Space Shuttle: Difference between revisions

The RCS system consists of three modules, one forward at the nose and two at the OMS pods. The forward module contains 14 primary and 2 secondary thrusters, each aft module carries 12 primary and two secondary thrusters. Propellant reserves in each module are 1,477 lb of oxidizer and 928 lb of MMH. Each primary thruster has 870 lb of thrust with an ISP of 289 s, the secondary Vernier thrusters produce a mere 24 lb each with an ISP of 228 s. Due to geometric constraints, the thrusters are not aligned with the main spacecraft axes or in the same plane (for instance, there is no purely downward firing nose thruster, as its nozzle would have to fire through the heat shield). The layout of the whole system is shown below:

 

Not all thrusters point orthogonal, and not all thrusters have the same nominal thrust - the complete list is as follows

 

[[File:RCS Break Down Table.gif|600px|List of Space Shuttle RCS thrusters and orientation]]

 

All of these thrusters are faithfully modeled in FG with their actual orientation and nominal thrust values, including the system of Vernier thrusters, equipping the Space Shuttle with a grand total of 51 distinct engines.

: A 'stick controls thrust' scheme in which the OMS pod modules are not used. This causes significant mode mixing and has very limited roll control (the roll moment only comes from the position difference between left-mounted and right-mounted upward and downward firing thrusters)

 

: A 'stick controls rate' scheme in which the Vernier thrusters are used to maneuver the Shuttle. The Verniers are not very powerful and moreover fire in an awkward geometry, so there is significant mode mixing into translations when using them and the response of the Shuttle is very slow - the mode should mainly be used for automatic attitude hold as it is very propellant-friendly.

: A translational DAP in which the stick controls translational thrust along the spacecraft x, y and z axes. Stick to idle commands no thrust, but the Shuttle will of course retain its relative velocity to a fix point until counter-thrust is used. RCS translation can be used for emergency de-orbit burns if the OMS is not available. Limited compensation is done for cross-coupling to rotational modes.

 

: A translational DAP in which 'attitude hold' is commanded for all rotation channels. This makes this mode very stable and controllable at the expense of an increased propellant consumption - use e.g. for a precision approach to a docking.