Originally Posted by
caped crusader
Whilst design work for a probe on Sentinel was completed my understanding is that the fitting of a probe was considered high risk and Sentinel entered into service without an AAR capability.
All the probe work was complete, it was only deleted to save money (circa £60m as I recall)
The plain facts were, with no facility for extra crew or rest facilities provisioned, there was little point in flying for longer than 12 hours on Sentinel.