Author Topic: MCT Speculation and Discussion Thread 4  (Read 610889 times)

Offline Rocket Surgeon

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Re: MCT Speculation and Discussion Thread 4
« Reply #560 on: 10/02/2015 01:55 AM »
I've got a question about the general biconic MCT (both integrated and non-integrated). It looks like the abort rockets are designed to save pretty much everything north of the fuel tank, but would it be better to have a small, dedicated abort section? Essentially just cram everyone into the nose and pop it off if something goes wrong. Something like the recent planete-mars biconic design, and maybe double it as a solar storm shelter. That way the abort engines could be small and even use a storable propellants (like hypergolics or solids) or (my personal favorite) use methalox that is temporarily charged when they are likely to be needed (ie during launch or possibly entry).

Given that the abort rockets aren't being used for landing, and you're only focusing on saving the people, it could save a fair bit on weight.

http://planete-mars.com/analyse-dun-concept-mars-colonization-transport-mct-a-deux-lancements/4/
« Last Edit: 10/02/2015 02:03 AM by Chris Bergin »

Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #561 on: 10/02/2015 04:20 AM »
Or how about this radical idea. Drop the abort capsule altogether. I've argued this before, but the idea seems to be very ingrained in people, almost like the idea of landing a shuttle with wings "horizontally" on Mars. Both ideas make just as much sense, IMO.  (In other words, not much sense)

There is no place to abort to when landing on or taking off from Mars. If you find launch abort essential for Earth departure, shuttle people up while the MCT is in LEO being refueled.

At some point you've got to put "big boy pants" on if you want to go to Mars. Or roll a hard six. Or name your own analogy. :)
« Last Edit: 10/02/2015 05:24 AM by Lars-J »

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #562 on: 10/02/2015 07:13 AM »
What does it take to keep Raptor ready for ignition from takeoff? Let the full MCT be the escape capsule. It may not cover every catastrophic event but should be able to get MCT away from a first stage for anything short of an explosion without any advance warning time.


Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #563 on: 10/02/2015 07:33 AM »
Or how about this radical idea. Drop the abort capsule altogether. I've argued this before, but the idea seems to be very ingrained in people, almost like the idea of landing a shuttle with wings "horizontally" on Mars. Both ideas make just as much sense, IMO.  (In other words, not much sense)

There is no place to abort to when landing on or taking off from Mars. If you find launch abort essential for Earth departure, shuttle people up while the MCT is in LEO being refueled.

We know that most flights will be for cargo - they don't need an abort system.

It is likely, in my opinion, that crew and cargo MCT will be identical (at least at first). What makes them different would be the cargo for the crew MCT would be the hab.

First crew sizes are likely to be quite small - under 15. So will fit into a couple of Dragon 2.

We've been told that payload back is ~ 25% of payload there, so ~ 25 tonnes. It is really hard to fit an abort system (capsule?) + hab for 100 (or even 15) into 25 tonnes - even if they return dry and empty.

Later flights might use an optimised crew MCT.

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #564 on: 10/02/2015 07:47 AM »
Sending a passenger MCT back should not be a problem with 25t cargo. Sending passengers and consumables may  become a problem even if way less than 100.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #565 on: 10/02/2015 07:57 AM »
That approach doesn't really work to maximize the rest of the vehicle.

EITHER:
The MCT launches full of fuel and has lots of delta V, which maximizes the payload mass fraction to orbit, but has a TWR too low to use for launch abort
OR:
The MCT launches empty of fuel and has high TWR, but with low enough delta V that part or all of the BFR has to come close to, or reach, orbit.  This lowers payload mass fraction by a large amount, or for a fixed payload makes the BFR required substantially larger.
OR:
The MCT launches with an order of magnitude more engine power than it will require for the rest of the mission, which is retained as waste mass throughout the rest of the mission, reducing space for other payload, or increasing launch requirements, by a large factor.
« Last Edit: 10/02/2015 08:01 AM by Burninate »

Offline docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #566 on: 10/02/2015 09:20 AM »
That approach doesn't really work to maximize the rest of the vehicle.

