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April13: Apollo 13

Apollo 13,NASA,

Apollo 13 was the third lunar landing attempt. This mission was designed to land on the moon in the Fra Mauro area in the moon with crew members consisting of James A Lovell, Jr; John L Swigert, Jr; Fred W Haise, Jr. The launch for Apollo 13 was scheduled on Saturday April 11, 1970 at13:13 CST.As preplanned it launched on the stipulated date but at five and a half minutes after liftoff, the crew members felt a little vibration. Ground tests before launch indicated the possibility of a poorly insulated supercritical helium tank in the LM's descent stage so the flight plan was modified to enter the LM three hours early in order to obtain an onboard readout of helium tank pressure. The first two days ran into a couple of minor surprises. At 46 hours 43 minutes Joe Kerwin, the CapCom on duty, said, ''The spacecraft is in real good shape as far as we are concerned. We're bored to tears down here.'' It was the last time anyone would mention boredom for a long time.

The time was 2108 hours on April 13.At 55 hours 46 minutes, the crew finished a 49 minute TV broadcast showing how comfortably they lived and worked in weightlessness. Nine minutes later, Oxygen tank No 2 blew up, causing No 1 tank also to fail. The Apollo 13 command modules normal supply of electricity, light, and water was lost, and they were about 200,000 miles from Earth. The message came in the form of a sharp bang and vibration. Warning lights indicated the loss of two of Apollo 13’s three fuel cells, which were a prime source of electricity.
The Apollo 13 malfunction was caused by an explosion and rupture of oxygen tank No. 2 in the service module. The explosion ruptured a line or damaged a valve in the No. 1 oxygen tank, causing it to lose oxygen rapidly. The service module bay No. 4 cover was blown off. All oxygen stores were lost within about 3 hours, along with loss of water, electrical power, and use of the propulsion system.

The first thing the crew did, without any panic, was to try to close the hatch between the Command Module and the Lunar Module. They reacted spontaneously, like submarine crews, closing the hatches to limit the amount of flooding. First Jack and then Lovell tried to lock the reluctant hatch, but the stubborn lid wouldn't stay shut. Exasperated, and realizing that there wasn't a cabin leak, they strapped the hatch to the CM couch. The pressure in the No 1 oxygen tank continued to drift downward; passing 300 psi, now heading toward 200 psi.

The crew became dehydrated throughout the flight and set a record that stood up throughout Apollo: Lovell lost fourteen pounds, and the crew lost a total of 315 pounds, nearly 50 percent more than any other crew. Those stringent measures resulted in the crew finishing with 282 pounds of water, about 9 percent of the total.

One of the biggest question was, ''How to get back safely to Earth?''. The LM navigation system wasn't designed to help in this situation. Before the explosion, at 30 hours and 40 minutes, Apollo 13 had made the normal midcourse correction, which would take it out of a free return to Earth trajectory and put it on a lunar landing course. Now the task was to get back on a free return course. The ground computed a 35 second burn and fired it 5 hours after the explosion. As they approached the Moon, another burn was computed; this times a long 5 minute burn to speed up the return home. It took place 2 hours after rounding the far side of the Moon.

The Command Module navigational platform alignment was transferred to the LM but verifying alignment was difficult. Ordinarily the alignment procedure uses an on board sextant device, called the Alignment Optical Telescope (AOT), to find a suitable navigation star. Then with the help of the on board computer it verifies the guidance platform's alignment. However, due to the explosion, a swarm of debris from the ruptured service module made it impossible to sight real stars.

An alternate procedure was developed to use the sun as an alignment star. Lovell rotated the spacecraft to the attitude Houston had requested and when he looked through the AOT, the Sun was just where it was expected. The alignment with the Sun proved to be less than a half a degree off. The ground and crew then knew they could do the 5 minute PC + 2 burn with assurance, and that would cut the total time of the voyage to about 142 hours.

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 degrees F and condensation formed on all the walls.

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 safe guards built into the command module after the disastrous Apollo 1 fire in January 1967, no arcing took place.

Four hours before landing, the crew shed the service module; Mission Control had insisted on retaining it until then because everyone feared what the cold of space might do to the unsheltered CM heat shield. Photos of the Service Module showed one whole panel missing, and wreckage hanging out, it was a sorry mess as it drifted away. Three hours later the crew left the Lunar Module Aquarius and then splashed down gently in the Pacific Ocean near Samoa.
Published: 2008-02-23
Author: Anurag Ghosh

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