• Data Set Overview

• =================

• Data Set Description

• ====================

This Data Set consists of Voyager 1 Jupiter Encounter Ephemeris Data in Heliographic Coordinates covering the Period from 1979-02-26 to 1979-03-24.

Two Versions, both covering the same Time Period, but containing slightly different Data, are provided. One Version was generated by the Voyager Magnetometer (MAG) Team from Voyager 1 SEDR, the other by the PDS/PPI Node using the VG1_JUP.BSP and PCK00003.TCP SPICE Kernels.

Two Versions of the Spacecraft Ephemeris Data are provided as an attempt to correct some of the Problems in the Voyager SEDR while preserving the Ability to reproduce early Results. The original SEDR Data has a Variety of Problems, which may affect the Knowledge of the Spacecraft Position, or conversely, the Timing associated with certain Events such as Ring Plane Crossings. The SPICE SPK Kernel provided on this Disk includes Corrections to some, but not all, of the Problems associated with the Voyager SEDR. The Navigation and Ancillary Information Facility (NAIF) at JPL may issue a new Voyager SPK Kernel in the Future that will further improve the Knowledge of the Spacecraft Location in Inertial Space.

There are other Differences in the two Versions of Ephemeris Data that are the Result of Improvements in the Knowledge of some of the Physical Constants associated with Jupiter and its Moons. Since the Voyager Era, there have been Updates to the Orientation of the Jovian Spin Axis expressed via its Right Ascension and Declination, the Radius of Jupiter, as well as the Orbital Characteristic and other Physical Parameters of many of the Moons of Jupiter. These Changes affect the stated Position of the Spacecraft in Jovigraphic Coordinate Systems like System III without changing the Position of the Spacecraft in Inertial Space. The Spin Rate of Jupiter is not changed from the System III (1965) Rate of 9 h 55 min 29.71 s (870.536° per Day). The SPICE Planetary Constants Kernel (PCK) contains both the current IAU Definitions of the Physical Constants for the Bodies within in the Jovian System (as Data) as well as the older IAU Definitions (as Comments). This is an ASCII Text File (PCK00003.TCP) and Users of the Ephemeris Data are encouraged to review it.

• SEDR Generated Ephemeris
• ========================

+------------------------------------------------------+
| Parameter Characteristics | Value |

| Data Supplier | NSSDC |
| Data Sampling Rate | 96 SECONDS |
| Data Set Start Time | 1979-02-26T00:00:35.897Z |
| Data Set Stop Time | 1979-03-24T22:47:56.304Z |
+------------------------------------------------------+

• SPICE Generated Ephemeris
• =========================

+------------------------------------------------------+
| Parameter Characteristics | Value |

| Data Supplier | S. JOY |
| Data Sampling Rate | 48 SECONDS |
| Data Set Start Time | 1979-02-26T00:00:35.897Z |
| Data Set Stop Time | 1979-03-24T22:49:32.304Z |
+------------------------------------------------------+

• Parameters

• ==========

• SEDR Generated Ephemeris

• ========================

+--------------------------------------------------------------------------------------------------------------------------------------------+
| Parameter Name | Resolution/Units | Description |

| time | 96 s | Time of the Sample (UT) in the Format YYYY-MM-DDTHH:MM:SS.SSSZ |
| m65536 | counts | Spacecraft Clock Counts, mod 65536 |
| mod60 | counts | Spacecraft Clock Counts, mod 60 |
| fds_line | counts | Spacecraft Clock Counts, fds_line |
| sc_x | AU | Heliocentric Spacecraft Position, Cartesian Coordinates, X Component |
| sc_y | AU | Heliocentric Spacecraft Position, Cartesian Coordinates, Y Component |
| sc_z | AU | Heliocentric Spacecraft Position, Cartesian Coordinates, Z Component |
| vel_x | km/s | Heliocentric Spacecraft Velocity, Cartesian Coordinates, X Component |
| vel_y | km/s | Heliocentric Spacecraft Velocity, Cartesian Coordinates, Y Component |
| vel_z | km/s | Heliocentric Spacecraft Velocity, Cartesian Coordinates, Z Component |
| sc_r | AU | Heliocentric Spacecraft Position, Spherical Coordinates, Radial Distance (Range) |
| sc_lat | degrees | Heliocentric Spacecraft Position, Spherical Coordinates, Latitude |
| sc_lon | degrees | Heliocentric Spacecraft Position, Spherical Coordinates, Longitude |
| SolEquatorial_to_HG | | Solar Equatorial to Heliographic Coordinates Rotation Matrix containing nine 1PE15.8 Elements |
| HG_to_EarthOrbTrue | | Heliographic to Earth Orbit True Coordinates Rotation Matrix containing nine 1PE15.8 Elements |
| Spacecraft_to_HG | | Payload (Spacecraft) to Heliographic Coordinates Rotation Matrix containing nine 1PE15.8 Elements |
+--------------------------------------------------------------------------------------------------------------------------------------------+

