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Last Shuttle External Tank Rolling Out on July 8
External tank ET-138
Space Shuttle Endeavour launches into an early morning sky at NASA's Kennedy Space Center. External tank ET-138 (top) will help launch Space shuttle Endeavour (bottom) into space on its last mission later this year. (Image credit: NASA)
The last external tank scheduled to fly on a space shuttle mission will roll out at NASA's Michoud Assembly Facility in New Orleans July 8. On Wednesday, July 7, Mark Bryant, vice president of the External Tank (ET) Program for Lockheed Martin Space Systems, answered your questions about the external tank.

More About External Tank ET-138
Designated ET-138, it will be loaded onto a barge to begin its 900-mile sea journey to NASA's Kennedy Space Center, Fla. The external tank, the "gas tank" for the orbiter, holds the propellants used by the space shuttle main engines. It also is the "backbone" of the shuttle during launch, providing structural support for attachment with the solid rocket boosters and orbiter. It is the only component of the space shuttle that is not reused. Approximately 8.5 minutes into the flight, with its propellant used, the tank is jettisoned into the ocean.

Taller than a 15-story building and more than 27 feet in diameter, the external tank absorbs the 7.8 million pounds of thrust of the three space shuttle main engines and solid rocket boosters during a space shuttle launch. It feeds 145,000 gallons of liquid oxygen and 390,000 gallons of liquid hydrogen to the main engines.

The three main components of the external tank include the liquid oxygen tank, liquid hydrogen tank and the collar-like intertank, which connects the two propellant tanks. The intertank houses instrumentation and processing equipment and provides the attachment structure for the solid rocket boosters.

When ET-138 arrives at Kennedy, processing will begin to mate it with shuttle Endeavour and solid rocket boosters for the STS-134 mission, scheduled to launch no earlier than mid-November. The mission will deliver the Express Logistics Carrier 3 and the Alpha Magnetic Spectrometer to the International Space Station. It will be the 36th shuttle mission to the space station and the 134th and final scheduled shuttle flight.

Michoud Space Systems workers, of Lockheed Martin Corporation, Littleton, Colo., have delivered 135 flight tanks to NASA during the 25 years of flying the space shuttle.

Work will be completed on one additional external tank, ET-122, which was at Michoud during Hurricane Katrina in August 2005 and damaged by falling debris. It is being restored to flight configuration and is scheduled for delivery to Kennedy in late September to serve as the “Launch on Need” tank, if needed, for STS-134.

About Mark Bryant
Mark Bryant Mark Bryant is vice president of the External Tank (ET) Program for Lockheed Martin Space Systems, which builds the Space Shuttle External Tank at the NASA Michoud Assembly Facility in New Orleans. He is responsible for the design, production, delivery, and flight of the ET during the Space Shuttle fly-out period.

Bryant’s career with Lockheed Martin began in 1985, following six years as an oilfield engineer for Schlumberger. Starting as a facilities engineer, he rose through the ranks to senior manager of Materiel Subcontract Support in 1998, director of Materiel Sourcing in 2002, External Tank deputy project manager for non-Return to Flight activities in 2003, External Tank deputy project manager in 2007, and now his present position.

NASA astronaut Tony Antonelli presented Bryant with the NASA Leadership Award on June 17, 2010. A native of Chattanooga, Tennessee, he holds a degree in Mechanical Engineering from the University of Tennessee and an MBA from Tulane University.

Chat Transcript

Mark: Hi everyone, Mark here. We're getting the chat set up and ready to start answering your questions in about 20 minutes. We have some good ones already coming in and we're working on those. Thanks!

(Moderator Jason): Today's chat is scheduled to begin at 11am ET. Please begin to ask your questions by typing them into the box at the bottom of the screen and clicking the 'Ask' button on the right. We'll begin answering questions in about ten minutes. Thanks for your patience.

(Moderator Jason): Hello everyone. Our chat will begin momentarily. Thanks for your patience.

john: Do you reuse external tanks?

