Author Topic: MCT Speculation and Discussion Thread 4  (Read 610614 times)

Online MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2260 on: 06/12/2016 06:04 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.

In my opinion Boca Chica is not suitable for the MCT manufacturing site. Other places in the Brownsville area maybe. That we have not seen an environmental impact statement is perhaps an indication that SpaceX have found a site that does not need one (existing large factory or facility?) or that they think an environmental impact statement will be a formality (contaminated land, brownfield site?).

If Musk thinks 2024 MCT is possible, then he must see a way forward, but I have no clue about what that path is.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2261 on: 06/12/2016 06:05 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.
Yeah, that's certainly a possibility. Boca Chica isn't perfect for daily launches, but for the first decade or two, when the launch rate is more modest, it could certainly function as the first BFR launch site. SpaceX seems to not have a problem with multiple launch sites nor with solutions that only are going to work for a few years or a decade or so.

And SpaceX knows how to make big structures quickly and cheaply. Look at the HIF at LC-39A. I'm not worried about the buildings.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2262 on: 06/12/2016 06:06 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.

In my opinion Boca Chica is not suitable for the MCT manufacturing site. Other places in the Brownsville area maybe. That we have not seen an environmental impact statement is perhaps an indication that SpaceX have found a site that does not need one (existing large factory or facility?) or that they think an environmental impact statement will be a formality (contaminated land, brownfield site?).

If Musk thinks 2024 MCT is possible, then he must see a way forward, but I have no clue about what that path is.
Boca Chica doesn't have to be the manufacturing site, it just has to be nearby so that transporting a large structure isn't too hard.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline the_other_Doug

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Re: MCT Speculation and Discussion Thread 4
« Reply #2263 on: 06/12/2016 06:28 PM »
Also, the "local manufacturing site" is likely going to be at least partially an assembly site.  They likely won't want to truck BFR stages around -- too large -- but I bet the engines and whatever serves as an octaweb (the thrust and plumbing structures) could still be made at one primary site, like Hawthorne, and shipped out to the tank manufacture/stage assembly sites.

It's not like there would be no manufacturing happening near the BFR launch sites, but the only things that, it would seem, are required to be built near the launch site are the tanks/stage structures.  A lot of pieces will be sub-assemblies that are manufactured elsewhere and shipped to the BFR sites in by conventional means...
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Online MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2264 on: 06/12/2016 06:44 PM »
Also, the "local manufacturing site" is likely going to be at least partially an assembly site.  They likely won't want to truck BFR stages around -- too large -- but I bet the engines and whatever serves as an octaweb (the thrust and plumbing structures) could still be made at one primary site, like Hawthorne, and shipped out to the tank manufacture/stage assembly sites.

It's not like there would be no manufacturing happening near the BFR launch sites, but the only things that, it would seem, are required to be built near the launch site are the tanks/stage structures.  A lot of pieces will be sub-assemblies that are manufactured elsewhere and shipped to the BFR sites in by conventional means...

Possibly, but Hawthorne will be at or near capacity with F9/FH, as reusability reduces the need for first stages, an increased flight rate would increase second stage production*. It is much easier to build on a greenfield site than trying to cram production for completely different (and bigger elements). That said the avionics is probably going to be similar so could be produced at Hawthorne with little difficulty.

[*] in future a reusable raptor based second stage might reduce Hawthorne production requirements, but probably not until the early 2020's.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2265 on: 06/12/2016 07:44 PM »
Also, the "local manufacturing site" is likely going to be at least partially an assembly site.  They likely won't want to truck BFR stages around -- too large -- but I bet the engines and whatever serves as an octaweb (the thrust and plumbing structures) could still be made at one primary site, like Hawthorne, and shipped out to the tank manufacture/stage assembly sites.

It's not like there would be no manufacturing happening near the BFR launch sites, but the only things that, it would seem, are required to be built near the launch site are the tanks/stage structures.  A lot of pieces will be sub-assemblies that are manufactured elsewhere and shipped to the BFR sites in by conventional means...

Possibly, but Hawthorne will be at or near capacity with F9/FH, as reusability reduces the need for first stages, an increased flight rate would increase second stage production*. It is much easier to build on a greenfield site than trying to cram production for completely different (and bigger elements). That said the avionics is probably going to be similar so could be produced at Hawthorne with little difficulty.

