Guidance, Navigation and Control. Guidance Navigation and Control (GN&C) The guidance, navigation and control system is an essential ingredient in all

Guidance, Guidance, Navigation and Navigation and

ControlControl

Guidance Navigation and Control (GN&C)Guidance Navigation and Control (GN&C)

The guidance, navigation and control system is an The guidance, navigation and control system is an essential ingredient in all of the Orbiter's flight essential ingredient in all of the Orbiter's flight phasesphases

Programmed flight segments are tested and loaded Programmed flight segments are tested and loaded into the Orbiter's digital data system for the entire into the Orbiter's digital data system for the entire mission – but:mission – but:

Memory limitations in the General Purpose Computers Memory limitations in the General Purpose Computers cannot manage all of the instructions in a single loadcannot manage all of the instructions in a single load

Launch, orbit entry, on-orbit operations, deorbit, and Launch, orbit entry, on-orbit operations, deorbit, and reentry and aerodynamic flight operations are separated reentry and aerodynamic flight operations are separated into mission segmentsinto mission segments d due to the memory limitations ue to the memory limitations

Guidance Navigation and Control (GN&C)Guidance Navigation and Control (GN&C)

Basic definitionsBasic definitions

GuidanceGuidance – the process of using the current estimate of position and – the process of using the current estimate of position and velocity of the spacecraft to determine subsequent control system velocity of the spacecraft to determine subsequent control system commands so that the spacecraft will arrive at a specified trajectory commands so that the spacecraft will arrive at a specified trajectory point in a specified orientation and at a specified time point in a specified orientation and at a specified time

NavigationNavigation – the process of measuring current position and velocity of – the process of measuring current position and velocity of the spacecraft with respect to a reference frame, and extrapolating the spacecraft with respect to a reference frame, and extrapolating these data to determine future position and velocitythese data to determine future position and velocity

ControlControl – the process of correcting, or maintaining, the spacecraft for a – the process of correcting, or maintaining, the spacecraft for a desired attitude or trajectory in order to support the guidance desired attitude or trajectory in order to support the guidance

GN&CGN&C

GN&C system GN&C system organizationorganization

GuidanceGuidance

GN&CGN&C

GuidanceGuidance

Three primary flight software segments are loaded for the three Three primary flight software segments are loaded for the three separate flight phases of the Orbiter's mission operationsseparate flight phases of the Orbiter's mission operations

Those software segments are for the three flight phases:Those software segments are for the three flight phases: AscentAscent OrbitOrbit Reentry and landingReentry and landing

Other instruction sets are placed in the mass memory storage for Other instruction sets are placed in the mass memory storage for other flight and test operationsother flight and test operations

GN&CGN&C

GuidanceGuidance

Guidance elements on the Orbiter consist of Guidance elements on the Orbiter consist of software modules that transform crew software modules that transform crew commands and/or computed state vector commands and/or computed state vector changes into steering commands to the flight changes into steering commands to the flight control functionscontrol functions

Thrust Vector ControlThrust Vector Control

OMS/RCSOMS/RCS

Aero surfacesAero surfaces

GN&CGN&C

GuidanceGuidance

Both guidance and command functions Both guidance and command functions vary with flight phasevary with flight phase

1. Launch through SRB separation1. Launch through SRB separation

Guidance programs use an open loop Guidance programs use an open loop scheme which computes commands scheme which computes commands based only upon pre-determined table based only upon pre-determined table values for roll, pitch and yaw attitudesvalues for roll, pitch and yaw attitudes

GN&CGN&C

GuidanceGuidance

2. SRB separation through MECO2. SRB separation through MECO

Guidance software employs a closed-loop, Guidance software employs a closed-loop, interactive scheme which targets specific interactive scheme which targets specific conditions at MECO, including specific velocity, conditions at MECO, including specific velocity, specific radius from Earth's surface, specific specific radius from Earth's surface, specific flight path angle, and specific orbital inclinationflight path angle, and specific orbital inclination

GN&CGN&C

GuidanceGuidance

3. Guidance software routines that include 3. Guidance software routines that include orbital insertion, orbital operations and orbital insertion, orbital operations and deorbit burns are called Powered Explicit deorbit burns are called Powered Explicit Guidance (PEG) routinesGuidance (PEG) routines

Each PEG routine is assigned a specific number Each PEG routine is assigned a specific number for a specific operationfor a specific operation

GN&C - GuidanceGN&C - Guidance

Block diagram of the guidance elements related Block diagram of the guidance elements related to the Orbiter's GN&C functionsto the Orbiter's GN&C functions

GN&CGN&C

NavigationNavigation

Navigational data for the flight mission is generated Navigational data for the flight mission is generated by the automated sensor systems on the Orbiter and by the automated sensor systems on the Orbiter and SRBsSRBs

Accurate position and orientation information is Accurate position and orientation information is placed in the Orbiter's navigational data base for placed in the Orbiter's navigational data base for inertial settingsinertial settings GPS data is used as primary navigation throughout most of GPS data is used as primary navigation throughout most of

the missionthe mission

ControlControl

GN&CGN&C

ControlControl

Control functions on the Orbiter include the SRBs Control functions on the Orbiter include the SRBs and SSMEsand SSMEs Both employ thrust vector control to keep the Orbiter on Both employ thrust vector control to keep the Orbiter on

the planned trajectory throughout the ascent to orbitthe planned trajectory throughout the ascent to orbit

Directional thrust from the engines is aided by the Directional thrust from the engines is aided by the Orbiter's aerosurfaces and RCS to reduce loading Orbiter's aerosurfaces and RCS to reduce loading on the STS structureon the STS structure

GN&CGN&C

ControlControl

The same aerosurfaces are used for flight in the The same aerosurfaces are used for flight in the atmosphere on reentry, descent and landingatmosphere on reentry, descent and landing

Additional Orbiter control functions are furnished byAdditional Orbiter control functions are furnished by Reaction Control System thrusters (ascent, orbit, descent)Reaction Control System thrusters (ascent, orbit, descent) Orbital Maintenance System thrusters while on orbitOrbital Maintenance System thrusters while on orbit

GN&C - ControlGN&C - Control

Orbiter GN&C Orbiter GN&C primary primary elements and elements and data flow for data flow for both automated both automated input and manual input and manual flight controlflight control


Feedback and correctionFeedback and correction

STS flight control hardware includes the SRB and STS flight control hardware includes the SRB and SSME thrust vector control operations during SSME thrust vector control operations during ascent,ascent, Includes some use of the aero surfaces for load Includes some use of the aero surfaces for load

relief during ascentrelief during ascent

On orbit, the OMS and RCS thrusters are used On orbit, the OMS and RCS thrusters are used exclusivelyexclusively During descent, a combination of the aero During descent, a combination of the aero

surfaces and RCS thrusters are used for Orbiter surfaces and RCS thrusters are used for Orbiter trajectory controltrajectory control



