Author Topic: MCT Speculation and Discussion Thread 4  (Read 503120 times)

Online philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #80 on: 06/16/2015 08:44 PM »
If the MCT is completely refueled on Mars for launch back to earth, all of the fuel will not be needed to get the TEI burn.  There will be quite a bit of fuel left.  So the MCT could fire and slow down before earth reentry, or it could slow down using aerocapture for a few orbits to slow down.  Also, there will probably be only a crew return, not 100 people.

Crew?
Why?
MCT should be able to return to Earth empty.  (And as needed provide occasional return transport for humans needing to return)

On the way out assuming several 10s of passengers it would be astounding if there were not several engineers capable of specialized training as "flight engineers" to repair anything repairable by humans.  No astronaut corps test pilots needed, just FEs similar to on the shuttle.

Crew mass & life support is wasted mass and money.

     You may be correct aboutthe need for a crew, but people are still a bit primitive.  They'd be more than a bit nervous to trust their lives to nothing more than machines.  I'm pretty sure that they'd want at least a minimal crew orf pilot, navigator/copilot and at least one engineer.  (A dedicated doctor/medic would also likely be a good idea).  If nothing else, to keep the passengers calm during the flight.

     While machines are pretty good at doing their jobs, nobody will want to risk a several billion dollar investment on the possibility that a IC chip will fry because of a stray cosmic ray and send the craft wandering off into space or worse, come c rashing down on Earth at 6 to 7 KMS.

Huh?  I said that trained Flight Engineer passengers would be aboard. They are better at fixing the IC chip problem than pilots and/or setting a new heading.  Pilots, co-pilots and navigators are not needed.  Engineers can easily learn nav functions, not that they'd ever need to perform them. Realize that these flights will occur in a decade when driverless trucks & autos are commonplace.  It's not the 1960s in space.

Good point about the MD.  I should have also mentioned that out of the 50 or 100 passengers there should be one doctor passenger or at least EMT/nurse.  I would expect the colony to want such medical folks as well as engineers so that requirement should not be a problem.  STEM folk by necessity will comprise the majority of colonists.
« Last Edit: 06/16/2015 08:50 PM by philw1776 »
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Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #81 on: 06/16/2015 09:09 PM »
A single MCT won't be billions of dollars of investment or the $500k per passenger figure will be impossible. An order of magnitude less like $100-400 million. Also, electronics can easily be made reliable enough. We have lots an lots of experience running spacecraft for years at a time without maintenance. 6-9 months won't be a challenge for a company that will launch thousands of satellites into LEO.
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Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #82 on: 06/16/2015 09:52 PM »
At the end of they day, F9R and FHR will be doing the vast bulk of the sat launches.

Surely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)

[I would think the customers would end up forcing the decision. In much the same way that few were interested in F1 when they could fly as a secondary payload on F9 for half the price.]

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #83 on: 06/16/2015 10:30 PM »
At the end of they day, F9R and FHR will be doing the vast bulk of the sat launches.

Surely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)

[I would think the customers would end up forcing the decision. In much the same way that few were interested in F1 when they could fly as a secondary payload on F9 for half the price.]

Only SpaceX knows their long term plans for sure, obviously.  But I can't imagine they have any plans of retiring FH or F9 once MCT starts flying.  For several reasons.
When you have a hammer, everything looks like a nail.  But not everything is a nail.

They're investing a lot of money into the F9/FH infrastructure.  And they'll want to get an ROI on that.  All the tooling and production for Falcon already exists so all you save by shutting down Hawthorne is the overhead there.

And I think it's just a matter of the right tool for the job.  Most commercial comsats will be able to fly on F9R v1.2.  The F9US is cheap.  That'll be a cheap launch.  It's hard to imagine them launching a big Saturn V size (or larger) LV for such a comsat, even if it's fully reusable. 

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #84 on: 06/17/2015 01:07 AM »


That brutal 12-14 kms entry to Earth is something everyone who is talking about this direct Earth return is glossing over, that is beyond Apollo speeds, the only thing that can survive that kind of heat, dynamic pressure and g-force is a dense capsule with thick heavy ablatives.

