Author Topic: MCT Speculation and Discussion Thread 3  (Read 348142 times)

Offline Ben the Space Brit

  • Senior Member
  • *****
  • Posts: 7206
  • A spaceflight fan
  • London, UK
  • Liked: 806
  • Likes Given: 900
Re: MCT Speculation and Discussion Thread 3
« Reply #380 on: 04/24/2015 09:21 am »
Personally, I'd have electromechanical wheels in the landing pads so that MCT could taxi itself should it be necessary (say, roll over to the base to mate to a pressurised crew transfer 'sky space bridge'). Think of them as massively scaled-up versions of the propulsion system on MSL and the MERs.

In fact, I'd make that a standard part of any large scale crewed base establishment and support effort. Instead of precision landing, land them just nearby and roll over to a convenient location. Then, when they're empty, roll away to their final storage location or back to the aluminium grid launch pad.
"Oops! I left the silly thing in reverse!" - Duck Dodgers

~*~*~*~

The Space Shuttle Program - 1981-2011

The time for words has passed; The time has come to put up or shut up!
DON'T PROPAGANDISE, FLY!!!

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 6809
  • California
  • Liked: 8485
  • Likes Given: 5384
Re: MCT Speculation and Discussion Thread 3
« Reply #381 on: 04/24/2015 08:29 pm »
Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.

No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.

Offline spacenut

  • Senior Member
  • *****
  • Posts: 5181
  • East Alabama
  • Liked: 2587
  • Likes Given: 2895
Re: MCT Speculation and Discussion Thread 3
« Reply #382 on: 04/24/2015 08:34 pm »
This is why a vehicle or vehicles of some sort should be landed on the first lander to take people and supplies over to wherever robotic equipment has landed to set up housing.  That being said, a 100 ton lander on Mars would weigh 40 tons, but that is still quite heavy.  I think some type of flat plains area should be used for landers. 

Offline llanitedave

  • Senior Member
  • *****
  • Posts: 2286
  • Nevada Desert
  • Liked: 1545
  • Likes Given: 2052
Re: MCT Speculation and Discussion Thread 3
« Reply #383 on: 04/24/2015 10:28 pm »
Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.

No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.


Regardless, Mars wheels are going to have to be mastered if the colony is going to work.  But I agree, the landers shouldn't have to be pulled around.
"I've just abducted an alien -- now what?"

Offline Lobo

  • Senior Member
  • *****
  • Posts: 6915
  • Spokane, WA
  • Liked: 672
  • Likes Given: 437
Re: MCT Speculation and Discussion Thread 3
« Reply #384 on: 04/24/2015 11:58 pm »


Agreed.  So you resolve this by not having the engines in the heat shield at all.  That gets back to the biconic aeroshell with engines at the aft.  Essentially a wingless Spaceshuttle that lands on it's SSME's.

Given the number of designs with engines embedded behind deployable heat shield doors, I would think the "wingless" Space Shuttle design is far from given.  The simplicity of landing with a Dragon-style vertical lander on Mars is not something to be given up lightly.

Well, we can't say anything is a given or not given until SpaceX announces something official.  ;-)

But some of these designed you posted pictures of are comparing apples to Oranges, or are some artist's fiction.  None of the addresses both Issues MCT will have to. 
1)  To be fully reusable, rather than 1-shot.
2)  To get itself back off the surface after it lands. which introduces a lot of issues like a large high performance engine needed, rather than just some low ISP landing thrusters.  All Mars Landers to date had those in one form or another, but none of them had to get back up and back through TEI.  Heck Dragon could land on Mars and it's a capsule.  It just can't get itself back to Earth.  So that's a very different issue that makes capsule designs much more problematic.

Image #1:  I can't see where the heat shield is on this.  The whole bottom is shaded, and I can't see the other side.  But this almost looks like the heat shield is on the other side, given the odd shape of it's bottom.  This looke more like a "wingless shuttle" than a capsule.

Image #2:  Again, where's the heat shield.  Is it on the other side?  Is this a wingless shuttle too?  Or did it have a jettisonable heatshield on the bottom.  If so, then it's not reusable like MCT will be.  MCT won't [likely] be jettisoning it's heat shield.  Otherwise it couldn't land back on earth.  If it were to some how be able to brake itself into LEO (how?) it would need a new heatshield brought up and attached in LEO.  Which seems...unnecessarily complex.

