Delta II suffers pad problem – Dawn may be delayed

by Chris Bergin

United Launch Alliance engineers have been forced to cease processing of the Delta II launch vehicle, which is set to carry NASA’s Dawn spacecraft from LC-17B at Cape Canaveral Air Force Station.

Mating of the solid rocket motors is likely to be delayed by one week, after the crane – used to hoist the solids into place along the outside of the Delta II’s first stage – broke down with a bushing problem.


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Sources note that the process to replace the bushing will take a week, a delay that may not be absorbed before the June 30 launch target. Evaluations are set to take place once mating has resumed.

The problem occurred during the mating of the first of nine solid rocket motors on Wednesday, with the process ceasing due to noise being heard from the top of the crane, which was followed by troubleshooting.

A decision was made on Thursday to stop mating operations until the crane’s vendor brings a replacement part – to be installed ahead of certification.

The Delta II being used to launch Dawn is the 7925-H version, the heavier-lift model of the standard Delta II that uses larger solid rocket boosters (GEM-46).

Dawn was originally set to launch in June of 2006, before a program review of the mission – to explore two of the largest bodies in the asteroid belt, Vesta and dwarf planet Ceres – was subsequently cancelled due to technical issues and cost-growth.

However, the mission was then reinstated for the June, 2007 launch, following protests from planetary scientists.

The Dawn spacecraft is powered by an Ion engine, which, at its maximum thrust, can expend only about 0.25 kg of xenon per day, changing the spacecraft’s velocity by 10 m/s.

The spacecraft is destined to rendezvous and orbit both Vesta and Ceres in 2011 and 2015, respectively. The trip from Earth to Vesta is about 2 billion miles, while the journey from Vesta to Ceres is about 1 billion miles.

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