Planetary Ephemeris — Robotics/Celestial Phenomena

Planetary Ephemeris

Robotics / Celestial Phenomena

Where one body is relative to another: the position of Target relative to Center at the input Julian date, in the ICRF frame, and its velocity – read from JPL's Development Ephemeris (the DE file you supply) and evaluated by JPL's own algorithm.

Ports

• JD (TDB) – the Julian date in Barycentric Dynamical Time, [1,1]. A UTC date is about 69 s off.
• position – Target relative to Center, [3,1], ICRF, in km, m or AU by Units.
• velocity – its rate, [3,1], in km/s, m/s or AU/day by Units.

Parameters

• Ephemeris Model – which JPL Development Ephemeris: DE405, DE421, DE423, DE430 or DE432t (default DE405, Simulink's). Each covers its own span of dates.
• Ephemeris Folder – the folder holding JPL's published ASCII files for that model, header.4xx and the asc*.4xx data files, exactly as they download from ssd.jpl.nasa.gov/ftp/eph/planets/ascii/ (for DE432t, name them .432). Absolute, or relative to the project folder. The block reads them once and shares them. ICore ships no ephemeris: you supply the file, as MATLAB's support package does, and the files need cover only the dates you run.
• Center / Target – Sun, Mercury, Venus, Earth, Moon, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, Solar system barycenter or Earth-Moon barycenter; default Earth and Moon.
• Units – km and km/s (default), m and m/s or AU and AU/day. JPL answers km and km/day: km/s divides the rate by 86400, m and m/s multiply by 1000 first, and AU uses the ephemeris's own astronomical unit.
• Use Date Range – Off (default) or On. On, a date outside Start Date..End Date has no answer, as one outside the loaded data has; and an export carries only that range's records, so an export needs it On.
• Start Date / End Date – the range's Julian dates (TDB), default 2458849.5 and 2469807.5 (2020-01-01 and 2050-01-01, Simulink's).
• Action – what a date with no answer does: Error (default) stops the run naming the date; Warning reports it once per run; None says nothing. With Warning and None the outputs are NaN.
• Sampling Time (s) – zero or less inherits the solver's rate; a positive value runs the block at that period.

Notes

• Stateless: each date is answered on its own.
• Simulink's None and Warning actions answer a date outside the data by extending the nearest record's polynomial, measured on R2026a; that is not an ephemeris, and this block answers NaN there instead.

Code export

Python, MATLAB, Java, Rust, C and C++. Each carries only the 32-day records the date range falls in, packed to the coefficients its answer reads, and JPL's own evaluation of them, operation for operation as the block computes it – so Use Date Range must be On, and an export with it Off stops and says so. A date outside the range or the carried records answers NaN: a deployed core cannot stop, so Action Error answers NaN there too. The three HDL targets (VHDL, Verilog, SystemVerilog) and PLC Structured Text are not offered – an export to one of them stops and names this block – because a Julian date (about 2.4 million) cannot sit on a Q16.16 port, whose range ends at ±32768, and the records are thousands of constants.

Simulink bridge

Import and export, mapped to Aerospace Blockset's aerolibcelestial/Planetary Ephemeris: Ephemeris Model ↔ ephemerisModel, Center ↔ center, Target ↔ target, Units ↔ units (km,km/s, m,m/s, AU,AU/day), Use Date Range ↔ useDateRange, Start Date ↔ startDate, End Date ↔ endDate and Action ↔ action, all 1:1. Ephemeris Folder does not cross: Simulink reads MATLAB's support package. epochFormat is always Julian date and outputVelocity always on, because the other settings move Simulink's ports; an import that sets either otherwise is reported. The Simulink block has no SampleTime, so the rate stays on the ICore side.