Crewmen aboard the USS Iwo Jima hoist the Apollo 13 Command Module aboard ship after successful splashdown in the Pacific. Tragedy had been narrowly averted.

Courtesy NASA __1970: __Apollo 13 splashes down in the Pacific Ocean near Samoa, recovering from a barely survivable explosion in space.

Apollo 13 launched from Cape Canaveral on April 11, intended to be the third manned lunar landing. The crew — James A. Lovell Jr., John L. Swigert Jr. and Fred W. Haise Jr. — experienced a slight vibration shortly after launch, but things were going normally until 55 hours, 55 minutes into the flight.

Oxygen tank No. 2 exploded, causing No. 1 to fail and start leaking rapidly. Warning lights started blinking. The astronaut's supplies of air, water, light and electricity were imperiled ... 200,000 miles from Earth.

Swigert radioed Mission Control in Texas: "Houston, we've had a problem here." The 1995 hit film Apollo 13 used a more dramatic version: "Houston, we have a problem."

NASA had engineered some redundancy into the Apollo systems, but it was an extremely close scrape. The plan now was to scrap the lunar landing, swing around the moon and return home. The crew clambered from the Command Module into the attached Lunar Module as a lifeboat.

__Oxygen: __There was plenty in the LM, because more oxygen was available from the tanks that would have supplied liftoff from the moon's surface.

__Light and electricity: __All noncritical systems were turned off, reducing power consumption to one-fifth of normal. But without the heat generated by those systems, the temperature inside the capsule dropped to 38 degrees Fahrenheit. LM power was used to recharge batteries in the CM for eventual re-entry in the Earth's atmosphere.

__Water: __LM systems needed water for cooling. So the crew conserved water by drinking little and eating only wet foods. They became severely dehydrated, losing about 10 pounds each. But the water lasted.

__Carbon dioxide removal: __The LM had lithium hydroxide canisters to remove the CO2 for two men for two days, not three men for four days. Under the guidance of Mission Control, the astronauts attached the CM canisters to the LM system with a pipeline made of plastic bags, cardboard and tape, all of which NASA had placed on board. Kluge city.

__Getting home: __The navigation system was transfered from CM to LM, but the alignment needed to be checked. Debris from the explosion made it hard for the astronauts to fix upon any distant stars. So NASA instructed the crew to use the nearest one: the sun. Precise navigation was essential, because returning to the Earth at too steep an angle would cause the CM to burn up in the atmosphere. Too tangential an angle could skip the module out into space forever. Fire or ice.

After four days of alternating terror and hope, the three astronauts climbed back to the CM for re-entry an hour before splashdown. Everything worked out.

The Apollo 13 Accident Review Board later determined the cause of the explosion. Improvements to the command module in 1965 raised the permissible voltage to the oxygen-tank heaters from 28 to 65 volts DC. But the heater switches weren't likewise upgraded. The final launch-pad test ran the heaters hot and long. Wires near the heaters were cooked at 1,000 degrees Fahrenheit — enough, it was learned later, to "severely degrade teflon insulation. The thermostatic switches started to open ... and were probably welded shut." NASA also found that other warning signs had been ignored, and the oxygen tank was a potential bomb that became a real bomb.

Source: NASA

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