Aerodynamics May Explain Space Shuttle Breakup: possible causes, consequences of Columbia disaster

http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/et.html#et-tps

EXTERNAL TANK

The external tank contains the liquid hydrogen fuel and liquid oxygen oxidizer and supplies them under pressure to the three space shuttle main engines in the orbiter during lift-off and ascent. When the SSMEs are shut down, the ET is jettisoned, enters the Earth's atmosphere, breaks up, and impacts in a remote ocean area. It is not recovered.

The largest and heaviest (when loaded) element of the space shuttle, the ET has three major components: the forward liquid oxygen tank, an unpressurized intertank that contains most of the electrical components, and the aft liquid hydrogen tank. The ET is 153.8 feet long and has a diameter of 27.6 feet.

Beginning with the STS-6 mission, a lightweight ET was introduced. Although future tanks may vary slightly, each will weigh approximately 66,000 pounds inert. The last heavyweight tank, flown on STS-7, weighed approximately 77,000 pounds inert. For each pound of weight reduced from the ET, the cargo-carrying capability of the space shuttle spacecraft is increased almost one pound. The weight reduction was accomplished by eliminating portions of stringers (structural stiffeners running the length of the hydrogen tank), using fewer stiffener rings and by modifying major frames in the hydrogen tank. Also, significant portions of the tank are milled differently to reduce thickness, and the weight of the ET's aft solid rocket booster attachments were reduced by using a stronger, yet lighter and less expensive titanium alloy. Earlier several hundred pounds were eliminated by deleting the anti-geyser line. The line paralleled the oxygen feed line and provided a circulation path for liquid oxygen to reduce accumulation of gaseous oxygen in the feed line while the oxygen tank was being filled before launch. After propellant loading data from ground tests and the first few space shuttle missions was assessed, the anti- geyser line was removed for STS-5 and subsequent missions. The total length and diameter of the ET remain unchanged.

The ET is attached to the orbiter at one forward attachment point and two aft points. In the aft attachment area, there are also umbilicals that carry fluids, gases, electrical signals and electrical power between the tank and the orbiter. Electrical signals and controls between the orbiter and the two solid rocket boosters also are routed through those umbilicals.

LIQUID OXYGEN TANK

The liquid oxygen tank is an aluminum monocoque structure composed of a fusion-welded assembly of preformed, chem-milled gores, panels, machined fittings and ring chords. It operates in a pressure range of 20 to 22 psig. The tank contains anti-slosh and anti-vortex provisions to minimize liquid residuals and damp fluid motion. The tank feeds into a 17-inch- diameter feed line that conveys the liquid oxygen through the intertank, then outside the ET to the aft right-hand ET / orbiter disconnect umbilical. The 17-inch-diameter feed line permits liquid oxygen to flow at approximately 2,787 pounds per second with the SSMEs operating at 104 percent or permits a maximum flow of 17,592 gallons per minute. The liquid oxygen tank's double-wedge nose cone reduces drag and heating, contains the vehicle's ascent air data system (for nine tanks only) and serves as a lightning rod. The liquid oxygen tank's volume is 19,563 cubic feet. It is 331 inches in diameter, 592 inches long and weighs 12,000 pounds empty.

INTERTANK

The intertank is a steel / aluminum semimonocoque cylindrical structure with flanges on each end for joining the liquid oxygen and liquid hydrogen tanks. The intertank houses ET instrumentation components and provides an umbilical plate that interfaces with the ground facility arm for purge gas supply, hazardous gas detection and hydrogen gas boiloff during ground operations. It consists of mechanically joined skin, stringers and machined panels of aluminum alloy. The intertank is vented during flight. The intertank contains the forward SRB-ET attach thrust beam and fittings that distribute the SRB loads to the liquid oxygen and liquid hydrogen tanks. The intertank is 270 inches long, 331 inches in diameter and weighs 12,100 pounds.

