# Maneuver Segment

Use a Maneuver segment to model an Impulsive, Finite, or Optimal Finite maneuver.

Select Impulsive, Finite, or Optimal Finite from the Maneuver Type drop-down menu to define the type of maneuver.

You can define unique parameters for all three maneuver types for the same segment, but only the active type is used when running the MCS.

For an Impulsive Maneuver, Astrogator calculates the new state of the spacecraft by adding a Delta-V vector to the final state velocity of the previous segment. This new state is then added to the ephemeris and passed to the next segment.

A Finite Maneuver is effectively a Propagate segment with thrust. It uses the defined propagator to propagate the state, accounting for the acceleration due to thrust. The selected engine model specifies the magnitude of the thrust vector and the selected attitude control specifies the direction of the thrust vector. Like Propagate segments, each calculated point is added to the ephemeris, and propagation continues until Astrogator reaches a stopping condition.

The Optimal Finite Maneuver is fundamentally different from both the Impulsive and Finite Maneuvers. In those maneuvers, you set both the thrust attitude and the thrust magnitude. However, for an Optimal Finite Maneuver, while you select the thrust magnitude, Astrogator computes the thrust attitude and, optionally, the maneuver duration in order to optimize a certain objective function and meet a set of constraints. Additionally, the solution of an Optimal Finite Maneuver problem requires an initial guess. This initial guess is often a rough approximation of the vehicle's orbital states, thrust attitude, and maneuver duration for the maneuver objective in question. The initial guess is then iteratively refined by a numerical optimization library. For additional details, see Maneuver Optimization Using Direct Transcription Methods and Initial Guesses for Finite Maneuver Optimization. For other optimization-related Astrogator features, refer to the SNOPT and IPOPT search profile documentation.

## About thrust vectors

The "thrust vector" describes the direction of acceleration applied to a satellite. This direction is opposite to the exhaust of an engine. For example, for a single chemical rocket engine mounted to a satellite, the thrust vector is opposite to the direction of the center of the exhaust plume flames. If the satellite uses more than one engine together in a thruster set, the thrust vector is along the direction of the combined effective acceleration. This direction is determined by calculating the sum of the acceleration vectors of each individual thruster.