To get a list of updated files in the SPDF archive, download the nightly catalog 
<https://spdf.gsfc.nasa.gov/pub/catalogs/filelist.gz> 
and use the diff command to compare with a previously-saved catalog to 
find changes in the time in between.  See script below.

We also have extensive web services for getting data files, plots, listings, orbits:

CDAWeb <https://cdaweb.gsfc.nasa.gov/WebServices/REST/>
SSCweb <https://sscweb.gsfc.nasa.gov/WebServices/REST/> for orbits

mv spdf.curr spdf.prev
curl "https://spdf.gsfc.nasa.gov/pub/catalogs/filelist.gz" | zcat | sort -k4 > spdf.curr
diff spdf.prev spdf.curr > spdf.diff
egrep "^< " spdf.diff > deleted_files
egrep "^> " spdf.diff > new_files
# to get new files
cat new_files|colrm 1 46|xargs -I{} -t wget "https://spdf.gsfc.nasa.gov/{}"