Author Topic: MCT Speculation and Discussion Thread 4  (Read 624035 times)

Online RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #2860 on: 09/24/2016 11:40 PM »
Lot of talk here seem to be about a single vehicle that will launch from earth, land on mars, and then return to earth.

That's the conventional wisdom around here. We'll find out Tuesday if it is correct.

Musk isn't one to waste things, surely he will be using Red Dragon vehicle to handle the Mars orbit to ground bit and the IST will just handle the Earth to Mars bit?

Dragon is far too small to handle the amount of cargo/passengers mentioned, about 100 tonnes. It also can't takeoff from Mars and get back in orbit.

It seems a bit risky to me to design a vehicle capable of being launch from earth with dozens of passengers and all their supplies sent to land to Mars and expect the same vehicle to do the reverse again.

It's up to the engineers to figure out how to do the mission at an acceptable level of risk. The first generation ITS could launch without its small crew. They could dock later with a Dragon. Of course, that doesn't help for the return trip.

Offline Bob Shaw

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Re: MCT Speculation and Discussion Thread 4
« Reply #2861 on: 09/25/2016 12:13 AM »
Dragons might make excellent Star Wars style escape pods for the MCT, lifeboats able to save the human cargo...

Offline Owlon

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Re: MCT Speculation and Discussion Thread 4
« Reply #2862 on: 09/25/2016 01:24 AM »
Dragons are heavy and carry a bunch of nasty, toxic hypergolic fuel. They're on the order of 1 ton per passenger fully fueled, which eats your entire payload budget with 100 passengers. Much more efficient to have a monolithic escape pod for the whole crew if you're going to have one at all.

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #2863 on: 09/25/2016 02:13 AM »

1- Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft (only)

With a modified version of BFS serving as cargo ships. And a modified version of the cargo-ships serving as the fuel-tugs. And a modified version of the fuel-tugs serving as the fuel-depot(s).

[And upon Musk mentioning this, we'll spend every day until the damn thing flies arguing angrily over whether they are standalone designs manufactured separately, or merely exchangeable modules (passenger/cargo/fuel) that fit into a single standard BFS. "Musk clearly said..." "No, read his actual..." For years. With half our comments getting deleted and a few of us getting banned. It's gonna be awesome.]

2- Number of Raptor Engines on BFR (1st stage)
     20 < N < 30.

3- Diameter of BFR (1st stage)
     12m (if BFS is cylindrical/biconic)
     15m (if BFS is elongated capsule)
...because they'll want to simplify manufacturing by using common tank tooling for everything, hence the Mars EDL method sets the diameter of the BFS, which sets the maximum diameter of the fuel-tug BFS, which sets the maximum diameter of the BFR tanks, which is the diameter of the BFR.

5- LAS Architecture
     a) No LAS - BFS is the escape mechanism

A very small chance of...
     c) BFS contains smaller 'ejection pod' where humans reside during launch
...but I doubt it. If you design an ejection pod capable of carrying 100 people away from a BFR launch, then you've created an entirely separate manned "capsule" which can be used for launching crew/passengers into orbit separately from the BFS. In which case, you'd change the whole architecture of the mission and probably look at orbital assembly, SEP, blah blah blah. But I'm hardly going to complain if they come up with something obvious-in-hindsight clever.

6- Shape and Landing Mode of BFS
     c) Cylindrical or biconic - vertical landing

Although I prefer...
     a) Capsule (perhaps elongated), w/ TPS on base
...with the Raptors arranged above the base, a la Superdracos, accepting the cosine losses in return for a much simpler design that works both on Mars and for Earth landing without any extra engines. But the required length of the fuel tanks may exclude a capsule-like design.

7- Mars and Earth return
     a) BFS does direct entry into Mars and Earth atmosphere

8-  Use of non-chemical thrust
     a) Not part of the plan

9-BONUS ROUND
     a) Once BFR is proven, it will replace all F9 derived vehicles for SpaceX's commercial satellite launches.

