fifty years ago April 17, 1970 Archives

What Went Wrong with Apollo-13?

The malfunction, which forced the Apollo-13 astronauts to abandon their moon landing plans and head back home, occurred in their spacecraft’s electric generating system. The system is known as a “fuel cell.” It manufactures electric energy by chemical reactions between hydrogen and oxygen. These reactions simultaneously produce water and heat. In the spacecraft, this water replenishes the astronauts’ reservoir for drinking. Some of the heat is recycled into the fuel cell system and the rest of the heat is considered waste and disbursed into space through radiators.

Fuel cells were little more than laboratory curiosities until their potential usefulness in spacecraft triggered their advanced development. Three fuel cell powerplants serve the Apollo spacecraft. The three units are housed in the service module, the cylindrical compartment attached to the command module in which the astronauts live. The service module contains equipment and supplies needed on a flight. The command and service modules jointly make up what is generally called the commandship or main spacecraft, as distinguished from toe moon landing craft, or lunar module. The hydrogen and oxygen are stored in the service' module at cryogenic (very low) temperatures in a semi-gas, semi-liquid state under severe compression.

Each fuel cell system consists of 31 individual cells connected in series and enclosed in metal pressure jackets. To produce electricity, an electrolyte also is needed which consists of 83 per cent potassium hydroxide and 17 per cent water. The power-producing chemical reaction starts when the electrolyte temperature exceeds 300 degree F. The temperature has to remain above 385 degree F for the reaction to continue. Some of the recycled heat is used to help maintain the electrolyte at the needed temperature.

The astronauts said they heard a “bang” just before two of their fuel cells stopped furnishing electricity. Though the cause of this malfunction is not known, it is believed to have been a rupture in a pressure tank containing oxygen or hydrogen, or in a connecting line or in tone of the associated valves, switches or other plumbing fixtures of that system. This, in turn, could have been caused by a hit by a micro-meteorite — one of the pebble-like projectiles which race through space in great abundance. Unmanned spacecraft have recorded numerous such hits, but there has been no record of any manned spacecraft being damaged or otherwise affected by meteorites.

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Printable version | Jul 10, 2020 7:44:35 PM | https://www.thehindu.com/archives/what-went-wrong-with-apollo-13/article31359848.ece

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