Author Topic: MCT Speculation and Discussion Thread 4  (Read 504994 times)

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #600 on: 10/06/2015 08:17 AM »
No one is going to be unloading cargo by HAND, your going to be using forklifts, scissor-lifts movers and other wheeled equipment to take out large containers which would then be taken into garages or coupled to pressurized areas, this is what we do already on ISS for Christ sake.  The lack of basic knowledge of logistical functions here is maddening sometimes.

MCT doesn't need life-support because their is only a need for ONE vehicle variant which is a universal carrying shell, you put pressurized habitat modules (which has all the life-support equipment in it) in when you want to carry passengers and you put cargo containers in it when you want to carry cargo.  Why is this so hard to understand?  It is infinity more flexible and efficient then any other configuration.

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #601 on: 10/06/2015 09:18 AM »
10 or 100 people per flight.

10 people means 10 times the number of manned flights. Which means 10 times the likelihood of a flight with crew loss. Will people say, oh well, it is only 10 people, not 100, that's OK? I doubt it.

Plus that many facilities don't scale linearly so a flight with 100 people will be a lot more efficient.

Offline GregA

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Re: MCT Speculation and Discussion Thread 4
« Reply #602 on: 10/06/2015 09:40 AM »
That's like asking why do we have airplanes that are full of only people and ones that are full of only air-freight.  That's the nature of every mature transportation system to make a very sharp distinction of between a cargo carrying trip and a passenger trip, it makes the logistics simpler and maximizes passenger comfort.

In spacecraft going to mars we have a huge savings in propellants if we go slow but this is deleterious to human health so we send them fast and freight slow, this is all the incentive we need to segregate passengers and freight trips.  And their is almost certainly a reduction in marginal mass needed as passenger counts grow due to the redundancy needed for probabilistic equipment failure and the ability to time-share public space and amenities, that's why the service is better on a 747 then on a piper-cub.
I think that's a fair analogy but raises my reasoning because it doesn't respond to that.

My comment stemmed originally from the intense debate about there not being enough space per person in an MCT, so the concept of unused space on a separate ship is worth exploring. I imagine that there is lots of open space on cargo planes also that your average person would happily use instead of being crammed in economy... but there are far more passenger flights than cargo and not enough money in offering that space in that case.

Then there was a comparison made about having an ECLSS 12 times larger than ISS to handle 12 times the people. (I thought you were saying that actually). Hence my question about whether that's true or whether there are useable efficiencies of scale. meekGee's thread on taking Oxygen and CO2 chemical scrubber certainly implies 10 times the oxygen and scrubbers for 10 times the people, but there's more to it.

I do agree that if the cargo MCTs can be sent on a slow run that's great, provided they can still launch as often. And yes as you and guck fan say you get better facility usage etc if you've got a larger number - and that means you don't need as many spare toilets etc.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #603 on: 10/06/2015 07:06 PM »
A top mounted thruster system like this would be inherrently stable, unlike landing on a tail engine (F9 booster)....like a helicopter is stable with it's thrust up on top and it's mass hanging below it.

I'm rather surprised that you aren't aware of the Pendulum Fallacy: https://en.wikipedia.org/wiki/Pendulum_rocket_fallacy

Don't be surpised...I never claimed to be a rocket engineer.  ;-)
Although I am a mechanical engineer...but work in liquid and fluids.  Been a long time since my Dynamics class in college.  heheheh.

But thanks for sharing.  Always good to become more educated.

But I don't know that my stated bit about inherent stability is incorrect.  Just not exactly as I stated.

Down farther in the article it talks about "Solution" and the Apollo LAS system.  That's more like what this would be.  The LAS thrusters would be on top of a fairly tall cylinder (not nearly as bad as F9 booster, but still), and would be pressure fed fast reacting powerful engines.  The engines would be canted outwards and downwards.  And can react to keep the stack upright during hover and landing.  In that, would it not be similar to a helicopter?  Why is a helicopter more stable than something like the LLRV? Why does a bamboo-copter work with the shaft haning down, but not with it pointed up? (with reversed blade pitch)
And in this way I think they'd act more like the F9 core grid fins, which are placed up high to provide force (via air resistance rather than a jet of thrust) to help stabilize the core for landing.
I don't know that Goddard's rocket concept is quite the same thing?

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #604 on: 10/06/2015 07:30 PM »
Nice concept. But quite frankly, I like the concept developed in L2 better.

If you aren't willing to show/share it, don't bring it up here. This kind of information sand boxing is why I'm not joining L2 anytime soon. Just my personal opinion...

Lobo:  Is that L2 vehicle concept posted anywhere where us plebs can read it?

As I'm sure you remember I favor the 2nd of your scenarios, "Another is launching MCT dry on a 2nd stage rather than the integrated design, with just enough propellant to power it's LAS engines.  So the whole dry MCT is aborted and lands.  For a nominal launch, it docks with the depot, and the 2nd stage does it's own EDL and returns to launch site."


