NASA's EVA Project Office is considering the retrieval of the Upper Atmosphere Research Satellite (UARS) using the Space Shuttle.
According to the 10 May 2001 XA/EVA Project Office Weekly Activity Report:
"Concept Review for Possible Retrieval of the Upper Atmosphere Research Satellite (UARS)
EVA Project Office personnel supported a concept review for the possible Space Shuttle retrieval of the UARS on May 3, 2001. At this point, several different options are still under consideration. The mission would require at least one scheduled EVA to secure various deployable components on the spacecraft. UARS was originally designed to be compatible with EVA operations, so most of the tasks appear to be feasible. An EVA splinter meeting is scheduled for May 10, 2001, to further discuss the EVA requirements for this proposed mission."
According to NASA "The Upper Atmosphere Research Satellite (UARS) is the first systematic, comprehensive and detailed satellite investigation of the stratosphere, mesosphere, and lower thermosphere. Routine remote observations are made over a range of altitudes from the lower stratosphere to the lower thermosphere. The breadth of measurements, in terms of altitude and number of parameters, facilitates the understanding of upper atmosphere structure and behavior."
The specific mission objectives, as listed by NASA, are to study: energy input and loss in the upper atmosphere; global photochemistry of the upper atmosphere; dynamics of the upper atmosphere; the coupling among these processes; and the coupling between the upper and lower atmosphere.
UARS was launched by Space Shuttle Discovery on the STS-48 mission on 12 September 1991. The UARS was designed for deployment by the Shuttle's Remote Manipulator System (RMS) and was released into orbit on 15 September 1991.
UARS was built around a standard Multimission Modular Spacecraft (MMS) coupled to an Instrument Module (observatory) that includes ten science instruments and various mission-unique components. The Multimission Modular Spacecraft provides Guidance, Navigation and Communications (GN&C) and power supply (via solar arrays) for the observatory's instrumentation.
When originally launched, the spacecraft's power supply was sufficient to allow all instrumentation to operate without sharing of resources. However, performance problems arose with UARS Battery-1 (one of the three main batteries) requiring that instrument operations to be scheduled to make use of less than optimal power supplies. The spacecraft continues to return scientific data.