IMAP-Lo - Final tweaks before data release

[vineetbansal]

This issue is to keep track of some changes requested by the IMAP-Lo team before the first release of their maps:

• Change to the star sensor binning due to a flight software update.

  imap_processing/imap_processing/lo/l1b/lo_l1b.py

  Line 2155 in 4eb90bc

  sample_centers = (bin_indices + 0.5) * deg_per_bin

  before 5/22, remain as sample_centers = (bin_indices + 0.5) * deg_per_bin
  From 5/22 and so on, revise as sample_centers = (bin_indices + 0.0) * deg_per_bin

  i.e., before 5/22, bin to the center, while since 5/22 with FSW 4.8, bin to the left.

• Pivot angle thresholds have changed - all values are 2x the previous ones:

  before:

    # Background-rate thresholds [counts/s] by pivot-angle range (low, high) [deg].
    # Each value is (ram_threshold, anti_ram_threshold).
    PIVOT_ANGLE_THRESHOLDS = {
        (88.0, 92.0): (0.014, 0.007),
        (73.0, 77.0): (0.0175, 0.00875),
        (103.0, 107.0): (0.0112, 0.0056),
    }
  

  after:

    # Background-rate thresholds [counts/s] by pivot-angle range (low, high) [deg].
    # Each value is (ram_threshold, anti_ram_threshold).
    PIVOT_ANGLE_THRESHOLDS = {
        (88.0, 92.0): (0.028, 0.014),
        (73.0, 77.0): (0.035, 0.0175),
        (103.0, 107.0): (0.0224, 0.0112),
    }
  

[tmplummer]

@nschwadron, is the star sensor sync status available in any Lo science telemetry? Currently the L1B prostar processing takes the l1a star, l1a spin and l1b housekeeping as inputs. It would be ideal if the star sensor sync status is available in one of those packets. Then we can easily switch the bin-center shift based on that telemetry. If not, the easiest alternative for now is to hard code the 5/22/2026 date. Since I really don’t like hard coding things, if we go that route, I would recommend writing up a follow up issue to implement a more flexible solution that will work in case the sync flag ever gets disabled.

[tmplummer]

It has been confirmed that the star-sync state is available in the nhk telemetry in the ifb_ctrl_star_sync variable. It looks like on 5/22, the value changes from "DS" to "EN" (disabled to enabled). I don't know what the appropriate logic is do determine what to use on a repoint when the change occurs.

[tmplummer]

Related to this ticket: #3270. @vineet, please keep this in mind as you address this ticket.