Although the control and determination components of Although the control and determination components of the Orbiter have precise limits of operation, the feedback the Orbiter have precise limits of operation, the feedback measurements of the effects of the control thrust must be measurements of the effects of the control thrust must be just as precisejust as precise

The measured control thruster effect on the vehicle is, in The measured control thruster effect on the vehicle is, in essence, feedback in the control and determination essence, feedback in the control and determination systemsystem

Error calculations and feedback components that are Error calculations and feedback components that are included in the flight control computations ensure that included in the flight control computations ensure that the actual trajectory will conform to the desired trajectory the actual trajectory will conform to the desired trajectory at a given position and time, depending on the flight at a given position and time, depending on the flight phasephase


Trajectory correction example for the STS that portrays an initial excessive boost with Trajectory correction example for the STS that portrays an initial excessive boost with a subsequent correction to arrive at the calculated MECO (Main Engine Cutoff) a subsequent correction to arrive at the calculated MECO (Main Engine Cutoff) position with the correct orientation and velocityposition with the correct orientation and velocity



Important navigation function onboard the Orbiter is the Important navigation function onboard the Orbiter is the aerodynamic load management during ascent and reentryaerodynamic load management during ascent and reentry

Wind shear loads encountered in the lower and/or middle Wind shear loads encountered in the lower and/or middle atmosphere can trigger vehicle rotation commands to relieve atmosphere can trigger vehicle rotation commands to relieve transverse loads than could affect the structural integrity of the transverse loads than could affect the structural integrity of the Orbiter, ET and SRB assemblyOrbiter, ET and SRB assembly

A rotation into the direction of the wind shear to correct for the A rotation into the direction of the wind shear to correct for the induced yaw and maintain the trajectory plane alignment with induced yaw and maintain the trajectory plane alignment with the Orbiter's Z axis is shown in the next slidethe Orbiter's Z axis is shown in the next slide


NavigationNavigation

GN&C - NavigationGN&C - Navigation

The STS navigation system uses integrated sensor The STS navigation system uses integrated sensor data and computed data to determine actual and data and computed data to determine actual and planned position, velocities, and accelerationsplanned position, velocities, and accelerations

Primary position, velocity and acceleration reference Primary position, velocity and acceleration reference is a computed data set called the state vector is a computed data set called the state vector State vector also includes time and coordinatesState vector also includes time and coordinates


Primary coordinate system is the geocentric Primary coordinate system is the geocentric equatorial coordinate systemequatorial coordinate system Earth-centeredEarth-centered X-axis points to vernal equinoxX-axis points to vernal equinox

2-dimensional geocentric coordinates are 2-dimensional geocentric coordinates are measured in degrees asmeasured in degrees as Right ascension (longitude)Right ascension (longitude) Declination (latitude)Declination (latitude)


M50 geocentric M50 geocentric equatorial equatorial coordinate systemcoordinate system

Precessed from 1950Precessed from 1950

Primary (X) axis Primary (X) axis Lies in equatorial Lies in equatorial

planeplane Points at the vernal Points at the vernal

equinoxequinox

Z axis points along the Z axis points along the Earth's north rotational Earth's north rotational axis (celestial poleaxis (celestial pole))


State VectorState Vector

Accurate position and velocity values for the Orbiter Accurate position and velocity values for the Orbiter are extrapolated from navigational sensors or are extrapolated from navigational sensors or ground fixes and placed in M50 coordinate ground fixes and placed in M50 coordinate representationrepresentation

The state vector consists of:The state vector consists of: X, Y and Z position values of the Orbiter in ft from X, Y and Z position values of the Orbiter in ft from

Earth's center (M50)Earth's center (M50) Vz, Vy and Vz velocities in ft/s Vz, Vy and Vz velocities in ft/s A time value calculated for the instantaneous vector A time value calculated for the instantaneous vector

in GMT in GMT


State VectorState Vector

The state vector is updated continuously for The state vector is updated continuously for use in: use in:

Vehicle trajectory guidance calculations Vehicle trajectory guidance calculations

Vehicle pointing for specific targets Vehicle pointing for specific targets

Monitoring the health of GN&C system from Monitoring the health of GN&C system from groundground


Local Vertical Local Local Vertical Local HorizontalHorizontal

Maintains the Orbiter in Maintains the Orbiter in horizontal orientation with horizontal orientation with the Earth’s surfacethe Earth’s surface ±±Z at Earth’s centerZ at Earth’s center +X in direction of flight+X in direction of flight

Used for Used for Crew orientationCrew orientation Orbiter thermal Orbiter thermal

managementmanagement Payload bay Payload bay

radiators towards radiators towards EarthEarth

Rendezvous and Rendezvous and dockingdocking


Navigation system inputsNavigation system inputs

Inputs for the GN&C navigation calculations are selected for Inputs for the GN&C navigation calculations are selected for the specific flight phase and for the STS or Orbiter's control the specific flight phase and for the STS or Orbiter's control functions functions

These nav sensors provide the necessary data for maintaining These nav sensors provide the necessary data for maintaining accurate position and velocity data used in projecting the accurate position and velocity data used in projecting the Orbiter's trajectory and attitude in the state vector calculationsOrbiter's trajectory and attitude in the state vector calculations

Software and hardware modules in the Orbiter's data systems Software and hardware modules in the Orbiter's data systems formulate any necessary correctionsformulate any necessary corrections Corrections are then converted into command instructions to the Corrections are then converted into command instructions to the

flight control functions for the specific flight operationsflight control functions for the specific flight operations

GN&CGN&C - Navigation - Navigation

Nav sensor inputsNav sensor inputs


Navigation input sensorsNavigation input sensors

Inertial navigation unitsInertial navigation units Inertial Measuring Units (IMUs) (3) Inertial Measuring Units (IMUs) (3) Accelerometer Assemblies (AAs) (2) Accelerometer Assemblies (AAs) (2) Rate Gyro Assemblies (RGAs) (6) Rate Gyro Assemblies (RGAs) (6)

Electronic navigationElectronic navigation TACAN (3) TACAN (3) Microwave Scan Beam Landing System (MSBLS) (3) Microwave Scan Beam Landing System (MSBLS) (3) Global Positioning System (GPS) (3) Global Positioning System (GPS) (3) Radar Altimeter (2) Radar Altimeter (2)

Crew operated sensorsCrew operated sensors Star Tracker Star Tracker Crew Optical Alignment Sight (COAS) Crew Optical Alignment Sight (COAS)

Aerodynamic dataAerodynamic data Air data probes (2) Air data probes (2)


Inertial Measuring UnitsInertial Measuring Units

Each Orbiter has three Each Orbiter has three redundant IMUs that are the redundant IMUs that are the principal inertial sensors during principal inertial sensors during all flight phases from launch all flight phases from launch through the approach and through the approach and precision landingprecision landing GPS systems provide GPS systems provide

primary absolute position primary absolute position and velocity data for the and velocity data for the vehiclevehicle

