Solar System Target Confirmation Chart FAQ

The following are some standard questions that PIs have about their solar system target confirmation charts. If you do not find the answer to your question here please contact your Program Coordinator.

  • What is the equinox of the indicated position?
  • J2000

  • What is the location of the observer?
  • The center of the Earth unless otherwise indicated.

  • What are the strange symbols that appear in the systems of some of the outer planets?
  • These symbols show the locations of satellites for which we know the positions but not the size and rotational information.

  • What is this "NOMINAL" roll angle?
  • HST must always keep it's solar arrays pointed toward the Sun -- this requires the field of view to have one preferred orientation on the sky for any target and date of observation. The nominal roll will change with time, and can be varied by up to +/- 30 degrees or so if the solar elongation at the time of observation is greater than 90 degrees. See the HST Primer for more details.

  • How are orientation requirements handled?
    1. If the visit has an ORIENT requirement, the chart is drawn at an angle within the range of the requirement.
    2. If the visit has an ORIENT FROM or a SAME ORIENT requirement, the chart is drawn at an angle which should satisfy the requirement according to the HST long range plan.
    3. If the visit has no orientation restrictions, the chart is drawn at nominal roll.

  • How are POS TARG, SAME POS AS, and PATTERN requirements handled?
  • For a given target/visit combination, the first exposure that observes the target is examined. If that exposure has a POS TARG, SAME POS AS, and/or PATTERN that will be depicted in the confirmation chart. If subsequent exposures have different pointings, they are ignored. Likewise, if the first exposure that observes the target does not have any offset, then no offset will be shown in the chart even if later exposures do have offsets.

  • Which apertures are displayed?
  • Ideally, solar system target confirmation charts would show only the aperture that the visit uses; but sometimes it is not that simple. What if the visit uses more than one aperture? Do we draw each one? Do we start making a separate confirmation chart for every exposure? We could just show all of the apertures all of the time, but some instruments have many apertures, and that makes the chart harder to read. As an attempt to walk the middle ground, the charts show the most popular subset of apertures for each instrument.

    If you would like charts that show apertures that are different from the standard set, just contact your program coordinator.

  • Each chart is drawn to represent a specific time. How is this time chosen?
  • First, we determine all of the times that the visit can be scheduled. We choose one of those scheduling opportunities and determine the exact start time of the visit at the chosen scheduling opportunity. We then draw each target in the visit at the start time of the visit unless the target's solar system target windows cannot be satisfied at the start of the visit. In that case, we draw the target at the start of its first solar system target window after the start of the visit.

    The times shown in the charts are not necessarily the times atwhich the observations will actually execute.

    Confirmation charts are intended to verify the geometric constraints before scheduling so that problems may be caught and corrected. The times shown in the charts are times when the target's geometric constraints can be satisfied. They are not times from an actual schedule. If we waited to make the charts after the visit was scheduled, we could show the exact time for each target; but it would defeat the purpose of the charts because it would then be too late to make any changes to correct any problems that might be found.

  • Can I get confirmation charts for another time?
  • Yes, ask your program coordinator.

    Last update February 22, 2017. Comments to: Tony Roman