diff --git a/src/sorcha/ephemeris/__init__.py b/src/sorcha/ephemeris/__init__.py
index 95b04531..47428b31 100644
--- a/src/sorcha/ephemeris/__init__.py
+++ b/src/sorcha/ephemeris/__init__.py
@@ -7,10 +7,6 @@
     create_ecl_to_eq_rotation_matrix,
 )
 from .simulation_data_files import (
-    DATA_FILE_LIST,
-    JPL_PLANETS,
-    JPL_SMALL_BODIES,
-    DE440S,
     make_retriever,
 )
 from .simulation_geometry import (
diff --git a/src/sorcha/ephemeris/simulation_data_files.py b/src/sorcha/ephemeris/simulation_data_files.py
index dddd7697..6184731c 100644
--- a/src/sorcha/ephemeris/simulation_data_files.py
+++ b/src/sorcha/ephemeris/simulation_data_files.py
@@ -1,75 +1,7 @@
 import pooch
 
-# Define variables for the file names
 
-DE440S = "de440s.bsp"
-EARTH_PREDICT = "earth_200101_990827_predict.bpc"
-EARTH_HISTORICAL = "earth_620120_240827.bpc"
-EARTH_HIGH_PRECISION = "earth_latest_high_prec.bpc"
-JPL_PLANETS = "linux_p1550p2650.440"
-JPL_SMALL_BODIES = "sb441-n16.bsp"
-LEAP_SECONDS = "naif0012.tls"
-META_KERNEL = "meta_kernel.txt"
-OBSERVATORY_CODES = "ObsCodes.json"
-OBSERVATORY_CODES_COMPRESSED = "ObsCodes.json.gz"
-ORIENTATION_CONSTANTS = "pck00010.pck"
-
-# Dictionary of filename: url
-URLS = {
-    DE440S: "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/de440s.bsp",
-    EARTH_PREDICT: "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_200101_990827_predict.bpc",
-    EARTH_HISTORICAL: "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_620120_240827.bpc",
-    EARTH_HIGH_PRECISION: "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_latest_high_prec.bpc",
-    JPL_PLANETS: "https://ssd.jpl.nasa.gov/ftp/eph/planets/Linux/de440/linux_p1550p2650.440",
-    JPL_SMALL_BODIES: "https://ssd.jpl.nasa.gov/ftp/eph/small_bodies/asteroids_de441/sb441-n16.bsp",
-    LEAP_SECONDS: "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/lsk/naif0012.tls",
-    OBSERVATORY_CODES_COMPRESSED: "https://minorplanetcenter.net/Extended_Files/obscodes_extended.json.gz",
-    ORIENTATION_CONSTANTS: "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/pck00010.tpc",
-}
-
-# Convenience list of all the file names
-DATA_FILE_LIST = [
-    DE440S,
-    EARTH_PREDICT,
-    EARTH_HISTORICAL,
-    EARTH_HIGH_PRECISION,
-    JPL_PLANETS,
-    JPL_SMALL_BODIES,
-    LEAP_SECONDS,
-    META_KERNEL,
-    OBSERVATORY_CODES,
-    OBSERVATORY_CODES_COMPRESSED,
-    ORIENTATION_CONSTANTS,
-]
-
-# List of files that need to be downloaded
-DATA_FILES_TO_DOWNLOAD = [
-    DE440S,
-    EARTH_PREDICT,
-    EARTH_HISTORICAL,
-    EARTH_HIGH_PRECISION,
-    JPL_PLANETS,
-    JPL_SMALL_BODIES,
-    LEAP_SECONDS,
-    OBSERVATORY_CODES_COMPRESSED,
-    ORIENTATION_CONSTANTS,
-]
-
-# List of kernels ordered from least to most precise - used to assemble META_KERNEL file
-ORDERED_KERNEL_FILES = [
-    LEAP_SECONDS,
-    EARTH_HISTORICAL,
-    EARTH_PREDICT,
-    ORIENTATION_CONSTANTS,
-    DE440S,
-    EARTH_HIGH_PRECISION,
-]
-
-# Default Pooch registry to define which files will be tracked and retrievable
-REGISTRY = {data_file: None for data_file in DATA_FILE_LIST}
-
-
-def make_retriever(directory_path: str = None, registry: dict = REGISTRY) -> pooch.Pooch:
+def make_retriever(auxconfigs, directory_path: str = None) -> pooch.Pooch:
     """Helper function that will create a Pooch object to track and retrieve files.
 