Each propellant tank has a vent and relief valve at its forward end. This dual-function valve can be opened by ground support equipment for the vent function during prelaunch and can open during flight when the ullage (empty space) pressure of the liquid hydrogen tank reaches 38 psig or the ullage pressure of the liquid oxygen tank reaches 25 psig.

The liquid oxygen tank contains a separate, pyrotechnically operated, propulsive tumble vent valve at its forward end. At separation, the liquid oxygen tumble vent valve is opened, providing impulse to assist in the separation maneuver and more positive control of the entry aerodynamics of the ET.

There are eight propellant-depletion sensors, four each for fuel and oxidizer. The fuel-depletion sensors are located in the bottom of the fuel tank. The oxidizer sensors are mounted in the orbiter liquid oxygen feed line manifold downstream of the feed line disconnect. During SSME thrusting, the orbiter general-purpose computers constantly compute the instantaneous mass of the vehicle due to the usage of the propellants. Normally, main engine cutoff is based on a predetermined velocity; however, if any two of the fuel or oxidizer sensors sense a dry condition, the engines will be shut down.

The locations of the liquid oxygen sensors allow the maximum amount of oxidizer to be consumed in the engines, while allowing sufficient time to shut down the engines before the oxidizer pumps cavitate (run dry). In addition, 1,100 pounds of liquid hydrogen are loaded over and above that required by the 6-1 oxidizer / fuel engine mixture ratio. This assures that MECO from the depletion sensors is fuel-rich; oxidizer-rich engine shutdowns can cause burning and severe erosion of engine components.

Four pressure transducers located at the top of the liquid oxygen and liquid hydrogen tanks monitor the ullage pressures.

Each of the two aft external tank umbilical plates mate with a corresponding plate on the orbiter. The plates help maintain alignment among the umbilicals. Physical strength at the umbilical plates is provided by bolting corresponding umbilical plates together. When the orbiter GPCs command external tank separation, the bolts are severed by pyrotechnic devices.

The ET has five propellant umbilical valves that interface with orbiter umbilicals: two for the liquid oxygen tank and three for the liquid hydrogen tank. One of the liquid oxygen tank umbilical valves is for liquid oxygen, the other for gaseous oxygen. The liquid hydrogen tank umbilical has two valves for liquid and one for gas. The intermediate-diameter liquid hydrogen umbilical is a recirculation umbilical used only during the liquid hydrogen chill-down sequence during prelaunch.

The ET also has two electrical umbilicals that carry electrical power from the orbiter to the tank and the two SRBs and provide information from the SRBs and ET to the orbiter.

A swing-arm-mounted cap to the fixed service structure covers the oxygen tank vent on top of the ET during the countdown and is retracted about two minutes before lift- off. The cap siphons off oxygen vapor that threatens to form large ice on the ET, thus protecting the orbiter's thermal protection system during launch.

ET RANGE SAFETY SYSTEM

range safety system

Various parameters are monitored and displayed on the flight deck display and control panel and are transmitted to the ground.

The contractor for the external tank is Martin Marietta Aero space, New Orleans, La. The tank is manufactured at Michoud, La. Motorola, Inc., Scottsdale, Ariz., is the contractor for range safety receivers.

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Table of Contents

Information content from the NSTS Shuttle Reference Manual (1988)
Last Hypertexed Thursday August 31 09:40:49 EDT 2000
Jim Dumoulin (dumoulin@titan.ksc.nasa.gov)

"I can say this; the Ceramic tiles are not like the ceramics you find in a local store. I can grab the material and crush it in my hand. Feels almost like foam. I have a piece of it here in my office and it has dents from my fingers. "

You may have a piece of SIRCA from the leading edge. I know that NASA was experimenting with it a few years ago. SIRCA = Silicon Impregnated Reusable Ceramic Ablative. It is not a true "ablative" -- When brand new it is white. After its first use the surface layer heats up and ablates to form a hard black surface which provides a standoff protecting the rest of the leading edge tile.

I share your views about the streaming telemetry; it's always captured, uninterrupted, throughout each mission's duration.

