Author Topic: MCT Speculation and Discussion Thread 4  (Read 505466 times)

Offline oldAtlas_Eguy

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Re: MCT Speculation and Discussion Thread 4
« Reply #200 on: 06/21/2015 05:52 PM »
Why would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?

I would guess more like 30-35 tons.

Just the propellant tank portion, 5 Raptor engines and possibly landing legs too would weight ~40mt. Now add the reentry shield and the cargo bay structure. Of course the cargo variant will not have as high a dry weight as the crew variant but where is the tradeoff in crew payload size and crew vehicle dry weight increase. If you could get the cargo variant to have a dry weight as low as 60mt then reduce the payload size of the crew variant (crew + supplies) to only 60mt on a crew variant that dry weight 100mt things will work out better in that the overall system becomes smaller. You shrink the size and maybe some savings on the propellant tank dry weight due to smaller tanks.

My only problem with the estimates is that the more detail we go the heavier the MCT gets.

My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.

My visualization for a reusable Earth orbit tanker Upper Stage for the BFR is a slightly smaller volume all fuel vehicle that adds little to the launch weight of the BFR and has about 10% lower dry weight than the MCT cargo. Running some numbers this morning I am only seeing 120mt of propellant left over (after margins) to transfer to a depot.  Note the idea is that there doesn't need to be active cooling on the tanker since it goes immediately to its offload rendezvous.  I want this vehicle to be specially designed because operationally it flies the most. With 4.1 flights per MCT going to Mars, plus whatever flights get made to satisfy other BLEO business the depot, MCTs and other LEO and Earth based Mars infrastructure gets used for.  So a small fleet of these makes sense. Cargo MCTs may well work for just launching cargo bound anywhere in LEO or beyond and I suspect that there will  be far less volume of this than keeping the depot topped up so no need to specifically develop a LEO cargo MCT.
Yes, the depot could be a specially equipped MCT for 0 boil-off since it would have large enough tanks to refuel 1+ MCT's for Earth departure. This would make it easy to orbit the depots since they are just another cargo specialized version of the MCT which are then manufactured in the 10's to 100's.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #201 on: 06/21/2015 06:05 PM »
Why would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?

I would guess more like 30-35 tons.

Just the propellant tank portion, 5 Raptor engines and possibly landing legs too would weight ~40mt. Now add the reentry shield and the cargo bay structure. Of course the cargo variant will not have as high a dry weight as the crew variant but where is the tradeoff in crew payload size and crew vehicle dry weight increase. If you could get the cargo variant to have a dry weight as low as 60mt then reduce the payload size of the crew variant (crew + supplies) to only 60mt on a crew variant that dry weight 100mt things will work out better in that the overall system becomes smaller. You shrink the size and maybe some savings on the propellant tank dry weight due to smaller tanks.

My only problem with the estimates is that the more detail we go the heavier the MCT gets.

My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.

My visualization for a reusable Earth orbit tanker Upper Stage for the BFR is a slightly smaller volume all fuel vehicle that adds little to the launch weight of the BFR and has about 10% lower dry weight than the MCT cargo. Running some numbers this morning I am only seeing 120mt of propellant left over (after margins) to transfer to a depot.  Note the idea is that there doesn't need to be active cooling on the tanker since it goes immediately to its offload rendezvous.  I want this vehicle to be specially designed because operationally it flies the most. With 4.1 flights per MCT going to Mars, plus whatever flights get made to satisfy other BLEO business the depot, MCTs and other LEO and Earth based Mars infrastructure gets used for.  So a small fleet of these makes sense. Cargo MCTs may well work for just launching cargo bound anywhere in LEO or beyond and I suspect that there will  be far less volume of this than keeping the depot topped up so no need to specifically develop a LEO cargo MCT.
Yes, the depot could be a specially equipped MCT for 0 boil-off since it would have large enough tanks to refuel 1+ MCT's for Earth departure. This would make it easy to orbit the depots since they are just another cargo specialized version of the MCT which are then manufactured in the 10's to 100's.

