Author Topic: MCT Speculation and Discussion Thread 4  (Read 502975 times)

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2240 on: 06/11/2016 09:16 PM »
As large as its likely to be, and with baked in habitation, could a BFS be considered a lunar "base" if left in place? Guessing it depends on ease of egress/ingress, crew rotation landers and power generation, but still.
If Tiangong can be considered a space station, then sure, why the heck not?
I doubt the hab will be baked in, which probably helps. Thermal control during the month long day/night cycle is an issue though.
According to Musk, it will be.

We know that return payload is 25 tonnes. If the hab were integrated into the BFS (and it is still counted as payload) then it is likely yo be too heavy to be returned. But if it isn't returned then how can crew return.

Return from Mars is a strong constraint on the architecture, there are lots of potential architectures that can "land the whole thing" with 100 tonnes of payload, but very few that can return 25 tonnes within one synod. About the only one I can see working is a modular habitat of 25 tonnes (wet fully provisioned), able to carry 25 crew, which may be left on Mars or returned within 1-4 BFS.

Offline docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #2241 on: 06/11/2016 09:25 PM »
We know that return payload is 25 tonnes. If the hab were integrated into the BFS (and it is still counted as payload) then it is likely yo be too heavy to be returned. But if it isn't returned then how can crew return.

Return from Mars is a strong constraint on the architecture, there are lots of potential architectures that can "land the whole thing" with 100 tonnes of payload, but very few that can return 25 tonnes within one synod. About the only one I can see working is a modular habitat of 25 tonnes (wet fully provisioned), able to carry 25 crew, which may be left on Mars or returned within 1-4 BFS.

If we go back to the Max Fagin presentation only a fraction of the BFS returns to Earth, leaving (for lack of a better term) a large logistics module on Mars and the ERV much lighter. Fagin shows an "über-Dragon" style configuration with integrated sidewall engines (tiltable?) If these are only enough get it to LMO (easier on the ISRU needs) a pre-positioned depot could provide the deltaV home. The interstage between "über-Dragon" and the logistics module protects the formers heat shield inbound. 
« Last Edit: 06/11/2016 09:44 PM by docmordrid »
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Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2242 on: 06/11/2016 09:44 PM »
We know that return payload is 25 tonnes. If the hab were integrated into the BFS (and it is still counted as payload) then it is likely yo be too heavy to be returned. But if it isn't returned then how can crew return.

Return from Mars is a strong constraint on the architecture, there are lots of potential architectures that can "land the whole thing" with 100 tonnes of payload, but very few that can return 25 tonnes within one synod. About the only one I can see working is a modular habitat of 25 tonnes (wet fully provisioned), able to carry 25 crew, which may be left on Mars or returned within 1-4 BFS.

If we go back to the Max Fagin presentation only a fraction of the BFS returns to Earth, leaving (for lack of a better term) a large logistics module on Mars. Fagin shows an "über-Dragon" style configuration with integrated sidewall engines. If these are only enough get it to LMO (easier on the ISRU needs) a pre-positioned depot could provide the deltaV home. The interstage between "über-Dragon" and the logistics module protects the formers heat shield inbound.

It is very unlikely that the Max Fagin presentation is the MCT architecture, he would have been prevented by non-disclosure agreement from using SpaceX IPR.

Offline docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #2243 on: 06/11/2016 09:45 PM »
IP protections don't cover obviousness. See rocket landings on barges. See here for another split vehicle config,

http://forum.nasaspaceflight.com/index.php?topic=33224.0

« Last Edit: 06/11/2016 09:50 PM by docmordrid »
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Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2244 on: 06/11/2016 10:20 PM »
IP protections don't cover obviousness. See rocket landings on barges. See here for another split vehicle config,

I'm not talking about patents, I'm talking about trade secrets. It might be obvious, but there are several other "obvious" ways of doing the MCT. Saying which of these "obvious" ways SpaceX has chosen is a trade secret and would be covered under the non-disclosure terms of standard contracts of employment

Offline docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #2245 on: 06/11/2016 11:12 PM »
In most jurisdictions a trade secret is 'not generally known or reasonably ascertainable by others.' We also don't know if his slide was approved or not under an NDA. They do seem to like leaving bread crumbs. Keeps the chatter level up.
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2246 on: 06/11/2016 11:40 PM »
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2247 on: 06/11/2016 11:54 PM »
We know that return payload is 25 tonnes. If the hab were integrated into the BFS (and it is still counted as payload) then it is likely yo be too heavy to be returned. But if it isn't returned then how can crew return.

