Trigger 66 Description

Sequence: S05, ...
Trigger 66 ( Titan Closest Approach with 80-KHz WBR)
This mode assumes a background survey mode, such as 8A or A0, is running, although the HFR settings are set for the "Inner Magnetosphere Night-Time" mode, with fast time constants, as in Triggers A0 or 8E. The duty cycle of the Langmuir Probe and the WFR are increased, and 80-KHz WBR is added.

First of all, Trigger 66 overlays fast WFR data acquisition. In order to do this,the LFDR data acquisition is stopped (it can be synthesized on the ground, using the fast WFR data.) A WFR snapshot, in its nominal 5-channel and 2048-sample mode, is acquired every 24 seconds. The WFR is run in toggle mode, so these snapshots alternate between 25 Hz mode and 2.5 KHz mode. In addition to stopping the LFDR data acquisition, the data compression algorithm for the WFR is changed to "packed" mode, so that this faster data rate can be accomplished. The 80-KHz WBR is added, using the EX antenna, but the sample size is limited to 1536 compressed bytes in order to accomplish a particular bitrate. The target bit rate is 100 kbps. Actual measured bitrates look like about 55.5 kbps for the S&ER-3 telemetry mode (maximum 60.928 kbps), and 103.6 kbps for higher pickup rates. The former was measured in C37, the latter during C38.

The Langmuir Probe sweep rate is increased to once every 24 seconds. While a faster rate would be desirable, this would cause interference in the WFR data, also being acquired every 24 seconds. Between each LP sweep, a 432-point density mode measurement is made at 20 Hz. Additionally, the Langmuir Probe sweep, a down-up ramp type of sweep, is done in Medium Range mode, so the voltage range is +4V to -4V. The density measurement is done in fixed bias mode, at +4V.

Receiver Frequency Range Sensors Time between Snapshots
MFR 25 - 12 KHz EZ, BZ 32 seconds
WFR 1 - 25 Hz EX,EW,BX,BY,BZ 48 seconds
WFR .1 - 2.5 KHz EX,EW,BX,BY,BZ 48 seconds
HFR 3.6 KHz - 16 MHz EX, EW 8 or 16 seconds
LP N/A Langmuir Probe 24 seconds
WBR 0 - 80 KHz EX 0.125 second


The HFR is in the newest version of "Nighttime Survey" mode, which now includes both auto- and cross-correlations for H1, and modified integration constants for all bands. This mode is defined by: 

          Correlations Channels    Integ.           Size Frequency
Band Ant. Auto- Cross- per Band df Period Rep Steps kHz  Start - Stop
---- ---- ----- ------ -------- -- ------ --- ----- ---- ------------
ABC   2E    y     y       32    n    500  1              3.6-319KHz
HF1   2E    y     y        2    n     40  1     60    25 0.325-1.825MHz
HF2   1E    n     n        1    n     40  1     72   200 1.825-16.225MHz
 
Bands ABC require 1.580 sec to complete, H1 requires 2.852 sec, and
H2 requires 2.534 sec for a total of 6.966 sec per sweep.  The hfr
cycle time is 8.000 seconds.


No Sounder measurements are made in this mode. No onboard dust detection is done either.