Lars, Impaler,

There's nothing really L2-ish about the concepts the "team" I'm a part of has been posting on L2.  I think mainly the other members preferred the smaller L2 viewership than the public forum as the feed back is usually a little more focused.  Things can get more tangential on the public forum.
Plus there's some SpaceX employees and other who'll comment on L2, but don't on the public forum.
Hyperion5 is really the guy who usually is the "spokesman".

But I can answer questions and comment on it, just from my working with the team.  I guess technically the L2 discussions by others need to stay there...but again, this is just some of our work for fun.  There's nothing "secret" about it or anything.  So ask if you have a question.  :-)   

Impaler,

In a nut shell, we've been looking at 3 concepts.
A SuperDragon type large capsule was the initial favorite of the rest of the Team.  Very much like you described.  It's big advantage is that is has a conservative reentry profile like a capsule.  The main draw back is you need to have engine doors in your heat shield.  Not for landing, that's done with a combination LAS/landing thruster system very much like Dragon 2.  But for taking off again, and in-space burns.
Also, a biconic which essentially does the same thing as the Capsule, but with a biconic EDL profile, which is more complex than a Capsule.  But it has better L/D ratio and you don't need doors in your heat shield for your engines.

But the integrated biconic design that you and I discussed/debated back thread seems to be the one coming out on top for many of the reasons I suspected it would.  But the design is more refined as we've investigated it.  It has the best efficiency to LEO (as it's just one stage instead of two, so no mass is duplicated like a dedicated 2nd stage).  We've added an LAS to the top, as I've discussed here.  My original Integrated biconic concept didn't have an LAS.  But the difficulties of landing on a vacuum Raptor on Earth meant some means of landing would need to be added.  Vacuum Raptor can land on Mars, but would need a retractable nozzle or separate landing thrusters or something to land on Earth.  So we've been looking at having the nose lifeboat abort engines also double as landing engines on Earth, and landing assist on Mars.
Looks like it will mass around that of the Super Capsule concept, but a little more than the Non Integrated Biconic with the dedicated S2.   It also is the most simple, with just 2 pieces to develop rather than 3.  It can do duty as a tanker, depot, and satellite launcher too...with variants of the Mars vehicle.

But the Super Capsule is the most mature concept.  The two biconics are still being played with.


As far as visualization.  For the SuperDragon MCT and Non integrated biconic MCT, just picture a 12m wide Raptor powered reusable booster, with some sort of 2nd stage with 3 vacuum Raptors in a tripod configuration with a cental [new] methalox landing engine to land it.  It 's still in the works, but it will probably look similar to the Falcon 9 reusable upper stage concept of SpaceX's..just with a central landing engine.
Then on top, you have a really big Dragon 2, or a biconic.

For the Integrated biconic, it'd look like this, but on top of that 12m booster, when sitting on the pad.
 
« Last Edit: 10/06/2015 07:34 PM by Lobo »

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #605 on: 10/06/2015 07:46 PM »
I'd like to offer a completely different MCT LAS for consideration:

Considering that the MCT will certainly have high efficiency Methalox engine(s) for its main thrust (and perhaps landing?) the issue seems to be the delay time required to 'spin up' the turbines in the case of a mid flight abort.  So this means that the MCT really only needs a short burst (<4-5 seconds?) of high thrust  (5gs?) to pull it safely away from a disintegrating 1st stage.  Correct?

So, how about placing an LAS set of engines, with associated fuel, in the interstage between the booster and the MCT?  Under normal conditions, the MCT would stage, leaving the interstage attached to the booster, and  the booster plus interstage/LAS would RTLS and be completely reused.  Under abort conditions, the LAS engines would fire and the interstage/LAS would separate from the booster and propel the MCT a distance away.  The MCT main engine(s) (Raptors?) would spin up during this LAS firing period, then the MCT would detach from the interstage and proceed to do an abort landing.

The LAS could be fast acting, high thrust (poor ISP) hypergols, or even (gulp) solids.  This system wouldn't need to be very massive, given its short firing duration, but it would admittedly still be considerable parasitic mass hurting the RTLS effort.

I like this idea because (1) no parasitic mass going to orbit and beyond, penalizing the whole system, (2) entire system is reusable, and (3) unlike 'puller' LAS systems, you don't require that the LAS system cleanly separate from the manned portion as an additional staging event, lest you have LOM.

Thoughts?

Originally I thought of this for the lifeboat LAS on the IBMCT.  One issue with it is over pressure, you probably need blow out panels or something otherwise you could get an overpressure in the interstage and damage the bottom of the lifeboat.  I think the CST-100 LAS has something like that.

