A spaceship is moving around the Earth in a 500- x 1000km orbit. At apogee, a retrorocket is fired in a direction exactly opposite to the spaceship's velocity vector. The magnitude of the retrorocket deltaV is such that the spaceship will impact the Earth after travelling an Earth-centred angle of 90 degrees.
a) What is the magnitude of deltaV?
b) How much time elapsed between retrofire and impact?