This tool enables you to select times during the Cassini Tour when Cassini's viewpoint satisfies specified geometric constraints. Simply enter the desired lower or upper limit (or both) on any field in the form, click "Submit," and a table of the time intervals that satisfy the constraints is returned. You can then, for example, cut and paste the times into the Cassini/Saturn Viewer tool to generate a diagram of the viewing geometry for that moment. Leave the form blank for any parameters that you do not wish to constrain.
NOTE: This tool is operational but not currently supported. Its primary purpose was for Cassini mission planning. An update may be released to support the Cassini extended mission.
This tool uses a table of viewing geometry parameters sampled every ten minutes during the Cassini tour. The tool simply searches the database for all rows in the table that match the constraints and groups consecutive rows together in the output. Because of the sampling, viewing opportunities that exist for shorter than ten minutes might be missed. In addition, the estimated duration of a particular viewing geometry could be in error by +/- ten minutes.
The viewing geometry is actually tabulated for the planet, not the rings. Keep in mind that, particularly when close in, the rings can span a signficant range of phase angles, distances, solar hour angles, etc.
The time limits of the table are from May 1, 2004 (about three months before Saturn orbit insertion) to July 1, 2007.
Note that orbit numbers are 0, A, B, C, 3, 4, ... in the revised tour. This is because two orbits in the original tour were changed into three in the revised tour. With this nomenclature, subsequent orbit numbers are unchanged.
You may select between "yyyy-mm-dd" and "yyyy-ddd" date formats. You always have freedom to use either format in input fields; this merely affects the format of the output.
You may select between planetographic and planetocentric latitude; planetocentric is the default. The planetocentric latitude is equivalent to the ring opening angle. The difference can be ~5 degrees at mid-latitudes.
The observation time gives the time UTC at which the given viewing geometry occurs. Times are given by default in PDS format, of the form "yyyy-mm-ddThh:mm:ss.sss". However, in the queries, times can be entered in a broad range of formats; click here for the gory details.
The orbits are numbered from one apoapse to the next. The first
orbit, containing SOI, is number 0.
Range
Range is the distance to the center of Saturn in units of Saturn radii, 60330 km.
The sub-spacecraft latitude is the latitude on the planet directly beneath the spacecraft, in degrees. It can range from -90 to 90. It is roughly equivalent to the ring opening angle. Note that it is negative for views of the south side of the rings and positive for views of the north side.
The sub-solar latitude is the latitude on the planet directly beneath the Sun, in degrees. It can range from -90 to 90. However, it is always negative during the Cassini Tour because the Sun shines on the south side of the rings.
The solar angle hour measures the spacecraft-planet-antisolar direction as projected into the ring plane, in degrees. It can range from 0 to 360. It is measured in the direction of ring rotation so SHA=90 places Cassini above the morning quadrant of the rings (where the ring material has just emerged from shadow) and SHA=270 places Cassini above the evening quadrant (where ring material is heading into the shadow).
The phase angle is the spacecraft-planet-Sun angle, in degrees. It can range from 0 to 180.
The duration is the approximate time interval over which a specified viewing geometry exists, in hours. Note that this value can be in error by up to +/- 10 minutes.
Last updated 20 July 2001