Image #3:  Ok...so what was protecting thos engines during entry?  Did it have a portion of the heat sheild jettison?  And if so, see my comments about that on Image #2.

Image #4:  That image is from "Voyage" by Stephen Baxter.  Great book!  I highly recommend it.  That is the Mars lander Baxter put in his novel.  But that is an expendable two-stage lander like the LEM.  It had a conventional capsule shaped descent module (described by Baxter that it was chosen over other more advanced bionic designs because of it's heritage and that they "know" it would survive, where biconics hadn't been tried before....and if they are going to risk Humans on the very first trip (there was only funding for just one manned trip to Mars) they wanted to go with a proven and stable design. 
It's top and central core were the ascent module.  It blasted off from the capsule bottom back to LMO for rendezvous with the MTV.  It was really an Apollo redux, but with a lander descent module that could withstand atmospheric entery.  Again, this lander can't get itself off the surface whole, only the ascent module portion could get back to LMO, just like the Apollo LEM.  The ascent module engines were protected within the MEV like the LEM AM engine was, and the descent module portion was destoyed when the ascent module blasted off.    The whole lander couldn't take back off again with it's landing thrusters (even if it could have been refueled) and it wasn't reusable.  A good safe one shot design but it would share little in common with what MCT is supposed to do.

A biconic has a lot of advantage over a capsule.  It has a large surface area, so it's TPS doesn't have to be quite as thick and it's terminal velocity is slower.  The engines are in the afte and not exposed to the atmospheric entry, or the supersonic terminal velocity slip stream like those of a capsule.  Although it's not impossible to have doors in your heat shield...the shuttle, X-37B, and Dreamchaser do after all for their landing gear...having a large main engine with a large nozzle which gimbals is more problematic than landing gear.  Assuming such a capsule design would have Superdraco like landing thrusters, and then one or more Raptors tucked behind the heat shield, then you have to retract those doors (that can be done on the ground if there are separate side wall landing thrusters) but then you need enough room for those main engines to gimbal, so the doors need to be much wider than the nozzles.  and then those doors need to close again prior to Earth EDL or else you have the Columbia all over again. 
That's on top of landing gear which will need to come through the heat shield as well.  So there will need to be several doors in the heat shield. 

I'm sure it -could- be made to work.  But why force it when you don't have to?  A biconic "wingless shuttle" design solves all of that.  You can even get around needing to have legs extend through the heat shield on its' side in various ways, include just having jackstand like legs come straight down from the MPS (if the diameter is wide enogh to be stable, similar to your pictures #2)  or you could have blisters around the MPS housing the legs.  With a shape not unlike your image 1.  The legs could fold out from those blisters to give MCT a wider stance on the surface. 
Because while there are vehicles which have had doors in their TPS, there's never been one that's had to close those doors again prior to anther reentry.  They open once after atmospheric entry and that's it.  They're closed on the ground an checked out before sent back up.  So avoiding that dynamic portion of the heat shield and making it all static/passive increases mission safety.
« Last Edit: 04/25/2015 12:12 am by Lobo »

Offline Lobo

  • Senior Member
  • *****
  • Posts: 6915
  • Spokane, WA
  • Liked: 672
  • Likes Given: 437
Re: MCT Speculation and Discussion Thread 3
« Reply #385 on: 04/25/2015 12:03 am »
I also think SpaceX should develop their Raptor engine like the BE-3 that can throttle from 30% to 110%.  That would make for easier landing on earth or Mars.

I believe the RD-180 could throttle down to around 30%.  As Raptor will be staged combustion like the RD-180, I would -assume- that 30% is not too big of an issue for Raptor.  If they do which to land with Raptor, rather than just use it for 2nd stage/in-space/Mars ascent propulsion, then they may be able to design it with a little lower throttle point.  Even if Raptor is inefficient at that low throttle point it's immaterial.  All it's needing to do is get MCT on the surface.  Superdraco thrusters will be inefficient too, but they don't need to have a high ISP, so a low ISP deeply throttle Raptor might not be a major problem.

Again, if they want to try to land on Raptor rather than have some dedicated landing thrusters.

