Author Topic: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)  (Read 389064 times)

Offline Dave G

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #980 on: 01/13/2018 04:49 PM »

Musk said it takes 6 BFS/tanker launches to refuel a BFS for Mars, but that gives a propellant payload of about 185tones, not 150 tonnes.
That's because this misinformation keeps being repeated. He said 5 tanker flights not 6
Right.  6 total BFR flights per mission.  5 BFS Tankers.  1 BFS Cargo / Passenger.

However, I believe this is based on the initial BFS Tanker being identical to the BFS Cargo version.  In the future, Musk said the plan was to eventually build a dedicated BFS tanker, presumably to reduce the number of tanker flights.

Offline aero

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #981 on: 01/13/2018 04:56 PM »
The order of usage of BFR/BFS

1- Cargo
2- Tanker
3- HSF
4- Interplanetary Cargo
5- Interplanetary HSF
6- P2P


P2P is the last implementation to be applied to this system. By the time it is applied it will be a well understood system with known quantities from multiple examples over multiple flight profiles the life of engines and airframes and all manner of flight hardware.

Between steps 1 through 5 there may not be much of a duration on the order measured in months not years. But between 5 and 6 the duration is likely to be measured in years. By the time that P2P for this system would be an acceptable implementation for the general public use there is likely to be as much as 10 years passing from the first manned interplanetary flights. In which case thousands of people will have gone and come back from space (LEO, Moon, Mars) before P2P is attempted.

The order is not arbitrary because each step is dependent on the previous step and represents incremental improvements to allow the achievement of the step over that of the previous step.
What about p2p cargo?

I've been reading this thread and am a little surprised that no-one has mentioned the prototypes. They will be the first BFS's, they will have engines, tanks and the outer mold line in the near-final shape. They will be used as P2P vehicles on the test range. Only when they fly reliably will SpaceX start working the above list. Will they work the above list (in their chosen order) or will there be parallel model builds?

Or does anyone think that Elon Musk will skip the prototyping step?
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Offline Dave G

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #982 on: 01/13/2018 05:04 PM »
The order of usage of BFR/BFS

1- Cargo
2- Tanker
3- HSF
4- Interplanetary Cargo
5- Interplanetary HSF
6- P2P

Hmmm.  Not sure I would count the inner passenger arrangements as different BFS versions.  More like variations of the same version.  But maybe I'm mincing words here.

My point is that the outer skin and tank configurations will have fewer variations, namely:
Cargo
Passenger (with windows)
Satellite delivery (clamshell, shown below)
Dedicated tanker (long term, with different tank configuration)

Short term, they'll use the BFS Cargo version as a Tanker, but eventually, Musk said they'll build a dedicated optimized Tanker, presumably to lower the number of Tanker flights.
« Last Edit: 01/13/2018 05:14 PM by Dave G »

Offline Dave G

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #983 on: 01/13/2018 05:09 PM »
I've been reading this thread and am a little surprised that no-one has mentioned the prototypes. They will be the first BFS's, they will have engines, tanks and the outer mold line in the near-final shape. They will be used as P2P vehicles on the test range. Only when they fly reliably will SpaceX start working the above list. Will they work the above list (in their chosen order) or will there be parallel model builds?

Or does anyone think that Elon Musk will skip the prototyping step?

From everything I've read, it seems the first BFS will be the Cargo version.  This will also be used as the initial BFS Tanker.  The first two Mars missions in 2022 will use the BFS Cargo version.


Offline Robotbeat

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #984 on: 01/13/2018 05:09 PM »

Musk said it takes 6 BFS/tanker launches to refuel a BFS for Mars, but that gives a propellant payload of about 185tones, not 150 tonnes.
That's because this misinformation keeps being repeated. He said 5 tanker flights not 6
Right.  6 total BFR flights per mission.  5 BFS Tankers.  1 BFS Cargo / Passenger.