[*] in future a reusable raptor based second stage might reduce Hawthorne production requirements, but probably not until the early 2020's.
...could happen in late 2010s, too. I've suspected they'd start with a Raptor upper stage before MCT. I'm unsure if they will or not, but it's certainly a possibility, since a Raptor upper stage for Falcon 9 and Heavy is mentioned in the USAF contract for Raptor.
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Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2266 on: 06/12/2016 07:59 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.

I don't get 14 refuelings as there is excess capacity in the Km/sec budget which as I responded above to another poster translates into propellant to LEO.
The dry mass listed for the BFS is for the Mars transport vehicle.  I assume a lesser dry mass for the stripped down tanker to LEO version.  I ran the numbers again and get 6-7 tanker trips which I agree is too many for a cost effective campaign.  SX will do better.
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Offline Mark S

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Re: MCT Speculation and Discussion Thread 4
« Reply #2267 on: 06/12/2016 08:15 PM »
If y'all are saying that SpaceX needs to be building the BFR factory and launch facilities right now, well -- maybe they are.

Yes, I am saying that SpaceX would have to be building the production facilities and launch site right now, and much much more. I don't think there is any evidence of that, and it would all be much too large to keep secret. The factory will have to have a welding tool that is twice the diameter of the vertical welding facility for SLS, and probably much taller. The launch site will have to be qualified for launching a vehicle with twice the thrust of the Saturn-V. The transporter/tilt-up gantry will have to be the length of a football field. The MCT itself will dwarf anything launched to space except for ISS, how could it possibly be far enough along (in total secrecy) to be ready to launch in six years?

I'm not saying all of this is impossible. I'm saying that I do think it would be impossible for it all to be ready for launch in six years, with no one hearing a peep of any such activity already under way.

I would love to be proven wrong, though. :)

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2268 on: 06/12/2016 10:18 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.

I don't get 14 refuelings as there is excess capacity in the Km/sec budget which as I responded above to another poster translates into propellant to LEO.
The dry mass listed for the BFS is for the Mars transport vehicle.  I assume a lesser dry mass for the stripped down tanker to LEO version.  I ran the numbers again and get 6-7 tanker trips which I agree is too many for a cost effective campaign.  SX will do better.

Can I get the numbers for your Tanker dry mass and the expected propellant delivery per trip, I don't see how it can get the BFS vehicle full in the 7 trips your proposing as it would need to offload ~200 mt per flight.  Between landing propellant reserves and the dry mass of something that is basically just a 2nd stage I don't think you have that much propellant offload capacity, 10 flights seems more reasonable.

All that said I agree even 6-7 refueling flights is not viable, and no amount of Dry mass shaving on RB's part is going to make it work.  This is why I belive the only viable architecture is a SEP tug based system in which propellant is pre-placed into high Earth orbit and Mars orbit.  The BFS is radically smaller and goes from LEO to EML-2, refuels, goes to Mars, refuels, launches to LMO, refuels and then returns to Earth, all the DeltaV legs are ~4 km/s and allow fast transit times and only requires a vehicle carry around 300 mt of propellant.


Offline matthewkantar

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Re: MCT Speculation and Discussion Thread 4
« Reply #2269 on: 06/12/2016 10:41 PM »
Yes, I am saying that SpaceX would have to be building the production facilities and launch site right now, and much much more. I don't think there is any evidence of that, and it would all be much too large to keep secret. The factory will have to have a welding tool that is twice the diameter of the vertical welding facility for SLS, and probably much taller. The launch site will have to be qualified for launching a vehicle with twice the thrust of the Saturn-V. The transporter/tilt-up gantry will have to be the length of a football field. The MCT itself will dwarf anything launched to space except for ISS, how could it possibly be far enough along (in total secrecy) to be ready to launch in six years?

I'm not saying all of this is impossible. I'm saying that I do think it would be impossible for it all to be ready for launch in six years, with no one hearing a peep of any such activity already under way.

I would love to be proven wrong, though. :)

The Saturn V was designed and launched in five years or so, with all of its launch infrastructure. The money for it was off the charts, but computing power, rocketry, and manufacturing have come a long way since the 1960s. 2024 is 8 years away. It an audacious plan, but who know what resources Mr Musk might be able to tap push this thing forward.

Matthew


Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2270 on: 06/12/2016 11:11 PM »
Any attempt to throw 'computing power' and 'manufacturing' into the same improvement over time comparison is insane and shreds your credibility, the differences are astronomical.  Concrete cures at the same speed now as it did in 1950, if anything launch pads and related construction is slower now.

