Author Topic: MCT Speculation and Discussion Thread 3  (Read 348150 times)

Offline sheltonjr

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Re: MCT Speculation and Discussion Thread 3
« Reply #420 on: 04/28/2015 04:27 pm »
Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.

I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.

Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.

A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.

Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.

The MCT is divided into 6 Floors from bottom to top with the following characteristics:

| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|--------------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

Distributed MCT engines require a minimum thrust around 50 MT and 250 MT Maximum.

What amount did you set aside for ship power generation?  Waste recycling for 100.  Is this amount your 'systems' set aside? 

My concept for power generation is solar panels that would fold up like the petals of a flower from the bottom of the MCT towards the top. The actuator at the bottom would be similar to the ones used by the grid fins, being able to pitch and roll. This would require a stiff composite panel for the solar panels to mount too and perhaps a thin layer of Pica-X to protect it from the heat.  While this does add weight to the MCT, These fold down solar panels would work both in space and on Mars. Being able to roll the panel towards the Sun will increase their performance.

If approximately %50 of the MCT surface area can be covered by these solar panel "petals", They would generate 92KW in Earth orbit and 40KW on Mars. Calculations are based on these solar panels: http://www.azurspace.com/index.php/en/products/products-space/space-solar-cells

The systems level would contain all the systems used on the MCT for ship operations; Flight control computers, cryo-coolers, Communications and telemetry; For Crewed MCTs it would also include all the systems for life support and entertainment including water and air recycling, etc..  They Systems floor would provide hallways to allow easy access to all equipment and spares so the MCT can be maintained by the crew in Space and on Mars. 

I do not think a MCT this size can support 100 people. I would not want to be on it with that many people. The first three floors if only used for crew would be the size of a large house at around 4000 ft2. And Zero gravity will make utilization of that space more efficient. That would be very packed house for 5-6 months.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 3
« Reply #421 on: 04/28/2015 04:50 pm »
We are very close on volume estimates 1500 vs 1700.  The surface areas are 176 vs 230 so your bi-conic has a lower basaltic-coefficient (assuming the same mass), that paired with the superior lift-2-drag ratio of a biconic over a capsule would make for a considerably improve EDL, and reduced retro-propulsion needs.


Which I'm sure is why the biconic shape has been a favorite in many concepts for a Mars lander in many concepts over the years.  Although the traditional capsule shape is what it is becuase it's inherrently self orienting during EDL.  which is why it's been used so often over the years....even on most Mars landers to date.  But a really large lander on Mars has needs that make alternative shapes with other benefits in consideration.


I'm wondering how such a vehicle serves as a 2nd-stage for launch from Earth though.  If you have similar volume for cargo, habitat and systems as I estimate (700 m^3 total) your left with only 1000 MT of propellents.  We know all stages under the MCt will be reusable and if the F9 reusables staging is a reliable indicator then the first stage will only do about 2 km/s (staging at Mach 6), leaving a whopping 7-8 km/s for this 2nd stage vehicle to do.  Full to the brim with propellents it would only be able to do ~140 MT to LEO, minus the 100 MT payload that leaves an impossibly small 40 MT for the dry mass of the MCT.  It seems that a normal 2nd stage is going to be necessary in the stack to deliver 3-4 km/s before the MCT separates and acts as the 3rd stage.

This is my central argument that given the reasonable mass/volume of the MCT as a lander on Mars, it can't do the whole job of being a second stage during Earth launch when it is loaded with cargo.

I agree that 40mt seems a bit lean for dry mass of MCT.  The dry mass of the S-II was 45mt.  And while that's 1960's tech, it was still a fairly well designed/light stage of it's size.  Today they could probably make such a stage a little lighter, but I'd have a hard time thinkign MCT could be less than the mass of the S-II at a minmum.  I'm thinking at least 50-60 for some reason.

I also agree that the booster would stage pretty early, so as to be "low and slow" for RTLS.  That's why I very much like the Saturn INT-21 as an analog here.  The S-1C was a large booster that also staged low and slow.  The S-II was a very large 2nd stage which provided all of the rest of the dV needed to get the payload to LEO.   If INT-21 had every flown as INT-21 anyway.  It essentially did when putting Skylab in orbit.
It was estimated that INT-21 could have put almost 120mt into LEO.  Plus the dry mass of the S-II at 45mt plus (I'm assuming) a couple of tonnes of residuals at SECO.  We'll call that 160mt to LEO in total roughly.
That's be 100mt of cargo plus a 60mt MCT.  Which may be a little skinny still, but now we're at a very plausible point.
J2 had 40s better ISP than Raptor, so MCT would need a little more propellant to get that same 160mt gross to LEO.  But LCH4 is a lot more dense than LH2. 

