This morning I completed the weekly PSL FAMIS tasks.
HPO Pump Diode Current Adjustment (FAMIS 8448)
I immediately noticed that something was off; the power reading for DB1 was around 83%, when it was > 86% when I finished last week. That is a large decline over 7 days, so I trended the individual laser diodes of the diode box (1st attachment). Something happened with Diode 3 of DB1 on November 10th. The laser diode power was last adjusted on Nov. 7, and the increase can be seen in the attached trend. After this though, the power for laser diode 3 began increasing, finally hitting some tipping point on Nov. 10th at ~17:41 UTC; at this point the diode laser dropped over the course of ~7 hours and stabilized. The effect this had on the overall diode box power can be seen in the final plot of the attachment (H1:PSL-OSC_DB1_PWR). It is unclear at this time what caused this behavior; investigation continues.
Continuing with the FAMIS task, I turned the ISS OFF and adjusted the operating current of the HPO DBs. The results are summarized in the below table and a screenshot of the PSL Beckhoff main screen is attached for future reference.
| Operating Current (A) | ||
| Old | New | |
| DB1 | 51.6 | 51.9 |
| DB2 | 54.0 | 54.1 |
| DB3 | 54.0 | 54.1 |
| DB4 | 54.0 | 54.1 |
I should note that in the last 2 weeks, I have had to increase the operating current of DB1 by 0.6 A (0.3 A per week). This is a change from the usual 0.1-0.2 A weekly increase. It should also be noted that all of the DBs were increase by 0.3 A last week. The increase should remain roughly linear, and a departure from linearity can be an early indication of a failing DB. I will continue to monitor this.
I also adjusted the operating temperatures of the HPO DBs, changes summarized in the below table.
| Operating Temperature (°C) | ||||||||
| DB1 | DB2 | DB3 | DB4 | |||||
| Old | New | Old | New | Old | New | Old | New | |
| D1 | 27.5 | 26.5 | 19.5 | 19.5 | 21.0 | 20.5 | 22.0 | 22.0 |
| D2 | 27.5 | 26.5 | 19.0 | 19.0 | 25.0 | 24.5 | 19.5 | 19.5 |
| D3 | 27.5 | 26.5 | 20.0 | 20.0 | 25.0 | 24.5 | 21.0 | 21.0 |
| D4 | 27.5 | 26.5 | 18.0 | 18.0 | 22.0 | 21.5 | 19.5 | 19.5 |
| D5 | 27.5 | 26.5 | 18.0 | 18.0 | 26.0 | 25.5 | 21.5 | 21.5 |
| D6 | 27.5 | 26.5 | 18.5 | 18.5 | 20.5 | 20.0 | 21.5 | 21.5 |
| D7 | 27.5 | 26.5 | 19.0 | 19.0 | 21.5 | 21.0 | 21.5 | 21.5 |
Despite this, the HPO is still only outputting 154.1 W, down from the 155.0 W I left it at after last week's adjustment. I will continue to keep an eye on DB1, and investigation into the DB1 diode #3 glitch discussed above will continue. This completes FAMIS 8448. The ISS is back ON.
PSL Power Watchdog Reset (FAMIS 3676)
I reset both PSL power watchdogs at 18:03 UTC (10:03 PST). This completes FAMIS 3676.
Attached are plots of the TEC voltage and operating temps for the individual diodes of DB1. The short spikes early in the graphs are from my adjustments from last week (testing new operating temps to see if laser output power improved). Interestingly enough, at the time of the power runaway for diode 3, the TEC voltage for that diode was also changing; this is not seen on any of the other 6 laser diodes in the DB. At this same time, however, the operating temperature of the diode did not register a change. Investigation continues.