But I think we're moving them outside to eliminate that concept, and then so they can be used for landing assistance.
A large Capsule design could have the LAS outside like Dragon 2 for abort and for landing.  It has the disadvantage if having these inefficient engines have to slow down the MCT during MArs EDL.  It's not an issue of Earth because of the much slower terminal velocity, but on MArs, you are still supersonic at terminal velocity.  The large Capsule LAS/landing engines have cosine losses, and cannot have very large nozzles due to size constrains in their mounting...like Superdracos can't.
With the biconics, they can actually use the much more efficient Raptor to provide all that dV, and then actually land on Raptor, and/or cut in the LAS thrusters for hover and landing. 

GORDAP - I like it! If abort is only practical for Earth launch, it is an elegant solution.

The MCT will somehow need to be able to use Methalox for its thrusters - not sure how that will work. Would there be smaller LOX and Methane containers that are pressurized at high pressure (continuously refilled from the main tanks) that feed the maneuvering thrusters? One could also imagine such a system could be scaled up for abort/landing thrusters.

Separate pressurized tanks for the LAS/landing engines.  So they will be fast acting and responsive.  They would be filled on the pad on Earth, and then filled from the main tanks on Mars prior to ascent. 
They could be drained to the main tanks for the cruise to Mars, and then refilled  before Mars EDL.  Ditto for the return trip.  That way the cryo's don't need to be stored in the separate tanks for very long.  That would be figured out in development.


Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #606 on: 10/06/2015 07:55 PM »
[LAS lifeboat]

Essentially you've added the cost of developing a 100-person Super-Dragon capsule, with the added cost of integrating it into MCT like a matryoshka doll. (And you rarely actually use it. Most of the time, all of its independent systems are just dead weight. And it won't have the develop-use-update-use pattern that SpaceX prefers.)

If you're going to the expense of developing an extra vehicle, why not just use the 100-person "lifeboat" as a shuttle to ferry passengers to LEO when the MCTs are fuelled and ready to go? It doesn't need to go to Mars.

That was actually my original thought.   Not to have an LAS on the Integrated Biconic MCT.  Others thought it needed it, as later during colonization they'd want to launch all 100 people on the MCT rather than have a separate ferry.
For early exploration missions Dragon 2 would be sufficient, no separate system needed as crews will only be maybe 6-7.

But again, others felt it should have one.  And I see their logic.

Also, without one, MCT will need a way to land on Earth.  It can land on Mars on vacuum Raptor, but not at sea level.  You may need separate landing thrusters -anyway-, this is a way to get double duty out of them. 

The lifeboat would be similar to Heidmann's concept Lars posted a page or two back.  A flight deck in the nose with a bulkhead and hatch between it and the rest of the hab.  Not much more to it that that.  Not quite like a separate spacecraft.  It'd just have a traditional biconic EDL profile if separated. 

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #607 on: 10/06/2015 07:58 PM »
The difference is, that in an abort, the MCT (assuming it is its own second stage) has to be abortet including its entire mass of fuel. I  think I remember that the dry mass of the MCT is about 20 % of its wett mass. So the 3g in normal operation would be reached near dry mass. The 5 g abort would be reached at wett mass. The force on the metal structure is F=m*a, mass times acceleration. Wett mass is 5 times dry mass, acceleration is higher, and air resistance is higher. So during about, the structure of MCT must take I would guess more than 10 times the force of normal operation. The metal structure must be sized accordingly.

Semmel,

Not, not exactly.  An integrated biconic MCT would be impractical to abort the entire thing as it's main tanks may be loaded with propellant.  Rather it would have a separable noze section with more reasonably sized LAS thrusters, which would double as landing engines if there's no abort, as the whole integrated biconic MCT would be landed pretty much empty.  So they can abort the lifeboat, or land the whole craft on Earth, and on Mars with Raptor doing most of the desceleration from terminal velocity.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #608 on: 10/06/2015 08:11 PM »

In the one stage BFR your looking at the combo 2nd stage MCT vehicle is going to be considerably more massive then the smaller and un-fueled one I'm looking at, that will mean probably 3x more thrust needed for separation.  Rather then the 9 million N I'm estimating for a 200 mT MCT your looking at 27 million N, the thrust of 12 raptor engines.  I see a problem with rapidly initiating that much thrust INSIDE the interstate when the vehicle is still assembled, it would be like setting off a bomb.  So the thrust must be vented laterally with Dragon like canted rocket nozzles along the perimeter of the inter-stage.  With the cosine loss were looking at something like 400 Super Draco equivalent rockets.  Do able probably by having multiple bands of nozzles such that the entire outer surface of the inter-stage is nozzles.  But we should be aware that were increasing the number of parasitic engines, though they parasatizing the first stage rather then the 2nd which means they count for only 1/10th as much in final payload.

No, a separable lifeboat with externally mounted engines.  Which will do double duty to land.  Aborting a fully fueled integrated MCT would be impractical.  A separate LEO taxi would be a much better solution if you didn't want a separable lifeboat.

