More on ASTOR
From the FAS website:
The dual mode Synthetic Aperture Radar (SAR)/Moving Target Indicator (MTI) is the main sensor in the ASTOR system, enabling radar data to be available in near real time for processing and exploitation both on the platform and the ground. This provides monitoring of land-based targets to assess military capability and behaviour patterns. Targets can be classified at long range for interdiction, with wide area MTI surveillance used to determine the position of a variety of vehicles travelling over a wide range of radial velocities. The ASTOR Dual Mode Radar (DMR) is a developed version of the ASARS 2 radar, Enhanced ASARS, which is currently in use with the U-2R.
To pick up on your question regarding UAVs, the UK Military does not - as yet - operate a UAV with the strategic reach and SAR capability provided by ASTOR. The current crop of larger UAVs tend to be employed (badly perhaps) in Full-motion-video EO or IR roles and the advantages of a SAR capability tend to get overlooked i.e. you can't look through a cloud with EO, but you can with SAR.
I would envision UAVs and ASTOR complementing each other's capabilities; the trick will be in fusing the data in a meaningful and timely fashion.
I hope this helps.
SBG