Offline Lobo

  • Senior Member
  • *****
  • Posts: 6915
  • Spokane, WA
  • Liked: 672
  • Likes Given: 437
Re: MCT Speculation and Discussion Thread 3
« Reply #386 on: 04/25/2015 12:11 am »
Sorry about that, thought you were describing a alternative vehicle from the one in your sketches, a bi-conic that lands vertically on it's tail indeed has no heat-shield penetration issues (other then landing legs). 


Ahhh...no problem.

The legs don't necessarily have to protrude through the side heat shield.  I did post one image showing that, but as I said in my reply to Hyperion, there's other ways around it.  In fact, Hyperion posted a couple of pics illustrating those alternatives.

Pic 1:  shows legs deploying through the side TPS.

Pic 2:  Extendable jack-stand like legs that come pretty much straight down.  The H/W ratio of MCT would be a factor in that to make sure it's stance was wide enough.

Pic 3:  blisters or nacels on the sides which legs could exend out and even more of an angle, for a wider stance.  (Again, I almost think this picture is a biconid with the TPS on the other side.  The dorsal side is shown to us.  That MPS on the bottom just doesn't look set of for atmospheric entry that way.

Offline BobHk

  • Full Member
  • ***
  • Posts: 324
  • Texas
  • Liked: 91
  • Likes Given: 173
Re: MCT Speculation and Discussion Thread 3
« Reply #387 on: 04/25/2015 02:34 am »
This is why a vehicle or vehicles of some sort should be landed on the first lander to take people and supplies over to wherever robotic equipment has landed to set up housing.  That being said, a 100 ton lander on Mars would weigh 40 tons, but that is still quite heavy.  I think some type of flat plains area should be used for landers.

Isn't MCT supposed to deliver 100 tons (at least the later versions)?  Assuming 5 or more raptors, remaining fuel on Mars landing and dry mass of the lander plus 100 tons of cargo/people... even more unlikely to work on wheels of any kind that would be effective on unprepared terrain.

Offline Impaler

  • Full Member
  • ****
  • Posts: 1283
  • South Hill, Virgina
  • Liked: 372
  • Likes Given: 0
Re: MCT Speculation and Discussion Thread 3
« Reply #388 on: 04/25/2015 05:14 am »
Lets try to do some volume estimates for MCT and think about how much propellent that would hold.

I'm imagining a 15 m diameter Dragon v2 shaped capsule.  That is almost exactly 4 times the diameter of Dragon meaning that the MCT would have 66x the volume of Dv2.  Dragon v2 I estimate to be 24 m^3 in its EXTERIOR dimensions by calculating it as a simple truncated cone 3.7 m in diameter, 4.7 m high and with a 15 degree wall slope.  This means the capsule style MCT is ~1500 m^3

Dry mass of Dragon v1 was 3180 kg (according to some VERY old numbers so take it with a grain of salt).  Assuming mass directly scaling with volume that would mean a ~200 MT vehicle before any payload or propellents.  But many parts of the vehicle will not scale cubically, such as the heat-shield which while 16x larger in area would not need to become 4x thicker.  I'm thinking 100-150 MT is a reasonable dry mass range.

Allocation of volume, lets go with 100 m^3 for integrated crew space, 500 m^3 for cargo-hold inside which additional passenger accommodation modules can be carried and connected with the integral space.  Take another 100 m^3 for miscellaneous uses and that leaves 800 m^3 in propellent tanks.  LOX/Methane propellent averages out to right around 1 MT per m^3 so we would be looking at take off propellent of up too 800 MT.

Offline symbios

  • Full Member
  • **
  • Posts: 246
  • Elon Musk fan
  • Sweden
  • Liked: 152
  • Likes Given: 739
Re: MCT Speculation and Discussion Thread 3
« Reply #389 on: 04/25/2015 09:06 am »
I like your reasoning Impaler, you at least try to use logic and not a pet theory of how it should be done. As Musk would say; use the first principles.

You are missing that the MCT will probably be a two stage system.

Booster and transfer stage. Where the transfer stage is both upper stage and payload in one. So when you calculate you have to include the US mass.
I'm a fan, not a fanatic...

Offline symbios

  • Full Member
  • **
  • Posts: 246
  • Elon Musk fan
  • Sweden
  • Liked: 152
  • Likes Given: 739
Re: MCT Speculation and Discussion Thread 3
« Reply #390 on: 04/25/2015 09:43 am »
I’m fairly new at this. And for you people here that work with this will see any flaws in my logic straight away, please comment so I can adjust my thinking.

