Quote from: Norm38 on 02/20/2018 03:17 amnickel-iron-lead isn't light weight. How thick a layer do they need? Does it flake off? Or wear away? How much mass is that for large tanks?Once again: An Invar liner is the last resort. Elon said that they look for a coating that can be sprayed on.
nickel-iron-lead isn't light weight. How thick a layer do they need? Does it flake off? Or wear away? How much mass is that for large tanks?
Another solution could the inner most layers of the tanks be made from something like Nonburnite which can handle -260C to +280C.This should exceed anything they'll see in service by a good margin.https://omnexus.specialchem.com/tech-library/article/nonburning-high-heat-composite-material-of-the-future
I wonder if the coating would be spray foam insulation, BFS needs insulation for deep space and Mars surface (to avoid freezing out dry ice). But urethane foam seems like it would be just as bad as carbon epoxy in the face of hot GOX. A silica fiber based insulation sounds like a better bet but I don't know if they could spray it.
Quote from: Patchouli on 02/21/2018 04:49 amAnother solution could the inner most layers of the tanks be made from something like Nonburnite which can handle -260C to +280C.This should exceed anything they'll see in service by a good margin.https://omnexus.specialchem.com/tech-library/article/nonburning-high-heat-composite-material-of-the-futureUnfortunately XCOR is now defunct. Does anyone know what happened to the nonburnite IP?Quote from: envy887 on 02/21/2018 03:21 amI wonder if the coating would be spray foam insulation, BFS needs insulation for deep space and Mars surface (to avoid freezing out dry ice). But urethane foam seems like it would be just as bad as carbon epoxy in the face of hot GOX. A silica fiber based insulation sounds like a better bet but I don't know if they could spray it.Such materials do exist and are in use for refurbishing furnaces. I've no idea how fragile or heavy they are.
Not heavy at all, but lightweight silica materials rather brittle. Aerogel and the Shuttle tiles are two examples.
Now that we've seen the actual composite section, there's an attempt at reddit to estimate its thickness: https://www.reddit.com/r/SpaceXLounge/comments/9javua/quick_bfr_structural_carbon_fiberre_calculations/, the result is 12 to 25mm.The teslarati article has a photo that gives more details, by trying to complete the circle I estimated the thickness (the white border) as 50mm.So does this thickness seem excessive? I couldn't find the thickness of the NASA/Boeing test tank. For aircraft like A350, it looks like the composite fuselage is only a few mm thick.
It could be two thin walls 50 mm apart with flutes between. This is how Boeing and NASA constructed the 5 m diameter composite test tank.https://www.nasa.gov/feature/case-study-nasaboeing-composite-launch-vehicle-fuel-tank-scores-firsts
Quote from: envy887 on 10/01/2018 01:10 pmIt could be two thin walls 50 mm apart with flutes between. This is how Boeing and NASA constructed the 5 m diameter composite test tank.https://www.nasa.gov/feature/case-study-nasaboeing-composite-launch-vehicle-fuel-tank-scores-firstsI can not find any references in the Composite Cryotank Technologies and Demonstration project towards applicability to reusable launch vehicles. As I understand it the project requirements were for disposable launch vehicle technologies.I'm no composites expert but the flutes do not strike me as a stress cycle life enhancing solution. Intuition may be wrong here but the opppaite.seems more likely. To paraphrase Dan Raskin's view from the top talk: as few miracles as possible please.
Composite sandwich panels are very common in aerospace applications, since like isogrids/orthogrids they reduce weight while increasing strength and stiffness. The savings over solid structures are massive, which means margins can be higher, which makes reuse much easier.
Quote from: envy887 on 10/01/2018 01:46 pm Composite sandwich panels are very common in aerospace applications, since like isogrids/orthogrids they reduce weight while increasing strength and stiffness. The savings over solid structures are massive, which means margins can be higher, which makes reuse much easier.Granted. How many of these sandwich constructions see use as multi-cycle mild-cryo containers? You'll notice F9 fairing is sandwich, fuselage is not, not the bulk of it at the very least. Airframes rarely carry cryogenic fluid.The savings are moot if it introduces catastrophic failure modes.
Detecting delaminations between the sandwitch faces can be a problem, as you can't simply inspect in the middle.
Alternatively SpaceX could easily and cheaply use the filament winding process to create a crude isogrid via selective thickening of some axial and helical paths during winding process. Eg 5mm average wall thickness with wide 20-30mm thick ribs over ~10% of surface area.
You don’t need to embed the ultrasonic sensors. You can do inspection with a fluid filled finger.Digital X ray sensors can also be done. Doesn’t require embedding either.Parts can be repaired with resign injection and patching techniques.