Author Topic: How BFR Earth-to-Earth Might Actually Get Started  (Read 115789 times)

Offline mikelepage

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #480 on: 09/22/2018 12:48 pm »
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..

Just re-emphasising my caveat. Space hotels won't be as cheap as you're talking about for at least a decade or more.  The currently cheapest quoted figure (that I know about) is the BA330, which is supposed to rent out 1/3 the station at $25 million for 60 days, so not sure where you're getting your figures from?

I'm talking about how BFR P2P might get started, not later on when it's flying 10+ times a day and we already have numerous space hotels.  When you still have relatively low numbers of passengers paying single-digit-millions for the experience.  Just trying to imagine what the interim business model looks like.
« Last Edit: 09/22/2018 12:50 pm by mikelepage »

Offline speedevil

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #481 on: 09/22/2018 07:08 pm »
<snip comment of mine>
Just re-emphasising my caveat. Space hotels won't be as cheap as you're talking about for at least a decade or more.  The currently cheapest quoted figure (that I know about) is the BA330, which is supposed to rent out 1/3 the station at $25 million for 60 days, so not sure where you're getting your figures from?
The price of steel off-the-shelf large cryogenic tanks rated to 100PSI, plus the cost to lift them at the same price/kilo as 'economy flight' passengers.
Clearly outfitting them would add to the cost.
But, not by more than an  order of magnitude.

BA330 has lots of highly complex folding architecture and advanced composite skins.
But, if you can make it from a lightly modified commercial steel tank, not actually bother with folding, and outfit it with components already designed for your BFS, it may get a lot cheaper.

Offline mikelepage

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #482 on: 09/23/2018 05:29 am »
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.

Just looking back and I realise it was you speedevil who started the BFS SSTO thread.   

One advantage of having people float around in an un-densely packed BFS is the chance to reduce your dry mass considerably.  What I was getting at with having large spaces to float around in (plus a few dozen acceleration couches and optionally some cabins) was that this would be a very lightweight configuration of BFS.  Perhaps light enough to make SSTO possible.

If you can fly passenger BFS P2P without a booster stage, that very quickly increases the number of destinations you can fly to, because of how much smaller space ports/exclusion zones could be if they only have to deal with BFS, not BFB.  That's what maximises your flight rates.

EDIT: would be curious to see some estimates of how much less noisy a BFS takeoff would be versus the full stack? Not sure how to calculate it myself.


« Last Edit: 09/23/2018 05:32 am by mikelepage »

Offline speedevil

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #483 on: 09/23/2018 10:18 am »
One advantage of having people float around in an un-densely packed BFS is the chance to reduce your dry mass considerably.  What I was getting at with having large spaces to float around in (plus a few dozen acceleration couches and optionally some cabins) was that this would be a very lightweight configuration of BFS.  Perhaps light enough to make SSTO possible.

I find it amusing that it is sort-of-plausible that large empty spaces may mass more than a small minimal passenger compartment added on, because the air in the main compartment weighs over a ton, which if you vented it would obviously increase payload.

I have not found quickly a nice constraint on suborbital launches, but in short, it is problematic to assume that you can simply get the range by computing a parabola - for example.

As an example - if you're coming in at 7000m/s and 45 degrees, your reentry is something like 100G.
This means that real world trajectories have to minimise vertical velocity on reentry to something that can be cancelled aerodynamically before the atmospheric density doubles in the next 5km.
So, it can't be much beyond 300m/s or so.

You need to spend a large amount of propellant on a vertical braking burn, or alternatively, countering gravity when in the suborbital portion of the flight and not ascending beyond the bare minimum altitude.

Offline hkultala

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #484 on: 09/23/2018 10:36 am »
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.

Just looking back and I realise it was you speedevil who started the BFS SSTO thread.   

One advantage of having people float around in an un-densely packed BFS is the chance to reduce your dry mass considerably.  What I was getting at with having large spaces to float around in (plus a few dozen acceleration couches and optionally some cabins) was that this would be a very lightweight configuration of BFS.  Perhaps light enough to make SSTO possible.

Floating around in large open spaces would be terrible for the people when the floating ends and the ship hits back to atmosphere and starts to decelerate quickly. On these P2P flights there should be always some fixed structure close to grab on and quickly pull oneself to the acceleration couch when the ship approaches the atmosphere.

And carbon fiber walls inner can be very light.

The extra weight of the crew configuration comes more from things like life support systems and radiation-shielded outer walls than passive inner walls.

Offline speedevil

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #485 on: 09/23/2018 12:13 pm »
Floating around in large open spaces would be terrible for the people when the floating ends and the ship hits back to atmosphere and starts to decelerate quickly. On these P2P flights there should be always some fixed structure close to grab on and quickly pull oneself to the acceleration couch when the ship approaches the atmosphere.

Or, well, do a 20cm/s burn to get all the passengers to one end.
Quote
The extra weight of the crew configuration comes more from things like life support systems and radiation-shielded outer walls than passive inner walls.
'Crew configuration' can't mean one thing.

1000m^3 pressurised volume, for example, you need no life support at all for flights of an hour, and a hundred passengers.

(one eighth or so of the total volume is breathed, so it will get notably more humid)


Offline Lar

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Re: How BFR Earth-to-Earth Might Actually Get Started
« Reply #486 on: 02/16/2019 10:43 pm »
There is a continuation of this discussion here (altohugh there is a good chance the threads will get merged)

https://forum.nasaspaceflight.com/index.php?topic=47450
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

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