Ariel 5 was a joint British and American space observatory dedicated to observing the sky in the X-ray band. It was launched on October 15, 1974 from the San Marco platform in the Indian Ocean and operated until 1980. It was the penultimate satellite to be launched as part of the Ariel programme. It was designed to fit a resource budget of 2 kg, 1 bit per second, and 1 W. The All-sky monitor (ASM) was two one-dimensional pinhole cameras scanned most of the sky every spacecraft revolution. The angular resolution was 10 x 10°, with an effective area of cm2 (sq in), and a bandpass of 3-6 keV.