I see the depot as much larger than that. I would prefer to see passenger carrying MCT's launch in pairs as close to simultaneously as possible. Also because of the intensity of the black body radiation of the earth and its daytime reflection of heat, I see the depot needing far more active cooling than the MCT which will only need to keep its propellant from boiling off near Mars and between Mars and Earth but will not need to keep it cool for long in the 10 radii range of the Earth. I also see the depot with a hab as transit station, and a place where PicaX can be recoated on MCT's along with engine swaps (engines taken off BFR tanker stages)
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #202 on: 06/21/2015 06:06 PM »


My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.


I don't believe integrated habitat and direct Earth-reutrn are compatible.

The problem I see is that the mass of the habitat if it is a module or integrated will be considerably above the 25% return payload limit which Musk stated was needed to make the direct earth-return possible, and I don't think anyone can claim that Musk is being conservative in this number.

Their is simply no way to offload 75% of the mass of an integrated habitat, all the passengers, all their baggage and personal effects, even all the waste products accumulated during transit wouldn't be 75%.  You would need to actually strip out most or all the ECLSS equipment from the vehicle which really defeats the purpose of having an integrated habitat.

If it's going to be left on Mars (which is a win-win by both providing needed equipment and reducing costly return mass) then a module designed to be removed is the way to go.  I would even go so far as to advocate for a large wheeled vehicle/habitats to make removal from the lander and aggregation easier, much like this concept


Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #203 on: 06/21/2015 06:30 PM »


My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.


I don't believe integrated habitat and direct Earth-reutrn are compatible.


An integrated hab for 6-10 people could probably mass less than 25 tonnes, so it seems possible for initial missions. Later missions with more would need a larger hab and that could not be integrated.

So I believe you have made an important point, integrated habs have no long term future on the MCT, so will probably not be designed in the first place.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #204 on: 06/21/2015 07:00 PM »
Related, but going off in a slightly different direction:

My favorite,

Quote from: Musk

I mean, if you do a densified liquid methalox rocket with on-orbit refueling, so like you load the spacecraft into orbit and then you send a whole bunch of refueling missions to fill up the tanks and you have the Mars colonial fleet - essentially - that gets built up during the time between Earth-Mars synchronizations, which occur every 26 months, then the fleet all departs at the optimal transfer point.

Elon Musk at MIT
http://shitelonsays.com/transcript/elon-musk-at-mits-aeroastro-centennial-part-2-of-6-2014-10-24

One of the issues that has been discussed many times is reducing passenger travel times from the amount of time the lowest energy Hohman orbit takes, however, when you consider the launch windows for Mars, each launch window leaves you the opportunity for higher and lower energy launches that vary in flight duration by as much as 3 months more or less than the ideal Hohmann orbit. However at any time during the approximately 3 month long launch window there is an optimum energy launch to Mars and the flight profile of that launch in terms of flight duration and arrival time will have significant impact on the logistics of Mars operations:

Roughly speaking any launch that flies the optimum(for ΔV) course for its launch time that occurs before the date of the optimum Hohmann orbit launch date arrives as many days later than the Hohmann transfer would as it departs early. So if you launch 2 weeks before the optimum Hohmann orbit launch date and take the optimum orbit for that time (which goes a little outside Mars orbit then comes back to meet Mars) you travel for 4 weeks longer than the Hohmann orbit. Contrawise those launches that occur after the date of the optimum Hohmann orbit launch also have an apoapsis further out than Mars but they pass Mars long before their apoapsis. So a craft leaving 2 weeks after the optimum Hohmann orbit to Mars on the optimum path for that time, arrives 2 weeks before a flight on the Hohmann transfer.  You can cut the flight time to Mars down to about 5 months without too much extra ΔV, however if you are doing that just for passenger carrying MCT's you have to realize that he cargo launched at that time would be (if launched on the most energy efficient orbit) will be arriving much later than the people (6-7 weeks for cargo on a Hohmann transfer).
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #205 on: 06/21/2015 10:02 PM »


My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.