• SPICE Generated Ephemeris
• =========================

+-----------------------------------------------------------------------------------------------------------------------------------------------------+
| Parameter Name | Resolution/Units | Description |

| time | 48 s | Time of the Sample (UT) in the Format YYYY-MM-DDTHH:MM:SS.SSSZ |
| R | AU | Heliographic Spacecraft Position, Spherical Coordinates, Radial Distance (Range) |
| LAT | degrees | Heliographic Spacecraft Position, Spherical Coordinates, Latitude |
| LON | degrees | Heliographic Spacecraft Position, Spherical Coordinates, Longitude |
| LocTime | hours | Angular Separation between the Meridian containing the Sun and the one containing the Spacecraft converted |
| | | converted to a Time. The Sun Meridian is defined to be Noon (12.000), with Midnight (0.000) opposite it. |
| | | Dawn (6.000) and Dusk (18.000) are where the Sun rises and sets according to the Rotation of the Planet. |
+-----------------------------------------------------------------------------------------------------------------------------------------------------+

• Coordinate System
• =================

The Heliographic Coordinate System is a Heliocentric System defined in the Reference Epoch of 1950. The Unit Vectors which define the Coordinate System are as follows:

• Heliographic Cartesian Coordinates
• ==================================

• X points towards the the First Point of Aries in the Solar Equatorial Plane on the Vernal Equinox of the Reference Epoch 1950, positive away from the Sun
• Y completes the right-handed Set, Y = X ⨯ Z
• Z points along the Spin Axis of the Sun, positive above the Equatorial Plane

• Heliographic Spherical Coordinates
• ==================================

• R gives the Distance from the Position of the Sun at the Reference Epoch to the Spacecraft in AU
• LAT gives the Angle between the Solar Equatorial Plane of the Reference Epoch measured in the Plane containing the Solar Spin Axis of that Epoch, positive above the Equatorial Plane
• LON gives the Longitude is Zero in the Direction of the Ascending Node at the Reference Epoch (X Direction) and increasing in the Direction of Planetary Orbital Motion (note that LON does not rotate with the Sun)

For the SPICE Data, the Value of an Astronomical Unit is set equal to 149,674,000 km. The Longitude of the Ascending Node was calculated using the Equation:

LON = (74° 22') + 0.84' * (year-1900)

The Inclination of the North Pole Sun measured relative to the Ecliptic was defined as being 7° 15' in 1950.

• Data Coverage
• =============

+--------------------------------------------------------------------------+
| Filename | Records | Start Date and Time | Stop Date and Time |

| SEDR057 | 6046 | 1979-02-26T00:00:35.897Z | 1979-03-04T23:58:11.925Z |
| SEDR064 | 6071 | 1979-03-05T00:00:35.925Z | 1979-03-11T23:59:08.059Z |
| SEDR071 | 6065 | 1979-03-12T00:00:44.059Z | 1979-03-18T23:58:20.235Z |
| SEDR078 | 5303 | 1979-03-19T00:00:44.236Z | 1979-03-24T22:47:56.304Z |
| SPICE057 | 12093 | 1979-02-26T00:00:35.897Z | 1979-03-04T23:59:47.925Z |
| SPICE064 | 12142 | 1979-03-05T00:00:35.925Z | 1979-03-11T23:59:56.059Z |
| SPICE071 | 12131 | 1979-03-12T00:00:44.059Z | 1979-03-18T23:59:56.236Z |
| SPICE078 | 10607 | 1979-03-19T00:00:44.236Z | 1979-03-24T22:49:32.304Z |
+--------------------------------------------------------------------------+