This is why it is not valid to design spacecraft by only looking at Delta-V and tank sizes and imagining that a giant 2nd stage can do the job of direct Earth return from Mars surface just because it can hold the propellents to launch to Earth.  It would literally be crushed like an empty beer can against ones forehead when it hits the Earth's atmosphere.

A 2nd stage that can return from Earth orbit is a vastly simpler thing to do because the speed is half (and the energy is a quarter), and it is fairly easy to slow down the 2nd stage by several kms with residual propellents, and to employ disposable things like parachutes because it only needs to perform ONE landing before servicing rather then two, and lastly it can be made much less reliable in landing because it's unmanned, no one dies horribly if it crashes or burns up on reentry unlike MCT.

The thing is....this is all a moot point to your argument.  Whether MCT is it's own 2nd stage to LEO or it sits atop a dedicated unique 2nd stage won't change the fact that MCT will need to have -large- tanks.  It will be mostly propellant tank by volume just to do the TMI burn and Mars EDL retropropulsion....and to get itself off the surface of Mars, even if it were only going to LMO before getting refueled there rather than all the way back in one shot.
It will be mostly a large propellant tank, with some legs, engines, and some cargo or hab internal volume.

Having MCT be it's own 2nd stage rather than having a separate dedicated 2nd stage won't change that.  MCT can't then become just a simple larger Dragon capsule. 
With a dedicated reusable 2nd stage, then it's just a giant 3rd stage, rather than a giant 2nd stage.  Maybe a little smaller.  Not much else changes.  So it's a bit of a moot argument.

Yes, designing a vehicle that is returning just form LEO is vastly more simple than designing one that's coming back from interplanetary speeds.  You are correct.  But, there's not an either/or option.  SpaceX must figure out how to get a large rocket stage back from Mars and land it on Earth.  They already need to solve that long pole issue.  A vehicle they design to handle that, can already return to Earth from LEO easily enough, without the [easy] development of a separate LEO only vehicle even necessary.

Ok beer can metaphor was not a good one because folks are interpreting it as implying that tanks would not have ANY internal pressure.  That's not what I was trying to imply, pressurizing the tank to give it more rigidity is always a good idea and would only require a modest amount of gas to be reserved for that purpose.

But I'm doubtful that their can be enough internal pressure in the tank to allow it to withstand the dynamic pressure of reentry, which is intense.  The formula is 1/2 * Ballistic coefficient * velocity ^2, thus a direct interplanetary Earth reentry is on the order of x10 higher pressure then an Entry from Mars orbit.


And please stop repeating that big-tank are the ONLY way, I have shown you several times how the vehicle can designed with much smaller tanks, your not a fan of these options but it is dishonest to begin your argument with your preferred solution as the only option, it is simply begging the question.

First off you can go to LMO and then dock with a transit vehicle like Mars Semi-Direct, no one here can claim that they are unfamiliar with Semi-Direct.  Second, inflatable tanks in the cargo-hold, even rigid tanks in the cargo hold if you think inflatables are to low TRL.

Offline TomH

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Re: MCT Speculation and Discussion Thread 4
« Reply #85 on: 06/17/2015 01:32 AM »
Surely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)

....I can't imagine they have any plans of retiring FH or F9 once MCT starts flying.  For several reasons.
When you have a hammer, everything looks like a nail.  But not everything is a nail.  it's...a matter of the right tool for the job...It's hard to imagine them launching a big Saturn V size (or larger) LV for such a comsat, even if it's fully reusable.

Agreed. Semi trucks haul mail cross country because that's the most cost efficient truck for that task. Jeep sized vehicles deliver to local mailboxes because that is the most cost efficient vehicle for that task. You don't use a maul when driving a finish nail. You use a finish nail hammer. Vice versa when demolishing a wall. You use the right tool for the job, and there is no single tool that does every job.

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #86 on: 06/17/2015 02:11 AM »
Surely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)
[...] Semi trucks haul mail cross country because that's the most cost efficient truck for that task. Jeep sized vehicles deliver to local mailboxes because that is the most cost efficient vehicle for that task. You don't use a maul when driving a finish nail. You use a finish nail hammer. Vice versa when demolishing a wall. You use the right tool for the job, and there is no single tool that does every job.