The IMU is a three-axis gimbaled The IMU is a three-axis gimbaled unit that measures spatial unit that measures spatial acceleration of the vehicle in acceleration of the vehicle in three dimensionsthree dimensions The STS’ linear The STS’ linear

accelerometer and rate gyro accelerometer and rate gyro units provide acceleration units provide acceleration data on Orbiter motion in data on Orbiter motion in three axes, but without the three axes, but without the inertial (fixed) reference inertial (fixed) reference frameframe


Inertial Measuring UnitsInertial Measuring Units

Since the IMU maintains a fixed reference during its active Since the IMU maintains a fixed reference during its active operation, it must be initialized with starting coordinates and operation, it must be initialized with starting coordinates and allowed to stabilize during its startupallowed to stabilize during its startup

The Orbiter's IMUs use two accelerometers on a four-gimbal The Orbiter's IMUs use two accelerometers on a four-gimbal assembly to measure acceleration and orientation changesassembly to measure acceleration and orientation changes

IMU data is used to display the Orbiter's attitude with respect to IMU data is used to display the Orbiter's attitude with respect to the selected coordinate system on the Orbiter's cockpit the selected coordinate system on the Orbiter's cockpit navigation displaynavigation display

Coordinate references include the M50, LVLH, celestial Coordinate references include the M50, LVLH, celestial coordinates, POPS, and otherscoordinates, POPS, and others


Inertial Measuring UnitInertial Measuring Unit

Dimensions Dimensions H=10.3”H=10.3”W=12.0”W=12.0”D=22.0”D=22.0”

Weight Weight 56.5 lbs56.5 lbs

PowerPower 28 Vdc28 Vdc


Accelerometer Assemblies (AA)Accelerometer Assemblies (AA)

The Orbiter’s four Accelerometer Assemblies The Orbiter’s four Accelerometer Assemblies contain two identical single-axis accelerometerscontain two identical single-axis accelerometers

Used to sense vehicle accelerations along two of the Used to sense vehicle accelerations along two of the vehicle's body axesvehicle's body axes One senses vehicle acceleration along the lateral (left - One senses vehicle acceleration along the lateral (left -

right) Y axisright) Y axis The other senses vehicle acceleration along the normal The other senses vehicle acceleration along the normal

(vertical) Z axis.(vertical) Z axis.


Accelerometer Accelerometer Assemblies (AA)Assemblies (AA)

The four AAs are The four AAs are located in the crew located in the crew compartment mid compartment mid deck forward deck forward avionics baysavionics bays

AA units are AA units are convection cooledconvection cooled

Require a 5-minute Require a 5-minute warmup periodwarmup period


Rate Gyro Assemblies (RGA)Rate Gyro Assemblies (RGA)

Rate Gyro Assemblies are used to sense vehicle rotation rates Rate Gyro Assemblies are used to sense vehicle rotation rates about the Orbiter's three coordinate axesabout the Orbiter's three coordinate axes

Each of the four RGAs (labeled 1, 2, 3, and 4) contain three Each of the four RGAs (labeled 1, 2, 3, and 4) contain three identical single-degree-of-freedom rate gyrosidentical single-degree-of-freedom rate gyros

Each gyro senses rotation about one of the vehicle axesEach gyro senses rotation about one of the vehicle axes

Each RGA includesEach RGA includes One gyro sensing roll rate (about the X axis)One gyro sensing roll rate (about the X axis) One gyro sensing pitch rate (about the Y axis)One gyro sensing pitch rate (about the Y axis) One gyro sensing yaw rate (about the Z axis)One gyro sensing yaw rate (about the Z axis)


Rate Gyro Assemblies (RGA)Rate Gyro Assemblies (RGA)

The RGA roll rates are the primary feedback The RGA roll rates are the primary feedback to the Flight Control System during ascent, to the Flight Control System during ascent, entry, insertion, and deorbitentry, insertion, and deorbit Flight Control System must have valid rate Flight Control System must have valid rate

feedback in all three axes to maintain accurate feedback in all three axes to maintain accurate control inputscontrol inputs

GN&C – AA & RGA LocationGN&C – AA & RGA Location

GN&C – Navigation InstrumentsGN&C – Navigation Instruments

Star TrackerStar Tracker

Orbiter's Star Tracker instrument is a dual optical Orbiter's Star Tracker instrument is a dual optical telescope unit used to measure vehicle line-of-sight telescope unit used to measure vehicle line-of-sight vectors to stars, or to orbiting targetsvectors to stars, or to orbiting targets

Star Tracker assembly is in the forward RCS section Star Tracker assembly is in the forward RCS section beneath retractable protective doors used for beneath retractable protective doors used for insulating the mechanism from the heat and insulating the mechanism from the heat and changing environment during launch and the heat of changing environment during launch and the heat of reentryreentry


Star TrackerStar Tracker

Star tracker doors also provide protection from Star tracker doors also provide protection from micrometeoroid impact while on orbitmicrometeoroid impact while on orbit

Light shade and shutter assemblies protect Light shade and shutter assemblies protect telescopes from bright sunlight and the reflected telescopes from bright sunlight and the reflected light from the Moon and Earthlight from the Moon and Earth

GN&C – Nav InstrumentsGN&C – Nav Instruments


Star Tracker - useStar Tracker - use

Provided reasonably accurate updates of the Orbiter's Provided reasonably accurate updates of the Orbiter's position to correct for the gradual IMU driftposition to correct for the gradual IMU drift

Provided alignment of IMUs on orbit approximately every Provided alignment of IMUs on orbit approximately every 12 hours due to mechanical error buildup (automated now 12 hours due to mechanical error buildup (automated now by GPS system)by GPS system)

Provided attitude determination before major thrust Provided attitude determination before major thrust operations operations Employs catalog of approximately the 50 brightest Employs catalog of approximately the 50 brightest

stars for orientationstars for orientation Two star sightings used to calculate Orbiter attitude Two star sightings used to calculate Orbiter attitude Star separation requirement of 60Star separation requirement of 60oo to 120 to 120oo used to used to

minimize errorminimize error

Now used as backup for GPSNow used as backup for GPS


Crew Optical Alignment Sight (COAS)Crew Optical Alignment Sight (COAS)

Before the addition of GPS systems on the Orbiters, the Crew Before the addition of GPS systems on the Orbiters, the Crew Optical Alignment Sight was used if IMU alignment was in error Optical Alignment Sight was used if IMU alignment was in error by more than 1.4 degreesby more than 1.4 degrees

This large of an error would render the star tracker unable to This large of an error would render the star tracker unable to acquire and track starsacquire and track stars

COAS is now used primarily to visually track targets during COAS is now used primarily to visually track targets during rendezvous and proximity operationsrendezvous and proximity operations

COAS can be used to visually verify tracking of the correct star by COAS can be used to visually verify tracking of the correct star by the minus Z star trackerthe minus Z star tracker


Crew Optical Alignment Crew Optical Alignment Sight (COAS)Sight (COAS)

