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Planetary Ephemeris

Implement position and velocity of astronomical objects

Library

Environment/Celestial Phenomena

Description

The Planetary Ephemeris block uses Chebyshev coefficients to implement the position and velocity of the target object relative to the specified center object for a given Julian date. The Target parameter specifies an astronomical object. The block implements the ephemerides using the Center parameter for an astronomical object as the reference.

The block uses the Chebyshev coefficients that the NASA Jet Propulsion Laboratory provides.

    Tip   As Julian date input for the block, you can use the Julian Date Conversion block or the Aerospace Toolbox juliandate function to calculate the Julian date. You can also calculate your own Julian date and input it using the Constant block.

This block implements the position and velocity using the International Celestial Reference Frame. If you want the planetary ephemeris position value relative to Earth in Earth-fixed (ECEF) coordinates, use the Direction Cosine Matrix ECI to ECEF block.

Dialog Box

Units

Specify the output units:

Units

Position

Velocity

km,km/s

km

km/s

Au,AU/day

astronomical units (AU)

AU/day

Epoch

Select one of the following:

  • Julian date

    Julian date to implement the position and velocity of the Target object. When this option is selected, the block has one input port.

  • T0 and elapsed Julian time

    Julian date, specified by two block inputs:

    • A fixed starting epoch (T0).

    • Variable elapsed time between T0 and the desired model simulation time.

    T0 plus the variable elapsed time cannot exceed the maximum Julian date for the specified Ephemerides.

Ephemeris model

Select one of the following ephemerides models defined by the Jet Propulsion Laboratory.

Ephemerides ModelDescription

DE405

Released in 1998. This ephemerides takes into account the Julian date range 2305424.50 (December 9, 1599 ) to 2525008.50 (February 20, 2201).

This block implements these ephemerides with respect to the International Celestial Reference Frame version 1.0, adopted in 1998.

DE421

Released in 2008. This ephemerides takes into account the Julian date range 2414992.5 (December 4, 1899) to 2469808.5 (January 2, 2050).

This block implements these ephemerides with respect to the International Celestial Reference Frame version 1.0, adopted in 1998.

DE423

Released in 2010. This ephemerides takes into account the Julian date range 2378480.5 (December 16, 1799) to 2524624.5 (February 1, 2200).

This block implements these ephemerides with respect to the International Celestial Reference Frame version 2.0, adopted in 2010.

    Note:   This block requires that you download ephemeris data with the Support Package Installer. Click the Get data button to start the installer. For more information, see aeroDataPackage.

Center

Select a center body (astronomical object) or reference body as a point of reference for the Target barycenter position and velocity measurement.

Target

Select a target body (astronomical object) or reference body as a point of reference for the barycenter position and velocity measurement.

Action for out of range input

Specify the block behavior when the block inputs are out of range.

ActionDescription

None

No action.

Warning

Warning in the MATLAB® Command Window, model simulation continues.

Error (default)

MATLAB returns an exception, model simulation stops.

Calculate velocity

Select this check box to calculate the velocity of the Target barycenter relative to the Center barycenter and add a second block output.

Inputs and Outputs

InputDimension TypeDescription

First

Scalar

  • Julian date (TJD) (default) — One input. Specify a date between the minimum and maximum Julian date.

  • Fixed Julian date (T0JD) plus the elapsed Julian time (ΔTJD) between the fixed date and the ephemeris time. — Two inputs, where the first input is T0JD and the second input is ΔTJD. ΔTJD must be a positive number. The sum of T0JD and ΔTJD must fall between the minimum and maximum Julian date.

The block Epoch parameter controls the number of block inputs.

See the Ephemerides parameter for the minimum and maximum Julian dates.

Second (Optional)

Scalar

ΔTJD — Elapsed Julian time (ΔTJD) between the fixed date and the ephemeris time. The sum of T0JD and ΔTJD must fall between the minimum and maximum Julian date.

See the Ephemerides parameter for the minimum and maximum Julian dates.

OutputDimension TypeDescription

First

Vector

Barycenter position (XICRF1) of the Target object relative to the barycenter of the Center object. Units are km or astronomical units (AU).

    Tip   This block outputs the barycenter position in Earth-centered inertial (ECI) coordinates. To convert these coordinates to Earth-centered Earth-fixed (ECEF), use the Direction Cosine Matrix ECI to ECEF block.

Second (Optional)

Vector

Velocity (VICRF) of the barycenter of the Target object relative to the barycenter of the Center object. Units are km/s or astronomical units (AU)/day.

Reference

Folkner, W. M., J. G. Williams, D. H. Boggs, "The Planetary and Lunar Ephemeris DE 421," IPN Progress Report 42-178, 2009.

Ma, C. et al., "The International Celestial Reference Frame as Realized by Very Long Baseline Interferometry," Astronomical Journal, Vol. 116, 516–546, 1998.

Vallado, D. A., Fundamentals of Astrodynamics and Applications, McGraw-Hill, New York, 1997.

See Also

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External Web Sites

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