delusionofgrandeur

The next launch attempt of Space Shuttle Atlantis for STS-122 has been postponed until January 2008 due to faults with the ECO sensors in the Liquid Hydrogen fuel tank of the Space Shuttle System.

Launch had originally be scheduled for last Thursday but two of the four Engine Cut-Off Sensors in the liquid hydrogen section of the external tank failed to respond during fuelling. NASA requires that all four ECO sensors respond during tanking prior to launch. On Sunday’s launch attempt one of the four sensors failed to respond during tanking and the launch was scrubbed.

The postponement to the 10th of January is to allow time for engineering teams to evaluate the sensor problem and I’d also hazard a guess, to avoid any possible issues with the Shuttle’s annual ‘Y2K bug’. The bug is a potential issue with on-board computers when the calendar rolls over from one year to the next. This wouldn’t directly be a problem for a Shuttle launched in the next few days but it could perhaps become a problem if damage to the orbiter required an STS-3xx crew rescue mission.

The ECO sensor issue is a tricky one, they can’t risk them not working properly as a turbopump failure could lead to a ‘catastrophic’ engine failure. As I understand it, when the Space Shuttle Main Engine (SSME) turbopumps are at operating speed, fuel flow must be maintained for safe operation. A normal shutdown would be a controlled throttle-back of the engines so the turbopumps would spin down gradually. A sudden cutoff of the fuel would actually cause an rpm increase and failure (presumably uncontained) of the turbopump.

At a recent Mission Management team press briefing, they discussed the possibilities for fixing the ECO sensor issue. The MMT are optimistic that the fault lies in the avionics which are contained within the orbiter and can be accessed while on the pad. If, however, the fault lies at the sensors themselves within the base of the external tank, a roll-back to the vehicle assembly building may be required, perhaps even with the tank being demated from the stack. The MMT did mention that they had gained access to the tank while on the pad on a previous mission “a long time ago” but pointed out that it was a very difficult process involving removing an area of insulation foam, removing a panel of the tank and then putting it all back together again. The foam would then have to be re-applied in situ.

In the mean time, station life goes on. Progress M-62 is scheduled to launch to the ISS on the 23rd of December. The unmanned cargo vessel is expected to dock with the station on the 26th.

This entry was posted on Monday, December 10th, 2007 at 3:31 pm and is filed under Space.You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.