Cheat sheet for problems with parallel buffer dumps
These are some things to know that may be helpful resolving parallel
buffer dumping issues:
Things to know:
- Exposures need to be longer than the buffer dump, in order for the dump to occur in parallel.
The dump can overlap some part of the exposure overhead, but not the overhead that immediately follows the exposure.
This overhead can be on the order of less than 10 seconds that cannot be overlapped by the STIS buffer dump,
but it can vary in length.
- The ACS internal buffer can store the equivalent of 1 WFC full-frame exposure, or 16 SBC exposures.
The buffer must be dumped if a commanded ACS exposure will exceed the remaining buffer capacity.
A completely filled buffer can be dumped in parallel with the commanded exposure if longer than 339
seconds. If the buffer is only partially filled when the dump must occur, an exposure time proportionately
shorter than 339 seconds will still accommodate the parallel buffer dump. If another instrument is
used in parallel-mode observing with ACS, its parallel buffer dump exposure-time requirements must
be added to those for ACS.
- After the first WFC3/UVIS exposure, each exposure must be >= 348 sec, or
after two short exposures, the next exposure must be >=664 sec. (This is because
the WFC3 buffer can hold two full
frame images, but when it dumps it must be able to dump both images in their
entirety during the next exposure to be dumped in parallel.) A fuller
explanation can be found in the : instrument handbook.
- These times assume that CR-Split=No. If not, the pieces of the split must
meet these minimums.
- For WFC3/IR exposures the buffer can hold two full frame 15 sample
exposures. As with the UVIS, dumping one exposure in parallel will require a >=
348 sec exposure and dumping two exposures in
parallel require a >=664 sec exposure. But note that unlike UVIS the IR data can
be partially dumped. A fuller explanation can be found in the instrument
- When instruments are used in parallel it becomes more difficult to ensure
that buffer dumps are done in parallel. This is because the instruments have to
take turns dumping their buffers to the solid state recorder.
- You won't be able to get more than 4 full frame exposures in a normal orbit with
ACS/WFC and WFC3/UVIS. You may be able to get more with WFC3/IR. Consider using
subarrays if appropriate for your science.
- If there is a short exposure, put that one first (since nothing has to dump
in parallel to it) or put it last.
- COS and STIS have pretty short dump times and adding them to the parallels
does not make things significantly more complicated. But if TIME-TAG is being
used only one TIME-TAG exposure can be
in each Prime/Parallel group.
- If you are doing a CVZ observation, the final dump needs to be fit into the
final orbit because there is no occultation in which to to bury it.
- The last exposure for a particular instrument in a visit will be dumped in series
regardless of whether there is room to dump it in parallel to the prime
observation. So if you are ending parallels for an instrument early in a visit,
consider adding a short
parallel with that instrument at the end of the visit to delay the serial dump
until the end.
Note that you can also retrieve any of these example proposals into APT using File - Retrieve from STScI.