NASA Tackles Fuel-Sensor Problems
NASA is finally getting a break.
New test results have revealed why fuel sensors on the space shuttle are misbehaving, a problem that has baffled engineers and forced the delay of six launches since mid-2005, including Atlantis’ liftoff Dec. 6. The breakthrough clears the way for Atlantis to try to launch Feb. 7, as NASA officials had hoped.
The problem: a loose electrical plug in circuits that carry the signals from sensors that tell NASA whether the shuttle’s fuel tank is about to run dry. Final quality testing started over the weekend on a redesigned electrical plug that engineers believe will solve the problem. One already has been installed in the shuttle’s fuel tank, and technicians hoped to finish patching the tank’s surface at the installation site over the weekend.
"Everyone’s kind of excited around here right now," says Chad Bryant of NASA’s Marshall Space Flight Center, who supervised the testing. "We know what the problem is, and we know how to fix it."
Even so, the delay in Atlantis’ mission, which will deliver a laboratory to the International Space Station, has already caused a ripple effect. At least one of the six shuttle missions set for 2008 has been delayed, and more could be affected.
If major delays accumulate, the space station, which is still a work in progress, could remain unfinished. Only the shuttle can haul the heavy pieces of the station to orbit, and the shuttle fleet will be retired in mid-2010 — whether the station is done or not — to make way for a safer and more reliable spaceship.
Resolution of the sensor problems would eliminate the biggest source of launch delays in the past three years. Engineers think that the extensive testing over the past five weeks has found the culprit.
Early troubleshooting pointed to the wires and electrical plugs that carry the sensors’ electrical signal to the outside of the tank:
*Wires in the fuel tank carry the signal from the sensors to the tank’s outer wall. There, the wires attach to a device that contains 37 sockets, which are like tiny versions of the sockets in a home electrical outlet.
*Fitting into the sockets are prongs that protrude from a thick plate embedded in the wall of the tank. The plate has a second set of prongs facing outside the tank. These exterior prongs plug into sockets outside the tank. Wires lead from those sockets to an electronics box in the shuttle.
Technicians took the wires, prongs and external sockets off Atlantis and exposed them in the laboratory to the pressures and temperatures they feel as fuel fills the tank. The electrical signal from the sensor did not get through the equipment — the same problem that occurred when Atlantis was gassed up for launch.
Engineers believe that they’ve prevented glitches by soldering the pins to the external sockets, ensuring a good path for the electrical signal. They’re still looking for the problem’s ultimate cause.
"We need another piece of the puzzle in order to say we’re absolutely confident that we’ve got it," Bryant says. "But we’re becoming more confident by the day."