Quote from: sheltonjr on 04/25/2015 07:46 pmHere 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 MTCargo <= 100 MTTotal Fuel = 473 MTMCT 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?
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 MTCargo <= 100 MTTotal Fuel = 473 MTMCT 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.
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.
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.
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.
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.
| 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 MTCargo <= 100 MTTotal Fuel = 473 MTMCT 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.
Quote from: BobHk on 04/26/2015 07:01 pmQuote from: sheltonjr on 04/25/2015 07:46 pmHere 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 MTCargo <= 100 MTTotal Fuel = 473 MTMCT 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-cellsThe 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.
Quote from: Hyperion5 on 04/27/2015 02:17 amWith 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!Quote from: sheltonjr on 04/25/2015 07:46 pmHere 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.QuoteBiconic: 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.
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 .
Quote from: sheltonjr on 04/25/2015 07:46 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 MTCargo <= 100 MTTotal Fuel = 473 MTMCT 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.
Quote from: sheltonjr on 04/28/2015 04:27 pmMy 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-cellsThe 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?
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-cellsThe 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.
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.
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 self-sustenance is established
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.