Testing Starship heatshield hex tiles pic.twitter.com/PycE9VthxQ — Elon Musk (@elonmusk) March 17, 2019

Musk tweeted that the tiles are hexagonal-shaped because that provides "no straight path for hot gas to accelerate through the gaps." The tiles will be installed on the windward side, towards the direction of re-entry, "with no shielded need on the leeward side."

The hottest sections will have a "transpiration cooling" system, with microscope pores on the exterior that allow water or methane to ooze out and cool the exterior. That would minimize damage on the heat shields and allow the Starship to return to service shortly after a flight merely by refilling the heatshield reservoir. "Transpiration cooling will be added wherever we see erosion of the shield," tweeted Musk. "Starship needs to be ready to fly again immediately after landing. Zero refurbishment."

After a day worth of hard work, the workers at #SpaceX have finally installed the first raptor on #StarHopper . Congratulations to Elon musk and all the hard workers at SpaceX. It's almost time for StarHopper to purr like a kitten🐱🔥🚀. pic.twitter.com/YIhbNhqJEk — Austin Barnard🚀 (@austinbarnard45) March 16, 2019

Starship development is proceeding apace in other areas, as well. As spotted by "aspiring space kid" Austin Barnard, SpaceX recently fitted its "Starhopper" Starship prototype with a Raptor engine for the first time, and plans to do test hops soon, possibly within a week. The tests will take place at SpaceX's Texas test site near Boca Chica Beach, but the craft won't go very far. "First (really short) hops with one engine [only]," said Musk. "Suborbital flights with three."