I don't believe integrated habitat and direct Earth-reutrn are compatible.


An integrated hab for 6-10 people could probably mass less than 25 tonnes, so it seems possible for initial missions. Later missions with more would need a larger hab and that could not be integrated.

So I believe you have made an important point, integrated habs have no long term future on the MCT, so will probably not be designed in the first place.

I should have been more clear, an integrated habitat that carries all the OUTBOUND passengers (nominally 100) would be incompatible with direct Earth-return.

A small one would not be physically impossible but it would cut into outbound mass and be a poor idea, I favor simply using a smaller return module which would be landed as part of preparatory cargo missions.

Ultimately if we are talking about multiple hundreds or even thousands of colonists per year then then the only architecture that makes sense is a large 'space-liner' and 'space-freighter' transit vehicle with electric propulsion combined with much smaller landing craft that can cycle rapidly between orbit and surface at Mars and Earth. 

That's why I'm looking at much smaller landers, they flow much more easily into the kind of future high volume system that would ultimately be necessary while still being viable early exploration vehicles when paired with modest SEP stages that we can produce now.  Direct-return vehicles are essentially a dead-end configuration because they have a low maximum flight rate, so why go down that path.

Lastly you have a low risk spiral development path, as follows

1) BFR with reusable 2nd stage - Compete with SLS, launch constellation sats to LEO, multiple large satellites to GTO, larger LEO station construction, revenue streams secured immediatly.

2)  MCT lander, do some lunar landings for NASA as shake-down cruises, or as a large crew delivery vehicle to LEO stations if they are getting big enough.

3)  Develop in-situ propellent production, send it to Mars on a one way lander, retire lots of risk.

4)  SEP pusher stage that can take the lander to and from Mars, now all the parts are ready for an initial Mars landing with the crew traveling in a habitat in the lander that remains on the surface.

5) Develop a BIG transit habitat, or just buy it from Bigelow, build up a much larger base and send more people by using the transit hab and a denser 'sleeper-car' module in the lander just for brief launch-landing.

6)  Make a much bigger SEP vehicle with orbital assembly, stick 6-8 of the big transit habs on it along with hundreds of cargo containers.  Use the landers multiple times per trip to take cargo and passengers down from the larger transit vehicle.
« Last Edit: 06/22/2015 01:05 AM by Impaler »

Offline CyclerPilot

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Re: MCT Speculation and Discussion Thread 4
« Reply #206 on: 06/21/2015 11:30 PM »

The landing gear mass is almost certainly driven by the force of impact with the surface NOT the static weight of the vehicle, in other words objects still have inertia irregardless of gravity.  And even if static weight weight were the concern you would need to size the legs based on the gross take off weight which we all agree will be greater then landing weight.

F9 first stage has 8% of dry mass in the leg system, and this is designed for flat artificial surfaces and is not carry precious human cargo.  The LEM had around 3% of touch down mass in legs, but that was a soft-touchdown with a deeply throttling engine, not the SpaceX 'hover-slam'.

I think Gross take off Weight will be ~450 mT total, not these monstrous 1000 ton figures.  And their would not be any kind of integral habitat in a 'crew' version.  Their will just be a single version with an unpressurized cargo bay into which a habitat module would be placed.

Max Q is aerodynamic pressure peak, in the Martian atmosphere it is an almost irrelevant force compared to the force experienced during launch from Earth, it is not the same as max g-forces which is what would be relevant for not crushing the vehicle.
You are correct about mass vs. weight, but I would think the Martian landing will be at lower speed due to the lower gravity (wider tolerance for v=0 altitude=0 point).  Good point about Mars GLOW though I think we would both agree that that should not be the peak force on the legs (Earth landing will).

Good comparison on the lunar lander vs F9 S1 legs.  The F9 legs had the additional constraints of having to be deployable, aerodynamic when folded, support a higher COV vehicle, and as you mentioned a higher speed impact (through the nominal should be close to 0).  Probably all the same constraints the MCT legs will have.