In all likelihood, every bit and byte of data, up to the moment of explosion, should be recovered and serve as the most reliable source for nailing down the cause of this tragedy.

And what a wonderful address just now by the President...what a man.

I completely agree. The telemetry data should tell all.

You may have a piece of SIRCA from the leading edge. I know that NASA was experimenting with it a few years ago. SIRCA = Silicon Impregnated Reusable Ceramic Ablative. It is not a true "ablative" -- When brand new it is white. After its first use the surface layer heats up and ablates to form a hard black surface which provides a standoff protecting the rest of the leading edge tile.

Thanks! My specialty is mission control/operations, not thermal design. It was given to me a few years ago.

Bump.

I believe NASA possibly knows what happend. Do you agree with this?

Already knows what *happened* too.....Jesh....

"And what a wonderful address just now by the President...what a man. "

Amen to that. "We know that they didn't return to Earth but they did return safely home." Maybe I screwed that up a little but that is a beautiful thought.

Here's my tribute. I've had this song going in my head for at least a month, now, I suspect, prophetically. It's the theme song from the new Enterprise, "Faith of the Heart".http://scifi.myrealm.co.uk/audio/enterprise2.mp3

Local CH 11 reporting a SS tile found WEST of I-35 and south of Dallas in Waxahachie area ... the "tile video" from reporter on the scene shows the Space Shuttle tile laying on roof ... woman woke up to 'thud' sound ...

http://www.lockheedmartin.com/michoud/et/description.htm

The External Tank (ET) is the only non-reusable major component of the Space Shuttle system that consists of the ET, the Orbiter and the two Solid Rocket Boosters. The ET is the single largest element at 154 feet long and 27.6 feet in diameter, and during launch it serves as the structural backbone of the shuttle, absorbing most of the six million pounds of thrust generated during flight and providing propellant to the Orbiter’s three main engines.

A new version of the ET, the Super Lightweight Tank (SLWT), is 7,500 pounds lighter than the previous Lightweight Tank design. The reduced weight is a result of component redesign and the use of Weldalite™, an aluminum-lithium (Al-Li) alloy developed by Lockheed Martin. The Al-Li alloy is 30 percent stronger and five percent less dense than the aluminum alloy previously used in manufacturing ETs.

The first SLWT flew as part of STS-91 on June 2, 1998.

Weighing 58,500 pounds empty and 1.6 million pounds when filled with cryogenic propellants, the ET supplies over 535,000 gallons of liquid oxygen and liquid hydrogen to the Orbiter's engines. The 7,500-pound weight savings resulting from the SLWT increases shuttle payload capacity by a similar amount. The performance increase is vital to the building and supplying of the International Space Station.

Lockheed Martin is under contract to the NASA Marshall Space Flight Center to assemble ETs at Michoud Assembly Facility in New Orleans through 2001. Negotiations are currently underway for the production of additional ETs to support the Space Shuttle program.

External Tank Components

The liquid oxygen tank is an aluminum monocoque structure composed of a fusion-welded assembly of preformed, chem-milled gores, panels, machined fittings and ring chords. It operates in a pressure range of 20 to 22 pounds per square inch. The tank contains anti-slosh and anti-vortex provisions to minimize liquid residuals and damp fluid motion. The tank feeds into a 17-inch-diameter feed line that conveys the liquid oxygen through the intertank, then outside the ET to the aft right-hand ET / orbiter disconnect umbilical. The 17-inch-diameter feed line permits liquid oxygen to flow at approximately 2,787 pounds per second with the Space Shuttle Main Engines operating at 104 percent or permits a maximum flow of 17,592 gallons per minute. The liquid oxygen tank's nose cone reduces drag and heating and serves as a lightning rod. The liquid oxygen tank's volume is 19,563 cubic feet. It is 331 inches in diameter and 592 inches long.