So you calculated 140mt to LEO.  The good news is we're actually pretty close to 160mt (minimum) with that.  We just need to get another 20mt or 30mt to LEO.  So as an integrated spacecraft/upper stage, how large does it need to be to get there?  Play with MCT/S-II analog's size until you get say 160mt to LEO, or 170mt.  What size is that stage now?  If it's too tall to be a stable lander, we can make it 11m instead of 10m wide, or even 12m.  Again, just using the S-II as an analog to demonstrate that MCT might not need to be some 15+m wide spacecraft.  10m may work, or just a bit wider.
The booster's width and height then would just be set to match MCT once MCT's dimensions are established.

Keep in mind that until we hear something to the contrary, I think we have to assume that MCT will take itself from the surface of Mars all the way back to the surface of Earth itself.  So we're talking a big stage regardless.  Even if there were 2 stages under the MCT spacecraft, it would still need to be very large in order to do that.  Perhaps a bright bulb could calculate the volume and mass of methalox needed to get say 60mt of dry mass directly from the surface of Mars to the surface of Earth.  Let's see what we are talking about there, and then compare it with our methalox mass and volume needs to get 160mt gross from "low and slow" staging (2 km/s?) to LEO.  Assuming an integrated 2nd stage/MCT, MCT would need enough propellant capacity to do both of those functions, so whichever one is the greater propellant needed would be the driver in the size of MCT's tanks.




Offline Lobo

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Re: MCT Speculation and Discussion Thread 3
« Reply #422 on: 04/28/2015 06:09 pm »

With regards to where the heat shields went, they either were retracted back into the vehicle or were deployed and disposed during Martian atmospheric entry.  Obviously they're not perfect analogies for an MCT design, but they should prove that capsule designs are a very plausible MCT design option.  Alterations can be made after all!


Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.
I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.
Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.
A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.
Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.


I want to point out another reason I don't think MCT will be a capsule shape.

Unlike every other capsule that's been designed in the history of space flight intended to enter into a planet with an atmosphere...MCT will have to get itself back off the ground.  Apollo didn't have to.  Dragon doesn't have to, CST-100 won't have to, Viking and the MER's and MSR didn't have to, etc.  So the capsule shape didn't have to house really large propellant tanks.  Just some small RCS thruster propellant tanks that can be stuffed into the spare geometric volume of the shape. 

But MCT will need a LOT of propellant to get itself back to Earth.  It'll in fact, be mainly a big fuel tank with a crew cabin bolted on, as opposed to most capsules to date which have been crew cabins (or cago volume) with a heat shield bolted on.  What's the most geometrically efficient shape to have large volumes of two propellants?  Cylinders....which is why almost all rocket stages have always been cylinders (with a few exceptions).   It'll be mainly a rocket stage...with a crew cabin bolted on.  Which is also why I think it'll do double duty as MCT's 2nd stage for ascent to LEO as well as get itself to Mars and back to Earth.  It'll already be essentailly a rocket stage by necessity.  Why pay to develop a separate dedicated 2nd stage for MCT.
A biconic aeroshell shape is also a cylinder.   Thus...logic would lean towards MCT being a cylindrical shape with a biconic EDL profile, as opposed to a capsule with a blunt body EDL profile.

So it's not just because you don't have to have doors in your heatshield for the engines with a cylindrical biconic shape....that's just a bonus.  It's not just that the biconinc has more surface area and better L/D ratio so it can milk more dV out of the atmosphere with more mild deceleration...that's just another bonus.  It's not just that you don't have to risk lighting your Raptor main engines on the Mars sruface and risk debris being blown up into your bottom heat shield damaging it....that's just another bonus with the TPS on the side. etc.

It's that MCT will be a big fuel tank with a crew cabin bolted on (top or bottom), and a cylinder is the most efficient geometry for a bi-propellant tank....and fortunately that happns to make a biconic shape.
With a giant capsule, you either have tanks with very odd/inefficient/difficult geometries to utilize that internal volume, or you have cylindrical tanks wrapped by a capsule shell...which then leaves a lot of inefficient internal volume around the tanks.  And as we know, in a space craft, no cubic inch of internal volume is desired to be wasted.

So let's not get too distracted with the concept of doors in the heat shield for the engines.  I don't think that's a show stopper given sufficient time and money during development.  But I also think it'd be desriable to avoid if possible, for the various reasons discussed.