Also, looks like dry mass of the Integrated biconic won't be much too more than that of the non integrated biconic.   It's a little longer, but the extra tank alloy and additional TPS to cover it doesn't add a lot of mass.  And it's much more efficient to LEO.  It's less efficient after that because it is a little heavier, but that's not too big of an issue because you have fuel in LEO, and fuel on the Mars surface.  So you just need to put a little more in orbit, and make a little more on the surface.  Where this an Apollo type mission where you had to bring all of your return propellant with you, then every kg of mass is critical.  Then multiple stages give a definate advantage.

The decisive factor I think is that in a 2 stage BFR with the abort engines atop the 2nd stage and below a smaller MCT is that you can abort during both first AND second stage burn.  You only give up the abort motor once full Earth orbit has been achieved.  Where as with a one stage BFR your in a black zone after first stage separation and yet your still attached to a potential bomb which has 6-7 raptor engines which might set the thing off.

can do that with the separable lifeboat nose.
Also, can do an abort on approach to Mars or Earth if there was a problem with the whole MCT.  The nose could do it's own EDL.  Obviously there'd have to be some resources available on Mars or aborting to the surface just means a slow death marooned on the surface.  But if it has 100 people, that means there will be a whole colony already there.  If it had just an exploration crew, the lifeboat would be large enough to support a small crew for at least some time.  Hopefully there'd be like a backup MCT already placed there, like MArs Direct and Semi-Direct.  Abort options are dependent on that. 

The main advantages of the 3-piece MCT's is that then aborting the entire MCT becomes an option, because you launch it dry other than the abort propellant.  You don't need a separable design.


Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #609 on: 10/06/2015 08:25 PM »
6 posts in a row? Is there some obscure forum record you are trying to break, Lobo? ;)
« Last Edit: 10/06/2015 08:26 PM by Lars-J »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #610 on: 10/06/2015 09:35 PM »
Ok let me just touch base on terminology and what looks to be a set of acronyms that will describe them.

Super Dragon Mars Colonial Transport (SDMCT):  A dragon shaped vehicle which lands with a bottom side heat-shield and is powered by either side-wall engines or a heat-shield penetrating central engine.  It launches on a 2 stage rocket which is essentially an enormous F9 colloquially known as the BFR.  Least imaginative design, initially popular with many but now falling out of favor.  Would abort as Dragon dose by pushing away the whole vehicle from the 2nd stage.

Separate Bi-conic Mars Colonial Transport (SBMCT): A obviously bi-conic vehicle with bottom mounted engines and a horizontal high lift entry orientation that keeps engines and other systems in the rear.  Propellant would be in the nose of the vehicle and cargo in the base just above engines.  Launches on top of a conventional 2 stage rocket comparable to the SDMCT.  Would abort similar to SDMCT by pushing the whole vehicle away from the 2nd stage.  Designed around single stage to Low Mars orbit and a 'semi-direct' like architecture.  My currently preferred solution.

Integrated Bi-conic Mars Colonial Transport (IBMCT) A modification of the SBMCT which 'integrates' it with the 2nd stage of the rocket it would launch on such that their is a bi-conic nose and a cylindrical aft body, the tip of the nose is an abort capsule, the next section down is cargo and propellant fills the cylinder.  Launches on a single stage rocket which is similar to the first stages of the alternative configurations.  Designed specifically for Single stage Direct Earth return.  Lobo and others currently preferred solution.

Dose that look like an accurate depiction of the current positions?

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #611 on: 10/06/2015 10:27 PM »
6 posts in a row? Is there some obscure forum record you are trying to break, Lobo? ;)

Sorry, I hadn't caught up in the last few days so was trying to catch up today.  :-)

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #612 on: 10/06/2015 10:50 PM »
Ok let me just touch base on terminology and what looks to be a set of acronyms that will describe them.

Super Dragon Mars Colonial Transport (SDMCT):  A dragon shaped vehicle which lands with a bottom side heat-shield and is powered by either side-wall engines or a heat-shield penetrating central engine.  It launches on a 2 stage rocket which is essentially an enormous F9 colloquially known as the BFR.  Least imaginative design, initially popular with many but now falling out of favor.  Would abort as Dragon dose by pushing away the whole vehicle from the 2nd stage.

Separate Bi-conic Mars Colonial Transport (SBMCT): A obviously bi-conic vehicle with bottom mounted engines and a horizontal high lift entry orientation that keeps engines and other systems in the rear.  Propellant would be in the nose of the vehicle and cargo in the base just above engines.  Launches on top of a conventional 2 stage rocket comparable to the SDMCT.  Would abort similar to SDMCT by pushing the whole vehicle away from the 2nd stage.  Designed around single stage to Low Mars orbit and a 'semi-direct' like architecture.  My currently preferred solution.

