A small piece of space shuttle external tank insulation foam (encircled in red).

NASA's current space workhorse: the space shuttle.

Image Credit: NASA

A close-up view of the top of the external tank and the tanking adapter.
Image Credit: NASA public Webcam

The space shuttles ECO (engine cut-off) sensor system.
Image Credit: NASA

The space shuttles ECO (engine cut-off) sensor system.
Image Credit: NASA

The space shuttles ECO (engine cut-off) sensor system.
Image Credit: NASA

The space shuttles ECO (engine cut-off) sensor system.
Image Credit: NASA

The space shuttles ECO (engine cut-off) sensor system.
Image Credit: NASA

The space shuttles ECO (engine cut-off) sensor system.
Image Credit: NASA

Space Shuttle ECO-Sensor: System Overview
Image Credit: NASA

The sensing element of the space shuttle's engine cutoff sensors. Watch closely and you can see the platinum wire run over the sensing element. It is the change in that wires resistance that ultimately indicates if it is "wet" or "not".
Image Source: NASA, magnification: Rainer Gerhards

The ECO sensor mountpoint inside the space shuttle's external tank. As can be seen, they are mounted close to each other.

Illustration of feed-through electrical connections at the external tank liquid hydrogen tank structural interface, near the aft end of the tank.
Image Credit: NASA/MSFC

Schematic of the space shuttle's feedthrough connector.
Image Credit: NASA/STS-14 FRR

How the space shuttle feedthrough connector is fixed to the tank. Note the fixation on the inside.
Image Credit: NASA STS-114 FRR

The complete waiver page for the ET ECO sensor system from the STS-114 flight readiness review.
Credit: NASA