The MetOp satellites each weighs over 4000 kg and measure 17.6 m x 6.5 m x 5.2 m after the solar array and antennas have deployed following launch. Once MetOp is in the correct position the solar array, which is on the zenith side of the satellite, is gently deployed to face the Sun. This procedure takes up to 17 minutes and happens in two stages. Initially, the solar array arm rotates 120° up and over. Then the large eight-section panel opens out to face the Sun. There are three satellites in the series, launched sequentially to ensure continuous observations for numerical weather prediction – the basis for weather forecasting.