We receive the same error messages that we experienced for the first and second epoch planning when running the Visit Planner.-2095652375----- Attempting Submission 2 (Wed Dec 18 19:28:56 GMT 2013) -----
----- Attempting Submission 3 (Wed Feb 12 03:16:52 GMT 2014) -----We receive the same error messages that we experienced for the first and second epoch planning when running the Visit Planner.Imaging Comet C/2013 A1 (Siding Spring) to Support Risk Assessment for Mars Orbiters during the Close Mars EncounterNewly discovered comet C/Siding Spring passes Mars on October 19, 2014 at a distance of only 134,000 km. Such a close encounter of a dynamically new comet is extremely rare, providing an opportunity for instruments on Mars to observe it around close approach and for studying the interactions between the coma and the Martian atmosphere. However, comet dust also poses a potential risk to NASA's Mars-orbiting spacecraft. We request four HST DD orbits to observe C/Siding Spring in three epochs between October 2013 and March 2014, to characterize the comet's environment. Our goals are to measure the dust activity and its temporal evolution, characterize the coma and tail morphology and colors (to constrain the dust particle size distribution), investigate features or jets near the nucleus, and determine the nucleus' size and rotation state. The proposed studies will provide valuable information about this dynamically new comet and will help in planning future observations (from both Mars- and Earth-based facilities). These studies will provide critical input for assessing the hazards to Mars orbiters. DD time is requested because the potential risks from the dust coma were not fully recognized until after the normal Cycle 21 GO proposal deadlines (when the comet's orbit determination accurately predicted the Mars encounter), and waiting until the normal Cycle 22 will be too late to obtain the necessary data. HST's high angular resolution is essential for the proposed observations as C/Siding Spring is still ~5 AU from the Sun, with a coma only a few arcsec in size.The total of four orbits are divided into three epochs. The first epoch contains two orbits, separated by 1-2 orbits for a total duration of 4.5-6 hrs, and should be scheduled as early as possible, nominally in the week of October 27 to November 2. The second and third epochs contain one orbit each, to be scheduled between December 15 and 31, 2013 and March 1 and 15, 2014, respectively. The plan for the second and third epochs observations will be refined before the scheduling using the newly available information of the brightness of the comet from the first epoch of observations and future ground-based observations.
For the first epoch of two orbits, we plan to use the same sequence as used for C/ISON observations (GO-13198), given the similar brightness and observing geometry of C/Siding Spring. Specifically, we will use F606W and F438W filters, and two exposure levels for the F606W filter. We will execute a two point dithering pattern with 0.5" offset on both horizontal and vertical directions between the first half and the second half in each orbit to avoid bad pixels affecting our analysis. The exposure times will be 50 s and 272 s for the F606W filter, and 300 s for the F438W filter. Given the small extent of the comet, we plan to use 1k-by-1k subarray mode for this epoch.
The second and the third epochs will nominally have similar sequence. But we will need to update the exposure time later, and probably replace the F606W filter with a narrower F775W filter for less contamination from the gas coma if the comet is bright enough then. We may also switch to larger subarray, e.g., 2k-by-2k, to accomodate the possibly larger angular size of the comet.
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Second epoch planning, 12/18/2013
We decided to postpone the second epoch from the nominal end of December to January 21 to capture the orbit plane crossing observing geometry of the comet. Based on scaling with heliocentric and geocentric distance from the first epoch to the second, the brightness of the comet is expected to increase by a factor of ~2.4. To accomodate the expected larger size of the comet, we plan to switch to 2K2C-SUB frame for F606W filter, while keep the C1K1C-SUB frame for F438W filter. We propose to set a roll range of HST as 65-69 to put the comet along the diagonal direction of the FOV to cover the tail as much as possible. For the same reason, we offset the FOV to put the comet center at (500, 500) pixels from the sunward chip corner for F606W filter, and (300, 300) pixels for F438W filter. We also included a 1", 2-point dither for each filter to avoid bad pixels. We also updated the ephemeris of the comet with the most recent JPL orbit solution #35 by using a new target, C2013A1-JPL35.
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Third epoch planning, 02/11/2014
The third epoch has one orbit, and has to be executed before March 14, 2014, after which C/Siding Spring moves to within 50 deg solar avoidance zone for HST. We do not expect much change in the comet's brightness and size. Therefore, we will use the same sequence as used for the second epoch. The comet will still be offset from the default pointing to along one diagonal direction in order to best accomodate the length of the tail. The orbital elements of the target is updated under a new target name, C2013A1-JPL40, using the most recent orbital solution from JPL. In order to have as long baseline between the second and the third epochs as possible, we prefer scheduling the third epoch later in the specified window than earlier.SOLAR SYSTEMDefaultfalsefalsefalsefalsefalseSUPPORTEDSOLAR SYSTEMSolution reference: JPL #23, data arc 2012-10-04 to 2013-09-29COMETComet C/2013 A1 (Siding Spring)TYPE=COMET,Q=1.399472914416551,E=1.000441510580912,I=129.0231581865663,O=300.9664722950736,W=2.42938109781337,T=25-OCT-2014:11:51:11,TTimeScale=TDB,EQUINOX=J2000,EPOCH=11-MAR-2013,EpochTimeScale=TDBEARTHSOLAR SYSTEMSolution reference: JPL #35, data arc 2012-10-04 to 2013-12-13COMETComet C/2013 A1, JPL Orbit Solution #35TYPE=COMET,Q=1.399258352456117,E=1.000543709462318,I=129.0248840897145,O=300.970049823124,W=2.43082528025856,T=25-OCT-2014:10:15:53,TTimeScale=TDB,EQUINOX=J2000,EPOCH=14-MAY-2013,EpochTimeScale=TDBEARTHSOLAR SYSTEMSolution reference: JPL #40, data arc 2012-10-04 to 2014-01-27.COMETComet C/2013 A1, JPL Orbit Solution #40TYPE=COMET,Q=1.399152105508586,E=1.000578660274613,I=129.0258592449619,O=300.9723496637724,W=2.432871735990672,T=25-OCT-2014:09:43:03,TTimeScale=TDB,EQUINOX=J2000,EPOCH=27-JUN-2013,EpochTimeScale=TDBEARTHWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF438WWFC3/UVISImagingNoNoF438WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF775WWFC3/UVISImagingNoNoF438WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF775W/private/var/folders/bf/5vn1xpgs2_97fpjxw1m9kbxm0000gn/T/OPVisit5856233900934831643.xml1383068698000332.0112008437204(Tic-Visit
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