However, I believe this is based on the initial BFS Tanker being identical to the BFS Cargo version.  In the future, Musk said the plan was to eventually build a dedicated BFS tanker, presumably to reduce the number of tanker flights.
This depends on the transit time and the exact window used (i.e. 2022 vs 2024, etc). Worst-case may be 5 tanker flights, but best case could be half that (relevant for cargo).
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Offline john smith 19

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #985 on: 01/13/2018 06:15 PM »
SpaceX is not in business to make money.  Their goal is Mars.  Making money is just a means toward that goal.
Except if Musk wanted to go to Mars without making a surplus he'd have set up a charity instead.  :(

Practically if an organization wants to do something involving a lot of investment that no bank will touch they have to fund it. That means from having prices that exceed their costs.

That's called making a profit IRL.

And for the Musks goals they have to be big profits
Quote from: Dave G
If they could get to Mars, without making money, they would.  In fact, Musk's initial vision was to throw away $100 million to fund launching a small greenhouse on Mars.

This is why SpaceX isn't a publicly traded company.  They're not in business to make money.
They won't get anywhere Mars if they don't. Being private means they don't have to distribute them and can't be pressured into doing so by some random stranger coming in one day and taking a significant stake and forcing them into doing so.
Quote from: Dave G
Having said that, SpaceX has no real reason to reduce launch prices with flight proven boosters.  No one is anywhere near undercutting them.  So they can take that extra profit and apply it to BFR.
Which suggests they will do exactly the same with BFR/BFS pricing once it enters service.

It won't lower the $/lb price to LEO anytime soon but it will probably get SX to Mars faster.

People will decide for themselves wheather that order of priorities makes them happy or not.

Musk said it takes 6 BFS/tanker launches to refuel a BFS for Mars, but that gives a propellant payload of about 185tones, not 150 tonnes.
That's because this misinformation keeps being repeated. He said 5 tanker flights not 6
Thanks for pointing that out. It also suggests an error in my propellant calculations for my Mars settlement game.

Because as it stands if the total of structure + payload for a tanker remains (85 +150 tonnes) to get down to 5 flights means the BFS has to be no more than fifteen (15) tonnes.

That suggests the BRS tanker will be very different to BFS. I could believe the passenger version could drop 35t of human dedicated hardware stuff , but not close to 70t.

I'll be looking for faults in my model.

However for those who are prepared to gamble it's not a bug here's a copy of my current mars settlement game, the 2nd sheet of which covers the propellant loads and potential costs, treating BFR, passenger and tanker BFRS as separate vehicles so you can vary their properties.

Just a reminder this was built to look at what it would take to get a million people to Mars within a little over a century, but propellant and BFS costs are quite a big part of that.

Usual rules. Cells with Blue borders are the ones you change to see effects and red dots on cells hold default values and sources of the original numbers. 
« Last Edit: 01/13/2018 06:17 PM by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Dave G

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #986 on: 01/13/2018 07:15 PM »
SpaceX is not in business to make money.  Their goal is Mars.  Making money is just a means toward that goal.
Except if Musk wanted to go to Mars without making a surplus he'd have set up a charity instead.  :(
Not necessarily. Wealthy philanthropist types may invest in SpaceX without much regard for return.  SpaceX doesn't need to be a 501(c) for that to happen.  The key is that the investors share SpaceX's vision. Or maybe they're just Elon's rich buddies.

To be clear, I'm not saying this is the major source of SpaceX's cash flow, but it could easily get them over a hump.

My main point is that most other companies are primarily motivated by short-term profit, and their plans are basically derived from that.  By contrast, SpaceX's plans are primarily motivated by colonizing Mars.  That's why they've designed a huge expensive rocket that can be reused hundreds of times. Then after that, they figured out a way to make money on it, in order to cost justify the huge upfront expense.  Totally reverse order from most other companies.

Quote from: Dave G
Having said that, SpaceX has no real reason to reduce launch prices with flight proven boosters.  No one is anywhere near undercutting them.  So they can take that extra profit and apply it to BFR.
Which suggests they will do exactly the same with BFR/BFS pricing once it enters service.

