Kosmos 638 (Russian: Космос 638) was an uncrewed test of the 1975 Apollo–Soyuz Test Project Soyuz.

It carried an APAS-75 androgynous docking system.

This was followed by another uncrewed test of this spacecraft type, Kosmos 672.

[2] When the air was released from the orbital module (which is ejected before re-entry of the capsule) it caused unexpected motions with the spacecraft.

This article about one or more spacecraft of the Soviet Union is a stub.