Strain-gauged pins take the stress of NASA lifeboat

Strainsert strain gauged clevis pins supplied by Variohm Components have been used on NASA’s X-38 emergency Crew Return Vehicle. Designed as a lifeboat for the International Space Station, the CRV will glide unpowered from orbit back to earth and use a steerable parafoil parachute to assist landing. Instead of using conventional wheeled landing gear, the CRV will land on three skids.

In order to be able to measure the forces actually experienced by the skids and thereby ensure that they meet requirements, NASA purchased three specially designed Strainsert clevis pins. These pins were integrated into the port, starboard and nose pin joints of the skids. To meet the design brief which stipulated the ability to take a high impact load over a high temperature range with little adaptation to the existing skid hardware, Strainsert provided pins with strain gauges internally bonded down small diameter holes along the neutral axis of the pin. The gauges were placed at pre-determined sensing points and were oriented to measure shear forces seen by the pin, the output of the strain gauge being directly proportional to the applied load.

The one-inch diameter pins were manufactured from a nickel plated steel alloy and rated at just over 18 tonnes. Tests, including an unpiloted descent from an orbiting Space Shuttle, are planned for later this year.