Attitude Profile

Calculate shortest quaternion rotation

Since R2020b

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Libraries:
Aerospace Blockset / Spacecraft / Spacecraft Dynamics

Description

The Attitude Profile block calculates the shortest quaternion rotation that aligns the primary alignment vector with the primary constraint vector. A quaternion is defined using the scalar-first convention. Aerospace Blockset™ uses quaternions that are defined using the scalar-first convention.

Provide the primary constraint as either a pointing mode:

• Point at nadir

• Point at celestial body

• Point at LatLonAlt

or via a custom constraint vector. The block then aligns secondary alignment and constraint vectors as much as possible without breaking primary alignment.

The library contains three versions of the Attitude Profile block preconfigured for these common attitude control modes:

• Nadir Pointing — Point at nadir

• Geographic Pointing — Point at LatLonAlt

• Sun Tracking — Point at celestial body with Sun as the celestial target

For more information on the coordinate systems the Attitude Profile block uses, see Algorithms.

Examples

Hohmann Transfer with the Spacecraft Dynamics Block

Model a Hohmann transfer of a spacecraft between two circular coplanar orbits.

Open Live Script

Analyzing Spacecraft Attitude Profiles with Satellite Scenario

Propagate orbit and attitude states in Simulink^® and visualize computed trajectory and attitude profile in a satellite scenario.

Open Live Script

Ports

Input

X — Velocity state vector position

3-element vector

Position state vector of spacecraft at time t_utc.

Data Types: double

V — Velocity state vector

3-element vector

Velocity state vector of spacecraft at time t_utc, specified as a 3-element vector.

Dependencies

To enable this port, set Constraint coordinate frame (CCF) to LVLH.

Data Types: double

q — Spacecraft attitude

4-element vector

Attitude of the spacecraft at t_utc, represented as a quaternion from body frame to port coordinate frame, specified as a 4-element vector.

Data Types: double

t_utc — Current data or time

scalar

Current date or time, specified as a scalar, as a Julian date.

Dependencies

To enable this port, perform one of these:

• Set Pointing mode to Point at celestial body or Point at LatLonAlt

• Select the Allow pointing mode change during run check box.

Data Types: double

μ l — Geodetic latitude and longitude

2-element vector

Geodetic latitude and longitude (deg) of a terrestrial point of interest, specified as a 1-D array of size 2. This port is used together with altitude when Pointing mode is Point at LatLongAlt. This location is used as the primary constraint.

Dependencies

To enable this port, do one of these:

• Set Pointing mode to LatLonAlt.

• Select the Allow pointing mode change during run check box.

Data Types: double

h — Altitude

scalar

Altitude of terrestrial point of interest, specified as a scalar. This port is used together with geodetic latitude and longitude when Pointing mode is Point at LatLongAlt. This location is used as the primary constraint.

Dependencies

To enable this port, do one of these:

• Set Pointing mode to LatLonAlt.

• Select the Allow pointing mode change during run check box.

Data Types: double

A1_b — Primary alignment vector

3-element vector

Primary alignment vector (in body frame), specified as a 3-element vector.

Dependencies

To enable this port, set Primary alignment (body-frame) to Port.

Data Types: double

A2_b — Secondary alignment vector

3-element vector

Secondary alignment vector (in body frame), specified as a 3-element vector.

Dependencies

To enable this port, set Secondary alignment (Body-frame) to Port.

Data Types: double

C1_lvlh — Primary constraint vector

3-element vector

Primary constraint vector, specified as a 3-element vector, in constraint coordinate frame.

Dependencies

To enable this port, set:

• Pointing mode to Custom.

• Primary constraint (CCF) to Port.

Data Types: double

C2_lvlh — Secondary constraint

3-element vector

Secondary constraint vector, specified as a 3-element vector.

Dependencies

To enable this port, set Secondary constraint (CCF) to Port.

Data Types: double

Output

q_tgtb — Quaternion rotation

4-element vector (scalar first)

Quaternion rotation by which to rotate from the spacecraft current orientation to the desired orientation (in body frame), returned as a 4-element vector.

Dependency

To enable this port, select the Output rotation from current to updated attitude check box.

