# What are the two orange tabs stuck on opposite edges of each window of the ISS cupola?

The YouTube video ONE OF THE MOST DETAILED ISS TOUR!!! is cited in several Q&A here, and shows a tour and explanation of the ISS by astronaut Steven Swanson.

Today I noticed between 28:30 and 31:20 that each of the seven windows in the ISS cupola shows a pair of orange stick-on tabs on opposite edges of the glass. Sunlight can be seen through them, showing what looks like four circuit board traces and three "pads".

What is the function of these devices, what do they connect to, and have they always been there?

I'm guessing they are not for security or burglar detection.

above x2: Screenshots from here, first is zoomed/sharpened.

• Those traces make me think of thermistors. Maybe the temperature of the glass is measured here? Nov 13, 2018 at 12:04
• "Thanks", @uhoh! I've never noticed those tabs before and now I see them in every picture! :) Like the "cue dots" in old films, once my projectionist friend showed them to me, I could never un-see them. Nov 13, 2018 at 15:10
• @OrganicMarble exactly, me too, same thing (re windows, not cue dots, but now that you mention it...) Perhaps it's a glitch in the matrix type thing.
– uhoh
Nov 13, 2018 at 15:18
• peel off tabs to get to the tasty astronaut treats inside Nov 13, 2018 at 22:20
• Probably just hinges to open the windows when it gets hot on the ISS... ;-) Nov 14, 2018 at 8:14

These are part of the cupola window temperature control system. Each window has window heaters and temperature sensing modules (these orange tabs) to make sure the windows don't get too hot or too cold. For example, if the window gets too hot, the astronauts would be instructed to close the cupola's shutters. Because of the traces I assume that each orange sticker contains two thermistors for redundancy or is simply a four wire sensor such as an RTD.

https://directory.eoportal.org/web/eoportal/satellite-missions/i/iss-cupola

• I disagree, not two sensors, but one in four wire configuration. Using the four wire circuit for resistance measurement, the influence of cable resistance to the result of sensor resistance could be made to almost zero.
– Uwe
Nov 13, 2018 at 12:13
• Can you find the place in your link that mentions that these tabs are part of the temperature sensing system? I don't doubt it, more likely than strain gauges or anything else I can think of, but right now it seems to be just an educated guess. Thanks!
– uhoh
Nov 13, 2018 at 13:42
• The reference does not support your answer as far as I can tell. Nov 13, 2018 at 15:08
• My former colleague Robert Frost says they are RTDs here quora.com/What-if-the-windows-in-the-ISS-Cupola-got-over-heated Nov 13, 2018 at 15:17
• @uhoh Under primary hardware "thermistors" are listed as part of the window assembly. Judging by the amount of detail on the page, I don't see what else they could be. Nov 13, 2018 at 15:35