At 9:56 a.m. EST this morning, the launch of Space Shuttle Atlantis was officially postponed for at least 24 hours. The postponing of the launch had to do with an unknown difficulty involving the sensors in the shuttle’s liquid hydrogen tank.
“[We detected] a failure in sensors three and four 16 minutes into fast-fill,” said Shuttle Test Director, Doug Lyons, in an emergency status briefing.
As part of a routine test of the liquid hydrogen tank’s sensors, a command is sent to the sensors to simulate the tanks being empty. During this simulation two of the four sensors registered “wet” instead of “dry”. This malfunction is only excusable if three of the four sensors still register “dry”.
These tests of the tank’s sensors are performed to make sure that the engines never run out of fuel, or “shut off dry,” which could cause them extreme damage. The sensors act as a back-up indicator of the fuel tank’s levels to the primary engine cut-off system. Officials speculate that the error could involve an open circuit in the sensors’ wiring.
The shuttle tanks will remain at a stabilized condition of “stable replenish” while a team of engineers run troubleshooting procedures. After this the tanks will be emptied of their fuel for further analysis. The Mission Management team will then meet at 4 p.m. EST to discuss the appropriate course of action.
At this time there is no official guarantee that the shuttle will launch by it’s next launch window of 3:04 p.m. EST, Dec. 7, but the date was given in order to preserve the option of launching at that time.
“The team remains confident that we can work our way through this,” Lyons said.
If the shuttle does not launch by Dec. 13, it will be removed from the launch pad for further assessments. The next available launch window will be Jan. 2. The last time a launch was postponed to the point where the shuttle was rolled away from it’s launch pad was during mission STS-114.