Author Topic: MCT Speculation and Discussion Thread 3  (Read 348210 times)

Offline llanitedave

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Re: MCT Speculation and Discussion Thread 3
« Reply #240 on: 04/18/2015 12:17 am »
But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.

Ehm, you know airplanes, right? They transport hundreds of people without a rescue systems. When they fail, everyone on board dies. It just happens rarely enough for the society to accept the risk.

How old are you? If you're over 25 you should be aware that crashes were MUCH more common even 20 years ago than today and MUCH higher before that. Society "accepted" it (but complained a lot anyway) because air travel was fast and relatively "safe" and people were more concerned with "time" than safety.
(The math did show that you were more likely to die in a car crash than a plane crash but cars rarely carried over 70 passengers so "individually" the odds were on your side :) )

Rockets are inherently more dangerous than aircraft. They are put under more stress and perform across a much greater envelope than any aircraft and it is NOT that hard to design in sufficient safety to mitigate almost all the dangers involved so why NOT do so?

Wow. Not hard? What planet are you from... This has to be one of the most stunning proclamations I have read on this forum. There will always be mass penalties and engineering compromises. Making the Shuttle as safe as you seem to want it would have crippled it.

Accept the risk and move on. You yourself wrote "Rockets are inherently more dangerous than aircraft", so more risks will be expected and accepted. If this bothers you, others will gladly take your place in line.

Here's the ultimate safe vehicle for you: One that doesn't go anywhere.


If SpaceX loses an MCT or BFR full of paying customers, they will face a bigger risk of bankruptcy than the passengers themselves risked prior to buying tickets.  It's in SpaceX's interest to make those craft as safe as possible.
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Offline Lars-J

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Re: MCT Speculation and Discussion Thread 3
« Reply #241 on: 04/18/2015 12:25 am »
Here's the ultimate safe vehicle for you: One that doesn't go anywhere.

If SpaceX loses an MCT or BFR full of paying customers, they will face a bigger risk of bankruptcy than the passengers themselves risked prior to buying tickets.  It's in SpaceX's interest to make those craft as safe as possible.

Only up to a point. The same applies to the manufacturer of any vehicle, or owner of any fleet.

If you don't think you are rolling the dice every time you cross the street, drive/ride in car, sit on a train, fly in an aircraft, then you are kidding yourself.

Again, if you want complete safety, don't fly at all. Problem solved.

Offline spacenut

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Re: MCT Speculation and Discussion Thread 3
« Reply #242 on: 04/18/2015 12:41 am »
If they are going to Mars, they probably will make them sign a waiver.  It was their decision.  They knew the dangers. 

On the other side, launch failures are rare these days.  Even the shuttle with all it's dangers only lost two out of over 100+ launches.  Soyuz percentage is about the same. 

Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #243 on: 04/18/2015 12:58 am »
Impaler.  Good comments.  A few additional ones in response.

These integrated 2nd stage concepts have some unavoidable problems.

*  No possible abort during launch, the propellent mass is simply too high for the large vehicle to have any appreciable acceleration away from an exploding 1st stage.  For our early missions when crews are just a handful of explorers it's easy enough to put them on F9 to rendezvous with the MCT that launches un-manned.  But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.


The MCT going to MArs would launch first, and be uncrewed.  Several subsecquent launches would come up bringing propellant and other provisions.  Lastly would come up the crew and probably the LH2 feedstock for making the methalox on the surface.
So the Mars-MCT doesn't need an LAS system.  The other LEO-MCT could have one, as it could withstand the mass penalty of it.  It would just then take more launches to get the adequate propellant, provisions, and crew to the Mars-MCT prior to departure. 

However, we need to really ask ourselves, what would the LAS on the LEO-MCT need to be?  If the 2nd stage -is- the Spacecraft, then really the only "abort" scenario is if the booster is failing during the first 2-2.5 minutes of ascent.  Once staging has occured and the upper stage lit, there's really no abort option.  If it blows up, there's a LOC.  If there's some other issue, it can actually divert to an alternate landing area and come back down and land before reaching orbit.

If the MCT spacecraft where to have landing thrusters like Dragon, the LEO-MCT could be built with enough of them to do an emergency separation from the booster and much the spacecraft away from the booster.

