separation is initiated when the three solid rocket motor chamber
pressure transducers are processed in the redundancy management
middle value select and the head- end chamber pressure of both SRBs
is less than or equal to 50 psi. A backup cue is the time elapsed
from booster ignition.
The separation sequence is
initiated, commanding the thrust vector control actuators to the null
position and putting the main propulsion system into a second-stage
configuration (0.8 second from sequence initialization), which ensures
the thrust of each SRB is less than 100,000 pounds. Orbiter yaw attitude
is held for four seconds, and SRB thrust drops to less than 60,000 pounds.
The SRBs separate from the
external tank within 30 milliseconds of the ordnance firing command.
The forward attachment point
consists of a ball (SRB) and socket (ET) held together by one bolt.
The bolt contains one NSD pressure cartridge at each end. The forward
attachment point also carries the range safety system cross-strap wiring
connecting each SRB RSS and the ET RSS with each other.
The aft attachment points consist
of three separate struts: upper, diagonal and lower. Each strut contains
one bolt with an NSD pressure cartridge at each end. The upper strut
also carries the umbilical interface between its SRB and the external
tank and on to the orbiter.
There are four booster separation
motors on each end of each SRB. The BSMs separate the SRBs from the
external tank. The solid rocket motors in each cluster of four are ignited
by firing redundant NSD pressure cartridges into redundant confined
detonating fuse manifolds.
The separation commands issued
from the orbiter by the SRB separation sequence initiate the redundant
NSD pressure cartridge in each bolt and ignite the BSMs to effect a