! Proposal 6963, submission 1 ! PI: David Elkin ! Received Fri May 31 10:45:48 EDT 1996 ! From: elkin@stsci.edu ! 6963 ! Hubble Space Telescope Cycle 6 Phase II Proposal Template ! Refer to the HST Phase II Proposal Instructions to fill this out ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! !=================================================================== Proposal_Information Title: OTA Calibration at Low Limb Angle Proposal_Category: CAL/OTA Scientific_Category: Cycle: 6 Investigators PI_Name: David Elkin PI_Institution: STScI CoI_Name: Sylvia Baggett CoI_Institution: STScI CoI_Name: Luis Colina CoI_Institution: STScI CoI_Name: Massimo Stiavelli CoI_Institution: STScI Contact: Questions Observing_Description: Fifty (50) WFPC2 calibration exposures shall be scheduled when possible previous to earth occultation and subsequent to the science data taking at the end of visibility intervals terminating in bright earth avoidance. The exposures shall extend into the bright earth limb avoidance region (15.5 to 20 degrees) which precedes earth occultation. The bright earth limb avoidance angle limit for the entire proposal shall be set at 15.5 degrees, with the option to reset the value of this limit before the end of the program. This adjustment of the limit can probably most easily be accomplished in SPIKE. Ten (10) exposures shall use the F814W (4 chips), and forty (40) exposures shall use the F606W filter (4 chips). Eight (8) exposures in F814W shall be taken at a duration of 100 seconds. The worst-case SNR expected is 2.8/pixel (ETC for a worst-case brightness of 21 Vmag/sq-as at a 60-degree solar-zenith angle and a 20-degree limb angle). Two (2) single-exposure visits in F814W shall be taken at a duration of 40 seconds at the very end of an SI visibility interval to restrict limb angle to 15.5 degrees. The worst-case SNR expected is 5.9/pixel (ETC for a worst-case brightness of 19 Vmag/sq-as at a 60-degree solar-zenith angle and a 16-degree limb angle). Thirty (30) exposures in F606W shall be taken at a duration of 60 seconds. The worst-case SNR expected is 3.3/pixel (ETC for a worst-case brightness of 21 Vmag/sq-as at a 60-degree solar-zenith angle and a 20-degree limb angle). Ten (10) single-exposure visits in F606W shall be taken at a duration of 40 seconds at the very end of an SI visibility interval to restrict limb angle to 15.5 degrees. The worst-case SNR expected is 9.1/pixel (ETC for a worst-case brightness of 19 Vmag/sq-as at a 60-degree solar-zenith angle and a 20-degree limb angle). At least four exposures per week are desired over a three month time span. Scheduling shall take place at the end of calendar building on a no-impact basis to an otherwise completed flight calendar. The ten F814W exposures shall be scheduled first as they are desired in the June time frame or as soon as possible afterwards. The forty F606W exposures shall be scheduled subsequently. Sequences of one, two, three, and four exposures per visit are available for selection. TRANSFORMATION is expected to "casually" merge all exposures in a visit into a single alignment for maximum efficiency. Visits shall be scheduled to terminate at the end of the SI visibility interval when the 15.5-degree bright limb limit is reached. Single exposure visits shall be scheduled only when the exposure begins at or below the 20-degree angle. Multiple-exposure visits may be scheduled with the first exposure beginning above the 20-degree limit if it ends below the 20-degree limit. Scheduling shall commence on a given flight calendar with an attempt to schedule the 40-second single-exposure visits at the very end of the SI visibility interval first. Next, schedule a 4-exposure visit. If not possible, continue in order to attempt to schedule a 3-exposure visit, 2-exposure visits, and finally 1-exposure visits. In the target list below, dummy values for RA and DEC are provided since arbitrary values are needed by the RPS2 software. Pointing shall be determined when a calibration visit is added to a flight calendar. A 2.5 arcmin offset in declination from the previous scheduled pointing shall remove the calibration from the previous field. If possible, the sign of the offset shall be chosen to make the absolute value of the declination approach 61.5 degrees. Interleaver observing opportunities shall be attempted on flight calendars for multi-orbit visits since the offset is small. A bright object check shall be performed for objects at Vmag=13 or brighter in any of the four chips. Remove the calibration observation from the flight calendar if violated. Also remove the calibration observation from the flight calendar if the brightest object has Vmag between 13 and 17 and the time to the next external WFPC2 exposure or dark calibration before a decontamination is less than 30 minutes. This check is conservative since saturation effects typically disappear after 20 minutes. Scheduling shall be restricted to 1) Places on the calendar having a long SI visibility interval duration to minimize limb angle change over exposure duration, and to 2) Times when a substantial fraction of the bright earth limb is illuminated so that a significant level of earth background occurs. The initial criterion for the first is 80 minutes for the eight F814W 100-second exposures, 60 minutes otherwise. The initial criterion for the second is 60% of the visible forward earth. Do not schedule during or immediately subsequent to a moving target observation. The program shall be periodically reviewed by the proposers to confirm that observations are taking place as desired and that there is an even sampling of limb angle and sun position. Scheduling criteria shall be adjusted if needed during the program. The telemetry mode is H. Abstract: Earth background at low limb angle is detected in two filters in all four chips to determine received intensity over the range 15.5 to 20 degrees. Sequences of one, two, three or four one-minute exposures per visit are scheduled where possible without impact to an otherwise completed flight calendar. Observations are distributed in time and in sun position. ! Real_Time_Justification: ! Calibration_Justification: ! Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: NEP Alternate_Names: Description: CALIBRATION, SCATTERED LIGHT TEST Position: RA=0H 0M 0.00S +/- 0.1S, DEC=0D 0' 0.0" +/- 0.1" Equinox: J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: J2000 Annual_Parallax: Flux: SURF(V)= 18.5 +/- 0.2, V=13.1 +/- 0.1 Comments: SPSS operations shall reset pointing to be offset 2.5 arcmin in declination from previous pointing (see Observing_Description). ! Mag/arcsec**2. Corresponds to maximum ! V-background (18.7) from earth ! reflection (albedo 0.7) at a 15.5- ! degree limb and a 0-degree solar- ! zenith angle, and zodiacal light ! V-background (21.0), based upon ! preliminary WFPC2 data analysis. ! BEGIN F814W SINGLE EXPOSURE VISITS Visits Visit_Number: 1 Visit_Requirements: PCS MODE G ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ! PCS MODE [Fine | Gyro] ! GUIDing TOLerance ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN