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Table of ContentsBrief Guide to Doing SPICE Hands-On Lessons Using WGC Overview WGC and WGC Tutorial URLs Doing ``Remote Sensing'' Hands-On Lesson Using WGC Kernels Used Time Conversion (convtm) Obtaining Target States and Positions (getsta) Spacecraft Orientation and Reference Frames (xform) Computing Sub-spacecraft and Sub-solar Points (subpts) Intersecting Vectors with a Triaxial Ellipsoid (fovint) Doing ``In-situ Sensing'' Hands-On Lesson Using WGC Kernels Used Step-1: ``UTC to ET'' Step-2: ``SCLK to ET'' Step-3: ``Spacecraft State'' Step-4: ``Sun Direction'' Step-5: ``Sub-Spacecraft Point'' Step-6: ``Spacecraft Velocity'' Doing ``Geometric Event Finding'' Hands-On Lesson Using WGC Kernels Used Find View Periods Find Times when Target is Visible Doing ``Binary PCK'' Hands-On Lesson Using WGC Moon rotation (mrotat) Earth rotation (erotat) Brief Guide to Doing SPICE Hands-On Lessons Using WGC
Overview
Instructions for each lesson are provided in a separate section below. They follow the lesson steps and individual assignments within each step, indicate which WGC computation panels (``calculations'') should be used and what inputs should be entered or selected in these calculations, and what key outputs should be expected from WGC. Where applicable, they indicate that a particular quantity computed in the lesson cannot be computed by WGC. WGC and WGC Tutorial URLs
http://wgc.jpl.nasa.gov:8080/webgeocalc/#NewCalculationThe WGC tutorial is provided at:
https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Tutorials/pdf/individual_docs/47_webgeocalc.pdf Doing ``Remote Sensing'' Hands-On Lesson Using WGCKernels Used
Time Conversion (convtm)
Time system UTC Time format Calendar date and time Input time 2004 jun 11 19:32:00 Output time system TDB Output time format Seconds past J2000WGC will return the following ET seconds past J2000:
140254384.184620To compute calendar ET in the default format, specify/select the following inputs in the ``Time Conversion'' calculation:
Time system UTC Time format Calendar date and time Input time 2004 jun 11 19:32:00 Output time system TDBWGC will return the following calendar ET time string:
2004-06-11 19:33:04.184625 TDBTo compute calendar ET in a custom format, specify/select the following inputs in the ``Time Conversion'' calculation:
Time system UTC Time format Calendar date and time Input time 2004 jun 11 19:32:00 Output time system TDB Custom format YYYY-MON-DDTHR:MN:SC ::TDBWGC will return the following calendar ET time string:
2004-JUN-11T19:33:04To compute spacecraft clock time, specify/select the following inputs in the ``Time Conversion'' calculation:
Time system UTC Time format Calendar date and time Input time 2004 jun 11 19:32:00 Output time system Spacecraft clock (SCLK=-82)WGC will return the following SCLK time string:
1/1465674964.105 Obtaining Target States and Positions (getsta)
Target PHOEBE Observer CASSINI Reference frame J2000 Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2004 JUN 11 19:32:00 State representation RectangularWGC will return the following state vector, km and km/s:
-119.92092897 2194.13933986 -57.63897986 -5.98023114 -2.11880531 -0.29482213To compute the apparent position of Earth as seen from CASSINI in the J2000 frame and one way light time between CASSINI and the apparent position of Earth, specify/select the following inputs in the ``State Vector'' calculation:
Target EARTH Observer CASSINI Reference frame J2000 Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2004 JUN 11 19:32:00 State representation RectangularWGC will return the following position vector, km, and one way light time, s:
353019393.12261910 -1328180352.14030500 -568134171.69730540 4960.42691203To compute the apparent position of Sun as seen from Phoebe in the J2000 frame, specify/select the following inputs in the ``State Vector'' calculation:
Target SUN Observer PHOEBE Reference frame J2000 Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2004 JUN 11 19:32:00 State representation RectangularWGC will return the following position vector, km:
376551465.27159620 -1190495630.30282120 -508438699.11000470Note that WGC will also compute the distance between Sun and Phoebe body centers, km:
1348176829.09957000but it cannot convert this distance to AUs. Spacecraft Orientation and Reference Frames (xform)
Target PHOEBE Observer CASSINI Reference frame IAU_PHOEBE Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2004 JUN 11 19:32:00 State representation RectangularWGC will return the following state vector, km and km/s:
-1982.63976162 -934.53047112 -166.56259513 3.97083213 -3.81249566 -2.37166299WGC does not have a separate calculation to compute angles between directions to objects and instrument boresights or axes of a reference frame, making such computations not possible in general. But for cases when the axis is ``Z'' such computations can be done using the ``State Vector'' calculation with the ``Spherical Coordinates'' output, in which the colatitude is equal to the desired angle. To compute the angular separation between the apparent position of Earth and the CASSINI high gain antenna boresight, specify/select the following inputs in the ``State Vector'' calculation:
Target EARTH Observer CASSINI Reference frame CASSINI_HGA Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2004 JUN 11 19:32:00 State representation SphericalWGC will return the following output colatitude, deg:
71.92414848 Computing Sub-spacecraft and Sub-solar Points (subpts)
Target PHOEBE Reference frame IAU_PHOEBE Observer CASSINI Sub-point type Near point on ellipsoid Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2004 JUN 11 19:32:00 Position representation RectangularWGC will return the following position vector, km:
104.49789074 45.26884577 7.38331473Note that WCG will compute the altitude but it will be labeled ``Observer Distance (km)'' in the output table and will have the following distance, km:
2084.11604205To compute the apparent sub-solar point on Phoebe as seen from CASSINI in the IAU_PHOEBE frame , specify/select the following inputs in the ``Sub-Solar Point'' calculation:
Calculation type Sub-Solar Point Target PHOEBE Reference frame IAU_PHOEBE Observer CASSINI Sub-point type Near point on ellipsoid Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2004 JUN 11 19:32:00 Position representation RectangularWGC will return the following position vector, km:
78.68071625 76.87865160 -21.88456729 Intersecting Vectors with a Triaxial Ellipsoid (fovint)
Target PHOEBE
Reference frame IAU_PHOEBE
Observer CASSINI
Ray vector CASSINI_ISS_NAC
field-of-view boundary vectors
Light propagation To observer
Light-time algorithm Newtonian
Stellar aberration Corrected for stellar aberration
Time system UTC
Time format Calendar date and time
Input time 2004 JUN 11 19:32:00
Position representation Rectangular
WGC will return the following position vectors, km:
91.02635667 67.19017758 2.03016242 91.02635667 67.19017758 2.03016242 91.02635667 67.19017758 2.03016242 91.02635667 67.19017758 2.03016242To compute the planetocentric longitudes and latitudes of the FOV boundary vector surface intercept points in the IAU_PHOEBE frame, specify/select the following inputs in the ``Surface Intercept Point'' calculation:
Target PHOEBE
Reference frame IAU_PHOEBE
Observer CASSINI
Ray vector CASSINI_ISS_NAC
field-of-view boundary vectors
Light propagation To observer
Light-time algorithm Newtonian
Stellar aberration Corrected for stellar aberration
Time system UTC
Time format Calendar date and time
Input time 2004 JUN 11 19:32:00
Position representation Planetocentric
WGC will return the following longitudes and latitudes, deg:
36.43251123 1.02800787 36.55583078 7.49186596 43.42988023 7.37325329 43.23917363 0.86454948Both computations above also returned the illumination angles the FOV boundary vector surface intercept points but these angles were omitted from the output shown above. To compute the Cartesian position vectors of the FOV boresight surface intercept point in the IAU_PHOEBE frame, specify/select the following inputs in the ``Surface Intercept Point'' calculation:
Target PHOEBE Reference frame IAU_PHOEBE Observer CASSINI Ray vector CASSINI_ISS_NAC boresight Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2004 JUN 11 19:32:00 Position representation RectangularWGC will return the following position vector, km:
86.39001297 72.08919557 8.25459687To compute the planetocentric longitude and latitude of the FOV boresight surface intercept point in the IAU_PHOEBE frame and the illumination angles at this point, specify/select the following inputs in the ``Surface Intercept Point'' calculation:
Target PHOEBE Reference frame IAU_PHOEBE Observer CASSINI Ray vector CASSINI_ISS_NAC boresight Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2004 JUN 11 19:32:00 Position representation PlanetocentricWGC will return the following longitude and latitude, deg:
39.84371945 4.19587780and the following incidence, emission, and phase angles, deg:
18.24722120 17.85830930 28.13948173WGC cannot compute the local solar time at the boresight intercept point. Doing ``In-situ Sensing'' Hands-On Lesson Using WGCKernels Used
Step-1: ``UTC to ET''
Time system UTC Time format Calendar date and time Input time 2004-06-11T19:32:00 Output time system TDB Output time format Seconds past J2000WGC will return the following ET seconds past J2000:
140254384.184620 Step-2: ``SCLK to ET''
Time system Spacecraft clock (SCLK=-82) Time format Spacecraft clock string Input time 1465674964.105 Output time system TDB Output time format Seconds past J2000WGC will return the following ET seconds past J2000:
140254384.183430Either the input SCLK time or these output ET seconds past J2000 should be used as the input time in all remaining ``In-situ Sensing'' lesson steps in order for WGC to compute values matching the results provided in the programming lesson. The output ET seconds may be saved for future use in the WGC ``Saved Values'' area by simply clicking on them with the left mouse button. The saved value can then be drag-n-dropped from the ``Saved Values'' area into the empty ``Time:'' box in the next calculation. Step-3: ``Spacecraft State''
Target CASSINI Observer SUN Reference frame ECLIPJ2000 Light propagation No correction Time system TDB Time format Seconds past J2000 Input time 140254384.183430 State representation RectangularWGC will return the following state vector, km and km/s:
-376599061.91656125 1294487780.92915730 -7064853.05469811 -5.16422619 0.80171891 0.04060306 Step-4: ``Sun Direction''
Target SUN Observer CASSINI Reference frame CASSINI_INMS Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system TDB Time format Seconds past J2000 Input time 140254384.183430 State representation RectangularWGC will return the following position vector, km:
-391245772.45811266 1188593024.20844320 501745827.05297270 Step-5: ``Sub-Spacecraft Point''
Target PHOEBE Reference frame IAU_PHOEBE Observer CASSINI Sub-point type Near point on ellipsoid Light propagation No correction Time system TDB Time format Seconds past J2000 Input time 140254384.183430 Position representation PlanetocentricWGC will return the following longitude and latitude, deg:
23.42315899 3.70979740WGC cannot compute the direction from the CASSINI spacecraft to the sub-spacecraft point in the INMS frame. Step-6: ``Spacecraft Velocity''
Doing ``Geometric Event Finding'' Hands-On Lesson Using WGCKernels Used
Find View Periods
Target MEX
Observer DSS-14
Reference frame DSS-14_TOPO
Light propagation To observer
Light-time algorithm Converged Newtonian
Stellar aberration Corrected for stellar aberration
Time system TDB
Time format Calendar date and time
Time range 2004 MAY 2 to 2004 MAY 6,
step 300 seconds
Coordinate condition Latitude is greater than 6
Output time unit hours
Complement result window no
Result interval adjustment No adjustment
Result interval filtering No filtering
WGC will return the following interval start and stop times:
2004-05-02 00:00:00.000000 TDB 2004-05-02 05:35:03.096376 TDB 2004-05-02 16:09:14.078641 TDB 2004-05-03 05:33:57.257816 TDB 2004-05-03 16:08:02.279561 TDB 2004-05-04 05:32:50.765340 TDB 2004-05-04 16:06:51.259358 TDB 2004-05-05 05:31:43.600189 TDB 2004-05-05 16:05:40.994061 TDB 2004-05-06 00:00:00.000000 TDBMake sure to save these output intervals in the WGC ``Saved Values'' area using the ``Save All Intervals'' button to make them available for use as input to the next step of the lesson. Find Times when Target is Visible
Calculation type Occultation Event Finder Occultation type Any Front body MARS Front body shape Ellipsoid Front body frame IAU_MARS Back body MEX Back body shape Point Back body frame Observer DSS-14 Light propagation To observer Light-time algorithm Converged Newtonian Time system TDB Time format Calendar date and time Output time unit hours Complement result window yes Result interval adjustment No adjustment Result interval filtering No filteringTo use the time intervals found by the previous step as the input to this calculation, select ``List of Intervals'' in the ``Input times:'' selector and drag and drop saved intervals from the ``Saved Values'' area into the empty ``List of intervals:'' box. WGC will return the following interval start and stop times:
2004-05-02 00:00:00.000000 TDB 2004-05-02 04:49:30.827635 TDB 2004-05-02 05:35:03.096376 TDB 2004-05-02 05:35:03.096376 TDB 2004-05-02 16:09:14.078641 TDB 2004-05-02 20:00:22.514122 TDB 2004-05-02 21:01:38.222068 TDB 2004-05-03 03:35:42.256777 TDB 2004-05-03 04:36:42.484694 TDB 2004-05-03 05:33:57.257816 TDB 2004-05-03 16:08:02.279561 TDB 2004-05-03 18:46:26.013964 TDB 2004-05-03 19:46:54.618795 TDB 2004-05-04 02:21:44.562990 TDB 2004-05-04 03:21:56.347988 TDB 2004-05-04 05:32:50.765340 TDB 2004-05-04 16:06:51.259358 TDB 2004-05-04 17:32:25.809031 TDB 2004-05-04 18:32:05.975318 TDB 2004-05-05 01:07:48.264966 TDB 2004-05-05 02:07:11.601765 TDB 2004-05-05 05:31:43.600189 TDB 2004-05-05 16:05:40.994061 TDB 2004-05-05 16:18:35.560693 TDB 2004-05-05 17:17:27.717224 TDB 2004-05-05 23:54:04.672052 TDBNote that the returned list contains 13 intervals instead of 12 shown in the output of this step in the programming lesson. This is due to a bug in the current version of WGC, which in some cases returns bogus zero-length intervals in addition to the actual intervals when the output window complement is requested. In this case the second interval in the output is a bogus singleton interval that should not be there. WGC's output window filtering option can be used as a workaround to remove such intervals before the WGC window complement algorithm is fixed. Doing ``Binary PCK'' Hands-On Lesson Using WGCMoon rotation (mrotat)
To compute the Moon-Earth direction using the low accuracy PCK and the IAU_MOON frame, specify/select the following inputs in the ``State Vector'' calculation:
Target EARTH Observer MOON Reference frame IAU_MOON Light propagation To observer Light-time algorithm Converged Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2007 JAN 1 00:00:00 State representation PlanetocentricWGC will return the following longitude and latitude, deg:
3.61310222 -6.43834182To compute the Moon-Earth direction using a high accuracy PCK and the MOON_ME frame, specify/select the following inputs in the ``State Vector'' calculation:
Target EARTH Observer MOON Reference frame MOON_ME Light propagation To observer Light-time algorithm Converged Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2007 JAN 1 00:00:00 State representation PlanetocentricWGC will return the following longitude and latitude, deg:
3.61122841 -6.43950148WGC cannot compute angular separation between the Moon-Earth direction vectors in the IAU_MOON and MOON_ME frames. To compute the Moon-Earth direction using a high accuracy PCK and the MOON_PA frame, specify/select the following inputs in the ``State Vector'' calculation:
Target EARTH Observer MOON Reference frame MOON_PA Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2007 JAN 1 00:00:00 State representation PlanetocentricWGC will return the following longitude and latitude, deg:
3.59331861 -6.41758189WGC cannot compute angular separation between the Moon-Earth direction vectors in the MOON_ME and MOON_PA frames. To compute the sub-Earth point on the Moon using a high accuracy PCK and the MOON_ME frame, specify/select the following inputs in the ``Sub-Observer Point'' calculation:
Target MOON Reference frame MOON_ME Observer EARTH Sub-point type Near point on ellipsoid Light propagation To observer Light-time algorithm Converged Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2007 JAN 1 00:00:00 Position representation PlanetocentricWGC will return the following longitude and latitude, deg:
3.61141894 -6.43950142To compute the sub-Earth point on the Moon using a high accuracy PCK and the MOON_PA frame, specify/select the following inputs in the ``Sub-Observer Point'' calculation:
Target MOON Reference frame MOON_PA Observer EARTH Sub-point type Near point on ellipsoid Light propagation To observer Light-time algorithm Converged Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2007 JAN 1 00:00:00 Position representation PlanetocentricWGC will return the following longitude and latitude, deg:
3.59350886 -6.41758182WGC cannot compute the distance between the sub-Earth points computed in the MOON_ME and MOON_PA frames. Earth rotation (erotat)
To compute the Earth-Moon direction using a low accuracy PCK and the IAU_EARTH frame, specify/select the following inputs in the ``State Vector'' calculation:
Target MOON Observer EARTH Reference frame IAU_EARTH Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2007 JAN 1 00:00:00 State representation PlanetocentricWGC will return the following longitude and latitude, deg:
-35.49627162 26.41695855To compute the Earth-Moon direction using a high accuracy PCK and the ITRF93 frame, specify/select the following inputs in the ``State Vector'' calculation:
Target MOON Observer EARTH Reference frame ITRF93 Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2007 JAN 1 00:00:00 State representation PlanetocentricWGC will return the following longitude and latitude, deg:
-35.55428578 26.41915557WGC cannot compute the separation angle between the Earth-Moon vectors in IAU_EARTH and ITRF93 frames. WGC cannot compute the IAU_EARTH and ITRF93 +X and +Z axis separation angles. To compute the DSS-13-Moon azimuth and elevation using a high accuracy PCK and the DSS-13_TOPO frame, specify/select the following inputs in the ``State Vector'' calculation:
Target MOON Observer DSS-13 Reference frame DSS-13_TOPO Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2007 JAN 1 00:00:00 State representation PlanetocentricWGC will return the following longitude and latitude, deg, that are equivalent to the azimuth (AZ=-LON) and elevation (EL=LAT):
-72.16900637 20.68948821To compute the sub-solar point on Earth using a low accuracy PCK and the IAU_EARTH frame, specify/select the following inputs in the ``Sub-Solar Point'' calculation:
Target EARTH Reference frame IAU_EARTH Observer SUN Sub-point type Near point on ellipsoid Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2007 JAN 1 00:00:00 Position representation PlanetocentricWGC will return the following longitude and latitude, deg:
-177.10053149 -22.91037699To compute the sub-solar point on Earth using a high accuracy PCK and the ITRF93 frame, specify/select the following inputs in the ``Sub-Solar Point'' calculation:
Target EARTH Reference frame ITRF93 Observer SUN Sub-point type Near point on ellipsoid Light propagation To observer Light-time algorithm Newtonian Stellar aberration Corrected for stellar aberration Time system UTC Time format Calendar date and time Input time 2007 JAN 1 00:00:00 Position representation PlanetocentricWGC will return the following longitude and latitude, deg:
-177.15787351 -22.91259307WGC cannot compute the distance between the sub-solar points computed in the IAU_EARTH and ITRF93 frames.
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