The liquid hydrogen tank is an aluminum semimonocoque structure of fusion-welded barrel sections, five major ring frames, and forward and aft ellipsoidal domes. Its operating pressure range is 32 to 34 pounds per square inch. The tank contains an anti-vortex baffle and siphon outlet to transmit the liquid hydrogen from the tank through a 17-inch line to the left aft umbilical. The liquid hydrogen feed line flow rate is 465 pounds per second with the Space Shuttle Main Engines at 104 percent or a maximum flow of 47,365 gallons per minute. At the forward end of the liquid hydrogen tank is the ET / orbiter forward attachment pod strut, and at its aft end are the two ET / orbiter aft attachment ball fittings as well as the aft solid rocket booster-ET stabilizing strut attachments. The liquid hydrogen tank is 331 inches in diameter, 1,160 inches long, and has a volume of 53,518 cubic feet.

The intertank is a steel / aluminum semimonocoque cylindrical structure with flanges on each end for joining the forward liquid oxygen and aft liquid hydrogen tanks. The intertank houses ET instrumentation components and provides an umbilical plate that interfaces with the ground facility arm for purge gas supply, hazardous gas detection and hydrogen gas boiloff during pre-launch operations. It consists of mechanically joined skin, stringers and machined panels of aluminum alloy. The intertank is vented during flight. The intertank contains the forward solid rocket booster (SRB)-ET attach thrust beam and fittings that distribute the SRB loads to the liquid oxygen and liquid hydrogen tanks. The intertank is 270 inches long and 331 inches in diameter.

To prevent the super cold liquid oxygen (-297 degrees F) and liquid hydrogen (-423 degrees F) from forming ice on the outside surfaces of the ET, a multi-layered thermal protection coating approximately one inch thick is applied. The insulation allows the ET to withstand the extreme internal and external temperatures generated during prelaunch, launch and flight.

At launch, propellants are pressure-fed at a combined rate of 1,035 gallons per second through 17-inch diameter feed lines to the Orbiter’s engines. Eight and one-half minutes into flight, with the Orbiter and ET at an altitude of about 71 nautical miles, the main engines are cut off and the ET is jettisoned. The tank slowly tumbles, reenters the atmosphere and burns up, with small surviving parts safely falling into remote areas of the Pacific or Indian Oceans.

ET Weight Savings Means More Payload

The first Space Shuttle powered by an External Tank flew on April 12, 1981. The version of the ET used on the initial launches weighed 76,000 pounds. A subsequent redesign program netted a 10,000-pound weight savings on the ET. Because the ET and orbiter have virtually reached gravitational escape velocity when the Et is jettisoned, every pound reduced from the ET results in another pound that can be taken to orbit. Thus the 66,000-pound Lightweight Tank, introduced on the sixth Space Shuttle mission in 1983, resulted in substantial improvements to shuttle payload performance.

The weight-savings continued in 1998 with the Super Lightweight Tank weighing another 7,500 pounds less. This opened the door for the Space Shuttle to carry the heavier components of the International Space Station.

Related NASA's Fact Sheet site: A Walk Around the Space Shuttle for information on the other components (Orbiter and Solid Rocket Boosters) of the Space Shuttle.

"would be an aerodynamic structural breakup of the shuttle caused by it rolling at the wrong angle. Remember, after reentry, the shuttle is descending without power"

All of the huge "S" turns which reduce speed are executed over the western states and are completely computer controlled.

Pilot control returns at subsonic speeds for landing.

The computer program that operates this speed reduction might have been sabotaged.

I believe NASA possibly knows what happend. Do you agree with this?

I don’t think so. I personally can’t even speculate what happened.

http://www.arnold.af.mil/aedc/newsreleases/1999/99-041.htm

NEWS RELEASE
United States Air Force
Air Force Materiel Command

Office of Public Affairs
Arnold Engineering Development Center
100 Kindel Drive
Arnold AFB, TN 37389-2213
(931) 454-5586
http://www.arnold.af.mil

Writer: Danette Duncan
Date: March 19, 1999
Release # 99-041
Photo # none

AEDC Performs Shuttle Materials Test for NASA/Lockheed Martin

ARNOLD AFB, Tenn.—Arnold Engineering Development Center is assisting the National Aeronautics Space Administration with improvements in existing Space Shuttle materials.

