Author Topic: How BFR Earth-to-Earth Might Actually Get Started  (Read 115792 times)

Offline docmordrid

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #460 on: 09/16/2018 11:40 am »
The preview pic for BFS apparently has 7 sea level raptors, and no vacuum raptors, but a skirt that is speculated to substitute for a vacuum nozzle - perhaps in combination with throttling down the outer 6 engines. This again puts fuel on the fire for BFS use as a single stage to orbit, which would greatly reduce the logistical challenges for P2P BFS transport around the Earth.

I hope this is true, but 7 Raptors is still not enough, the TWR at liftoff is ~1.02.

Given the Raptor specs from 2017, yes. But as we've seen from this announcement - nothing is sacred.
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Offline speedevil

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #461 on: 09/16/2018 12:09 pm »
The preview pic for BFS apparently has 7 sea level raptors, and no vacuum raptors, but a skirt that is speculated to substitute for a vacuum nozzle - perhaps in combination with throttling down the outer 6 engines. This again puts fuel on the fire for BFS use as a single stage to orbit, which would greatly reduce the logistical challenges for P2P BFS transport around the Earth.

I hope this is true, but 7 Raptors is still not enough, the TWR at liftoff is ~1.02.
1.03, if you count RCS thrust. :)
But as the other poster said, everything seems in principle back on the table, from higher thrust Raptors to vacuum extensions, to perhaps even slightly subscale from BFS2017.
And if the dry weight is low enough, TWR of 1.1, with a RCS that can hold the ship steady in 60MPH winds might just work.

Offline philw1776

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #462 on: 09/16/2018 12:17 pm »
Nowhere as glamorous as SSTO, but I've previously speculated that early on SpaceX will likely test the 1st stage BFR with a depleted # of engines saving time & $ to validate design basics. 
Note that say a 19 engine BFR booster would get a BFS with 60 tonnes "payload" into LEO thereby opening up P2P opportunities around the globe with a lower cost vehicle.  Trips like NY or Miami to/from Western Europe offshore ports would only need the BFS.
I do think an upgrade in Raptor thrust specs is needed for any BFS w/o booster applications.
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Offline mikelepage

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #463 on: 09/17/2018 06:39 am »
The preview pic for BFS apparently has 7 sea level raptors, and no vacuum raptors, but a skirt that is speculated to substitute for a vacuum nozzle - perhaps in combination with throttling down the outer 6 engines. This again puts fuel on the fire for BFS use as a single stage to orbit, which would greatly reduce the logistical challenges for P2P BFS transport around the Earth.

I hope this is true, but 7 Raptors is still not enough, the TWR at liftoff is ~1.02.
Quote
Given the Raptor specs from 2017, yes. But as we've seen from this announcement - nothing is sacred.

1.03, if you count RCS thrust. :)
But as the other poster said, everything seems in principle back on the table, from higher thrust Raptors to vacuum extensions, to perhaps even slightly subscale from BFS2017.
And if the dry weight is low enough, TWR of 1.1, with a RCS that can hold the ship steady in 60MPH winds might just work.

Am I correct in thinking that if Raptor specs stayed the same, you'd need a mass saving of ~94 metric ton out of ~1300 metric ton liftoff mass to take you from TWR 1.02 to 1.1?  Call it 100 tons you need to save, which could come both from using a configuration with a lower dry mass, and from moving less passengers/cargo at a time.

Think about the mass savings for a version of the passenger BFS that never leaves LEO. Use the same aeroframe, but you don't need solar panels, cabins, a radiation shelter, or large water stores (which alone would probably mass >20 ton).  If I was going point to point, aside from good acceleration couch and numerous windows, I would actually want to have a large empty space in which to jump/fly around in microgravity, perhaps with large elastic nets arranged around the outer surface for passengers to grab onto and bounce off.

There's no way that wouldn't be the preferred option to spending 24 hours in transit as I'm going to do on my way to IAC next Saturday.

Offline sanman

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #464 on: 09/17/2018 09:01 am »
Would a P2P BFR flight have only passengers and no crew?

I'm assuming it would have no captain/pilot - and the flight would probably be too short for any significant cabin service. So what kind of staff/personnel would have to be onboard?

If there were multiple flights per day, would said staff/personnel be able to serve on all of those multiple flights? Or would they have to be replaced after each flight?

