Solid Rocket Booster Rate Gyro Assemblies

The solid rocket booster RGAs are used exclusively during first-stage ascent as feedback to find rate errors from lift-off to two to three seconds before SRB separation. There are three RGAs on each SRB, each containing two identical single-degree-of-freedom rate gyros for sensing rates in the vehicle pitch and yaw axes similar in function to the orbiter RGAs. The maximum outputs for the SRB RGAs are 10 degrees per second.

The SRB RGAs sense pitch and yaw rates, but not roll rates, during the first stage of ascent. Because the SRBs are more rigid than the orbiter body, these rates are less vulnerable to errors created by structural bending. They are thus particularly useful in thrust vector control.

The three RGAs in each SRB are mounted on the forward ring within the forward skirt near the SRB-external tank attach point.

The SRB RGA SOP converts the 12 voltages representing a rate into units of degrees per second. These rates are used by the flight control system during first-stage ascent as feedback to identify rate errors, which are used for stability augmentation. The pitch and yaw axes and a combination of rate, attitude and acceleration signals are blended to provide a common signal to the space shuttle main engines and SRB thrust vector control during first stage. In the roll axis, rate and attitude are summed to provide a common signal to the SSMEs and SRB thrust vector control.

Each of the SRB RGAs is hard-wired to a flight aft MDM to the GPCs through flight-critical buses 5, 6 and 7. In the GPCs, the SOP applies the rate compensation equation to each of the left or right pitch and yaw rates. The compensated rate signals are sent to redundancy management, where the mid value software scheme selects the best data for use and failure detection.

The SRB RGAs are commanded to null and switched out of the flight control system two to three seconds before SRB separation; SRB yaw and pitch rate data are then replaced with orbiter pitch and yaw RGA data.

The RGA/accel red caution and warning light on panel F7 will be illuminated to inform the flight crew of an RGA failure.

The RGA contractor is Northrop Corp., Electronics Division, Norwood, Mass.