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Forum:	Mercury - Gemini - Apollo
Topic:	USAF Gemini B (MOL) cabin atmosphere

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<table border=0 cellpadding=0 cellspacing=0 width="600"><TR><td bgcolor="#000000"><TABLE BORDER=0 cellpadding=4 border=0 cellspacing=1 WIDTH="100%"><TR bgcolor="#660000"><TD COLSPAN=2><CENTER><FONT SIZE="2" COLOR="#ffffff" FACE="sans-serif">T O P I C     R E V I E W</font></CENTER></TD></TR><TR bgcolor="#494949"><TD valign=top><FONT SIZE="2" FACE="sans-serif">oly</FONT></TD><TD><FONT SIZE="2" FACE="sans-serif">Does anyone here know why the U.S. Air Force Gemini B (Manned Orbiting Laboratory or MOL) program wanted to use a helium/oxygen helox cabin atmosphere? <P>Given that helox increases the energy required to start combustion, it also results in flames that spread substantially faster. There must have been some sound reasoning why helox was preferred over nitrox or pure oxygen. <BR></FONT></TD></TR><TR bgcolor="#333333"><TD valign=top><FONT SIZE="2" FACE="sans-serif">SpaceAholic</FONT></TD><TD><FONT SIZE="2" FACE="sans-serif">Don't know if this was the specific rational but one upside would be removal of narcosis as a risk factor. Depending on what cabin pressure they were intending to run, exposure to pure O2 for extend periods introduces risk of pulmonary/CNS toxicity.</FONT></TD></TR><TR bgcolor="#494949"><TD valign=top><FONT SIZE="2" FACE="sans-serif">oly</FONT></TD><TD><FONT SIZE="2" FACE="sans-serif">Great point and something for me to work with.<P>The design has been reported to have the cabin atmosphere changed to helium-oxygen in place of the pure oxygen environment of Gemini. At launch, the crew was to breathe pure oxygen in their suits while the cabin was filled with pure helium. During ascent, oxygen from the suit system would slowly bring the cabin atmosphere up to the helium-oxygen content of the station itself. <P>Given that these USAF MOL program designs were pre-Apollo 1 fire, it appears that the Air Force had already identified that the associated risks of pure oxygen environments in spacecraft were similar to the safe practices required for aircraft. As the program derived from Dynasoar, at some point, a helium/oxygen environment was identified as the preferred system and significant design work had been applied to provide a safe working environment for crews during long-duration spaceflight. <P>I am yet to determine if the helium-oxygen system derived from Dynasoar or if it evolved during MOL but I am keen to find any information regarding the decision making process.</FONT></TD></TR></TABLE></td></tr></table>

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