Author Topic: MCT Speculation and Discussion Thread 4  (Read 503866 times)

Offline Jcc

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Re: MCT Speculation and Discussion Thread 4
« Reply #640 on: 10/08/2015 01:09 AM »
Why wouldn't a Mars escape trajectory arc over some? Do you wait until Mars rotates exactly towards Earth and then launch? I'm being a little facetious, but you get the idea, you need to turn anyway, so why not reduce gravity losses while you are doing it.

Offline M_Puckett

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Re: MCT Speculation and Discussion Thread 4
« Reply #641 on: 10/08/2015 01:18 AM »
http://www.iflscience.com/space/huge-spacex-announcement-coming-soon-could-be-mars-mission

Ok Chris, you knew we were going to get ahold of this eventually. ;D

First question:  Bigger than a Breadbox?

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #642 on: 10/08/2015 01:25 AM »
[separate launch "taxi"]
That means you have two spacecraft to design from the start rather than one, but that's certainly an option.

But you propose two spacecraft in one. The LAS you propose is a separate spacecraft, according to you capable of full EDL. But it must also be integrated back into the MCT in a way that doesn't just allow it to break away as a LAS, doesn't just require it to be integrated tightly enough to handle re-entry while acting as the nose of the MCT (while still being able to break-away instantly), but its engines must also be able to serve as the landing engines for the whole MCT, both on Mars and on Earth.

(Plus you want another non-LAS "explorer" MCT for smaller crews. Plus yet another MCT design for cargo. So four spacecraft.)

I can't fathom how you think that is going to be somehow easier to nest two spacecraft inside each other like matryoshka dolls than to build them independently.

To use an analogy, do you think is would be cheaper/easier to design a car whose drivers-side wheels, seat and side panels split off to become a motorbike, or to just design a normal car and a separate normal motorbike?

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #643 on: 10/08/2015 01:42 AM »

First, it won't be just a few missions.  Probably all the missions for the first couple decades.  There will be many exploration missions with just a small crew before they can possibly think about actual colonization with large numbers of colonists.  You have to explore various potential location looking for a promising site with favorable conditions for a colony.  Then you have to test out the new systems which the colony will use, and test out resource collection, etc.  Not to mention I think it highly likely NASA would jump in bed with them as soon as it were to look likley they could land people on Mars.  They'll provide fund which will be beneficial for SpaceX, but they'll have their own agenda of places they want to go too. 

And you can only fly out every 2 years.  So, after maybe 20 years of Mars mission, you are ready to put 100 colonists on an MCT, what do you do then?
That's the question.


I'd like to second this emotion, Gradualism is the way things actually happen.  Far too much of the speculation about MCT assumes the usage will be immediately at some kind of designed maximum threshold and permanent settlements will be put down at the first spot on mars where mankind puts it's first footprints.  Initially mobility should be maximized to the point that I would recommend putting a single large rover/hab vehicle in each MCT to go completely nomad without a base of any kind other then having to return to the MCT for Earth return.    For example I might see a typical mission progression something like...

1 MCT with a crew of 6 + 1 cargo MCT
2 MCT with a crew of 12 each + 2 cargo MCT
4 MCT with a crew of 25 each + 12 cargo MCT
8 MCT with a crew of 50 each + 20 cargo MCT
20 MCT with crew of 100 each + 50 cargo MCT

In each stage your expanding crew while reducing mobility hardware for surface use and doing increasing amounts of base construction and consolidation.  Each of these 5 phases might take a decade which is hardly any time when we consider that's only 4 1/2 launch opportunities, less then the number of Apollo landings.

I've been developing a number of schemes for how to increase the tonnage sent to mars using the same basic bi-conic vehicle by leveraging it with auxiliary vehicles, mostly SEP spacecraft which would improve the efficiency and scale of the whole transport infrastructure over time while eliminating the need to constantly integrate new features into MCT.  The base vehicle alone would do a bare-bones mission and only the whole vehicle portfolio dose the huge volumes but they do them far more efficiently then simply having fleets of MCT's.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #644 on: 10/08/2015 01:58 AM »
Why wouldn't a Mars escape trajectory arc over some? Do you wait until Mars rotates exactly towards Earth and then launch? I'm being a little facetious, but you get the idea, you need to turn anyway, so why not reduce gravity losses while you are doing it.

No, by my understanding the gravity loss is minimized by moving away from the planet as fast as possible, that's why you go strait up and out and your launch window would be during the time of day when the line on which you want to escape mars on is as close to your local zenith as possible.  Their might be some deflection of your assent trajectory because the latitude your at means the ground normal is not actually point in that direction (planetary tilt matters here too) but your not arcing over to do 90% of your thrusting parallel to the ground as in an assent to orbit.