     Parameters
@@ -79,7 +11,8 @@ def make_retriever(directory_path: str = None, registry: dict = REGISTRY) -> poo
     registry : dictionary, optional
         A dictionary of file names to SHA hashes. Generally we'll not use SHA=None
         because the files we're tracking change frequently. Default = REGISTRY
-
+    auxconfigs: dataclass
+        Dataclass of auxiliary configuration file arguments.
     Returns
     -------
     : pooch
@@ -92,7 +25,7 @@ def make_retriever(directory_path: str = None, registry: dict = REGISTRY) -> poo
     return pooch.create(
         path=dir_path,
         base_url="",
-        urls=URLS,
-        registry=registry,
+        urls=auxconfigs.urls,
+        registry=auxconfigs.registry,
         retry_if_failed=25,
     )
diff --git a/src/sorcha/ephemeris/simulation_driver.py b/src/sorcha/ephemeris/simulation_driver.py
index a2a6c984..cb742c92 100644
--- a/src/sorcha/ephemeris/simulation_driver.py
+++ b/src/sorcha/ephemeris/simulation_driver.py
@@ -116,13 +116,13 @@ def create_ephemeris(orbits_df, pointings_df, args, sconfigs):
         ephemeris_csv_filename = os.path.join(args.outpath, args.output_ephemeris_file)
 
     verboselog("Building ASSIST ephemeris object.")
-    ephem, gm_sun, gm_total = create_assist_ephemeris(args)
+    ephem, gm_sun, gm_total = create_assist_ephemeris(args, sconfigs.auxiliary)
     verboselog("Furnishing SPICE kernels.")
-    furnish_spiceypy(args)
+    furnish_spiceypy(args, sconfigs.auxiliary)
     verboselog("Generating ASSIST+REBOUND simulations.")
     sim_dict = generate_simulations(ephem, gm_sun, gm_total, orbits_df, args)
     pixel_dict = defaultdict(list)
-    observatories = Observatory(args)
+    observatories = Observatory(args, sconfigs.auxiliary)
 
     output = StringIO()
     in_memory_csv = writer(output)
diff --git a/src/sorcha/ephemeris/simulation_parsing.py b/src/sorcha/ephemeris/simulation_parsing.py
index ef458e16..d09890f8 100644
--- a/src/sorcha/ephemeris/simulation_parsing.py
+++ b/src/sorcha/ephemeris/simulation_parsing.py
@@ -3,14 +3,9 @@
 import numpy as np
 import spiceypy as spice
 from pooch import Decompress
-
 from sorcha.ephemeris.simulation_constants import RADIUS_EARTH_KM
 from sorcha.ephemeris.simulation_geometry import ecliptic_to_equatorial
-from sorcha.ephemeris.simulation_data_files import (
-    OBSERVATORY_CODES,
-    OBSERVATORY_CODES_COMPRESSED,
-    make_retriever,
-)
+from sorcha.ephemeris.simulation_data_files import make_retriever
 from sorcha.ephemeris.orbit_conversion_utilities import universal_cartesian
 
 
@@ -134,7 +129,7 @@ class Observatory:
     Class containing various utility tools related to the calculation of the observatory position
     """
 
-    def __init__(self, args, oc_file=OBSERVATORY_CODES):
+    def __init__(self, args, auxconfigs, oc_file=None):
         """
         Initialization method
 
@@ -142,22 +137,25 @@ def __init__(self, args, oc_file=OBSERVATORY_CODES):
         ----------
             args : dictionary or `sorchaArguments` object
                 dictionary of command-line arguments.
+            auxconfigs: dataclass
+                Dataclass of configuration file arguments.
             oc_file : str
                 Path for the file with observatory codes
         """
         self.observatoryPositionCache = {}  # previously calculated positions to speed up the process
 
-        if oc_file == OBSERVATORY_CODES:
-            retriever = make_retriever(args.ar_data_file_path)
+        if oc_file == None:
+            retriever = make_retriever(auxconfigs, args.ar_data_file_path)
 
             # is the file available locally, if so, return the full path
-            if os.path.isfile(os.path.join(retriever.abspath, OBSERVATORY_CODES)):
-                obs_file_path = retriever.fetch(OBSERVATORY_CODES)
+            if os.path.isfile(os.path.join(retriever.abspath, auxconfigs.observatory_codes)):
+                obs_file_path = retriever.fetch(auxconfigs.observatory_codes)
 
