Body Mounted Attitude Gyro: Difference between revisions

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Simply put, Body Mounted Attitude Gyros (BMAGs) are rate gyros mounted in a fixed reference to the spacecraft itself.
The Body Mounted Attitude Gyros, or BMAGs, help to back up to the IMU. The two assemblies are capable of detecting the spacecraft's rate. This information is sent to the Gyro Display Coupler, or GDC, which adds the rate to its current know attitude, updating its knowledge spacecraft's orientation. There are two sets of rate gyros that are referred to as BMAGs one and two. Both of these can be activated or powered off through their rotary switches on MDC-7.


As a backup to the complex IMU, the Apollo CSM engineers decided to use rate gyros, much like those in the IMU, and mount them to the spacecraft directly. These gyros can then give the rate of angular change referenced to the spacecraft instead of inertial space.
Both gyro assemblies are typically caged and determine only the spacecraft's rate. The rate is then sent to the GDC. The three BMAG switches on MDC-1 determine which set of gyros the GDC receives rate data from. Setting a switch to either Rate 1 or Rate 2 determines which BMAG the GDC receives rate from in that axis. BMAG one is capable of being uncaged to determine attitude errors. The center setting of the BMAG switches, Att 1/Rate 2, tells the GDC to accept rate data from BMAG 2 and attitude data from BMAG 1. In order to do this, BMAG one must be uncaged by the ECA. This is done automatically when setting a BMAG switch to the center position.
 
Maintaining attitude in space requires two separate functions. Remembering a reference attitude and knowing the rate at which the spacecraft is turning. By adding the angular rate to the remembered reference, the current spacecraft attitude can be calculated.
 
The BMAGs determine the angular rates and the Gyro Display Coupler (GDC) receives these angular rates and adds them to the current attitude, thus remembering the attitude difference from the original reference in real time.
 
This was a primitive, but reliable backup to the CMC for attitude reference, and allowed Apollo 12 to monitor the ascent when lightning caused the CMC to loose it's inertial reference during the boost phase of flight.


[[Category:Stabilization and Control System]]
[[Category:Stabilization and Control System]]
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Latest revision as of 21:45, 21 January 2011

The Body Mounted Attitude Gyros, or BMAGs, help to back up to the IMU. The two assemblies are capable of detecting the spacecraft's rate. This information is sent to the Gyro Display Coupler, or GDC, which adds the rate to its current know attitude, updating its knowledge spacecraft's orientation. There are two sets of rate gyros that are referred to as BMAGs one and two. Both of these can be activated or powered off through their rotary switches on MDC-7.

Both gyro assemblies are typically caged and determine only the spacecraft's rate. The rate is then sent to the GDC. The three BMAG switches on MDC-1 determine which set of gyros the GDC receives rate data from. Setting a switch to either Rate 1 or Rate 2 determines which BMAG the GDC receives rate from in that axis. BMAG one is capable of being uncaged to determine attitude errors. The center setting of the BMAG switches, Att 1/Rate 2, tells the GDC to accept rate data from BMAG 2 and attitude data from BMAG 1. In order to do this, BMAG one must be uncaged by the ECA. This is done automatically when setting a BMAG switch to the center position.

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