Shuttle Discovery will not be launching until “at least” Monday of next week after fault was noted with the Orbiter- similar problem to what occurred on the first tanking test.
The failure of one of the Engine Cut Out Sensor (ECO) was never fully understood from the last incident relating to the sensor and was classed as an Unexplained Anomaly (UA). The stand-down could be from one day to ending the attempt in July. (A full update will be published on the 14th (PM)) When all four of the LH2 ECO Sensors were switched to dry, all of them worked, including the number two sensor – which has caused the scrub today. “Basically when they performed the liquid level sensor check, the LH2 #2 sensor failed to show DRY,” noted a source. “The LOX Left #2 sensor, which was switched simultaneously, indicated dry – and is still indicating dry just in case the LH2 sensor suddenly switches in. “When they switched all FOUR of the LH2 ECO sensors to dry, all of them worked (including #2),” he added. “This might be a problem with the system used to test the sensors, or – more likely – a problem with the Orbiter electronics. Nothing is ruled out though, and we don’t know when the next attempt will be. “Obviously we can’t know until they have a good handle on the problem. If they get it solved completely, and fast – it’s a 24-hour turnaround. That’s the only way we’ll be doing that.” A fault with an ECO sensor was detected on the first Tanking Test on a different External Tank (ET-120), with a second ECO failing during the drain of the Liquid Hydrogen from the External Tank (ET). The Shuttle has four ECOs – with all four needing to be operational or else a launch attempt would be scrubbed. With this similar problem being noted this time, the problem does appear to be with the Orbiter. If the issues are with the Avionics Box on the Orbiter then the troubleshooting may take a fair amount of time, given that sources have previously noted than no spare boxes are available. A large ice build-up issue has also been noted on the on the LH2 feedline, near the tank’s aft dome. No information has been made available to whether this was a problem with the new heaters added to reduce ice build-up – which is a debris concern.
The fault came the liquid level sensor check was performed.
“Right now nobody knows where the problem is, but – as you can guess – we’re thinking that the problem is in the Orbiter electronics.”