Return from Mars is a strong constraint on the architecture, there are lots of potential architectures that can "land the whole thing" with 100 tonnes of payload, but very few that can return 25 tonnes within one synod. About the only one I can see working is a modular habitat of 25 tonnes (wet fully provisioned), able to carry 25 crew, which may be left on Mars or returned within 1-4 BFS.

If we go back to the Max Fagin presentation only a fraction of the BFS returns to Earth, leaving (for lack of a better term) a large logistics module on Mars. Fagin shows an "über-Dragon" style configuration with integrated sidewall engines. If these are only enough get it to LMO (easier on the ISRU needs) a pre-positioned depot could provide the deltaV home. The interstage between "über-Dragon" and the logistics module protects the formers heat shield inbound.

It is very unlikely that the Max Fagin presentation is the MCT architecture, he would have been prevented by non-disclosure agreement from using SpaceX IPR.

I agree with Mike, no integrated Hab, rather 4 Hab modules 25 mt a piece placed inside BFS, 3 are left behind on Mars, 1 is returned.  This minimizes return mass and maximizes useful buildup of infrastructure on Mars.

It also makes moving the habs much easier then the Fagin single-massive block concept which dose not look to be intended for movement at all.  Modular habs allow a single common BFS to handle cargo and crew and for crew to return on a different BFS then they arrive in just exchanging habs, this means a faulty BFS doesn't strand the crew on Mars and allows all cargo delivery BFS landings to act ac backups for the crew.

The BFS shape I see is one with the cargo hold at the bottom, Propellant above and engines on the size in 2 pairs with only a slight canting of the engines similar to Dragon capsule.

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2248 on: 06/12/2016 12:25 AM »

Pretty much what I think the the BFS/MCT will be, with a few minor changes:
1. larger (longer) cargo hold.
2. slightly better mass fractions (but maybe not on the first MCT).
3. slightly less delta-v required to reach orbit, difference from your figures gives margin.

I'm OK with all that.
I expect to receive some shocks in September
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Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2249 on: 06/12/2016 12:37 AM »
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

2 good observations.

First, the tanks.  You're on target.  What I did was simply compute volume and weight of cylinders to estimate the mass of the rocket, etc.  I do NOT mean that the propellant tank is really18m for example,  My bad. There is a big O2 tank and a separate methane tank.  They have rounded ends in reality, making them longer.  A 15m wide rocket does not really have a 15m wide tank.  Again the simplification is used to estimate mass, thrust, etc. and not length of rocket which however I believe will still be squat under 100m.  Engines, interstage, whatever.  I needed to add prose to be clear on that.

Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.

« Last Edit: 06/12/2016 12:39 AM by philw1776 »
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Offline Bob Shaw

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Re: MCT Speculation and Discussion Thread 4
« Reply #2250 on: 06/12/2016 12:54 AM »
In line with the philosophy of reuse mfck articulated...

I could see the MCT being "partially strippable"... if you had cabins for 100, but are only returning 20 people why carry all of that back? if the fittings, panels, wiring, plumbing etc was designed to be modular and reusable it could be removed by humans and used in outfitting the base.

Or just stacked up outside under Mylar sheets, ready for use sometime soon. Every last screw and panel should be recovered - nothing should return to Earth which has a value on Mars!

Offline Bob Shaw

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Re: MCT Speculation and Discussion Thread 4
« Reply #2251 on: 06/12/2016 12:59 AM »
Remember Mars has a atmosphere and has water cycles (water vapor and water ice, does not have liquid phase). So to mine all the water you need, you compress the air and liquefy the water vapor in the atmosphere. Admittedly you would have to compress a lot of atmosphere for a little bit of water but the advantage is you do not have to go out and dig it up! Once the quantities needed become very high then comes the mining of water. But for the initial methalox manufacture for the return trip this method would be an easy one to implement and would not require complex equipment just plenty of power. Compressing gas takes a great deal of energy. But you need the atmosphere compressed for other parts of the methalox manufacture as well.

