Former NASA employees stated that the latest test video of the largest spacecraft in history again showed the problems and limitations of its heat shield. From their point of view, any of the existing technologies of this type is too complicated to implement Elon Musk's vision of fast and maintenance-free reusability of Starship.
During the 13th flight tests, Starship achieved significant results: almost all elements of the program, except for the braking of the first stage, were performed normally. The ship, having avoided the destruction of the aerodynamic rudders or damage to the hull, safely and gently sank into the Indian Ocean, after which it sailed over its surface for more than a hundred kilometers, showing high tightness.
However, white streaks were visible on part of the 18,000 ceramic tiles of the ship's heat shield. They are left over from the ablative thermal protection applied between the tiles. Some of the latter had damaged edges, a small number of them were lost during re-entry into the atmosphere. Former NASA engineer Dan Rusky, who studied materials for heat shields for almost forty years of his work at the Agency, commented on the situation to ArsTechnica.
"Starship's current thermal protection system is a dead end for all missions requiring full and rapid reusability," he stated. According to him, NASA faced similar difficulties half a century ago when developing shuttles. They used tens of thousands of ceramic tiles to protect the aluminum hull of the ship from heating when entering the atmosphere. Raski is a fairly experienced developer, one of the creators of the PICA material (a phenol-impregnated ablative material). A modified version of this material is used for thermal protection of the Crew Dragon spacecraft, which delivers US and Russian astronauts into space.
NASA's attempts to deal with ceramic thermal insulation regularly led to failure. Although the shuttles were originally planned to be used dozens of times a year (and only then could they provide reasonable prices for launching cargo into space), in practice, it always took many months to find defects in the heat shield and repair it. This was one of the reasons why other ships approved by the Agency never had ceramic thermal protection again.
Raski, along with former astronaut Charles Kamarda and Charles Miller, who temporarily led NASA before Isaakman, conducted an analysis of the possibility of rapid reusability for Starship and concluded that the situation remains difficult. In the footage of the ship sailing at sea, white traces are visible, which mean that a small amount of gases passed between the ceramic tiles during braking and partially blew away the ablation layer. The same is indicated by the damaged edges of a part of the tiles. Cracks on other tiles mean that the ceramics used are still too fragile for a quick, maintenance-free reuse of the ship.
Without it, Starship could well be used to launch thousands of large satellites into space or deliver people to the Moon and Mars. But many thousands of flights to Mars, which Musk considers necessary for colonizing the Red Planet, will become unrealistic.
The fact is that for such flights, each Starship with people and cargo must be refueled at least a couple dozen times. That means that literally tens of thousands of Starship tanker launches will be required, essentially ships of the same design, but carrying only liquid oxygen and methane. With fast reusability, you can launch the same tanker several times a day. Then it will take quite a few of them. But with a pause between reuse of at least two weeks, about a thousand tankers will be needed.
Raski believes that it makes sense to organize a NASA program to study new types of heat shields and materials for them. At the same time, it is unclear how much this will help. Ceramic thermal protection does not yet have clear alternatives: the same PICA has been made in an autoclave for a long time, but it works by ablation, in which the material is blown off the surface of the spacecraft. Applying it before each flight is even longer and more difficult than repairing ceramic tiles.
An alternative approach was proposed by Elon Musk himself in the late 2010s: to cool the steel surface of Starship by evaporation of liquid methane pumped under the shell of the ship where thermal protection is needed. This method simplifies reusability without repair, but requires the consumption of large volumes of liquid methane, which would reduce the payload of the ship itself.
It is not yet known which way SpaceX's developments will go in this case, but judging by the company's history of dealing with technical challenges, one way or another a solution will be found. The more difficult question remains whether this will be achieved in the 2020s.
