GLS
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I was looking at both at the same time... man, I need to sleep...
This is the one:
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News Changes to the SpaceX BFR rocket.
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I was looking at both at the same time... man, I need to sleep...
This is the one:
(only official live stream)
RisingFury
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I wonder at what point do they call this a sunk cost...
Thunder Chicken
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Proof testing composites really isn't useful except for perhaps a single test after manufacturing and before installation in the ship. If they repeatedly proof test it prior to propellant loading, they are just increasing the load cycles on the COPV, and guaranteeing loss of the vehicle if it does pop during the test. The mediation described in the report tells me that they don't yet understand how composites fail under cyclic loading. Fibers fail incrementally, transferring their load to the other fibers, until all the remaining fibers are overloaded and fail exponentially fast. COPVs hold pressure, until the don't. Inadvertently hitting the tank against something during installation, or perhaps chafing damage during in-flight vibrations, can initiate this damage failure cascade. These tanks could perform flawlessly on a series of flights and still explode. Just like the OceanGate Titan - the COPV started to fail on dive 80. It finally failed on dive 88. Every intervening dive was adding more and more damage and lowering stress margins until it rapidly failed.
Inspecting lined COPVs for damage is really difficult as acoustic methods won't work because of the combination of materials with different acoustic properties. X-ray is similarly challenging. There are some novel thermal methods that basically look at transient temperature deviations when the tank is suddenly filled with a fluid at a uniform temperature, these deviations being correlated to a change in thermal conductivity due to delamination of the layers. But these are still bleeding edge NDT methods, and they require visual access to all surfaces of the tank.
If you recall, the Starship hull itself was initially going to be composite, but they switched to stainless steel as the strength to weight ratio and the strength as a function of temperature made it a better choice. I am thinking that sooner or later they are going to lose enough vehicles due to COPV failures that they may realize that metal tanks might be a lot less hassle for the weight savings. Nominally a COPV is something like 20-30% lighter than an all metal tank depending on size, but if you have to add more covers and liners and other things to keep them safe, the weight savings goes to 0. And metal tanks CAN be much more easily inspected for flaws - that NDT technology is mature.
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Urwumpe
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Well, on the other hand, COPVs are standard everyday technology already. It makes no sense to use a different or older technology, especially not in spaceflight, where COPVs originated from. If you use and test a technology the wrong way, its not the technology that is the problem.
Thunder Chicken
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They are standard everyday technology...being used in a unique application. The use of a technology should be based on engineering principles and physics, not just because it is expected in a spacecraft. I don't believe enough is known, by SpaceX engineers or anyone else, whether COPVs are fully appropriate for what they are attempting to do with Starship. They want a spacecraft that can be quickly reused multiple times like an airliner. Where have we heard that before...?
NASA went through this with COPVs on the shuttles. They had very poor understanding of the long term behavior of COPVs used in the orbiter. They did some limited testing and developed some crude cyclic failure models that predicted that the COPVs should have failed after a certain number of cycles that the shuttles had already exceeded. They basically declared those models excessively conservative, and resorted to a lot of expensive inspection of dubious utility, and even then they really didn't know how long they could be used. They were gambling, just as they did with foam strikes on the TPS and burn-throughs of the SRB o-ring joints.
SpaceX can either 1) follow NASA's lead and gamble, 2) do a VERY deep research dive into composites and sort out and understand COPVs in every bit of relevant flight parameter space, or 3) utilize different/older tank technologies that may be better understood and more amenable to monitoring and inspection at the expense of performance. Option 1 is cheap and lets them use light tanks proof tested with lots of hopium. Option 2 is a research program that not even NASA could undertake, with corresponding massive costs in time and money, and Option 3 will add weight and lower system performance. They'll probably go with Option 1. So I believe they are destined to repeat the overall experience of NASA with the shuttles, hopefully with fewer fatalities.
Urwumpe
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And a lot of water flowed down the Rhine since 1972. Already in the 1990s, you had been practically ordering COPV as standard parts in spaceflight and had to order metal tanks as custom production.
Thunder Chicken
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And how many of these were flown repeatedly on vessels that do RTLS every mission?
GLS
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steph
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One must always be optimistic. Could blow up on the pad , or before it reaches 300 hPa. But destacking due to wind would be a sight to behold
GLS
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GLS
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Live stream of EverydayAstronaut:
GLS
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75 minutes to go...
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