Simple Ascent Propagator
The simple ascent propagator creates an ascent trajectory based on launch and insertion parameters. The trajectory is a simple curve rising vertically from the launch pad that turns over smoothly to insert the launch vehicle into orbit with a zero flight path angle at the insertion point using the specified velocity. The propagator models the motion along the path using a cubic polynomial in time, so that the velocity profile is a quadratic polynomial in time, rising from zero to arrive at the end time with the specified burnout velocity.
When the time of flight is short, considering the specified burnout velocity and the path length of the motion, the velocity will become greater than the burnout velocity before the end time and then slow down to arrive at the burnout velocity at the end time. Unreasonably short times of flight may produce speeds during the flight that are greater than escape speed. Such a short time of flight doesn't model actual launches well. On the other hand, if the time of flight is very long, then the quadratic polynomial connecting the start and end times would force the speed just after launch to be negative (i.e., move downward rather than upward), which obviously is not a realistic launch velocity profile. In that case, the propagator holds the vehicle on the pad for a time before lifting off. After liftoff, the propagator models the velocity profile as a quadratic polynomial that starts with zero acceleration. This represents the longest time of flight that it can model with a quadratic polynomial for velocity, meeting the specified launch conditions.
To define the simple ascent propagator:
- Select the SimpleAscent propagator on the Trajectory page.
- If necessary, change Start Time, Stop Time, and Step Size. Use the current scenario time period by clicking the down arrow and selecting Use Scenario Interval.
- Select and define the simple ascent propagator elements.
Simple Ascent propagator elements