Used for rendezvous Used for rendezvous positioningpositioning

Used for navigation Used for navigation augmentation augmentation

Can be used as backup for Can be used as backup for GPSGPS

Originally used for Originally used for correcting large IMU error correcting large IMU error is greater than 1.4is greater than 1.4oo since since the Star Tracker could not the Star Tracker could not identify sources with a identify sources with a large alignment errorlarge alignment error


TACAN (Tactical Air Navigation)TACAN (Tactical Air Navigation)

Orbiter's TACAN electronic navigation units determine slant range and Orbiter's TACAN electronic navigation units determine slant range and azimuth (magnetic bearing) to a TACAN or VHF omnirange tactical air azimuth (magnetic bearing) to a TACAN or VHF omnirange tactical air navigation (VORTAC) ground stationnavigation (VORTAC) ground station

Both TACAN and VORTAC stations provide navigation signals Both TACAN and VORTAC stations provide navigation signals worldwide for military and VOR-equipped civilian aircraftworldwide for military and VOR-equipped civilian aircraft

TACAN and VORTAC operate at L-band frequencies - approximately 1 GHzTACAN and VORTAC operate at L-band frequencies - approximately 1 GHz

Each of the three TACANs that operate redundantly have two antennasEach of the three TACANs that operate redundantly have two antennas Covered with TPS tilesCovered with TPS tiles One on the Orbiter's lower forward fuselageOne on the Orbiter's lower forward fuselage One on the Orbiter's upper forward fuselageOne on the Orbiter's upper forward fuselage


TACAN operationsTACAN operations

Used for RTLS and 2-dimensional navigation during descent Used for RTLS and 2-dimensional navigation during descent

Used for update backup of the Orbiter state vector during descent Used for update backup of the Orbiter state vector during descent

Maximum signal range is 400 nm from TACAN stationMaximum signal range is 400 nm from TACAN station

Distance (range) measurements from ground station based on timed Distance (range) measurements from ground station based on timed signal (rho) signal (rho)

Angle from ground station based on signal phase received (theta) Angle from ground station based on signal phase received (theta)

Orbiter-ground voice communications are available through TACAN Orbiter-ground voice communications are available through TACAN navigation linknavigation link


Microwave Scanning Beam Landing System (MSBLS)Microwave Scanning Beam Landing System (MSBLS)

The Orbiter’s 3-dimensional landing system is a version of the military The Orbiter’s 3-dimensional landing system is a version of the military microwave landing system called the Microwave Scan Beam Landing microwave landing system called the Microwave Scan Beam Landing System (MSBLS)System (MSBLS)

Twin scanning beams provide elevation and azimuth data for the Twin scanning beams provide elevation and azimuth data for the Orbiter's navigation receiversOrbiter's navigation receivers

Third dimension comes from the transmitted Distance Measuring Third dimension comes from the transmitted Distance Measuring Equipment (DME) transponderEquipment (DME) transponder

Same as for aircraft instrumented with DME equipmentSame as for aircraft instrumented with DME equipment

Each of the three independent MSBLS receivers converts the dual-Each of the three independent MSBLS receivers converts the dual-frequency scanned beams from the ground station into position frequency scanned beams from the ground station into position information for the navigation and guidance software that command information for the navigation and guidance software that command the Orbiter's aero surface controlsthe Orbiter's aero surface controls

Transition from the Orbiter's descent to the MSBLS approach is made Transition from the Orbiter's descent to the MSBLS approach is made with the Terminal Area Energy Management (TAEM) systemwith the Terminal Area Energy Management (TAEM) system


Microwave Scanning Beam Landing SystemMicrowave Scanning Beam Landing System

Energy of the Orbiter (primarily altitude = potential energy, Energy of the Orbiter (primarily altitude = potential energy, speed = kinetic energy, and relative wind = energy dissipation) speed = kinetic energy, and relative wind = energy dissipation) is evaluated within the TAEM software, along with wind speed, is evaluated within the TAEM software, along with wind speed, and air density measurementsand air density measurements

Calculations are made then made for Orbiter aero control Calculations are made then made for Orbiter aero control functions to place the trajectory at a well-defined intercept functions to place the trajectory at a well-defined intercept point for the approach and landingpoint for the approach and landing

Initial intercept is on an imaginary cylindrical Heading Initial intercept is on an imaginary cylindrical Heading Alignment Circle (HAC)Alignment Circle (HAC) Similar to an aircraft procedure turnSimilar to an aircraft procedure turn


Microwave Scanning Beam Microwave Scanning Beam Landing SystemLanding System

This procedure allows the This procedure allows the GN&C functions to maintain an GN&C functions to maintain an accurate glide path to the accurate glide path to the MSBLS precision approach.MSBLS precision approach.

Guidance software continues to Guidance software continues to control the Orbiter from signal control the Orbiter from signal recognition to touchdown and recognition to touchdown and runway rolloutrunway rollout

Guidance cues are displayed on Guidance cues are displayed on Horizontal Situation Indicator Horizontal Situation Indicator (HSI)(HSI)


Microwave Scanning Beam Landing SystemMicrowave Scanning Beam Landing System

Three complete units on each Orbiter for redundancyThree complete units on each Orbiter for redundancy

Dual Ku-band beams are independently scanned to produce a position Dual Ku-band beams are independently scanned to produce a position matrix matrix

Determines azimuth and elevation angles from touchdown on landing Determines azimuth and elevation angles from touchdown on landing runway runway Elevation beam scanned 0Elevation beam scanned 0oo to +29 to +29oo Azimuth beam scanned ±13.5Azimuth beam scanned ±13.5oo from runway centerline from runway centerline

Azimuth beam includes DME (Distance Measuring Equipment) range Azimuth beam includes DME (Distance Measuring Equipment) range signal signal DME signal timing used to determine distance from landing DME signal timing used to determine distance from landing

threshold threshold


Microwave Scanning Microwave Scanning Beam Landing Beam Landing SystemSystem

Usable signal Usable signal distance distance approximately 15 nm approximately 15 nm

Orbiter acquires Orbiter acquires signal on or near signal on or near Heading Alignment Heading Alignment Circle exitCircle exit Approximately 8 Approximately 8

to 12 nm from to 12 nm from HAC HAC

Approximately Approximately 18,000' altitude18,000' altitude


Global Positioning System (GPS)Global Positioning System (GPS)

The Orbiters are now outfitted with the military NAVSTAR 3-dimensional The Orbiters are now outfitted with the military NAVSTAR 3-dimensional navigation system known as the Global Position System (GPS)navigation system known as the Global Position System (GPS)

GPS is an inherently stable and accurate satellite navigation toolGPS is an inherently stable and accurate satellite navigation tool

Selected because of the anticipated decommissioning of military TACAN Selected because of the anticipated decommissioning of military TACAN stations by the Department of Defensestations by the Department of Defense