That seems to be what SpaceX thought with Falcon 1 and Falcon 9. But the F9 quickly ate the F1's market, so they cancelled it to save money.

I can't imagine a client wanting to use a semi-expendable rocket when a cheaper secondary/tertiary payload slot is available on a fully reusable HLV. People seem hung up over the size, all that matters is the price.

(Those semis will often carry many small packages because the per-item cost is lower than carrying them individually in a smaller vehicle.)

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #87 on: 06/17/2015 03:42 AM »

I can't imagine a client wanting to use a semi-expendable rocket when a cheaper secondary/tertiary payload slot is available on a fully reusable HLV. People seem hung up over the size, all that matters is the price.

(Those semis will often carry many small packages because the per-item cost is lower than carrying them individually in a smaller vehicle.)

People seem to be trying to compare BFR cost to launch satellites with other existing or near term launchers (Ariane 5, SLS, F9 etc etc).  But that is not what my argument is about, it is about which VISION FOR BFR is cheaper to launch satellites with.  Musk's goal is not to slightly undercut existing launchers, it is to create massive paradigm-shifting reductions in $ to LEO, even if BFR launch blows every other launch vehicle out of the water it still needs to compete with variants of itself.

I'm arguing that BFR with mostly normal reusable 2nd stage is better at launching satellites then BFR with the giant MCT combo 2nd stage.  These latter will cost LESS because a 2nd stage even reusable is a much simpler and lower mass vehicle then the whole MCT which has MUCH more demanding requirements on lifespan, reentry heat, lifespan etc etc. 

The first stage is identical and presumably all other logical and launch related costs are too, so the only difference is in the 2nd stages, one which is conventional with a voluminous payload fairing which is light and designed for optimal mass delivery to orbit, the other is a huge heavy vehicle totally over engineered for this job and has a small cargo hold. 

Their is no contest the normal 2nd stage will out perform the giant vehicle to any orbit, just as an EELV booster outperformed the shuttle at launching satellites.  And the normal 2nd stage is going to be vastly cheaper to develop as well, the only argument that anyone has left is that because Elon absolutely MUST have his Mars oriented vehicle he will choose to shoehorn it into every possible usage even for things it is not optimized for so as to amortize the cost over as many flights as possible.  I don't recall that strategy working well for Shuttle. 

Musk is blessed with inordinate patience, he could have blown his money on a stunt ages ago but has always focused on building a viable BUSINESS first and foremost.  In pursuit of greater revenue he is now getting into the satellite business.  He doesn't leave any potential revenue source on the table.  Se Musk is not going to pass on designing the best conventional satellite launcher simply because he also wants to use the vehicle for Mars adventures, he knows that it must be a viable vehicle in it's own right.
« Last Edit: 06/17/2015 03:51 AM by Impaler »

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #88 on: 06/17/2015 03:59 AM »
EDIT: moved to MCT thread, where it's more appropriate
500 m^3 is a reasonable cargo-hold but their would be no integral habitat as many have speculated, it makes much mores sense to load a large module into the cargo-hold which can be removed and left on the Mars surface to minimize the return mass.  This also has the advantage of eliminating separate crew and cargo variants.

It is also extremely inefficient in structural mass. MCT is all about efficiency in structural mass.

The most mass efficient thing is to NOT make it integral to the MCT.  The time when structural mass efficiently maters most is take off, and if we indent to me offloading people and not taking them back to Earth then all that habitat mass would be pure dead-weight on take off.
A single MCT won't be billions of dollars of investment or the $500k per passenger figure will be impossible. An order of magnitude less like $100-400 million. Also, electronics can easily be made reliable enough. We have lots an lots of experience running spacecraft for years at a time without maintenance. 6-9 months won't be a challenge for a company that will launch thousands of satellites into LEO.
Of course, transit time is just ~3 months, not 8, so that's a big difference right there. Additionally, they likely did not sleep in shifts like you would on MCT colonization runs.
MCT is a radical design. Acknowledge that and move on.

Okay, this meme has reached an extreme.  We need to do some scoping.