Integrated Bi-conic Mars Colonial Transport (IBMCT) A modification of the SBMCT which 'integrates' it with the 2nd stage of the rocket it would launch on such that their is a bi-conic nose and a cylindrical aft body, the tip of the nose is an abort capsule, the next section down is cargo and propellant fills the cylinder.  Launches on a single stage rocket which is similar to the first stages of the alternative configurations.  Designed specifically for Single stage Direct Earth return.  Lobo and others currently preferred solution.

Dose that look like an accurate depiction of the current positions?

Yup, pretty close.  Except we've been referring to #2 as a "Non-Integrated Biconic MCT" or "NIBMCT", just for clarity between the two biconics.  And at least so far we've assumed crew and cargo on top of the tanks, not below.  This could actually be a full biconic...essentailly a capsule shape but nose/side entry (see McDonnell-Douglas X-33 biconic concept below)  Or it could be a cylinder with a biconic nose like the IBMCT...just shorter due to the smaller tanks, and with two Raptors rather than 3.
It could have a full vehicle LAS like the Super Dragon with LAS engines located in the MPS around the Raptors, or actually have a separable upper section too.  The biconics can do that because they take the TPS with them.  If you separate a capsule you leave the TPS behind and so you need to have another...which adds more mass...although it's certainly possible.

Super Dragon is the most mature, followed by IBMCT and then NIBMCT. 

There's still some debate about how much of the top of IBMCT (or NIBMCT) to take off with the LAS.  Just a "flight deck" in the nose?  Which could hold just 100 people (see Heidmann's concept Lars posted), or a crew of 7 plus a fair amount of hab space for exploration crews?  Or the flight deck plus the cylindrical hab volume below it?  So all the hab/ECLSS/etc stays with the lifeboat rather than being split apart?  As it probably wouldn't add too much mass?
Or everything north of the tanks, including cargo deck?  This seems unlikely because in exploration missions, the cargo would be mainly surface equipment and unneeded to keep with the abort for Earth ascent, and it would be left on the Mars surface for a Mars ascent abort anyway....and could add maybe 50mt of added mass that the LAS needs to pull away.
The argument for it is that could be millions of dollars of equipment, and SpaceX may want to keep it in case of abort to use for another mission.

I suppose it really depends on how big the LAS system needs to be to land the whole vehicle on Earth.  At that size, how much can it abort?  Just the nose?  The nose + hab cylinder?  The nose + hab cylinder + cargo deck?  If it's already big enough to land on Earth that it can abort everything north of the tanks, then why not?  But kinda doubt it will be.  Landing is much less dV than for a fast abort away from an exploding booster I think.
But we've not investigated it that far yet.

The Full vehicle aborts of SDMCT and NIBMCT-option, of course do keep all the cargo along with the whole vehicle.



Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #613 on: 10/06/2015 11:03 PM »
We can all agree that MCT is SSTO on MARS, and that means the only means of abort would be disassembly of the vehicle via something like a nose-cone escape crew capsule.

This should be avoided because we shouldn't even HAVE an integrated crew cabin, if the MCT simply has a large cargo hold in which cargo or crew modules are interchangeably placed then it becomes possible to make a powered escape module and place this into the vehicle when ever crew are on board.

This won't weigh down the vehicle when it is serving in a cargo only flight (which will be probably x10 more numerous then crewed flights) and it allows us to change and modify the crew carrying modules for evolving needs and numbers, from small crews which will initially live inside the MCT to future high volume passenger counts which will immediately disembark.

Also note that when aborting to the Mars surface your possible landing sights are very nearly a great circle around Mars as your point of landing varies becomes a track of the landing point of a sub-orbital flight, if it is late in the MCT assent phase and thrust is lost then your looking at a landing sight possibly on the opposite side of the planet from where you launched.  Not a feasible distance from a base for rescue to pick up survivors even if they were landed without a scratch, an extremely difficult matter when your basically performing full EDL which is a process which requires considerable heat-shields and retro-propulsion.


That last is where a separable lifeboat LAS has an advantage.  Since MCT is a SSTO for Mars ascent, if there's an explosive problem with the main propulsion system, the crew is lost.  That'd be the case for full vehicle abort of the SDMCT and NIBMCT.  The LAS lifeboat can get away and then "fly" down range to a landing spot within it's ascent trajectory.  What they do when they land safely is another story.

If in the early exploration phase, the returning crew is small.  If the lifeboat is of sufficient size to support them until they can get to a backup vehicle somewhere else on the surface, then that would be good.  If later in colonization phase, there'd be a full colony with presumably long range rovers that could be dispatched for rescue.  The returning MCT should only have a small crew though, as most would be colonists left there.  So you really shouldnt' have to rescue 100 people, unless there's some abort from orbit and the lifeboat lands somewhere far away form the intended LZ 

The IBMCT would have 3 Raptors, but only two are needed for Mars ascent (maybe only one).  It has 3 because 3 are needed to get it from booster staging to LEO.  So it has engine-out backup for Mars EDL (with LAS assist) and it has engine out backup for Mars ascent.  And if the MPS exploded, it's LAS can abort the lifeboat away.

