The feasibility of performing on-orbit servicing of the NASA Goddard Space Flight Center (GSFC) Gamma Ray Observatory (GRO) was initially addressed by TRW during the later portion of the Phase C development contract in 1981/82. The current post CDR GRO design reflects a capability for on-orbit changeout of the two Multimission Modular Spacecraft (MMS) modular power system (MPS) modules and the MMS communications and data handling (CADH) module via EVA. In addition, the design incorporates a capability for on-orbit refueling (OOR). The GRO design also incorporates a capability of EVA override operations for the deployment, restowage, and jettison of the GRO solar array and high-gain antenna appendages, the grapple fixture, and the electrical umbilical interface