Not really possible to get water by compression. Water vapour is about 0.03%, so for every kg of water you would need to compress and liquefy 3 tonnes of water <air>.
Compression requires much too much work.  It should be fairly simple to use dessicants to dry out the air, then extract the water by heating the dessicant.  This is one of the most common technologies today to dry compressed air or indoor ice rinks (and was part of the original Mars direct proposal).  alternatively you can compress a refrigerant, and use that to create a cold surface on which the water in the air will condense out.  Any of these solutions will require a minimum of about 1000 btu/lb or 2300 kJ/kg of water, the phase change energy of water.

Basically, you need an energy gradient to extract work - in this case, 'work' equates to water. Some energy can be stored, but the beauty of energy is that it can also be *transformed*.

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2252 on: 06/12/2016 03:13 AM »
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

2 good observations.

First, the tanks.  You're on target.  What I did was simply compute volume and weight of cylinders to estimate the mass of the rocket, etc.  I do NOT mean that the propellant tank is really18m for example,  My bad. There is a big O2 tank and a separate methane tank.  They have rounded ends in reality, making them longer.  A 15m wide rocket does not really have a 15m wide tank.  Again the simplification is used to estimate mass, thrust, etc. and not length of rocket which however I believe will still be squat under 100m.  Engines, interstage, whatever.  I needed to add prose to be clear on that.

Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.
Your dry mass is too high.
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Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2253 on: 06/12/2016 05:19 AM »
Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.

When I did similar calculations (what seems like an age ago) I got 7 - 9 refuelling flights.

I think that brute force is the method they will choose, at least initially.

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2254 on: 06/12/2016 01:00 PM »
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

2 good observations.

First, the tanks.  You're on target.  What I did was simply compute volume and weight of cylinders to estimate the mass of the rocket, etc.  I do NOT mean that the propellant tank is really18m for example,  My bad. There is a big O2 tank and a separate methane tank.  They have rounded ends in reality, making them longer.  A 15m wide rocket does not really have a 15m wide tank.  Again the simplification is used to estimate mass, thrust, etc. and not length of rocket which however I believe will still be squat under 100m.  Engines, interstage, whatever.  I needed to add prose to be clear on that.

Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.
Your dry mass is too high.

4.5% for 1st stage may be high.  I'm in the camp of those who say minimum 6 legs.  I hope it's high, but I think the BFR has to be more robust, read heavier, if it really is a quick turn around, only very minor refurbishment vehicle.  I think today's F9 has unresolved issues there.

As to the BFS, with all the exotica of engines placed high for Mars landing & takeoff, cargo arrangement complications and robust TPS that lasts many re-entries at interplanetary velocities, I don't buy the dry mass under 100mT thinking for such a complex, lightly serviced vehicle.
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Offline Mark S

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Re: MCT Speculation and Discussion Thread 4
« Reply #2255 on: 06/12/2016 02:48 PM »
a few more teasers before the september reveal:

https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/

1 red dragon in 2018, 'at least 2' in 2020, then first flight of MCT in 2022...
Bold mine.

From the article:

Quote
Then in 2022, Musk said he hoped to launch what the company now sometimes refers to as the Mars Colonial Transporter, designed to bring a colony to Mars.

I'm sorry, but this is nuts  somewhat optimistic. You all realize that 2022 is only six years away, right? Regardless of the fact that Dragon v2 hasn't flown yet, and regardless of the fact that FH hasn't flown yet; NOTHING concrete about BFR/MCT has even been released, and Musk is talking about launching one in six years. Six. Years.

Six years to get BFR off the ground, literally. To build a factory on the scale of Michoud (only bigger) for fabrication and assembly of BFR and MCT. To build a huge HIF to handle the 12.5m or 15m cores, or heck even to lease one of the VAB high bays and get it fitted out for BFR. To build all of the ground support infrastructure and ground transportation. To get the entire Raptor engine (not just components) off of the drawing board and into the test stands and validated.

Heck, you guys are still arguing over where the thing will be built and launched from. Do you think that would really be the case if they were going to be rolling off the assembly line in less than six years?