Do you guys think we could separate, semantically:

A) A Gemini/Apollo-grade opposition-class mission to Mars.  Flags, footprints, a 1-4 weeks EVAs, and imported propellant.  At the end of this, we should have the technology for landing on Mars and returning to Earth at best-case unimproved sites.  May end up doing weak ISRU, but only with pre-landed hardware.  Population of 1's of people.

B) The sensible conjunction-class mission to Mars.  ~18 months on the surface, capable of weak ISRU return, experimenting with strong ISRU.  At the end of this, we should have the technology for landing on Mars and returning in a robust manner, pioneered experimentally at a range of unimproved sites.  Population of 10's of people.

C) The next step after that, a larger crew charged with maximizing geological exploration and innovating construction & ISRU techniques;  At the end of this, we should have the technology for landing on Mars and returning iteratively improved, and standardized at unprepared sites with 'strong' (hydrogen-harvesting) ISRU.  We should be able to mine ice, and bury habitats.  We should be able to reuse as much of the mission hardware as possible.  Population of 100's of people.

D) The next step after that, a mission charged with delivering and building Antarctica-grade accommodations for permanent scientific bases;  At the end of this, we should have the technology for landing on Mars and returning streamlined and improved with a ground-based ISRU system and ground-based habitats, as well as experimental agriculture, and should be able to deploy the first synod-round inhabited Mars bases, with people serving spaced tours of duty.  An ISRU station on Phobos/Deimos begins to become feasible to assist in providing return propellant at this point.  Population of 1000's of people.

E) The next step after that, a mission charged with delivering people to a permanent scientific base and building out industrial capacity, fleshing out most of the mass balance remaining between the station and self-sufficiency;  At the end of this, we should have the capacity to send people to Mars for permanent habitation at multiple sites, with only a modest, steady number of supply vessels per year.  Landing and takeoff should be routinized at Mars-side spaceports, and brought down to affordable levels with use of Aldrin cycler habitats and steerage-grade rendezvous capsules.  With this load it starts to make sense to begin to build small NTRs for crew capsule transfers.  Population of 10,000's of people.

F) Bootstrapping self-sufficiency and economic productivity with a population of 100,000's of people.  Domestic production of necessities.  Ability to sustain internal supplychain independently until the durable goods wear out.

G) Some exports, able to support unrestricted internal population growth, and sufficient industry to serve as a backup for human society, 1,000,000's of people.

Now: NASA's traditional approach is to try and cost out a series of missions that go beyond A (after carefully examining it for merit), and deep into B, with 4-6 people.  Right now their official line is 'we can do B on the current budget in 2037... maybe?' while their unofficial belief seems to be 'all we can show without doubling or tripling the HSF budget is increasingly advanced Powerpoints and progressively delayed 20-years-off launch times'. 

Musk appears to want, for SpaceX's first mission, to go straight through and complete all of B and straight through into C, with hardware that might still be useful for the first part of D.  This is an extremely ambitious, many would say non-credible plan.  It would certainly require NASA to increase its HSF budget by a factor of 10, and maybe more than that, for them to accomplish this;  Musk has been wildly successful with Falcon relative to what NASA expected its development costs to be, however, so we're unwilling to say he can't do it for only what NASA would pay him, a few billion a year, to outsource its HSF development (by leapfrogging their tech readiness until Congress breaks down and cancels the current path).

Now, Musk made comments about how far he eventually wanted to go with SpaceX's Mars program, and what it should cost and he said:
Quote
Musk’s $500,000 ticket price for a Mars trip was derived from what he thinks is affordable.

"The ticket price needs to be low enough that most people in advanced countries, in their mid-forties or something like that, could put together enough money to make the trip," he said, comparing the purchase to buying a house in California. [Photos: The First Space Tourists]

He also estimated that of the eight billion humans that will be living on Earth by the time the colony is possible, perhaps one in 100,000 would be prepared to go. That equates to potentially 80,000 migrants.

Musk figures the colony program — which he wants to be a collaboration between government and private enterprise — would end up costing about $36 billion. He arrived at that number by estimating that a colony that costs 0.25 percent or 0.5 percent of a nation’s gross domestic product (GDP) would be considered acceptable.

