This is NSSDC's primary  directory for holding spacecraft data
for ftp access.  It is organized primarily by spacecraft series (if
relevant), spacecraft, experiment, data set, time span.  Where judged to
be user effective, some deviations from this standard are made.

This nssdcftp directory structure is currently shared by NSSDC and the 
SPDF (Space Physics Data Facility), which until recently were part of 
the same organization, but are now separate entities, under different 
organizations.

This directory was initially comprised from two distinct sources: data
being moved from NSSDC's NDADS nearline optical disk jukebox environment
and data moved from NSSDC's preexisting anonymous environment on a
computer called nssdc.

Data moved from the VMS NDADS environment have had companion "attribute
files" generated by NSSDC's "DIONAS" software.  Attribute files are
bundled by DIONAS with data files for NSSDC's permanent DLT-jukebox-based
archive, but are held in separate subdirectories in this environment.
These attribute files are further discussed in a separate file in this
high level directory called attribute_files.txt.

Some ASCII or gzipped-ASCII data sets of this overall directory are
graphically browsable and subsettable through ftpbrowser at
http://nssdc.gsfc.nasa.gov/ftphelper/.

The principal spacecraft data ftp-accessible from NSSDC not included in
this spacecraft_data directory are planetary and some other image data
available from the images directory (on a level with this
spacecraft_data directory) and the CDF-formatted (Common Data Format) data 
underlying CDAWeb which are ftp-accessible from 
ftp://cdaweb.gsfc.nasa.gov/pub/istp/. For more informatioin on CDAWeb, see
http://cdaweb.gsfc.nasa.gov/.

NSSDC has much data, still offline, to make ftp-accessible from
this directory.  We welcome your input in our prioritizing data sets for
making network-accessible.  You may find information about spacecraft, 
experiments, and data, for any given spacecraft, at 
http://nssdc.gsfc.nasa.gov/nmc/sc-query.html, or see the NSSDC homepage at
http://nssdc.gsfc.nasa.gov/,
where other services of NSSDC are also described. 
The SPDF homepage can be found at http://spdf.gsfc.nasa.gov. 

JHK, 4/26/02
Updated, HKH, 4/26/2006