[themoogle]

"The SpaceX explosion on June 28th was caused by a failed strut in the rocket's upper stage liquid oxygen tank, SpaceX chief executive officer Elon Musk said today. The strut was one of several hundred used to hold together the helium pressure vessels in the tank......"

Goes from saying Oxygen tank to helium tank... wait what? is the helium tank inside the oxygen tank?

[agildehaus]

Yep. Here's a photo from inside the LOX tank during a previous flight:

http://i.szoter.com/741dc2bcf5762a48.jpg

The two arrows point to the struts holding down a helium tank.

[Nadya]

It's a liquid oxygen tank with a helium pressure vessel in the liquid oxygen tank. Nowhere does it say helium tank.

[seanflyon]

It seems like you are drawing a distinction between "tank" and "pressure vessel", could you explain what the difference is?

[Nadya]

A pressure vessel does a bit more than a tank. While a tank may house liquids/gasses, it typically does not regulate or maintain a certain amount of pressure that is different from the natural, ambient pressure.

Anyways - perhaps it was my misreading or an edit after-the-fact by the parent (can posts even be edited on HN after responded to? I haven't tested or taken particular notice of it), they seemed to be confused that the statement switched from talking about an oxygen tank and then a helium tank (as if both were the same tank) and were confused about which gas the tank contained, when in fact there are 2 containers and not 1 with the gas being mixed up. I was simply clarifying that. There is a helium pressure vessel and an oxygen tank - not an oxygen tank that is later called a helium tank.

I don't remember seeing the question appended at the end when I responded:

>is the helium tank inside the oxygen tank?