The need to improve space mechanism reliability is underscored by a long history of flight failures and anomalies caused by malfunctioning mechanisms on spacecraft and launch vehicles. Some examples of these failures are listed in the table. Mechanism anomalies continue to occur a nd to be a cause of catastrophic mission failures.
Several factors cause problems for space system mechanisms.
The space environment produces wide temperature ranges, thermal gradients, and rapid changes in temperature, which can bind the moving parts of mechanisms. Ultraviolet radiation and vacuum cause the properties of many materials to degrade to unacceptable levels or to behave differently in space than on Earth, making it difficult to simulate operation during ground tests. The lack of gravity in space causes mechanisms to operate differently than on the ground. Sometimes the effects of zero gravity can be simulated to some degree in ground testing, such as by offloading the weight of a deployable appendage. Other effects, such as lubricant migration, cannot be simulated and must be considered in the design.