             # if the file is not local, download, and decompress it, then return the path.
             else:
                 obs_file_path = retriever.fetch(
-                    OBSERVATORY_CODES_COMPRESSED, processor=Decompress(name=OBSERVATORY_CODES)
+                    auxconfigs.observatory_codes_compressed,
+                    processor=Decompress(name=auxconfigs.observatory_codes),
                 )
 
         else:
diff --git a/src/sorcha/ephemeris/simulation_setup.py b/src/sorcha/ephemeris/simulation_setup.py
index 3a21782c..6a75d396 100644
--- a/src/sorcha/ephemeris/simulation_setup.py
+++ b/src/sorcha/ephemeris/simulation_setup.py
@@ -11,13 +11,7 @@
 import numpy as np
 
 from sorcha.ephemeris.simulation_constants import *
-from sorcha.ephemeris.simulation_data_files import (
-    make_retriever,
-    JPL_PLANETS,
-    JPL_SMALL_BODIES,
-    META_KERNEL,
-    ORDERED_KERNEL_FILES,
-)
+from sorcha.ephemeris.simulation_data_files import make_retriever
 
 from sorcha.ephemeris.simulation_geometry import (
     barycentricObservatoryRates,
@@ -32,9 +26,12 @@
 from sorcha.utilities.generate_meta_kernel import build_meta_kernel_file
 
 
-def create_assist_ephemeris(args) -> tuple:
+def create_assist_ephemeris(args, auxconfigs) -> tuple:
     """Build the ASSIST ephemeris object
-
+    Parameter
+    ---------
+    auxconfigs: dataclass
+        Dataclass of auxiliary configuration file arguments.
     Returns
     ---------
     Ephem : ASSIST ephemeris obejct
@@ -46,9 +43,9 @@ def create_assist_ephemeris(args) -> tuple:
     """
     pplogger = logging.getLogger(__name__)
 
-    retriever = make_retriever(args.ar_data_file_path)
-    planets_file_path = retriever.fetch(JPL_PLANETS)
-    small_bodies_file_path = retriever.fetch(JPL_SMALL_BODIES)
+    retriever = make_retriever(auxconfigs, args.ar_data_file_path)
+    planets_file_path = retriever.fetch(auxconfigs.jpl_planets)
+    small_bodies_file_path = retriever.fetch(auxconfigs.jpl_small_bodies)
     ephem = Ephem(planets_path=planets_file_path, asteroids_path=small_bodies_file_path)
     gm_sun = ephem.get_particle("Sun", 0).m
     gm_total = sum(sorted([ephem.get_particle(i, 0).m for i in range(27)]))
@@ -59,27 +56,31 @@ def create_assist_ephemeris(args) -> tuple:
     return ephem, gm_sun, gm_total
 
 
-def furnish_spiceypy(args):
+def furnish_spiceypy(args, auxconfigs):
     """
     Builds the SPICE kernel, downloading the required files if needed
+    Parameters
+    -----------
+    auxconfigs: dataclass
+        Dataclass of auxiliary configuration file arguments.
     """
     # The goal here would be to download the spice kernel files (if needed)
     # Then call spice.furnish(<filename>) on each of those files.
 
     pplogger = logging.getLogger(__name__)
 
-    retriever = make_retriever(args.ar_data_file_path)
+    retriever = make_retriever(auxconfigs, args.ar_data_file_path)
 
-    for kernel_file in ORDERED_KERNEL_FILES:
+    for kernel_file in auxconfigs.ordered_kernel_files:
         retriever.fetch(kernel_file)
 
     # check if the META_KERNEL file exists. If it doesn't exist, create it.
-    if not os.path.exists(os.path.join(retriever.abspath, META_KERNEL)):
-        build_meta_kernel_file(retriever)
+    if not os.path.exists(os.path.join(retriever.abspath, auxconfigs.meta_kernel)):
+        build_meta_kernel_file(auxconfigs, retriever)
 
     # try to get the META_KERNEL file. If it's not there, error out.
     try:
-        meta_kernel = retriever.fetch(META_KERNEL)
+        meta_kernel = retriever.fetch(auxconfigs.meta_kernel)
     except ValueError:
         pplogger.error(
             "ERROR: furnish_spiceypy: Must create meta_kernel.txt by running `bootstrap_sorcha_data_files` on the command line."
@@ -181,11 +182,11 @@ def precompute_pointing_information(pointings_df, args, sconfigs):
     pointings_df : pandas dataframe
         The original dataframe with several additional columns of precomputed values.
     """
-    ephem, _, _ = create_assist_ephemeris(args)
+    ephem, _, _ = create_assist_ephemeris(args, sconfigs.auxiliary)
 
-    furnish_spiceypy(args)
+    furnish_spiceypy(args, sconfigs.auxiliary)
     obsCode = sconfigs.simulation.ar_obs_code
-    observatories = Observatory(args)
+    observatories = Observatory(args, sconfigs.auxiliary)
 