The reason I think they will all be pressurized is that I think having an aero shell and a separate pressure vessel is a waste of mass.  The exception to this would be if you are leaving the habitat behind on mars.  With a top or side TPS I think a pressurized volume is all but required. Are you assuming a capsule design with the TPS on the bottom? 

Regarding max Q and max Gs.  I agree with you in the general sense, but I think we may be talking past each other.  Different phases of flight have different masses, and a larger mass at a given G load requires more structure.  There are also different "sources" of force acting on the MCT (inner stage, engine thrust structure, TPS, nose).  The highest G phase will be the peak pressure on most structural members, but not all.

At max Q (earth assent) the MCT structure has to support the aerodynamic pressure plus the payload mass (times Gs) plus the full propellant mass (times Gs) (yes I'm assuming combined S2, you might not be).  My point was that certain structural members will see a higher pressure at max Q than at higher G phases of the flight (MECO, SECO, mars assent, and mars or earth entry)

Edit: spelling
« Last Edit: 06/21/2015 11:47 PM by CyclerPilot »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #207 on: 06/22/2015 01:42 AM »

You are correct about mass vs. weight, but I would think the Martian landing will be at lower speed due to the lower gravity (wider tolerance for v=0 altitude=0 point).  Good point about Mars GLOW though I think we would both agree that that should not be the peak force on the legs (Earth landing will).

Agree that static weight is not an issue, it is speed of impact with the surface.  But I disagree that gravity will be the main determinant of that, on both Mars and Earth the vehicle will be under propulsive decent and gravity is simply a part of that 'dance' the Raptor engine is TOO MUCH thrust to hover on at either Earth or Mars (230 mT hover on Earth, 605 mT on Mars), no one belives MCT would have that much mass at touchdown.  I favor a set of vernier engines specifically to make a softer touchdown (and avoid cratering the surface)

Good comparison on the lunar lander vs F9 S1 legs.  The F9 legs had the additional constraints of having to be deployable, aerodynamic when folded, support a higher COV vehicle, and as you mentioned a higher speed impact (through the nominal should be close to 0).  Probably all the same constraints the MCT legs will have.

LEM landing legs deployed too, though not nearly as much as F9, I think Apollo was also trying DESPERATELY to shave mass on everything, often leaving little or no safety margin.  SpaceX is going to make more robust systems as they want these things to not break which makes them both safe and reusable.  A comparison of the actual design threshold impact speed would be an interesting comparison.  Lastly the F9 landing legs have to have a very wide stance to accommodate the tall slender vehicle (and it is still falling over as of the last attempt), LEM was very squat which it needed because it landed on some considerable slope angles.

The reason I think they will all be pressurized is that I think having an aero shell and a separate pressure vessel is a waste of mass.  The exception to this would be if you are leaving the habitat behind on mars.  With a top or side TPS I think a pressurized volume is all but required. Are you assuming a capsule design with the TPS on the bottom?

I have never heard of an space vessel in which the outer aero shell IS the pressure vessel, I would speculate that it presents for too much of a thermal pathway into the vessel and would literally COOK the passengers, note that reentry capsules get quite warm inside during re-entry and this is with considerable insulation between the TPS and pressure vessel.  So I do not believe what your describing is possible.

Leaving habitats on surface is exactly what I proposed.  The overall shape I'm going with (originally Lobo's configuration) is that of a biconic with TPS on the top/sides, engines and legs on the bottom and an unpressurized cargo-bay door on the side.

Regarding max Q and max Gs.  I agree with you in the general sense, but I think we may be talking past each other.  Different phases of flight have different masses, and a larger mass at a given G load requires more structure.  There are also different "sources" of force acting on the MCT (inner stage, engine thrust structure, TPS, nose).  The highest G phase will be the peak pressure on most structural members, but not all.

