02/14/00
Cruise Activity Request (CAR) Form
Revised for UVIS 02/14/00
Observation Name: URSPEC
Submitted By: Joshua Colwell
Measurement Objective: Spatially resolved reflected solar spectrum from rings spanning A
ring to C ring.
Scientific Objective: Measure radial variations in ring reflectance properties in the ultraviolet,
providing information on abundance and distribution of sub-micron grains and abundance of
ice in the rings. Multiple iterations at different viewing geometries and quadrants in the rings
probes azimuthal variations and effect of spokes on reflected UV spectra.
Activity Description: Orient UVIS slit perpendicular to rings in ring plane (slit is in the Saturn
radial direction in ring plane). Track Saturn center, with an offset angle around the spacecraft
X axis such that the UVIS boresight is in the center of the B ring. Spatial resolution along the
slit provides spectra at different ring radii spanning the main rings when observation is made at
a distance of 1 million km from Saturn center.
Activity Start Time : See attached list.
Activity Duration: (per iteration) 15,360 seconds.
Number Of Iterations: See attached list.
Interval Between Iterations: See attached list.
Target : Tracking target body is Saturn; observation target is Saturn’s rings.
Pointing: Use IVP Target tracking (TARGET_IVP module in CASPER, just target tracking in
IVP). Observation is made when Cassini is on sunlit side of rings (southern sub-spacecraft
latitude) and at a distance of about 106 km from Saturn center. Track Saturn center, with an
offset angle around the spacecraft X axis such that the UVIS boresight is in the middle of the B
ring. For the nominal observing distance of 106 km this is an XOFFSET=5.5 degrees (96
milliradians). Orient slit in the radial direction in the ring plane so that one end of slit lies at
the inner edge of the rings and the other end lies at the outer edge of the rings. Twist angle
(secondary pointing) determines which quadrant of the rings is observed. (With CASPER,
select Z+Rings for Twist in the TARGET_IVP module and click on the appropriate part of the
rings.) Track Saturn with constant offset for duration of observation.
Estimated Data Volume: (in Mbits) 17.7 Mbits.
Instrument Set Up: USTARE. IP = 512 seconds. FUV XBIN = 1, YBIN = 1. Low resolution
slit. SQRT9 compression. EUV off. DPR = 1.152×103 bps. PPR = 8.7 packets/64 seconds.
Notes: See attached example plots and list of observation opportunities. List includes desired
quadrant of rings to be observed.
02/14/00
Start Time
(UTC)
2005 May 1 08:00
Sub-S/C
Latitude
-17.5
Distance
(million km)
1.15
Phase
Angle
23.25
Solar
Angle
104.8
2005 May 19 14:00
-17.7
1.13
28.96
56.84
2005 Jun 6 18:00
-17.5
1.14
21.92
68.53
2005 Jun 25 00:00
-17.5
1.13
32.23
68.72
2006 Oct 11 10:00
-39.6
0.52
95.25
22.28
2007 Jan 31 00:00
-31.6
1.02
109.92
37.26
2007 Feb 18 00:00
-29.7
1.03
111.25
88.44
2007 Mar 7 20:00
-52.2
0.76
52.31
110.71
Emission Notes
Angle
81.59 Morning
quadrant
85.68 Evening
quadrant
68.86 Morning
quadrant
69.4
Evening
quadrant
86.24 Noon quadrant.
X offset = 12
degrees.
92.99 Early afternoon.
X offset = 6
degrees
52.83 6 p.m. X offset =
5.2 degrees
81.35 5 a.m. X offset =
8 degrees