Mission Overview
  ================
    The Earth and Sun cross Saturn's ring plane every 13-15 years.
    Because of the orbital characteristics of Saturn and Earth,
    these ring plane crossing (RPX) events can be either triple
    (with Earth crossing the ring plane three times) or single
    (with Earth crossing the ring plane only once).  Single
    crossings generally occur with Saturn very close to solar
    conjunction, and so are difficult to observe from the Earth.
    Triple crossings are generally much more favorable to
    Earth-based observers.
 
    The period around a Saturn RPX enables Earth-based astronomers to
    study a wide range of phenomena not observable at any other
    time.  Direct measurements of ring thickness and vertical ring
    warps become possible.  Precise timing of the crossings make it
    possible to better determine Saturn's rotation pole.  With the
    rings becoming very thin and faint, detections of faint outer
    rings and tiny ring-moons become possible.  Also, satellite
    eclipses, occultations and mutual events during the RPX period
    can be used to refine satellite orbits throughout the Saturn
    system.
 
    A triple RPX occurred in 1995-1996.  Earth passed through the
    plane of Saturn's rings on May 22, 1995, August 10, 1995 and
    February 11, 1996.  Of these events, only the third was
    difficult to observe due to Saturn's proximity to the Sun.  The
    Sun also crossed the ring plane as well, November 17-21, 1995.
    Astronomers carried out a wide range of Saturn observations
    during this period.
 
    The next two Saturn RPXs crossings will be unfavorable from
    Earth: they are both single events occurring on 4 September
    2009 and 23 March 2025.  Earth-based observers will not get a
    favorable edge-on view of Saturn's rings until the triple RPX
    events of 2038-2039.
 
    Although no formal NASA 'mission' was organized for the 1995
    RPX, data acquired for Saturn and its rings and moons were some
    of the best obtained since the Voyager encounters and serve as
    a useful bridge to the upcoming Cassini mission in 2004-2008.
    To foster the combined analysis of data from different sources
    and thereby to maximize the scientific return from this
    'mission', the PDS Rings Node is archiving data from the
    1995-1996 RPX in a series of CDROMs.
 
 
  Mission Phases
  ==============
    Four major events occurred during the Saturn ring plane
    crossing period---three Earth crossings and one Sun crossing.
    The mission phases listed below have been chosen somewhat
    arbitrarily to be centered on these four events, plus the two
    extended periods before and after the crossings.
 
 
    PRE-RPX
    -------
      The pre-RPX phase extended up to the time approximately three
      weeks before Earth's first ring plane crossing.
 
      Spacecraft Id                   : 'N/A'
      Target Name                     : S RINGS, SATURN, MIMAS,
                                        ENCELADUS, TETHYS, DIONE,
                                        RHEA, TITAN, HYPERION,
                                        IAPETUS, PAN, ATLAS,
                                        PROMETHEUS, PANDORA, JANUS,
                                        EPIMETHEUS, HELENE, TELESTO,
                                        CALYPSO
      Mission Phase Start Time        : 1994-01-01
      Mission Phase Stop Time         : 1995-05-01
      Spacecraft Operations Type      : 'N/A'
 
 
    EARTH-RPX-1
    -----------
      The Earth-RPX-1 phase spanned the period around the first
      Earth crossing of Saturn's ring plane, which occurred at
      approximately 5:21 UTC on 22 May 1995.  This was a crossing
      from the north (lit) side to the south (unlit) side.
 
      Spacecraft Id                   : 'N/A'
      Target Name                     : S RINGS, SATURN, MIMAS,
                                        ENCELADUS, TETHYS, DIONE,
                                        RHEA, TITAN, HYPERION,
                                        IAPETUS, PAN, ATLAS,
                                        PROMETHEUS, PANDORA, JANUS,
                                        EPIMETHEUS, HELENE, TELESTO,
                                        CALYPSO
      Mission Phase Start Time        : 1995-05-01
      Mission Phase Stop Time         : 1995-07-01
      Spacecraft Operations Type      : 'N/A'
 
 
    EARTH-RPX-2
    -----------
      The Earth-RPX-2 phase spanned the period around the second
      Earth crossing of Saturn's ring plane, which occurred at
      approximately 20:55 UTC on 10 August 1995.  This was a
      crossing from the south (unlit) side to the north (lit) side.
 
      Spacecraft Id                   : 'N/A'
      Target Name                     : S RINGS, SATURN, MIMAS,
                                        ENCELADUS, TETHYS, DIONE,
                                        RHEA, TITAN, HYPERION,
                                        IAPETUS, PAN, ATLAS,
                                        PROMETHEUS, PANDORA, JANUS,
                                        EPIMETHEUS, HELENE, TELESTO,
                                        CALYPSO
      Mission Phase Start Time        : 1995-07-01
      Mission Phase Stop Time         : 1995-10-01
      Spacecraft Operations Type      : 'N/A'
 
 
    SUN-RPX
    -------
      The Sun-RPX phase spanned the period around the Sun's
      crossing from the north side to the south side of Saturn's
      ring plane, which occurred from approximately 18:15 UTC 17
      November 1995 to 12:00 UTC on 21 November 1995.  At this time
      Earth's viewpoint was approximately 2.6 degrees north of the
      rings.
 
      Spacecraft Id                   : 'N/A'
      Target Name                     : S RINGS, SATURN, MIMAS,
                                        ENCELADUS, TETHYS, DIONE,
                                        RHEA, TITAN, HYPERION,
                                        IAPETUS, PAN, ATLAS,
                                        PROMETHEUS, PANDORA, JANUS,
                                        EPIMETHEUS, HELENE, TELESTO,
                                        CALYPSO
      Mission Phase Start Time        : 1995-10-01
      Mission Phase Stop Time         : 1996-01-01
      Spacecraft Operations Type      : 'N/A'
 
 
    EARTH-RPX-3
    -----------
      The Earth-RPX-3 phase spanned the period around the third and
      final Earth crossing of Saturn's ring plane, which occurred
      at approximately 23:36 UTC on 11 February 1996.  This was a
      crossing from the north (unlit) side to the south (lit) side.
      This period occurred rather close to solar conjunction and so
      was not well observed.
 
      Spacecraft Id                   : 'N/A'
      Target Name                     : S RINGS, SATURN, MIMAS,
                                        ENCELADUS, TETHYS, DIONE,
                                        RHEA, TITAN, HYPERION,
                                        IAPETUS, PAN, ATLAS,
                                        PROMETHEUS, PANDORA, JANUS,
                                        EPIMETHEUS, HELENE, TELESTO,
                                        CALYPSO
      Mission Phase Start Time        : 1996-01-01
      Mission Phase Stop Time         : 1996-03-01
      Spacecraft Operations Type      : 'N/A'
 
 
    POST-RPX
    --------
      The post-RPX phase began shortly after the third Earth
      crossing of Saturn's ring plane.
 
      Spacecraft Id                   : 'N/A'
      Target Name                     : S RINGS, SATURN, MIMAS,
                                        ENCELADUS, TETHYS, DIONE,
                                        RHEA, TITAN, HYPERION,
                                        IAPETUS, PAN, ATLAS,
                                        PROMETHEUS, PANDORA, JANUS,
                                        EPIMETHEUS, HELENE, TELESTO,
                                        CALYPSO
      Mission Phase Start Time        : 1996-03-01
      Mission Phase Stop Time         : 1997-01-01
      Spacecraft Operations Type      : 'N/A'

PDS4 note: awaiting LID references to facilities and telescopes
- ISAAC NEWTON GROUP 4.2-M WILLIAM HERSCHEL TELESCOPE