The SDMCT and NIBMCT have only two engines, as they don't do Earth ascent.  If there's an engine out at Mars ascent, there's some issue of how to handle it.  One engine thrusting at full throttle should keep it aloft long enough to burn off enough propellant so the LAS system can land it again for an emergency landing.  It might not be able to get to orbit, but it should be able to do a controlled emergency landing.  And it depends when the engine were to fail, far enough up just one engine should still get it home.


Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #614 on: 10/06/2015 11:26 PM »
No one is going to be unloading cargo by HAND, your going to be using forklifts, scissor-lifts movers and other wheeled equipment to take out large containers which would then be taken into garages or coupled to pressurized areas, this is what we do already on ISS for Christ sake.  The lack of basic knowledge of logistical functions here is maddening sometimes.

MCT doesn't need life-support because their is only a need for ONE vehicle variant which is a universal carrying shell, you put pressurized habitat modules (which has all the life-support equipment in it) in when you want to carry passengers and you put cargo containers in it when you want to carry cargo.  Why is this so hard to understand?  It is infinity more flexible and efficient then any other configuration.

And you have nothing in it to be a tanker (perhaps stretched tanks within the same Outer Mold Lines).  Just a big empty volume.

And you have some cryo-refrigeration equipment in it as a depot.

And you put a payload bay behind the nose to deploy FH and D4H class satellites to GTO.  The vehicle then comes back around on the GTO eliptical orbit to Earth, where it does a small deorbit burn and does Earth EDL.  Not expendable PLF required.

The working idea is that all concepts would have a Dragon 2 like nose hatch (maybe about 5m wide or so) under which could be a docking collar.  Tanker and depot dock in LEO and proceed to do a slow spin to settle propellants in the bottom of the tanks where it can then be pumped from the tanker to the depot, and later from the depot to MCT.  Propellant lines would run from the nose to the tanks.  (unless there's a way to pump liquids in zero g without using centrifugal forces?  That's a bit of a gray area.)
The crew MCT would also have an access tunnel for access to the flight deck and on through to the hab area below it.
The Sat launcher would have a payload bay under the nose cap instead of a docking collar or access tunnel.  Something like Rocketplane Kistler K-1 (below).  The sat launcher has no need to refuel, so no need for a docking collar installed.
OML's are the same.

This is where I prefer the IBMCT.  Just one vehicle, rather than than two including the dedicated SII.  It's not an expendable "dumb" stage, it has to be it's own LEO reusable spacecraft in it's own right.  And may or may not share much with the booster and MCT.  There's extra cost in that.
The IBMCT would have the same tank tooling, bulkheads, etc as the booster.  So just 2 pieces with a lot of commonality.  That wouldn't be the case for the Super Capsule.  And may or may not be for NIBMCT depending on it's design.  If a full biconic, then it won't share much with anything else.  If a cylinder/biconic then it might, but it will run into issues that using booster sized tank tooling and domes will make the LOX tanks too big using 12m domes, because the tanks are smaller than IBMCT.  So you might need custom tankage anyway.


Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #615 on: 10/06/2015 11:38 PM »
I still think it makes little sense to have a LAS on a Mars SSTO such as "MCT". And in that case, it really makes no sense to put the crew (and cargo?) on top. It produces significant operational difficulties during when ground handling the vehicle on Mars.

One significant factor that needs to be taken into account for a biconic vehicle (which I advocate) is a the mass distribution. It needs to be have the proper balance when almost empty (normal atmospheric entry & landing), and it needs to be able to also have the proper balance for a near full propellant load. (Earth or Mars abort) Also, when near empty of propellant the vehicle must also be properly balanced for a full cargo load vs empty.

To handle this range, the layout that makes most sense (IMO) is to put the cargo/crew in the middle of the vehicle - with the LOX tank above, and Methane tank below. This would allow a balanced biconic sideways reentry with ANY cargo load, and ANY propellant load.

EDIT: See image below for how that might look, in this DC-Y(?) drawing:
« Last Edit: 10/06/2015 11:41 PM by Lars-J »

Offline RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #616 on: 10/06/2015 11:55 PM »
The first generation MCT is only going to carry a small crew, not the 100 passengers needed for colonization. So, instead of a separate LAS, the crew can ride up on a Dragon to meet the MCT in orbit.

Once the BFR and MCT stack is shown to be reliable, the crew can launch with the MCT.

Economics and insurance might demand a LAS even if the engineers don't think it is needed. Since we're talking about private spaceflight instead of the government, I'm sure they will need a LAS for the crew. Look at how much it costs the airlines when they are sued after a fatal crash. It might also be hard to find more colonists after 100 die in a BFR explosion.

