"NASA announced today July 1 to 19 is the new launch planning window for Space Shuttle Discovery's mission, designated STS-121. The new window gives the agency time to do additional engineering work and analysis to ensure a safe flight for Discovery and its crew."
Shuttle launch pushed to July, Orlando Sentinel
Summary of comments by Wayne Hale:
We had an interesting set of meetings. Decisions were made today at 2:00 pm.
There is a problem with low-level sensors - ECO sensors in the ET. There may be a problem in manufacturing these sensors - in the way that the wires are attached to the sensors. It is possible for sensors to read erroneously i.e. "dry" when in fact that the tanks are not dry. This seems to happen over time as tank has been moved around.
Earliest launch date is 1 July. The vehicle may well be ready ahead of time. But we need to launch during daylight for at least two more flights - STS-121 and STS-115 - to see what is happening with the External Tanks.
We will be entering ET from the bottom. Foam will be removed. This sensor was made 10 years ago - in 1996. It appears to have shifted in its reading when it was transported last summer - before STS-114.
We are all very optimistic that we can wrap up the rest of our work - this additional 6 weeks will allow us to wrap up other work - such as looking at the aerodynamics. We look forward to a launch around 1 July. I remain optimistic that we can get three missions off this year.
The decision made today was not based on schedule. We made this based on relative risk and safety. This is not a shortcoming on the manufacturer's part. This is a very reliable part that they have improved over the years.
"NASA officials told NBC News on Tuesday that they have decided to delay the space shuttle Discovery's launch from May until at least July 1 while engineers replace four fuel-level sensors in the shuttle's external fuel tank."
Editor's earlier note: Shuttle program management has not yet made a decision to change out ECO sensors in the External Tank designated for STS-121. If that change out does occur, up to a month would be required. As to whether there will be a launch date slip from the current target date in May to the next available one in July, that decision has not been made yet - although a variety of NASA sources suggest that this is the likely outcome. There will be PRCB sessions throughout the week with a variety of options on the table. Sources note that any decision to move to July would not be just because of the sensor change-out per se - but rather, as the result of an accumulation of a number of issues that have arisen in previous weeks. As one senior NASA source put it today "we're trying to do what the CAIB told us to do - and listen to the hardware."