So I'm wondering if the switch to stainless is enabled by the switch to skydiver reentry..
Of course, the alloy(s) to be used are likely to be different from the example alloy above, but Elon's remark about it being a heavy metal suggests a dense but extremely strong non-iron-based material to me.
Quote from: meekGee on 12/09/2018 03:55 amSo I'm wondering if the switch to stainless is enabled by the switch to skydiver reentry..Do you have information that the switch is to stainless steel, specifically?The paper that Elon liked on Twitter:Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexesThe report is paywalled, but the following is from the publicly viewable abstract:Unlike traditional interstitial strengthening, such ordered interstitial complexes lead to unprecedented enhancement in both strength and ductility in compositionally complex solid solutions, the so-called high-entropy alloys (HEAs). The tensile strength is enhanced (by 48.5 ± 1.8 per cent) and ductility is substantially improved (by 95.2 ± 8.1 per cent) when doping a model TiZrHfNb HEA with 2.0 atomic per cent oxygen, thus breaking the long-standing strength-ductility trade-off.Of course, the alloy(s) to be used are likely to be different from the example alloy above, but Elon's remark about it being a heavy metal suggests a dense but extremely strong non-ferric metal alloy to me.
If they're switching from composites to stainless steel; does that reduce the net payload of BFR to low Earth orbit from about 100 metric tons to less than 90? Or even 80?! ...Still, if less than 90 tonnes; that would still kick SLS butt because of full reusability...
Quote from: MATTBLAK on 12/09/2018 05:11 amIf they're switching from composites to stainless steel; does that reduce the net payload of BFR to low Earth orbit from about 100 metric tons to less than 90? Or even 80?! ...Still, if less than 90 tonnes; that would still kick SLS butt because of full reusability...You cannot make the assumption that dry weight will increase.One of the reasons for going this direction is weight reduction. Counter intuitive is that a heavier material results in total lower mass.
Quote from: oldAtlas_Eguy on 12/09/2018 05:18 amQuote from: MATTBLAK on 12/09/2018 05:11 amIf they're switching from composites to stainless steel; does that reduce the net payload of BFR to low Earth orbit from about 100 metric tons to less than 90? Or even 80?! ...Still, if less than 90 tonnes; that would still kick SLS butt because of full reusability...You cannot make the assumption that dry weight will increase.One of the reasons for going this direction is weight reduction. Counter intuitive is that a heavier material results in total lower mass.Yes true. But I somehow doubt that they'll be going down the the 'Atlas balloon' tank road. Maybe Elon has just encountered the sheer difficulties of trying to fabricate gargantuan 'bubble-free' composites and has decided to take a leaf out of aircraft and ship building techniques? I'm just sayin' - I'm not a trained engineer, but my speculation is not entirely uninformed... Maybe if it results in a - pick a figure from the aether - only 10% or 15% percent increase in dry mass; Elon would be correct in assuming/believing that would be worth it? Certainly if it could speed up development and prototyping somewhat.
Or Elon is less persnickety about using the word "render" (instead of "pics") than people in this forum.
Additionally, if the Super Heavy is also stainless, does this mean staging higher is possible, as the Super Heavy is more heat tolerant and can do sportier re-entries?
Quote from: gin455res on 12/09/2018 05:48 amAdditionally, if the Super Heavy is also stainless, does this mean staging higher is possible, as the Super Heavy is more heat tolerant and can do sportier re-entries?Doing RTLS does impose a limit to the practical S1 dV. It would already be flying a rather lofted trajectory to help minimize the boostback burn, but at a certain point you really start to eat the losses from the rocket equation (and a worse propellant mass fraction doesn't help.) So I really doubt the constraint is re-entry.
I don't think we can ignore those high entropy alloys in the PhysOrg article Musk liked,https://phys.org/news/2018-11-strength-ductility-high-entropy-alloy-oxygen.html