At max Q (earth assent) the MCT structure has to support the aerodynamic pressure plus the payload mass (times Gs) plus the full propellant mass (times Gs) (yes I'm assuming combined S2, you might not be).  My point was that certain structural members will see a higher pressure at max Q than at higher G phases of the flight (MECO, SECO, mars assent, and mars or earth entry)

Edit: spelling

I see your point, both forces are unique and would need to be evaluated separately on each part of the ship.  G-force max is generally right before 'burn out' aka at the last bit of propellent being used, a throttle down on the engines is typically employed to limit this g-force.  As the MCT will have less cargo on Mars launch it is likely that max g-force is felt on Mars assent, or alternatively they simply do a deeper throttle-down to keep the peak comparable to the peak experienced at Earth.  I think the force limit will be comparable to what a Dragon capsule experiences.
« Last Edit: 06/22/2015 01:52 AM by Impaler »

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #208 on: 06/22/2015 02:27 AM »
A 5-person crew's luxurious tourist hab is a 25-person crew's adequate expedition hab is a 100-person crew's short-term transfer hab.  Design once, and use it for multiple campaigns.
« Last Edit: 06/22/2015 02:27 AM by Burninate »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #209 on: 06/22/2015 02:45 AM »
A 5-person crew's luxurious tourist hab is a 25-person crew's adequate expedition hab is a 100-person crew's short-term transfer hab.  Design once, and use it for multiple campaigns.

The only thing that would be common to all three of these would be the pressure vessel and the means of securing it inside the vessel (assuming your talking about a removable module), everything internal would need to be radically different due to the ECLSS needs, the floor layouts, bunks etc etc.

Still I agree you would save money and development time by having at least that level of commonality and the reuse of a proven design would likely be desirable from a safety standpoint too.

Offline CyclerPilot

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Re: MCT Speculation and Discussion Thread 4
« Reply #210 on: 06/22/2015 03:15 AM »


Agree that static weight is not an issue, it is speed of impact with the surface.  But I disagree that gravity will be the main determinant of that, on both Mars and Earth the vehicle will be under propulsive decent and gravity is simply a part of that 'dance' the Raptor engine is TOO MUCH thrust to hover on at either Earth or Mars (230 mT hover on Earth, 605 mT on Mars), no one belives MCT would have that much mass at touchdown.  I favor a set of vernier engines specifically to make a softer touchdown (and avoid cratering the surface)
Agreed on the terminal landing thrusters.  On my design back in the first thread I actually used pressure fed metholox thrusters for the entire EDL (Earth and Mars) without using raptor at all.  I am re-thinking that, especially now that raptor is smaller.  Raptor would have an ISP advantage in the super-sonic retro-propulsion.  Terminal landing is where raptor is far from ideal.

Landing with raptor alone on Mars would be very difficult and risky.  Impossible without a prepared surface.  Earth landing would require the flow separation issues to be solved.

I have never heard of an space vessel in which the outer aero shell IS the pressure vessel, I would speculate that it presents for too much of a thermal pathway into the vessel and would literally COOK the passengers, note that reentry capsules get quite warm inside during re-entry and this is with considerable insulation between the TPS and pressure vessel.  So I do not believe what your describing is possible.

Leaving habitats on surface is exactly what I proposed.  The overall shape I'm going with (originally Lobo's configuration) is that of a biconic with TPS on the top/sides, engines and legs on the bottom and an unpressurized cargo-bay door on the side.

You are correct about the thermal issues  but I wasn't clear enough in my description. I was also toying with the same TPS configuration for my next design (top and side).  The integrated pressure vessel I proposed would double as the load bearing structure behind the TPS.  I think this would save several tons over your proposal, but your proposal saves tens of tons by having the hab pull double duty as cargo.  Then saves several hundred tones of ISRU propellant on mars per return flight.  So you might have converted me. ;) 

Your rigid hab left behind has a lot of merit, especially in the first dozens or hundreds of flights.  A few months back I proposed an inflatable hab used in transit being left behind for the same effect.  I also had sketched a 180ş side door for an unpressurized cargo version before, though I can't remember if I posted it here.  When I have time to sit down with excel and cad again and turn my hand-waving into something concrete, we will see what I come up with.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #211 on: 06/22/2015 04:38 AM »
I'm all for integrating some of the layers that normally make up a space craft, metallic TPS which I favor can be combined with the aero-shell and would be right over the skeletal frame members which take the dynamic pressure and g-forces.  As I favor an unpressurized cargo-bay the interior is all just tanks, plumbing, framing and some sheet-metal to nominally separate the cargo-hold from the rest of the interior.

