Ariel 4, known pre-launch as UK 4, was a British ionospheric research satellite, which was operated by the Science and Engineering Research Council. It was launched 11 December 1971, aboard an American Scout rocket. Experiments were designed to meet one scientific objective, making it the first mission-oriented satellite for the UK. It was also the first satellite in the Ariel programme to contain an American experiment. Ariel 4 decayed from orbit on 12 December 1978