Offline matthewkantar

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Re: MCT Speculation and Discussion Thread 4
« Reply #2271 on: 06/12/2016 11:59 PM »
Any attempt to throw 'computing power' and 'manufacturing' into the same improvement over time comparison is insane and shreds your credibility, the differences are astronomical.  Concrete cures at the same speed now as it did in 1950, if anything launch pads and related construction is slower now.

Easy there. I made no attempt equate those improvements, the commas are there to number them into a list. I am fairly sure the speed at which concrete dries will not determine the schedule. Are you sure you want to describe me as an 'insane?' Hyperbole like that is more unhinged than anything I wrote.

Matthew

Online Lar

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Re: MCT Speculation and Discussion Thread 4
« Reply #2272 on: 06/13/2016 12:01 AM »
Civil engineering hasn't got a lot faster (from when you break ground, because concrete doesn't cure any faster), but design times can be far less, since you have less empirical and grinding manual calculation, and more simulation. So the pad construction, even if a bit faster, certainly is a long lead time item. 

That said ...The closer you get to compute-ish things, the faster cycles are getting...  circuit board designs for new phones certainly are a lot faster than they were. Look up how long the first Princess phone was in development, perhaps. Then think about how many features it had. Not even a built in calculator, much less the ability to shoot cat videos. Then think about the cycle time to go from the Galaxy S5 to S6...

So I expect that if the resources and will are there, MCT is **barely** doable to have a first launch in 2022. If you claim it's impossible, you're wrong, it's not impossible. (show your work if you disagree!!). If you claim it's improbable, you're probably right.

The Musk way is to set crazy impossible deadlines that rely on everything going perfectly perfect, and expect people to do their best to deliver.  I'll be delighted if MCT only slips one synod...
« Last Edit: 06/13/2016 12:06 AM by Lar »
"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

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2273 on: 06/13/2016 01:46 AM »

Can I get the numbers for your Tanker dry mass and the expected propellant delivery per trip, I don't see how it can get the BFS vehicle full in the 7 trips your proposing as it would need to offload ~200 mt per flight.  Between landing propellant reserves and the dry mass of something that is basically just a 2nd stage I don't think you have that much propellant offload capacity, 10 flights seems more reasonable.

All that said I agree even 6-7 refueling flights is not viable, and no amount of Dry mass shaving on RB's part is going to make it work.  This is why I belive the only viable architecture is a SEP tug based system in which propellant is pre-placed into high Earth orbit and Mars orbit.  The BFS is radically smaller and goes from LEO to EML-2, refuels, goes to Mars, refuels, launches to LMO, refuels and then returns to Earth, all the DeltaV legs are ~4 km/s and allow fast transit times and only requires a vehicle carry around 300 mt of propellant.

Yes, you may...

VLEO   8.7   
V  needed by S2 for LEO only   6300   V=VLEO-DeltaV Stage1
TOTAL Mass to LEO   300   m1=m0/(EXP(V/Ve)
BFS Propellant excess mT   75   
Tanker Mass Saving   25   
Tanker Propellant to LEO   200   
# of Tanker Flights for Mars   6.9   

Translation to English...
Excess delta V meant excess propellant to LEO; I had reserved landing propellent in spreadsheet
Tanker dry mass at 100mT, a savings of 25mT
~7 refueling flights needed
« Last Edit: 06/13/2016 01:48 AM by philw1776 »
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2274 on: 06/13/2016 04:59 AM »
Your only allowing 900 m/s for all drag and gravity losses which looks to be too low by around 300 m/s as I can't find any vehicle with total losses of less then around 1200 m/s.  That would drop your mass in LEO by about 25 mt and put the flight total at an even 8 which is roughly meeting in the middle of our earlier estimates.  Alternatively stretching your vehicle will likely make up the difference.

I'm willing to accept 8 as the best estimate for refueling flights needed to perform this all-chemical brute-force mission architecture when performing a fast crew transfer.  Do you have an estimate for what could be sent on a slow cargo flight?

