User: From the passage below, please extract the official starting date of the United States Space Force.
Assistant: The United States Space Force Act was signed into law as part of the National Defense Authorization Act on December 20, 2019. This act reorganized the Air Force Space Command and other space elements into the United States Space Force, and officially created the first new independent military service since the Army Air Forces were reorganized as the U.S. Air Force in 1947.