It won't lower the $/lb price to LEO anytime soon but it will probably get SX to Mars faster.
Once BFR is flying regularly, their goal of colonizing Mars will still be there.  In order to achieve it, they'll need to lower BFR prices to around $500,000 per round trip ticket, or ~50 million for ~6 BFR launches.

Also, if SpaceX is successful, I believe competitors will spring up.  In fact, I think Elon wants this to happen.

Online speedevil

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #987 on: 01/13/2018 11:34 PM »
My point is that the outer skin and tank configurations will have fewer variations, namely:
Cargo
Passenger (with windows)
Satellite delivery (clamshell, shown below)
Dedicated tanker (long term, with different tank configuration)

Short term, they'll use the BFS Cargo version as a Tanker, but eventually, Musk said they'll build a dedicated optimized Tanker, presumably to lower the number of Tanker flights.

I consider the list of vehicles as aspirational at best.

Cargo is only needed if there is a near-term market for large satellites. (all payloads I checked for F9 that have launched will fit through the door of the 'passenger' version.)

A simple outer-moldline version of the 'passenger' variant with no windows pretty much meets all near-term needs.
You pull out all the creature comforts if you need to launch more than a handful of F9 class satellites at a time, or to deliver fuel.

If you've managed to do enough cycles on this variant that passenger transport looks viable, you can fit small windows with a hacksaw using the very comprehensive stress and thermal data you got from this.

Only if it's gotten really quite popular with actual passenger service for large numbers of people would you bother making the variant with the large relatively heavy windows.

Remember any plausible passenger service implied demonstrated loss rates well under 2%, which on the flipside means you can waste ~50 launches in inefficiencies before an optimised version makes any sense at all.
(exact number varies depending on refurbishments, and that 50 may be 1000)

Offline Dave G

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #988 on: 01/14/2018 03:38 AM »
A simple outer-moldline version of the 'passenger' variant with no windows pretty much meets all near-term needs.
That's the Cargo version (see first image below).  SpaceX plans to fly 2 of these to Mars in 2022.

If you've managed to do enough cycles on this variant that passenger transport looks viable, you can fit small windows with a hacksaw using the very comprehensive stress and thermal data you got from this.
Assuming this is possible, that would be modification of the outer skin and/or tank configuration, which is how I defined the 4 different BFS versions.

Remember any plausible passenger service implied demonstrated loss rates well under 2%...
I'm sure there are people who would be willing to take greater risks than this to get to Mars.  In the 1800's, the pioneers that settled the Western U.S. faced higher risks than this.

Cargo is only needed if there is a near-term market for large satellites.
For networks that use smaller satellites, they generally use a lot more of them, so that would use the Satellite delivery (a.k.a. clam shell) BFS version (see 2nd image below)


« Last Edit: 01/14/2018 03:50 AM by Dave G »

Online speedevil

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #989 on: 01/14/2018 03:45 AM »
Cargo is only needed if there is a near-term market for large satellites.
For networks that use smaller satellites, they generally use a lot more of them (see 2nd image below)

Which can all fit just fine out of a standard 'passenger' door.

Offline Dave G

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #990 on: 01/14/2018 04:01 AM »
Cargo is only needed if there is a near-term market for large satellites.
For networks that use smaller satellites, they generally use a lot more of them (see 2nd image below)

Which can all fit just fine out of a standard 'passenger' door.

Not sure about that.  Deploying satellites that way would be much more complicated, it it's possible at all.

Also, 'passenger' door implies windows, which aren't needed on the BFS Satellite delevery version.

Online speedevil

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #991 on: 01/14/2018 07:34 AM »
Cargo is only needed if there is a near-term market for large satellites.
For networks that use smaller satellites, they generally use a lot more of them (see 2nd image below)

Which can all fit just fine out of a standard 'passenger' door.


