Space shuttle Discovery blasted off on its 12-day flight on 27th July from the Kennedy Space Centre in Florida. This was the first flight for two and half years following the re-entry disaster of Columbia in 2003.

It was a spectacular sight as it roared up into a bright blue sky to the cheers of spectators, astronaut families and US space agency staff. The aim of Discovery's flight will be to test safety measures brought in after the Columbia accident and re-supply the International Space Station.

This would have been good news for the gas companies that supply NASA and especially the Shuttle Series. Air Products has an exclusive contract to supply liquid hydrogen to the Shuttle series (in Cape Canaveral) and is a duel supplier of hydrogen with Praxair to the Engine Testing Centre in Louisiana. Air Products supplies liquid oxygen to the Space Centre in Florida while Air Liquide has a contract to supply nitrogen gas from its Merrit Island ASU in Florida.

However, concerns about debris or rubber cladding falling off the main rocket support tank and damaging the protective heat shield resulted in NASA postponing future flights until the situation is resolved. This put a dampener on the space programme's activities and for the gas companies who supply the Shuttle Series.

Where are the gases used?

Part of the primary thrust generation of the Shuttle Series comes from the side rockets attached to the Shuttle support tank (External Tank). However, these are chemically based thrusters that are jettisoned during the early stages of the launch. The Shuttle needs additional thrust to escape the Earth's gravitational pull and so the Shuttle itself has powerful rocket engines that use hydrogen and oxygen as a fuel source – mainly supplied through the lightweight cryogenic Shuttle External Tank, under the belly of the Shuttle.

Space Shuttle external tank ///NASA

The Space Shuttle External Tank (ET) contains the liquid hydrogen fuel and liquid oxygen (the 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 hits the ocean somewhere far from land. It is not recovered. The ET is constructed by Lockheed Martin for NASA at the Michoud Assembly Facility. There is a forward liquid oxygen tank, an unpressurized intertank that contains most of the electrical components and the aft liquid hydrogen tank; this is the largest part, but it is relatively light.

Click for larger image///NASA

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 240 to 250 kPa absolute pressure. The tank contains anti-slosh and anti-vortex provisions to minimize liquid residuals and damp fluid motion. The tank feeds into a 430 mm 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 430 mm diameter feed line permits liquid oxygen to flow at approximately 1 264 kg/s with the SSMEs operating at 104 % or permits a maximum flow of 1 099 m³/s. 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 554.0 m³. It is 8.41 m in diameter, 15.0 m long and weighs 5.4 tons empty.

Liquid hydrogen tank

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 220 to 230 kPa absolute. The tank contains an anti-vortex baffle and siphon outlet to transmit the liquid hydrogen from the tank through a 430 mm line to the left aft umbilical. The liquid hydrogen feed line flow rate is 211 kg/s with the SSMEs at 104 % or a maximum flow of 2.988 m³/s. 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 SRB-ET stabilizing strut attachments. The liquid hydrogen tank is 8.4 m in diameter, 29.46 m long, and has a volume of 1,515m³ and a dry weight of 13 tons.

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