Calculation Object Components

Calculation objects are components with several uses. There are three general ways in which you can use calculation objects in Astrogator:

Results for target sequence constraints
Elements of reports and graphs
Properties within other components, such as stopping conditions

The calculation objects that are available in Astrogator are in the following table.

Astrogator Calculation Objects

Type	Description
Epoch	This is the epoch of a given state in the Mission Control Sequence (MCS).
Access	This is the access between objects.
Cartesian Elements	These are the X, Y, and Z components of position and velocity vectors.
Cartesian STM	These are the 36 position and velocity state transition matrix elements for use in combination with the State Transition Matrix propagator function. They are valid for Consecutive Propagate segments, Finite Maneuver segments, and Optimal Finite Maneuver segments in the Run Current Nodes mode. They are expressed in Cartesian components, and you can choose the coordinate system. The default is Earth Centered Inertial.
Constants	These are constant values that are accessible to in-line calculation objects and scripting tool scripts. They include gravitational parameter, gravity coefficient, pi, reference radius, and speed of light.
Delaunay Elements	These are Delaunay G, H, L, and Semi-Latus Rectum.
Environment	Includes atmospheric density, pressure, and temperature.
Equinoctial Elements	Includes equinoctial h, k, p, q, and mean longitude.
Formation	These are relative values for use in formation flying.
Geostationary	These are calculations that you can use for geostationary orbits. The longitude drift rate calculation object is computed as: where T is the instantaneous J2 period of the satellite and T_Earth is the rotation period of the Earth. For more information, see the GeoStationary data provider.
Geodetic	Includes latitude, longitude, altitude, height above terrain, latitude rate, longitude rate, and altitude rate.
Ground Track	This is the repeating ground track error to be measured at the equator (as a distance).
Keplerian Elements	These are the classical elements that specify an orbit by its size, shape, and three-dimensional orientation in space.
Maneuver	Includes Delta-V (integrated along orbit path), fuel mass, fuel density, fuel used, inertial V magnitude, inertial Vx, inertial Vy, inertial Vz, specific impulse, tank pressure, tank temperature, thrust vector X, thrust vector Y, thrust vector Z, total mass, and total mass flow rate. DeltaV Squared: Square of DeltaV integrated along path MCS DeltaV: Sum of DeltaV magnitude for all maneuvers in MCS MCS DeltaV Squared: Sum of squares or square of the sum of DeltaV magnitudes for all maneuvers in the MCS
Math	Includes absolute value, difference, maximum value, minimum value, negative, mean value, median value, and standard deviation, as described below: An Absolute Value object expresses the absolute value of the reference calculation object. A Difference object expresses the difference of the reference calculation object between two points in time. The first point is the beginning of the segment where the difference object is placed. The second point is the current time at the end of the segment. A Minimum Value or Maximum Value object expresses the minimum or maximum value — at an ephemeris point within the segment — of the reference calculation object. A Negative object expresses the negative value of the reference calculation object. A Mean Value object expresses the mean or average value of the reference calculation object using all the ephemeris points in the segment. A Median Value object expresses the median value of the reference calculation object using all the ephemeris points in the segment. A Standard Deviation object expresses the population standard deviation of the reference calculation object using all the ephemeris points in the segment.
Mean Elements	These include Kozai-Izsak and Brouwer-Lyddane means.
Multibody	Includesb-plane elements, delta declination, and right ascension, as well as the Jacobi constant for CR3BP propagations.
Other Orbit	These include miscellaneous orbit values such as Beta Angle and Longitude of Periapsis.
Power	Included are internal, processed, and solar array.
Relative Motion	These are the relative values compared to a reference satellite.
SEET	SEET This includes the following space environment components: DamageFlux, DamageMassFlux, GeoMagFieldDipoleL, GeoMagFieldFineLineSeparation, ImpactFlux, ImpactMassFlux, SAAFluxIntensity, and VehicleTemperature.
Scalar	This is a scalar value based on any Calculation component from the Analysis Workbench.
Scripts	These are Custom functions and MATLAB, VBScript, or JScript in-line functions. To use any MATLAB function, you must be able to connect to MATLAB. STK will automatically start a session and connect when required. In-line functions are used for simple computations that are not in the standard catalog of calculation objects. These functions have three attributes: CalcArguments, InlineFunc, andUnitDimension. When you use an in-line calculation object, STK creates a function with the inputs listed in CalcArguments. It returns the value computed by the InlineFunc, with a name derived from the calculation object name.
Segments	A Difference Across Segments object functions as a Difference math object but is calculated relative to another segment. A Difference Across Segments Across Satellites object also functions as a Difference math object but is calculated relative to a segment in the MCS of another Astrogator satellite. A Position Difference Across Segments object calculates the vector magnitude difference between Cartesian positions of the initial (or final) states of two MCS segments. The first segment is the segment that this object belongs to, and the second segment is a reference segment. A Position Velocity Difference Across Segments object calculates the vector magnitude difference between Cartesian positions and velocities of the initial (or final) states of two MCS segments. The first segment is the segment that this object belongs to, and the second segment is a reference segment. A Value at Segment object expresses the initial or final value of a calculation object at a specified segment. A Value at Segment Other Satellite object functions as the Value at Segment object but references a segment in the MCS of another Astrogator satellite. A Velocity Difference Across Segments object calculates the vector magnitude difference between Cartesian velocities of the initial (or final) state of two MCS segments. The first segment is the segment that this object belongs to, and the second segment is a reference segment. Sequence DeltaV: Sum of Delta-V magnitudes for all maneuvers in a sequence Sequence DeltaV Squared: Sum of squares or square of sum of Delta-V magnitudes for all maneuvers in a sequence
