STK ASTROGATOR
Astrogator is used for interactive
spacecraft maneuvers and trajectory design.
Mission Control Sequence
The Mission Control Sequence (MCS)
defines your overall space mission.
The MCS functions as a graphicalprogramming language, in which
mission segments dictate how
Astrogator calculates the trajectory ofthe spacecraft. Available segments:• Initial State• Launch• Follow• Maneuver• Propagate• Hold• Update• Sequence• Backward
Sequence• Target Sequence• Return• Stop

Maneuvers
Impulsive maneuver. Calculates anew state vector by adding the defineddelta-V vector to the velocity of the final
state of the previous segment, adding
this new state to the ephemeris, andpassing it to the next segment.
Finite maneuver. Effectively a propagate segment with thrust specified byparticular engine and steering models.
Optimal finite maneuver. Collocationbased trajectory optimization mech–anism to produce finite maneuvers withoptimal steering. Option supports lowthrust trajectory optimization problems.

Target Sequence
A Target Sequence is a structuralelement that can be used to define
maneuvers and propagations interms of the goals they are intended
to achieve. Targeting sequences
are controlled through profiles thatcome in three forms: search, segment
configuration, and scripting tool.

High-fidelity orbit
propagation
Astrogator’s flight-proven algorithms
include:• Force models for third-body effect• Solar radiation pressure• Atmospheric drag• Geopotential models• Thermal pressure and albedo• Solid and ocean tides• A broad set of numerical integrators

Search profiles
Search profiles are used to define goals
and modify variables to achieve them.
Differential corrector. The differentialcorrector profile targets specific values,defined as independent variables. Thetarget sequence changes the valueof independent variables as neededto achieve the goal defined by thedependent variables using a rootfinding algorithm:• Newton-Raphson method• Secant method

SNOPT Optimizer. The SNOPT Optimizer search profile uses the general purpose, large-scale, nonlinear programming solver SNOPT (Sparse Nonlinear
OPTimizer) to achieve a certain goal,
represented by a cost function and aset of constraint functions. SNOPT usesa Sequential Quadratic Programming(SQP) algorithm to iteratively modify aset of decision variables or controls tofind a feasible, optimum solution. You
can supply the exhaustive set of SNOPT
algorithm options through the Astrogator interface and access a detailed log
file for post-solution analysis.
IPOPT Optimizer. The IPOPT Optimizer
profile uses the large-scale nonlinear
programming solver IPOPT (InteriorPoint OPTimizer) to minimize or maximize a certain cost function in thepresence of constraints. IPOPT implements an interior-point, line-searchfilter method, and is capable handlingsparse optimization problems with up tomillions of variables and constraints. Youcan supply the exhaustive set of IPOPT
algorithm options through the Astrogator interface and access a detailed log
file for post-solution analysis.
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STK ASTROGATOR
Plugins. You can define plugins to
implement search algorithms that are
not included in Astrogator.

Segment configuration
profilesThese profiles change segments within
the target sequence.
• Change Maneuver Type• Change Propagator• Change Return Segment• Change Stop Segment• Change Stopping Condition State• Run Target Sequence Once• Seed Finite Maneuver

Scripting tool profiles
A scripting profile can function as either:• A search profile• Segment configuration profile
The profile will execute the script it
contains each time that the profile is run.

Automatic sequences
Automatic Sequences can be assigned
to Propagate and Maneuver (Finite)segments, and function as subroutines
by executing in response to specified
stopping conditions of those segments.

Component technology
Astrogator includes a component
browser and editor for selecting andcustomizing:• Calculation objects• Central bodies• Constraints• Custom functions• Engine models• MCS segments• Power sources• Propagator functions• Propagators• Stopping conditions• Thruster sets

You can also:• Create unique components for use inbuilding mission control sequencesusing The Vector Geometry Tool in
STK Analysis Workbench.
• Use components as target and stop
values, and as the basis for reports.

Spacecraft configuration
In an Initial State, Launch, or Follow
segment, you can define the fuel tankand other spacecraft physical values
using the Spacecraft Parameters andFuel Tank tabs.
In addition, most of these properties canbe modified at a later point in the space
mission scenario in an Update segment.

Scripting tool
The Scripting tool is a utility within
Astrogator that allows you to write
scripts in JScript, VBScript, or MATLAB
that will interact with object attributes,
calculation object components, andcustom-defined parameters to perform
a variety of functions to augment thelogic of the Mission Control Sequence.

Design tool library
Lambert Solver. Set initial and final
states based on STK objects or central
bodies, use specialized options todefine departure and arrival conditions,and export an Astrogator sequencebased on the resulting Lambert solution.

Closed-loop maneuvercontrol
Model closed-loop propulsion systems
and maneuver control laws to analyze
missions that include near-field
rendezvous, proximity operations,
station-keeping, planetary landing, andformation flying.
Analyze fuel requirements, thruster
duty cycles, and control-law stability/robustness, among others.

Multiple views of space
missions
View a mission or a mission segmentfrom as many perspectives anddistances as your screen allows.
• Display multiple 3D views of themission.
• View spacecraft trajectories in inertial,
fixed or any user-defined frame.
• Monitor spacecraft during successive
calculation iterations of the targeter in
3D for critical insight into the targeting
solution.

Formation flying
Astrogator models multiple spacecraft
flying in formation, thus permitting
you to analyze and calculate complex
maneuvers that support formationflying activities, such as imaging,satellite maintenance missions, gravity
field determination, and constellation
maintenance.

User variables
Astrogator is capable of incorporating
additional variables during propagate
and finite maneuver segments. WithinAstrogator, these variables are called“user variables” and are defined in theMCS Options window. These variables
are carried through the MCS with therest of the spacecraft state, and are
saved at each time step as part of theephemeris.

Astrogator reports
In addition to Astrogator specific reportstyles available through the Report& Graph Manager, Astrogator cangenerate three special reports thatprovide information about the executionof MCS segments:• MCS Segment Summary• Astrogator Log File
• Differential Corrector Log

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