If Space Shuttle astronauts experienced ~3G during launch ascent, then would P2P BFR travelers likely experience something comparable?
Would this require them to certify their fitness before traveling?

Also, would the P2P passengers be expected to wear flight suits?

Offline Cheapchips

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #465 on: 09/17/2018 09:11 am »

I'd go with full autonomous vehicle with a safety cabin crew in flight suits.  It's not like a pilot can ever land the spaceship in the event of a problem.

For passengers, no flight suits.  Possibly an equivalent of drop down masks for emergencies.  Passengers don't need to move around in the event of a decompression event.  A zip up inflatable bag? One for advance concepts?

Offline speedevil

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #466 on: 09/17/2018 09:29 am »
Would a P2P BFR flight have only passengers and no crew?
That would be a somewhat odd decision.
If you are talking about the optimistic case - 'cheaper than an economy airfare', that pretty much means $1000 and around a thousand passengers.

For $1000 plane tickets, it is usual for the flight to be very extended - say 8h.
In the US, each cabin crew member costs the airline $200 per employee per day, so they cost perhaps more than $200/flight.

If you believe BFR may fly twenty times a day, in its mature form, that crew cost per-trip cost would drop almost tenfold.
(Assuming you can't find people working for minimum wage as they get to stare out the window in 0G for 20 minutes a day, or qualifying as Moon shuttle crew)
$20 per flight means the only cost is them displacing a passenger, pretty much.

If you are in business, your absolute #1 priority is getting repeat customers, and encouraging word of mouth. 'I went to space and everyone puked, there was screaming, and I hated it after the first 30s' is not something you want your average customer to be saying.

You absolutely need enough staff to cope with most worst-case scenarios, or at least placate customers, and be a visible face of the carrier to defuse things.
It would not surprise me if these two factors lead to 'ridiculous' levels of crewing on BFS - something like one per eight passengers, with the crewperson sitting in the middle of the group they are responsible for.
You want those passengers loaded _fast_ and more crew tightly controlling small groups is one way to achieve that.

initial operations are the key here.
A crewmember per passenger is quite likely on initial flights, as BFS is not at all mass constrained, and SpaceX will want to train up crews rapidly for expansion.



Offline sanman

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #467 on: 09/20/2018 03:53 am »
What kind of G-forces are passengers likely to experience while on a P2P flight of BFR, given what we now know?

Would it be within the range of 3 G's or less? Or would it be higher than that?

Is it likely that prospective passengers would need a medical physical examination or some waiver in order to fly?

Given that this isn't required for current intercontinental flights, how would these issues impact the business model / viability?

Offline TripleSeven

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #468 on: 09/20/2018 04:01 am »
What kind of G-forces are passengers likely to experience while on a P2P flight of BFR, given what we now know?

Would it be within the range of 3 G's or less? Or would it be higher than that?

Is it likely that prospective passengers would need a medical physical examination or some waiver in order to fly?

Given that this isn't required for current intercontinental flights, how would these issues impact the business model / viability?

if a medical exam is not required to start, the first time someone croaks from the g loads and the company gets sued...it will :)

Offline oiorionsbelt

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #469 on: 09/20/2018 05:13 am »
What kind of G-forces are passengers likely to experience while on a P2P flight of BFR, given what we now know?

Would it be within the range of 3 G's or less? Or would it be higher than that?

Is it likely that prospective passengers would need a medical physical examination or some waiver in order to fly?

Given that this isn't required for current intercontinental flights, how would these issues impact the business model / viability?

if a medical exam is not required to start, the first time someone croaks from the g loads and the company gets sued...it will :)
The Tower of terror has G loads of 6.3 no medical exam required.
  What kinds of loads do you think the BFS will see?

Offline sanman

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #470 on: 09/20/2018 06:11 am »
I'm assuming the acceleration during ascent, and maybe Q-max, as well as the final landing burn will be where the most G-forces are felt.

So I guess the landing won't be as bad as F9's hoverslam, since there are more engines to turn off, and thus more scope for reducing thrust-to-weight.

And yet, with an airline model, the number of passengers and payload mass could vary a lot. Could those aft cargo bins be used as weight-balancers to sort of balance the loads?

Offline meekGee

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #471 on: 09/20/2018 06:28 am »
I'm assuming the acceleration during ascent, and maybe Q-max, as well as the final landing burn will be where the most G-forces are felt.

