How to Read a Weekly Timeline

The Preliminary Observing Timeline Report (POTR or "weekly timeline") lists the planned HST observations for a given interval. The timeline generally begins on Monday and usually covers 1 week.

The report is usually generated about 17 days prior to the beginning of a week's observations. Observations on this report will usually be executed, but problems with the spacecraft, scientific instruments, communications contacts or other events beyond our control may disrupt the timeline. A Target of Opportunity observation may also disrupt the timeline.

The report is 132 columns wide.


The report header lists the date the report was generated and the SMS identifier. The SMS (Science Mission Specification) is a detailed description of the HST's activities and uniquely identifies a specific timeline.

The SMS name is of the form YYDOYVVV, where YY is the year, DOY is the day of the year of the first day in the timeline and VVV is the version (the version number is not significant).

The report header also lists the start and end dates of the timeline.


A "Scheduling Unit" (SU) is equivalent to a visit in RPS2.

Scheduling Unit
Begin UT
Earliest start time in YYYY DOY HH:MM:SS for this SU.
End UT
Latest end time in HH:MM:SS for this SU.
Scheduling Unit Identifier => pppppss:vv where:
ppppp = proposal ID
ss = SU number for that proposal (base 36)
vv = version number of the SU (usually 01)
The times used in the Weekly Timeline are the scheduling unit (SU) times. Observations belonging to the same SU will have the same SU begin and end times. Each observation in the SU will have a separate entry in the report.

Principal Investigat
1st 10 characters of the Principal Investigator's last name
Exp #
Exposure number this observation in the form VV-EEE where
VV is the visit (SU) number and EEE is ???
1st 10 characters of target name
Science Instrument
Main SI used by this observation
SI Operating Mode used by this observation
Aperture(s) (up to 4) associated with this observation
Spectral Elements
Filters/gratings (up to 4) associated with this observation
Exposure Time
Exposure time in seconds
The next 3 columns are identifiers used by the scheduling software:
Observation Set ID (An obset is generally one or more alignments that can use the same Guide Star(s) or Pointing Control System mode
Alignment ID (An alignment is generally one or more exposures, done back to back, with the same telescope pointing)
Exposure ID (An exposure is essentially one instrument operation. Exposure IDs are different than Proposal Logsheet Line numbers.)
Note: SU, Obset, Alignment and Exposure IDs are base 36 (01, 02..., 09, 0A, 0B, ..., 0Z, 10, ...)

Copyright © 2005 The Association of Universities for Research in Astronomy, Inc. All Rights Reserved.

Glenn Miller (
Last updated: 10 March 2005