Mass is everything in space. It is the limiting factor for everything. We do not know the mass.

I divide the mass of the transfer stage of the MCT into three parts - vehicle, cargo and tankage (fuel).

We know the cargo mass that we want to get to Mars; 100 mt.
If we knew the vehicles mass we could calculate the fuel.
We do not know the vehicle mass.

We could set some limits on the unknown mass of the vehicle by making some assumptions:

-   The shorter the trip the lower the fuel needed (less mass), so assume we are only going to LEO to refuel.
   We can have more capacity for tankage than we have fuel in them. This is only about vehicle mass.
-   The booster that takes us part way to LEO are assumed to be 12-15 M lbs. and we are fairly good guess
   about the ISP of the engines.
-   We have a fairly good guess about the ISP of the transfer stage (US) of the MCT.

So using these assumptions can we calculate the max allowed mass of the MCT transfer stage vehicle AND is this mass reasonable? Could this be calculated both using 12 Mlbs and 15Mlbs on the booster?
I'm a fan, not a fanatic...

Offline fast

  • Member
  • Posts: 98
  • Liked: 23
  • Likes Given: 28
Re: MCT Speculation and Discussion Thread 3
« Reply #391 on: 04/25/2015 10:25 am »
Sorry about that, thought you were describing a alternative vehicle from the one in your sketches, a bi-conic that lands vertically on it's tail indeed has no heat-shield penetration issues (other then landing legs). 


Ahhh...no problem.

The legs don't necessarily have to protrude through the side heat shield.  I did post one image showing that, but as I said in my reply to Hyperion, there's other ways around it.  In fact, Hyperion posted a couple of pics illustrating those alternatives.

Pic 1:  shows legs deploying through the side TPS.

Pic 2:  Extendable jack-stand like legs that come pretty much straight down.  The H/W ratio of MCT would be a factor in that to make sure it's stance was wide enough.

Pic 3:  blisters or nacels on the sides which legs could exend out and even more of an angle, for a wider stance.  (Again, I almost think this picture is a biconid with the TPS on the other side.  The dorsal side is shown to us.  That MPS on the bottom just doesn't look set of for atmospheric entry that way.

biconic looks good. You are correct, legs not a problem. Just wrong rendering: TPS must be on the opposite side from ramp.

Offline Impaler

  • Full Member
  • ****
  • Posts: 1283
  • South Hill, Virgina
  • Liked: 372
  • Likes Given: 0
Re: MCT Speculation and Discussion Thread 3
« Reply #392 on: 04/25/2015 04:47 pm »
You are missing that the MCT will probably be a two stage system.

I didn't miss that, I simply disagree.  I believe the traditional 2 stages + capsule will be the way SpaceX goes, same configuration as Falcon9 + Dragon.

The logic behind combining MCT with 2nd stage was to provide huge propellent tanks for both TMI and direct Earth return from Mars surface.  But both these things can be done with just the smaller more conservative capsule base MCT if your smart about it.

For TMI you simply keep the 2nd stage that launched the MCT attached, load the propellent into it rather then the MCT and do a TMI burn with that 2nd stage.  The stage can even do a boost-back and return to Earth surface.

To do Earth return we fill both the integral tanks of the MCT capsule AND inflatable tanks that have been brought along in a deflated state.  These inflatables fill the now empty cargo hold.  If 300 MT can be held in this way (note that on Mars this is the same load on the payload-bay floor that the 100MT of cargo exerted on Earth), then the combined propellent load would reach 1100 MT.  A direct Earth return DeltaV would be ~6.8 km/s which at Raptor ISP of 360 will mean a dry mass of no more then 15%.  With 1100 MT of propellent a dry mass of 200 MT can be sent which covers the MCT and a small return payload.

If internal volume is traded between the integral tanks and the payload bay and larger inflatable tanks are used then an even larger payload bays should be possible without harming return DeltaV.  An higher volume payload bay is very desirable for transporting low density cargoes.

If we wish to just go to Low Mars orbit (for example to meet a dedicated in-space vehicle, visit Phobos, or just do a suborbital hop) then integral tanks alone should be able to do this, allowing the cargo hold to once again carry cargo up to it's full load while retaining propellent for landing.
« Last Edit: 04/25/2015 04:55 pm by Impaler »

Offline sheltonjr

  • Full Member
  • *
  • Posts: 148
  • Liked: 63
  • Likes Given: 37
Re: MCT Speculation and Discussion Thread 3
« Reply #393 on: 04/25/2015 07:46 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.

