Shuttle Boosters to sport APU fuel pump safety redesign from STS-134

A redesign to the Solid Rocket Booster (SRB) Thrust Vector Control (TVC) Auxiliary Power Unit (APU) fuel pump will be implemented on STS-134 and STS-133 – currently the final two “scheduled” shuttle flights. The redesign will eliminate the highest – although extremely unlikely to occur – “critical 1″ failure scenario, which holds the potential of a LOV/C (Loss of Vehicle/Crew) event.
APU Fuel Pump:
There are two self-contained, independent HPUs (Hydraulic Power Units) on each SRB. Each HPU consists of an Auxiliary Power Unit (APU), Fuel Supply Module (FSM), hydraulic pump, hydraulic reservoir and hydraulic fluid manifold assembly.
The HPU components are mounted on the aft skirt between the rock and tilt actuators – which are part of the Thrust Vector Control system that drives the SRB nozzle to aid the steering of the stack during first stage ascent.
The APUs and their fuel systems are isolated from each other, with each FSM (tank) containing 22 pounds of hydrazine.
The fuel tank is pressurized with gaseous nitrogen at 400 psi, which provides the force to expel (positive expulsion) the fuel from the tank to the fuel distribution line, maintaining a positive fuel supply to the APU throughout its operation.
Fuel ...