diff --git a/src/sorcha/ephemeris/simulation_driver.py b/src/sorcha/ephemeris/simulation_driver.py
index a008798c..39f1ab8c 100644
--- a/src/sorcha/ephemeris/simulation_driver.py
+++ b/src/sorcha/ephemeris/simulation_driver.py
@@ -122,7 +122,7 @@ def create_ephemeris(orbits_df, pointings_df, args, sconfigs):
     verboselog("Generating ASSIST+REBOUND simulations.")
     sim_dict = generate_simulations(ephem, gm_sun, gm_total, orbits_df, args)
     pixel_dict = defaultdict(list)
-    observatories = Observatory(args, sconfigs)
+    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 930f0803..d09890f8 100644
--- a/src/sorcha/ephemeris/simulation_parsing.py
+++ b/src/sorcha/ephemeris/simulation_parsing.py
@@ -129,7 +129,7 @@ class Observatory:
     Class containing various utility tools related to the calculation of the observatory position
     """
 
-    def __init__(self, args, sconfigs, oc_file=None):
+    def __init__(self, args, auxconfigs, oc_file=None):
         """
         Initialization method
 
@@ -137,7 +137,7 @@ def __init__(self, args, sconfigs, oc_file=None):
         ----------
             args : dictionary or `sorchaArguments` object
                 dictionary of command-line arguments.
-            sconfigs: dataclass
+            auxconfigs: dataclass
                 Dataclass of configuration file arguments.
             oc_file : str
                 Path for the file with observatory codes
@@ -145,17 +145,17 @@ def __init__(self, args, sconfigs, oc_file=None):
         self.observatoryPositionCache = {}  # previously calculated positions to speed up the process
 
         if oc_file == None:
-            retriever = make_retriever(sconfigs.auxiliary, args.ar_data_file_path)
+            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, sconfigs.auxiliary.observatory_codes)):
-                obs_file_path = retriever.fetch(sconfigs.auxiliary.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(
-                    sconfigs.auxiliary.observatory_codes_compressed,
-                    processor=Decompress(name=sconfigs.auxiliary.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 d5522616..e825c869 100644
--- a/src/sorcha/ephemeris/simulation_setup.py
+++ b/src/sorcha/ephemeris/simulation_setup.py
@@ -186,7 +186,7 @@ def precompute_pointing_information(pointings_df, args, sconfigs):
 
     furnish_spiceypy(args, sconfigs)
     obsCode = sconfigs.simulation.ar_obs_code
-    observatories = Observatory(args, sconfigs)
+    observatories = Observatory(args, sconfigs.auxiliary)
 
     # vectorize the calculation to get x,y,z vector from ra/dec
     vectors = ra_dec2vec(
diff --git a/tests/ephemeris/test_pixdict.py b/tests/ephemeris/test_pixdict.py
index 59765441..4c404efb 100644
--- a/tests/ephemeris/test_pixdict.py
+++ b/tests/ephemeris/test_pixdict.py
@@ -84,7 +84,7 @@ def test_pixeldict(tmp_path):
     furnish_spiceypy(args,configs)
 
     sim_dict = generate_simulations(ephem, gm_sun, gm_total, orbits_df, args)
-    observatory = Observatory(sconfigs=configs,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 4d6988f6..a136e784 100644
--- a/tests/ephemeris/test_simulation_parsing.py
+++ b/tests/ephemeris/test_simulation_parsing.py
@@ -5,9 +5,8 @@
 from sorcha.utilities.sorchaConfigs import sorchaConfigs, auxiliaryConfigs
 
 def test_observatory_compared_to_original():
-    sconfigs = sorchaConfigs()
-    sconfigs.auxiliary = auxiliaryConfigs()
-    observatory = sp.Observatory(sconfigs=sconfigs,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
@@ -19,9 +18,8 @@ def test_observatory_compared_to_original():
 
 
 def test_observatory_for_moving_observatories():
-    sconfigs = sorchaConfigs()
-    sconfigs.auxiliary = auxiliaryConfigs()
-    observatory = sp.Observatory(sconfigs=sconfigs,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)