Stacksat 1 to 3 & P87-2 (USA-56 to USA-58)

The U.S. military's STACKSAT mission involved the launch of three similar technology spacecraft, POGS & SSR, TEX and SCE.

PDD (Prototype Deployment Device) was an experimental mechanical latch designed for use in zero-gravity, which was tested as a secondary payload on the Stacksat launch. It was attached to the payload adaptor situated between the Altair-3A upper stage and the bottom spacecraft.