User Manual 4.1 Maneuvers : Différence entre versions

Version du 28 juin 2018 à 08:39

Introduction

Scope

The scope of this section is to present the maneuver models available through the Patrius libraries.

Javadoc

All the classes related to maneuvers are in the following packages:

Links

None as of now.

Useful Documents

None as of now.

Package Overview

The maneuver package fr.cnes.sirius.patrius.forces.maneuvers contains:

• Continuous maneuvers: both constant and variable)
• Impulsive maneuvers
• Maneuvers sequences
• An analytical model for small maneuvers

Features Description

Continuous Thrust Maneuver

Continuous thrust maneuvers are defined using the class ContinuousThrustManeuver. With it, you can either define:

• A constant maneuver
• A variable maneuver

A maneuver contains the following parameters:

• A start date / end date: this can be defined either:
  • With a start date and a duration (former method)
  • With event detectors, first detector for starting the maneuver, second detector for stopping the maneuver. Action.STOP is required to trigger (start/stop) the thrust. Any other action will be discarded.

When using event detectors, pay attention to events that may occur several times. If you want the maneuver to perform only once, the event detectors have to be included in a nth occurrence detector or its shouldBeRemoved() method have to return true. Otherwise the maneuver may be performed more than once: if a maneuver starts at the perigee (using a perigee detector) and stops at the apogee (using an apogee detector), then a maneuver will start at every perigee and stop at every apogee.

• A frame in which the thrust direction is provided. This can either be:
  • A generic frame
  • A local orbital frame LOFType
  • The spacecraft frame (in this case, attitude is mandatory to compute transform from spacecraft frame from propagation frame)

• A PropulsiveProperty which contains:
  • Thrust: it can be either constant (using double) or variable (using IDependentVariable<SpacecraftState>). If defined as constant, thrust is then defined as a Parameter and derivative with respect to thrust can be computed
  • ISP: it can be either constant (using double) or variable (using IDependentVariable<SpacecraftState>)

• A MassProvider used to compute total mass of spacecraft

• A TankProperty indicating the tank to use for the maneuver

If your propagation starts within a maneuver, two methods are available to manually start/stop a maneuver :

• isFiring()
• setFiring(final boolean isFiring)

A user wanting to start a propagation during a maneuver will call setFiring(true) before launching the propagation. This is useful since maneuver start and stop criteria are defined through event detectors. This mecanism is available for any non-impulsive maneuver i.e. ContinuousThrustManeuver and ConstantThrustError.

The construction possibilities are listed in the following array:

All this possibilities lead to 12 constructors.

Below are examples with constant and variable thrust maneuvers.

Constant Thrust Maneuver

In this case, the thrust, the ISP and the acceleration direction are constant values.

Here is an example of a constant maneuver of direction [1, 0, 0] in TNW frame.

final double thrust = 420;
final double isp = 318;
final Vector3D direction = Vector3D.PLUS_I;
final PropulsiveProperty propulsiveProperty = new PropulsiveProperty(thrust, isp);
final TankProperty tankProperty = new TankProperty(1000.);
final ContinuousThrustManeuver maneuver = new ContinuousThrustManeuver(date, duration, propulsiveProperty, direction, massProvider, tankProperty, LOFType.TNW);

Partial derivatives with respect to thrust can be computed. To do so, you either:

• Define your own thrust as a parameter:

final double thrustParam = new Parameter("Thrust", 420);
final double ispParam = new Parameter("ISP", 318);
final PropulsiveProperty propulsiveProperty = new PropulsiveProperty(thrustParam, ispParam);

And then call maneuver.addDAccDParam(..., thrustParam, ...)

• Or retrieve the thrust parameter:

final double thrust = 420;
final double isp = 318;
final PropulsiveProperty propulsiveProperty = new PropulsiveProperty(thrust, isp);
finl Parameter thrustParam = propulsiveProperty.getThrustParam();

And then call maneuver.addDAccDParam(..., thrustParam, ...)

Variable Thrust Maneuver

In this case, the thrust, the ISP and the acceleration direction can be variable values.

Here is an example of a variable maneuver of variable direction in TNW frame and variable thrust and ISP.

final IDependentVariable<SpacecraftState> thrust = ...;
final IDependentVariable<SpacecraftState> isp = ...;
final IDependentVectorVariable<SpacecraftState> direction = ...;
final PropulsiveProperty propulsiveProperty  = new PropulsiveProperty(thrust, isp);
final TankProperty tankProperty = new TankProperty(1000.);
final ContinuousThrustManeuver maneuver = new ContinuousThrustManeuver(date, duration, propulsiveProperty, direction, massProvider, tankProperty, LOFType.TNW);

No implementation of IDependentVariable<SpacecraftState> and IDependentVectorVariable<SpacecraftState> are provided in Patrius. You can however easily create your own.

Remember that partial derivatives with respect to thrust cannot be computed using variable maneuvers.

Impulse Maneuver

This ImpulseManeuver class implements the EventDetector interface.
This maneuver is provided with an underlying event detector; when an underlying event is triggered, and only if its action is set to STOP, the maneuver is triggered and the current SpacecraftState is reset. An increment or a decrement is applied to its velocity and a ratio is applied to the mass. These changes depend on the direction of variation of the integration variable (time) during integration : propagation or retro-propagation case.

List of maneuvers

The class ManeuversSequence handles the creation and the operations on a list of maneuvers; the maneuvers that can be added to the list are the following ones :

• Impulse maneuvers;

• Continue constant maneuvers;

• Continue maneuvers with variable thrust and ISP;

The user can do the following operations on the list:

• add a new maneuver; to add it, the following conditions must be met:
  • there must be no superposition between the new maneuver and any maneuver in the list.
    If the new maneuver is an impulse one and its triggering event detector is not a date detector, it always adds the maneuver (there is no way to know in advance its date). Otherwise if the new maneuver is an impulse one and its triggering event detector is a date detector, it gets the date of the maneuver from the triggering detector and uses this information to check the superposition;
  • the time between the end of the previous maneuver and the start of the new maneuver, as well as the time between the end of the new maneuver and the start of the next maneuver, must be bigger than a threshold value. The threshold value depends on the type of maneuver (impulse or continue) and can be chosen by the user.

• remove a maneuver already in the list;

• get the number of maneuvers in the list;

• add all the maneuvers of the list to the propagator;

The following lines show the usage of the class:

final ManeuversSequence sequence = new ManeuversSequence(0.0, 0.0);
// add the maneuvers to the sequence:
sequence.add(constantManeuver);
sequence.add(impulseManeuver);
// apply the maneuvers to the propagator:
sequence.applyTo(numericalPropagator);

Getting Started

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