MadSci Network: Physics

Re: Why do shuttle astronouts experience less G forces than Apollo ones did?

Date: Wed Jun 21 10:08:15 2000
Posted By: David Ellis, Researcher, NASA Lewis Research Center
Area of science: Physics
ID: 960170955.Ph

I'm afraid that the reference that had the Apollo program astronauts experiencing 9 g's is incorrect. At 4 to 6 g's the human body begins to have serious problems ranging from visual impairment to blackout. At 9 g's virtually everyone will blackout even with a G-suit. For some additional information on g forces and their effect on the human body, try looking at Acceleration of Blackout in Fighter Pilots.

According to Compton's Interactive Encyclopedia, astronauts generally experience around 2 to 3 g's. That is actually less than fighter pilots and most roller coaster rides. The biggest difference is they experience these forces for approximately 9 minutes, the time it takes to get into orbit.

The point where maximum g forces are experienced varies by launch system and mission. In the case of the Apollo program, maximum g forces would have been experienced just before first stage cutoff when the largest rocket motors, the five F-1 engines, were firing at full power while the weight of the spacecraft was substantially reduced by the burning of almost all the first stage propellants.

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