The United States' GDP in 2010 was $14.5 trillion; 0.25 percent of $14.5 trillion is $36 billion. If all 80,000 colonists paid $500,000 per seat for their Mars trip, $40 billion would be raised.

"Some money has to be spent on establishing a base on Mars. It’s about getting the basic fundamentals in place," Musk said. "That was true of the English colonies [in the Americas]; it took a significant expense to get things started. But once there are regular Mars flights, you can get the cost down to half a million dollars for someone to move to Mars. Then I think there are enough people who would buy that to have it be a reasonable business case."

He was, to my eye, pretty clearly talking about phases E, F, and G, and not on a design basis.  He has no mission plan for those phases, but $500k is what he thinks is required to achieve G on a private basis simply because there aren't enough people in the world with more than $500k to spend if G is available, to support those numbers of passengers.

To *get* from where we are in 2015, to phases E, F, and G, there's going to need to be vehicles that come first, vehicles that accomplish the earlier phases of a Mars program.  Vehicles that ride a 10-20m BFR in the 2020's-2030's.  I ask again that you find a way to distinguish between the earlier vehicles, and the later vehicles, because they will have wildly different technological capabilities and requirements.  Saying "But SpaceX is magic and MCT is an ambitious project!" only gets you so far - it doesn't get you to $500k/passenger, 3 month transits, and, for that matter, giant domed cities filled with one-way-ticket passengers.  I'm ready to extend an order of magnitude of credulity given Musk's track record, but there's too many orders of magnitude of progress there, relative to where we are now: It's portraying a future where we're 1,000 to 10,000 times more efficient at this than we are currently.  If Musk does eventually get there, he's certainly not going to start there from day 1.

So: We're talking about different vehicles and mission paradigms, some that come earlier and some that come later. "MCT" is no longer sufficient if you want to talk about the latter.  What do you guys want to call them?
« Last Edit: 06/17/2015 04:02 AM by Burninate »

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #89 on: 06/17/2015 04:41 AM »
You're now inventing some new whole bunch of vehicles from whole cloth? Not interested. We have very little to go on for the Mars Colonial Transporter, but that's what we have to go on for this thread, not inventing something new. There are other threads for what SpaceX might do before MCT.
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Offline Krevsin

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Re: MCT Speculation and Discussion Thread 4
« Reply #90 on: 06/17/2015 05:41 AM »

I can't imagine a client wanting to use a semi-expendable rocket when a cheaper secondary/tertiary payload slot is available on a fully reusable HLV. People seem hung up over the size, all that matters is the price.

(Those semis will often carry many small packages because the per-item cost is lower than carrying them individually in a smaller vehicle.)

People seem to be trying to compare BFR cost to launch satellites with other existing or near term launchers (Ariane 5, SLS, F9 etc etc).  But that is not what my argument is about, it is about which VISION FOR BFR is cheaper to launch satellites with.  Musk's goal is not to slightly undercut existing launchers, it is to create massive paradigm-shifting reductions in $ to LEO, even if BFR launch blows every other launch vehicle out of the water it still needs to compete with variants of itself.

I'm arguing that BFR with mostly normal reusable 2nd stage is better at launching satellites then BFR with the giant MCT combo 2nd stage.  These latter will cost LESS because a 2nd stage even reusable is a much simpler and lower mass vehicle then the whole MCT which has MUCH more demanding requirements on lifespan, reentry heat, lifespan etc etc. 

The first stage is identical and presumably all other logical and launch related costs are too, so the only difference is in the 2nd stages, one which is conventional with a voluminous payload fairing which is light and designed for optimal mass delivery to orbit, the other is a huge heavy vehicle totally over engineered for this job and has a small cargo hold. 

Their is no contest the normal 2nd stage will out perform the giant vehicle to any orbit, just as an EELV booster outperformed the shuttle at launching satellites.  And the normal 2nd stage is going to be vastly cheaper to develop as well, the only argument that anyone has left is that because Elon absolutely MUST have his Mars oriented vehicle he will choose to shoehorn it into every possible usage even for things it is not optimized for so as to amortize the cost over as many flights as possible.  I don't recall that strategy working well for Shuttle. 