     # vectorize the calculation to get x,y,z vector from ra/dec
     vectors = ra_dec2vec(
diff --git a/src/sorcha/utilities/generate_meta_kernel.py b/src/sorcha/utilities/generate_meta_kernel.py
index 45a5d34a..c38a92c4 100644
--- a/src/sorcha/utilities/generate_meta_kernel.py
+++ b/src/sorcha/utilities/generate_meta_kernel.py
@@ -1,10 +1,6 @@
 import os
 import pooch
 
-from sorcha.ephemeris.simulation_data_files import (
-    META_KERNEL,
-    ORDERED_KERNEL_FILES,
-)
 
 """
     An example output from running `build_meta_kernel_file` might look like
@@ -29,7 +25,7 @@
 """
 
 
-def build_meta_kernel_file(retriever: pooch.Pooch) -> None:
+def build_meta_kernel_file(auxconfigs, retriever: pooch.Pooch) -> None:
     """Builds a specific text file that will be fed into `spiceypy` that defines
     the list of spice kernel to load, as well as the order to load them.
 
@@ -37,13 +33,14 @@ def build_meta_kernel_file(retriever: pooch.Pooch) -> None:
     ----------
     retriever : pooch
         Pooch object that maintains the registry of files to download
-
+    auxconfigs: dataclass
+        Dataclass of auxiliary configuration file arguments.
     Returns
     ---------
     None
     """
     # build meta_kernel file path
-    meta_kernel_file_path = os.path.join(retriever.abspath, META_KERNEL)
+    meta_kernel_file_path = os.path.join(retriever.abspath, auxconfigs.meta_kernel)
 
     # build a meta_kernel.txt file
     with open(meta_kernel_file_path, "w") as meta_file:
@@ -51,7 +48,7 @@ def build_meta_kernel_file(retriever: pooch.Pooch) -> None:
         meta_file.write(f"PATH_VALUES = ('{retriever.abspath}')\n\n")
         meta_file.write("PATH_SYMBOLS = ('A')\n\n")
         meta_file.write("KERNELS_TO_LOAD=(\n")
-        for file_name in ORDERED_KERNEL_FILES:
+        for file_name in auxconfigs.ordered_kernel_files:
             shortened_file_name = _build_file_name(retriever.abspath, retriever.fetch(file_name))
             meta_file.write(f"    '{shortened_file_name}',\n")
         meta_file.write(")\n\n")
diff --git a/src/sorcha/utilities/retrieve_ephemeris_data_files.py b/src/sorcha/utilities/retrieve_ephemeris_data_files.py
index 85d06a3a..9696c0d5 100644
--- a/src/sorcha/utilities/retrieve_ephemeris_data_files.py
+++ b/src/sorcha/utilities/retrieve_ephemeris_data_files.py
@@ -4,11 +4,7 @@
 import pooch
 
 from functools import partial
-from sorcha.ephemeris.simulation_data_files import (
-    make_retriever,
-    DATA_FILES_TO_DOWNLOAD,
-    DATA_FILE_LIST,
-)
+from sorcha.ephemeris.simulation_data_files import make_retriever
 from sorcha.utilities.generate_meta_kernel import build_meta_kernel_file
 
 
@@ -35,7 +31,7 @@ def _decompress(fname, action, pup):  # pragma: no cover
         pooch.Decompress(method="auto", name=os.path.splitext(fname)[0]).__call__(fname, action, pup)
 
 
-def _remove_files(retriever: pooch.Pooch) -> None:  # pragma: no cover
+def _remove_files(auxconfigs, retriever: pooch.Pooch) -> None:  # pragma: no cover
     """Utility to remove all the files tracked by the pooch retriever. This includes
     the decompressed ObservatoryCodes.json file as well as the META_KERNEL file
     that are created after downloading the files in the DATA_FILES_TO_DOWNLOAD
@@ -45,9 +41,11 @@ def _remove_files(retriever: pooch.Pooch) -> None:  # pragma: no cover
     ------------
     retriever : pooch
         Pooch object that maintains the registry of files to download.
+    auxconfigs: dataclass
+        Dataclass of auxiliary configuration file arguments.
     """
 
-    for file_name in DATA_FILE_LIST:
+    for file_name in auxconfigs.data_file_list:
         file_path = retriever.fetch(file_name)
         print(f"Deleting file: {file_path}")
         os.remove(file_path)
diff --git a/src/sorcha/utilities/sorchaConfigs.py b/src/sorcha/utilities/sorchaConfigs.py
index 40ee694f..5730a71f 100644
--- a/src/sorcha/utilities/sorchaConfigs.py
+++ b/src/sorcha/utilities/sorchaConfigs.py
@@ -780,6 +780,201 @@ def _validate_expert_configs(self):
         self.vignetting_on = cast_as_bool_or_set_default(self.vignetting_on, "vignetting_on", True)
 
