Answer to question:
Work done by external forces (excluding gravitational force) is negative.
Since for satellites in orbit (where G is the gravitational constant, r is the radius of the orbit, M is the mass of the planet and m is the mass of the satellite), kinetic energy increases. Hence is positive.
Work done by gravity is positive as the radial displacement is in the same direction as that of the force. Work done by gravity =
According to the Work-Energy Theorem, net work = work done by gravity + work done by external force = . Hence, work done by external force = . [/spoiler]