SpaceX has performing admirably in its efforts to move the U.S. one step closer to being able to put its own astronauts into orbit again. The company was able to successfully launch its Crew Dragon capsule early this month, and the capsule later splashed down safely on return from the ISS. SpaceX and its CEO, Elon Musk, have a future that sees SpaceX doing more than putting astronauts into low Earth orbit; and that future includes interplanetary missions.
Before those missions can be considered, the spacecraft that will be used has to be built and tested; SpaceX is into that testing process with Musk offering up a video of the critical heat shield tiles in testing. Heat shield tiles are the difference between life and death for astronauts on re-entry to the Earth's atmosphere, as an incredible amount of heat from friction builds on the outside of the spacecraft. Musk recently tweeted that the spacecraft's heat shields performed as expected in recent testing.
Testing Starship heatshield hex tiles pic.twitter.com/PycE9VthxQ— Elon Musk (@elonmusk) March 17, 2019
The hexagonal heat shield tiles are made from stainless steel, and transpiration cooling would drill tiny holes into the tiles at the hottest parts of the hull of the spacecraft. Those holes would allow heat inside the tiles, where much of the heat would be eliminated via the flash evaporation of a liquid; that liquid could be water or liquid methane. The benefit of using liquid water is that the fluid offers better cooling per unit of mass than liquid methane with the downside being additional plumbing complexity and spaceship mass. If liquid methane is used, the cooling process could be accomplished using the spacecraft's fuel but would offer less cooling efficiency.
Musk says that the torches used to test the tiles created temperatures as high as 1,650 Kelvin, or about 2,500F. This new type of heat shield is very different from the ablative heat shield that SpaceX uses on the Crew Dragon and Cargo Dragon capsules. Ablative heat shield tiles must be replaced with each mission, while the stainless steel heat shield for the orbital-class Starship aims to allow the spacecraft to be ready to fly again immediately with no refurbishment needed between missions. Musk said via Twitter that the transpiration cooling would be added to the heat shield anywhere erosion is found.