Every "Bang!" gets closer to "The Real Thing". The news said it was a planned "Bang!" - is this so? I'd rather a planned bang on earth than an unplanned bang in space!
Not planned. They had a CH4 fuel leak after shutting off the engines. I don't particularly like that big skirt they have around the engines. Gases can be trapped in there. Most byproducts of combustion around the craft after shutting the engines are in intermediary chemical reactions (highly reactive radicals and unfinished combustion compounds, and usually poisonous), which is why even for a hydrogen+oxygen engine like the Space Shuttle, you can't be close for some time after a firing test (there's like 16 intermediary steps between hydrogen + oxygen and water molecules when you burn hydrogen very fast. The only time you go from hydrogen to water cleanly is in hydrogen fuel cells, literally assembling molecule by molecule slowly in aqueous solution - fast hydrogen combustion is very dirty).
I'm glad the launch & flight were successful, anyway. There are obviously some issues, but getting closer with every test. As for the skirt, would vents help, or would they defeat the purpose of the skirt?
The overall design is sort-of an old-fashioned traditional space ship look look, and I like that - it's very comforting that a space ship looks like something out of a science fiction magazine illustration!! I'm reading quite a bit of the more old sci-fi magazine stories at the moment, and although there aren't too many illustrations to go by, some of the cover pictures are grand! Mind you, a lot of the depictions and descriptions of the alien people and creatures are a bit strange!
Vents might help. But if you look at conventional rockets, they don't have skirts. Ever. The bell nozzles are always protruding below the end of the body of the rocket. The closest I can think of is the Soviet Era N1 moon rockets which also used a large number of small engines, but even then, the space under the fuel tank was not so enclosed with a large volume where gasses can accumulate (in my iwn perspective). Even SpaceX' smaller reusable rockets, the smaller Falcon X series, which land in the same fashion, none of them have a skirt around the bell nozzles. Honestly, I don't really know (but do have an idea about) what purpose it serves, whether structural, or otherwise.
One possibility is that it's means as thermal protection for hypersonic re-entry. The Space shuttle has a large spoiler under the aft engines, which serves as both an aerodynamic attitude control device, as well as thermal protection for the engines.
(I miss the Space Shuttle. It will *always" be my "first and only one" reason for studying what I did).
I'm thinking that perhaps the circular skirt is designed to provide protection to the engine nozzle regardless of the axis rotation angle of the rocket when it re-enters the atmosphere. You see, the only thing you have to stop the rocket from rolling about its long axis during atmospheric re-entry are the fin pairs, front and back that each form a "dihedral angle" which is a method to create roll stability in aircraft, At very high altitudes, however, you'll depend on attitude control rockets, because there is very little on the way of aerodynamic forces to help those fins do their job. If the rocket only has that flap in the windward side (belly), and enters the atmosphere "belly up" or "sideways" for whatever reason, the engine nozzles would be unprotected from the plasma flow as the density of the air increases and while the craft stabilizes aerodynamically - I don't know it's a very wild guess on my part, but it's the only thing I can think of.
I understood at the beginning of the project that even with the stainless steel skin, the SN-X rockets would incorporate *some sort* of extra thermal protection system besides the stainless steel skin. But with Musk everything is so mysterious and ever changing and this is such an unconventional rocket. I have not seen any extra thermal protection implemented at all in the SN series of rockets. Quite the contrary, the last time anyone seriously considered metal skins was about 20 years ago with the X-33 Lockheed Martin demonstrator vehicle, which used Inconel slabs bolted over an aluminum mesh around fibreglass tanks. Before the Space Shuttle, steel was considered in the 1960s, during the age of "DynaSoar" lifting bodies, and before that, it was the Silbervogel, a Nazi-Era suborbital bomber design. Metal in general is very difficult to use as a thermal protection system, not only because of the melting temperature, but also because it is chemically reactive with the radical compounds found in the plasma of hypersonic re-entry flows (it literally burns).
I think that this is due to what I heard from Elon Musk, where he was explaining that the re-entry trajectory is unusual in that the vehicle is slowed down as much as possible while staying "above" the atmosphere for as long as possible before "plunging in." The net effect is to reduce the initial airflow speed around the vehicle, which reduces drag (friction) once you plunge in, reducing heat at the skin, and thus allowing for "non-exotic" thermally resistant materials to be used - like stainless steel, as opposed to the Space Shuttle which needs the high performance silica-fibre-based brick and "quilt" system.
I know the Space Shuttle needs to re-enter the atmosphere as quickly as possible to gain positive aerodynamic stability (and control its trajectory to ground in a predictable manner), with its wing(s) and rudder. This means a very "hot" re-entry. AFAIK most re-entry vehicles "want" to re-enter as quick as possible for that reason: control and design of trajectory. But this "Starship" is so big relative to its weight that its body alone may generate enough lift force from the start, thus allowing for a slower re-entry trajectory. Like I said, this is no ordinary rocket, Everything from the manufacture method (welding outside, like water tank), through the materials and mission are different. I just stare at it in fascination. Plus it looks like a Buck Rogers Art Deco rocket, to begin with which is just unreal.
But yeah, they need to work on proper ventilation under that skirt once it's sitting on the ground. Even without a detonation event, the gasses are very toxic.
