On-screen chemistry
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Explosion
It appeared that a heater and stirrer in the CM’s oxygen
tank did not turn off correctly and created the explosive
pressures which lead to the accident. Fortunately
the tank exploded out into space rather than into
the spacecraft. However, this meant the astronauts
were now in a critical situation as the CM could no
longer maintain a clean air supply. The crew moved
into the Lunar Module (LM) and used its resources
as a ‘lifeboat’. Without this option they would almost
certainly have died.
Mission Control at Houston considered all of
the possible flight plans and combinations of
engine firing which could bring the astronauts
home safely. The best option would still take
four days... The LM was designed to support
two people for two days on the moon, not
three people for a four day trip home. This
meant they had very limited electrical power,
heating and drinking water, which must be
conserved. They had enough oxygen for the trip but
the critical issue was carbon dioxide.
Too much CO2
Normally about 0.04% of air is CO2. As the level of CO2
rises, it causes our respiratory rate to increase. High
levels of CO2 can lead to headaches, confusion and
eventually loss of consciousness.2 About 3% of expired
air is CO2, so in a small space such as the LM, the levels
will quickly rise.
NASA
It is 1970 and Apollo 13 blasts-off successfully on the
US’s third mission to land on the Moon. Two days out
and 200 000 miles from Earth, an oxygen tank ruptures,
damaging other tanks and the spacecraft’s electrical
system in the Command Module (CM) prompting the
crew’s immortal lines ‘Houston, we’ve had a problem’. For
the three astronauts, the mission now is to return to Earth
safely. Hollywood tells the story in the film Apollo 13,
where Tom Hanks plays commander Jim Lovell.1
PICTURE CREDIT
Apollo 13 – lithium hydroxide saves the day
Apollo 13 mission
badge
The LM used cylindrical canisters of lithium hydroxide
(anhydrous) in the air circulating system as scrubbers to
remove the excess CO2 (lithium carbonate and water are
produced) and keep the air clean.
2LiOH + CO2 → Li2CO3 + H2O
However, there were not enough spare canisters in the
LM to support the crew for four days. The CM had an
adequate supply but these units didn’t fit the equipment
in the LM as they were the wrong shape. The crew had
to ‘lash-up’ a device to solve this problem using a space
suit hose, cardboard, tape and the extra canisters.
NASA
After a nail-biting blackout period as the lunar module
re-entered the Earth’s atmosphere, the LM and her crew
splashed-down safely in the Pacific Ocean. Despite
the complex trajectory calculations, engine firing
and computer problems on the way home, the crew
ultimately survived due to the little canisters of LiOH.
References
1 Apollo 13, Columbia, 1995.
2 Frances Ashcroft, Life at the extremes. London:
Flamingo, 2001
Apollo 13 space craft
launch
InfoChem
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