NOTE:  I understand that this is not a true biconic shape.  I'm just using it as a reference term.  It'd be technically a "biconic nosed cylinder" I suppose.  Or a "blunt nosed cylinder", depending on what's determined to be better.

So, although the better L/D ratio of the biconic over the capsule is a bonus, not the driving factor in my opinion, I did find this bit interesting from wikipedia.

Quote
Biconic:  The biconic is a sphere-cone with an additional frustum attached. The biconic offers a significantly improved L/D ratio. A biconic designed for Mars aerocapture typically has an L/D of approximately 1.0 compared to an L/D of 0.368 for the Apollo-CM. The higher L/D makes a biconic shape better suited for transporting people to Mars due to the lower peak deceleration.
Arguably, the most significant biconic ever flown was the Advanced Maneuverable Reentry Vehicle (AMaRV). Four AMaRVs were made by the McDonnell-Douglas Corp. and represented a significant leap in RV sophistication. Three of the AMaRVs were launched by Minuteman-1 ICBMs on 20 December 1979, 8 October 1980 and 4 October 1981. AMaRV had an entry mass of approximately 470 kg, a nose radius of 2.34 cm, a forward frustum half-angle of 10.4°, an inter-frustum radius of 14.6 cm, aft frustum half angle of 6°, and an axial length of 2.079 meters. No accurate diagram or picture of AMaRV has ever appeared in the open literature. However, a schematic sketch of an AMaRV-like vehicle along with trajectory plots showing hairpin turns has been published.[12]
 
The DC-X, shown during its first flight, was a prototype single stage to orbit vehicle, and used a biconic shape similar to AMaRV.
Opportunity rover's heat shield lying inverted on the surface of Mars.AMaRV's attitude was controlled through a split body flap (also called a "split-windward flap") along with two yaw flaps mounted on the vehicle's sides. Hydraulic actuation was used for controlling the flaps. AMaRV was guided by a fully autonomous navigation system designed for evading anti-ballistic missile (ABM) interception. The McDonnell Douglas DC-X (also a biconic) was essentially a scaled up version of AMaRV. AMaRV and the DC-X also served as the basis for an unsuccessful proposal for what eventually became the Lockheed Martin X-33.

Another interesting bit from there was how apparently the AMaRV was able to make hairpin turns.  That indicates a pretty high level of aerodynamic steerability is possible with the shape. 
« Last Edit: 04/28/2015 06:13 pm by Lobo »

Offline TomH

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Re: MCT Speculation and Discussion Thread 3
« Reply #423 on: 04/28/2015 07:43 pm »
| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|-----------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

The CH4 is the fuel. You are using that word to mean the fuel and the oxidizer, which together are known as the propellant. You will be taken seriously by no one if you don't distinguish correctly between fuel and propellant.
« Last Edit: 04/28/2015 07:46 pm by TomH »

Offline BobHk

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Re: MCT Speculation and Discussion Thread 3
« Reply #424 on: 04/28/2015 09:37 pm »
Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.

I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.

Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.

A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.

Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.

The MCT is divided into 6 Floors from bottom to top with the following characteristics:

| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|--------------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

Distributed MCT engines require a minimum thrust around 50 MT and 250 MT Maximum.

What amount did you set aside for ship power generation?  Waste recycling for 100.  Is this amount your 'systems' set aside? 

My concept for power generation is solar panels that would fold up like the petals of a flower from the bottom of the MCT towards the top. The actuator at the bottom would be similar to the ones used by the grid fins, being able to pitch and roll. This would require a stiff composite panel for the solar panels to mount too and perhaps a thin layer of Pica-X to protect it from the heat.  While this does add weight to the MCT, These fold down solar panels would work both in space and on Mars. Being able to roll the panel towards the Sun will increase their performance.

If approximately %50 of the MCT surface area can be covered by these solar panel "petals", They would generate 92KW in Earth orbit and 40KW on Mars. Calculations are based on these solar panels: http://www.azurspace.com/index.php/en/products/products-space/space-solar-cells

The systems level would contain all the systems used on the MCT for ship operations; Flight control computers, cryo-coolers, Communications and telemetry; For Crewed MCTs it would also include all the systems for life support and entertainment including water and air recycling, etc..  They Systems floor would provide hallways to allow easy access to all equipment and spares so the MCT can be maintained by the crew in Space and on Mars. 

I do not think a MCT this size can support 100 people. I would not want to be on it with that many people. The first three floors if only used for crew would be the size of a large house at around 4000 ft2. And Zero gravity will make utilization of that space more efficient. That would be very packed house for 5-6 months.