EITHER:
The MCT launches full of fuel and has lots of delta V, which maximizes the payload mass fraction to orbit, but has a TWR too low to use for launch abort
OR:
[The MCT launches empty of fuel and has high TWR, but with low enough delta V that part or all of the BFR has to come close to, or reach, orbit.  This lowers payload mass fraction by a large amount, or for a fixed payload makes the BFR required substantially larger.
OR:
The MCT launches with an order of magnitude more engine power than it will require for the rest of the mission, which is retained as waste mass throughout the rest of the mission, reducing space for other payload, or increasing launch requirements, by a large factor.

Musk has already said MCT will refuel in orbit. It seems reasonable that this could happen at both ends, if needed.
« Last Edit: 10/02/2015 09:23 AM by docmordrid »
DM

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #567 on: 10/02/2015 09:25 AM »
That approach doesn't really work to maximize the rest of the vehicle.

I don't see it that way. I already stated that it will not be able to speed away from an explosion without warning. But it can separate from a failing first stage with shut down engines. Being heavy it would have to burn a lot of fuel before it can land. There is that one point that it will not have enough time to go through a lengthy precooling period. That's why I asked if Raptor can be kept in a state ready for ingnition throughout launch.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #568 on: 10/02/2015 06:33 PM »
I ran across this MCT speculation/article, from the French chapter of the Mars Society: (my apologies if this has already been discussed)

ANALYSIS OF A CONCEPT IN MARCH COLONIZATION TRANSPORTATION (MCT) LAUNCHES TWO [google translation]
http://planete-mars.com/analyse-dun-concept-mars-colonization-transport-mct-a-deux-lancements/

If you have the chrome browser, it will automatically translate the site for you.

Here are some interesting images from the MCT architecture of this article:
Image 1: Two MCT's docking in LMO for propellant transfer
Image 2: Launch abort module interior
Image 3: Launch abort module from behind
Image 4: MCT landed horizontally on Mars
Image 5: MCT interior
Image 6: BFR base
Image 7: BFR/MCT stack

In is an interesting concept, but I'm not sure that horizontal landing is practical. And their MCT seems to be lacking any kind of engines for propulsion.

Hmmm...this seems so familiar, where have I seen this before?

Oh yea...from me...earlier in this thread....  :-)

(except with vertical landing rather than horizontal).

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1401739#msg1401739


Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #569 on: 10/02/2015 06:41 PM »
BTW, here is a link to the author's (Richard Heidmann) previous articles on the subject: http://planete-mars.com/author/heidmann/

He has really gone all in on the horizontal landing idea... Anything else doesn't seem to enter his mind as a possibility.

Looks like Heidmann evolved some from his space plane looking concept to a more cylindrical bionic concept...like mine.  :-)

He does like that horizontal landing and take off thing though.  And not quite sure how HCT gets itself from booster staging to LEO without aft engines.  It just pitches horizontal after staging be enigne ignition?

I still like the vertical style with aft engines myself.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #570 on: 10/02/2015 07:23 PM »
That approach doesn't really work to maximize the rest of the vehicle.

I don't see it that way. I already stated that it will not be able to speed away from an explosion without warning. But it can separate from a failing first stage with shut down engines. Being heavy it would have to burn a lot of fuel before it can land. There is that one point that it will not have enough time to go through a lengthy precooling period. That's why I asked if Raptor can be kept in a state ready for ingnition throughout launch.

Or how about this radical idea. Drop the abort capsule altogether. I've argued this before, but the idea seems to be very ingrained in people, almost like the idea of landing a shuttle with wings "horizontally" on Mars. Both ideas make just as much sense, IMO.  (In other words, not much sense)

There is no place to abort to when landing on or taking off from Mars. If you find launch abort essential for Earth departure, shuttle people up while the MCT is in LEO being refueled.

At some point you've got to put "big boy pants" on if you want to go to Mars. Or roll a hard six. Or name your own analogy. :)


First crew sizes are likely to be quite small - under 15. So will fit into a couple of Dragon 2.

We've been told that payload back is ~ 25% of payload there, so ~ 25 tonnes. It is really hard to fit an abort system (capsule?) + hab for 100 (or even 15) into 25 tonnes - even if they return dry and empty.

