Voir la source de User Manual 4.9 Slew

__NOTOC__ 
== Introduction ==
=== Scope ===
A slew performs the transition between two attitude laws.

=== Javadoc ===
The attitude objects linked to slews are available in the package fr.cnes.sirius.patrius.attitudes.

{| class="wikitable"
|-
! scope="col"| Library
! scope="col"| Javadoc
|-
|Patrius
|[{{JavaDoc4.9}}/fr/cnes/sirius/patrius/attitudes/package-summary.html Package fr.cnes.sirius.patrius.attitudes]
|}

=== Links ===
None as of now.

=== Useful Documents ===
None as of now.

=== Package Overview ===
The slew conception is split into two features:
* The slew computation. Classes ''computing'' the slew are provided in PATRIUS.
* The slew realization. All classes realizing a slew implements the <code>Slew</code> interface. Slews are mainly of two types:
** Analytical slews (such as <code>ConstantSpinSlew</code>
** Pre-computed slews stored in a <code>TabulatedSlew</code>. In this case, a slew ''computer'' will compute the tabulated ephemeris of the slew.

A slew is bounded in time and as a result inherits the [ATT_LEG_Home AttitudeLeg] interface.

== Features ==
=== Constant spin slew ===
The constant spin slew is a basic slew maneuver type. Between the initial quaternion and the final one, a spherical linear interpolation describes the behavior of the spacecraft.
Two constraint types are available:
* Duration constraint: spin is computed to match constraint.
<syntaxhighlight lang="java">final Slew slew = new ConstantSpinSlew(firstAttitude, secondAttitude);</syntaxhighlight>
* Angular velocity constraint: initial slew date or final slew date is computed to match constraint.
** Initial slew date is known:
<syntaxhighlight lang="java">final Slew slew = new ConstantSpinSlewComputer(angularConstraint).compute(pvProvider, initialLaw, initialDate, finalLaw, null);</syntaxhighlight>
** Final slew date is known:
<syntaxhighlight lang="java">final Slew slew = new ConstantSpinSlewComputer(angularConstraint).compute(pvProvider, initialLaw, null, finalLaw, finalDate);</syntaxhighlight>

=== Spin bias slew ===
The two spin bias slew is a slew maneuver type. The velocity depends on the value of the slew angle.

In order to compute properly the slew, the user must specify the initial and final laws, the parameters of the two angular velocity fields, plus the stabilisation margin:

<syntaxhighlight lang="java">final TwoSpinBiasSlewComputer computer = new TwoSpinBiasSlewComputer( 
    step, theta_max, tau, epsInRall, omega2, theta, epsOutRall, omega1, dtStab);</syntaxhighlight>

Once the slew maneuver is defined, the computation can be performed on an orbital state using the following method:
<syntaxhighlight lang="java">
final TabulatedSlew slew = computer.compute(startLaw, initialDate, finalLaw, null);
</syntaxhighlight>

The slew is then represented by a generic <code>TabulatedSlew</code> which stores the slew under a tabulated ephemeris.

=== ISIS Spin bias slew ===
This spin bias slew is a slew with a trapezoidal angular velocity profile:
- Constant acceleration phase
- Constant angular velocity phase (zero acceleration phase)
- Constant decceleration phase

[[File:ISISSpin2.png|center]]

This slew can be computed using methods:<br>
- <code>IsisSpinBiasSlewComputer.computeAnalytical</code>: this class provides an analytical solution to the slew<br>
- <code>IsisSpinBiasSlewComputer.computeNumerical</code>: this class provides an numerical solution to the slew
The two classes returns close results ( < 1E-2 rad), though analytical solution is more accurate.

The slews can be used in two ways:<br>
- Provide an initial law, an initial date and a target final law<br>
- Provide an final law, a final date and a target initial law<br><br>
'''Warning''': slew computed in both ways will never be exactly the same depending on user-chosen convergence threshold and maximum number of iterations (result will be exactly the same if convergence threshold is lower than machine precision and number of allowed iterations high enough to support convergence).

The slew has then to be calculated using method <code>compute()</code>.
The slew is then represented by a generic <code>TabulatedSlew</code> which stores the slew under a tabulated ephemeris.
Finally the slew can be used like any other slew.

== Getting Started ==
{{specialInclusion prefix=$theme_sub section="GettingStarted"/}}

== Contents ==
=== Interfaces ===

{| class="wikitable"
|-
! scope="col"| Interface
! scope="col"| Summary
! scope="col"| Javadoc
|-
|'''AttitudeLeg'''
|This interface extends the AttitudeProvider interface and adds the time interval of validity notion to the attitude laws.
|[{{JavaDoc4.9}}/fr/cnes/sirius/patrius/attitudes/AttitudeLeg.html AttitudeLeg]
|-
|'''Slew'''
|This interface implements a generic slew model set.
|[{{JavaDoc4.9}}/fr/cnes/sirius/patrius/attitudes/Slew.html Slew]
|}

=== Classes ===

{| class="wikitable"
|-
! scope="col"| Class
! scope="col"| Summary
! scope="col"| Javadoc
|-
|'''ConstantSpinSlew'''
|This class implements the constant spin slew maneuver profile.
|[{{JavaDoc4.9}}/fr/cnes/sirius/patrius/attitudes/ConstantSpinSlew.html ConstantSpinSlew]
|-
|'''TabulatedSlew'''
|This class implements a generic tabulated slew, once computed with one of the computer classes.
|[{{JavaDoc4.9}}/fr/cnes/sirius/patrius/attitudes/TabulatedSlew.html TabulatedSlew]
|-
|'''AngularVelocitiesPolynomialSlew'''
|This class implements a generic angular velocities polynomial slew.
|[{{JavaDoc4.9}}/fr/cnes/sirius/patrius/attitudes/AngularVelocitiesPolynomialSlew.html AngularVelocitiesPolynomialSlew]
|-
|'''ConstantSpinSlewComputer'''
|This class computes a constant spin slew into a ConstantSpinSlew.
|[{{JavaDoc4.9}}/fr/cnes/sirius/patrius/attitudes/slew/ConstantSpinSlewComputer.html ConstantSpinSlewComputer]
|-
|'''TwoSpinBiasSlewComputer'''
|This class computes a two spin bias slew into a TabulatedSlew.
|[{{JavaDoc4.9}}/fr/cnes/sirius/patrius/attitudes/slew/TwoSpinBiasSlewComputer.html TwoSpinBiasSlewComputer]
|-
|'''IsisSpinBiasSlewComputer'''
|This class computes an ISIS spin bias slew into a TabulatedSlew.
|[{{JavaDoc4.9}}/fr/cnes/sirius/patrius/attitudes/slew/IsisSpinBiasSlewComputer.html IsisSpinBiasSlewComputer]
|}

[[Category:User_Manual_4.9_Attitude]]