Mark: No, we don't reuse them. They're the only element of the shuttle vehicle that's not reused. We spend a few years building them, it performs for 8.5 minutes, and then it's jettisoned, enters the Earth's atmosphere, breaks up, and impacts in the South Pacific.

john: Why is the external tank reddish?

Mark: That's the color of the insulating foam that's applied to the external surface of the tank. When the foam is first applied -- it's a light tan, then exposure to UV rays darkens or reddens the foam over time.

TheCFiles: Also-if you still have more Shuttle missions planned through 2010, why would this be the last external fuel tank? Don't you need others for the other Shuttle Missions?

Mark: There are currently two more missions planned to be flown: one late in 2010 and one early in 2011. The tank for the next flight in late 2010, ET-137, is already at KSC and being prepared for launch. The tank we're delivering tomorrow, ET-138, will fly on the mission in early 2011, the last currently planned flight.

JimSa: What happens to the external tanks after separation from the launched shuttle?

Mark: The tanks fall back into the atmosphere because they don't have quite enough speed to reach orbit. As they enter the atmosphere, aerodynamic forces and heating causes the tanks to break up and impact in a remote area of the South Pacific.

JimSa: The tanks have been transported across the Gulf of Mexico on a large barge. Is there a future use for the barge?

Mark: The current barge was originally built to haul a new generation of shuttle solid rocket boosters from a plant in Mississippi. When that program was cancelled, the barge was modified to haul external tanks, which allowed us to retire some old WW2 vintage barges. The barge should be able to be readily modified to support the movement of large space structures.

atlantis: Have you any news on the status and delivery date of et-122?

Mark: ET-122 was previously delivered to NASA but was being modified for return to flight following the loss of Columbia. The tank was undergoing these modifications at the Michoud Assembly Facility when Hurricane Katrina struck, and the tank was damaged. We're currently repairing the tank and implementing the performance improvements with a plan to deliver the tank to NASA in Sept. 2010. The tank is currently planned to serve as a potential rescue mission for the last planned flight.

TheCFiles: Looking at photos of EFT arriving by barge, and being assembled into VAB. I can't see how they actually lift the EFT vertically inside the VAB, there are no cables visible. How is that done?

Mark: It is lifted by a crane with cables attached to the solid rocket booster forward attach fittings on the external tank. You can't see the cables just due to the distance of the camera.

Michael_C: Why were the External Tanks on STS-1 and STS-2 painted white? Thank you.

Mark: If you look at all previous rockets, they were all painted white. There was also a concern about exposing the insulating foam to the environment. That concern was resolved, and the paint was eliminated as part of a weight-savings program. It reduced the weight of the tank by several hundred pounds, providing useful payload capacity to the shuttle.

TheCFiles: What sort of material is the exterior of the EFT made up of, to withstand the heat of launch and main rocket engines into orbit?

Mark: It's made of a isocyanate foam with some high temperature ablator materials in certain locations. The foam not only protects the structure from the heat of ascent and radiant heat from the engines, but it also prevents ice and liquid air formation on the outside of the tank as well as maintaining propellant quality during pre-launch.

(Moderator Jason): We're getting a lot of great questions so far. Keep them coming! To submit a question of your own, please type it into the box at the bottom of the window. When ready, simply click the 'Ask' button to the right to submit your question to the queue. Thanks for your patience as we answer your questions.

atlantis: Please can you tell me if there will be television coverage on nasa tv of the ceremony tomorrow?

Mark: Yes, NASA will provide live coverage beginning at 8:45 Central time on NASA TV.

Akarsh_Valsan: Sir, why did NASA stop flying the Space Shuttle Atlantis?

