SPICEKernels.jl

Fetch NASA's generic SPICE kernels from within Julia!

Installation

Choose one of the following!

pkg> add SPICEKernels

import Pkg
Pkg.add("SPICEKernels")

Overview

SPICEKernels.jl provides a simple interface for downloading, caching, and inspecting all of NASA's publicly available Generic Kernels. A continuous integration pipeline is used to check NASA's HTTP server every week, and any changes to the names of the available kernels result in a new patch version of this package. The point is, if you're using this package, a simple Pkg.update() ensures that all of the kernel links are up-to-date and working, and all of the kernel docstrings accurately describe their contents. Each kernel can be called like a function, i.e. de440s(); this returns a path to the kernel file, downloading it from NASA's server if necessary. As a result, you can pass each kernel right to SPICE.jl's furnsh function for loading into the local kernel pool.

using SPICE, SPICEKernels

furnsh(
    de440s(),                   # position and velocity data for major solar system bodies
    latest_leapseconds_lsk(),   # timekeeping, parsing epochs
    gm_de440(),                 # mass parameters for major solar system bodies
    pck00011(),                 # physical properties of major solar system bodies
)

Features

As mentioned above, each kernel can be downloaded, cached, and inspected for the expected kernel contents.

Kernel Fetching

Each kernel is represented as an instance of a SPICEKernels.SPICEKernel subtype. All kernel types are callable, so you can call them like a function to download (if not previously cached) the kernel file and return a path to the local file. By default, all kernels are cached to Julia's scratchspace: see SPICEKernels.SPICE_KERNEL_DIR. You can override this behavior with the ignorecache keyword argument. You can copy the fetched ephemeris file to a new location by using the directory keyword argument.

You can download kernels from other locations, both local and remote, by using the fetchkernel function; internally, each kernel type is calling this function! So, while this package only provides instances for NASA's generic kernels, you can download any SPICE kernel that is accessible through a link. If you prefer to keep the kernel as a type for clarity in your code, you can construct your own kernels through the kernel function.

Inspection

During the kernel-updating continuous integration pipeline, SPICE Toolkit executables are used to attempt to inspect the contents of each kernel. The file size, SPICE executable output, and the date of the inspection are all provided (most) kernels' docstrings. If you're wondering what ephemeris file to download, check the docstrings! For example, see the output below, which was produced using v1.0 of this package.

help?> ?de440s
search: de440s de440 gm_de440 moon_de440_220930 moon_pa_de440_200625

  A SPK kernel of size 31.2 MB, linked from https://naif.jpl.nasa.gov [1]. Calling
  this variable like a function will return a path to the file, downloading to
  scratchspace if necessary.

  Extended Help
  ≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡

  This kernel's link was sourced on 2023-09-02.

  References
  ============

  [1] https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/de440s.bsp

  Description
  =============


  BRIEF -- Version 4.1.0, September 17, 2021 -- Toolkit Version N0067


  Summary for: de440s.bsp

  Bodies: MERCURY BARYCENTER (1)  SATURN BARYCENTER (6)   MERCURY (199)
          VENUS BARYCENTER (2)    URANUS BARYCENTER (7)   VENUS (299)
          EARTH BARYCENTER (3)    NEPTUNE BARYCENTER (8)  MOON (301)
          MARS BARYCENTER (4)     PLUTO BARYCENTER (9)    EARTH (399)
          JUPITER BARYCENTER (5)  SUN (10)
          Start of Interval (ET)              End of Interval (ET)
          -----------------------------       -----------------------------
          1849 DEC 26 00:00:00.000            2150 JAN 22 00:00:00.000