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SpaceX BFR [video]

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Re: SpaceX BFR [video]

#251

Post by njarboe »

ryandrake wrote: post #242
njarboe wrote: post #241

Earlier quoted context omitted.

Why don't you start working on Holodecks. Musk wants to get humanity off this rock. Funding the building of a ship designed to land anywhere in the solar system, including Earth, by using it for Earth transport is brilliant. If one can make the trip from New York to Shanghai in 40 minutes, for the same fuel per person and ticket price as an airplane, why not. Having a fully reusable rocket will be amazing. Once relia…

I fully applaud efforts to "get humanity off the rock". To the extent that building a rocket airline helps move humanity toward this goal, great! But, other than as a stepping stone to something bigger, this just seems like a silly distraction. As for the very HN-ish "why don't you just go make XYZ?" retort, obviously it's because, like most of us (and unlike Elon Musk), I don't have the necessary truckloads of $100…

I think the retort is coming from the fact that to do something amazing like building a reusable rocket (or other great, but easier projects) takes much more than money in the bank. It takes a whole lot of talented people working very hard for a long time. The leader of such people will need an amazing amount of dedication, work, skill, time, luck, drive, smarts, charisma, sacrifice, friends, money, charm etc. to pull it off. If the leader does not have a burning passion for the goal, giving up is the likely outcome with all the problems along the way. So when someone says that this person should be dedicated to some other goal, even though the one they are doing is great, that does not make any sense. The leader and the people working with him have a passion for a certain idea and the skills to work on towards that project. Those are not fungible to another project. Move Musk and all the people working at SpaceX to working on the Holodeck would just be useless and a waste.

Technology does not just progress by magic or money. People must do the hard work. The world is awash in capital at this moment with negative interest rates in some places. Physical resources (or money) is not the limitation for getting most new things done in the world at the moment. It is the complicated process of getting people working together, taking a million false steps, and not giving up before finally figuring out how to reach a goal.

Re: SpaceX BFR [video]

#252

Post by justin66 »

mikeash wrote: post #249
justin66 wrote: post #247

Earlier quoted context omitted.

> 1) Problem during launch. There's been one successful use of a launch escape system in rocketry history[1], and such a system has never been developed for a shuttle type craft. I'm not sure if you're aware, but this is a feature of the latest version of SpaceX's capsules. I'm sure it would exist for their larger vehicles. edit: although I'm just not sure what you'd do during an abort with all that fuel that larger…

I'm not so sure. The Dragon 2 integrates a launch escape system by using the same engines that are also intended for propulsive landing (which is now probably off the table for good, but that was the idea). The BFR ship won't have near enough TWR when fully loaded for its landing engines to double as launch escape engines, and I see no evidence of any other engines. The fact that the BFR ship serves as both second st…

> which is now probably off the table for good, but that was the idea

Oh, that's interesting. What makes you say so?

Re: SpaceX BFR [video]

#253

Post by Retric »

mstade wrote: post #182
simonh wrote: post #138

Earlier quoted context omitted.

It’s a really good question. Supersonic jets were always heavily constrained due to noise pollution issues with the sonic boom. They weren’t allowed to fly over land at supersonic speeds, relegating them to trans-oceanic routes. Now yes this system will have such problems on launch, but as they go pretty much straight up out of the atmosphere compared to a jet, the vast majority of the journey is in space where that’…

If people think supersonic jets are loud, they’re in for a treat with rockets. Anyone who’s ever witnessed a launch at KSC (I have) will probably say two things: it’s awesome, and it’s LOUD. Not ear popping kind of loud, but VERY loud nonetheless, and you feel it too if you’re close enough. (Really recommend a viewing at the LC39 observation gantry, it’s awesome!) I was watching that video and kept thinking that plat…

Airports are in cities. Even 10 miles out to the ocean would make a massive difference without taking that long.

Re: SpaceX BFR [video]

#254

Post by justin66 »

mikeash wrote: post #250
justin66 wrote: post #248

Earlier quoted context omitted.

> if you can land propulsively in the water, surely you can land propulsively at the landing pad. I think if you take off and you immediately find that one of the rocket motors isn't gimballing correctly, or something else looks off with the engines, it might be prudent to abort before building up a lot of velocity. (not to mention aborting before something explodes) It's certainly easier.

Land back at the takeoff point then?

I don't think that's always going to be possible, but yeah, that's probably the first choice.

I imagine the most problematic abort in something like a NY to London flight would be if multiple engines fail several hundred miles out. All kinds of velocity in the wrong direction if you want to fly back, not enough thrust to maintain the proper trajectory towards the target. I think there are bound to be some scenarios where you can do a limping, powered landing (the vehicle probably only needs one or two working engines) but you have to do it downrange.

