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  • APOLLO 13

    After the successful completion of Apollo 11, the first manned landing on the moon (commanded

    by Neil Armstrong in the command module Columbia and lunar module Eagle) and Apollo 12,

    NASA was ready for its next mission to the moon. Apollo 13, the third manned lunar landing and

    exploration mission, had been tentatively scheduled in July 1969 for launch in March 1970, but

    by the end of the year the launch date had been shifted to April.

    In August 1969 crew assignments for Apollo 13 were announced: James A. Lovell commanded

    the prime crew, which included Thomas K. Mattingly II as command module pilot and Fred W.

    Haise as lunar module pilot. Their backups were John Young, John Swigert, and Charles Duke.

    The target for the mission was the Fra Mauro Formation, a site of major interest to scientists,

    specifically a spot just north of the crater Fra Mauro, some 550 kilometers (340 miles) west-

    southwest of the center of the moon's near side.

    Days before the mission, backup LM pilot Charlie Duke inadvertently exposed the crew to German measles. Command module pilot, Ken Mattingly, turned out to have no immunity to

    measles and was replaced by backup command module pilot Jack Swigert.

    The movie Apollo 13 incorrectly states that James Lovell's crew was chosen to fly Apollo 13 after the original crew commanded by Alan Shepard was removed due to an inner ear

    problem that Shepard had. Actually it was Apollo 14 that Shepard's crew was removed from.

    The spacecraft was launched on April 11,1970, and the mission was quite routine for the first two

    days.

    Space flight missions after Apollo 12 had become so routine that many news agencies stopped covering the stories. They complained that NASA had made going to the moon

    boring.

    At five and a half minutes after liftoff, Swigert, Haise, and Lovell felt a little vibration. Then the center engine of the S-II stage shut down two minutes early. This caused the remaining

    four engines to burn 34 seconds longer than planned, and the S-IVB third stage had to burn

    nine seconds longer to put Apollo 13 in orbit.

    At 30 hours and 40 minutes after launch (30:40 ground elapsed time, or g.e.t.), the crew ignited

    their main engine to put the spacecraft on a hybrid trajectory, a flight path that saved fuel in

    reaching the desired lunar landing point. At 46:40 the crew routinely switched on the fans in the

    oxygen tanks briefly. A few seconds later the quantity indicator for tank number two went off the

    high end of the scale, where it stayed. The tanks were stirred twice more during the next few

    hours; and at 55:53, after a master alarm had indicated low pressure in a hydrogen tank, the

    Mission Control Center (MCC) directed command module pilot Jack Swigert to switch on all

    tank stirrers and heaters. Immediately thereafter the crew heard a loud "bang" and felt unusual

    vibrations in the spacecraft. Mission controllers noticed that all telemetry readings from the

    spacecraft dropped out for 1.8 seconds. In the CM, the caution and warning system alerted the

    crew to low voltage on d.c. main bus B, one of two power distribution systems in the spacecraft.

    At this point command module pilot Jack Swigert told Houston, "Hey, we've had a problem

    here."

  • Thirteen minutes after the explosion, Lovell happened to look out of the left-hand window, and saw the final evidence pointing toward potential catastrophe. "We are venting something

    out into the- into space," he reported to Houston. Jack Lousma, the CapCom replied, "Roger,

    we copy you venting." Lovell said, "It's a gas of some sort." It was oxygen gas escaping at a

    high rate from the second, and last, oxygen tank.

    Because of the interruption of telemetry that had just occurred, flight controllers in the MCC had

    difficultly for the next few minutes determining whether they were getting true readings from the

    spacecraft sensors or whether the sensors had somehow lost power. Before long, however, both

    MCC and the crew realized that oxygen tank number two had lost all of its contents, oxygen tank

    number one was slowly losing its contents, and the CM would soon be out of oxygen and without

    electrical power. Among the first actions taken were shutting down one fuel cell and switching

    off nonessential systems in the CM to minimize power consumption; shortly after, the second fuel

    cell was shut down as well. When the remaining oxygen ran out, the CM would be dead; its only

    other power source was three reentry batteries providing 120 ampere-hours, and these had to be

    reserved for the critical reentry period.

    An hour and a half after the "bang," MCC notified the crew that "we're starting to think about the

    lifeboat" using the lunar module (LM) and its limited supplies to sustain the crew for the rest of

    the mission. Plans for such a contingency had been studied for several years, although none had

    anticipated a situation as grave as that of Apollo 13. Many of these studies were retrieved and

    their results were adapted to the situation as it developed.