Mark: The last mission, STS-132, was the last planned flight of Atlantis. It's currently planned to be used for a rescue mission for the last flight, should that be necessary. Following that, Atlantis will be retired along with the rest of the space shuttle orbiter fleet, Discovery and Endeavour.

capbeto: Hello! What is the final destiny of three shuttles? Thanks! (from Argentina)

Mark: The final disposition of the space shuttles is being determined at this time. Stay tuned. :)

TheCFiles: Since the EFT is transported by barge across the Gulf from LA to FL, is the oil spill and great amount of oil on the water surface affecting that process? Are you having to reroute at all?

Mark: There's no impact to the route planned for the transport of the Pegasus barge and ET-138 due to the oil spill.

Akarsh_Valsan: Hi Mark, can you explain the need of a gas tank?

Mark: The external tank serves two primary functions: it serves as the structural backbone of the space shuttle vehicle, tying the solid rocket boosters, orbiter, and tank into one integrated stack. It also provides the fuel and oxidizer for the space shuttle main engines, located on the orbiter. The orbiter itself doesn't carry any fuel or oxidizer internally for its main engines and relies upon the external tank for that function.

the_last_et: How long does take build one?

Mark: The length of time to build a tank is driven by how many shifts you work, and by the additional process controls put in place following the loss of Columbia. The lightweight version of the external tank used to take about two years to build. The current super lightweight version with the post-Columbia modifications and process controls takes more than three years, start to finish.

JohnMain: Does the tank contain a lt of control systems? or is it more of a dumb container?

Mark: The tank doesn't contain a lot of control systems. It does have a suite of pressure, temperature, and liquid level sensors that feed information to the orbiter and to ground systems. The tank, however, is far from being a "dumb container." It's a very highly engineered, highly efficient structure that serves critical functions for safe shuttle operations.

JimSa: How long does it take to fill the external tank with propellant?

Mark: It takes about three hours to completely fill the tank with fuel and oxidizer, just prior to launch at KSC.

Shelby: Has anybody ever captured video (from ground or orbit) of an ET re-entry?

Mark: Yes. Early in the space shuttle program the US Navy filmed the re-entry and breakup of several external tanks for NASA. Some film clips of this event are available at

Davidmh: How are the tank and the shuttle separated? Is there any side propeller in the tank?

Mark: Explosive bolts are fired that separate the external tank from the orbiter. The orbiter then fires thrusters to physically move away from the tank.

the_last_et: So where does it impact?

Mark: Remote areas of the South Pacific.

jlunt73: What is the weight of the external fuel tank?

Mark: The current version of the external tank, which we call the super lightweight tank, weighs about 58,500 pounds when empty. The previous version, the lightweight tank, weighed about 66,000 pounds. The original version, the standard weight tank, weighed about 76,000 pounds.

Michael_C: Is the External Tank on display at the U.S. Space and Rocket Center in Huntsville a real tank? In other words, was the tank produced to fly or was it produced specifically for the display? Thank you.

Mark: The tank is "a real tank." It wasn't built to fly, it was built as a test article and spent several years in the test stands at the Stennis Space Center in south Mississippi, providing fuel and oxidizer for space shuttle main engine testing.

(Moderator Jason: Great questions so far. To ask your own, type it out in the box at the bottom of the window and submit it by clicking the 'Ask' button on the right. That will send it into the queue. Thanks for your patience as we work to answer your questions.

asdf: Why does the tank in the photo at the top of this page look yellow, instead of the usual orange? Has there been a change in the composition of the foam?

Mark: The tank in the photo has recently applied foam on it, which is a lighter color. The foam darkens and reddens -- or becomes more orange -- over time due to UV exposure.

TheCFiles: Thanks, I get it now. Originally shuttle program was supposed to end in 2010. Any particular reason it's being pushed back to early 2011?

Mark: It's been necessary to modify the payloads for the last two shuttle missions and these mods are the driving factor to reschedule to missions to Nov. 1, 2010 and Feb. 26, 2011.

Cyberspew: How are the tanks delivered to KSC?