So I guess the landing won't be as bad as F9's hoverslam, since there are more engines to turn off, and thus more scope for reducing thrust-to-weight.

And yet, with an airline model, the number of passengers and payload mass could vary a lot. Could those aft cargo bins be used as weight-balancers to sort of balance the loads?
FWIW, max-Q is max combined aero and inertial load on the airframe, not max g.  During ascent, that happens towards fuel depletion.

During descent, they might coincide, and a second look at the simulation video will tell you all you need to know, I think.

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Online JamesH65

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #472 on: 09/20/2018 09:26 am »
What kind of G-forces are passengers likely to experience while on a P2P flight of BFR, given what we now know?

Would it be within the range of 3 G's or less? Or would it be higher than that?

Is it likely that prospective passengers would need a medical physical examination or some waiver in order to fly?

Given that this isn't required for current intercontinental flights, how would these issues impact the business model / viability?

if a medical exam is not required to start, the first time someone croaks from the g loads and the company gets sued...it will :)

I doubt it. As poster above shows, you don't need medical examinations for fairground rounds that pull more than 3G, and they rarely get sued.  I get thrown around in the train I come in to work on, because the track is so bad, they are instantaneous jerks of > 3G. I've have race car crashes where I pulled much more than that. I didn't sue the other drivers or the track.

G load is a certainty on the BFS, its not like they can do anything about it, so will be in any commercial contract of flight that you will encounter these loads and you sign off against them. Its not an unusual occurence, it's not something that SpaceX can mitigate again or prevent - it will be there.


Offline speedevil

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #473 on: 09/20/2018 09:44 am »
G load is a certainty on the BFS, its not like they can do anything about it, so will be in any commercial contract of flight that you will encounter these loads and you sign off against them. Its not an unusual occurence, it's not something that SpaceX can mitigate again or prevent - it will be there.
They can mitigate it in some cases.
Acceleration during launch can be reduced. You can cap it to around 1.5G at the cost of two thirds or so of the payload. (rough numbers).
Similarly, during entry, a lighter vehicle may experience lower G loading in some phases of reentry by doing similar trades - though the lift/drag number, which is set by the vehicle aerodynamics constrains this a lot.

Blips from the main engine during entry may be able to improve the effective L/D and keep the vehicle in a region it can slow down more gently, but this is again going to use a lot more landing propellant.

Back of the envelope numbers indicate that approximately five times the propellant per passenger might get you a 1.5G ascent and a 2-2.5G max descent.
(this may require either separate ascent and descent vehicles or tanking in the middle)

Offline Zed_Noir

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #474 on: 09/21/2018 01:00 am »
Have an amusing thought. It will be quicker to take a BFR in Perth Australia to LA then flyback to Sydney Australia than commercial airlines. IIRC from the SpaceX P2P video it about 40 minutes between Perth and LA, and about 30 minutes between Sydney and LA. Add in a hour to layover between flights at LA. So about two and a half hours travel time by P2P from Perth to Sydney along with all the major cities on the Australia East coast and New Zealand.

Presuming it cost about $1000 USD per BFR flight. Would this be serious competition to domestic long-haul airlines?

Offline mikelepage

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #475 on: 09/21/2018 12:38 pm »
Have an amusing thought. It will be quicker to take a BFR in Perth Australia to LA then flyback to Sydney Australia than commercial airlines. IIRC from the SpaceX P2P video it about 40 minutes between Perth and LA, and about 30 minutes between Sydney and LA. Add in a hour to layover between flights at LA. So about two and a half hours travel time by P2P from Perth to Sydney along with all the major cities on the Australia East coast and New Zealand.

Presuming it cost about $1000 USD per BFR flight. Would this be serious competition to domestic long-haul airlines?

Ha!  ;D But no. Not a chance.  At least for the foreseeable future, I think this will only be good for flights 1/4 to 1/2 way around the world. Although your mentioning layovers did prompt an idea I'd not thought of before.

Unlike planes, two BFS can dock to one another whilst in flight, which gives you an option for "space-overs".  Rather than just having lots of ~30 minute point to point trips, you could have a "daisy chain" system, where you have a network of spaceports and BFSs.  Each BFS need only launch (say) once daily, but they would all launch sequentially into a standard inclination orbit, and dock with two other BFSs during each flight.  That means each passenger can access the whole network of destinations, while also experiencing space, and still make trips around the planet in much less time.


