Space Shuttle Discovery to roll onto launchpad on June 14

NASA announced Space Shuttle Discovery will roll onto its launch pad on June 14. The fully-assembled Shuttle stack, orbiter, ET and twin Solid Rocket Boosters, will be mounted on the Mobile Launcher Platform and delivered to the pad via a Crawler Transporter. The four-mile journey from the Vehicle Assembly Building to the pad starts at 3 a.m. EDT and will take about six hours.

One major change to Discovery's new external fuel tank is the addition of a heater on the feedline bellows to prevent ice forming during fueling and launch. The bellows is a joint on the outside of the tank, not insulated with foam, to allow expansion, contraction and movement during fueling of super-cold liquid oxygen before launch. The line feeds oxygen to the Shuttle main engines at start-up and throughout the 8.5 minute climb to orbit.

Another change to the external tank is in the hydrogen diffuser. A diffuser is a fabricated tube, which consists of a core and screen assembly. It diverts the flow into radial jets that are dispersed by the wire screen. There are two diffusers per ET at the top of the hydrogen and oxygen tanks. Discovery's new ET uses a certified plain, two wire weave. ET-120 had a tighter woven mesh than was expected. The data review showed the out-of-specification diffuser may have been the contributing cause of a liquid hydrogen pressurization problem. A vent valve cycled 13 times during the tanking tests, versus the standard eight to nine times. The valve opens and closes to ensure the liquid hydrogen stays at the correct pressure in the final two minutes prior to launch.