 
+@dataclass
+class auxiliaryConfigs:
+    de440s: str = "de440s.bsp"
+    """filename of de440s"""
+    de440s_url: str = "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/de440s.bsp"
+    """url for de4440s"""
+
+    earth_predict: str = "earth_200101_990827_predict.bpc"
+    """filename of earth_predict"""
+    earth_predict_url: str = (
+        "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_200101_990827_predict.bpc"
+    )
+    """url for earth_predict"""
+
+    earth_historical: str = "earth_620120_240827.bpc"
+    """filename of earth_histoical"""
+    earth_historical_url: str = (
+        "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_620120_240827.bpc"
+    )
+    """url for earth_historical"""
+
+    earth_high_precision: str = "earth_latest_high_prec.bpc"
+    """filename of earth_high_precision"""
+    earth_high_precision_url: str = (
+        "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_latest_high_prec.bpc"
+    )
+    """url of earth_high_precision"""
+
+    jpl_planets: str = "linux_p1550p2650.440"
+    """filename of jpl_planets"""
+    jpl_planets_url: str = "https://ssd.jpl.nasa.gov/ftp/eph/planets/Linux/de440/linux_p1550p2650.440"
+    """url of jpl_planets"""
+
+    jpl_small_bodies: str = "sb441-n16.bsp"
+    """filename of jpl_small_bodies"""
+    jpl_small_bodies_url: str = "https://ssd.jpl.nasa.gov/ftp/eph/small_bodies/asteroids_de441/sb441-n16.bsp"
+    """url of jpl_small_bodies"""
+
+    leap_seconds: str = "naif0012.tls"
+    """filename of leap_seconds"""
+    leap_seconds_url: str = "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/lsk/naif0012.tls"
+    """url of leap_seconds"""
+
+    meta_kernel: str = "meta_kernel.txt"
+    """filename of meta_kernal"""
+
+    observatory_codes: str = "ObsCodes.json"
+    """filename of observatory_codes"""
+
+    observatory_codes_compressed: str = "ObsCodes.json.gz"
+    """filename of observatory_codes_compressed"""
+    observatory_codes_compressed_url: str = (
+        "https://minorplanetcenter.net/Extended_Files/obscodes_extended.json.gz"
+    )
+    """url of observatory_codes_compressed"""
+
+    orientation_constants: str = "pck00010.pck"
+    """filename of observatory_constants"""
+    orientation_constants_url: str = "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/pck00010.tpc"
+    """url of observatory_constants"""
+
+    data_file_list: list = None
+    """convenience list of all the file names"""
+
+    urls: dict = None
+    """dictionary of filename: url"""
+
+    data_files_to_download: list = None
+    """list of files that need to be downloaded"""
+
+    ordered_kernel_files: list = None
+    """list of kernels ordered from least to most precise - used to assemble meta_kernel file"""
+
+    registry: list = None
+    """Default Pooch registry to define which files will be tracked and retrievable"""
+
+    @property
+    def default_url(self):
+        """returns a dictionary of the default urls used in this version of sorcha"""
+        return {
+            "de440s": self.__class__.de440s_url,
+            "earth_predict": self.__class__.earth_predict_url,
+            "earth_historical": self.__class__.earth_historical_url,
+            "earth_high_precision": self.__class__.earth_high_precision_url,
+            "jpl_planets": self.__class__.jpl_planets_url,
+            "jpl_small_bodies": self.__class__.jpl_small_bodies_url,
+            "leap_seconds": self.__class__.leap_seconds_url,
+            "observatory_codes_compressed": self.__class__.observatory_codes_compressed_url,
+            "orientation_constants": self.__class__.orientation_constants_url,
+        }
+
+    @property
+    def default_filenames(self):
+        """returns a dictionary of the default filenames used in this version"""
+        return {
+            "de440s": self.__class__.de440s,
+            "earth_predict": self.__class__.earth_predict,
+            "earth_historical": self.__class__.earth_historical,
+            "earth_high_precision": self.__class__.earth_high_precision,
+            "jpl_planets": self.__class__.jpl_planets,
+            "jpl_small_bodies": self.__class__.jpl_small_bodies,
+            "leap_seconds": self.__class__.leap_seconds,
+            "meta_kernel": self.__class__.meta_kernel,
+            "observatory_codes": self.__class__.observatory_codes,
+            "observatory_codes_compressed": self.__class__.observatory_codes_compressed,
+            "orientation_constants": self.__class__.orientation_constants,
+        }
+
+    def __post_init__(self):
+        """Automagically validates the auxiliary configs after initialisation."""
+        self._create_lists_auxiliary_configs()
+        self._validate_auxiliary_configs()
+
+    def _validate_auxiliary_configs(self):
+        """
+        validates the auxililary config attributes after initialisation.
+        """
+        for file in self.default_filenames:
+            if file != "meta_kernel" and file != "observatory_codes":
+                if (
+                    self.default_filenames[file] == getattr(self, file)
+                    and getattr(self, file + "_url") != self.default_url[file]
+                ):
+                    logging.error(f"ERROR: url for {file} given but filename for {file} not given")
+                    sys.exit(f"ERROR: url for {file} given but filename for {file} not given")
+
+                elif (
+                    self.default_filenames[file] != getattr(self, file)
+                    and getattr(self, file + "_url") == self.default_url[file]
+                ):
+                    setattr(self, file + "_url", None)
+
+    def _create_lists_auxiliary_configs(self):
+        """
+        creates lists of the auxililary config attributes after initialisation.
+
+        Parameters
+        -----------
+        None.
+
+        Returns
+        ----------
+        None
+        """
+
+        self.urls = {
+            self.de440s: self.de440s_url,
+            self.earth_predict: self.earth_predict_url,
+            self.earth_historical: self.earth_historical_url,
+            self.earth_high_precision: self.earth_high_precision_url,
+            self.jpl_planets: self.jpl_planets_url,
+            self.jpl_small_bodies: self.jpl_small_bodies_url,
+            self.leap_seconds: self.leap_seconds_url,
+            self.observatory_codes_compressed: self.observatory_codes_compressed_url,
+            self.orientation_constants: self.orientation_constants_url,
+        }
+
+        self.data_file_list = [
+            self.de440s,
+            self.earth_predict,
+            self.earth_historical,
+            self.earth_high_precision,
+            self.jpl_planets,
+            self.jpl_small_bodies,
+            self.leap_seconds,
+            self.meta_kernel,
+            self.observatory_codes,
+            self.observatory_codes_compressed,
+            self.orientation_constants,
+        ]
+
+        self.data_files_to_download = [
+            self.de440s,
+            self.earth_predict,
+            self.earth_historical,
+            self.earth_high_precision,
+            self.jpl_planets,
+            self.jpl_small_bodies,
+            self.leap_seconds,
+            self.observatory_codes_compressed,
+            self.orientation_constants,
+        ]
+
+        self.ordered_kernel_files = [
+            self.leap_seconds,
+            self.earth_historical,
+            self.earth_predict,
+            self.orientation_constants,
+            self.de440s,
+            self.earth_high_precision,
+        ]
+
+        self.registry = {data_file: None for data_file in self.data_file_list}
+
+
 @dataclass
 class sorchaConfigs:
     """Dataclass which stores configuration file keywords in dataclasses."""
@@ -820,6 +1015,9 @@ class sorchaConfigs:
     expert: expertConfigs = None
     """expertConfigs dataclass which stores the keywords from the EXPERT section of the config file."""
 
