Retrofittable satellite systems for an in-orbit host satellite comprising an enhancement module for adding a capability to the in-orbit host satellite, modifying the function of the in-orbit host satellite, and/or extending the function of the in-orbit host satellite. The in-orbit, retrofittable satellite system comprises a transfer vehicle for transferring the enhancement module from a first to a second location and a service vehicle for receiving the enhancement module from the transfer vehicle and installing the enhancement module on the in-orbit host satellite. In-orbit space situational awareness systems, comprising one or more in-orbit host satellites having one or more enhancement modules attached thereto, the enhancement modules comprising sensors such as satellite spatial location/position sensors, range sensors, navigation sensors, and/or proximity sensors for detecting other objects in-orbit, their location, speed, acceleration, orbital trajectory or the like, wherein the enhancement modules communicate to create a mesh network between the satellites.