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.

(red star) 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

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.



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