Launch Segment
Use the Launch segment to model a simple spacecraft launch from Earth or another central body. The method is like that employed by the Simple Ascent propagator for Launch Vehicle and Missile objects. The trajectory produced is a simple curve rising vertically from the launch pad that turns over smoothly to insert the launch vehicle into orbit with the specified flight path angle at the insertion point using the specified velocity. Astrogator models the vehicle path in spherical coordinates as a radial change and spherical arc length from the launch point, which has values modeled as following the path an ellipse. Astrogator models the radial change as the Y value and the arc length as the X value, where (X,Y) follows the path of an ellipse from one semiaxis to another, typically from semimajor axis to semiminor axis.
To define a Launch segment, you must define parameters for the launch trajectory, the launch location, the burnout point, and (optionally) the burnout velocity. Specific launch location and burnout point parameters are framed in separate sections of the window, and you can access the burnout velocity parameters from the burnout section.
The following table describes the general trajectory parameters of a Launch segment:
Field | Description |
---|---|
Central Body | The default central body of any Launch segment is the Earth. To select a different central body for the launch, click to open the Select Central Body window. Click the desired central body to highlight it and then click . |
Step Size | Specify the time interval between calculated ephemeris output points. |
Use State From Previous Segment | Select this check box to define the launch location parameters by using the state of the spacecraft at the end of the previous segment. The launch location parameters and the Pre-Launch Time field become unavailable. |
Pre-Launch Time |
Specify the amount of time before the spacecraft's launch that it appears in the scenario. The vehicle will remain at the launch position until beginning of the launch epoch. |
Ascent Type | Specify the order of the spline used to generate the motion along the ellipse:
|
Initial Acceleration | If you select Quartic Motion as the Ascent Type, specify the initial acceleration. |
Launch parameters
After defining the general parameters of the launch, you must define the location and start time of the launch. The following table describes the launch location parameters:
Field | Description |
---|---|
Launch Coordinate Type | Select between:
|
Epoch | Specify the date and time of the launch. |
Set Mission Elapsed Time Epoch to Launch Epoch | Select this check box to set the Mission Elapsed Time epoch to the Launch epoch when running the MCS. |
Latitude | Specify the latitude of the launch location. |
Longitude | Specify the longitude of the launch location. |
Radius/Altitude | Specify the radius (planetocentric) or altitude (planetodetic) of the launch location. |
Import Facility Location
You can load a facility from the STK facility database to define the launch location by clicking to open the Facility Database dialog box. STK will not add the facility to the current scenario. Instead, it imports the facility information to populate the launch location parameter fields.
Select Facility
You can select a facility in the current scenario to define the launch location by clicking
to open the Select Facility dialog box. Click the desired facility to highlight it and then click . This button only appears if there is at least one facility in the scenario.Burnout parameters
After defining the general trajectory and launch location parameters, select the Burnout tab to define the location of the burnout point and the burnout velocity.
First, select one of the following options for Specify burnout state in, which determines the set of parameters to specify the burnout. various and the central- body-fixed Cartesian system.
- The central-body-fixed Cartesian system: Specify Time of Flight and fully specify the six position and velocity components of the burnout state in the standard STK central-body-fixed Cartesian system for the current central body.
- A spherical coordinate system: Specify Time of Flight as well as position and velocity in some combination of parameters defined in the following two tables. These parameters depend on the selections of the burnout coordinate type (a spherical system) and burnout velocity type.
Burnout general parameters
Specify the burnout general parameters according to the descriptions in the following table:
Field | Description |
---|---|
Burnout | Select the type of burnout specification from among the following options:
|
Time of Flight |
Specify the time from launch to burnout. If the time of flight is too short, then the vehicle will attain a velocity higher the burnout velocity before it reaches the end time, and then slow down to reach the specified burnout velocity. If the time of flight is too long, Astrogator will hold the vehicle motionless on the pad for a time before liftoff. After liftoff, the velocity monotonically increases until the end time. |
Latitude |
Specify the latitude of the spacecraft at burnout. (Geodetic or Geocentric) |
Longitude |
Specify the longitude of the spacecraft at burnout. (Geodetic or Geocentric) |
Azimuth |
Specify the azimuth of the launch trajectory. This is the angle defining the launch direction, measured from north toward east. (Launch Az / Alt or Launch Az / Radius) |
Downrange Dist |
Specify the downrange distance of the spacecraft from launch at burnout. This is the distance along a great arc from the launch location to the burnout subsatellite point. (Launch Az / Alt or Launch Az / Radius) |
Radius/Altitude | Specify the radius (Geocentric or Launch Az / Radius) or altitude (Geodetic or Launch Az / Alt) of the spacecraft at burnout. |
Burnout Velocity parameters
The following table describes the parameters used to define burnout velocity:
Field | Description |
---|---|
Burnout Velocity | Select one of the following options for the type of burnout velocity specification:
|
Fixed Velocity | If you selected the Use Fixed Velocity option, specify the velocity magnitude in the fixed frame. |
Inertial Velocity | If you selected the Use Inertial Velocity option, specify the velocity magnitude in the inertial frame. |
Inertial Velocity Azimuth | If you selected the Use Inertial Velocity option, specify the inertial velocity azimuth, which is the angle from the projection of north in the local horizontal plane to the inertial velocity vector, right handed. |
Inertial Horizontal Flight Path Angle | If you selected the Use Inertial Velocity option, specify the inertial horizontal flight path angle, which is the angle from the local horizontal to the inertial velocity vector, positive toward the radius. It is also 90 degrees minus the vertical flight path angle. |
Spacecraft Parameters and Fuel Tank
Use the Spacecraft Parameters and Fuel Tank tabs to manually define the Spacecraft Configuration.
User Variables
Use the User Variables tab to set initial values for user variables defined for the mission.