Thanks for your response.  Have you considered reduced solar generation on Mars due to location/weather (seasonally longer periods of darkness depending on location, sand storms lasting longer than a day) and what they're storing the energy in when the sun isn't present, like battery systems and their mass/volume?  What would you consider a reasonable core temperature for MCT and what amount of power generation on planet would be needed to keep the ship livable and functional with power generation left over for other uses? 

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 3
« Reply #425 on: 04/29/2015 02:43 am »

With regards to where the heat shields went, they either were retracted back into the vehicle or were deployed and disposed during Martian atmospheric entry.  Obviously they're not perfect analogies for an MCT design, but they should prove that capsule designs are a very plausible MCT design option.  Alterations can be made after all!


Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.
I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.
Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.
A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.
Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.


I want to point out another reason I don't think MCT will be a capsule shape.

Unlike every other capsule that's been designed in the history of space flight intended to enter into a planet with an atmosphere...MCT will have to get itself back off the ground.  Apollo didn't have to.  Dragon doesn't have to, CST-100 won't have to, Viking and the MER's and MSR didn't have to, etc.  So the capsule shape didn't have to house really large propellant tanks.  Just some small RCS thruster propellant tanks that can be stuffed into the spare geometric volume of the shape. 

But MCT will need a LOT of propellant to get itself back to Earth.  It'll in fact, be mainly a big fuel tank with a crew cabin bolted on, as opposed to most capsules to date which have been crew cabins (or cago volume) with a heat shield bolted on.  What's the most geometrically efficient shape to have large volumes of two propellants?  Cylinders....which is why almost all rocket stages have always been cylinders (with a few exceptions).   It'll be mainly a rocket stage...with a crew cabin bolted on.  Which is also why I think it'll do double duty as MCT's 2nd stage for ascent to LEO as well as get itself to Mars and back to Earth.  It'll already be essentailly a rocket stage by necessity.  Why pay to develop a separate dedicated 2nd stage for MCT.
A biconic aeroshell shape is also a cylinder.   Thus...logic would lean towards MCT being a cylindrical shape with a biconic EDL profile, as opposed to a capsule with a blunt body EDL profile.

So it's not just because you don't have to have doors in your heatshield for the engines with a cylindrical biconic shape....that's just a bonus.  It's not just that the biconinc has more surface area and better L/D ratio so it can milk more dV out of the atmosphere with more mild deceleration...that's just another bonus.  It's not just that you don't have to risk lighting your Raptor main engines on the Mars sruface and risk debris being blown up into your bottom heat shield damaging it....that's just another bonus with the TPS on the side. etc.

It's that MCT will be a big fuel tank with a crew cabin bolted on (top or bottom), and a cylinder is the most efficient geometry for a bi-propellant tank....and fortunately that happns to make a biconic shape.
With a giant capsule, you either have tanks with very odd/inefficient/difficult geometries to utilize that internal volume, or you have cylindrical tanks wrapped by a capsule shell...which then leaves a lot of inefficient internal volume around the tanks.  And as we know, in a space craft, no cubic inch of internal volume is desired to be wasted.

So let's not get too distracted with the concept of doors in the heat shield for the engines.  I don't think that's a show stopper given sufficient time and money during development.  But I also think it'd be desriable to avoid if possible, for the various reasons discussed.

NOTE:  I understand that this is not a true biconic shape.  I'm just using it as a reference term.  It'd be technically a "biconic nosed cylinder" I suppose.  Or a "blunt nosed cylinder", depending on what's determined to be better.

So, although the better L/D ratio of the biconic over the capsule is a bonus, not the driving factor in my opinion, I did find this bit interesting from wikipedia.

Quote
Biconic:  The biconic is a sphere-cone with an additional frustum attached. The biconic offers a significantly improved L/D ratio. A biconic designed for Mars aerocapture typically has an L/D of approximately 1.0 compared to an L/D of 0.368 for the Apollo-CM. The higher L/D makes a biconic shape better suited for transporting people to Mars due to the lower peak deceleration.
Arguably, the most significant biconic ever flown was the Advanced Maneuverable Reentry Vehicle (AMaRV). Four AMaRVs were made by the McDonnell-Douglas Corp. and represented a significant leap in RV sophistication. Three of the AMaRVs were launched by Minuteman-1 ICBMs on 20 December 1979, 8 October 1980 and 4 October 1981. AMaRV had an entry mass of approximately 470 kg, a nose radius of 2.34 cm, a forward frustum half-angle of 10.4°, an inter-frustum radius of 14.6 cm, aft frustum half angle of 6°, and an axial length of 2.079 meters. No accurate diagram or picture of AMaRV has ever appeared in the open literature. However, a schematic sketch of an AMaRV-like vehicle along with trajectory plots showing hairpin turns has been published.[12]
 