Musk is blessed with inordinate patience, he could have blown his money on a stunt ages ago but has always focused on building a viable BUSINESS first and foremost.  In pursuit of greater revenue he is now getting into the satellite business.  He doesn't leave any potential revenue source on the table.  Se Musk is not going to pass on designing the best conventional satellite launcher simply because he also wants to use the vehicle for Mars adventures, he knows that it must be a viable vehicle in it's own right.
Again, while SpaceX is comprised of brilliant engineers and has an insane(ly dedicated) leader, it isn't made entirely out of money, nor does it have infinite time. Making and improving on the MCT will take up a lot of their money and time (in fact I'm pretty sure all of it) which they won't be able to spend on reusable BFR upper stage design.

Unless the MCT simply refers to a specific combination of a BFR reusable upper stage and payload which I think is an entirely viable option.

So they'll either use a modified MCT design for their comsat launch operations, or they will maintain their F9R and FHR lines.

Funnily enough, with a depot in space, the Falcon 9 and Falcon Heavy can go fully reusable without even needing a tug.

Comparing the shuttle to the MCT is not a valid comparison (yet) because the shuttle never really optimized for cost and because we do not know the specifics of the MCT outside its target preformance and cost figures (both of which are supremely vague and general) while having perfect retrospective view on both of those figures for the STS.

Offline fast

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Re: MCT Speculation and Discussion Thread 4
« Reply #91 on: 06/17/2015 01:48 PM »
And back to design concepts, it is the most fun  :)

What if BFR and MCT will be the essentially same thing?
Kind of universal module sized similar to S-IC, 9 Raptors at the bottom, with lending legs, around 1900mt.
 
Than all thing will be three core (I know, Elon said one-core, but look at F5), MCT in the center will have less fuel load replaced by cargo bay and improved thermal protection, and probably have less than 9 Raptors(3?).

Just a thought to standardize and reduce cost...

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #92 on: 06/17/2015 04:12 PM »

And please stop repeating that big-tank are the ONLY way, I have shown you several times how the vehicle can designed with much smaller tanks, your not a fan of these options but it is dishonest to begin your argument with your preferred solution as the only option, it is simply begging the question.

First off you can go to LMO and then dock with a transit vehicle like Mars Semi-Direct, no one here can claim that they are unfamiliar with Semi-Direct.  Second, inflatable tanks in the cargo-hold, even rigid tanks in the cargo hold if you think inflatables are to low TRL.

I -did- say your concept might be smaller.  But you seemed to be implying that by putting MCT on top of a dedicated 2nd stage, then it won't be a flying gas tank any more.  It'll be just a giant Dragon or something, and you'll avoid the issues of getting a large fuel tank through EDL.
That's incorrect.   You may have smaller tanks, but they'll still be large in relation to the overall vehicle. 
It's not what I am or am not a fan of, but what must be at a minimum.  MCT must be a single stage to Mars orbit vehicle at a minimum.  And thus, it will still be a big gas can that must get through EDL, whether it does direct return or not...whether it's it's own 2nd stage on Earth ascent or not.

:-)
 

Offline oldAtlas_Eguy

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Re: MCT Speculation and Discussion Thread 4
« Reply #93 on: 06/17/2015 04:19 PM »
The key item that will stabilize the designs of the BFR and MCT is the Raptor. Once a Raptor test article exists then design values with low technical risks for bell size, engine weight, thrust, and ISP will exist along with an low risk model for manufacturing costs for a production Raptor based on the test article. Once SpaceX has that the 1st stage can be designed with low technical risk (low variation of its actual production version capabilities). With a 1st stage then the US or MCT designs can be done because the diameter and capabilities of the 1st stage are a known in a tradeoff engineering model.

So until that first test article enters testing on a test stand SpaceX itself only will have engineering goals for the system and few actual specifications: diameters, GLOW, payload weights, etc.

Our excursion into BFR/MCT design is only a fleshing out of the design scope (architectures and capabilities) and issues with design, development and operations of such a vehicle will be a help to SpaceX but in the end it will be a SpaceX design to meet their goals of cost (development, manufacture, operations[reuse number of times]) and capability (size, destinations, in-space operations [single vs multi launch to reach destination], reentry, landing, and reuse).

