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 - 10 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 16 n 500 1 3.6-319 kHz
H1 2E y y 2 n 40 1 60 25 325k-1.8MHz
H2 1E n n 1 n 40 1 72 200 1.8M-16MHz
Bands ABC require 1.58 sec to complete, H1 requires 2.85 sec, and H2 requires 2.53 sec
for a total of 6.97 sec per sweep. The time between analyses can be set to 16
seconds to reduce the bit rate, or to 8 seconds if that isn't necessary.
No Sounder measurements are made in this mode. No onboard dust detection is done either.