Hatch Counterbalance Pressurized Cylinders
  • Pressurized cylinders for charging the side hatch opening actuator, called the counterbalance.
  • Originally pressurized with gaseous nitrogen at 5,000 psi.
  • Enabled a fully suited astronaut inside the Command Module to open the 350 pound weight of the combined side hatch and outer cover in 3 seconds.
  • NASA photo shows the counterbalance at the lower hatchway of Apollo 17 during recovery operations, with cylinders indicated by the arrow.
  • One cylinder was opened prior to launch, with the ground crew closing the hatch against the counterbalance pressure after astronaut ingress.
  • The second cylinder was available for in-flight use if needed.
  • Markings on the cylinders record the part and serial numbers, date, weight, quality control inspections, and caution notes.
  • One cylinder is dated 7-22-69, filled as Apollo 11 was returning from the first lunar landing.
  • Ref. “Apollo Command Module Side Access Hatch System,” N70-21447.

0.41 lbs. (0.19 kg) (empty)






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