    Shortly after the accident, mission commander James Lovell reported seeing a swarm of particles

    surrounding the spacecraft, which meant trouble. Particles could easily be confused with stars,

    and the sole means of determining the spacecraft's attitude was by locating certain key stars in the

    onboard sextant. Navigational sightings from the LM were difficult in any case as long as it was

    attached to the command module, and this would only complicate matters. Flight controllers

    decided to align the lunar module's guidance system with that in the command module while the

    CM still had power. That done, the last fuel cell and all systems in the command module were

    shut down, and the crew moved into the lunar module. Their survival depended on this craft's

    oxygen and water supplies, guidance system, and descent propulsion engine (DPS). Normally all

    course corrections were made using the service propulsion system (SPS) on the service module,

    but flight controllers ruled out using it, partly because it required more electrical power than was

    available and partly because no one knew whether the service module had been structurally

    weakened by the explosion. If it had, an SPS burn might be dangerous. The DPS would have to

    serve in its place.

    Soon after the explosion, the assessment of life-support systems determined that although oxygen

    supplies were adequate, the system for removing carbon dioxide (CO2) in the lunar module was

    not. The system used canisters filled with lithium hydroxide to absorb CO2 as did the system in

    the command module. Unfortunately the canisters were not interchangeable between the two

    systems, so the astronauts were faced with plenty of capacity for removing CO2 but no way of

    using it. A team in Houston immediately set about improvising a way to use the CM canisters,

    using materials available in the spacecraft.

    The trip was marked by discomfort beyond the lack of food and water. Sleep was almost impossible because of the cold. When the electrical systems were turned off, the spacecraft

    lost an important source of heat. The temperature dropped to 38 F and condensation formed

    on all the walls.

  • During all of these deliberations the atmosphere in the lunar module was gradually accumulating

    carbon dioxide as the absorbers in the environmental control system became saturated. Members

    of MSC's Crew Systems Division devised a makeshift air purifier by taping a plastic bag around

    one end of a CM lithium hydroxide cartridge and attaching a hose from the portable life-support

    system, allowing air from the cabin to be circulated through it. After verifying that this jury rig

    would function, they prepared detailed instructions for building it from materials available in the

    spacecraft and read them up to the crew. For the rest of the mission the improvised system kept

    the CO2 content of the atmosphere well below hazardous levels.

    The decision to recover in the Pacific fixed the time line for the remainder of the mission and

    imposed some rigid constraints on preparations for reentry. The final course correction had to be

    made with the LM engine; command module systems had to be turned on and the guidance

    system aligned; the service module had to be discarded; and when all preparations had been

    made, the lunar module would be cut loose. In all these preparations the power available from the

    CM's reentry batteries was a limiting factor. From the PC + 2 burn until about 35 hours before

    reentry the sequence of activation of CM systems was worked out, checked in the simulators, and

    modified. Fifteen hours before beginning reentry the revised sequence of activities was read to

    the crew, to give them time to review and practice it.

    A most remarkable achievement of Mission Control was quickly developing procedures for powering up the CM after its long cold sleep. Flight controllers wrote the documents for this

    innovation in three days, instead of the usual three months. The Command Module was cold

    and clammy at the start of power up. The walls, ceiling, floor, wire harnesses, and panels

    were all covered with droplets of water. It was suspected conditions were the same behind the

    panels. The chances of short circuits caused apprehension, but thanks to the safeguards built

    into the command module after the disastrous Apollo-1 fire in January 1967, no arcing took

    place. The droplets furnished one sensation as we decelerated in the atmosphere: it rained

    inside the CM.

    The husbanding of expendable resources, particularly electrical power, paid off on the morning of

    landing, when it was discovered that power reserves in the LM were adequate to allow use of it in

    the CM. Some of the early CM activities could then be done at a less hurried pace. The Apollo 13

    command module splashed down within a mile of the recovery carrier with about 20 percent of its

    battery power remaining. Three weary, chilled astronauts came aboard the U.S.S. Iwo Jima on

    April 17 and were flown to Hawaii for an emotional reunion with their families.

    Mission Control teams and their hundreds of helpers were no less drained. The usual cigars were

    lighted up after recovery, but the splashdown parties that evening were subdued: most of those

    who went quit early and went home to bed. Their efforts were recognized the next day when

    President Richard M. Nixon, on his way to Hawaii, stopped in Houston to present the Presidential

    Medal of Freedom, the nation's highest civilian award, to the entire team.

    http://sps.k12.mo.us/khs/science/earth/lessons/astronomy/apollo_13/apollo_13.htm