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Sep 29, 2017, 03:08 PM
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BFR updates

"We will start construction of the 1st ship around the 2nd quarter of next year."

Like something from a movie about averting the destruction of the human race. Pretty intense stuff, but lions are pretty sure you can't test the in situ propellent plant for the 1st time on the same mission the 1st astronauts are going on. As expected, it was lighter than last year's show because of the renewed focus on their mission backlog instead of the BFR.

Delta wings are back. It has assumed the familiar shuttle shape. At least the shuttle designers got that part right. Unfortunately, he couldn't make the heat shield reusable. They're not going fly around with enough material to make it reusable. They're going to spend a huge amount of money replacing it for every flight.

He didn't show the engine layout of the new 1st stage. Perhaps the BFR guy focused on just the new 2nd stage & he only has a rough idea of the new 1st stage.

Unlike last year's design, the current design looks like it could actually happen & he was clean shaven which added more credibility. The payload is now 1/2 of last year's. The timeline is the same as last year, but he's able to do it in the existing factory.

Using a BFR to fly around Earth is a bit silly. The Concorde already proved no-one cares about high speed air travel, so he's not going to make money on that. The security lines & boat trip to the launch pad will comprise most of the time. At least it would solve the problem of sonic booms over land.

Transferring propellant using control thrusters to create milli-g acceleration was another sketchy idea, along the lines of the crossfeed line. Instead of burning fuel for the full duration of the prop transfer, just use electric pumps. At least we finally got to see the prototype oxygen tank, encrusted in ice, explode. It apparently met the design requirements.

Regarding the Raptor engine, ISP was reduced from 382s in vacuum to 375s. Sea level ISP was reduced from 334s to 330s. Chamber pressure was reduced from 300atm to 250atm. Thrust in vacuum was reduced from 3500kN to 1900kN. Thrust at sea level was reduced from 3050kN to 1700kN. Note how the last 1% in ISP requires a 17% increase in chamber pressure, which requires a 44% increase in thrust. The last bit of theoretical engine efficiency is truly a monstrous amount of effort.
Last edited by Jack Crossfire; Sep 29, 2017 at 11:15 PM.
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Sep 29, 2017, 09:15 PM
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You are probably wright about the SST angle, but taking a boat from downtown to a launchpad in the harbor would save an hour+ each way vs having to go to JFK in traffic. Concorde just wasn't fast enough to outweigh all the schlepping involved in 2000's air travel.

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