+    auxiliary: auxiliaryConfigs = None
+    """auxiliaryConfigs dataclass which stores the keywords from the AUXILIARY section of the config file."""
+
     pplogger: None = None
     """The Python logger instance"""
 
@@ -873,6 +1071,7 @@ def _read_configs_from_object(self, config_object):
             "LIGHTCURVE": lightcurveConfigs,
             "ACTIVITY": activityConfigs,
             "EXPERT": expertConfigs,
+            "AUXILIARY": auxiliaryConfigs,
         }
         # when adding new sections in config file this general function needs the name of the section in uppercase
         # to be the same as the attributes defined above in lowercase e.g. section INPUT has attribute input
@@ -1160,7 +1359,7 @@ def PrintConfigsToLog(sconfigs, cmd_args):
 
     if sconfigs.activity.comet_activity == "comet":
         pplogger.info("Cometary activity set to: " + str(sconfigs.activity.comet_activity))
-    elif sconfigs.activity.comet_activity == "none":
+    elif sconfigs.activity.comet_activity == None:
         pplogger.info("No cometary activity selected.")
 
     pplogger.info("Format of ephemerides file is: " + sconfigs.input.eph_format)
diff --git a/src/sorcha_cmdline/bootstrap.py b/src/sorcha_cmdline/bootstrap.py
index 43c34cf5..0a566140 100644
--- a/src/sorcha_cmdline/bootstrap.py
+++ b/src/sorcha_cmdline/bootstrap.py
@@ -41,8 +41,6 @@ def execute(args):
     #
     from sorcha.utilities.retrieve_ephemeris_data_files import (
         make_retriever,
-        DATA_FILE_LIST,
-        DATA_FILES_TO_DOWNLOAD,
         _check_for_existing_files,
         _decompress,
         _remove_files,
@@ -50,17 +48,22 @@ def execute(args):
     )
     from functools import partial
     import concurrent.futures
+    from sorcha.utilities.sorchaConfigs import auxiliaryConfigs
 
