Tuesday, September 28, 2021

Starship 20 Gets First Cryo Tests, Loses Some Tiles

Last night, Starship S20 had its first ever cryogenic testing, seemingly passing except for the loss of some Thermal Protection System (TPS) tiles around the cold gas Reaction Control System (RCS) thrusters and the header tank in the nose area.  It was the first time S20 has been put through any of the common tests done to other Starships.  

Effectively SpaceX’s first Starship or Super Heavy test of any kind in more than two months, it thankfully didn’t take long for things to get interesting. Before the pad had even been cleared of the last few remaining workers, Starship S20 violently shed a good dozen or so fragile heat shield tiles. CEO Elon Musk quickly confirmed speculation that Starship S20 had effectively jetted the tiles off its nose during a brief test of high-pressure cold gas maneuvering thrusters, coincidentally around the same time as SpaceX began to pressurize the rocket for its first tests.

A view later into the test, venting supercold gas from a vent which looks to be on the Liquid Oxygen (LOX) tank.  (Image from @bocachicagal, NASASpaceflight.com)  It was still daylight at the start of the test was when the TPS tiles fell off.

(Image credit to Nic Ansuini via Twitter.  Some photo processing to increase brightness and add the red circles where tiles are missing by me, SiG)

If you remember the loss of space shuttle Columbia with all of the crew on board, losing tiles might make you twitch a bit.  Losing TPS tiles can be serious, but it wasn't at all unexpected.  There have been only two vehicles to date that used non-ablative heat shields in the form of ceramic of tiles: the Space Shuttles and the Russian/Soviet Buran. You can essentially see in Nic Ansuini's picture that a large majority of the tiles on S20 are the same size hexagons.  The only exception seems to be on flaps/wings, the edge of one is visible in the bottom middle of the vehicle picture.  The tiles on a Shuttle were generally different sizes and different shapes, glued into place.  It was a much more "one of a kind" approach to creating a space vehicle rather than the vision for Starship of producing hundreds or thousands of identical vehicles. 

Going into what was believed to be Starship S20’s first ambient-temperature pressure test and cryogenic proof test, the loss of some heat shield tiles was almost universally expected. In a structure as large as Starship, even just the thermal contraction of steel at supercool temperatures (and expansion as it warms back up) could change the rocket’s diameter an inch or so, potentially causing tiles to scrape or press against each other. About the size of a dinner plate and the thickness of an average paperback book, Starship’s ceramic heat shield tiles have proven to be very fragile, with dozens routinely chipping, cracking, and shattering during and after installation on Ship 20.

One unique (and no less unproven) aspect of Starship is SpaceX’s decision to mount its heat shield directly to the thin steel propellant tanks and skin that make up the rocket’s entire airframe. SpaceX’s first stab at the problem involves studs/pins welded – by robot – directly to the exterior of Starship’s tanks and skin. By embedding small metal plates inside each cast tile, they can be easily installed by aligning the tile and pressing it against each set of three barb-like pins, which then irreversibly lock in place. Over most of Starship’s hull, SpaceX then tacks on blankets of off-the-shelf ceramic wool insulation before tiles are installed on top of that steel and blanket sandwich. Compared to the Space Shuttle and Russia’s Buran, ... Starship’s thermal protection system (TPS) is incredibly simple. Of course, the challenges imposed on heat shields by mechanical stresses during launch/landing, orbital reentry, and a need for rapid reusability are anything but simple.

The roads in Boca Chica were closed briefly tonight (so far).  Although they reserved road closures from 3 PM to midnight tonight, the road was closed at 5:30 PM and reopened at 6:38 PM.  Without a clear message from SpaceX that last night's test was successful, we can't be sure if that was the case or if they decided to rebuild something (or things) and test again.   



1 comment:

  1. I like the idea, but I think it will need some additional work. And testing. Fortunately, I bet this is only plan A, and that there's a plan B, C, and D . . .