The standard aluminum 80 cubic foot tank on a 40 feet
water dive would provide about
45 minutes of breathing time per tank
http://scuba.about.com/od/scuba101/p/How-Long-Does-A-Scuba-Tank-Last.htm
25 Scuba tanks for 45 minutes each
1125 min = 18.75 hours
http://www-pao.ksc.nasa.gov/history/apollo/flight-summary.htm
Liquid Oxygen takes up 1/10 of the size at 300 degrees below zero Fahrenheit
Even so, Apollo 16 Astronauts would require 4.735 back packs
What apparatus would heat the frigid liquid oxygen enough to be breathable
at the right temperature - not to hot and not too cold - within seconds?
The back packs of the Astronauts could not hold enough air
as they did not recharge their tanks during the lunar landing.
Boy: "How could astronauts breathe so long on such small air tanks?"