The DC-X, shown during its first flight, was a prototype single stage to orbit vehicle, and used a biconic shape similar to AMaRV.
Opportunity rover's heat shield lying inverted on the surface of Mars.AMaRV's attitude was controlled through a split body flap (also called a "split-windward flap") along with two yaw flaps mounted on the vehicle's sides. Hydraulic actuation was used for controlling the flaps. AMaRV was guided by a fully autonomous navigation system designed for evading anti-ballistic missile (ABM) interception. The McDonnell Douglas DC-X (also a biconic) was essentially a scaled up version of AMaRV. AMaRV and the DC-X also served as the basis for an unsuccessful proposal for what eventually became the Lockheed Martin X-33.

Another interesting bit from there was how apparently the AMaRV was able to make hairpin turns.  That indicates a pretty high level of aerodynamic steerability is possible with the shape.
I generally agree, however Mars has really thin atmosphere. A capsule shape may not be a problem.


But yes, I agree that we should be thinking of MCT mostly as what a reusable upper stage might look like (with a crew cabin bolted on--or likely integrated somewhat).
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Offline CyclerPilot

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Re: MCT Speculation and Discussion Thread 3
« Reply #426 on: 04/29/2015 04:27 am »
Someone asked up thread how big the tanks have to be to return a 60 ton dry mass MCT to Earth's surface.

Assuming 8.2 km/s dv (4.4 km/s Mars launch, 3.8 km/s TEI).  I am assuming a non-optimum launch window because the MCT needs to return in the same synod.  I also assume a 380 ISP vac-optimised Raptor.

There needs to be prop reserved for EDL on Earth, likely not done with a vac-optimised 380 ISP raptor, but less effiecent thrusters.  I used 15 tons (providing 700 m/s to an empty MCT at 320 s ISP) for a total of 75 tons through TEI.

Mass of prop required?  603 tons.  Add 8 tons of prop for every ton of cargo you want to bring back. 

This huge prop requirement has several effects on the architecture.  The ISRU infrastructure on Mars needs to be massive.  Also you can see how critcal minimizing dry mass will be.   The MCT will be stripped on mars not only to supply the martians, but to reduce return trip dry mass.  I personally think the crew MCT will have a modular/removable hab .

Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #427 on: 04/29/2015 04:55 am »
Lobo makes a good case for a bi-conic shape, and really when were debating between a Dragon style capsule with a 15 degree wall slope and a bi-conic with perhaps 10 degrees the difference is really small.  It's more a debate between the orientation of the vehicle during entry, either bottom-forward or side-forward.  Given the similar volumes discussed the final diameter and shape of the MCT is really splitting hairs.

I think the disagreement is more centered on what the vehicle will be CAPABLE of largely due to disagreements over the dry mass estimate.  I simply don't find dry masses under 100 mT credible given what MCT needs to do and the volume it will have.  Comparisons to Staurn V stages don't seem credible when these were expendable rocket stages that are hold nothing but propellents and are not capable of EDL on Mars.  I feel that only extrapolations from manned craft that carry cargo and perform atmospheric re-entry are logical (Dragon, Orion, Shuttle Orbiter all of these would make more sense), simply saying that MCT will do the ADDITIONAL task of being a second stage doesn't make it have the mass/volume ratio of a traditional 2nd stage, it just makes it a harder vehicle to engineer as it has more demands put upon it.

Also I find some flaws in the extrapolations from the Saturn 2nd Stage.  Lobo states this stage completes the delivery to LEO, it dose not, at 2nd stage engine cut off the vehicle is only going 7 km/s and a burn of the 3rd stage is necessary to actually reach LEO, though it is a modest one of just under 1 km/s.  In addition the first stage of the Saturn V stages at mach 8 rather then the expected BFR staging at mach 6 due to reusability constraints, while this is still 'lower and slower' then F9 current staging it is not a match for BFR.  Together this means the S-II had 1.5 km/s less Delta-V to achieve then the proposed 2nd-stage MCT would need to do to get to orbit.  Lastly Lobo states the INT-21 would have delivered 140 mT to orbit, but it was actually rated at 115 mT.

All together this just seems a bridge too far for me to believe the MCT can be combined with it's 2nd stage, though I think it could do considerable 3rd-stage duty and thus significantly reduce the ultimate Delta-V burden on the 2nd stage.
« Last Edit: 04/29/2015 05:00 am by Impaler »

Offline symbios

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Re: MCT Speculation and Discussion Thread 3
« Reply #428 on: 04/29/2015 08:52 am »
Someone asked up thread how big the tanks have to be to return a 60 ton dry mass MCT to Earth's surface.