I like SpaceX and they are doing amazing things. But come on. Please apply a little common sense when these kinds of pronouncements are made. Two days after the article was published and three pages on in this thread, I would expect to see some kind of discussion about how that would even be possible.

Cheers!

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2256 on: 06/12/2016 03:40 PM »
So basically you're saying that Musk is deliberately lying about his plan date then since none of these activities you cite have happened yet.  I do not believe this to be so.
I am extremely skeptical about the 2022 etc. dates but I believe that Musk has a plan, a plan that requires everything meets aggressive dates and goes right, but a plan that if this miracle happened would be feasible.

I think humans land on Mars in 2033.  2029 best case.
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Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2257 on: 06/12/2016 04:25 PM »
We don't know the development status of MCT. It could be anywhere from a few powerpoints which seem to hang together as an architecture, to having passed PDR (or the SpaceX equivalent) several months ago. About the only thing known in public is that the Raptor has had component level tests which have gone quite well.

It is now 8 months since Chris Bergin made that tweet https://forum.nasaspaceflight.com/index.php?topic=38593.0 and things will have moved on a lot since then. Chris has shared some of the information that he received in L2, I cannot say what that is, but just given the fact that things were far enough advanced for Chris to be shown data means that they were far enough advanced for the basic factory and launch site specs to be determined (not the detailed ones, but such things as floor area, overhead crane height, access requirements, thrust levels and landing pad requirements). These are enough to start looking for a factory and launch site, and if they have been at it for 8 months SpaceX probably have a pretty good idea about the possibilities.

Offline the_other_Doug

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Re: MCT Speculation and Discussion Thread 4
« Reply #2258 on: 06/12/2016 05:39 PM »
We don't know the development status of MCT. It could be anywhere from a few powerpoints which seem to hang together as an architecture, to having passed PDR (or the SpaceX equivalent) several months ago. About the only thing known in public is that the Raptor has had component level tests which have gone quite well.

It is now 8 months since Chris Bergin made that tweet https://forum.nasaspaceflight.com/index.php?topic=38593.0 and things will have moved on a lot since then. Chris has shared some of the information that he received in L2, I cannot say what that is, but just given the fact that things were far enough advanced for Chris to be shown data means that they were far enough advanced for the basic factory and launch site specs to be determined (not the detailed ones, but such things as floor area, overhead crane height, access requirements, thrust levels and landing pad requirements). These are enough to start looking for a factory and launch site, and if they have been at it for 8 months SpaceX probably have a pretty good idea about the possibilities.

And to tie it together to other "signs and indicators," for those who have been following the "Where will BFR launch from?" thread, if you look at SpaceX planning on building and launching BFRs in six years, the only place where they are currently beginning construction on new facilities is Boca Chica.

If y'all are saying that SpaceX needs to be building the BFR factory and launch facilities right now, well -- maybe they are.
-Doug  (With my shield, not yet upon it)

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Re: MCT Speculation and Discussion Thread 4
« Reply #2259 on: 06/12/2016 05:58 PM »
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

2 good observations.

First, the tanks.  You're on target.  What I did was simply compute volume and weight of cylinders to estimate the mass of the rocket, etc.  I do NOT mean that the propellant tank is really18m for example,  My bad. There is a big O2 tank and a separate methane tank.  They have rounded ends in reality, making them longer.  A 15m wide rocket does not really have a 15m wide tank.  Again the simplification is used to estimate mass, thrust, etc. and not length of rocket which however I believe will still be squat under 100m.  Engines, interstage, whatever.  I needed to add prose to be clear on that.

Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.
Your dry mass is too high.

4.5% for 1st stage may be high.  I'm in the camp of those who say minimum 6 legs.  I hope it's high, but I think the BFR has to be more robust, read heavier, if it really is a quick turn around, only very minor refurbishment vehicle.  I think today's F9 has unresolved issues there.

As to the BFS, with all the exotica of engines placed high for Mars landing & takeoff, cargo arrangement complications and robust TPS that lasts many re-entries at interplanetary velocities, I don't buy the dry mass under 100mT thinking for such a complex, lightly serviced vehicle.
And so you have 14 refuelings. That's not going to happen. That is definitely not what SpaceX is planning. Your dry masses are too high.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

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