The Trouble With Sensors IX

No really. The saga continues:
NASA has postponed today's scheduled launch of space shuttle Atlantis after discovering a problem with a sensor in the shuttle's fuel tank.

Atlantis was set to launch this afternoon in Florida, carrying a crew of seven and Columbus -- a European science lab.

The cancellation came after two of the four sensors in the shuttle's liquid hydrogen tank showed the tank was empty, even though there was fuel inside.

NASA spokesman Paul Foerman said at least three sensors must be functioning properly before a launch could go ahead, reports The Associated Press.

Yes you guessed it, it was those damn ECO sensors once again.

For those that haven't read my ECO sensors posts, this has been a never ending saga for NASA since at least 1986.

The ECO sensors are 4 identical sensors at the bottom of the external fuel tank of the shuttle that are used to read whether there is still liquid fuel in the main tank or not. Independent software creates an estimate of the fuel left, but the 4 sensors create redundancy that they still have fuel in the tank. A burn out could be let say not-so-good in the death category.

For some strange reason ECO sensors 3 and 4 have shown a propensity to fail intermittently. Evidence of the problem goes back to the 80's when NASA first amended the flight rule that required all 4 ECO sensors to be functioning properly.

My perpetual beef about this issue is that instead of trying to find the solution to this problem NASA has perpetually taken the "ignore and bury head in sand" approach.

No one knows why the ECO sensors fail. There were some theories by NASA engineers lobed about that it had to do with the sensor wiring, or possibly the interference from newly installed heaters on the shuttle. Both theories didn't pan out, and each time the issue came up they launched anyway.

My thinking is that whatever it is, it has a high chance of being location specific. ECO sensors 3 and 4 are both located on the same side of the shuttle ET. ECO sensors 1 and 2 have always peformed well, and I'm aware of no design differences between any of the sensors at the bottom of the tank.

With the amount of lost time that NASA has had to spend holding back launches because of this issue over the years you'd figure they would try to spend some up front time to figure out the cause... You know before someone dies?

The Trouble With Sensors VIII
The Trouble With Sensors VII
The Trouble With Sensors VI
The Trouble With Sensors V
The Trouble With Sensors IV
The Trouble With Sensors III
The Trouble With Sensors II
The Trouble With Sensors I


  1. The launch has now been postponed until no earlier than Januay 2nd. The reason that they didn't get off the ground today (Sunday, Dec. 9) was.... wait for it...


    an anomaly with the engine cutoff sensors. Bet you didn't see that one coming.

  2. Ed, I feel like I'm stuck in some sort of weird time loop where these ECO sensor issues keep on coming up, I suggest they haven't solved the problem, they launch anyways, the problem comes up again, I suggest they haven't solved the problem, they launch anyways, the problem comes up again...

    Oh well, I guess it isn't a major issue since no one has died yet. It's just a common practice by too many engineers to simply assume they fixed a problem without actually confirming it only to realize that really they didn't fix a darn thing.

    I see it too much at work, and strangely enough it happens at NASA as well.

  3. What you described is the same thing that brought down the Columbia. "Oh well, nobody has died due to foam-shedding yet, so it isn't a problem".