Project Vela was a project by the United States to develop and implement methods to monitor compliance with the 1963 Partial Test Ban Treaty. The development work was primarily performed by the Advanced Research Projects Agency and was overseen by the United States Air Force.
Project Vela consisted of three elements: Vela Uniform to monitor seismic signals to detect underground nuclear testing, Vela Sierra to detect atmospheric nuclear testing and Vela Hotel to detect nuclear testing from space.
"The USAF set up a nuclear detection system by launching twin satellites from Cape Canaveral into circular 57,000-mile-high orbits on opposing sides of the earth. The 496-pound (225 kg), 20-sided satellites, known as Project Vela Hotel or Project 823, could detect nuclear explosions from 186,000,000 miles away".