Space Shuttle Fuel
Space shuttle fuel will live to burn another day.
Roughly the same size as a DC-9 airliner, the space shuttle was the largest human spacecraft ever launched into orbit. It was so heavy, weighing nearly 150 tons with a full cargo load, that the shuttle required five massive engines to get it off the ground.
Each orbiter contained three Space Shuttle Main Engines (SSMEs). Built by Pratt & Whitney Rocketdyne, these liquid-fuel cryogenic engines weighed 7,700 pounds each. They burned 234,265 lbs of liquid hydrogen and nearly 1.4 million lbs of liquid oxygen stored in the shuttle’s external tank (ET). Each engine generated almost 1.8 meganewtons (400,000 lbf) of thrust at liftoff, and they each consumed 350 gallons of fuel per second over 8 minutes and 30 seconds of flight before main engine cutoff.
As powerful as these engines were, the SSMEs were insufficient to lift the space shuttle into orbit on their own. Two solid rocket boosters (SRBs) weighing 1.3 million lbs apiece were attached to each orbiter. Together they burned 2.2 million lbs of fuel during the first 2 minutes and 13 seconds of flight before falling away. The boosters provided 83 percent of the liftoff thrust for the space shuttle system.
The fuel the SRBs burned is called Ammonium Perchlorate Composite Propellant (APCP). It consists of ammonium perchlorate (oxidizer, 69.6% by weight), aluminium (fuel, 16%), a polymer (12.04%), an epoxy curing agent (1.96%), and iron oxide (0.4%). The aluminum was quite powerful as a fuel but difficult to accidentally ignite.
The SRBs had the largest solid-fuel motors ever flown, providing 80 percent more liftoff thrust than a single F-1 engine used on the Saturn V rocket. They were the first solid rockets to be used as the primary propulsion system for a human spaceflight system. After they burned out, the SRBs separated from the space shuttle and parachuted into the ocean for recovery and reuse.
Once the space shuttle reached orbit, it used its onboard Orbital Maneuvering System (OMS) to maneuver in space. OMS consisted of two packs at the back of the orbiter, each containing a single hypergolic engine. The OMS pods also included a set of reaction control system engines that used 18,020 lbs of monomethylhydrazine and 29,730 lbs of nitrogen tetroxide.
Space shuttle fuel factored into the the losses of both the Challenger and Columbia shuttles and their 14 crew members. The failure of a seal between two of the four solid-fuel segments on an SRB caused fuel to leak out and burn through the external tank, destroying Challenger. The seal was later redesigned and subsequently experienced no serious difficulties.
During the final flight of Columbia in 2003, foam used to insulate the super-cold liquids in the external tank broke away during launch and punched a hole in the wing of the orbiter. Heat penetrated the interior of Columbia during re-entry, causing it to break up. There was no escape for the crew.
Although the space shuttle program has ended, its propulsion systems will live on. NASA has now developed the shuttle-derived Space Launch System, a heavy-lift launcher that will use modified versions of the space shuttle’s main engines, solid-rocket boosters and external tank. Space shuttle fuel will live to burn another day.
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