The United States and Soviet Union poured billions of dollars into signals intelligence satellites during the Cold War.

These spacecraft were an invulnerable and invaluable means of collecting signals intelligence from their rivals.

Yet much of their work was in secret. Today, three decades on from the end of the Cold War, we are starting to learn more about the work of these satellites as documents are declassified and experts share their stories.

In our latest Electronic Warfare Podcast, we chat to Dr. Dwayne Day, a space historian who has written extensively on Cold War space SIGINT gathering.