Later flights might use an optimised crew MCT.

The team (for fun team...on our own time) I've been working with and Hyperion has posted some on over on L2 have preferred an LAS system. however, this was my original preference too.

Putting an extra Raptor on the integrated MCT.  AS well as on the booster.  That way if there's an engine out on the booster, it can compensate and get MCT to proper staging point.  If there's an engine out on MCT, then it can get nominally to Orbit, and then can abort the mission and come home.

This cannot get away from an exploding booster, as Burninate points out:

That approach doesn't really work to maximize the rest of the vehicle.

EITHER:
The MCT launches full of fuel and has lots of delta V, which maximizes the payload mass fraction to orbit, but has a TWR too low to use for launch abort
OR:
The MCT launches empty of fuel and has high TWR, but with low enough delta V that part or all of the BFR has to come close to, or reach, orbit.  This lowers payload mass fraction by a large amount, or for a fixed payload makes the BFR required substantially larger.
OR:
The MCT launches with an order of magnitude more engine power than it will require for the rest of the mission, which is retained as waste mass throughout the rest of the mission, reducing space for other payload, or increasing launch requirements, by a large factor.

But it can handle the most common failure, and engine problem. 
It could do an emergency separation from the booster early, but the engines would need to be brought on line, so there's a window from launch to that point where some multi-engine booster failure would result in no abort scenario. 

But yes, early missions will probably have 4-6 crew, and a single D2 can take them up to MCT in orbit, no LAS needed.  Missions will grow and two D2's would still be feasible.  The problem is later when you have 100 people.  That's a lot of D2's to fill it up.  At that point it would probably be desirable to launch them on MCT.  So either you need an LAS, or just take a more "Space Shuttle" or "Airliner" approach.  Lots of redundant system, but if something goes boom, there's not contingency for that.  By that time there'd probably literally be dozens of MCT launches, so hopefully you'd know then if it was reliable or not.
That was my original thought.

However, there are some LAS options with some benefits.

The first is a separable crew/hab section, like Heidmann has.  The crew is in their launch seats and that aborts off from an exploding booster.  Then it propulsively lands.  A lifeboat LAS.
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.
The 3rd option Burninate mentions, just to have a very overpowered integrated MCT is problematic because Raptors will need time to come up to ignition.  That's why pressure fed fast reacting engines like Superdracos would be necessary.  Even if Raptor could do it, then you have a lot more Raptors that you need for the rest of the mission.

So as I like my pet integrated biconic MCT concept from earlier in this thread, I go back to that at a separable crew section.  This some additional potention advantages other than just LAS.

1)  Once separated, it's a traditional biconic vehicle (see below).  It could be separated when in-bound to Mars or Earth if there's a problem with the rest of the vehicle.  As it will have the TPS system, it can do it's own EDL. 

2)  It could be used for launch abort when lifting off of Mars.  Although there would have to be some infrastructure on Mars for the crew to then be able to access.  Or they'd be marooned wherever the lifeboat landed.

3)  Additionally, it can be used to land MCT on Earth.  Raptor will be a vacuum nozzle, which could very well not work at sea level if it's too over expanded.   You'd need some sort of retractable nozzle, jettisonable nozzle, or something else.  But, the propulsive dV requirement for landing on Earth is pretty low.  Terminal velocity will be about 120MPH.  So the LAS system...if it were external like Dragon 2's, could be used to land MCT on Earth without Raptor needed.
The propulsive dV on Mars is much greater, but it's near vacuum so Raptor can be used to supply that efficiently on Mars, with the LAS thrusters being used for hover and landing assist. 
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.
Like super versions of the cold gas thrusters F9 booster uses.  And they'd be pressure fed, deeply throttleable, and fast reacting.  Very good for hovering and landing.

So, for reason #3, I do now favor having them.  This gets around actually having to hover and land on Raptor...which may be hard to design to react and throttle to that degree.  The ones positioned on the ventral (chin) side would need to be desinged in a way so they are protected during EDL.  But the Space shuttle has RCS/OMS thrusters in the nose that are protected during EDL, so I would think that could be done. 