The habitat I'm envisioning might make use of an inflatable section, such as a loft or water tank on the top that would only be expanded once on Mars.  NASA has built similar concept habitats.  The rigid portion would be 2 floors and mounted on set of wheels that can squat down and lower the vehicles height to allow it to fill as much of the cargo hold as possible.  Functionally it is a trailer that is ment to be towed by a second large vehicle 'locamotive' which would be sent ahead on a cargo flight.

The great height of the cargohold above the ground (largely due to the need to accommodate the Raptor nozzle bells above the surface means that it might be necessary to build up some earthen ramps to get the large vehicles in and out.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #212 on: 06/22/2015 07:37 AM »
Direct-return vehicles are essentially a dead-end configuration because they have a low maximum flight rate, so why go down that path.

But SEP stages and transit habs also have a low flight rate. So replacing a direct-return MCT with SEP, transit hab and a smaller MCT lander does not seem to be a win.

The main advantage of a direct-return MCT is that it can be maintained, refurbished and upgraded on Earth.

Any architecture which involves space-only or Mars-only stages has to explain how they will be maintained in space or on Mars. This is not an easy problem to solve, especially if we assume new and upgraded versions of SEP, transit hab and MCT lander are produced every few years. Earth has so many advantages, presence of jigs and tooling, unlimited supplies of water and other working fluids, a full local supply chain, local presence of the design engineers, clean rooms, large hangers under pressure, etc.

I think that the overheads of maintaining equipment off-earth removes any advantage your architecture might have in terms of lower initial mass in LEO,  at least until we reach colony sizes of 100,000.


Offline R7

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Re: MCT Speculation and Discussion Thread 4
« Reply #213 on: 06/22/2015 08:23 AM »
Sometimes I use a first approximation and say the cargo is as much as transport cost. That would average 500000 $ for one t. Averaged between simple tools and Intel CPUs.

The overall expense for an aspiring colonist has mushroomed into $10,500,000  :-\

Middle class no longer need to apply, very/ultra high networth individuals only.
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Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #214 on: 06/22/2015 02:46 PM »
I think large SEP tugs should be to take a lot of cargo and disposable landers to Mars since the cargo is 10:1 colonists.  MCT would be for colonists, larger cargo and time sensitive cargo.  Disposable landers could be designed to be salvaged for colonists building materials.  For instance legs could hold up solar panels.  Fuel tanks could be salvaged and grouped together for a fuel depot, or habitats, or the smaller landers could be refueled to launch argon from the Martian atmosphere to refuel SEP tugs, then re-land for refueling again and launching again. 

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #215 on: 06/22/2015 06:03 PM »
Direct-return vehicles are essentially a dead-end configuration because they have a low maximum flight rate, so why go down that path.

But SEP stages and transit habs also have a low flight rate. So replacing a direct-return MCT with SEP, transit hab and a smaller MCT lander does not seem to be a win.

The main advantage of a direct-return MCT is that it can be maintained, refurbished and upgraded on Earth.

Any architecture which involves space-only or Mars-only stages has to explain how they will be maintained in space or on Mars. This is not an easy problem to solve, especially if we assume new and upgraded versions of SEP, transit hab and MCT lander are produced every few years. Earth has so many advantages, presence of jigs and tooling, unlimited supplies of water and other working fluids, a full local supply chain, local presence of the design engineers, clean rooms, large hangers under pressure, etc.

I think that the overheads of maintaining equipment off-earth removes any advantage your architecture might have in terms of lower initial mass in LEO,  at least until we reach colony sizes of 100,000.