Spacecraft Properties	Includes drag, radiation pressure, and solar radiation pressure coefficient and area values of a spacecraft. You can use these objects to report how a propagator plugin changes these values over time. When the value of one these objects changes, Astrogator applies the new value to subsequent propagation steps and segments in the MCS. For built-in models that introduce time-varying areas and coefficients, namely the Variable Area and N-Plate models, the Drag and SRP calculation objects take on particular meanings as described below. Variable Area Drag and SRP models: The DragArea and SRPArea calculation objects reflect the associated areas used for a given time step in the ephemeris as prescribed by the corresponding file(s). Behavior of the Cd and Cr coefficients is unchanged from prior patterns by these models. Astrogator does not back-compute any quantities from the Variable Area Drag and SRP models; it keeps the values for area as per the original input. N-Plate Drag: For reporting purposes, Astrogator computes the DragArea calculation object by taking the "velocity-facing" area at a particular time step. Astrogator back-computes the Cd coefficient calculation object from the acceleration produced by the model only in the direction opposed to the velocity. Although such accounting generally captures the majority of the associated drag effects, neither of these scalar parameters completely reflect the contribution of the N-Plate Drag model to the total acceleration as experienced by the spacecraft under the numerical propagation. Astrogator neglects the perpendicular components in this reporting process. N-Plate SRP: Astrogator produces the SRPArea calculation object as the "Sun-facing" area for a particular ephemeris point. It back-computes the Cr coefficient calculation object only from the acceleration in the direction opposite to the Sun. Such accounting for reporting purposes in these scalar parameters does not capture the entire vector acceleration experienced by the spacecraft during numerical propagation. Unlike the case of a plugin changing the values, the various drag and coefficient values for these built-in models are applicable only for segments in which these models are active. Take the case, for example, where Astrogator propagates three subsequent segments in order. The first and third segments both use the DragArea parameter defined at the MCS level in some Initial State (or Update, etc.) segment. The second segment, between the first and third segments, uses the Variable Area Drag model. No plugins or other methods for changing the DragArea parameter are employed. In such a case, Astrogator will apply the constant MCS-level DragArea value to the first segment. For the second segment, it will use the Variable Area Drag model and report a varying value for DragArea. For the third segment, it will revert to the value of DragArea used in the first segment regardless of the DragArea value in effect at the end of the second segment. The behavior described in the Variable Area Drag model example — reverting parameters when the associated model is not employed — is consistent with how Astrogator reports all of the noted calculation objects for each of the built-in time-varying models described above. It is also consistent with the time of effect for the underlying models when Astrogator computes the full-vector accelerations consistent with constituent parameters (plates, coefficients, etc.). To have any value set by one of these models to persist into a subsequent segment, introduce an Update segment as appropriate. The effective drag and SRP area, as well as the effective Cd and Cr values, will be zero when the satellite altitude is outside the bounds of the density model, nominally -100 km to 2500 km. The effective Cr is also zero when the satellite is in shadow.
Spherical Elements	These are the cosine of vertical FPA, declination, declination rate, flight path angle, R magnitude, right ascension, right ascension rate, magnitude of the velocity vector, and velocity azimuth.
STM Eigenvalues	These are the 12 values that represent the real and complex parts of each of the six eigenvalues of the Cartesian STM. They are valid for the same conditions as the STM. You can choose the coordinate system, with the default being Earth Centered Inertial.
STM Eigenvectors	These are the 72 values that represent the real and complex parts of each of the six eigenvector components within each of the six eigenvectors of the Cartesian STM. They are valid for the same conditions as the STM. You can choose the coordinate system, with the default being Earth Centered Inertial.
Target Vector	This includes C3 energy, incoming and outgoing asymptotes, and other Target Vector elements.
Time	A Durationobject is measured from the satellite's initial epoch for an Astrogator satellite or from the first requested time for a non-Astrogator satellite. A Number of Revolutions object is computed as the duration divided by period. The duration is the same as the Duration calculation object. The period is the instantaneous period, in the mean or osculating sense, computed from the current inertial position and velocity vectors. This value will not always be monotonic.
UserValues	These are user variable values.
Vector	These are miscellaneous geometry objects such as vector components and dot product.