Data Types: double

q_new — Updated spacecraft attitude

4-element vector

Updated spacecraft attitude with respect to Port Coordinate Frame following the quaternion rotation, returned as a 4-element vector.

Dependency

To enable this port, select the Output attitude check box.

Data Types: double

Parameters

Output rotation from current to updated attitude — Output rotation

on (default) | off

To output the rotation, select this check box. Otherwise, clear this check box.

Programmatic Use

Block Parameter: outputError

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Output attitude — Output updated attitude

off (default) | on

To output the updated spacecraft attitude as a quaternion rotation from the body frame to the Port coordinate frame, select this check box. Otherwise, clear this check box.

Programmatic Use

Block Parameter: outputFinalAttitude

Type: character vector

Values: 'on' | 'off'

Default: 'off'

Port coordinate frame — Coordinate frame for position, velocity, and attitude ports

ICRF (default) | Fixed-frame

Coordinate frame for position, velocity, and attitude (q) ports. For more information about coordinate systems, see Algorithms.

Programmatic Use

Block Parameter: portFrame

Type: character vector

Values: 'ICRF' | 'Fixed-frame'

Default: 'ICRF'

Pointing mode — Primary vector alignment pointing mode

Point at nadir (default) | Point at celestial body | Point at LatLonAlt | Custom

Primary vector alignment pointing mode, specified as Point at nadir, Point at celestial body, Point at LatLonAlt, or Custom.

Programmatic Use

Block Parameter: pointingMode

Type: character vector

Values: 'Point at nadir' | 'Point at celestial body' | 'Point at LatLonAlt' | 'Custom'

Default: 'Point at nadir'

Allow pointing mode change during run — Allow pointing mode change during run

off (default) | on

To allow pointing mode change during run, select this check box. Otherwise, clear this check box.

Programmatic Use

Block Parameter: tunablePointing

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Celestial target — Celestial body

Sun (default) | Mercury | Venus | Moon | Mars | Jupiter | Saturn | Uranus | Neptune | Pluto | Solar system barycenter | Earth-Moon barycenter

Celestial body with which to align primary alignment vector.

Dependencies

To enable this parameter, set Pointing mode to Point at celestial body.

Programmatic Use

Block Parameter: celestialTarget

Type: character vector

Values: 'Sun' | 'Mercury' | 'Venus' | 'Moon' | 'Mars' | 'Jupiter' | 'Saturn' | 'Uranus' | 'Neptune' | 'Pluto' | 'Solar' | 'Solar system barycenter' | 'Earth-Moon barycenter'

Default: 'Sun'

Primary alignment (body-frame) — Primary alignment vector

Dialog (default) | Port

Primary alignment vector source, specified as Port or Dialog.

• Port — Specify port alignment array through the A1_b port.

• Dialog — Specify port alignment 3-element vector in the accompanying text box (default value of [0 0 1]).

Dependencies

To specify the port alignment array in a text box, set this parameter to Dialog.

Programmatic Use

Block Parameter: primaryAlignmentSrc | when primaryAlignmentSrc is 'Dialog', use primaryAlignment to set the primary alignment vector

Type: character vector

Values: 'Port' | 'Dialog' | primary alignment vector, specified 3-element vector

Default: 'Dialog'

Secondary alignment (body-frame) — Secondary alignment vector

Dialog (default) | Port

Secondary alignment vector source, specified as Port or Dialog.

• Port — Specify port alignment array through the A2_b port.

• Dialog — Specify port alignment 3-element vector in the accompanying text box (default value of [1 0 0]).

Dependencies

To specify the port alignment array in a text box, set this parameter to Dialog.

Programmatic Use

Block Parameter: secondaryAlignmentSrc | when secondaryAlignmentSrc is 'Dialog', use secondaryAlignment to set the secondary alignment vector

Type: character vector

Values: 'Port' | 'Dialog' | secondary alignment vector, specified as a 3-element vector

Default: 'Dialog'

Constraint coordinate frame, CCF — Constraint coordinate frame

ICRF (default) | Fixed-frame | LVLH | NED | Body-fixed

Coordinate frame in which constraint vectors are provided, specified as ICRF, Fixed-frame, LVLH, NED, or Body-fixed. For more information about coordinate systems, see Algorithms.

