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Atlantis Set To Launch At 2:47 P.M. ET Thursday, Feb. 7 After Russians Helpfully Move Progress Launch To Feb. 5

By | January 14, 2008

      Experts Think Sensor Woes Have Been Resolved, But Proof Comes When External Fuel Tank Is Filled

      Longer-Term Sensor-Data Fix To Be Mulled

      NASA experts believe they have figured out the cause of the difficult fuel gauge sensor data glitch that has kept Space Shuttle Atlantis sitting idle for more than a month on Launch Pad 39A at Kennedy Space Center, so a new launch target for the STS-122 Mission has been set for 2:47 p.m. ET Feb. 7.

      As well, the Space Shuttle Endeavour launch on the STS-123 Mission that had been set for Feb. 14 will now slip to mid-March.

      Each shuttle mission will take an enormous structural addition to be attached to the International Space Station (ISS).

      The Feb. 7 liftoff for Atlantis is possible thanks to flexibility by the Russians, who agreed to accelerate their launch of a Progress freighter spaceship. It will lift off Feb. 5 instead of Feb. 7. NASA officials don’t wish to have conflicts with both a Progress and a shuttle attempting to visit the ISS about the same time.

      In an intricately choreographed ballet in space, that earlier Progress voyage will permit both STS-122 and STS-123 to launch before the next Russian Soyuz mission in early April.

      The new launch manifest for the Progress vehicle, Atlantis and Endeavour will permit the space station Expedition 16 crew to complete the tasks they have trained for, including support of the launch and docking of Jules Verne, the first European Space Agency Automated Transfer Vehicle.

      The ATV is set for launch by Arianespace on an Ariane 5 rocket for sometime in February. (Please see separate story in the Launches section.)

      Targeting Feb. 7 to launch Atlantis also allows time to complete modifications to the engine cutoff sensor system that postponed two shuttle launch attempts in December.

      That mystifying sensor data glitch caused weeks of sleuthing by NASA personnel attempting to identify, locate and fix the problem. (Please see Space & Missile Defense Report, Monday, Jan. 7, 2008.)

      Hopefully, the cause has been found, in an electrical circuit that carries readings from the fuel gauge sensors near the bottom of the external fuel tank to the outside and on to the orbiter vehicle.

      Those sensors warn of low fuel, a critical function because if the fuel level hits zero and the engines continue running, a catastrophic explosion can occur.

      The problem seems to center in a pass-through connector that takes fuel gauge sensor data from inside the portion of the fuel tank where liquid hydrogen fuel is stored, and the data passes through to the tank exterior.

      Electrical contact pins in the sensor may have failed to make sufficient contact for the electrical current to pass along the circuit. Therefore, pins have been soldered in place. Also, NASA is going to create some slack in wiring leading to the pass-through connectors, so that if the wiring contracts when incredibly cold liquid hydrogen pours into the tank, and the wiring thus contracts, it won’t pull on the pass-through connector and break the electrical circuit.

      Thus far, evidence seems to indicate that is the problem that caused incorrect sensor data readings when the Atlantis external fuel tank was being filled for its first launch attempt on Dec. 6, a NASA source in Washington said.

      "They’ve assessed the data, and it points in the right direction" to indicate that the pass-through connector is the problem, the source said.

      "They are in the process of installing the new connector" on the Atlantis fuel tank now, the source said. And at this point, "all indications are … that this fix will address" the faulty sensor readings. "No data" indicate that this fix won’t work.

      That said, however, there is no absolute certainty here.

      "Nothing is certain … until we fill the tank" and see whether the sensor readings are correct, the source said.

      NASA officials are sufficiently confident that this fix will work that "the exact same fix is being implemented" on the fuel tank to be used with Space Shuttle Endeavour.

      For later missions, there may be some tweaks in the remedy, to improve it. There are "plans to discuss a longer-term fix," the source said.

      But for the near term, hopefully the fix for Atlantis and Endeavour will permit them to make a major advancement in building the space station as it moves at 17,500 miles an hour in orbit.

      The main objective for Atlantis during its STS-122 Mission to the station is to install and activate the European Space Agency Columbus laboratory, a room-sized addition that will provide scientists around the world the ability to conduct a variety of experiments in life, physical, and materials science, Earth observation and solar physics.

      Attaching Columbus to the space station and making the lab module operative will require multiple spacewalks.

      The crew includes Commander Steve Frick, Pilot Alan Poindexter, and mission specialists L�opold Eyharts (a European Space Agency astronaut), Stanley Love, Hans Schlegel (of ESA), Rex Walheim, and Leland Melvin.

      Then another major expansion of the space station will occur in the Shuttle Endeavour STS-123 Mission to deliver Kibo, the first section of the Japan Aerospace Exploration Agency laboratory module, and Dextre, the new Canadian robotics system, to the space station.

      NASA managers will meet in coming weeks to address the schedule of remaining shuttle flights beyond the Endeavour STS-123 Mission.

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