Launch Segment

Launch Parameters | Burnout Parameters

The Launch segment can be used to model a simple spacecraft launch from Earth or another central body. The methodology is similar to that employed by the Simple Ascent propagator for Launch Vehicle and Missile objects. The trajectory that is 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; if a trajectory with the specified flight path angle cannot be computed, a zero flight path angle trajectory will be used with a discontinuity in the last point to give the desired final velocity.

Typically, a launch vehicle manufacturer will supply a mission analyst with an insertion vector in the ECF frame, as well as the time of flight. Using Astrogator's Launch segment, you can then model the launch data received from the manufacturer and vary the launch time to meet other mission requirements.

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 the burnout velocity parameters can be accessed from the burnout section.

The general trajectory parameters of a Launch segment are described in the following table:

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 OK.
Step Size	Specify the time interval between calculated ephemeris output points.
Use State From Previous Segment	Select 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 will become grayed out.
Pre-Launch Time	Specify the amount of time before the spacecraft's launch that it will be created 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: Ellipse: Cubic Motion - the motion is computed on the basis of given positions and velocities. Ellipse: Quartic Motion - the motion is computed on the basis of given positions and velocities and initial acceleration.
Initial Acceleration	If Quartic Motion is selected 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 launch location parameters are described in the following table:

Field	Description
Launch Coordinate Type	Select between: Geocentric (Planetocentric) - the location is measured from the center of mass of the Earth or other central body. Geodetic (Planetodetic) - the location is measured along the normal to the surface of an ellipsoid defined with reference to the Earth (or other central body).
Epoch	Specify the date and time of the launch.
Set Mission Elapsed Time Epoch to Launch Epoch	Select to set the Mission Elapsed Time epoch to the Launch epoch when the MCS is run.
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 Import Facility Location... to open the Facility Database window. STK will not add the facility to the current scenario; it merely 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 Select Facility... to open the Select Facility window; click the desired facility to highlight it and then click OK. This button is only displayed if there is at least one facility in the scenario.

Burnout Parameters

After defining the general and launch location parameters, you must define the location of the burnout point and the burnout velocity.

Burnout

The burnout location parameters are described in the following table:

Field	Description
Burnout Point Definition	Select between: Geocentric (Planetocentric) - the burnout point is measured from the center of mass of the Earth or other central body. Geodetic (Planetodetic) - the burnout point is measured along the normal to the surface of an ellipsoid defined with reference to the Earth (or other central body). Launch Az / Alt - the burnout point is defined in reference to distance downrange along an azimuth, measured from the surface of the Earth or other central body. Launch Az / Radius - the burnout point is defined in reference to distance downrange along an azimuth, measured from the center of mass of the Earth or other central body.
Time of Flight	Specify the time of flight (the time from launch to burnout).
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 towards 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 sub-satellite 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

The parameters used to define burnout velocity are described in the following table:

Field	Description
Burnout Options	Select between: Use Fixed Velocity - the inclination of the final state of the launch segment is determined by the arc between the launch and insertion positions, and the horizontal flight path angle is set to zero. Use Inertial Velocity - the final state of the launch segment is solely and completely determined by the burnout position and velocity.
Fixed Velocity	If the Fixed Velocity option is selected, specify the velocity magnitude in the fixed frame.
Inertial Velocity	If the Inertial Velocity option is selected, specify the velocity magnitude in the inertial frame.
Inertial Velocity Azimuth	If the Inertial Velocity option is selected, specify the inertial velocity azimuth. Inertial velocity azimuth 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 the Inertial Velocity option is selected, specify the inertial horizontal flight path angle. Inertial horizontal flight path angle is the angle from the local horizontal to the inertial velocity vector, positive towards radius. It is also 90 degrees minus vertical flight path angle.

Spacecraft Parameters and Fuel Tank

The Spacecraft Parameters and Fuel Tank tabs can be used to manually define the Spacecraft Configuration.

User Variables

The User Variables tab can be used to set initial values for user variables that have been defined for the mission.