Discovery Space Shuttle External Tanks Near Disaster
Following the space shuttle disaster of Columbia when it broke apart upon re-entry on February 1 2003, the space shuttle fleet was grounded. NASA under took a massive certification and verification process that evaluated all of the space shuttles critical systems, and at the same time addressed the external tank foam debris, which was determined to be the primary cause of the Columbia disaster.
Discovery Space Shuttle flew 39 times from 1984-2011 making it the longest serving orbiter.
NASA sets May of 2005 as the launch target window, but when critical external tank test fails NASA scrapes the launch date and takes on a new investigation that reveilles and tangled web of mistakes that once again threatens to ground the space shuttle fleet.
Components of the Space Shuttles
The space shuttle is comprised of the orbiter, the main engines, the solid rocket boosters and the external tank. The 154 foot external tank supplies fuel to the space shuttle's main engines during launch and ascent. The structural backbone of the space shuttle, the external tank was the vehicle's only major component that was discarded after every launch. The lithium aluminum alloy tank is comprised of 2 fuel tanks. The forward tank called the liquid oxygen tank (lox tank) which contains 146,000 gallons of liquid oxygen. The rear liquid hydrogen tank (LH2 tank) contains 395,000 gallons of liquid hydrogen.
Every space shuttle launch requires a new external tank and NASA's Michoud Assembly Facility, in New Orleans Louisiana, was the obvious choice to build the external tanks for the space shuttles. It was the original manufacturing facility for the Saturn 5 rocket, the rocket that took man to the moon. Prior to the Columbia disaster, 113 completed external tanks were built, loaded on barges and transported to Cape Canaveral Florida where they are married to the space shuttles.
Space Shuttle external tank diffusers are faulty
Less than 45 days before the launch window, a company interested creating and supplying the screen material used on a critical piece of hardware called a diffuser, contacted engineers at NASA's Michoud Facility. The company requested several screen material samples used, to determine if they could meet the required specifications and when they analyzed the samples, they discovered that there were 2 different types of screen material.
The Space Shuttle external tank was the component that contained the liquid hydrogen fuel and liquid oxygen oxidizer.
The diffuser is used in the top of both the liquid oxygen tank and liquid hydrogen tank. When a space shuttle launches, the liquid level of the tanks start to drop and it forms a vacuum. To prevent the tank from collapsing in on its self, pressure is put back into the top of the tank. A diffuser is finely calibrated to put pressure back into the tank, matching the drain rate of the liquid fuel. It also disperses the pressure evenly so it dose not all go into one spot and cause one area to be to hot or to cold. If the rate is restricted, the vacuum pressure in the tank would restrict the fuel flow and cause the tank to collapse resulting in a catastrophic failure.
With space shuttle Discovery fully stacked and ready for a mission, NASA had to launch a full investigation. NASA had to find out if the external tank that was on Discovery had the correct diffuser screen material, and if not, they had to find out if the incorrect screen material would effect the diffuser performance.
One of the screen samples had a plain dutch weave, and the other had a duplex plain dutch weave. Though analyst NASA found out that the duplex plain dutch weave was not acceptable because it would restrict the uniform flow of pressure back into the external tank. Incorrect diffuser pressure could result in the external tank collapsing, or restrict the flow of fuel to the main engines causing catastrophic failure in loss of space shuttle and crew.
The diffusers in the completed external tanks already on space shuttle Discovery, could not be accessed for inspection. Investigators discover that 15 of 21 diffusers, that where in inventory and not yet installed, where constructed with the wrong material. The chance of faulty diffusers already installed in external tanks was high. With the Discovery shuttle already on the launch pad a standard critical tanking test is performed.
Diffusers in Discovery space shuttle are found to be faulty
The external tank compartments are filled with liquid oxygen and liquid hydrogen, and as testing begins, a liquid hydrogen pressurization relief valve is cycling more than normal. The valve is designed to open and close to insure that the liquid hydrogen stays at the correct temperature. Than engineers begin to receive intermittent reading for the liquid hydrogen sensors. The sensors serve as fuel gauges and send a signal to the main engines when the fuel is depleted telling the main engine to shut off. After the test a full system analysis indicate a problem with the hydrogen tank diffuser.
Further documentation investigations found that in inventory and diffusers installed on tanks, 31 diffusers were made with the wrong material. Of the 26 diffusers installed in 13 completed external tanks, 16 diffusers are faulty. The NASA team confirms that the hydrogen diffuser in Discovery's external tank is also one of the de-faulty diffusers.
Discovery Space Shuttle external tanks is changed out
Stored in the vehicle assembly building, is a external tank for the space shuttle Atlantis, but its diffusers are de-faulty as well. NASA's Michoud Facility sends a team of 30 technicians and engineers to replace the bad diffusers as the external tank is already prepped to all the return certifications requirements and is essentially ready to go. Changing the external tank on space shuttle Discovery will be quicker than having a new tank transported out from Louisiana.
The company that supplied the incorrect plain dutch weave screen for the diffusers went out of business, NASA's investigation team could not find out why the wrong material was delivered, having the same part number as the correct screens, to NASA's Michoud Assembly Facility. From than on NASA confirms the screen with magnification to check for the correct specification even if the paper work says it is correct. The paper work was also update to clarify the exact screen specifications.
Discovery Space Shuttle launch, July 26 2005
July 26 2005, space shuttle Discovery was finally launched, 2 years and 6 months after the space shuttle Columbia disaster. This was not the only time that Space Shuttle Discovery was on the edge of destruction.