Spacecraft No. 3A had been designated a thermal qualification test unit.

All of its systems and subsystems were flightworthy, with the exception of certain easily replaceable pieces of equipment such as the heatshield and ejection seats for which non-flight articles were substituted with NASA approval. Qualification testing comprised mission simulations in the altitude chamber, with all systems being operated to their duty cycles. During the next two months, the spacecraft was installed in the altitude chamber, completed a dry run test, and was accepted after a readiness review meeting. Thermal qualification testing began December 19.