Added the check_for_empty_orbit_files() method to AsfDaacSlcDownload

This method will iterate over all downloaded orbit files to ensure they have non-zero size, otherwise a RuntimeError is raised.
This is to ensure we fail during the SLC download job, rather than waiting until the SCIFLO job to detect that an empty orbit file was downloaded.
This will make it easier to retry said downloads once a valid orbit file is available.

data_subscriber/asf_slc_download.py

@@ -1,9 +1,11 @@
 
+import glob
 import json
 import netrc
 import os
 from datetime import datetime, timedelta
 from pathlib import PurePath, Path
+from os.path import abspath, getsize, join
 
 import requests
 
@@ -89,6 +91,12 @@ def perform_download(self, session: requests.Session, es_conn, downloads: list[d
 
             self.download_orbit_file(new_dataset_dir, product_filepath)
 
+            # We've observed cases where the orbit file download seems to complete
+            # successfully, but the resulting files are empty, causing the PGE/SAS to crash.
+            # Check for any empty files now, so we can fail during this download job
+            # rather than during the SCIFLO job.
+            self.check_for_empty_orbit_files(new_dataset_dir)
+
             if additional_metadata['processing_mode'] in ("historical", "reprocessing"):
                 self.logger.info(
                     "Processing mode is %s. Attempting to download ionosphere correction file.",
@@ -223,6 +231,20 @@ def download_orbit_file(self, dataset_dir, product_filepath):
 
         self.logger.info("Added orbit file(s) to dataset")
 
+    def check_for_empty_orbit_files(self, dataset_dir):
+        self.logger.info("Checking for empty orbit file downloads within %s", dataset_dir)
+
+        orbit_file_pattern = join(abspath(dataset_dir), "*.EOF")
+
+        for orbit_file_path in glob.iglob(orbit_file_pattern):
+            if getsize(orbit_file_path) == 0:
+                raise RuntimeError(
+                    f"Orbit file {orbit_file_path} was downloaded but empty.\n"
+                    f"This download job will need to be retried once a valid orbit "
+                    f"file is available."
+                )
+        else:
+            self.logger.info("All downloaded orbit files are non-empty")
     def download_ionosphere_file(self, dataset_dir, product_filepath):
         try:
             output_ionosphere_filepath = ionosphere_download.download_ionosphere_correction_file(