So you really need to look at what and how you are aborting.  MCT landing engines should be able to do an emergency separation in any condition but a catestrophic booster explostion....and those would be pretty rare.  If you feel you need to be able to abort during a full booster explostion, more landing thrusters could be added, or a large tractor down, or something else.  Again, that wouldn't be needed for the Mars MCT as that would launch unmanned.
And as you say, earlier flights where the system doesn't have a lot of flights under it's belt, they may launch the crews on Dragon.  I can't imagine early Mars missions would have more than like 14 people anyway.  Two Dragons can do that. 


* Highly unstable landing on Mars, with is extreme height your in great danger of toppling over.  Even if cargo hold is in the bottom as Lobo's sketch indicates the tanks above are going to have residual propellent, and center of mass will be higher above the ground then the leg base is wide.  We have seen how difficult it is to keep F9 first stage strait on landing and that is on a flat surface.  On Mars your surface can be both rocky AND it can give-way during landing or even after, say if subsurface ice sublimates you end up like the Leaning tower of Pisa.

Both these problems make the system more dangerous then I think is acceptable.

Hard to know if the cargo would be on the bottom, or on top and use a swing out crane or something.
This stability issue will be the issue with any vertical lander, and I don't know if SpaceX is looking at anything but a a vertical lander.  So issues of landing will be inherrent whether my integrated stage concept, or a separate dedicated spacecraft.
Remember, whatever that spacecraft looks like, it will need to carry enough propellant on board to get itself back to Earth.  So it will be tall no matter what, unless they switch to a horizontal lander or something.

Thx for the reply Lobo and for taking these issues seriously.

You speak of a 'Mars-MCT' and 'LEO-MCT' but I've always assumed one type of vehicle, and unless the LEO variant is staged different from the 'combined 2nd stage' design used on the Mars variant then it has the same abort difficulty. 


Abort both static at the launch pad and during the first stage burn is generally the most dangerous part of a rocket launch so having this a 'black zone' is very serious even if the time period is brief.  Catastrophic booster explosion (or a loss of guidance control on the Booster which is going to force a self-destruct) is indeed TEH scenario for which abort systems are designed, virtually ever disaster scenario necessitating abort starts with or goes through a catastrophic booster explosion.  I am though less concerned with the MCT itself blowing up during assent even when it is acting as a 2nd or even 3rd stage. 

But I am quite confident that no amount of engines can be attached to this large MCT to push it away from the first stage, you would need more engines on it then are in the first stage.  Think about the masses and accelerations.  The first stage of BFR is likely to have 20+ raptor engines and it accelerates the whole rocket off the launch pad at a small fraction of a G, aka Thrust:Weight is just slightly >1.  That second stage is maybe a third of the total mass on the launch pad but to effectively abort you need Thrust:Weight of around 5, meaning you would need an absurd ~30 engines to push the second stage away at abort speed, and that's assuming it can even withstand that much acceleration.

A traditional 'capsule on 2 stages' that the F9 uses would still be difficult challenge to abort, I think it will need something like 6-8 Raptor engines around it like the Super-Draco's on the Dragon capsule.

As for the cargo placement within the vehicle, I have to imagine that with a vertical landing the cargo being in the nose is absolutely prohibitive because of the top-heavy nature, it would be virtually guaranteed to fall over, the logistics of unloading are just another headache.  The low, nearly ground level cargo hold depicted in your sketch seems to me the only viable means to do such a vehicle.



« Last Edit: 04/18/2015 01:03 am by Impaler »

Offline AncientU

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Re: MCT Speculation and Discussion Thread 3
« Reply #244 on: 04/18/2015 05:55 pm »
If SpaceX loses an MCT or BFR full of paying customers, they will face a bigger risk of bankruptcy than the passengers themselves risked prior to buying tickets.  It's in SpaceX's interest to make those craft as safe as possible.

If they are to see their Mars goals achieved, they will lose more than one MCT/BFR.
Great deeds are not for the faint of heart (i.e., there's no free lunch).
The obsession with avoiding risk in our society is pathological.

Note that many airlines have lost a load of paying passengers, and this even today when commercial flight is routine (and safer than driving).  The reasons that they go bankrupt are not the inherent risks of flying.
« Last Edit: 04/18/2015 05:57 pm by AncientU »
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Offline Eerie

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Re: MCT Speculation and Discussion Thread 3
« Reply #245 on: 04/18/2015 06:03 pm »
The obsession with avoiding risk in our society is pathological.