Offline GregA

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Re: MCT Speculation and Discussion Thread 4
« Reply #617 on: 10/07/2015 12:09 AM »
The returning MCT should only have a small crew though, as most would be colonists left there.

Is there any reason to assume there is a "crew" vs "colonists"?
I think of them all as passengers.... does "crew" imply active employees of the SpaceX Transport?

We believe that the system will be mostly (all?) automated, and we know that the radiation maximums will prevent someone making several Earth-Mars trips (or even one!). So while some people will go back, I'm not sure there's a crew.

The working idea is that all concepts would have a Dragon 2 like nose hatch (maybe about 5m wide or so) under which could be a docking collar.  Tanker and depot dock in LEO and proceed to do a slow spin to settle propellants in the bottom of the tanks where it can then be pumped from the tanker to the depot, and later from the depot to MCT. 

Elon said at one stage that the MCT would go up first and then have tankers top it up. An interim depot adds complexity but reduces wait-time for passengers - and I can see it'd be safer for passengers to have a single depot fill-up.

Would you mind sharing the thought processes here?
(and thanks for all the thought sharing you've done here, L2 as well as the work itself!)

« Last Edit: 10/07/2015 12:11 AM by GregA »

Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #618 on: 10/07/2015 12:34 AM »
Isn't LOX heavier than Liquid methane? Also it will take twice the lox to burn the methane.  So shouldn't the Lox tank be on bottom with the Methane on top?   I also like the idea of a plug nozzle engine as depicted in the sketch.  It is not only a good engine all the way from ground to vacuum, but it can also become the heat shield when coming through the atmosphere from space.  Yes debris can flash back when landing on Mars, however, one could just have longer landing legs, that can retract after landing to lower the spacecraft.  Then raise the craft back up for take off. 
« Last Edit: 10/07/2015 12:36 AM by spacenut »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #619 on: 10/07/2015 02:33 AM »

That last is where a separable lifeboat LAS has an advantage.  Since MCT is a SSTO for Mars ascent, if there's an explosive problem with the main propulsion system, the crew is lost.  That'd be the case for full vehicle abort of the SDMCT and NIBMCT.  The LAS lifeboat can get away and then "fly" down range to a landing spot within it's ascent trajectory.  What they do when they land safely is another story.

If in the early exploration phase, the returning crew is small.  If the lifeboat is of sufficient size to support them until they can get to a backup vehicle somewhere else on the surface, then that would be good.  If later in colonization phase, there'd be a full colony with presumably long range rovers that could be dispatched for rescue.  The returning MCT should only have a small crew though, as most would be colonists left there.  So you really shouldnt' have to rescue 100 people, unless there's some abort from orbit and the lifeboat lands somewhere far away form the intended LZ 

The IBMCT would have 3 Raptors, but only two are needed for Mars ascent (maybe only one).  It has 3 because 3 are needed to get it from booster staging to LEO.  So it has engine-out backup for Mars EDL (with LAS assist) and it has engine out backup for Mars ascent.  And if the MPS exploded, it's LAS can abort the lifeboat away.

The SDMCT and NIBMCT have only two engines, as they don't do Earth ascent.  If there's an engine out at Mars ascent, there's some issue of how to handle it.  One engine thrusting at full throttle should keep it aloft long enough to burn off enough propellant so the LAS system can land it again for an emergency landing.  It might not be able to get to orbit, but it should be able to do a controlled emergency landing.  And it depends when the engine were to fail, far enough up just one engine should still get it home.

In Early exploration any abort to surface is fatal because their is zero rescue infrastructure on the surface and no conceivable capsule could carry sufficient supplies to see them through more then a few days.  So I consider this a pointless abort.  By the time you have an infrastructure to do surface rescue your passenger count is much too high for the small capsule your proposing, it would need to be a large vehicle comprising a significant portion of the whole mass of the vehicle and would present great difficulty in landing as you going to be falling on a ballistic trajectory from a high altitude and need massive retro-propulsion to not impact the surface, it in no way resembles the kind of un-powered capsule landing that can be done on Earth.

IF your using a semi-direct architecture and their is a waiting transit vehicle in mars orbit then abort to orbit may be viable, in a direct earth return architecture anything greater then mars escape velocity but short of the target trajectory is a heliocentric orbit that misses the Earth giving you a long slow death in space.

Also note that in my Separate Bi-conic concept their are 4 raptor engines with mars assent being possible with either diagonal pair so engine out capability is their during mars assent.  The same 4 raptor engines give you whole vehicle abort on launch from Earth because your intentionally not filling propellant tanks to full to keep mass low enough for fast full abort after a brief 1 second burn from the inter-stage pusher system described earlier by GORDAP.



