NASA delays SLS rollback due to concerns over rocky path to launchpad

The road to the Moon is paved with... river rock?

NASA's Moon rocket is to trundle back into its shed today after a delay caused by concerns over the crawlerway.

The massive transporter used to move the Space Launch System between Vehicle Assembly Building (VAB) and launchpad requires a level pathway and teams have been working on the inclined pathway leading to the launchpad where the rocket currently resides to ensure there is an even distribution of rocks to support the mobile launcher and rocket.

The latest wet dress rehearsal was completed on June 20 after engineers "masked" data from sensors that would have called a halt to proceedings. Once back in the VAB, engineers plan to replace a seal on the quick disconnect of the tail service mast umbilical. The stack will then roll back to the launchpad for what NASA fervently hopes is the last time before a long hoped-for launch in late August.

That first launch is an uncrewed test of the Artemis system, and will result in the Orion capsule and European Service Module (ESM) being sent around the Moon and the capsule returning to Earth.

The crawlerway at NASA's Kennedy Space Center in Florida is a 4.2-mile (6.8km) road of rocks. Built back in the glory days of the Apollo program, the initial design of the road called for asphalt, but engineers realized that the material would not be able to handle the immense weight of the crawler transporter. Furthermore, it was discovered that turning the transporter would result in damage to the machinery as well as the road, necessitating a rethink.

Eventually, NASA selected river rock, mostly quartz, round and 3-4 inches in diameter. The rocks act as bearings when the crawler turns and absorb energy when crushed.

Wear and tear means the rock, laid 8-12 inches thick, needs replacing every 10 years depending on usage. Such is the intense crushing, first from the Saturn stacks, then the Shuttle, and now the SLS, that the rocks get ground down to the size of pebbles.

The last major upgrade happened in 2014 and engineers expect a repeat performance ahead of the launch of Artemis II, along with more frequent replacement of the rocks thanks to the sheer weight of the stack. ®

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