Now...how -much- do you abort?  Everything north of the tanks?  Or just a lifeboat crew section?
I favor the lifeboat crew section, and make that the biconic nose of the vehicle.  The nose aborts away from the cylinder. 
Or the nose plus whatever part of the cylinder is hab only, leaving a cargo deck with the tanks.  The reason being is if you have an exploration mission with say a crew of 7, you might have 50mt of cargo below the hab to support them on the surface.  How big does the LAS needs to be to take all of that cargo with it?
If you do want to land with the LAS system, it will have to be at least large enough to somewhat slow and hover about 125mt on Earth and 200 X 0.38g = 76mt equivalent on Mars.  A system that can do that might be able to quickly abort away about 35mt from an exploding booster, but not 70mt with cargo.

So there'd need to be some trades done to see how large it needs to be to double as a landing system, and then seem how much abort mass it can handle.  And figure a sweet spot from there.  Obviously the abort requirements are much greater than the hover and landing requirements.
 
(The bottom pic is the full integrated biconic MCT doing atmospheric entry.)

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #571 on: 10/03/2015 12:11 AM »
Nice concept. But quite frankly, I like the concept developed in L2 better. Hyperion et al. seem to have a better handle on the subject. Its very interesting to the development though and only good things can come from independent groups tackle the same problem.

It's actually evolved quite a lot towards the Integrated Biconic MCT I talked about here a few months ago, and the team has been fleshing out and posting on L2.  Heinmann's first concept was sort of a booster assisted SSTO space plane.  I like this better, but I don't really like the horizontal landing.  Seems like it'd be hard to keep the engines balancing the CoG if propellant is sloshing around.  And it'd have to have a side feed system, rather than a traditional bottom feed for a vertical configuration.  Not to mention you need engine doors in your TPS...which seems like it would be better if it can be avoided.
I think the difficulties of getting cargo and crew to the surface for a taller vertical lander are less than the difficulties of side/ventral side propulsion like this.

So I like ours better too.  :-)

Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #572 on: 10/03/2015 12:57 AM »
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

Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #573 on: 10/03/2015 12:58 AM »
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...
« Last Edit: 10/03/2015 01:00 AM by Lars-J »

Offline GORDAP

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Re: MCT Speculation and Discussion Thread 4
« Reply #574 on: 10/03/2015 01:08 AM »
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?

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #575 on: 10/03/2015 04:01 AM »
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."

I'm looking at a MCT vehicle that at launch has 175 mT total dry mass and a modest 20 mT of propellents for launch abort and landing.  That means a launch mass of 200 mT that needs to be pushed away from the rest of the vehicle in an emergency.  4 Raptor engines at their 2,300 KN each would provide sufficient thrust to accelerate the MCT away at about 5 g's which is comparable to a Dragon capsule.

Note that if abort occurs at anything other then during the early phases of the first stage burn then the MCT vehicle would certainly land in the ocean and as the location is unplanned a platform won't be available so it will be a touchdown into water (much like the early F9 first stage tests).  The empty tanks should make the vehicle buoyant but it would float quite low in the water such that cargo and passenger compartments would be well underwater.  Needless to say the salt-water contact would necessitate a considerable disassembling and rebuilding of the whole vehicle and it's engines, but I can't see any abort scenario that doesn't put the vehicle in the water if were launching from typical launch sites like Canaveral.  I think we should just be happy everyone is OK in such a situation.

In addition I've been thinking about a set a smaller faster operating vernier engines operating on Metho-Lox with the thrust equivalent to ~10 Super Dracos used primarily during touchdown on Mars and Earth.  I like your idea of placing these on the upper flanks of the vehicle as this solves a head-ache I've had with finding the space for them on the bottom of the vehicle and provides better leverage over the vehicle, and it will eliminate entirely any rocket plume impinging on the ground on Mars an important safety concern.  Cosine loses shouldn't be a problem as they fire for such time.  On Mars the bulk of supersonic retro-propulsion would be via Raptor at the highest efficiency.  Using these engines during abort should add an additional 8% more thrust so why not use it, besides they should start faster then the Raptors which is out main concern when using them for abort.

