8.4 STIS Restricted Engineering Modes
HST's STIS instrument can obtain data necessary for instrument maintenance, and the Astronomer’s Proposal Tool (APT) has parameters for specifying these STScI observations. |
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Format definitions
Boldface type indicates the name of an APT parameter or a value for a parameter.
Black text indicates an important note.
Magenta text indicates available but unsupported parameters (requires prior approval from STScI).
Red text indicates restricted parameters (for STScI use only).
Brown text indicates text file parameters.
Items in brackets - <value> - are required values.
Items in square brackets - [<value>] - are optional.
Mode = ALIGN Config = STIS
This Mode is used to move the STIS internal focus and tilt mechanisms via stored commanding for the purpose of on-orbit alignment of the aberration correction optics. ALIGN exposures do not acquire science data and must be interleaved with science mode exposures to obtain data, with the alignment mechanisms at a variety of positions for the ground alignment process. The values of the Optional Parameters specify the positions of the three alignment mechanisms in motor steps, relative to a nominal zero position.
The mechanism positions at nominal zero will be set via real-time command, which allows a preplanned scan of a mechanism’s position to be specified without knowledge of where in the mechanism range the scan will be executed. Since the absolute positions are set in real time, a check that the pre-planned scans about the nominal zero positions do not violate the mechanism range limits cannot be performed by the scheduling system. The proposer must ensure that the alignment scans are within the allowed limits.
ALIGN exposures may be interleaved with STIS science exposures as part of either a Tip/Tilt Raster Scan or a Focus Scan.
Target Name
The special value NONE must be specified.
Aperture or FOV
Do not enter a value.
Spectral Element
Do not enter a value.
Wavelength
Do not enter a value.
Optional Parameters
Note that no Optional Parameters may be used with ALIGN mode when the REQ UPLINK Special Requirement is used.
FOCUS =0 (default); –4791 to +4791 (steps)
Specifies the relative position from a nominal zero position of the STIS focus mechanism, in motor steps. The absolute position of the nominal zero is set by real-time command.
XTILT, YTILT =0 (default); –115 to +115 (steps) (for either)
Specifies the relative position from a nominal zero position of the STIS X or Y tilt alignment mechanism, in motor steps. The absolute position of the nominal zero is set via real-time command.
Note: If a particular position for any of these mechanisms is needed for a series of exposures, the appropriate parameter (FOCUS, XTILT, or YTILT) must be specified with the same value on every exposure in the series. If any parameter is specified on an exposure and then omitted on the subsequent exposure, the corresponding mechanism position will be moved back to the nominal zero.
Number of Iterations
The Number_of_Iterations must be 1.
Time Per Exposure
Proposers may specify a positive value of Time_Per_Exposure to provide for additional time after the move has completed to wait prior to the start of the subsequent STIS exposure. This time may be desirable if, for instance, the Corrector move in the ALIGN Mode exposure could adversely affect the thermal environment (due to running the motors) and a cool-down time is required before the science exposure. If no wait is needed, enter 0S.
Mode = ANNEAL Config = STIS
This Mode allows specification of periods of time during which STIS should be configured to anneal the CCD for removal of hot pixels. The total annealing time will be the specified exposure time plus a minimum default value (12 hours). ANNEAL exposures do not collect science data.
Because of the long time required to configure the STIS for ANNEAL Mode, ANNEAL exposures must be in a visit with no other exposures.
Target Name
The special value NONE must be specified.
Aperture or FOV
Do not enter a value.
Spectral Element
Do not enter a value.
Wavelength
Do not enter a value.
Optional Parameters
There are no Optional Parameters in this Mode.
Number of Iterations
The Number_of_Iterations must be 1.
Time Per Exposure
The value is the time to be added to the minimum default value (12 hours), which
will determine the total time for the annealing procedure.
Special Requirements
SAA CONTOUR defaults to model 11 (non-intersecting). The ANNEAL exposure only triggers the reconfigurations that actually perform the anneal process so this potentially long exposure does not have to avoid the SAA. Using any other model may result in inefficient scheduling with the potential for the CCD Detector to be left in unusual states longer than necessary. Changing to something other than model 11 should be thoroughly discussed with the Commanding, Engineering and Ops personnel and may require system level changes beyond what is capable in the proposal.