's Navy background, the logo also included the mottoes “Ex luna, scientia” ("From the moon, knowledge"), borrowed from the U.S.marker Naval Academymarker's motto, and "Ex scientia tridens," ("From knowledge, sea power"). The mission number appeared in Roman numerals as Apollo XIII. It is one of two Apollo insignia—the other being Apollo 11—not to include the names of the crew. (This was fortunate, considering that original crew member Ken Mattingly was replaced two days before the mission began.) It was designed by artist Lumen Winter, who based it on a mural he had done for the St. Regis Hotel in New York. The mural was later purchased by actor Tom Hanks, who portrayed Lovell in the movie Apollo 13, and now is on the wall of a restaurant in Chicago owned by Lovell's son.

Spacecraft location

A view of the controls in the command module on display at the Cosmosphere.

The command module shell was formerly at the Musée de l'Air et de l'Espacemarker, in Parismarker. The interior components were removed during the investigation of the accident and reassembled into BP-1102A, the water egress training module, and were subsequently on display at the Museum of Natural History and Science in Louisville, Kentuckymarker, until 2000. The command module and the internal components were reassembled, and Odyssey is currently on display at the Kansas Cosmosphere and Space Centermarker, Hutchinson, Kansasmarker.

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. (Had the mission proceeded as planned, the RTG would have been used to power the Apollo Lunar Surface Experiment Package, and then remained on the moon.) The RTG survived re-entry (as designed) and landed in the Tonga Trenchmarker. While it will remain radioactive for approximately 2,000 years, it does not appear to be releasing any of its 3.9 kg of radioactive plutonium.

Jim Lovell's lunar space suit helmet is located at the Museum of Science and Industrymarker in Chicago.

Popular culture

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.

Apollo 13, a film based on Lost Moon, Jim Lovell's and Jeffrey Kluger's book about the event, was released in 1995. It was directed by Ron Howard and starred Tom Hanks as Jim Lovell, Bill Paxton as Fred Haise, Kevin Bacon as Jack Swigert, Ed Harris as flight director Gene Kranz, Kathleen Quinlan as Marilyn Lovell and Gary Sinise as Ken Mattingly. Jim Lovell, Gene Kranz, and other principals have stated that this film depicted the events of the mission with reasonable accuracy, though some dramatic license was taken. Technical inaccuracies have also been noted. The film is among several to misquote Swigert's famous statement, "Houston, we've had a problem". However, the filmmakers purposely changed the line because the original quote made it seem that the problem had already passed. Overall, though, the film is praised for being both extremely accurate (dialogue between ground control and spacecraft for the film, with the above exception, was taken verbatim from NASA transcripts and recordings) and a cinematic masterpiece. The film was a critical and box office success, and was nominated for several Academy Awards including Best Picture, Best Supporting Actor (Harris) and Best Supporting Actress (Quinlan). The film engendered new interest in the history of the Apollo program and American space flight in general.

Portions of the events surrounding the Apollo 13 mission are dramatized in episode "We Interrupt This Program" of the 1998 miniseries From the Earth to the Moon, co-produced by Ron Howard and Tom Hanks. The story is presented from the perspective of television reporters competing for coverage of the mission.

Towing fees

Grumman Aerospace Corporation, the builder of the Lunar Module, issued an invoice for $312,421.24 to North American Rockwell, the builder of the Command Module (CM), for "towing" the crippled ship most of the way to the moon and back. The invoice included a 20% commercial discount, as well as a further 2% discount if North American were to pay in cash. North American politely declined payment, noting that they had ferried Grumman LMs to the moon on three previous occasions with no such reciprocal charges. The invoice was drawn up by Grumman pilot Sam Greenberg as a gag following Apollo 13's successful splashdown. He had earlier helped with the strategy for re-routing power from the LM to the crippled CM.


  1. Apollo 13 - A Successful Failure
  2. Apollo 13 Mission Operations Report
  3. Apollo 13 Timeline
  4. Apollo 14 Launch Operations (comments on Apollo 13 pogo), Moonport: A History of Apollo Launch Facilities and Operations, NASA
  5. Pogo, Jim Fenwick, Threshold - Pratt & Whitney Rocketdyne’s engineering journal of power technology, Spring 1992
  6. Mitigating Pogo on Liquid-Fueled Rockets, Aerospace Corporation Crosslink magazine, Winter 2004 edition
  7. Note that NASA's offical report ( REPORT OF APOLLO 13 REVIEW BOARD) does not itself use the word "explosion" in describing the tank rupture. Rupture disks and other safety measures were present to prevent a catastrophic explosion, and analysis of pressure readings and subsequent ground-testing determined that these safety measures worked as designed. See findings 26 and 27 on page 195 (5-22) of the NASA report.
  8. Lovell, Jim, and Jeffrey Kluger. Apollo 13. Boston: Houghton Mifflin, 2000. 83-87
  9. Account of Apollo 13 by James Lovell, NASA website
  10. "THE STIR THAT SAVED THE LIVES OF APOLLO 13's CREW", Jerry Woodfill, retrieved 27 January 2007
  11. report of the Apollo 13 review board
  12. The Apollo 13 Accident
  13. Donald K. Slayton, "Deke!" (New York: Forge, 1994), 236
  14. Donald K. Slayton, "Deke!" (New York: Forge, 1994), 237
  15. Apollo Lunar Surface Experiment Package (ALSEP)
  16. Invoice from [[Grumman Aerospace for towing the North American built CM]

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