No the flight rate is considerably higher for the lander because it is being loaded in Mars orbit and cycle rapidly between the surface and back to orbit, 100 flights per synod would easily be achievable.  That is 100 times more then the direct return lander.   A large frighter would carry mostly cargo and just 1 or 2 landers and it could easily take the lander back to Earth to land there and be serviced if needed once every synod.

The SEP vehicle itself dose 1 round trip per synod, but it is not being landed and relaunched, were only launching new cargo and propellent to it in LEO, this will utilize the launch vehicle far more efficiently.  With cargo inside landers and an all chemical TMI your looking at 1/6th of launch mass being usable cargo, 1/6th being the lander and 2/3rds propellents.   The efficiency of the SEP would make this 2/3rds cargo, 1/3 propellents.

Inspection and maintenance are important functions and will be done for landers on Earth, do not confuse the 'stay at Mars' normal operational practice with removing the vehicle from service for maintenance, airplanes are not maintained in the air or on the runway or at the terminal gate.  The SEP vehicle is effectivly a space-station and would have a life-span and maintenance needs much like ISS, if parts wear out they are replaced either internally or externally.

Upgrading of any significant parts (engines, structures, Thermal protection) is rarely done to vehicles of any kind.  As we expect a growing fleet you will simply see new models added to the fleet while older ones continue to serve until they are deemed obsolete or worn out (like airplanes).  The landers design is likely too interconnected to allow significant upgrading outside of engine upgrades as we saw in Merlin.  The SEP might see upgrades or replacement of it's thrusters as that technology improves, this would be done by spacewalk to detach and reattach a new engine block, so long as it is designed to be replaced it wouldn't be a problem.

Offline Ionmars

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Re: MCT Speculation and Discussion Thread 4
« Reply #216 on: 06/22/2015 11:20 PM »
Impaler and CyclerPilot, this idea should be compatible with the CONOPS you are developing:

Consider the passenger  version of MCT, the trans-Hab and the surface-Hab to be all the same unit. By this I mean that the passenger section and the propulsion section of MCT would be separate and functionally independent units, i.e. propulsion avionics entirely in the propulsion unit and ECLSS components entirely within the passenger unit.. The passenger unit would sit on top of the propulsion unit, which sports a wide heat shield on its underbelly for EDL. The bottom rim of the passenger unit would be joined to the top rim of the propulsion unit only by a ring of bolts through both rims.

Passengers would ride in this vehicle from Earth and land on Mars' surface. A mobile robotic arm that was previously deployed onto Mars' surface would remove the bolts holding the units together. Then a pre-deployed crane would raise the passenger unit and place it on the ground in a desirable location. The passengers have now landed on Mars along with a permanent habitat unit complete with ECLSS. The propulsion unit, now rather lightweight, could then be launched back to Earth and reused. Note that the heat shield on the underbelly also returns.

This system could also pre-deploy habitats on Mars prior to the first human landing.

As more colonists arrive and build ISRU-based habitats, these original habs would continue to be employed as backup in case of emergency or simply additional housing to give colonists more living space. Also note that not all habs would be permanently located on Mars; some would be launched back to Earth with persons wishing to return.

A cargo version of MCT could also perform double-duty. Once landed, the cargo unit would likewise be removed and set on the ground. Unloading cargo would proceed from ground level to ground level. After unloading, the cargo hatch door(s) would be closed and permanently welded shut, both the interior pressure vessel and the exterior shell. Now we have a sizable tank for storing propellants or other liquids produced on Mars.