P.S.  Oops, 300 m/s is what you get from Earth rotation so looks good.
« Last Edit: 06/13/2016 07:21 AM by Impaler »

Offline raketa

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Re: MCT Speculation and Discussion Thread 4
« Reply #2275 on: 06/13/2016 05:24 AM »
-Raptor engine I think is going to production very soon. They work  on it for 6 years.
-BFR is probably ready for building, I am just curious what design changes return stages give them:
 they will use heat shield for BRF
or during atmosphere heating  keeping slightly under power , to shield engine compartment?
-I am almost sure, that first crew to Mars will not have rocket ready with fuel for return trip, but Spacex guarantee them every 2 years, provide provision and supply for finishing ISRU and start return to Earth business.
I think we are not ready to have robotic facility to finish it without human presence and ability to fix, modify and adjust plan and build the plant.
-ISRU will have energy  enormous requirement, will solar be enough to provided?
-They will also need lot heat just to keep habs temperature up, without radioisotope thermoelectric generator at least as backup energy source, will be not wise in my opinion.

Offline raketa

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Re: MCT Speculation and Discussion Thread 4
« Reply #2276 on: 06/13/2016 05:37 AM »
I think they choosed diameter 15 meters because:
-MCT will have same diameter to have better characteristic during braking in Mars atmosphere, will be similar to shape of  Dragon 2 and have interesting lifting attributes, maybe even side engine for landing maneuvers, Raptor thrust will be not necessary.
-BFR will have better characteristic during braking in Mars atmosphere and safe more fuel for landing
-whole rocket will be under 100m height.

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Re: MCT Speculation and Discussion Thread 4
« Reply #2277 on: 06/13/2016 05:53 AM »
So I expect that if the resources and will are there, MCT is **barely** doable to have a first launch in 2022. If you claim it's impossible, you're wrong, it's not impossible. (show your work if you disagree!!). If you claim it's improbable, you're probably right.
It is good to discuss the optimal, albeit improbable, case. We can trust Elon that he has a timeline in his mind. I am more troubled with the payload for this launch. Developing surface systems is not considered trivial. Neither mining operaations. Especially troubled if robotic fuel production for MCT return is assumed before the first crewed lauch in '24. You need to understand soil properties at the chosen location to design mining and oxigen extraction. The '18 Dragon lander is said to be only a landing test. Then the Dragons launched in '20 have to study the soil and to do mining and O2 extraction experiments. Then, you have a little more than a single year to develop the equipment. Maybe, the '18 lander should be more than a landing experiment. Maybe, it will include drilling and analysis of the samples. (Some of you say that it  would be impossible to develop such payload for '18.) Then, the '20 landers can validate the mining/extraction methods developed on an informed basis. Maybe, the '20 landers include sample return...

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #2278 on: 06/13/2016 07:33 AM »
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!

To be honest?  "What could you possibly do in six years" is kind of ridiculous.  Many of the largest megaprojects of industrial humanity have been done on this sort of timescale.  In modern politics, a leader announcing a megaproject that won't be completed (or worse, have construction spending even ramp up) within his term has become an antipattern that costs us inordinately;  The successor predictably cancels it so they can announce their own, or never mentions it again.  "We'll do this by $time+20years" means very nearly nothing at all.  If you think that kind of timespan is genuinely required, it's usually a sign that you're not being a audacious enough to get anything whatsoever done - you don't want to commit the resources, don't care about the end goal, and aim to cruise on some political impetus gained by the initial announcement, which was essentially a lie.

I don't completely see the point of a privately run for-profit enterprise racing to Mars,  but I see even less point in them aiming to do so *slowly*.

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2279 on: 06/13/2016 11:27 AM »
Your only allowing 900 m/s for all drag and gravity losses which looks to be too low by around 300 m/s as I can't find any vehicle with total losses of less then around 1200 m/s.  That would drop your mass in LEO by about 25 mt and put the flight total at an even 8 which is roughly meeting in the middle of our earlier estimates.  Alternatively stretching your vehicle will likely make up the difference.

I'm willing to accept 8 as the best estimate for refueling flights needed to perform this all-chemical brute-force mission architecture when performing a fast crew transfer.  Do you have an estimate for what could be sent on a slow cargo flight?

P.S.  Oops, 300 m/s is what you get from Earth rotation so looks good.

No cargo estimate but as you can probably infer I made the 2nd stage ~ 7Km/sec capable so trading off Km/sec for payload & using trajectory browser you can get increased cargo for transit.  However it means a few tonnes more propellant in the Mars landing burn. 

Thanks for the informed critiques, people.
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

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