Programmatic Use

Block Parameter: constraintFrame

Type: character vector

Values: 'ICRF' | 'Fixed-frame' | 'LVLH' | 'NED' | 'Body-fixed'

Default: 'ICRF'

Primary constraint (CCF) — Primary constraint

Dialog (default) | Port

Primary constraint vector source, specified as Port or Dialog.

• Port — Specify primary constraint array through the C1_b port.

• Dialog — Specify port constraint 3-element vector in the accompanying text box (default value of [1 0 0]).

Dependencies

• To specify the port alignment array in a text box, set this parameter to Dialog.

• This parameter is affected when Constraint coordinate frame (CCF) is set to Custom.

Programmatic Use

Block Parameter: primaryConstraintSrc | when primaryConstraintSrc is 'Dialog', use primaryConstraint to set the primary constraint vector

Type: character vector

Values: 'Port' | 'Dialog' | primary constraint vector, specified as a 3-element vector

Default: 'Dialog'

Secondary constraint (CCF) — Secondary constraint

Dialog (default) | Port

Secondary constraint vector source, specified as Port or Dialog.

• Port — Specify secondary constraint array through the C1_b port.

• Dialog — Specify port constraint 3-element vector in the accompanying text box (default value of [0 1 0]).

After the primary alignment vector is aligned with the primary constraint vector, to fully define the rotation, the block attempts to align the secondary alignment vector with the rotation vector. The rotation vector should be the secondary constraint vector.

Whereas the primary constraint is enabled only for the custom pointing mode, the secondary constraint is always enabled.

Dependencies

To specify the port alignment array in a text box, set this parameter to Dialog.

Programmatic Use

Block Parameter: secondaryConstraintSrc | when secondaryConstraintSrc is 'Dialog', use secondaryConstraint to set the secondary constraint vector

Type: character vector

Values: 'Port' | 'Dialog' | secondary constraint vector, specified as a 3-element vector

Default: 'Dialog'

Algorithms

The Attitude Profile block uses Earth-centric and vehicle-centric coordinate systems.

Earth-Centric Coordinate Systems

The Earth-centric coordinate system uses the ICRF and fixed-frame coordinate systems:

• International Celestial Reference Frame. This frame can be treated as equal to the ECI coordinate system realized at J2000 (Jan 1 2000 12:00:00 TT. For more information, see ECI Coordinates.

• Fixed-frame — The fixed-frame for Earth this block uses is the International Terrestrial Reference Frame (ITRF). This reference frame is realized by the IAU2000/2006 reduction from the ICRF coordinate system. This frame is often described as the Earth-centered Earth-fixed reference frame.

Vehicle-Centric Coordinate Systems

The vehicle-centric coordinate system works in the Body frame, north-east-down (NED), and local vertical, local horizontal (LVLH) coordinate systems.

• Body frame — Fixed in both origin and orientation to the moving craft. For more information, see Body Coordinates.

• North-east-down — Noninertial system with its origin fixed at the aircraft or spacecraft center of gravity. For more information, see NED Coordinates.

• Local vertical, local horizontal — Also known as the spacecraft coordinate system, Gaussian coordinate system, or the orbit frame. LVLH is a rotating, accelerating frame commonly used in studies of relative motion, such as vehicle maneuvering. The axes of this frame are:

  • R-axis — Points outward from the spacecraft origin along its position vectors (with respect to the center of Earth). Measurements along this axis are referred to as radial.

  • S-axis — Completes the right hand coordinate system. This axis points in the direction of the velocity vector, but is only parallel to it for circular orbits. Measurements along this axis are referred to as along-track or transverse.

  • W-axis — Points normal to the orbital plane. Measurements along this axis are referred to as cross-track.

Version History

Introduced in R2020b

R2023a: Attitude Profile Block Update

To support idealized attitude control workflows, the Attitude Profile block has new parameters and an output port:

• Output rotation from current to updated attitude parameter

• Output attitude parameter

• q_new port