Quote from: gongora on 05/17/2017 12:28 amIf Block 4 is the thrust upgrade then the performance of Block 5 shouldn't be much better than Block 4.If the heat shielding is improved, smaller re-entry burn can be used, saving more fuel to the ascent phase, increasing reusable payload.Payload without reuse would not be increased.But I thought block 4 was mostly the titanium grid fins and has already flown? And the recently-test-exploded engine was the more powerful engine for block 5?
If Block 4 is the thrust upgrade then the performance of Block 5 shouldn't be much better than Block 4.
I maybe mistaken, but I thought Block 4 was the bolted Octoweb and a partial thrust increase and not much else.Not certain but I thought the titanium grid fins were Block 5 only.
But I thought block 4 was mostly the titanium grid fins and has already flown?
Quote from: hkultala on 11/18/2017 06:30 amBut I thought block 4 was mostly the titanium grid fins and has already flown?The Titanium grid fins have only flown once, and they flew on the last Block 3 first stage. So they’re not a Block 4 upgrade.
You'd use if it you expect to run hot (IE a lot of the ablative protection is worn off on every flight) or you want to radically lower maintenance between flights.
However to make that worthwhile you need the design to survive for enough reuses, and that's not happening at present.
Quote from: Robotbeat on 05/14/2017 04:28 amBlock 5 will have reusable TPS (my guess: carbon-carbon at least for parts of it) and legs that can fold back (i.e. without needing to be removed).For those that haven't seen it, this is from Tom Mueller's recent talk.
Block 5 will have reusable TPS (my guess: carbon-carbon at least for parts of it) and legs that can fold back (i.e. without needing to be removed).
Quote from: john smith 19 on 11/19/2017 07:43 pmYou'd use if it you expect to run hot (IE a lot of the ablative protection is worn off on every flight) or you want to radically lower maintenance between flights.Which describes the reuse goals of the Block 5 - to radically lower the maintenance between flights compared to Block 3/4.QuoteHowever to make that worthwhile you need the design to survive for enough reuses, and that's not happening at present.For the aluminum version sure, but the one use of the titanium fins looked successful.
I suspect the simplest answer is simply they have a stack of Aluminum fins and they work, so they're going to use them until they're used up.
Partly that, but also the life of the current generation booster stage is not long enough to justify Ti as well.
Quote from: john smith 19 on 11/21/2017 07:21 amPartly that, but also the life of the current generation booster stage is not long enough to justify Ti as well. Why would there be a correlation between the life of the booster and Ti grid fins? If they scrap the booster, they don't have to throw away the fins...
There should be a general SpaceX thread for broad interviews like this one.
Quote from: jpo234 on 11/21/2017 04:11 pmThere should be a general SpaceX thread for broad interviews like this one.You mean something like General Falcon and Dragon discussion (Thread 14)?
Why waste money on a sub system that can outlast the vehicle it's mounted on?
F9 Block 4 seems to be good for a life of 3 launches. Shotwell is saying Blk 5 will be good for 10. Titanium is much harder (and more costly) to machine.
The vehicle has to last longer to justify that. Likewise eliminating inspection and/or maintenance also shifts the balance to Titanium.
Regarding Shotwells interview I think the most interesting things were the that Raptor on F9 is not going to happen and F9 US recovery will not really be recovery but more to try and examine what damage is done to better inform the design of the BFS/BFR
Quote from: jpo234 on 11/21/2017 07:51 amQuote from: john smith 19 on 11/21/2017 07:21 amPartly that, but also the life of the current generation booster stage is not long enough to justify Ti as well. Why would there be a correlation between the life of the booster and Ti grid fins? If they scrap the booster, they don't have to throw away the fins...Why waste money on a sub system that can outlast the vehicle it's mounted on?...
Quote from: john smith 19 on 11/19/2017 07:43 pmYou'd use if it you expect to run hot (IE a lot of the ablative protection is worn off on every flight) or you want to radically lower maintenance between flights.Which describes the reuse goals of the Block 5 - to radically lower the maintenance between flights compared to Block 3/4.