GPS also offers the navigation data base a greater accuracy than that available GPS also offers the navigation data base a greater accuracy than that available from the integrated accelerations and estimates of atmospheric drag calculated from the integrated accelerations and estimates of atmospheric drag calculated in the GN&C softwarein the GN&C software

Orbiter's state vector was originally updated using:Orbiter's state vector was originally updated using: Inertial Measuring Units and rate gyros during ascent, orbit and deorbitInertial Measuring Units and rate gyros during ascent, orbit and deorbit Aerodynamic and radio navigation inputs near approach and landingAerodynamic and radio navigation inputs near approach and landing

Three-string GPS units have now become the primary, although not the Three-string GPS units have now become the primary, although not the only, data source for the state vectoronly, data source for the state vector


Global Positioning System (GPS)Global Positioning System (GPS)

Satellite signal navigation uses triangulation of timed signals Satellite signal navigation uses triangulation of timed signals from four or more of the 24 GPS satellites from four or more of the 24 GPS satellites Reception of three satellite signals provides 2-dimensional data Reception of three satellite signals provides 2-dimensional data Four satellite signals provide 3-dimensional data Four satellite signals provide 3-dimensional data More than 4 satellite signals provide increased accuracy More than 4 satellite signals provide increased accuracy

24 satellites located in 6 planes with 4 satellites in each plane 24 satellites located in 6 planes with 4 satellites in each plane Six separate orbit planes have 55Six separate orbit planes have 55oo inclination (60 inclination (60oo major axis major axis

alignment difference between planes)alignment difference between planes)

Provides global coverage except for high latitudes Provides global coverage except for high latitudes

Useful for low-Earth orbit, but not above 1000 kmUseful for low-Earth orbit, but not above 1000 km

Dual accuracy L-band signals are transmittedDual accuracy L-band signals are transmitted Military (P code) approximately 10 m accuracyMilitary (P code) approximately 10 m accuracy Civil (C/A) accuracy approximately 100 m accuracyCivil (C/A) accuracy approximately 100 m accuracy


Radar Altimeter (RA) Radar Altimeter (RA)

Two radar altimeters onboard the Orbiter measure absolute Two radar altimeters onboard the Orbiter measure absolute altitude between the Orbiter and the terrainaltitude between the Orbiter and the terrain

Reflected signals are transmitted with a broad 40Reflected signals are transmitted with a broad 40oo beam to beam to average the terrain variationaverage the terrain variation Both RA systems can operate simultaneously without affecting each Both RA systems can operate simultaneously without affecting each

otherother Each C-band system operates with two antennas (4 total), one for Each C-band system operates with two antennas (4 total), one for

transmitting and one for receiving.transmitting and one for receiving.

RA instrument has a 0’ to 9,000' readout RA instrument has a 0’ to 9,000' readout C-band operation (4.300 GHz) C-band operation (4.300 GHz) 4040oo radar beamwidth (better altitude representation is available radar beamwidth (better altitude representation is available

by averaging surface variation) by averaging surface variation) Data used for autoland and displayed for manual flight control Data used for autoland and displayed for manual flight control

GN&C – Aerodynamic Flight DataGN&C – Aerodynamic Flight Data

Air Data SystemAir Data System

The Orbiter's aerodynamic flight through the atmosphere requires The Orbiter's aerodynamic flight through the atmosphere requires accurate data to guide it from its high-altitude descent to the landing site accurate data to guide it from its high-altitude descent to the landing site with enough energy to reach the runway threshold but not so much as to with enough energy to reach the runway threshold but not so much as to overrun the stripoverrun the strip

Atmospheric data used for the Orbiter's descent comes from dual air Atmospheric data used for the Orbiter's descent comes from dual air probes that measure air flow pressure, differential pressure and air probes that measure air flow pressure, differential pressure and air temperaturetemperature

Air data is converted for updating the navigation state vector, including Air data is converted for updating the navigation state vector, including vehicle airspeed and altitudevehicle airspeed and altitude

Air data is also used to:Air data is also used to: Update flight control law computationsUpdate flight control law computations Provide display data for the commander's and pilot's Alpha Mach IndicatorsProvide display data for the commander's and pilot's Alpha Mach Indicators Compute altitude/vertical velocity indicator values, and CRT readoutsCompute altitude/vertical velocity indicator values, and CRT readouts Provide input for calculating steering and speed brake commandsProvide input for calculating steering and speed brake commands



Each of the two air data probes, which are analogous to the aircraft Each of the two air data probes, which are analogous to the aircraft pitot tubes, is mounted in a thermal tile-protected enclosure until its pitot tubes, is mounted in a thermal tile-protected enclosure until its deployment after reaching the lower atmospheredeployment after reaching the lower atmosphere

Both air data probes are deployed below 100,000' altitude and below Both air data probes are deployed below 100,000' altitude and below Mach 3.5Mach 3.5

The probes’ four pressure ports provide data on:The probes’ four pressure ports provide data on: Static pressureStatic pressure Total pressureTotal pressure Angle-of-attack upper pressureAngle-of-attack upper pressure Angle-of-attack lower pressureAngle-of-attack lower pressure


Air Data System probes – retracted (left) and extended (right)Air Data System probes – retracted (left) and extended (right)



The probes’ two temperature sensors provide data on air The probes’ two temperature sensors provide data on air flow temperature for air density calculationsflow temperature for air density calculations

Heaters within the probes are used to prevent icingHeaters within the probes are used to prevent icing

Data output from the air data calculations includesData output from the air data calculations includes Angle-of-attack (alpha) Angle-of-attack (alpha) True air speed (TAS) True air speed (TAS) Dynamic pressure (q) Dynamic pressure (q) Barometric altitude (pressure altitude) Barometric altitude (pressure altitude) Altitude rate (vertical velocity) Altitude rate (vertical velocity) Altitude acceleration Altitude acceleration



The Alpha Mach Indicator (AMI) flight instruments display The Alpha Mach Indicator (AMI) flight instruments display essential flight parameters relative to the spacecraft's motion essential flight parameters relative to the spacecraft's motion in the air massin the air mass Angle of attack (alpha)Angle of attack (alpha) Acceleration,Acceleration, Mach number/velocityMach number/velocity Knots equivalent airspeedKnots equivalent airspeed

Altitude/vertical velocity indicators display essential flight Altitude/vertical velocity indicators display essential flight parameters including:parameters including: Radar altitudeRadar altitude Barometric altitudeBarometric altitude Altitude rateAltitude rate Altitude accelerationAltitude acceleration

GN&C – Flight InstrumentsGN&C – Flight Instruments

Cockpit flight instrumentsCockpit flight instruments

Navigation and flight readout instruments in the Orbiter's Navigation and flight readout instruments in the Orbiter's flight deck closely resemble the instruments in a high-flight deck closely resemble the instruments in a high-performance aircraft performance aircraft

1. Operational performance of high-altitude-high performance 1. Operational performance of high-altitude-high performance aircraft and the Orbiter are similaraircraft and the Orbiter are similar

