Editing Human spaceflight (section)

==== Reliability ====
{{See also| Reliability engineering}}

The March 1966 [[Gemini 8]] mission was aborted in orbit when an [[attitude control system]] thruster stuck in the on position, sending the craft into a dangerous spin that threatened the lives of [[Neil Armstrong]] and [[David Scott]]. Armstrong had to shut the control system off and use the reentry control system to stop the spin. The craft made an emergency reentry and the astronauts landed safely. The most probable cause was determined to be an electrical short due to a [[static electricity]] discharge, which caused the thruster to remain powered even when switched off. The control system was modified to put each thruster on its own isolated circuit.

The third lunar landing expedition, [[Apollo 13]], in April 1970, was aborted and the lives of the crew—[[Jim Lovell|James Lovell]], [[Jack Swigert]], and [[Fred Haise]]—were threatened after the failure of a [[cryogenic]] [[liquid oxygen]] tank en route to the Moon. The tank burst when electrical power was applied to internal stirring fans in the tank, causing the immediate loss of all of its contents, and also damaging the second tank, causing the gradual loss of its remaining oxygen over a period of 130 minutes. This in turn caused a loss of electrical power provided by [[fuel cell]]s to the [[Apollo Command/Service Module|command spacecraft]]. The crew managed to return to Earth safely by using the [[Apollo Lunar Module|lunar landing craft]] as a "life boat". The tank failure was determined to be caused by two mistakes: the tank's drain fitting had been damaged when it was dropped during factory testing, necessitating the use of its internal heaters to boil out the oxygen after a pre-launch test; which in turn damaged the fan wiring's electrical insulation because the thermostats on the heaters did not meet the required voltage rating due to a vendor miscommunication.

The crew of [[Soyuz 11]] were killed on 30 June 1971 by a combination of mechanical malfunctions; the crew were [[asphyxia]]ted due to cabin decompression following the separation of their descent capsule from the service module. A cabin ventilation valve had been jolted open at an altitude of {{convert|168|km}} by the stronger-than-expected shock of explosive separation bolts, which were designed to fire sequentially, but in fact had fired simultaneously. The loss of pressure became fatal within about 30 seconds.<ref>{{Cite web|url=https://history.nasa.gov/SP-4209/ch8-2.htm|title=The Partnership: A History of the Apollo–Soyuz Test Project|access-date=20 October 2007|publisher=NASA|year=1974|archive-url=https://web.archive.org/web/20070823124845/https://history.nasa.gov/SP-4209/ch8-2.htm|archive-date=23 August 2007}}</ref>