Offline GregA

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Re: MCT Speculation and Discussion Thread 4
« Reply #645 on: 10/08/2015 03:45 AM »
Hans Koenigsmann .... "but at least 100 times is our goal."
Should have asked earlier - assume it's BFR here due to thread. Is that right? (MCT can only launch every 18 months, so 100 uses is over 50 years)

Offline colbourne

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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #647 on: 10/08/2015 07:25 AM »
That's just SpaceX selling a rocket to any who can plunk the money down, once the payload is released SpaceX's job is done.

Offline rpapo

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Re: MCT Speculation and Discussion Thread 4
« Reply #648 on: 10/08/2015 11:21 AM »
Hans Koenigsmann .... "but at least 100 times is our goal."
Should have asked earlier - assume it's BFR here due to thread. Is that right? (MCT can only launch every 18 months, so 100 uses is over 50 years)
Whoever said they would only make one MCT?
An Apollo fanboy . . . fifty years ago.

Offline GregA

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Re: MCT Speculation and Discussion Thread 4
« Reply #649 on: 10/08/2015 11:27 AM »
Not sure that relates to how many times each MCT is reused... ?

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #650 on: 10/08/2015 12:22 PM »
Hans Koenigsmann .... "but at least 100 times is our goal."
Should have asked earlier - assume it's BFR here due to thread. Is that right? (MCT can only launch every 18 months, so 100 uses is over 50 years)

One MCT launch to Mars requires a minimum of 3-4 launches. Each synod needs at least 2 MCT to maintain a station, more to expand it, say at least 3. That's 9-12 launches every synod of 26 months. That's a bare minimum. I am quite sure there will be more.

Offline symbios

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Re: MCT Speculation and Discussion Thread 4
« Reply #651 on: 10/08/2015 01:22 PM »
Hans Koenigsmann .... "but at least 100 times is our goal."
Should have asked earlier - assume it's BFR here due to thread. Is that right? (MCT can only launch every 18 months, so 100 uses is over 50 years)

One MCT launch to Mars requires a minimum of 3-4 launches. Each synod needs at least 2 MCT to maintain a station, more to expand it, say at least 3. That's 9-12 launches every synod of 26 months. That's a bare minimum. I am quite sure there will be more.

I think Mr Musk was quite clear that he would do all possible for the MCT to return to Earth during the same synod. This would enable the same MCT to be serviced and reused during the next synod. Possible or not that is the goal.
I'm a fan, not a fanatic...

Offline GregA

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Re: MCT Speculation and Discussion Thread 4
« Reply #652 on: 10/08/2015 01:33 PM »
Hans Koenigsmann .... "but at least 100 times is our goal."
Should have asked earlier - assume it's BFR here due to thread. Is that right? (MCT can only launch every 18 months, so 100 uses is over 50 years)

One MCT launch to Mars requires a minimum of 3-4 launches. Each synod needs at least 2 MCT to maintain a station, more to expand it, say at least 3. That's 9-12 launches every synod of 26 months. That's a bare minimum. I am quite sure there will be more.

Not that it matters I guess, but ... my question doesn't matter. It MUST be the BFR.

(Your answer generalises it to the Mars Colonial Transport system. Which means BFR and tankers etc)

If the goal is for the MCT component that goes to Mars to be reused 100 times, and that component launches once every synod, but Koenigsmann doesn't think it'll last 30 years, then obviously he's talking about something else. If 2 or 10 MCTs launch that's not the same as a single MCT being reused 2 or 10 times.... but it would reuse the BFR.

Anyway, think we're just splitting hairs over it. I fully expect a single BFR (first stage) to launch a couple of MCTs, a bunch of tankers etc each synod.

(I'll have a listen to the speech and see if there was something else)
« Last Edit: 10/08/2015 01:37 PM by GregA »

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #653 on: 10/08/2015 02:21 PM »
Not that it matters I guess, but ... my question doesn't matter. It MUST be the BFR.

(Your answer generalises it to the Mars Colonial Transport system. Which means BFR and tankers etc)

I did not generalize to the MCT. Or at least it was not my intention. When I wrote it I had it in the back of my mind that other uses are possible too.  ;)

If the goal is for the MCT component that goes to Mars to be reused 100 times, and that component launches once every synod, but Koenigsmann doesn't think it'll last 30 years, then obviously he's talking about something else. If 2 or 10 MCTs launch that's not the same as a single MCT being reused 2 or 10 times.... but it would reuse the BFR.

My take on the statement was that he meant it will not fly daily for 30 years which would be over 10,000 uses.

(I'll have a listen to the speech and see if there was something else)

It is in german and there was not much else in it for us space fans. It was an interview in a general news magazine.

Offline GregA

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Re: MCT Speculation and Discussion Thread 4
« Reply #654 on: 10/08/2015 08:57 PM »
My take on the statement was that he meant it will not fly daily for 30 years which would be over 10,000 uses.
Ahh, so in a sense he was recontextualising reuse, almost to say that the MCT's version of reuse is still much less than a plane.

