Impulsive Maneuver Segment

An Impulsive Maneuver segment has two tabs that define its parameters: Attitude and Engine.

Attitude

The Attitude Control field enables you to select the mode in which the maneuver pointing direction is prescribed. This section provides definitions for each of the five available options for this field and their associated parameters.

Along Velocity Vector / Anti-Velocity Vector

The satellite object’s attitude is such that the Delta-V vector aligns with or is opposite to the spacecraft's inertial velocity vector. The inertial reference frame depends on the central body of the satellite object. Either the thruster set or an engine model defines the Delta-V in the body frame. You can use More Options to specify the engine direction in the engine model. Finally, the constraint vector in More Options completes the attitude definition.

Parameter	Description
Delta-V Magnitude	This is the magnitude of the impulse to be added to the spacecraft velocity vector in distance/time.

Attitude

Attitude is the rotation between the body axes and the selected inertial reference axes, specified as either a set of Euler angles or as a quaternion. Astrogator finds the Delta-V direction in the inertial frame using this attitude definition. It also determines the thruster direction in the body frame either by the thruster set or, if using an engine model, by the engine direction specified in More Options.

Parameter	Description
Delta-V Magnitude	This is the change in spacecraft velocity due to the burn (distance/time).
Ref Axes	These are the reference axes used in modeling this maneuver.
Euler Angles	This is the attitude defined as a rotation from the reference axes to the body frame; enter values for angles 1, 2, and 3, and select a Sequence option.
Quaternion	This comprises the vector components (qx, qy, and qz) and the scalar component (qs) that define the quaternion from the reference axes to the body frame.

File

In this option, you provide an imported attitude file. Astrogator finds the Delta-V direction in the inertial frame using this attitude definition and the thruster direction in the body frame as described above.

Parameter	Description
Delta-V Magnitude	This is the change in spacecraft velocity in units of distance/time.
Filename	This is the name of the attitude file.
File Time Offset	This is a time offset relative to the file time. For example, if the offset value is two seconds, then the attitude for the maneuver at the current simulation time in STK is restricted from the file at the simulation time plus two seconds. An STK time of 12:00:00.000 would use the information in the file for 12:00:02.000. This is the same as increasing the epoch in the file by two seconds. See Attitude File for more information.

Thrust Vector

With this attitude control setting, you specify the Delta-V vector in some reference frame using either Cartesian or spherical components. Astrogator then computes the attitude so that the total thrust vector in the body frame, as specified by the thruster set or engine model, aligns with this vector in the reference axes. Astrogator then uses the constraint vector in More Options to complete the attitude definition.

Parameter	Description
Thrust Axes	This is the set of axes that specifies the thrust direction.
Cartesian	These are the components of the selected thrust axes (usually X, Y, and Z) that define the Delta-V vector in the reference axes.
Spherical	These are the azimuth, elevation, and magnitude that define the Delta-V vector in the reference axes, where azimuth is the angle between the X axis and the projection of the vector in the X-Y plane, positive toward Y. Allow Negative Spherical Magnitude – If you select this, the magnitude field of spherical elements is allowed to accept negative values. This option may be useful with targeting problems if you are uncertain of the direction of the maneuver. When using a negative value for magnitude, the Delta-V is in the opposite direction of the specified azimuth and elevation. The actual azimuth will be 180 degrees from the specified azimuth, and the actual elevation is the negative of the specified elevation.

Engine

The Engine tab defines the magnitude and the nature of the propulsion. The Engine parameters specified on this tab are used primarily to define the maneuver direction when using a thruster set to seed a finite maneuver and to update the fuel mass.

Parameter	Description
Engine Model	You can use Engine Model to quickly model the firing of a single engine. For more information, see Engine Model.
Thruster Set	Use Thruster Set to fire multiple engines simultaneously and to simulate off-pulsing or complex engine pointing. For more information, see Thruster Set.
Update Mass Based on Fuel Usage	If you select this, Astrogator updates the mass of the spacecraft as fuel consumed delta-M, using the rocket equation: V = V_eln(m₀/m_f) where V_e = exhaust velocity, m₀ = initial mass, and m_f = final mass. See the technical notes for the derivation of the equation relating change in mass to V.

Parameter

Description

Engine Model

You can use Engine Model to quickly model the firing of a single engine. For more information, see Engine Model.

Thruster Set

Use Thruster Set to fire multiple engines simultaneously and to simulate off-pulsing or complex engine pointing. For more information, see Thruster Set.

Update Mass Based on Fuel Usage

If you select this, Astrogator updates the mass of the spacecraft as fuel consumed delta-M, using the rocket equation:

V = V_eln(m₀/m_f)

where V_e = exhaust velocity, m₀ = initial mass, and m_f = final mass. See the technical notes for the derivation of the equation relating change in mass to V.