2. Convention in flight instrument displays the aerospace has not 2. Convention in flight instrument displays the aerospace has not changed dramatically over the years since the instruments changed dramatically over the years since the instruments have proven useful for the intuitive interpretation of complex have proven useful for the intuitive interpretation of complex flight operationsflight operations

Airspeed and attitude are two of the most important flight Airspeed and attitude are two of the most important flight instrument displays since aircraft and the winged Orbiter instrument displays since aircraft and the winged Orbiter spacecraft must operate in well defined spatial and speed spacecraft must operate in well defined spatial and speed limitslimits


Cockpit flight instrumentsCockpit flight instruments

Orientation is also necessary for high-speed or high-Orientation is also necessary for high-speed or high-performance aircraft navigationperformance aircraft navigation

Typical instrument configuration includesTypical instrument configuration includes 3-dimensional display of attitude and surface or 3-dimensional display of attitude and surface or

coordinate directioncoordinate direction Vertical distance and relative speedVertical distance and relative speed

Instruments on the Orbiter's flight panel include the basic Instruments on the Orbiter's flight panel include the basic information readouts plusinformation readouts plus Vertical speedVertical speed Vertical acceleration/decelerationVertical acceleration/deceleration

Flight InstrumentsFlight Instruments


Attitude Director Indicator (ADI)Attitude Director Indicator (ADI)

Attitude director Indicator is used for 3-dimensional representation of Attitude director Indicator is used for 3-dimensional representation of pitch, roll and yaw of the Orbiterpitch, roll and yaw of the Orbiter

Also displayed are the rotation rates around each axisAlso displayed are the rotation rates around each axis

Horizon reference is displayed as the boundary between the white (up Horizon reference is displayed as the boundary between the white (up or sky) hemisphere and the black (down or ground) hemisphereor sky) hemisphere and the black (down or ground) hemisphere

Position and orientation of the Orbiter is fixed and located at the Position and orientation of the Orbiter is fixed and located at the center positioncenter position

Coordinate reference orientation is selected manually or by the Coordinate reference orientation is selected manually or by the navigation display electronicsnavigation display electronics

GN&C – ADIGN&C – ADI


Horizontal Situation Indicator (HSI)Horizontal Situation Indicator (HSI)

A Horizontal Situation Indicator is found on the commander's and the pilot's flight A Horizontal Situation Indicator is found on the commander's and the pilot's flight panelspanels

Displays a pictorial view of the vehicle's position with respect to various navigation Displays a pictorial view of the vehicle's position with respect to various navigation referencesreferences

Instrument shows a top view or profile view of selected guidance, navigation and Instrument shows a top view or profile view of selected guidance, navigation and control parameters, such as directions, distances and course/glide path deviationcontrol parameters, such as directions, distances and course/glide path deviation

Flight crew uses this information to navigate, or to control or monitor vehicle Flight crew uses this information to navigate, or to control or monitor vehicle performanceperformance

HSIs are active during the entry and landing and the ascent/RTLS flight phasesHSIs are active during the entry and landing and the ascent/RTLS flight phases

Orientation of the HSI depends on Orientation of the HSI depends on Course of the OrbiterCourse of the Orbiter Selected navigational aid or reference trajectorySelected navigational aid or reference trajectory

GN&C – HSIGN&C – HSI


Heads-Up Display (HUD)Heads-Up Display (HUD)

Orbiter's heads-up display is a Orbiter's heads-up display is a reflected image on a transparent reflected image on a transparent reflector in the Commander/Pilot reflector in the Commander/Pilot forward viewforward view

Portrays critical landing dataPortrays critical landing data Relieves flight crew from having to Relieves flight crew from having to

glance at the flight instruments glance at the flight instruments during very busy approach and during very busy approach and landinglanding

HUD visual aid adds to the HUD visual aid adds to the operating safety of the Orbiter operating safety of the Orbiter during approach by reducing the during approach by reducing the observation-decision-reaction observation-decision-reaction workload during the landingworkload during the landing

Note the difference in shallow and Note the difference in shallow and steep glide path aimpointssteep glide path aimpoints


Alpha/Mach Indicator Alpha/Mach Indicator (AMI)(AMI)

Alpha-Mach indicator is a Alpha-Mach indicator is a tape-readout instrument that tape-readout instrument that displays:displays: VelocityVelocity Angle of attack (relative Angle of attack (relative

air flow, or alpha)air flow, or alpha) AirspeedAirspeed Vertical accelerationVertical acceleration

AMI data is used for the AMI data is used for the Commander's/Pilot's Commander's/Pilot's evaluation of vehicle evaluation of vehicle performanceperformance Becomes more critical as Becomes more critical as

the Orbiter approaches the Orbiter approaches the runwaythe runway

Flight OperationsFlight Operations

GN&C – Flight OperationsGN&C – Flight Operations

Guidance, navigation, and control software integrates the vehicle's Guidance, navigation, and control software integrates the vehicle's navigation data inputs in order to command the vehicle control systems navigation data inputs in order to command the vehicle control systems during the various flight phasesduring the various flight phases

Because these phases are so different in navigational inputs and Because these phases are so different in navigational inputs and control system output operations, and because the Orbiter's General control system output operations, and because the Orbiter's General Purpose Computers have such a small resident memory, the software is Purpose Computers have such a small resident memory, the software is divided into flight operations oriented blocks called Operational divided into flight operations oriented blocks called Operational Sequences (OPS)Sequences (OPS)

The five OPS modes are loaded sequentially into each of the GPCs to The five OPS modes are loaded sequentially into each of the GPCs to conserve memoryconserve memory

The one exception is GPC 5 which runs BFSThe one exception is GPC 5 which runs BFS Launch is OPS mode 1 that is preloaded into the GPCs on the launch pad for Launch is OPS mode 1 that is preloaded into the GPCs on the launch pad for

the three ascent stages to orbitthe three ascent stages to orbit OPS mode 2 used for operations while on-orbit is loaded from the mass OPS mode 2 used for operations while on-orbit is loaded from the mass

memory units after completion of orbit insertion with the OMS burn(s)memory units after completion of orbit insertion with the OMS burn(s) Deorbit preparation is under OPS mode 8Deorbit preparation is under OPS mode 8 Dorbit, descent, and landing are OPS mode 3 functionsDorbit, descent, and landing are OPS mode 3 functions


OPS Major Mode 1OPS Major Mode 1


Major FunctionsMajor Functions

GN&C - flight operations GN&C - flight operations SM SM PL - payload operations PL - payload operations


OPS ModesOPS Modes

OPS-1 GN&C launchOPS-1 GN&C launch

OPS-2 GN&C orbitOPS-2 GN&C orbit

OPS-2 SM orbit OPS-2 SM orbit

OPS-3 GN&C deorbit-landingOPS-3 GN&C deorbit-landing

OPS-8 GN&C on-orbit checkoutOPS-8 GN&C on-orbit checkout

OPS-9 GN&C prelaunch/post landing OPS-9 GN&C prelaunch/post landing

OPS-9 PL memory OPS-9 PL memory


Major ModesMajor Modes

GN&C OPS-1 (launch) 101, 102, 103, 104, 105, 106GN&C OPS-1 (launch) 101, 102, 103, 104, 105, 106