We may only have to wait 2 years for that Raptor test article to reach the test stand. Until then all we can do is highly speculate as to what SpaceX will do.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #94 on: 06/17/2015 04:29 PM »
And back to design concepts, it is the most fun  :)

What if BFR and MCT will be the essentially same thing?
Kind of universal module sized similar to S-IC, 9 Raptors at the bottom, with lending legs, around 1900mt.
 
Than all thing will be three core (I know, Elon said one-core, but look at F5), MCT in the center will have less fuel load replaced by cargo bay and improved thermal protection, and probably have less than 9 Raptors(3?).

Just a thought to standardize and reduce cost...

Setting aside Elon's actual words aside for a moment about it being single core, the 2-piece concept myself and a few others have been debating about would do what you are doing, but with just two pieces rather than 3.  One big monolithic RTLS booster, and one combo upperstage/spacecraft that can get itself to LEO where it will be refueled prior to going to Mars. 

If there were to be 3 pieces, then probably the concept Impaler has been advocating would be better, with a dedicated reusable 2nd stage between the booster and MCT/Spacecraft.  Then you essentially have a big dumb 2-stage LV that can be used a little more readily for other purposes than putting MCT in LEO.

Additionally, such a tri-core concept would have what engines on the central core/MCT?  Sea level Raptors as they'd be igniting at sea level.  Or vacuum Raptors as they'll be going to LEO and doing in-space burns?  Or would it launch without the central core lighting, like Titan III/IV?  And ignite the central core after booster sep?  I think that'd probably be the best way to approach such a concept, then you can have your vacuum Raptors on it. 
But then, each core would be narrower than a monolithic, and if MCT were core diameter, it'd be narrower too.  I think it'd be better for MCT to be as wide as feasible to help make it shorter and more stable when landing on the MArs surface.  Such a tri-core MCT would mean a pretty tall and skinny MCT.  Might look like the F9R booster when landing.  ;-)




Offline Sohl

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Re: MCT Speculation and Discussion Thread 4
« Reply #95 on: 06/17/2015 05:35 PM »
Try crushing a beer can containing several bars of pressure against your forehead.

Sheesh!  There's easier ways to enjoy a beer! :P

;)

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #96 on: 06/17/2015 05:50 PM »
And back to design concepts, it is the most fun  :)

What if BFR and MCT will be the essentially same thing?
Kind of universal module sized similar to S-IC, 9 Raptors at the bottom, with lending legs, around 1900mt.
 
Than all thing will be three core (I know, Elon said one-core, but look at F5), MCT in the center will have less fuel load replaced by cargo bay and improved thermal protection, and probably have less than 9 Raptors(3?).

Just a thought to standardize and reduce cost...

Setting aside Elon's actual words aside for a moment about it being single core, the 2-piece concept myself and a few others have been debating about would do what you are doing, but with just two pieces rather than 3.  One big monolithic RTLS booster, and one combo upperstage/spacecraft that can get itself to LEO where it will be refueled prior to going to Mars. 

Actually this looks to me like the first innovative new idea for a while.

Elon Musk said single core. But the idea behind that was to my understanding, not a 3 core heavy configuration because the central core would go too fast for easy RTLS and would incur heavy payload loos for reuse. This concept avoids that problem.

This concept would be like a first stage in two parts, something completely different. The "central core" would be the MCT. The vac engine problem might be solvable with a retractable engine bell extension. The mechanism shown in that Falcon Heavy animation seems to allow fast efficient reconnection so should not be a major problem for simple operation.

Two side cores with 9 engines each plus a central core with 5? engines would give a total number of engines 23 for lift off. Most of them would be switched off as soon as the T/W ratio allows it to retain fuel for reaching orbit.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #97 on: 06/17/2015 06:08 PM »
And back to design concepts, it is the most fun  :)

What if BFR and MCT will be the essentially same thing?
Kind of universal module sized similar to S-IC, 9 Raptors at the bottom, with lending legs, around 1900mt.
 
