NASA says it will fill up the space shuttle Atlantis’ fuel tank next week to diagnose a fuel-gauge problem that led to back-to-back launch delays.
Next Tuesday's tanking test could lead to a quick fix, putting Atlantis back on track for a launch as early as Jan. 2 to bring the European Space Agency's Columbus laboratory to the international space station. Or it could force NASA to take more time to study the vexing problem.
"We're going to go where the data leads us to go," shuttle program manager Wayne Hale told reporters Tuesday.
Hale said the trouble could be anywhere in the 100 feet (30 meters) of wiring between the four gauges at the bottom of the fuel tank and the shuttle itself, in any of the connectors or even in the sensors themselves. A diagnostic tool known as a time-domain reflectometer will be used to track down exactly where a break in the circuitry might be located.
At the same time, engineers will conduct other tests, mostly in laboratories, to try to figure out what is causing the gauges in Atlantis’ tank to malfunction every time they’re exposed to the super-cold liquid hydrogen that fuels the shuttle.
Last Thursday and again Sunday, some of the gauges failed as the shuttle’s external fuel tank was being loaded. Both times, the countdown was halted and the launch called off.
Although Hale said NASA's schedule still called for Atlantis' launch to take place no earlier than Jan. 2, he added that the actual date “could definitely be a little bit later than that.”
“I am very concerned about team fatigue,” he said during a news conference. “When we talk about no earlier than Jan. 2, part of the discussion is not only how quickly can we troubleshoot and fix this problem, but what is prudent to allow our folks to have a few days with their families, and rest and recuperate.”
Shuttle safety system
The four so-called engine cutoff sensors are part of a backup safety system that prevents the shuttle’s main engines from running on an empty fuel tank, a potentially catastrophic situation. Hale compared the system to the seat belt in an automobile.
"If you did have something bad happen to you, you'd be really glad that you had it," he said.
The sensors have malfunctioned off and on over the past two years, ever since shuttle flights resumed following the Columbia tragedy. "We thought we had it fixed, quite frankly, and found out that we did not," Hale said.
Hale was reluctant to discuss possible options if engineers cannot discover a cause for the problem. "I'll let you know when we have our tanking test done and we have some data," he said.
For NASA's most recent shuttle flights, only three of the four sensors had to work in order for liftoff to proceed. However, the flight rules were changed to require that all four gauges be in working order for Sunday's launch attempt. One of the gauges failed soon after tanking started — forcing the latest postponement.
Hale declined to speculate on whether the rules might be changed again. "We have tabled that discussion," he told reporters. "Our point is to try to fix this system today."
Reflectometer at work
For next Tuesday's tanking test, NASA will cut into the system’s wiring and install jumper cables leading to the reflectometer out on the launch pad.
The reflectometer — a device that sends out timed pulses — is commonly used by telephone and cable companies to track open circuits or other problems in their lines. When the pulses are sent through a circuit, part of the signal is reflected back by any flaw in the circuitry. By precisely measuring how long it takes for the echo to return, the device can indicate the location of the flaw.
NASA has used such devices before, but never as part of a shuttle fueling test, Hale said.
The astronauts at the space station, meanwhile, are expected to conduct a spacewalk that same day to shed more light on a flawed solar rotary joint. Two of Atlantis’ crew were supposed to go out and fully inspect the joint; officials want to move up the work now that the shuttle flight is off until January.
The joint controls the movement of a set of solar wings and, until it is fixed, cannot be used in the automatic mode to turn the wings toward the sun. It’s filled with steel grit because of grinding parts and may require several spacewalks next year to fix it.
This report includes information from The Associated Press and msnbc.com.