Last Friday, NASA brought STS-114’s countdown to a halt after a liquid hydrogen low-level fuel sensor inside the Space Shuttle Discovery's external tank failed during a routine pre-launch check. A dozen teams with hundreds of engineers around the country are working on the issue. Once it is resolved, the mission can commence and a new era in safer spaceflight will begin.
STS-114, also known as Return to Flight, will be the first shuttle mission since the Columbia was destroyed upon re-entry two-and-a-half years ago. The path to recovery since then has been long, involving complex investigations and upgrades all designed to prevent another tragedy. In fact, STS-114’s primary goal is to test these improvements.
For example, the bipod fitting that joins the external tank to the orbiter is susceptible to icing, due to the ultra-cold fuel the tank contains. Previously, NASA used thick sheets of foam to prevent this icing. But the Columbia accident occurred when this foam fell off the tank and damaged the shuttle’s left wing, letting superheated gasses inside.
NASA’s engineers have eliminated this foam from the 11 tanks in the shuttle fleet and replaced it with electric heaters that melt the ice. Similar heaters have been added to the liquid oxygen feedline bellows that carry fuel from the external tank to the orbiter.
Observation has been improved as well. NASA has upgraded the short-range, medium-range, and long-range tracking camera systems around Kennedy Space Center launch pads 39A and 39B, as well as the systems lining the nearby Atlantic coastline. Nine additional camera sites will provide unprecedented views of the launch so engineers can observe the flight well into its flight path.
The external tank now sports a digital camera, similar to a typical 35-mm commercial model, that will snap a series of photos as the tank separates from the orbiter. Discovery will transmit these images to the ground crew immediately, avoiding the delay required by retrieving and processing the previous film system.
Once in orbit, the new Orbiter Boom Sensor System will continue the inspections. This extension to the Canadarm inside Discovery’s payload bay houses a camera and a laser-powered measuring device the astronauts will use to scan the orbiter’s exterior. It also extends the boom an additional 100 feet, reaching around the spacecraft for the best possible views.
The orbiter’s leading wing edges now have 22 temperature sensors that measure how heat is distributed across their spans, taking 20,000 readings per second. The wings also have 66 accelerometers each to detect impacts and gauge their strength and location. After Discovery returns, technicians will use flash thermography to inspect the wings for flaws caused by stress and extreme heat.
Once the current sensor problem is resolved, NASA will restart the countdown, requiring about four days to prepare for a new launch. NASA is confident that it will be able to launch by July 31, the end of the current launch window.
For more information, go to the NASA web site.