I think that makes more sense to me... thanks guckyfan.

It is in german and there was not much else in it for us space fans. It was an interview in a general news magazine.

I'd only understand 70% probably and it would take my full attention.... but may be good to keep my ear active.

Then again your report on the useful bit is already better probably!.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #655 on: 10/08/2015 09:37 PM »
I think Mr Musk was quite clear that he would do all possible for the MCT to return to Earth during the same synod. This would enable the same MCT to be serviced and reused during the next synod. Possible or not that is the goal.

A one synod cycle require opposition trajectory and a short (1 month) stay on Mars.  This will not be the initial flight mode simply because their is not enough time to produce return propellants.  Only one propellant infrastructure is built up can that become the norm so I don't expect that for many years.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #656 on: 10/08/2015 11:03 PM »
You are still not getting what I'm trying to say.

Actually I do.  I just don't think it'll be a deal-breaker in the design like you do.  As in, I think if SpaceX were to go with something like this, they'll address the issue of balancing out the mass for atmospheric entry.

I don't think the current arrangement is particularly out of balance.  When the Space Shuttle was doing atmospheric entry after delivering a cargo, most of it's mass was in the tail and nose too, I believe?

But, if actual engineers working on it do deem that it would be out of balance enough, then they'll work out a way to balance it better.  Could even be as simple as extra propellants left in the tank as ballast.  That option seems particularly flexible actually, as especially for cargo-only missions, the mass distribution can vary form mission to mission depending on what cargo is packed into the cargo area between the top of the tanks and the nosecone. 

If moving one of the tanks to the nose is the -only- possible solution, then they can do that.  But it would eliminate pretty much any possibility of an LAS system for an integrated design.  It would be ok for a non integrated biconic doing a whole vehicle abort.
« Last Edit: 10/08/2015 11:29 PM by Lobo »

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #657 on: 10/08/2015 11:13 PM »

It has to be a separate spacecraft, or it can't operate as a escape vehicle. Such a double-vehicle would become hideously complex.


Yes.  That's probably why such a cylinder-cone vehicle with a separable nose cone with a crew hab has never been thought of before.

;-)
« Last Edit: 10/08/2015 11:50 PM by Lobo »

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #658 on: 10/08/2015 11:25 PM »
[separate launch "taxi"]
That means you have two spacecraft to design from the start rather than one, but that's certainly an option.

But you propose two spacecraft in one. The LAS you propose is a separate spacecraft, according to you capable of full EDL. But it must also be integrated back into the MCT in a way that doesn't just allow it to break away as a LAS, doesn't just require it to be integrated tightly enough to handle re-entry while acting as the nose of the MCT (while still being able to break-away instantly), but its engines must also be able to serve as the landing engines for the whole MCT, both on Mars and on Earth.

(Plus you want another non-LAS "explorer" MCT for smaller crews. Plus yet another MCT design for cargo. So four spacecraft.)

I can't fathom how you think that is going to be somehow easier to nest two spacecraft inside each other like matryoshka dolls than to build them independently.

To use an analogy, do you think is would be cheaper/easier to design a car whose drivers-side wheels, seat and side panels split off to become a motorbike, or to just design a normal car and a separate normal motorbike?

It's not really two spacecraft in one, like MCT+ S2 would be two completely separate spacecraft.  It's more a spacecraft, with an additional section.  Since everything below the lifeboat cannot function on it's own as it own spacecraft.
So unlike your analogy, it's more like a semi tractor and trailer.  They can be one combined vehicle, or the tractor can operate on it's own.   Hence the term "Integrated Biconic MCT".  Where a main propulsion stage is "integrated" with habitat, rather than two separate main propulsion stages on two vehicles.

Or I suppose, like a Command Module and Service Module. 

It's something we are looking into to address concerns of an LAS...and of landing on Earth.  Please let that be the last time I have to repeat that.  I'm wholly unqualified (and unpaid) to design an entire MCT all by myself, and I never claimed otherwise.
Yes, of course there are design challenges in this, just as there are in any design. 

Input is welcome, and if it's actually constructive I will take it back to the team and we can kick it around as see about concept modifications.  :-)




« Last Edit: 10/09/2015 12:06 AM by Lobo »

Offline TomH

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Re: MCT Speculation and Discussion Thread 4
« Reply #659 on: 10/08/2015 11:52 PM »
You are assuming the major risk is in the cruise phase. I assume it is during launch, TMI and landing

STS's major failures were during launch and landing, but those failures had to do with flawed design. The only serious in-flight failure Apollo ever had certainly was during cruise phase.
« Last Edit: 10/09/2015 12:01 AM by TomH »

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