I think this is more about NASA being a symbol. Cars, airplanes... those are routine risks. But astronauts are the High Priests of the religion of Progress, and people today don't like martyrs or human sacrifices.
« Last Edit: 04/18/2015 06:04 pm by Eerie »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #246 on: 04/18/2015 10:41 pm »
What's pathological is this belief by Space-Cadets that all the problems with our space program be be boiled down to 'timidness' and 'spinelessness', and taking greater risks with human life will magically yield the glory they seek.

It is a simplistic, self-gratifying message that conforms to the general anti-government ideology and 'nanny state' bogyman of the political right-wing.  But it bears no resemblance to reality, NASA engineers when faced with envelope pushing performance demands and inadequate funding (both the fault of Congress) have in fact sacrificed safety REPEATEDLY and become quite cavalier in doing so.

SpaceX success has been based on internally NOT making the mistakes Congress cripples NASA with, Musk adequately funded the company and it's internal development and he dose not make absurd performance demands.  This gives them the engineering headroom to make their system SAFER then NASA equivalents. 

Elon is smart, he knows this is what space travel needs to be if it has any chance of succeeding as a means of colonization.  People with large amounts of disposable income (and very good earning potential if they stay on Earth) are not going to accept 1-2% chances of dieing in a fireball on the launch pad to go to Mars, Mars is not THAT attractive of a place.  This is not 1620 in which religious dissidents and peasants in Europe consider a leaky boat to America better then wars and plagues in their home land, and even then the death rate in crossing the Atlantic was only 2% on the Mayflower, people are going to rightfully demand better then that after 500 years of improved living standards and technology development.

Offline Owlon

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Re: MCT Speculation and Discussion Thread 3
« Reply #247 on: 04/19/2015 01:12 am »
What's pathological is this belief by Space-Cadets that all the problems with our space program be be boiled down to 'timidness' and 'spinelessness', and taking greater risks with human life will magically yield the glory they seek.

It is a simplistic, self-gratifying message that conforms to the general anti-government ideology and 'nanny state' bogyman of the political right-wing.  But it bears no resemblance to reality, NASA engineers when faced with envelope pushing performance demands and inadequate funding (both the fault of Congress) have in fact sacrificed safety REPEATEDLY and become quite cavalier in doing so.

SpaceX success has been based on internally NOT making the mistakes Congress cripples NASA with, Musk adequately funded the company and it's internal development and he dose not make absurd performance demands.  This gives them the engineering headroom to make their system SAFER then NASA equivalents. 

Elon is smart, he knows this is what space travel needs to be if it has any chance of succeeding as a means of colonization.  People with large amounts of disposable income (and very good earning potential if they stay on Earth) are not going to accept 1-2% chances of dieing in a fireball on the launch pad to go to Mars, Mars is not THAT attractive of a place.  This is not 1620 in which religious dissidents and peasants in Europe consider a leaky boat to America better then wars and plagues in their home land, and even then the death rate in crossing the Atlantic was only 2% on the Mayflower, people are going to rightfully demand better then that after 500 years of improved living standards and technology development.

Nobody is somehow blaming this on the "nanny state". Decades down the line, launch may very well be the part of a journey to Mars least likely to fail. At some point it doesn't make sense to make design compromises in a low-margin system to catch every failure mode. It's not likely to be feasible to build a launch escape system that works on Mars, and not every abort from a failing booster on Earth is going to require a high-g escape.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 3
« Reply #248 on: 04/19/2015 01:23 am »
I can imagine an abort system which would work on Mars just fine. In fact, Dragon (or something similar) should do the job just fine since you could just shut down the engines on your ascent vehicle (the thin atmosphere doesn't transmit explosions much, so there's less urgency to out-run it) then land vertically Red-Dragon-style after boosting a bit away. It'd be plenty feasible. Not sure if it's necessary (or worth it), though.
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Offline NovaSilisko

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Re: MCT Speculation and Discussion Thread 3
« Reply #249 on: 04/19/2015 01:36 am »
How many times have we had this discussion on aborts with no definite conclusion again?

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 3
« Reply #250 on: 04/19/2015 01:47 am »
How many times have we had this discussion on aborts with no definite conclusion again?
People keep saying it can't feasibly be done, but that only shows they haven't thought very hard about it. Of course, whether or not it's worth it is far more subjective and probably can't even be answered this decade (speaking in the context of Mars colonization or large base level of activity).
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #251 on: 04/19/2015 06:21 am »
Nobody is somehow blaming this on the "nanny state". Decades down the line, launch may very well be the part of a journey to Mars least likely to fail. At some point it doesn't make sense to make design compromises in a low-margin system to catch every failure mode. It's not likely to be feasible to build a launch escape system that works on Mars, and not every abort from a failing booster on Earth is going to require a high-g escape.


