Just before collision, the total energy of two satellites is E = −
Gmm
2r
-
Gmm
2r
= −
Gmm
r
Let orbital velocity is V, then from momentum conservation 1 mv - mv = 2m × v1 ⇒ V1 = 0 i.e. velocity of combined mass is zero. Hence, combined mass falls towards earth. At this instant,the total energy of the system only consists of the gravitational potential energy given by U = −