Quote
Not sure about that.  Deploying satellites that way would be much more complicated, it it's possible at all.

Also, 'passenger' door implies windows, which aren't needed on the BFS Satellite delevery version.

Passenger door implies windows if you believe the fully fledged passenger version shown is the only one that may be built.

Are you seriously arguing that it is actually impossible to move things out of a door?

Especially when it doesn't much matter if it fails to deploy as long as it doesn't jam the door?
« Last Edit: 01/14/2018 09:41 AM by speedevil »

Offline john smith 19

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #992 on: 01/14/2018 11:18 AM »

Remember any plausible passenger service implied demonstrated loss rates well under 2%...
I'm sure there are people who would be willing to take greater risks than this to get to Mars.  In the 1800's, the pioneers that settled the Western U.S. faced higher risks than this.
Getting to Mars is one level of risk. That would be the people buying Conestoga wagons and/or forming wagon trains to go West.

A passenger service needs to be much safer. I'm not sure any aviation authority would allow a service with a 2% loss rate anywhere in the world. Obviously everyone is expecting a fully reusable system will establish a strong safety track record in a way ELV's don't and can't. The question is how strong? What level of safety can such a system demonstrate?
What generation of passenger airlines does that compare with as a loss rate? 1930s? 1940s?50s?60s?

Here's some data to put this in perspective.
https://www.statista.com/statistics/602675/global-jet-hull-lossaccident-rate-commercial-aviation/

https://thepointsguy.com/2015/02/how-safe-is-air-travel-the-statistical-truth/

In 2016 worst case was 2.16 hull loses / million flights or 0.000216%. The 2nd site mentioned puts it this way

2014 had 30 million commercial flights with 21 fatal accidents. Roughly a 1 in 1 430 000 chance of dying on a flight.

The chances that a first generation system, flying mass passengers in a never before used architecture will achieve equal safety numbers is practically zero, and the chances it will improve on those is basically delusional.

Musk is wrong. Those tickets will carry a disclaimer that says "You may die taking this trip."
« Last Edit: 01/14/2018 11:37 AM by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Dave G

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #993 on: 01/14/2018 11:59 AM »
Passenger door implies windows if you believe the fully fledged passenger version shown is the only one that may be built.
Passenger door sort of implies there are passengers on the ship, or at least that the ship is passenger capable.  For a cargo vehicle, it would be called a cargo door.  That was my point.  As I said, I believe there will be 4 BFS versions, starting with cargo.

Are you seriously arguing that it is actually impossible to move things out of a door?
Few things are impossible, given enough time and money.  The problem is the extra complexity of the satellite deployment system, i.e. how the small satellites would need to move around within the payload bay, and the higher cost and risk of failure associated with that.  The incident with Zuma emphasized the importance of a reliable payload adapter. That's my opinion anyway. Your mileage may vary.

Especially when it doesn't much matter if it fails to deploy as long as it doesn't jam the door?
Why would it not matter?  Satellites are expensive.

By the way, kudos to lamontagne, who posted the image below over on the Starlink thread.

Offline meekGee

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #994 on: 01/14/2018 12:14 PM »

Remember any plausible passenger service implied demonstrated loss rates well under 2%...
I'm sure there are people who would be willing to take greater risks than this to get to Mars.  In the 1800's, the pioneers that settled the Western U.S. faced higher risks than this.
Getting to Mars is one level of risk. That would be the people buying Conestoga wagons and/or forming wagon trains to go West.

A passenger service needs to be much safer. I'm not sure any aviation authority would allow a service with a 2% loss rate anywhere in the world. Obviously everyone is expecting a fully reusable system will establish a strong safety track record in a way ELV's don't and can't. The question is how strong? What level of safety can such a system demonstrate?
What generation of passenger airlines does that compare with as a loss rate? 1930s? 1940s?50s?60s?

