On Sunday, Musk shared a video (above) of heat-shield tiles passing a "full duration" test.
These tiles are the most recent iteration of the technology SpaceX is developing to cool and protect Starship as it re-enters Earth's atmosphere and attempts to land. Such protection is necessary because spacecraft plow through Earth's atmosphere at roughly 25 times the speed of sound when they return, creating scorching-hot plasma that can vaporize steel.
Previously, Musk had said that Starship's heat shield would "bleed" rocket fuel from tiny pores in the spaceship's skin, thereby cooling it down. But a full "bleeding" system would have faced a number of unprecedented challenges, since clogged pores could lead to the destruction of Starship.
Musk's new video suggests that SpaceX has decided to go with a combination of hexagonal tiles and sections of Starship that'd transpire fuel.
"Hexagonal tiles on most of windward side, no shield needed on leeward [back] side, transpiration cooling on hotspots," Musk said, later adding: "Transpiration cooling will be added wherever we see erosion of the shield. Starship needs to be ready to fly again immediately after landing. Zero refurbishment."
In effect, Musk was hinting at SpaceX's iterative test plan for Starship: Build one with a tile-based heat shield, get it into orbit, land it, then examine the tiles for wear. In the spots where tiles look especially battered by 2,000-degree-Fahrenheit plasma heating, engineers will try to implement the "bleeding" cooling system.