User Manual 3.3 Slew : Différence entre versions

Version actuelle en date du 28 février 2018 à 15:21

Introduction

Scope

A slew performs the transition between two attitude laws.

Javadoc

The attitude objects linked to slews are available in the package org.orekit.attitudes in the Orekit add-ons library.

Links

None as of now.

Useful Documents

None as of now.

Package Overview

The slew conception is described hereafter :

Legend :

• green : new objects
• grey : modified existing objects
• blue : existing objects

A slew is represented by the abstract class AbstractSlew, which implements the interface Slew. An slew describes how the spacecraft joins up two successive attitude laws: the classes heriting from AbstractSlew (like the class ConstantSpinSlew) contain the algorithms to compute the maneuver.

A slew is bounded in time and as a result inherits the 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 ([MAT_QRO_Rotations slerp interpolation]) describes the behavior of the spacecraft. In order to properly compute the slew, the user must specify the initial and final quaternion, plus a computation constraint:

• Minimal duration:
  • the initial and final date of the slew maneuver are given:
    

    final Slew slew = new ConstantSpinSlew(firstLaw, secondLaw, startDate, endDate);

  • the initial date of the slew maneuver and its duration are given:
    

    final Slew slew = new ConstantSpinSlew(firstLaw, secondLaw, startDate, true, 150., Constraint.DURATION);

  • the final date of the slew maneuver and its duration are given:
    

    final Slew slew = new ConstantSpinSlew(firstLaw, secondLaw, endDate, false, 150., Constraint.DURATION);

• Maximal angular velocity:
  • the initial (or final) date of the slew maneuver and the maximal angular velocity are given:
    

    final Slew slew = new ConstantSpinSlew(firstLaw, secondLaw, startDate, true, 0.2, Constraint.ANGULAR_VELOCITY);

Once the slew maneuver defined, the computation can be performed on an orbital state using the following method:

slew.compute(orbit);

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:

final TwoSpinBiasSlew slew = new TwoSpinBiasSlew(startLaw, finalLaw, initialDate, 
    step, theta_max, tau, epsInRall, omega2, theta, epsOutRall, omega1, dtStab);

Once the slew maneuver is defined, the computation can be performed on an orbital state using the following method:

slew.compute(orbit);

It is possible to get the attitude ephemeris representing the slew using the following method:

final TabulatedAttitude ephem = slew.getEphemeris();

Getting Started

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Contents

Interfaces

Classes

Tutorials

Tutorial 1

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Tutorial 2

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Tips & Tricks

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