That's a straw-man, I'm pointing out how someones proposal has ZERO abort capability in THE most dangerous time and place of a launch in THE most dangerous class of vehicle ever conceived by man and your accusing me of essentially demanding infinite safety. 

Telling a person that a new Car design should have a seat belt is not the same thing as demanding that cars be made out of pillow and go no more then 5 mph.  Basic safety systems in launch vehicles are well established and expecting that they at least maintain that standard is the only reasonable position on this issue.

If a person can not think of a MCT design that is at least as safe as a Falcon 9 launch then they should go back to the drawing board because Elon and SpaceX ain't interested.

Offline Ben the Space Brit

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Re: MCT Speculation and Discussion Thread 3
« Reply #252 on: 04/19/2015 12:36 pm »
FWIW, I repeat my proposal that the nose of MCT be essentially an up-sized (say, 5m-diameter) Dragon 2.0. During ascent and descent phases, the crew and passengers ride in there. In the event of an emergency, the aerodynamic outer shell of the MCT is jettisoned and the 'Super-Dragon' escape pod flies clear of the MCT with the objective of a safe landing as near to the launch site as possible (Mars) or just safe land- or sea-fall (Earth).
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Offline AncientU

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Re: MCT Speculation and Discussion Thread 3
« Reply #253 on: 04/19/2015 12:57 pm »
What's pathological is this belief by Space-Cadets that all the problems with our space program be be boiled down to 'timidness' and 'spinelessness', and taking greater risks with human life will magically yield the glory they seek.

...NASA engineers when faced with envelope pushing performance demands

This Space-Cadet (actually, I'm a scientist and space enthusiast for 50+ years) never referred to NASA...
But if you choose to wear it, it's your shoe.

The point I was making is that the SpaceX Mars goals are not compatible with zero risk tolerance.  Having the trip to Mars always decades in the future is the only zero risk strategy.

Note: What is pathological, in my thinking, is our society's (in US of A) aversion to perceived risk, based in part on our lack of technical education to judge actual risk.
« Last Edit: 04/19/2015 01:04 pm by AncientU »
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Offline AncientU

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Re: MCT Speculation and Discussion Thread 3
« Reply #254 on: 04/19/2015 01:18 pm »
As to MCT's LAS, I think it will have none.  This is because I'm one of the small minority here that think MCT will not take off from Earth with crew aboard.  Cargo, yes.  Provisions, yes. Heat shield for Earth re entry, no. Fuel for TMI, no.

 I don't think the 'fleet' of MCTs will ever return to Earth's surface.  Not sure about Mars surface either... after all, 'land the whole thing' is only four words.  And those words were in reference to the Mars end of the trip.
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Offline Burninate

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Re: MCT Speculation and Discussion Thread 3
« Reply #255 on: 04/19/2015 01:32 pm »
The only way a complete MCT would be capable of launch abort would be if it was launched with a minimal fuel load relative to its large capacity.  Full tanks don't work for high-G abort at max Q, there just isn't enough thrust.

This would require:

1) That crew is not onboard, because it will take months/years to fill those tanks and crew won't want to spend all that time waiting in orbit

2) That the MCT not be used to achieve orbit.  This means that there need to be two or more likely 3 stages *below* the MCT.

Better to just send the crew up at a later date, after the MCT is fueled in orbit.
-----

A nosecone capsule has been a repetitive conclusion in my designs.  I keep trying to remove it and finding it's congruent with some other purpose.
« Last Edit: 04/19/2015 01:33 pm by Burninate »

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 3
« Reply #256 on: 04/19/2015 02:08 pm »
If you don't think MCT will land back on Earth or even on Mars, then you are saying SpaceX will need to develop 2 additional large vehicles to do so. Dragon certainly isn't cheap enough to do this. Sounds like a very complicated and expensive architecture.
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Offline RonM

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Re: MCT Speculation and Discussion Thread 3
« Reply #257 on: 04/19/2015 02:28 pm »
I think there will be at least two versions of MCT.

In the exploration phase, each flight will have a small crew. The first version of the MCT will be mainly cargo for setting up a base and exploring. It will not have a LAS and the small crew can be sent up to the MCT on a single Dragon while the MCT is being refueled for the trip to Mars.