Offline Impaler

  • Full Member
  • ****
  • Posts: 1283
  • South Hill, Virgina
  • Liked: 372
  • Likes Given: 0
Re: MCT Speculation and Discussion Thread 3
« Reply #394 on: 04/25/2015 09:00 pm »
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.

I agree that tanks above cargo/habitats is the logical arrangement.  In a side mounted engine configuration the propellent lines should be quite short.  The radius of the bottom heat-shield may prove unusable for cargo though so some splitting up of propellents may be necessary.

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.

Again I agree that when transporting passengers the MCT dose not also deliver 100 MT of cargo, in essence the 100 MT figure is the relevant number only when flying unmanned.  I believe that passenger will be transported by placing special pressurized passenger-accommodation modules inside the cargo bay.  These modules will be permanently left on the Martian surface as living quarters.  This allows a bare bones integral habitat, it is really more like the 'galley' at the front of an airliner and has the external airlock, docking ports and other infrequent systems, the accommodation modules are like railway sleeper cars and are most of the bulk, they are also loaded with all the outbound food and consumables and air handlers so these scale directly with the number of passengers being transported.  I'm assuming 300 m^3 in module volume if the whole cargo hold is used, plus the 100 of the integral giving us 400 total for passenger transport configuration.  At full passenger loading their is no other cargo going to Mars other then the passengers and modules.  To bring people back from Mars the integral habitat can hold a handful which should be sufficient if people are really 'colonizing', if not then we simply retain the necessary number of passenger modules to handle the return rate.

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

Your total volume estimate matches my own at ~1500 m^3 though your going with a taller cone height my own math showed their was hardly any volume in the last few meters.  Comparatively your using a smaller unpressurized cargo-hold (383 vs 500), a considerably larger Habitat (257 vs 100), smaller integral tanks (567 vs 800) and a pressurized cargo area of 216 which I did not have.

But the factor that is most out of synch is the dry mass estimate for the vehicle, 65 MT is nearly half of my estimated upper range (100-150).  This seems too optimistic as it is about 33% of the direct Dragon scaling, rather then my own 50-75% estimate.  Whats your mass estimation method?


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.

The basic mission profile is good, my only real difference are less propellent in the MCT at launch primarily because of higher dry mass estimates.  And then a corresponding increase in Tanker delivered propellents and ISRU propellents.  It is clear that making the MCT dry mass as low as possible will have huge operational payoffs, but these crude extrapolations from Dragon mass are all I can manage.


It would be interesting if Lobo or others could do the same volume/mass estimate on the combined 2nd-stage style MCT concept.
« Last Edit: 04/25/2015 09:03 pm by Impaler »

Offline BobHk

  • Full Member
  • ***
  • Posts: 324
  • Texas
  • Liked: 91
  • Likes Given: 173
Re: MCT Speculation and Discussion Thread 3
« Reply #395 on: 04/26/2015 07:01 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? 

Offline Hyperion5

  • Full Member
  • ****
  • Posts: 1681
  • Liked: 1373
  • Likes Given: 302
Re: MCT Speculation and Discussion Thread 3
« Reply #396 on: 04/27/2015 02:17 am »


Agreed.  So you resolve this by not having the engines in the heat shield at all.  That gets back to the biconic aeroshell with engines at the aft.  Essentially a wingless Spaceshuttle that lands on it's SSME's.

Given the number of designs with engines embedded behind deployable heat shield doors, I would think the "wingless" Space Shuttle design is far from given.  The simplicity of landing with a Dragon-style vertical lander on Mars is not something to be given up lightly.

Well, we can't say anything is a given or not given until SpaceX announces something official.  ;-)

But some of these designed you posted pictures of are comparing apples to Oranges, or are some artist's fiction.  None of the addresses both Issues MCT will have to. 
1)  To be fully reusable, rather than 1-shot.
2)  To get itself back off the surface after it lands. which introduces a lot of issues like a large high performance engine needed, rather than just some low ISP landing thrusters.  All Mars Landers to date had those in one form or another, but none of them had to get back up and back through TEI.  Heck Dragon could land on Mars and it's a capsule.  It just can't get itself back to Earth.  So that's a very different issue that makes capsule designs much more problematic.

It's almost like dear Lobo did not glance at the thread-related materials found in that level of NSF that must not be named. ;)  No doubt he'll go back over there and look at them again before, right? :)  There are ways of going fully reusable with a capsule design that has heat shield doors, Lobo.  You use 8 Raptors on the sides (which would produce about 350 seconds of Isp on Mars) that you would use to land on Mars or Earth.  Then, when you need to launch off Mars, you open up the doors.  Multiple vacuum-optimized Raptor engines would then blast you into LMO and later perform the TEI burn.  So long as you refuel on Mars, an MCT will be large enough to make it all the way back to Earth on only one stage.  Full reuse is just as possible via a capsule design as your preferred design. 


Image #1:  I can't see where the heat shield is on this.  The whole bottom is shaded, and I can't see the other side.  But this almost looks like the heat shield is on the other side, given the odd shape of it's bottom.  This looke more like a "wingless shuttle" than a capsule.

Image #2:  Again, where's the heat shield.  Is it on the other side?  Is this a wingless shuttle too?  Or did it have a jettisonable heatshield on the bottom.  If so, then it's not reusable like MCT will be.  MCT won't [likely] be jettisoning it's heat shield.  Otherwise it couldn't land back on earth.  If it were to some how be able to brake itself into LEO (how?) it would need a new heatshield brought up and attached in LEO.  Which seems...unnecessarily complex.

Image #3:  Ok...so what was protecting thos engines during entry?  Did it have a portion of the heat sheild jettison?  And if so, see my comments about that on Image #2.

Image #4:  That image is from "Voyage" by Stephen Baxter.  Great book!  I highly recommend it.  That is the Mars lander Baxter put in his novel.  But that is an expendable two-stage lander like the LEM.  It had a conventional capsule shaped descent module (described by Baxter that it was chosen over other more advanced bionic designs because of it's heritage and that they "know" it would survive, where biconics hadn't been tried before....and if they are going to risk Humans on the very first trip (there was only funding for just one manned trip to Mars) they wanted to go with a proven and stable design. 

It's top and central core were the ascent module.  It blasted off from the capsule bottom back to LMO for rendezvous with the MTV.  It was really an Apollo redux, but with a lander descent module that could withstand atmospheric entery.  Again, this lander can't get itself off the surface whole, only the ascent module portion could get back to LMO, just like the Apollo LEM.  The ascent module engines were protected within the MEV like the LEM AM engine was, and the descent module portion was destoyed when the ascent module blasted off.    The whole lander couldn't take back off again with it's landing thrusters (even if it could have been refueled) and it wasn't reusable.  A good safe one shot design but it would share little in common with what MCT is supposed to do.

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!

A biconic has a lot of advantage over a capsule.  It has a large surface area, so it's TPS doesn't have to be quite as thick and it's terminal velocity is slower.  The engines are in the afte and not exposed to the atmospheric entry, or the supersonic terminal velocity slip stream like those of a capsule.  Although it's not impossible to have doors in your heat shield...the shuttle, X-37B, and Dreamchaser do after all for their landing gear...having a large main engine with a large nozzle which gimbals is more problematic than landing gear.  Assuming such a capsule design would have Superdraco like landing thrusters, and then one or more Raptors tucked behind the heat shield, then you have to retract those doors (that can be done on the ground if there are separate side wall landing thrusters) but then you need enough room for those main engines to gimbal, so the doors need to be much wider than the nozzles.  and then those doors need to close again prior to Earth EDL or else you have the Columbia all over again.

That's on top of landing gear which will need to come through the heat shield as well.  So there will need to be several doors in the heat shield. 

Heat shield doors (successfully) protecting spacecraft reentering Earth's atmosphere is nothing new, as they have never failed to protect the Shuttles from harm.  This is why Dragon 2 is going to use them for its landing gear.  What did in Columbia was foam detaching from the external tank and striking the orbiter's wing, damaging some of the heat shielding found there.  I'm surprised Jim didn't beat me to pointing that out.  If heat shield doors can protect landing gear through over 133 reentries, then why not engines? 

I'm sure it -could- be made to work.  But why force it when you don't have to?  A biconic "wingless shuttle" design solves all of that.  You can even get around needing to have legs extend through the heat shield on its' side in various ways, include just having jackstand like legs come straight down from the MPS (if the diameter is wide enogh to be stable, similar to your pictures #2)  or you could have blisters around the MPS housing the legs.  With a shape not unlike your image 1.  The legs could fold out from those blisters to give MCT a wider stance on the surface. 