And you have nothing in it to be a tanker (perhaps stretched tanks within the same Outer Mold Lines).  Just a big empty volume.

And you have some cryo-refrigeration equipment in it as a depot.

And you put a payload bay behind the nose to deploy FH and D4H class satellites to GTO.  The vehicle then comes back around on the GTO eliptical orbit to Earth, where it does a small deorbit burn and does Earth EDL.  Not expendable PLF required.

The working idea is that all concepts would have a Dragon 2 like nose hatch (maybe about 5m wide or so) under which could be a docking collar.  Tanker and depot dock in LEO and proceed to do a slow spin to settle propellants in the bottom of the tanks where it can then be pumped from the tanker to the depot, and later from the depot to MCT.  Propellant lines would run from the nose to the tanks.  (unless there's a way to pump liquids in zero g without using centrifugal forces?  That's a bit of a gray area.)
The crew MCT would also have an access tunnel for access to the flight deck and on through to the hab area below it.
The Sat launcher would have a payload bay under the nose cap instead of a docking collar or access tunnel.  Something like Rocketplane Kistler K-1 (below).  The sat launcher has no need to refuel, so no need for a docking collar installed.
OML's are the same.

This is where I prefer the IBMCT.  Just one vehicle, rather than than two including the dedicated SII.  It's not an expendable "dumb" stage, it has to be it's own LEO reusable spacecraft in it's own right.  And may or may not share much with the booster and MCT.  There's extra cost in that.
The IBMCT would have the same tank tooling, bulkheads, etc as the booster.  So just 2 pieces with a lot of commonality.  That wouldn't be the case for the Super Capsule.  And may or may not be for NIBMCT depending on it's design.  If a full biconic, then it won't share much with anything else.  If a cylinder/biconic then it might, but it will run into issues that using booster sized tank tooling and domes will make the LOX tanks too big using 12m domes, because the tanks are smaller than IBMCT.  So you might need custom tankage anyway.



I've said all along that an elongated 2nd stage would do tanker duty, and depots are in my opinion unnecessary, the MCT will act as it's own depot taking on propellants from visiting 2nd stages until it is full.  As MCT must depart Earth with some propellant for EDL at mars and must then hold significant amounts while on the martian surface (which while cold is still warmer then cryogenic LOX), so the MCT will have to have significant long-term cryo-storage capabilities likely through a combination of insulation and cryo-coolers, thus it makes an excellent depot. 

These cryo-systems along with radiators and solar arrays are the only systems that I would integrated into the vehicle.  Human habitats placed into the MCT are simply plugged into these utilities much like an RV.

As for the BFR I am looking at a 10 m core and 2nd stage, 19 Raptors on the core and 7 on the 2nd stage.  Gross take off mass of ~5,000 mT which would put 100 mT payload into LEO after reuse penalty which I'm estimating at 50% (first stage RTLS, 2nd once around the Earth to land at launch site).  This configuration would be used for conventional payload at the top in a fairing com-sat launches (3 at a time 10 mT each to GTO) as well as the any other high payload missions NASA can find and SpaceX's own LEO satellite swarms and finally with the stretched 2nd stage as the tanker delivery configuration with 100 mT of residual propellants to transfer.  Ideally we someday use this configuration to launch containerized cargo which will be loaded into the MCT in space so no longer have to launch the cargo and vehicle together.  This configuration is designed to maximize speed of turn around by minimizing waiting time to reassemble the vehicle and allows payloads to be readied separately and then mated to the 2nd stage just prior to launch.

A second higher power configuration is needed to launch the MCT when loaded with cargo but these are so infrequent (even if we were doing nothing but mars related launches propellant launches would be 3-4 times greater then MCT launches) it doesn't make sense to design the whole vehicle to do this one thing at the expense of smaller launches, rather is is a like today's modular rockets in which we boost the performance on only the edge cases with boosters.  In this case we use the F9H side booster and give it 4 Raptor engines making is very much resemble a Zenit booster, 6 of these raise the gross take off mass to ~7,200 mT and more then double the thrust, the boosters do a RTLS but the core will now be doing downrange landing.  With all the stops pulled out the payload should be over 200 mT to LEO which puts the MCT into orbit.


I don't know if you saw it earlier but I did a mass brake down of my MCT concept.  I'd like to see what the IBMCT comes out at.


Thermal protection at 5 kg/ m^2 over an area of 650 m^2:  5 mT

Tanks and Plumbing 5% of 300 mT propellant mass:  15 mT

Landing legs, 10% of touch down mass: 18 mT

4 Raptor Engines at 150:1 T:W ratio:  6 mT

Vernier Engines that can hover on landing at 100:1 T:W ratio:  1 mT

Solar, Radiator and computer systems:  5 mT

Structural skeleton, 1/3rd of dry mass: 25 mT

Total 75 mT dry mass
« Last Edit: 10/07/2015 03:23 AM by Impaler »

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