Do you think this is feasible?
« Last Edit: 06/27/2015 01:08 PM by Ionmars »
* Mars' orbit: a convenient service station for an asteroid-sized spaceship en-route to Ceres. *

Offline CyclerPilot

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Re: MCT Speculation and Discussion Thread 4
« Reply #217 on: 06/23/2015 01:53 AM »
Impaler and CyclerPilot, this idea should be compatible with the COOPS you are developing:

Consider the passenger  version of MCT, the trans-Hab and the surface-Hab to be all the same unit. By this I mean that the passenger section and the propulsion section of MCT would be separate and functionally independent units, i.e. propulsion avionics entirely in the propulsion unit and ECLSS components entirely within the passenger unit.. The passenger unit would sit on top of the propulsion unit, which sports a wide heat shield on its underbelly for EDL. The bottom rim of the passenger unit would be joined to the top rim of the propulsion unit only by a ring of bolts through both rims.

Passengers would ride in this vehicle from Earth and land on Mars' surface. A mobile robotic arm that was previously deployed onto Mars' surface would remove the bolts holding the units together. Then a pre-deployed crane would raise the passenger unit and place it on the ground in a desirable location. The passengers have now landed on Mars along with a permanent habitat unit complete with ECLSS. The propulsion unit, now rather lightweight, could then be launched back to Earth and reused. Note that the heat shield on the underbelly also returns.

This system could also pre-deploy habitats on Mars prior to the first human landing.

As more colonists arrive and build ISRU-based habitats, these original habs would continue to be employed as backup in case of emergency or simply additional housing to give colonists more living space. Also note that not all habs would be permanently located on Mars; some would be launched back to Earth with persons wishing to return.

A cargo version of MCT could also perform double-duty. Once landed, the cargo unit would likewise be removed and set on the ground. Unloading cargo would proceed from ground level to ground level. After unloading, the cargo hatch door(s) would be closed and permanently welded shut, both the interior pressure vessel and the exterior shell. Now we have a sizable tank for storing propellants or other liquids produced on Mars.

Do you think this is feasible?
Possible yes.  Here is a LINK to my old design with one big raptor.  Very similar to what you proposed.  My hab was detachable but for purposes of a LAS.  I never thought of leaving it behind.

The design (yours or mine) has a few shortcomings.

A bottom heat shield has to have a very large diameter to provide enough deltaV for 100 tons of cargo and the craft that contains it.  It also has too many seams to leave an opening for the engine bell and inner stage.  These seams need to be closed in space.  This adds a huge LOC risk.

A new (but modest) aero shell would be needed for mars assent.

Need to leave the hab on some return flight to return humans.

LAS escape pod is pretty heavy on mine(contains all cargo, ECLSS, ect).  Non existent on yours as far as I can tell.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #218 on: 06/23/2015 02:41 AM »
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.  Likewise their would need to be yet more on the now exposed top of the propulsion stage to allow it to land on Earth.  Lastly their is no way to send anyone or anything back to Earth which is required.

The crane necessary to remove this habitat would be monstrous, and it would need to be mobile both before and AFTER picking up the habitat for it to do anything other then put it on the ground right next to the propulsion section which needs to blast off again, a very bad place to be.  The crane would have a higher mass then what it is lifting and would be extremely dangerous.


I'm proposing a habitat that is INSIDE the lander and deployed by WHEELS down a ramp, I can't see anything being simpler then that, and am perplexed why anyone feels this needs improving.

Offline Oli

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Re: MCT Speculation and Discussion Thread 4
« Reply #219 on: 06/23/2015 03:38 AM »
Direct-return vehicles are essentially a dead-end configuration because they have a low maximum flight rate, so why go down that path.

But SEP stages and transit habs also have a low flight rate. So replacing a direct-return MCT with SEP, transit hab and a smaller MCT lander does not seem to be a win.

Any architecture which involves space-only or Mars-only stages has to explain how they will be maintained in space or on Mars.

- How about not having to design a huge jack of all trades space vehicle with razor thin margins? I think there's a history of great ambition leading to such projects in space flight. We all know how they ended.

- I think NASA considers reusing Habitat, SEP and pressure-fed hypergolic propulsion because these technologies have proven their durability respectively in-space maintainability. I'd say expendable Mars landers would be perfectly fine until a Mars colony is big enough to refurbish them with spare parts delivered from Earth.

« Last Edit: 06/23/2015 03:40 AM by Oli »

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