Assuming 8.2 km/s dv (4.4 km/s Mars launch, 3.8 km/s TEI).  I am assuming a non-optimum launch window because the MCT needs to return in the same synod.  I also assume a 380 ISP vac-optimised Raptor.

There needs to be prop reserved for EDL on Earth, likely not done with a vac-optimised 380 ISP raptor, but less effiecent thrusters.  I used 15 tons (providing 700 m/s to an empty MCT at 320 s ISP) for a total of 75 tons through TEI.

Mass of prop required?  603 tons.  Add 8 tons of prop for every ton of cargo you want to bring back. 

This huge prop requirement has several effects on the architecture.  The ISRU infrastructure on Mars needs to be massive.  Also you can see how critcal minimizing dry mass will be.   The MCT will be stripped on mars not only to supply the martians, but to reduce return trip dry mass.  I personally think the crew MCT will have a modular/removable hab .

Size wise on a vehicle with a diameter of 10 m you get about ~700 m2 of volume out of a 10 m high section depending on the angle of the walls. So is this a reasonable volume out of the MCT?
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Offline GORDAP

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Re: MCT Speculation and Discussion Thread 3
« Reply #429 on: 04/29/2015 11:18 am »
Someone asked up thread how big the tanks have to be to return a 60 ton dry mass MCT to Earth's surface.

Assuming 8.2 km/s dv (4.4 km/s Mars launch, 3.8 km/s TEI).  I am assuming a non-optimum launch window because the MCT needs to return in the same synod.  I also assume a 380 ISP vac-optimised Raptor.

There needs to be prop reserved for EDL on Earth, likely not done with a vac-optimised 380 ISP raptor, but less effiecent thrusters.  I used 15 tons (providing 700 m/s to an empty MCT at 320 s ISP) for a total of 75 tons through TEI.

Mass of prop required?  603 tons.  Add 8 tons of prop for every ton of cargo you want to bring back. 

This huge prop requirement has several effects on the architecture.  The ISRU infrastructure on Mars needs to be massive.  Also you can see how critcal minimizing dry mass will be.   The MCT will be stripped on mars not only to supply the martians, but to reduce return trip dry mass.  I personally think the crew MCT will have a modular/removable hab .

Nit, why does everyone insist the MCT will go into Mars orbit and then do a TEI burn?  I think there is a significant savings (10-20%?) in DV by going directly from Mars surface to Earth.  And with the exponential nature of the rocket equation, doesn't this translate into even bigger savings in fuel?  It just seems to me that there is absolutely no reason to loiter in Mars orbit before returning to Earth.  Sorta like me taking off on a cross country trip, but first circling my city a few times :-) 

CyberPilot, how much better do your numbers look if they do a direct launch from Mars to Earth?

Offline sheltonjr

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Re: MCT Speculation and Discussion Thread 3
« Reply #430 on: 04/29/2015 11:43 am »
| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|-----------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

The CH4 is the fuel. You are using that word to mean the fuel and the oxidizer, which together are known as the propellant. You will be taken seriously by no one if you don't distinguish correctly between fuel and propellant.

Ok, Are you a Lawyer?  :D  CH4 & LOX are a Bi-propellant, And I usually consider a propellant to be used for SEP (Argon, Xenon) or NEP systems (Hydrogen).  Fuel is a lot shorter and I believe understood. You saw how many times I used it.

Offline sheltonjr

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Re: MCT Speculation and Discussion Thread 3
« Reply #431 on: 04/29/2015 12:17 pm »
My concept for power generation is solar panels that would fold up like the petals of a flower from the bottom of the MCT towards the top. The actuator at the bottom would be similar to the ones used by the grid fins, being able to pitch and roll. This would require a stiff composite panel for the solar panels to mount too and perhaps a thin layer of Pica-X to protect it from the heat.  While this does add weight to the MCT, These fold down solar panels would work both in space and on Mars. Being able to roll the panel towards the Sun will increase their performance.

If approximately %50 of the MCT surface area can be covered by these solar panel "petals", They would generate 92KW in Earth orbit and 40KW on Mars. Calculations are based on these solar panels: http://www.azurspace.com/index.php/en/products/products-space/space-solar-cells

The systems level would contain all the systems used on the MCT for ship operations; Flight control computers, cryo-coolers, Communications and telemetry; For Crewed MCTs it would also include all the systems for life support and entertainment including water and air recycling, etc..  They Systems floor would provide hallways to allow easy access to all equipment and spares so the MCT can be maintained by the crew in Space and on Mars. 

