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Jul 10, 2017, 11:20 PM
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Spacex nuggets


The Shot Well was interviewed on the space show here http://www.thespaceshow.com/show/22-...wynne-shotwell . Here, she revealed they're renaming the ITS back to the BFR, big f*cking rocket. There was 1 of the few references to her husband, so the internet needs to stop writing Ms. They've fired the scaled raptor engine over 25 times, but have not even decided what its full size should be. The full size is determined by the knee in cost/performance & is converging on 2.5x the scaled size of 200,000lbf. They're now considering another Falcon 9 revision with raptors. Still impressive that the scaled raptor is as powerful as the final merlin. They could just swap in the scaled ones.


Their mane focus is the falcon heavy demo flight, dragon 2, & falcon 9 block 5. Then there's faring recovery, stage 2 recovery. There's no material investment on the BFR, the lunar flight, or any of the other stuff on Musk's twitter feed. There wasn't anything on what happened to the carbon fiber tank besides they're still trying. The Falcon 9 block 5 has valves rated for many cycles & tanks rated for many more pressure cycles. They're doing "some work" on the octaweb. Blocks below 5 can only fly 3 times.


It seems if Musk put just the effort on boring & hyperloop on the BFR, it would be a headline maker, but Tesla still isn't making money & there aren't enough roads to drive the number of cars he needs to sell. People are going to put a lot more miles on Teslas which are virtually free to operate than cheaper gas cars which cost more to operate. The boring & hyperloop are ways to transport more Teslas around.


Based on the interview, it seems the BFR is drifting to something beyond our lifetimes. The original presentation always did look like a vision of the distant future rather than a plan for our generation. A pad 39A devoid of all current structures, with what looked like a single piece of metal for a service tower, looked many generations into the future.


You can actually view podcasts by guest here http://www.thespaceshow.com/guest/gwynne-shotwell revealing Shot Well is a pretty frequent guest.


This show revealed the mighty Lars Blackmore, the guy who wrote the landing algorithm for Falcon 9. Reading through his pdf's reveals it's not a simple matter of PID loops like your Xiaomi quad copter. The mane limitation barring PID loops is fuel. The computer must compute the most optimum trajectory from its current position to landing, every millisecond, counting future changes in speed, mass, glide slope, air pressure.




The actuators on the grid fins have to be a lot more precise than your $10 hobbyking servo. The lag in engine shutdown requires predicting the final seconds of flight instead of waiting for a radar altimeter to show 0 & killing the fuel.


It's a convex problem so hard to solve, they used a code generator to generate C source code to solve it. The methods weren't possible before 2011. Precision, propulsive landing wasn't in the realm of possibility until the Mars missions of the 2000's.


All those evolutions needed to happen before Falcon 9 & the Falcon 9 landing algorithm was the last card for humans. There's no other way humans have a chance to live beyond the next extinction event.
Last edited by Jack Crossfire; Jul 11, 2017 at 12:46 PM.
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