You are not logged in.
Major change coming on the presurization tanks as they are going to a smaller more distributed system . Also the vacuum raptors are being more 3d printed with less parts, more cooling and higher output ISP. On this next flight.
Offline
Like button can go here
Composites are particularly vulnerable to impact damage. Anything small and hard thrown fairly fast will do that damage, and you won't see it just looking at it. Unless you have some sort of pre-damage imaging to compare, it is unlikely you would detect the damage. THAT is the risk you accept when you use these materials. There is no way around it.
As for "sabotage", the COPV tank is inside the nosecone of the upper stage. The rifle shooter would have to be inside the stage to hit the tank with a bullet. That would seem to be more nonsense than a real theory about what happened. Although a bullet from something more powerful than a rifle shooting 22 caliber long-rifle ammunition, would penetrate the nosecone and perhaps strike the COPV tank. That would be an unlikely long shot of a sabotage theory (if you'll excuse my choice of words).
But what if a rivet or bolt broke and threw a piece that happened to hit the COPV tank? A small piece of steel traveling more than about 100 mph would do internal damage to any carbon composite. There are composite materials that are impact and puncture damage-resistant, such as kevlar-vinyl ester, but these are nowhere near as stiff and strong as carbon-epoxy.
Here's another theory to consider: what if there was a weld defect at the joint between cylinder and tank head? The overwrap is likely not cloth, but carbon yarn wetted with epoxy resin, wound onto the cylinder section of the tank. The hoop stress in the cylinder section is twice the longitudinal stress in the cylinder section. Assuming the tank head is a hemisphere or a spherical segment, the stress in that metal membrane is equal to the longitudinal stress in the hoop section. That membrane can be thinner than the cylinder. Using too-thin a metal cylinder to save weight is what the composite overwrap counters. But if the weld has a defect, it locally raises the longitudinal stress at the joint, and that would cause the head to part from the cylinder.
Here's another: what if they didn't thicken the metal enough locally right at the weld joint cylinder-to-head? There's mismatched radial displacement at the joint, increasing stress there with bending stresses. The extra material is needed to "sop up" those bending stresses. Not enough extra thickness, and you have something straining plastically locally at the joint, leading to a very short fatigue life for the metal, and especially so in the heat-affected zone of the weld.
I can think up lots more. These are school-of-hard-knocks things coming from 2 decades doing aerospace defense work. Newbies wouldn't know much about it. This is the engineering art stuff.
GW
Last edited by GW Johnson (Today 09:24:30)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
Offline
Like button can go here
GW,
Aerospace has gone from natural composites to metals and now to synthetic composites. There's no acceptable substitute for their strength. Every modern airliner in existence uses truck loads of synthetic composites. All or almost all payload fairings and inter-stages are now made from composites as well, and for the same benefits. That's why they're so fuel efficient and light. They're not "bad" or "wrong", just different. There are some things you can do to metals that you cannot do to composites, such as throw debris at them. There are also many things that can be done with composites that are impossibilities with metals. Off the top of my head, all modern turbofans and turboprops use composite blades because they're less than half the weight of metal and many times stronger. When a fan blade does let go, a composite Kevlar ring around the fan section prevents the blade from penetrating into the cabin of the airliner. A 700bar storage tank would be ridiculously heavy if it was made from steel or Titanium thick enough to reliably contain the pressure. Thankfully, CFRP is much lighter and stronger- light enough to locate the Nitrogen storage tank onboard the vehicle to spin-up the pumps.
Yes, composites are more difficult to work with than metals in certain ways. Aluminum is also more difficult to work with than steel. That hasn't stopped us from using Aluminum, so it's not a valid reason to abandon the use of composites.
Online
Like button can go here
Kbd512:
I didn't say there was anything wrong or bad about composites. I just pointed out the impact damage vulnerability using carbon fiber or cloth. That results from the low elongation capability of carbon fibers. It is inherent. The other materials do not have the strength and stiffness needed for that option, but at least one of them is very resistant to impact and puncture damage. That is the kevlar-vinyl ester material used in airliner interiors, especially the floor deck panels. They found out back in 1958 not to use aluminum alloy floor panels: ladies' spike heels poked holes through those panels, simply walking. The kevlar-vinyl ester panels have successfully resisted that ever since.
I did point out ways that a composite overwrapped steel tank might fail. The ways I pointed to are defects in the metal weld zone, not the composite, which gets added later in the manufacturing process. Could be a weld defect, could be a bad joint design with too little added thickness near the weld. Some steel with a lot of elongation would survive only a single handful of pressurizations, before cracking apart, without the extra thickness to "sop up" the bending stresses coming from the radial displacement mismatch at the cylinder-to-head joint. A more "brittle" steel would fail immediately.
My guess is that these newbies at SpaceX (none over 40-45 years old, most are under 25-30) are welding as-supplied stock sheet metal together without any added thickness at the joint. With a single handful of fatigue cycles available at the weld joint in a pressure vessel, at the cylinder-head joint, "unexpected" failure is inevitable! The overwrap cannot prevent that, even if you lap it over the joint a bit! They need to use the weld joint shapes in the ASME boiler code.
And this same design flaw applies to a lesser degree to all the welded ring joints in the Starship and Superheavy hulls. Those are all heat-affected zones that are also affected by weld physical chemistry. They have less tolerance of strain than the base metal, even if you get full weld strength by doing electron beam welding, which SpaceX is NOT doing! I've seen the videos, they are stick-welding those hulls.
Makes you wonder where some of the methane (and maybe oxygen) leaks have come from, does it not? Maybe where all the ice particles came from, inside the cargo bay during that last flight? Since there was a LOX header tank in the nose, adjacent to a nitrogen COPV. Any sort of tank flaw, or any sort of plumbing defect, could cause such leaks. And many others not well understood up to now.
Just food for thought.
By the way, I actually like composite materials. I've built a lot of them with my own two hands, many years ago. Every material has a "right" application, and a "right" way to be processed. And a "right" way for the application to be designed, for that matter. You do it "wrong" at your peril.
GW
Last edited by GW Johnson (Today 14:22:33)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
Offline
Like button can go here