Mark: The tanks are delivered by barge to KSC. The tank is loaded on the barge at the Michoud Assembly Facility. The barge is then towed to Gulfport, MS, where the NASA booster recovery ship is waiting to take it on its ocean journey of 900 miles across the Gulf of Mexico and then up the Atlantic seaboard to Cape Canaveral and on to KSC.

Akarsh_Valsan: Why do you think liquid oxygen tank is important in a External tank?

Mark: The external tank provides fuel and oxidizer to the space shuttle main engines. Like every rocket, these engines must function in space where there's no oxygen. So the rocket, in this case the external tank, must carry the oxygen for the engines in addition to the fuel.

TheCFiles: What processes have you developed to limit amount of foam that breaks off and could potentially hit the shuttle?

Mark: We've pursued a twofold approach. In the first instance, we have eliminated or reduced the volume of foam applied to the tank where testing has demonstrated that could be successfully accomplished. In the second instance, we've implemented enhanced process controls such as test panels, video review of spray applications, increased inspections, and more refined engineering requirements. This approach has led to a dramatic reduction in instances of foam loss so that we're now producing the safest tanks we've ever delivered.

ray: Is the ET powered? Does it have any computing power on board?

Mark: The ET receives just enough power from ground systems or from the orbiter for its sensors and various heaters to function. It doesn't produce any power onboard, nor is there any computing power onboard the external tank. All the computing power is onboard the orbiter, which is a reusable system.

abishek: Sir if shuttle goes to space its no need for the boosters right?

Mark: The solid rocket boosters are not required in space. They are required to provide the necessary power during the first two minutes of flight to enable the orbiter to eventually reach orbit.

Akarsh_Valsan: Sir what is the significance of ET-138?

Mark: ET-138 is the last production tank to be delivered to the space shuttle program, and it's the last tank currently planned to be flown on a space shuttle mission. It represents the culimination of 37 years of dedicated work by a highly skilled and motivated team.

abishek(: Sir how the work of sts133 and sts 134 going?

Mark: The processing of space shuttle missions STS-133 and STS-134 are right on schedule for launch dates of Nov. 1, 2010 and Feb. 26, 2011, respectively. No current problems during processing.

ozziecortez: I know that a number of changes have been made to the external tank design since the first one flew in 1981. Can you give a brief overview of what the major changes have been? Thanks!

Mark: There have been three major change evolutions in the history of the external tank program. The first was a weight-savings program that took 10,000 pounds out of the tank and resulted in the lightweight version and was accomplished by eliminating the paint on the tank, eliminating instrumentation and lightening the structure. The second was another weight-savings program that implemented aluminum lithium alloy into the tank structure and reduced the tank weight by another 7,500 pounds and resulted in the super lightweight version of the tank. This version enabled NASA to execute the International Space Station program. The final iteration was the implementation of redesign and process controls to improve safety in the wake of the loss of Columbia.

(Moderator Jason): We've got time for a few more questions before the end of today's chat. Thanks to everyone so far for the excellent questions!

JimSa: Were external fuel tanks built for a specific shuttle or could they have been used on any shuttle without modification?

Mark: The tanks aren't built for specific shuttles. They can be used with any of the orbiters. But note that the super lightweight versions of the tank were built to allow the heaviest space station modules to be hauled to orbit.

abishek: Sir how many litres of fuel required for a shuttle to reach space?

Mark: It's about 390,000 gallons of liquid hydrogen, and about 145,000 gallons of liquid oxygen. I will leave it to you to make the liter conversion. :)

[Jul 7, 2010 9:03:51 AM PDT] Mark(P) I want to thank everyone for the great questions in today's chat. You can learn more at these links: and

(Moderator Jason): I'd like to give a big thanks to Mark for sitting down and chatting with us today. We hope you found today's chat interesting. Thanks for everyone asking all of the really great questions. Watch tomorrow's rollout ceremony for ET-138 live on NASA TV starting at 8:45am Central Time at

Steve Roy, 256-544-0034
Marshall Space Flight Center, Huntsville, Ala.