The one alternative to legs coming through the heat shield is to have them extend out from the sides of the MCT.  They might be embedded in the side or more exposed (and protected by heat shielding). 

Because while there are vehicles which have had doors in their TPS, there's never been one that's had to close those doors again prior to anther reentry.  They open once after atmospheric entry and that's it.  They're closed on the ground an checked out before sent back up.  So avoiding that dynamic portion of the heat shield and making it all static/passive increases mission safety.

Never been one?  Why exactly are we not counting a Shuttle orbiter?  That craft opened its heat shield doors after a reentry in order to land, and those doors were closed again for the next mission's reentry.  If I were to survey our experts, how many of them would say that opening and closing the Orbiter's landing gear doors once in space would likely result in a loss of mission?  My guess is the chance is quite slim, and in any case you would have time to get them retracted back in via a crew repair if absolutely necessary.  An MCT is not going to be opening and closing heat shield doors much more than a Shuttle did.  It will need to open and close them once on the way to Mars, and once on the way back.  For landing on both Mars and Earth you don't need to open heat shield doors whatsoever, as you can use the side-mounted Raptors and landing legs to touch down safely. 

Is there some additional risk?  Yes, but it's a manageable kind of risk, with the Shuttle's flight experience and the Dragon 2's design being the best evidence. 

« Last Edit: 04/27/2015 02:18 am by Hyperion5 »

Offline CyclerPilot

  • Member
  • Posts: 97
  • USA
  • Liked: 23
  • Likes Given: 0
Re: MCT Speculation and Discussion Thread 3
« Reply #397 on: 04/27/2015 04:16 am »
It would be interesting if Lobo or others could do the same volume/mass estimate on the combined 2nd-stage style MCT concept.

Regarding MCT dry mass.  I did a rough speculative design way back in Thread 2, so I thought I would share how I estimated that MCT dry mass.

I did a combined S2+MCT with separate pressure fed LAS/landing thrusters.

All masses in kg:
Raptors8,402
Main Prop tanks5,303
Landing legs   3,000
Heat shield2,213
pressure vessel26,460
8 Metholox Draco's3,200
Pressurized insulated tanks1,200
Radiators2,000
Solar panels3,841
Other misc mass4,926
Total Mass60,545

Obviously ultra optimistic, but I think the MCT has to be or it doesn't work.

Raptor.  I used a 100:1 t/w.  This was the old raptor (8.2 MN), so equivalent to 3 of the new, lower thrust raptors.

Prop Tanks.  Used Al-Li alloy.  12m dia. Common bulkhead.  Enough volume to store 1,000 tons of metholox prop.  40% margin gives 3mm walls.

Pressure vessel. I scaled up from Dragon.  So it does include a lot of misc systems.

Solar panels.  ZTJ Space solar panels.  8.4 kg/m^3.  457 m^3.  175kw Earth, 80kw Mars.  Shared structure with radiators.

Heat shield. pica X.  290 kg/m^3.  30mm thick.  Looking back at my old math, probably unrealisticly optimistic.

Misc mass covered a lot of structures and systems not covered elsewhere.

Everything else is a total guess, mainly based on scale up of similar systems in Falcon or Dragon.

Anyways there's some numbers to poke some holes in / get the conversation moving.

Offline RanulfC

  • Senior Member
  • *****
  • Posts: 4595
  • Heus tu Omnis! Vigilate Hoc!
  • Liked: 900
  • Likes Given: 32
Re: MCT Speculation and Discussion Thread 3
« Reply #398 on: 04/27/2015 05:46 pm »
We (ok at least me) are/is talking about protecting the craft that is landing from damage to it's engine/heathshield from impacts with 1cm sized gravel moving as much as 1.2km/s - one of the reasons why engines might be mounted on the outside and have a gimbal range from 0° from the vertical to 30° from the vertical (pointing out). That angling, and the fact that the engines are on the outer radius, also protects the landing site from being destabilized under the landing craft so that it can't take off without major earth moving, hoisting, etc.

Pretty sure the majority of the "early" MCT fights are simply going to have to "risk" it until something more "permanent" gets built. The main problem with lot of "gimbal" is that you have to have flexible connections and hoses and those increase your possible failure points.

