The Indian Space Research Organisation (ISRO) is set to launch two small earth observation satellites for the United Kingdom on Sunday. NovaSar and S1-4, weighing a total of 889 kg, will be set off from the first launch pad at Satish Dhawan Centre, Sriharikota at 10:00 pm into a 583-km sun-synchronous orbit. A satellite is said to be in a sun-synchronous orbit when it changes its orientation throughout the year to ensure that the angle of sunlight is the same every time it passes over a particular geographical area on the surface of the earth.