Update cosmicrays.py

csst_mci_sim/support/cosmicrays.py

@@ -202,6 +202,9 @@ class cosmicrays():
 
         cr_n = int(5000 * self.exptime / 565. * coveringFraction)
 
+        if cr_n < 1:
+            cr_n = 1
+
         covering = 0.0
 
         while covering < coveringFraction: