10.4 ACS Restricted Engineering Modes
HST's ACS instrument can obtain data necessary for instrument maintenance, and the Astronomer’s Proposal Tool (APT) has parameters for specifying these 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 = ACS/WFC or ACS/HRC
This Mode is used to move the ACS internal focus and tilt mechanisms for the WFC or SBC 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 proposer must ensure that the alignment scans are within the allowed mechanism limits. The mechanism positions corresponding to the nominal zero positions of the alignment scan will be set via real-time command. This will be accomplished in a program by specifying an ALIGN mode exposure with the special requirement REQ UPLINK. Because the positions of the mechanisms are set via real-time command, no Optional Parameters are permitted in conjunction with the REQ UPLINK Special Requirement in order to prevent commanding the mechanisms via stored commands.
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
FOCUS
= 0 (default); -858 to +858 (steps)
Specifies the relative position from a nominal zero position of the focus mechanism, in motor steps. The absolute position of the nominal zero is set by real-time command.
TILT
= NO (default), YES
Specifies whether a tilt of the corrector mechanisms will be commanded. If this parameter is set to YES, the maximum time required to move both cylinders of the tilt mechanism will be included in the alignment time.
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 ACS 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.
Special Requirements
Optional parameters are not allowed to be specified for ALIGN exposures with the REQ UPLINK Special Requirement.
Mode = ANNEAL Config = ACS
This Mode allows specification of periods of time during which ACS should be configured to anneal the CCDs for removal of hot pixels. The total annealing time will be the specified exposure time plus a minimum default value (6 hours). ANNEAL exposures do not collect science data. Because of the long time required to configure the ACS for ANNEAL Mode, an ANNEAL exposure must be the only exposure in its visit.
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 (6 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 ACS instrument to be left in the HOLD state (i.e., with several boxes powered off) 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.