Space Shuttle launch unlikely to be Sunday

credit NASA tv / caption: the hydrogen vent line connects to the external tank for space shuttle Discovery

NASA’s “rough cut” plan for solving the vent line issue is as follows

Proposed Troubleshooting plan:

• 24 hrs to inert tank   
• Get access
• Look for gross misalignment of QD [quick disconnect]
• Perform decay check
• Remove QD and inspect flight seal
• Recovery – install new flight seal
• Decay check
• Reconnect vent line
• Proceed with checkout and would reconvene if issues.

It is the reinstallation of the seal and the related retorque requirement that some NASA engineers think could have some wiggle room to bring the launch forward to Sunday but that assumes that it works and so the likely outcome is a Monday launch attempt 

The vent line issue is not new and the Shuttle programme has a standard approach to solve it, but this time it wasn’t working leading to the launch scrub, according to a Mission Management Team memo provided to Hyperbola  

Standard operating procedure is to start cycling the vent valve as an effort to clear any contaminants or ice build up.  This has worked in the past, but this time we were outside of our experience and with progressive opening and closing of the vent valve, the leak was getting worse.