<h2>Messenger Ephemeris</h2>
 
<UL>

  <li> MESSENGER Ephemeris data are calculated using SPICE kernels taken from the
           <a href="http://naif.jpl.nasa.gov/pub/naif/pds/data/mess-e_v_h-spice-6-v1.0/messsp_1000/data/" TARGET=_BLANK>
            PDS</a> (Planetary Data System).
    <br/><br/>   
    <li> <b>Earth Flyby</b><br/>
     -------------<br/>
       Earth Flyby is defined as the four week (28 day) period centered on closest approach to Earth.<br/><br/>
       Phase Start Time : 2005-07-19 (2005-200)<br/>
       Phase Stop Time  : 2005-08-16 (2005-228)<br/><br/> 
     
     <li>  <b>Venus 1 Flyby</b><br/>
     -------------<br/>
       Venus 1 Flyby is defined as the four week (28 day) 
       period centered on the first of the mission's two 
       closest approaches to Venus.<br/><br/>

       Phase Start Time : 2006-10-10 (2006-283)<br/>
       Phase Stop Time  : 2006-11-07 (2006-311)<br/><br/>

   
    <li>  <b>Venus 2 Flyby</b><br/>
     -------------<br/>
       Venus 2 Flyby is defined as the four week (28 day 
       period centered on the second of the mission's two 
       closest approaches to Venus.<br/><br/>

       Phase Start Time : 2007-05-23 (2007-143)<br/>
       Phase Stop Time  : 2007-06-20 (2007-171)<br/><br/>  

 
   <li>  <b>Mercury 1 Flyby</b><br/>
     -------------<br/>
       Mercury 1 Flyby is defined as the four week (28 day) 
       period centered on the first of the mission's three 
       closest approaches to Mercury.<br/><br/>

       Phase Start Time : 2007-12-31 (2007-365)<br/>
       Phase Stop Time  : 2008-01-28 (2008-028)<br/><br/>
 
   
    <li>  <b>Mercury 2 Flyby</b><br/>
     -------------<br/>
       Mercury 2 Flyby is defined as the four week (28 day) 
       period centered on the second of the mission's three 
       closest approaches to Mercury.<br/><br/>

       Phase Start Time : 2008-09-22 (2008-266)<br/>
       Phase Stop Time  : 2008-10-20 (2008-294)<br/><br/>  

    <li>  <b>Mercury 3 Flyby</b><br/>
     -------------<br/>
       Mercury 3 Flyby is defined as the four week (28 day) 
       period centered on the third of the mission's three 
       closest approaches to Mercury.<br/><br/>

       Phase Start Time : 2009-09-16 (2009-259)<br/>
       Phase Stop Time  : 2009-10-14 (2009-287)<br/><br/> 

   <li> <b>Mercury Orbit</b><br/>
     -------------<br/>
       The Orbit phase begins at Mercury orbit insertion
       and continues until the end of mission. This phase
       begins the most intensive science portion of the mission
       with full instrument utilization throughout the
       period.<br/><br/>

       Phase Start Time : 2011-03-04 (2011-063)<br/><br/> 
      

   <UL> <b>Coordinates :</b> <br/><br/>  
   <li><b>GSE</b> : Geocentric Solar Ecliptic -
         This system has its X axis towards the Sun and its Z axis
         perpendicular to the plane of the Earth's orbit around the
         Sun (positive North). Y completes the right-handed system.
   <li> <b>GSM</b> : Geocentric Solar Magnetospheric -
         This system has its X axis towards the Sun and its Z axis
         is the projection of the Earth's magnetic dipole axis
         (positive North) on to the plane perpendicular to the X
         axis. Y completes the right-handed system.
   <li> <b>VSO</b> : Venus Solar Orbital  - 
      X directed from the center of the planet toward the Sun, 
      Z is normal to the Venus orbital plane and positive toward the north celestial pole, 
      Y is positive in the direction opposite to orbital motion.
    <li> <b>MSO</b> : Mercury-centric Solar Orbital   -  
        the +X-axis points toward the Sun, 
        +Z points northward perpendicular to Mercury's orbit plane, and 
        Y completes the right hand system nominally directed opposite Mercury's orbital velocity around the Sun.
    <li> <b>MSM</b> : Mercury-centric Solar Magnetospheric - 

         This system has its X axis towards the Sun and its Z axis
         is the projection of the Mercury's magnetic dipole axis
         (positive North) on to the plane perpendicular to the X
         axis. Y completes the right-handed system.<br/>

         For now, assume that the position of the magnetic pole is
         coincident with the rotation axis of Mercury, i.e. 90
         degrees latitude and 0 degrees longitude.    
    <li><b>RTN</b> : Radial-Tangential-Normal coordinates - R point from Sun center to the spacecraft, T is formed by the cross product of the solar rotatio axis and R and lies in the solar equatorial plane, N is formed by the cross product of R and T and is the projection of the solar rotational axis on the plane of the sky.
    <li><b>HCI</b>: Heliocentric Inertial Frame -
         All vectors are geometric: no aberration corrections are used.
         The solar rotation axis is the primary vector: the Z axis points
         in the solar north direction.
         The solar ascending node on the ecliptic of J2000 forms the X axis.
         The Y axis is Z cross X, completing the right-handed reference frame.
    <li><b>HEE</b> : Heliocentric Earth Ecliptic Frame -

         All vectors are geometric: no aberration corrections are used.

         The position of the Earth relative to the Sun is the primary vector:
         the X axis points from the Sun to the Earth.

         The northern surface normal to the mean ecliptic of date is the
         secondary vector: the Z axis is the component of this vector
         orthogonal to the X axis.

         The Y axis is Z cross X, completing the right-handed reference frame.
    <li><b>HEEQ</b> : Heliocentric Earth Equatorial Frame -

         All vectors are geometric: no aberration corrections are used.

         The solar rotation axis is the primary vector: the Z axis points
         in the solar north direction.

         The position of the Sun relative to the Earth is the secondary
         vector: the X axis is the component of this position vector
         orthogonal to the Z axis.

         The Y axis is Z cross X, completing the right-handed reference frame.
    </UL>
    </UL>
<br/><br/>