Here's some data to put this in perspective.
https://www.statista.com/statistics/602675/global-jet-hull-lossaccident-rate-commercial-aviation/

https://thepointsguy.com/2015/02/how-safe-is-air-travel-the-statistical-truth/

In 2016 worst case was 2.16 hull loses / million flights or 0.000216%. The 2nd site mentioned puts it this way

2014 had 30 million commercial flights with 21 fatal accidents. Roughly a 1 in 1 430 000 chance of dying on a flight.

The chances that a first generation system, flying mass passengers in a never before used architecture will achieve equal safety numbers is practically zero, and the chances it will improve on those is basically delusional.

Musk is wrong. Those tickets will carry a disclaimer that says "You may die taking this trip."
I would say the public would accept a failure every 10 years, irrespective of launch volume.
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Offline Dave G

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #995 on: 01/14/2018 01:20 PM »
I would say the public would accept a failure every 10 years, irrespective of launch volume.
That's a good way to look at it.  I like it.

One small nit.  If it starts as a small number of private paying customers, it wouldn't matter if the general public approved or not.  That only comes into play if the mission is government funded, or when it gets to be high volume.

I'll also point out that that there's a certain segment of the population that's drawn to higher risk. The thrill of risking your life for something you consider meaningful, that's part of the attraction.

« Last Edit: 01/14/2018 01:22 PM by Dave G »

Offline meekGee

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #996 on: 01/14/2018 02:47 PM »
I would say the public would accept a failure every 10 years, irrespective of launch volume.
That's a good way to look at it.  I like it.

One small nit.  If it starts as a small number of private paying customers, it wouldn't matter if the general public approved or not.  That only comes into play if the mission is government funded, or when it gets to be high volume.

I'll also point out that that there's a certain segment of the population that's drawn to higher risk. The thrill of risking your life for something you consider meaningful, that's part of the attraction.
Of course.  0.1/yr is a statistical measure that's hard to apply during the first years.

There might be failures during development, and the usual suspects will run around crying "it's failed 3 times out of 100 even if the last 97 were successes..."

And some of the first 100 flights will be as you say intrinsicly high risk missions.

You also have to define "failure". When an airplane loses an engine and diverts, it is not considered a failure.  A water landing - sure, but nothing like an all-hands-lost crash.  A cargo plane crash generate a lot less angst than a passenger flight, even if both use the same plane.

The same spectrum will apply to frequent rocket service.
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Offline Negan

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #997 on: 01/14/2018 03:26 PM »
Cargo is only needed if there is a near-term market for large satellites.
For networks that use smaller satellites, they generally use a lot more of them (see 2nd image below)

Which can all fit just fine out of a standard 'passenger' door.

Not sure about that.  Deploying satellites that way would be much more complicated, it it's possible at all.

I don't see it being any harder than deploying equipment remotely on Mars which the first cargo ships are expected to do.

Offline ppb

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #998 on: 01/14/2018 05:09 PM »
Passenger door implies windows if you believe the fully fledged passenger version shown is the only one that may be built.
Passenger door sort of implies there are passengers on the ship, or at least that the ship is passenger capable.  For a cargo vehicle, it would be called a cargo door.  That was my point.  As I said, I believe there will be 4 BFS versions, starting with cargo.

Are you seriously arguing that it is actually impossible to move things out of a door?
Few things are impossible, given enough time and money.  The problem is the extra complexity of the satellite deployment system, i.e. how the small satellites would need to move around within the payload bay, and the higher cost and risk of failure associated with that.  The incident with Zuma emphasized the importance of a reliable payload adapter. That's my opinion anyway. Your mileage may vary.

Especially when it doesn't much matter if it fails to deploy as long as it doesn't jam the door?
Why would it not matter?  Satellites are expensive.

By the way, kudos to lamontagne, who posted the image below over on the Starlink thread.
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Offline Negan

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #999 on: 01/14/2018 05:22 PM »
Especially when it doesn't much matter if it fails to deploy as long as it doesn't jam the door?
Why would it not matter?  Satellites are expensive.

Because you can just bring the satellite back, fix the problem, and try again.

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