You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Space_Race

Context:
The two nations planned a joint mission to dock the last US Apollo craft with a Soyuz, known as the Apollo-Soyuz Test Project (ASTP). To prepare, the US designed a docking module for the Apollo that was compatible with the Soviet docking system, which allowed any of their craft to dock with any other (e.g. Soyuz/Soyuz as well as Soyuz/Salyut). The module was also necessary as an airlock to allow the men to visit each other's craft, which had incompatible cabin atmospheres. The USSR used the Soyuz 16 mission in December 1974 to prepare for ASTP.

Question:
ASTP stands for what?

Apollo-Soyuz Test Project