APT requires the observer to specify the BUFFER-TIME parameter for all COS TIME-TAG observations in order to effectively manage the onboard memory. The recommendations for the value of BUFFER-TIME have been modified for Cycle 21; in most cases we no longer advise truncating the BUFFER-TIME when the value returned by the ETC multiplied by 2/3 is longer than the exposure time. This allows COS to tailor the length of the planned buffer dumps to better match the amount of data collected. For some observing scenarios, these changes will allow shorter buffer dumps, and thus more observing time per orbit.
Observers preparing Phase II proposals should refer to Section 5.4 of the COS Instrument Handbook, which includes the latest recommendations. A new flow chart illustrating the process for choosing the BUFFER-TIME has been added (Figure 5.11). The process outlined there should be carefully followed to ensure the most efficient observing plan and the most on-target time.