GN&C OPS-2 (on-orbit) 201, 202, 203GN&C OPS-2 (on-orbit) 201, 202, 203

SM OPS-2 (on-orbit) 201, 202, 203 SM OPS-2 (on-orbit) 201, 202, 203

GN&C OPS-3 (deorbit-landing) 301, 302, 303, 304, 305GN&C OPS-3 (deorbit-landing) 301, 302, 303, 304, 305

GN&C OPS-8 (on-orbit checkout) 801GN&C OPS-8 (on-orbit checkout) 801

GN&C OPS-9 901GN&C OPS-9 901

PL OPS-9 901PL OPS-9 901


OPS-1 AscentOPS-1 Ascent

During this phase, During this phase, maximum aerodynamic maximum aerodynamic pressure is encountered pressure is encountered in the Mach 1-2 region, in the Mach 1-2 region, so those load limits are so those load limits are reduced by programmed reduced by programmed throttling back on the throttling back on the SSME thrustSSME thrust

A maximum structural A maximum structural surface load of 700 surface load of 700 pounds per square foot pounds per square foot (psf) is maintained by the (psf) is maintained by the GN&C systemGN&C system

Provides a safety Provides a safety margin between the margin between the maximum loading maximum loading possible and the safe possible and the safe limit loading of the limit loading of the structurestructure

GN&C Flight Operations - AscentGN&C Flight Operations - Ascent


OPS-2 Orbital flightOPS-2 Orbital flight

Any orbital changes during flight operations are first computed from Any orbital changes during flight operations are first computed from the manual or automated navigation inputs within the navigation and the manual or automated navigation inputs within the navigation and guidance software programs, then relayed to the control effectorsguidance software programs, then relayed to the control effectors

OMS/RCS system while on orbitOMS/RCS system while on orbit Aerosurfaces in flightAerosurfaces in flight

An automated flight system is integrated into the Orbiter's flight An automated flight system is integrated into the Orbiter's flight functions during the ascent, for on-orbit maneuvers, and for descentfunctions during the ascent, for on-orbit maneuvers, and for descent

The automated flight hardware and software is known as the Digital The automated flight hardware and software is known as the Digital Auto Pilot (DAP)Auto Pilot (DAP)


OPS-3 DeorbitOPS-3 Deorbit

Atmospheric reentry involves the greatest thermal loads as well Atmospheric reentry involves the greatest thermal loads as well as the greatest potential aerodynamic loading of all the Orbiter's as the greatest potential aerodynamic loading of all the Orbiter's flight phasesflight phases

To control the early-entry heating, the Orbiter is placed into a 40To control the early-entry heating, the Orbiter is placed into a 40oo pitch up attitude by the DAP pitch up attitude by the DAP Maintains a constant temperature with pitch adjustments to avoid Maintains a constant temperature with pitch adjustments to avoid

approaching the TPS tile heat load and temperature safety limits approaching the TPS tile heat load and temperature safety limits

Following this phase, an equilibrium glide phase is entered Following this phase, an equilibrium glide phase is entered Allows energy dissipation with S-turns to a bank angle of Allows energy dissipation with S-turns to a bank angle of

approximately approximately ±±3030oo

GN&C – Flight OperationsGN&C – Flight Operations Reentry profile boundaries for the OrbiterReentry profile boundaries for the Orbiter


OPS-3 Approach and landingOPS-3 Approach and landing

The unpowered Orbiter must glide from orbit to landing with an The unpowered Orbiter must glide from orbit to landing with an accuracy of better than one meter at touchdown, regardless of accuracy of better than one meter at touchdown, regardless of the atmospheric conditions, the descent trajectory, the the atmospheric conditions, the descent trajectory, the Orbiter's configuration, or its weightOrbiter's configuration, or its weight

To accommodate these and many other variables, the Orbiter's To accommodate these and many other variables, the Orbiter's navigation and guidance to a specific runway point includes navigation and guidance to a specific runway point includes transitions from its orbit exit to a precise, standardized landing transitions from its orbit exit to a precise, standardized landing procedure in similar fashion to aircraft precision approach and procedure in similar fashion to aircraft precision approach and landing operationslanding operations

The many variables included in the Orbiter's trajectory and the The many variables included in the Orbiter's trajectory and the flight conditions are folded into a standardized precise final flight conditions are folded into a standardized precise final landing approachlanding approach


OPS-3 Approach and landingOPS-3 Approach and landing

The approach uses a navigational aid in the form of The approach uses a navigational aid in the form of a calculated route called a transition to reach a fixed a calculated route called a transition to reach a fixed reference position for landingreference position for landing

This transition, like the procedure turn to align the This transition, like the procedure turn to align the aircraft with the runway, is a cylindrical-shaped aircraft with the runway, is a cylindrical-shaped navigational reference that aligns the Orbiter with navigational reference that aligns the Orbiter with the precision landing signals for the selected runwaythe precision landing signals for the selected runway

The Heading Alignment Circle (HAC), the imaginary The Heading Alignment Circle (HAC), the imaginary navigational reference is part of a larger guidance navigational reference is part of a larger guidance and navigation process that resides in the onboard and navigation process that resides in the onboard softwaresoftware


To ensure the Orbiter is aligned accurately with its final To ensure the Orbiter is aligned accurately with its final landing path, and that it has the proper speed at landing path, and that it has the proper speed at touchdown, the Terminal Area Energy Management touchdown, the Terminal Area Energy Management (TAEM) software is programmed to carefully control (TAEM) software is programmed to carefully control the important variables in an Orbiter's glide paththe important variables in an Orbiter's glide path

TAEM incorporates the Heading Alignment Circle to TAEM incorporates the Heading Alignment Circle to help manage the Orbiter's energy variables that help manage the Orbiter's energy variables that factor into the flight path to touchdown. The primary factor into the flight path to touchdown. The primary energy variables include:energy variables include: Orbiter's velocity (kinetic energy - positive energy) Orbiter's velocity (kinetic energy - positive energy) Orbiter's weight (kinetic energy - positive energy) Orbiter's weight (kinetic energy - positive energy) Orbiter's altitude (potential energy - positive energy)Orbiter's altitude (potential energy - positive energy) Orbiter's distance from touchdown (total drag - energy loss) Orbiter's distance from touchdown (total drag - energy loss) wind speed and direction (aerodynamic drag - energy loss) wind speed and direction (aerodynamic drag - energy loss) air density (aerodynamic drag - energy loss)air density (aerodynamic drag - energy loss)