Re: SpaceX BFR [video]

#255

Post by mikeash »

justin66 wrote: post #252
mikeash wrote: post #249

Earlier quoted context omitted.

I'm not so sure. The Dragon 2 integrates a launch escape system by using the same engines that are also intended for propulsive landing (which is now probably off the table for good, but that was the idea). The BFR ship won't have near enough TWR when fully loaded for its landing engines to double as launch escape engines, and I see no evidence of any other engines. The fact that the BFR ship serves as both second st…

> which is now probably off the table for good, but that was the idea Oh, that's interesting. What makes you say so?

Apparently I'm remembering an official statement!

https://spaceflightnow.com/2017/07/19/propulsive-landings-ni...

The reason seems to be a combination of NASA not being interested in propulsive landing (and they're funding most of Dragon 2) and deciding to go all-out on BFR instead of refining Dragon 2 further.

Re: SpaceX BFR [video]

#256

Post by mikeash »

justin66 wrote: post #254
mikeash wrote: post #250

Earlier quoted context omitted.

Land back at the takeoff point then?

I don't think that's always going to be possible, but yeah, that's probably the first choice. I imagine the most problematic abort in something like a NY to London flight would be if multiple engines fail several hundred miles out. All kinds of velocity in the wrong direction if you want to fly back, not enough thrust to maintain the proper trajectory towards the target. I think there are bound to be some scenarios w…

I'm not sure that the ship would be strong enough to withstand a water landing. It'll come down on its tail, and then it will (I think!) tip over, which will probably smash it to pieces.

Aborts also leave you with too much fuel on board, probably way too much fuel. You could burn it off with the engines, although you'd want to actually use it to reach your origin or destination if possible.

If you abort early, you can still reach the origin. If you abort late, you can still reach the destination on the remaining engines. So the pertinent question is: do these two regimes overlap, or is there a gap, and how big? I don't have the answers, and you may be right that there is one.

Re: SpaceX BFR [video]

#257

Post by thinkcontext »

simplicio wrote: post #236
thinkcontext wrote: post #230

Earlier quoted context omitted.

They can fly cargo. FedEx would definitely be able to market such a service.

Yea, but the main advantage of the system over air-travel is that it's fast. For most types of cargo, cost rather then speed is the main issue, especially if the difference is just on the scale of a few hours.

When shipping internationally if cost rather than speed is the concern you ship by boat. Shipping by rocket over a plane would just be another higher tier of service. If Musk's pricing is to be believed it would make shipping between continents potentially faster than shipping within the continent. That would change the industry.

Re: SpaceX BFR [video]

#258

Post by ryandrake »

njarboe wrote: post #251
ryandrake wrote: post #242

Earlier quoted context omitted.

I fully applaud efforts to "get humanity off the rock". To the extent that building a rocket airline helps move humanity toward this goal, great! But, other than as a stepping stone to something bigger, this just seems like a silly distraction. As for the very HN-ish "why don't you just go make XYZ?" retort, obviously it's because, like most of us (and unlike Elon Musk), I don't have the necessary truckloads of $100…

I think the retort is coming from the fact that to do something amazing like building a reusable rocket (or other great, but easier projects) takes much more than money in the bank. It takes a whole lot of talented people working very hard for a long time. The leader of such people will need an amazing amount of dedication, work, skill, time, luck, drive, smarts, charisma, sacrifice, friends, money, charm etc. to pul…

I think we agree on one point: To do great things, access to capital is necessary but not sufficient. If all it took was hard work, I'm sure lots of us would quit our jobs today and get started!

Re: SpaceX BFR [video]

#259

Post by lsaferite »

Florin_Andrei wrote: post #221
drinchev wrote: post #91

I think if we measure the travel time from door to door the benefits of the fast rocket shrink in a relation to where is located. With airplanes this is solved, by the big infrastructure ( cities sometimes have even 2-3 airports ). Where I live ( Berlin ) with a flight to NYC would look like : 1. City center -> TXL - 20m 2. Check-in / security - 30m ( no joke, the airport is small ) 3. Flight - 9h 15m 4. Check-out /…

One thing you're missing: For a very high profile requirement - say, some kind of huge emergency - you could land the BFR anywhere there's a solid surface the size of a soccer field. Zero infrastructure required. Getting it out of there again would be difficult, but you could have a team of experts and a whole lot of material resources literally drop down from the sky anywhere on Earth in a matter of hours. Most of t…

Military invasion forces and quick reaction forces would be much easier to insert with tech like that.
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