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Space Shuttle: Difference between revisions
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: This is a stick-controls-rates scheme which utilizes thrust vectoring for the OMS engines. It resembles in principle the ascent thrust vectoring, except for the fact that the OMS engines are far less powerful and hence rates and the transition to the set rate are a lot slower. Note that this DAP will only control the Shuttle if the OMS is firing. | : This is a stick-controls-rates scheme which utilizes thrust vectoring for the OMS engines. It resembles in principle the ascent thrust vectoring, except for the fact that the OMS engines are far less powerful and hence rates and the transition to the set rate are a lot slower. Note that this DAP will only control the Shuttle if the OMS is firing. | ||
If TVC for the OMS is not feasible (for instance because the OMS engine gimbal actuators are damaged), the OMS engines can also be fired with an RCS attitude-holding rotational DAP active (for example | If TVC for the OMS is not feasible (for instance because the OMS engine gimbal actuators are damaged), the OMS engines can also be fired with an RCS attitude-holding rotational DAP active (for example '''RCS DAP-A'''. In this case, attitude control is provided by the RCS thrusters and thrust by the OMS engines. | ||
=== The Reaction Control System === | === The Reaction Control System === | ||
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Below approximately Mach 6, the rudder starts to contribute to yaw stability and from Mach 3.5 down to Mach 2 where the yawing moment finally becomes positive only the rudder is used. The roll behavior of the orbiter before any FCS is somewhat skittish as the roll moment as a function of roll rate is not a large damping term over most of the Mach range. The FCS of the Shuttle in FG therefore does not place yaw and roll axis directly under pilot control. The rudder is always commanded to minimize beta and no pilot input for the rudder should be needed or used unless sideslip is explicitly desired. The elevons are commanded to provide a simple roll damper to make control smoother. | Below approximately Mach 6, the rudder starts to contribute to yaw stability and from Mach 3.5 down to Mach 2 where the yawing moment finally becomes positive only the rudder is used. The roll behavior of the orbiter before any FCS is somewhat skittish as the roll moment as a function of roll rate is not a large damping term over most of the Mach range. The FCS of the Shuttle in FG therefore does not place yaw and roll axis directly under pilot control. The rudder is always commanded to minimize beta and no pilot input for the rudder should be needed or used unless sideslip is explicitly desired. The elevons are commanded to provide a simple roll damper to make control smoother. | ||
The real Shuttle has in addition a | The real Shuttle has in addition a '''NO Y JET''' mode to stabilize the orbiter during entry in which the elevons are used to control yaw. This leads to significantly reduced roll control since roll then needs to be driven by adverse yaw till the rudder picks up sufficient airflow. This mode has been implemented since dev version of july 2017. | ||
=== A note on thruster efficiency in the atmosphere === | === A note on thruster efficiency in the atmosphere === | ||
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; Aerodynamical | ; Aerodynamical | ||
: This is an educational mode in which the Shuttle is flown similar to an airplane, i.e. the stick basically controls the airfoil positions, and in order to achieve level flight with stick neutral, trim has to be used. Since the Shuttle is yaw-unstable at high Mach numbers, this mode still has automatic stability augmentation, i.e. rudder and ailerons are commanded automatically to minimize sideslip. Entry can be flown with this mode starting in-orbit with | : This is an educational mode in which the Shuttle is flown similar to an airplane, i.e. the stick basically controls the airfoil positions, and in order to achieve level flight with stick neutral, trim has to be used. Since the Shuttle is yaw-unstable at high Mach numbers, this mode still has automatic stability augmentation, i.e. rudder and ailerons are commanded automatically to minimize sideslip. Entry can be flown with this mode starting in-orbit with '''RCS ROT ENTRY''' and illustrates the amount of work the rate controller has to do as well as gives a hands-on feeling for hypersonic aerodynamics. This however is somewhat challenging and it is possible to maneuver the Shuttle outside its stability envelope using too agressive maneuvers. Once below Mach 5, the Shuttle responds well and stable to direct aerodynamical control. | ||
=== Entry and touchdown structural and aerodynamical limits === | === Entry and touchdown structural and aerodynamical limits === | ||
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In case of a hydraulic failure, Priority Rate Limiting (PRL) for the airfoils is used to allocate the remaining power as efficiently as possible. Usually the elevons move with 20 deg/s and the rudder with 14 deg/s, however in the case of multiple hydraulic failures, these numbers are reduced to 13.9 deg/s for elevons and 7 deg/s for the rudder. The orbiter is still fully controllable in this case, but not as responsive to agressive maneuvers. | In case of a hydraulic failure, Priority Rate Limiting (PRL) for the airfoils is used to allocate the remaining power as efficiently as possible. Usually the elevons move with 20 deg/s and the rudder with 14 deg/s, however in the case of multiple hydraulic failures, these numbers are reduced to 13.9 deg/s for elevons and 7 deg/s for the rudder. The orbiter is still fully controllable in this case, but not as responsive to agressive maneuvers. | ||
As of June 2015, the APU and hydraulic system is modeled with a fair amount of detail and operated from a dedicated menu. APUs need to be started as part of the pre-launch checklist - refer to Help/Aircraft Checklists for the detailed procedure. | As of June 2015, the APU and hydraulic system is modeled with a fair amount of detail and operated from a dedicated menu. APUs need to be started as part of the pre-launch checklist - refer to Help/Aircraft Checklists for the detailed procedure. '''If the hydraulic system is not available during ascent, this will result in loss of the vehicle after SRB separation as there is no control over the Shuttle if the SSMEs can not be gimbaled.''' Also PRL for all airfoils is fully supported. | ||
Operation of the water spray boilers is realistically integrated into the heat transfer model of the Shuttle (see below), including the failure of overheating APUs. | Operation of the water spray boilers is realistically integrated into the heat transfer model of the Shuttle (see below), including the failure of overheating APUs. | ||
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The various phases of a Shuttle mission are generically subdivided into launch, orbit, entry, TAEM and approach. These can directly be accessed by appending the mission phase to the command line. This will automatically start the Shuttle in the correct configuration and the correct state for the mission selected. For instance, --aircraft=SpaceShuttle-TAEM --airport=KVBG will initialize a TAEM approach into Vandenberg, --aircraft=SpaceShuttle-orbit --lat=30.0 --lon=0.0 --heading=90.0 will initialize the Shuttle in a 30 deg inclination orbit. | The various phases of a Shuttle mission are generically subdivided into launch, orbit, entry, TAEM and approach. These can directly be accessed by appending the mission phase to the command line. This will automatically start the Shuttle in the correct configuration and the correct state for the mission selected. For instance, --aircraft=SpaceShuttle-TAEM --airport=KVBG will initialize a TAEM approach into Vandenberg, --aircraft=SpaceShuttle-orbit --lat=30.0 --lon=0.0 --heading=90.0 will initialize the Shuttle in a 30 deg inclination orbit. | ||
Note that --aircraft=SpaceShuttle-entry combined with an airport as location will | Note that --aircraft=SpaceShuttle-entry combined with an airport as location will ''not'' initialize you on an entry trajectory to that airport since the entry interface is several thousand miles away from the landing site and moreover the trajectory needed is not unique but depends on what you fly - you need to initialize the entry interface location by hand using latitude and longitude. | ||
Specific information on the mission phases can be found in the following articles: | Specific information on the mission phases can be found in the following articles: | ||
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''Annotated and condensed one'' | ''Annotated and condensed one'' | ||
[[Flying the Shuttle - Space Shuttle Checklists]] | |||