Can an ASTOR brain come back to the thread and explain in simple terms why it cannot do the Nimrod job? Obviously, opsec uppermost. I am hearing it is has an awesome capability.
Different roles - ASTOR tracks moving objects just like JSTARS (but with much reduced pie-carrying capacity due to MOD scrimping on airframe choice). The SAR image it takes is intended for general identification of those objects, these would then be passed to other platforms such as Watchkeeper for a more detailed look.
The MR2 is basically acting as a big Predator/Watchkeeper, using the MX-15 turret to keep an eye on the bad guys just like the US do with pred but with considerably more risk and much poorer access to Vegas.
The bit of kit MOD intends to do this job in the future is either Pred B or the new King Air 350ER's (also fitted with MX-15 - again with minimal pie-lift capacity).