The colonization version will need a LAS because with a large crew of up to a hundred they will have to launch with the MCT. A dozen or more Dragon launches to transfer the crew to the MCT doesn't make sense. The crew compartment will probably be on top and could be separated from the rest of the MCT during an emergency, making it easier to develop a LAS. This version of MCT will benefit from lessons learned from the first version.

Offline AncientU

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Re: MCT Speculation and Discussion Thread 3
« Reply #258 on: 04/19/2015 02:39 pm »
If you don't think MCT will land back on Earth or even on Mars, then you are saying SpaceX will need to develop 2 additional large vehicles to do so. Dragon certainly isn't cheap enough to do this. Sounds like a very complicated and expensive architecture.

Today's Dragon-2 is affordable for crew.  Reuse of first stages and Dragons will improve that cost.
Affordable for transferring small crews, that is (10-20 people).  That seems sufficient for the next ten years.
If cheap enough is constrained to the $500k/passenger, then no known combination of vehicles can qualify.

On-orbit refueling is the biggest challenge if MCT is going to land at the Mars end (besides MCT itself, of course). If a full propulsive landing of people on Mars is not part of MCT's design, then there will be additional technology needing development to get crew down (safely).  Taking back off from Mars using ISRU is incredibly more complicated and expensive than crew transfer.

Note: Making a 20-30 passenger Dragon-3 is not that difficult.




« Last Edit: 04/19/2015 02:41 pm by AncientU »
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #259 on: 04/19/2015 02:43 pm »
This Space-Cadet (actually, I'm a scientist and space enthusiast for 50+ years) never referred to NASA...
But if you choose to wear it, it's your shoe.

The point I was making is that the SpaceX Mars goals are not compatible with zero risk tolerance.  Having the trip to Mars always decades in the future is the only zero risk strategy.

Note: What is pathological, in my thinking, is our society's (in US of A) aversion to perceived risk, based in part on our lack of technical education to judge actual risk.

Space-Cadet-ism is an attitude and has nothing to do with technical experience or education, having these things just makes the attitude that much more inexcusable.

Again claiming that criticism of an unsafe vehicle design is a 'zero risk strategy' is a blatant straw-man.  I am not saying that we should stay on the ground forever, I am saying that SpaceX vehicle designs are not going to throw all safety concerns out the window for maximizing performance.

As to MCT's LAS, I think it will have none.  This is because I'm one of the small minority here that think MCT will not take off from Earth with crew aboard.  Cargo, yes.  Provisions, yes. Heat shield for Earth re entry, no. Fuel for TMI, no.

 I don't think the 'fleet' of MCTs will ever return to Earth's surface.  Not sure about Mars surface either... after all, 'land the whole thing' is only four words.  And those words were in reference to the Mars end of the trip.

Then what vehicle gets the passengers to orbit?  The goal is to be capable of taking 100 people per MCT, I can't see this being done with dozens of F9 flights as this would kill the cost competitiveness of the system.  Also everything we have been told about MCT says it will come back to Earth, Musk pounds on this point at every opportunity, it is GOSPEL.  If you don't believe it then your saying MCT development with FAIL, Musk would never even bother bringing a non reusable MCT to market.

The only way a complete MCT would be capable of launch abort would be if it was launched with a minimal fuel load relative to its large capacity.  Full tanks don't work for high-G abort at max Q, there just isn't enough thrust.

This would require:

1) That crew is not onboard, because it will take months/years to fill those tanks and crew won't want to spend all that time waiting in orbit

2) That the MCT not be used to achieve orbit.  This means that there need to be two or more likely 3 stages *below* the MCT.

Better to just send the crew up at a later date, after the MCT is fueled in orbit.
-----

A nosecone capsule has been a repetitive conclusion in my designs.  I keep trying to remove it and finding it's congruent with some other purpose.

All good points, but I think what will be done is that the MCT will be a 12-15m diameter capsule and will perform Dragon style abort with sidewall mounted raptor engines.  The main propellent tanks will be empty on launch but a number of smaller pressurized tanks will provide the brief burst necessary for abort as well as allow the raptor to start-up rapidly by bypassing the turbo-pump which takes too long to spin up.

The synod window and the refueling time will ultimately drive SpaceX toward the massive 'space liner' SEP vehicle that carries a few MCT rather then 'fleets' of MCT themselves just individually departing, that will happen only in the early exploration phase before real colonization and real volume demand.
« Last Edit: 04/19/2015 02:47 pm by Impaler »

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