I do not think a MCT this size can support 100 people. I would not want to be on it with that many people. The first three floors if only used for crew would be the size of a large house at around 4000 ft2. And Zero gravity will make utilization of that space more efficient. That would be very packed house for 5-6 months.

Thanks for your response.  Have you considered reduced solar generation on Mars due to location/weather (seasonally longer periods of darkness depending on location, sand storms lasting longer than a day) and what they're storing the energy in when the sun isn't present, like battery systems and their mass/volume?  What would you consider a reasonable core temperature for MCT and what amount of power generation on planet would be needed to keep the ship livable and functional with power generation left over for other uses? 

I have only done scratch the surface type of engineering to see what is feasible. From my analysis I believe that Elon and SpaceX may get the MCT solution to close. Though it will be close. 165MT MCT & Payload will take 3 BFR launches to mount an expedition to Mars. 1 MCT & 2 for Fuel.  If MCT mass grows then payload may need to decrease. Adding a third refueling BFR and increasing the size of the the already huge MCT, And it should be doable, At increased cost.

As for solar energy on Mars, Having fold-down petals on the outside of the MCT can be quickly used for both in space and on Mars. If SpaceX does what I am proposing they would need to figure out all the details that you mentioned. They may need to also add ground solar. 

The question I was trying to answer for myself for solar power, is it enough for a unmanned ISRU MCT to generate 470MT of CH4 & LOX in 25 months fully autonomously.  Peak solar power of 40KW and working with the daily temperature variations on Mars may be enough, but I do not have the time or the knowledge to know that with any certainty.

ISRU of propellant on Mars is the pivotal technology to make the MCT system work. My guess is the first MCT to land on Mars will be a ISRU MCT.  With about 1000 m3 of volume to utilize. The first MCT will have 2-3 Sabatier reactors and possibly 4 sources of hydrogen to experiment with. 1) High pressure Hydrogen brought from Earth, 2) Water brought from Earth, 3) Water from the atmosphere, 4) Water dug from the surface.

1-2 Rovers with back-hoes will also be included for scouting the area and digging trenches to look for water to deposit in the MCT.

If all goes to plan, the first MCT will have enough fuel for the second MCT to land to return to Earth and validate the MCT for the Earth return part of the mission.

Autonomously refueling between the two MCT should be a fun. A long hose, precision landing and reliable and capable rovers.

Offline spacenut

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Re: MCT Speculation and Discussion Thread 3
« Reply #432 on: 04/29/2015 01:21 pm »
Why couldn't the MCT actually be a two piece lander, that the bottom half stays on Mars as habitat and/or water, methane, or oxygen storage?  Either engines could be mounted on the sides or in the center that would stay with the upper half returning to earth.  The bottom half could be around the returning center.  It could be sealed over after returning ship detaches for internal living quarters.  Outside previous methane and oxygen tanks could be refilled with ISRU made fuel and oxygen which would offer some radiation protection.  If the lander is high enough off the ground, it could also be sealed around the outside bottom for underneath living areas, vehicle storage and compression/decompression chamber for EVA's on the surface to mine for water.  Why not just bring the center or top half of the spacecraft back to earth to be reused?  Less building would be required, just modification of the bottom or outer ring of the spacecraft.  Less fuel needed for return. 

Offline FishInferno

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Re: MCT Speculation and Discussion Thread 3
« Reply #433 on: 04/29/2015 01:46 pm »
Why couldn't the MCT actually be a two piece lander, that the bottom half stays on Mars as habitat and/or water, methane, or oxygen storage?  Either engines could be mounted on the sides or in the center that would stay with the upper half returning to earth.  The bottom half could be around the returning center.  It could be sealed over after returning ship detaches for internal living quarters.  Outside previous methane and oxygen tanks could be refilled with ISRU made fuel and oxygen which would offer some radiation protection.  If the lander is high enough off the ground, it could also be sealed around the outside bottom for underneath living areas, vehicle storage and compression/decompression chamber for EVA's on the surface to mine for water.  Why not just bring the center or top half of the spacecraft back to earth to be reused?  Less building would be required, just modification of the bottom or outer ring of the spacecraft.  Less fuel needed for return.

MCT is supposed to be completely reusable, and a 2-stage lander prohibits that.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 3
« Reply #434 on: 04/29/2015 02:29 pm »
It could be possible that a large hab or something fills the payload bay for trips that are full (100 passengers) and is left on the surface to grow the colony, but that for return trips, people have to be satisfied with smaller quarters.