From approximately 83,000' altitude, the TAEM From approximately 83,000' altitude, the TAEM navigation software guides the Orbiter to the navigation software guides the Orbiter to the approach and landing phase which is aligned with approach and landing phase which is aligned with the runwaythe runway This leads the Orbiter to the precision guidance This leads the Orbiter to the precision guidance

signals from the Microwave Scan Beam Landing signals from the Microwave Scan Beam Landing System (MSBLS) at approximately 10,000' above System (MSBLS) at approximately 10,000' above the runway for accurate touchdownthe runway for accurate touchdown


During the TAEM operations, the Orbiter's guidance software During the TAEM operations, the Orbiter's guidance software performs the following:performs the following:

S-TurnsS-Turns - If the vehicle is high on energy higher than - If the vehicle is high on energy higher than nominal speed or higher than nominal altitude, it dissipates nominal speed or higher than nominal altitude, it dissipates the excess by turning away from the HAC until the proper the excess by turning away from the HAC until the proper energy conditions are metenergy conditions are met

HAC AcquisitionHAC Acquisition - Turns the vehicle toward the targeted - Turns the vehicle toward the targeted tangent point on the HAC and flies to this point (see the tangent point on the HAC and flies to this point (see the following two figures)following two figures)

Heading Alignment CircleHeading Alignment Circle - Flies the vehicle around the HAC - Flies the vehicle around the HAC to the point at which the HAC is tangent to the runway to the point at which the HAC is tangent to the runway centerline, called the nominal energy point (NEP)centerline, called the nominal energy point (NEP)

Prefinal Prefinal - From the NEP, the Orbiter’s guidance system - From the NEP, the Orbiter’s guidance system takes the vehicle down the runway centerline until the takes the vehicle down the runway centerline until the proper approach-to-landing (A/L) conditions are met proper approach-to-landing (A/L) conditions are met (airspeed, altitude, flight path angle, distance off centerline)(airspeed, altitude, flight path angle, distance off centerline)


Within these functions, TAEM guidance Within these functions, TAEM guidance makes the necessary adjustments in the makes the necessary adjustments in the flight path due to the varying energy valuesflight path due to the varying energy values Altitude (gravitational potential energy)Altitude (gravitational potential energy) Airspeed (kinetic energy)Airspeed (kinetic energy) Vehicle mass (kinetic energy)Vehicle mass (kinetic energy) Wind (aerodynamic drag = energy Wind (aerodynamic drag = energy

dissipation)dissipation) Atmospheric density (energy dissipation)Atmospheric density (energy dissipation) Distance to touchdown (energy Distance to touchdown (energy

dissipation)dissipation)


TAEM, HAC, and NEPTAEM, HAC, and NEP


Digital Auto Pilot (DAP) flight systemDigital Auto Pilot (DAP) flight system

The Orbiter's Digital Auto Pilot is the heart of the The Orbiter's Digital Auto Pilot is the heart of the flight operational softwareflight operational software

The DAP software consists of several modes and The DAP software consists of several modes and submodes that control the different phases of submodes that control the different phases of Orbiter flight, including ascent, orbit and reentryOrbiter flight, including ascent, orbit and reentry

DAP software interprets orbital maneuver requests, DAP software interprets orbital maneuver requests, compares them to the vehicle's position, attitude and compares them to the vehicle's position, attitude and motion, then generates command inputs to the motion, then generates command inputs to the control effectors for either automatic or manual control effectors for either automatic or manual flightflight


Digital Auto Pilot (DAP) flight systemDigital Auto Pilot (DAP) flight system

First DAP operation is the ET separation function First DAP operation is the ET separation function known as the Transition DAP modeknown as the Transition DAP mode

From this point, the DAP functions as the mission From this point, the DAP functions as the mission autopilot and manual flight director for the crew until autopilot and manual flight director for the crew until the deorbit phasethe deorbit phase

The four DAP modes are:The four DAP modes are: Transitional DAP Transitional DAP Orbital DAP Orbital DAP RCS DAP RCS DAP OMS Thrust Vector Control (TVC) DAPOMS Thrust Vector Control (TVC) DAP


Manual Flight Manual Flight ControlsControls

Crew controls are Crew controls are available for available for operating all of operating all of the Orbiter's the Orbiter's control control effectors effectors (OMS/RCS or (OMS/RCS or aerosurfaces), aerosurfaces), either either manually, or manually, or with the with the automatic DAP automatic DAP functionsfunctions


Rotational Hand Rotational Hand Controller (RHC)Controller (RHC)

The RHC transmits manual The RHC transmits manual control signals to the control signals to the Flight Control System Flight Control System (FCS) to command (FCS) to command Orbiter rotations and Orbiter rotations and thrust vectoring on the thrust vectoring on the SSMEs and OMS nozzlesSSMEs and OMS nozzles

Three RHCs on the orbiter Three RHCs on the orbiter flight deckflight deck

Each RHC controls vehicle Each RHC controls vehicle rotation about the roll, rotation about the roll, pitch, and yaw axespitch, and yaw axes



Translational Hand Controller (THC)Translational Hand Controller (THC)

Two Translational Hand Controllers are used in the flight deckTwo Translational Hand Controllers are used in the flight deck One at the commander's stationOne at the commander's station One in the aft flight deckOne in the aft flight deck

THC transmits manual flight control signals to the FCS in order to THC transmits manual flight control signals to the FCS in order to command the RCS jets or OMS enginescommand the RCS jets or OMS engines

GN&C – Manual Flight OperationsGN&C – Manual Flight Operations


Speed Brake/Thrust Controller (SBTC)Speed Brake/Thrust Controller (SBTC)

Two speed brake thrust controllers in the Orbiter cockpitTwo speed brake thrust controllers in the Orbiter cockpit one on the left-hand side of the commander's station one on the left-hand side of the commander's station one on the pilot's left-hand side on the center consoleone on the pilot's left-hand side on the center console

Provide throttle capability for the SSME engines manually Provide throttle capability for the SSME engines manually during ascentduring ascent

Control speed with an increase/decrease in aerodynamic drag Control speed with an increase/decrease in aerodynamic drag by opening or closing the speed brakeby opening or closing the speed brake


Speed Brake/Thrust Controller (SBTC)Speed Brake/Thrust Controller (SBTC)

In the forward position, the SSME thrust level is maximum and the In the forward position, the SSME thrust level is maximum and the speed brake is at minimum (closed) for decreased dragspeed brake is at minimum (closed) for decreased drag

Depressing the TAKEOVER switch on either SBTC changes the SSME Depressing the TAKEOVER switch on either SBTC changes the SSME thrust-level setting during ascent, or speed brake position during thrust-level setting during ascent, or speed brake position during entry to manual controlentry to manual control

ReferencesReferences

NASA Space Transportation System Press Kit, 1988NASA Space Transportation System Press Kit, 1988

Shuttle Crew Operations Manual - Guidance, Navigation & Shuttle Crew Operations Manual - Guidance, Navigation & Control, NASAControl, NASA

Documents

Guidance, Navigation and Control. Guidance Navigation and Control (GN&C) The guidance, navigation and control system is an essential ingredient in all