BTW Lobo, you may be interested in an idea I've had for assisting a biconic vehicle in landing on Mars by use of a mechanically deployed and reusable decelerator.  The rear of the vehicle consists of body flaps much like the two steering flaps you've show on your concept, but they extend around the entire vehicle.  These extend right after the peak deceleration heating to widen the vehicle and steer it.  Once in the supersonic range the second expansion occurs in which telescoping spare extend from the back side of the flaps and deploy a cloth sail of nomex of some other comparable material between each spar.  This should slow the vehicle considerable while still allowing steering and because it's deployed after peak heating the fabric is not chard/ablated and is fully reusable while being thin and light.  It would still necessitate propulsive landing but it might save considerably on entry mass as the mass of a decelerator is generally less then the mass of propellant it replaces.






Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #576 on: 10/03/2015 04:03 AM »
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.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #577 on: 10/03/2015 05:29 AM »
Agreed, a pushing fast-start 1 second abort motor located in the interstate is a very clever solution.

I think the solid booster solution is viable (though SpaceX seems to dislike all pyrotechnics).  Also it doesn't need to really be the whole of the inter-stage, all you really need is a naked thrust-structure that connects the abort motor to the bottom of the MCT which can generate and transmit the ~9 million N of thrust.  As that is a lot of force I would recommend just sticking cones into the nozzles of the Raptors and pushing on them directly (a bit like the new center-pusher stage separator) so your reusing the thrust structure of the vehicle itself as if the engines were running without having to create new hard-points that bypass the engines.  As the Raptors start up they will simply push out the abort motors as they are burning out.

Based on the total impulse of the Shuttle boosters and their total mass I would estimate that to deliver 9 million N-s of total impulse would require 15 mT of solid rocket motors, quite heavy.  But total take off mass might be lessened by the fact that your putting less abort propellents in the MCT itself.  Still it is a hit to take on returning the stage it is on.  If that is a first stage it should be do able without much problem, but if it's a 2nd stage as I've proposed it looks like it could be problematic.


So I propose to do the Dragon abort trick, use the abort engine to land the 2nd stage in the event that no abort happens.  That means if their is an abort the 2nd stage is sacrificed even if the fault is in the first, but your probably fleeing an explosion that was going to destroy it anyway so no big loss.  Now the abort system isn't as parasitic because we MUST have smaller vernier engines to land a second stage, the main propulsion system of Vacuum Raptor engines is not going to cut it as their are too few engines and they can't throttle low enough or safely at Sea Level.  Though certainly the amount that we need for abort is over kill over what we would for just landing.

If a Super-Draco like liquid engine in used you would need A LOT of them, like 120 to get the same thrust, around a 10 m core you should just manage to get that on the vehicle in a giant ring of engines packed side by side.  In reality I think we will see some new engine several times more powerful then Super Draco (SuperDuber Dracos??) and the number will be more reasonable.  Still a large number of engines will make touch-down very easy, no only can you come to halt really fast but with such a large depth of throttle it should be possible to put the stage down on very delicate tooth-pick landing gear which should save considerable mass.

Offline Semmel

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Re: MCT Speculation and Discussion Thread 4
« Reply #578 on: 10/03/2015 12:52 PM »
Well, Lars.. I don't want to persuade anyone of joining L2. If you want to support the exististances of this Web page, join. If you think it's not worth it then don't. Your money, your choice.
We are not allowed in L2 to discuss public links and here we are not allowed to discuss content from within L2. My comment was unspecific because I don't have an other choice.

Offline Semmel

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Re: MCT Speculation and Discussion Thread 4
« Reply #579 on: 10/03/2015 01:02 PM »
I am not sure an interstage abort system would work. The mechanical loads on the MCT would be 10 or more times stronger during an abort than during normal operation. The MCT including fuel would need an acceleration of 5+gs as opposed to less than 1. Plus the force to overcome atmospheric pressure at max Q. The parasitic mass would be within the metal structure of MCT instead of fuel and abort angines. I am not sure that is lighter than a crew abort capsule. Also you can't abort from an exploding MCT during first ascend on earth or ascent on Mars. An ascent abort on Mars might be required when a colony is already established and an infrastructure for rescue on Mars is available.

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