I mean, we know that MCT also has to have very significant payload capabilities, so that should be a possibility even if MCT were designed with enough room for 100 passengers all by itself.
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Offline spacenut

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Re: MCT Speculation and Discussion Thread 3
« Reply #435 on: 04/29/2015 02:32 pm »
I know the MCT is supposed to be completely reusable.  However I was thinking hauling all the extra empty weight from Mars could be a waste of fuel, energy and time to make fuel.  A lot of tonnage of living space and fuel storage will be needed.  Why not used part of what was brought.  For instance, if say 50% of the fuel in LEO is used for TMI, 30% for landing on Mars, and 20% to return to Earth, 80% of the vehicle volume is empty and unused after landing on Mars.  One vehicle could make fuel and oxygen to store in the empty tanks.  One vehicle could used vented and dried out tanks for habitat, food storage, water storage (they are going to need a lot of water), growing plants, etc.  No engines would stay on Mars as they would be attached to the return vehicle.

 A lot of methane might be needed for melting Mars regolith for glass, aluminum, soft metals, to make objects and parts needed for colony construction.  So a lot of storage would be needed.  Methane could also be used in very hot melting ovens for harder metals such as iron and steel manufacturing.  More carbon and hydrogen could be added to methane for heavier fuels, butane, propane, even kerosene and diesel for hotter burning fuels needed for manufacturing. 

All this fuel and manufacturing will need storage tanks that could be provided by a two piece MCT. 

In my thinking, the MCT would have to be wide, 12-15m at least for this.  With the top portion or center portion a 5m diameter cylinder type unit return craft. 

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 3
« Reply #436 on: 04/29/2015 03:24 pm »
It could be possible that a large hab or something fills the payload bay for trips that are full (100 passengers) and is left on the surface to grow the colony, but that for return trips, people have to be satisfied with smaller quarters.

I mean, we know that MCT also has to have very significant payload capabilities, so that should be a possibility even if MCT were designed with enough room for 100 passengers all by itself.

I think they will not design MCT with 100 passengers going back to earth in mind. Early missions where everybody returns at some time will have a much smaller number of passengers. 100 person flights will be for colonists with mostly no intention to return.

Once the population rises above 1000 or several thousand it may no longer be possible to return everybody to earth at all. But that would be at a time where mostly selfsustenance is established.


Offline Ben the Space Brit

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Re: MCT Speculation and Discussion Thread 3
« Reply #437 on: 04/29/2015 03:32 pm »
My feeling is that MCT will be a LEO-to-Mars Surface architecture that will be customised with mission modules and extra fuel tanks for various different missions. For example, a 100-passenger flight may literally be a flying barrack block that will just land at the destination site, roll over, hook up to the rest of the colony and stay there. Engineers would come along later, remove the Raptor/Methane Merlin propulsion module and move it off for recycling elsewhere.

I think they will not design MCT with 100 passengers going back to earth in mind. Early missions where everybody returns at some time will have a much smaller number of passengers. 100 person flights will be for colonists with mostly no intention to return.

Once the population rises above 1000 or several thousand it may no longer be possible to return everybody to earth at all. But that would be at a time where mostly self-sustenance is established

Agreed; early missions may have as little as six crew (exploration/survey with the majority of the payload made up with things like a pressurised long-haul rover and sensors) with early colonial missions being around 20 personnel, mostly engineers. Some will remain on Mars for multiple MCT visits but the majority would return back to Earth every flight.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 3
« Reply #438 on: 04/29/2015 04:11 pm »
If MCT doesn't launch with people from Earth, then you're talking about doubling the development cost and probably also the per ticket price.

Refueling in Earth orbit, absolutely.
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Offline TomH

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Re: MCT Speculation and Discussion Thread 3
« Reply #439 on: 04/29/2015 04:18 pm »
I usually consider a propellant to be used for SEP (Argon, Xenon) or NEP systems (Hydrogen).  Fuel is a lot shorter and I believe understood. You saw how many times I used it.

Those gasses are the propellant in SEP, however regarding chemical propulsion, you are incorrect. The fuel and oxidizer are not together called fuel. They are propellant. The CH4 is the fuel and the LOx is the oxidizer. It's just that plain and simple. You do not get to redefine these things just because you feel like it. And again, if you insist on using terminology incorrectly, you will not be taken seriously. Rather than being defensive, wouldn't it be easier just to say, You are right; thanks for the correction? Fuel is shorter, however prop, the accepted abbreviation for propellant, is the same length.

See Robotbeat's closing tag line one post above.
« Last Edit: 04/29/2015 04:59 pm by TomH »

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