According to NASA, during several previous Space Shuttle flights, including the shuttle launched Nov. 29, 1998, the shuttle external tank experienced a significant loss of foam from the intertank. The material lost caused damage to the thermal protection high-temperature tiles on the lower surface of the shuttle orbiter. The loss of external tank foam material and subsequent damage to reentry tiles is a concern because it causes tile replacement costs to significantly increase,,u. however, it is not a flight safety issue. As a result, NASA-Marshall Space Flight Center selected AEDC to perform flight hardware materials tests on the shuttle’s external tank panels in the center’s von Karman Facility Supersonic Tunnel A. The purpose was to establish the cause of failure for the tank thermal protection materials at specified simulated flight conditions. "NASA chose AEDC due to its technical expertise and historical program successes," Steve Holmes, a NASA-MSFC technical coordinator, said.

The Lockheed Martin-manufactured non-reusable external tank, the largest element of the Space Shuttle, fuels the shuttle orbiter during powered flight and is comprised of three components—a liquid oxygen tank, a liquid hydrogen tank and an intertank assembly that connects the two propellant tanks. At the full capacity of 528,600 gallons of propellant, the external tank weighs 1.6 million pounds. The tank is covered with a multi-layered, spray-on foam insulation that provides thermal insulation for the tank against the extreme internal and external temperatures generated during prelaunch, launch and flight.

Wayne Hawkins, Sverdrup project engineer, explained the foam system is exposed to multiple forces, causing difficulty in determining the actual failure of the thermal protection system. "Multiple forces act on the foam system," Hawkins said. "The environmental factors include thermal protection system cell expansion, aerodynamic loading, highly variable local flow conditions, oscillating shocks, vibration, temperature and main external tank substrate flexure."

Although NASA and other facilities have performed a number of tests in an attempt to define the underlying root cause of this foam loss, they were not successful. At one time, the center’s 4-foot and 16-foot transonic aerodynamic wind tunnels were possibilities for the test, but Tunnel A’s ability to closely duplicate flight conditions and control both ambient pressure and test sample immersion time made it the facility of choice. Tunnel A is a continuous flow-variable density wind tunnel with an automatically driven flexible-plate nozzle and a 40- by 40-inch test section and can cover the Mach number range of 1.5 to 5.5.

"The ideal success for the test is the generation of foam loss on a consistent basis with simulated flight conditions," Hawkins said.

Although the AEDC Tunnel A tests did not replicate the in-flight failures, they did provide detailed measurements to better understand the flight environment and fundamental failure mode. From these tests, NASA determined the failure is caused principally by foam cell expansion due to external heating at approximately Mach 4 combined with pressure change and aerodynamic shear. Specialized miniature shear gages and other instrumentation were installed during the test to measure these forces. The customer and sponsor were pleased with the AEDC test results. "No other facility can test with articles/models as large as AEDC with conditions that can match flight," Holmes said.

Is there a black box, so to speak, on board the shuttles??

Yes, there are tape recorders. It is highly unlikely that they survived re-entry intact.

How long would it take them to examine their data, and given this was a catastrophic incident, don't you think it would be fairly easy for them to put their finger on it?

They recovered at least one after Challenger as I recall You recall correctly. But they are powered by the orbiter main busses, and stop recording as soon as the power goes off.

But isn't the data from those boxes being transmitted to the ground in real time?

I vote you as "1st with the Best Evaluation".

(7yrs on W. Coast Shuttle @ VAFB, CA [GSS]
30 yrs. aerospace)

EXTERNAL TANK

LIQUID OXYGEN TANK

INTERTANK

LIQUID HYDROGEN TANK

ET THERMAL PROTECTION SYSTEM

ET HARDWARE

ET RANGE SAFETY SYSTEM