+    # Bootstrap will always take the default filenames and urls (stored in auxiliaryConfigs) for the current version of sorcha.
+    # A user can download new files by running sorcha and specifying in the config file under the section [AUXILIARY] a new filename and url.
+
+    default_files = auxiliaryConfigs()
     # create the Pooch retriever that tracks and retrieves the requested files
-    retriever = make_retriever(args.cache)
+    retriever = make_retriever(default_files, args.cache)
 
     # determine if we should attempt to download or create any files.
     found_all_files = False
     if args.force:
-        _remove_files(retriever)
+        _remove_files(default_files, retriever)
     else:
         print("Checking cache for existing files.")
-        found_all_files = _check_for_existing_files(retriever, DATA_FILE_LIST)
+        found_all_files = _check_for_existing_files(retriever, default_files.data_file_list)
 
     if not found_all_files:
         # create a partial function of `Pooch.fetch` including the `_decompress` method
@@ -68,13 +71,13 @@ def execute(args):
 
         # download the data files in parallel
         with concurrent.futures.ThreadPoolExecutor() as executor:
-            executor.map(fetch_partial, DATA_FILES_TO_DOWNLOAD)
+            executor.map(fetch_partial, default_files.data_files_to_download)
 
         # build the meta_kernel.txt file
-        build_meta_kernel_file(retriever)
+        build_meta_kernel_file(default_files, retriever)
 
         print("Checking cache after attempting to download and create files.")
-        _check_for_existing_files(retriever, DATA_FILE_LIST)
+        _check_for_existing_files(retriever, default_files.data_file_list)
 
 
 if __name__ == "__main__":
diff --git a/tests/ephemeris/test_pixdict.py b/tests/ephemeris/test_pixdict.py
index af8f717b..ffe036f1 100644
--- a/tests/ephemeris/test_pixdict.py
+++ b/tests/ephemeris/test_pixdict.py
@@ -80,11 +80,11 @@ def test_pixeldict(tmp_path):
     filterpointing = precompute_pointing_information(filterpointing, args, configs)
     args = sorchaArguments(cmd_args_dict)
 
-    ephem, gm_sun, gm_total = create_assist_ephemeris(args)
-    furnish_spiceypy(args)
+    ephem, gm_sun, gm_total = create_assist_ephemeris(args,configs.auxiliary)
+    furnish_spiceypy(args,configs.auxiliary)
 
     sim_dict = generate_simulations(ephem, gm_sun, gm_total, orbits_df, args)
-    observatory = Observatory(args=None, oc_file=get_test_filepath("ObsCodes_test.json"))
+    observatory = Observatory(auxconfigs=configs.auxiliary,args=None, oc_file=get_test_filepath("ObsCodes_test.json"))
 
     pixdict = PixelDict(54800.0 + 2400000.5, sim_dict, ephem, "Z20", observatory, picket_interval=1, nside=32)
 
diff --git a/tests/ephemeris/test_simulation_parsing.py b/tests/ephemeris/test_simulation_parsing.py
index 73807347..a136e784 100644
--- a/tests/ephemeris/test_simulation_parsing.py
+++ b/tests/ephemeris/test_simulation_parsing.py
@@ -2,10 +2,11 @@
 import numpy as np
 import sorcha.ephemeris.simulation_parsing as sp
 from sorcha.utilities.dataUtilitiesForTests import get_test_filepath
-
+from sorcha.utilities.sorchaConfigs import sorchaConfigs, auxiliaryConfigs
 
 def test_observatory_compared_to_original():
-    observatory = sp.Observatory(args=None, oc_file=get_test_filepath("ObsCodes_test.json"))
+    auxconfigs = auxiliaryConfigs()
+    observatory = sp.Observatory(auxconfigs=auxconfigs,args=None, oc_file=get_test_filepath("ObsCodes_test.json"))
     obs = observatory.ObservatoryXYZ
 