Offline speedevil

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #476 on: 09/21/2018 02:10 pm »
Unlike planes, two BFS can dock to one another whilst in flight, which gives you an option for "space-overs".  Rather than just having lots of ~30 minute point to point trips, you could have a "daisy chain" system, where you have a network of spaceports and BFSs.  Each BFS need only launch (say) once daily, but they would all launch sequentially into a standard inclination orbit, and dock with two other BFSs during each flight.  That means each passenger can access the whole network of destinations, while also experiencing space, and still make trips around the planet in much less time.

You can - if you have enough in transit - have several of these hubs orbit, possibly in different inclinations, planes, and phasing.
It's a complex and fun optimisation problem, but it would substantially reduce total transit time over ~2 days or so that you get with one.

Offline Ludus

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #477 on: 09/22/2018 03:01 am »
How do you think a passenger P2P BFS would be configured? As many simple decks as will fit filled with some arrangement of couches? How would boarding work?

Offline mikelepage

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #478 on: 09/22/2018 05:59 am »
How do you think a passenger P2P BFS would be configured? As many simple decks as will fit filled with some arrangement of couches? How would boarding work?

Maybe eventually they'll pack them in tight to minimise costs, but for the first years/decade, I think the majority of passengers will care less about getting somewhere in 30 minutes, than fulfilling a lifelong dream to go to space.  With that in mind, I think the first flights will be longer (several orbits - see "daisy chain" concept above), and the priority will be maximising space per passenger. 

Because of launch, and the 2 phase reentry, the acceleration couches need to be able to support passengers in both orientations (belly first, then tail first).  Every one of the acceleration couches will need to have the passenger's head pointing towards the "dorsal" surface so passengers feel the g forces as if they were sitting (during belly first), then lying on their backs (during tail first).  You'll have cabins, with private windows, up this dorsal surface (each with one or two acceleration couches in them), and then the remainder of the acceleration couches will be arranged IMAX style in front of the main window at the top/front.

Internal to the cabins, also on the dorsal side, you'll have ladders/staircases from the entry hatchways up to the top (so yes, 2nd class passengers in the IMAX seating will still have to climb past 1st class cabins - some things never change), but other than that, I'd imagine the rest of the volume will be left very open, so that people can jump around in zero g during the flight.   Maybe they'd section off some areas with trampoline material so people can play games/sports in some areas, or waterproof material, so others can consume and play with drinks and food. 

Others still may want to have a quiet area, to float undisturbed like in a sensory deprivation chamber.  Lastly, I imagine many people will just want to stare out the window for the entire flight, so I think the experience will be quite different from plane flight - there's a potential for a real carnival atmosphere, of people moving around the BFS to experience different things. 

This potential for fun is why I don't think the 30 minute transit is going to be the most important thing. If you're travelling around the world, spending 4.5-6 hours doing a few orbits instead of 24+ hours cooped up in a plane is still a massive improvement, and to be able to play around in zero G will make it feel like it goes in an instant.

Offline speedevil

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #479 on: 09/22/2018 10:10 am »
How do you think a passenger P2P BFS would be configured? As many simple decks as will fit filled with some arrangement of couches? How would boarding work?

Maybe eventually they'll pack them in tight to minimise costs, but for the first years/decade, I think the majority of passengers will care less about getting somewhere in 30 minutes, than fulfilling a lifelong dream to go to space.  With that in mind, I think the first flights will be longer (several orbits - see "daisy chain" concept above), and the priority will be maximising space per passenger. 

It is a lot cheaper to let people float around and  look at stuff on a hotel module.
If they do in fact beat the numbers down to $1M/flight for passenger class transport, fixed non-inflatable 800m^3 habitat modules with one meter water radiation shielding are something you can get into orbit in six chomper launches, for $7M or so per for the bare pressurised module.

This contrasts with the BFS, costing $150M or so per.

Maximising flight rate is the key in beating down costs. if you're sending up un-densely packed BFS, and using them as hotel modules, you have effectively made your BFS  costs grow a hundredfold a flight or so.

If something stops BFS being readily reusable >>500 times, it can't do 'cheaper than economy air fair ($1000*1000)', and you may need to resort to low-flight-rate schemes to get it profitable..

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