Than all thing will be three core (I know, Elon said one-core, but look at F5), MCT in the center will have less fuel load replaced by cargo bay and improved thermal protection, and probably have less than 9 Raptors(3?).

Just a thought to standardize and reduce cost...

Setting aside Elon's actual words aside for a moment about it being single core, the 2-piece concept myself and a few others have been debating about would do what you are doing, but with just two pieces rather than 3.  One big monolithic RTLS booster, and one combo upperstage/spacecraft that can get itself to LEO where it will be refueled prior to going to Mars. 

Actually this looks to me like the first innovative new idea for a while.

Elon Musk said single core. But the idea behind that was to my understanding, not a 3 core heavy configuration because the central core would go too fast for easy RTLS and would incur heavy payload loos for reuse. This concept avoids that problem.

This concept would be like a first stage in two parts, something completely different. The "central core" would be the MCT. The vac engine problem might be solvable with a retractable engine bell extension. The mechanism shown in that Falcon Heavy animation seems to allow fast efficient reconnection so should not be a major problem for simple operation.

Two side cores with 9 engines each plus a central core with 5? engines would give a total number of engines 23 for lift off. Most of them would be switched off as soon as the T/W ratio allows it to retain fuel for reaching orbit.

It is innovative (good job fast).  And it could work for the reason you say.  It eliminates the central core that's staging too fast.  There's also be a booster core for the intermediate size LV that's been discussed over on the SFR thread.

But, I just don't know that it has advantages over an in-line wider core?  Do you see where this would be an advantage?  Maybe if they weren't planning to build the cores near the launch facility, this concept would result in thinner cores that are more easily transported.  But that's really not a problem unless SpaceX changes from what they've stated.

And it'd result in a tall and skinny MCT.  That's probably the major issue with it vs. monolithic, that I see.



Offline oldAtlas_Eguy

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Re: MCT Speculation and Discussion Thread 4
« Reply #98 on: 06/17/2015 06:27 PM »
Here goes. After calculating from chemical rockets only the weights needed to get cargo to mars surface and for a Human visit mission the following was the result. ISP of Vacuum Raptor 385. All tankers return to Earth. They need ~8mt of prop to do the return.

Cargo Mission:
1) 100mt payload at Mars surface
2) 140mt MCT dry weight at Mars surface (payload + vehicle)
-> 1.2km/s
3) 200mt wet weight at Deimos arrival
-> 3km/s
4) 440mt wet weight leaving L2 (300mt of propellant)
->13.3km/s
5) The cargo direct from Earth surface (140mt) + 3 tanker flights to L2 (delivering 100mt prop each)

Human Mission
1) 140mt Earth return MCT on Earth surface
->3.7km/s
2) 375mt Earth return MCT at departure from Deimos
3) 120mt dry weight at Deimos
->6km/s
4) 600mt wet weight at Mars surface fueled with 480mt of propellant from ISRU
5) 140mt dry weight landing
->1.2km/s
6) Mars SSTO 200mt wet weight arrival at Deimos
7) Earth return MCT 375mt wet weight at Deimos arrival
->3km/s
8 ) 1180mt MCT pair wet weight departure from L2
->13.3km/s
9) Direct from Earth 140mt Mars SSTO MCT, 140mt Earth Return MCT, 9 MCT Tankers to L2

Edit: added the Delta V values used in the calculations.
« Last Edit: 06/17/2015 06:45 PM by oldAtlas_Eguy »

Offline JasonAW3

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Re: MCT Speculation and Discussion Thread 4
« Reply #99 on: 06/17/2015 06:32 PM »
A single MCT won't be billions of dollars of investment or the $500k per passenger figure will be impossible. An order of magnitude less like $100-400 million. Also, electronics can easily be made reliable enough. We have lots an lots of experience running spacecraft for years at a time without maintenance. 6-9 months won't be a challenge for a company that will launch thousands of satellites into LEO.

As these craft are supposed to effectively be the DC-3s of space, acting as both cargo and passenger carriers, Billions would be possible.  After all, airliners cost tens of millions of dollars and most airline tickets are less than $400.
My God!  It's full of universes!

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