     # Reference tuples were taken from Matt Holman's original notebook
@@ -17,7 +18,8 @@ def test_observatory_compared_to_original():
 
 
 def test_observatory_for_moving_observatories():
-    observatory = sp.Observatory(args=None, oc_file=get_test_filepath("ObsCodes_test.json"))
+    auxconfigs = auxiliaryConfigs()
+    observatory = sp.Observatory(auxconfigs=auxconfigs,args=None, oc_file=get_test_filepath("ObsCodes_test.json"))
     obs = observatory.ObservatoryXYZ
 
     assert obs["250"] == (None, None, None)
diff --git a/tests/sorcha/test_sorchaConfigs.py b/tests/sorcha/test_sorchaConfigs.py
index a6a2f254..7007582d 100644
--- a/tests/sorcha/test_sorchaConfigs.py
+++ b/tests/sorcha/test_sorchaConfigs.py
@@ -17,6 +17,7 @@
     lightcurveConfigs,
     activityConfigs,
     expertConfigs,
+    auxiliaryConfigs,
 )
 
 # these are the results we expect from sorcha_config_demo.ini
@@ -103,6 +104,31 @@
     "randomization_on": True,
     "vignetting_on": True,
 }
+
+correct_auxciliary_URLs = {
+    "de440s.bsp": "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/de440s.bsp",
+    "earth_200101_990827_predict.bpc": "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_200101_990827_predict.bpc",
+    "earth_620120_240827.bpc": "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_620120_240827.bpc",
+    "earth_latest_high_prec.bpc": "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_latest_high_prec.bpc",
+    "linux_p1550p2650.440": "https://ssd.jpl.nasa.gov/ftp/eph/planets/Linux/de440/linux_p1550p2650.440",
+    "sb441-n16.bsp": "https://ssd.jpl.nasa.gov/ftp/eph/small_bodies/asteroids_de441/sb441-n16.bsp",
+    "naif0012.tls": "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/lsk/naif0012.tls",
+    "ObsCodes.json.gz": "https://minorplanetcenter.net/Extended_Files/obscodes_extended.json.gz",
+    "pck00010.pck": "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/pck00010.tpc",
+}
+correct_auxciliary_filenames = [
+    "de440s.bsp",
+    "earth_200101_990827_predict.bpc",
+    "earth_620120_240827.bpc",
+    "earth_latest_high_prec.bpc",
+    "linux_p1550p2650.440",
+    "sb441-n16.bsp",
+    "naif0012.tls",
+    "meta_kernel.txt",
+    "ObsCodes.json",
+    "ObsCodes.json.gz",
+    "pck00010.pck",
+]
 ##################################################################################################################################
 
 # SORCHA Configs test
@@ -119,8 +145,6 @@ def test_sorchaConfigs():
     # check each section to make sure you get what you expect
     assert correct_inputs == test_configs.input.__dict__
     assert correct_simulation == test_configs.simulation.__dict__
-    print(correct_filters)
-    print(test_configs.filters.__dict__)
     assert correct_filters == test_configs.filters.__dict__
     assert correct_saturation == test_configs.saturation.__dict__
     assert correct_phasecurve == test_configs.phasecurves.__dict__
@@ -131,6 +155,8 @@ def test_sorchaConfigs():
     assert correct_lc_model == test_configs.lightcurve.__dict__
     assert correct_activity == test_configs.activity.__dict__
     assert correct_expert == test_configs.expert.__dict__
+    assert correct_auxciliary_URLs == test_configs.auxiliary.__dict__["urls"]
+    assert correct_auxciliary_filenames == test_configs.auxiliary.__dict__["data_file_list"]
 
 
 ##################################################################################################################################
@@ -986,3 +1012,47 @@ def test_expertConfig_bool(key_name):
         error_text.value.code
         == f"ERROR: expected a bool for config parameter {key_name}. Check value in config file."
     )
+
+
+##################################################################################################################################
+
+# auxiliary config test
+
+
+@pytest.mark.parametrize(
+    "file",
+    [
+        "de440s",
+        "earth_predict",
+        "earth_historical",
+        "jpl_planets",
+        "leap_seconds",
+        "observatory_codes_compressed",
+        "orientation_constants",
+    ],
+)
+def test_auxiliary_config_url_given_filename_not(file):
+
+    aux_configs = {file + "_url": "new_url"}
+    with pytest.raises(SystemExit) as error_text:
+        test_configs = auxiliaryConfigs(**aux_configs)
+    assert error_text.value.code == f"ERROR: url for {file} given but filename for {file} not given"
+
+
+@pytest.mark.parametrize(
+    "file",
+    [
+        "de440s",
+        "earth_predict",
+        "earth_historical",
+        "jpl_planets",
+        "leap_seconds",
+        "observatory_codes_compressed",
+        "orientation_constants",
+    ],
+)
+def test_auxiliary_config_making_url_none(file):
+    aux_configs = {file: "new_filename"}
+
+    test_configs = auxiliaryConfigs(**aux_configs)
+    assert getattr(test_configs, file + "_url") == None