Quote
Yes, but that will only be done if more traffic is going there, so it will probably be the 2nd or later MCT to that site location that caries the earth moving equipment to do that. 

My point is that I think the MCT has to be designed (and operated) to minimize the risks to the MCT and to anything already on the ground. Angling the engines outward, having them outside of the radius of the craft, and ensuring that landing orientation of engines puts already landed equipment at the least risk is needed before landing pads are built up at a site that will experience significant future traffic.

Unless the FIRST MCT flight goes directly to the "colony" site I suspect it will be MUCH later than the second flight :)
However, once it IS decided that MCT flights will be going to a designated colony site then you MUST assume a higher flight rate in and out and therefore prepare for mitigation. Then the "first" colony MCT is going to carry what amounts bulldozer and other construction equipment.
Let me address/point out this:
I would seem that a small, deep crater with the center peak flattened out would likely be the best choice for this sort of launch pit.

Probably the best idea. It actually doesn't have to be very deep as once the MCT is a couple of meters up the "blast" out angle gets shallower and shallower and the blast itself dissipates rapidly with distance.

Figure one of the "main" criteria for a colony site is an already existing "port" area for MCT landings and take offs and find a convenient crater to use. Put the colony on the "surface" above the crater wall and you will have almost no issues with flying debris getting to it. Now you concentrate on protecting landed MCTs from landing or taking off MCTs. (I should probably point out that the MCT would benefit greatly from an outer layer of TransHab material as a buffer layer and a "skin" layer of flexible TPS blankets)

Towing versus "hopping" or using the MCT rockets: Even empty the rockets are going to throw rocks and debris so you want to avoid using them as much as possible in proximity to other MCTs or structures. So unless you're going to land far enough away to avoid any possible problems, (which brings up logistical concerns about getting cargo and passengers back and forth to the colony in a timely manner) you need to arrange and design the "port" to handle the problem within itself.

I'd not assume that the "legs" of the MCTs will be used at all OTHER than for landing and holding it upright for take off. It's going to be attached to the BFR stage so we can assume it will have "hard-points" that can be used on Mars as points where it can be lifted and supported. Light weight "dollies' or individual "jack" wheel sets can lift the MCT so that it can be towed into a "take-off" berm, (the image used to be quite popular, imagine a circular, low angled "wall" with a section MCT wide cut out facing away from any structures or MCT landing area) where it waits for loading, propellant and crew.

Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.

No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.

Nobody jacks up a fully loaded aircraft why would you assume they do so for an MCT? :) At landing it will be almost empty of propellants so its FAR from as heavy as you seem to be thinking.

"Landed where you need them?" Nice idea but how ACCURATE does that have to be? You "need" not to put the colony structure in danger, nor other already landed MCTs. 2km? 5km?

This is why a vehicle or vehicles of some sort should be landed on the first lander to take people and supplies over to wherever robotic equipment has landed to set up housing.  That being said, a 100 ton lander on Mars would weigh 40 tons, but that is still quite heavy.  I think some type of flat plains area should be used for landers. 

You'll have to have some sort of vehicles to move passengers and cargo from the landed MCT to the colony site, but if you're on 'flat-plains' then the MCTs have to landed far enough away to NOT be a danger to the colony. Even on Mars that's going to be several kilometers. Now add in separation from other MCTs...

A berm is simpler and safer and berms between the MCTs even more so but if your landing accuracy is "only" 1km that means each and every MCT landing "site" has to be a kilometer in diameter... ("Assuming" that the MCT hits dead center EVER time, otherwise you have to include that into your calculations)

Nothing impossible but its some basic considerations for operations.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 6809
  • California
  • Liked: 8485
  • Likes Given: 5384
Re: MCT Speculation and Discussion Thread 3
« Reply #399 on: 04/27/2015 05:58 pm »
Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.

No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.

Nobody jacks up a fully loaded aircraft why would you assume they do so for an MCT? :) At landing it will be almost empty of propellants so its FAR from as heavy as you seem to be thinking.

"Landed where you need them?" Nice idea but how ACCURATE does that have to be? You "need" not to put the colony structure in danger, nor other already landed MCTs. 2km? 5km?

If you have a colony you will need a LOT more accuracy, why else prepare pads? I imaging the requirement that you need to have pin-point accuracy. +/- just a few meters.

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1