A cargo version of BFS could carry 5-10 GEOsats like a freakin' cubesat ejector on F9. Or GEOsats could fly as secondary payloads on SpaceX's fuel launches. (Get someone else to pay for your fuel launches for future Mars flights.) An affordable, fully reusable HLV changes the rules of the game.

10-DOUBLE BONUS ROUND
     d) None of the above.

Musk tones his presentation way, way down, speaking only in generalities, out of concern that providing too much detail about a future plan, immediately after the loss of another F9, will create a negative impression on existing customers and provide fodder to anti-SpaceX lobbyists ("they're distracted by their Mars obsession and that's why... therefore we shouldn't...") and hence we won't get definitive answers to any of GORDAP's questions except (4), Raptor details (which I skipped.)

Dragons might make excellent Star Wars style escape pods for the MCT, lifeboats able to save the human cargo...

The image amuses me immensely. (As long as I don't think about the details.)

[edit: "could will", might did.]
« Last Edit: 09/25/2016 09:09 AM by Paul451 »

Offline raketa

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Re: MCT Speculation and Discussion Thread 4
« Reply #2864 on: 09/25/2016 06:17 AM »
1/MCT bassic  architecture
a/BFR 1 stage
b/BFS 2 stage:
Mars version
Tanker version
Cargo version for LEO, GEO ,Moon,Mars and beyond delivery

2/Engine number
At least 30 Report engine

3/LAS for Earth and Mars emergency launch and landing
Just to make system survivable for bad day
On Mars it will land back on surface and team in rovers will come to rescue departing party

4/BFS Shape
Engine in bottom shielded by engine thrust, very similar to Dragon 2, just bigger and more space for fuel.


5/Electric propulsion
 for offseason emergency trips to Mars and from Mars,  using Dragon 2 or small version BFS

6/BFS will launch directly to Mars


Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #2865 on: 09/25/2016 07:03 AM »
An affordable, fully reusable HLV changes the rules of the game.
To think that several years ago, this would have been considered an oxymoron. That reusability would have to be designed for existing markets, that they would have small payload capacities because they would need very high flight rates to be economically viable.

If there was a demand of 100-200mT/yr propellant in LEO, then a very small RLV could be profitable. No sufficiently large markets seem likely for Falcon 9 sized payloads in the near future.

The need for high flight rates still applies now for fully reusable rockets, but this time SpaceX and Blue Origin are expecting to expand the market. I'm not sure whether to consider "build it and they will come" as a viable business strategy or just wishful thinking. There's still a possibility that launchers such as BFR and New Glenn might not pan out. But if they do, space will open up like never before.
« Last Edit: 09/25/2016 07:19 AM by Pipcard »

Offline DJPledger

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Re: MCT Speculation and Discussion Thread 4
« Reply #2866 on: 09/25/2016 08:13 AM »
SpaceX may decide to bite the bullet and dev. an F-1 class version of Raptor for BFR to avoid an N-1 type design and to carry over the octaweb design heritage of F9. Raptor is said to be highly scalable so there is no reason whatsoever that several sizes of it for different tasks can be dev. maybe except for dev. cost.

EM did say the plan do use only one size of Raptor throughout the BFR/MCT architecture may change during his AMA in January 2015.

I am sure EM knows what happened to the N-1 and I can't imagine him being that stupid.

Edited to correct tense regarding N-1.

We will find out on Tuesday.
« Last Edit: 09/25/2016 01:14 PM by DJPledger »

Offline mfck

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Re: MCT Speculation and Discussion Thread 4
« Reply #2867 on: 09/25/2016 10:13 AM »
SpaceX may decide to bite the bullet and dev. an F-1 class version of Raptor for BFR to avoid an N-1 type design and to carry over the octaweb design heritage of F9. Raptor is said to be highly scalable so there is no reason whatsoever that several sizes of it for different tasks can be dev. maybe except for dev. cost.

EM did say the plan do use only one size of Raptor throughout the BFR/MCT architecture may change during his AMA in January 2015.

I am sure EM knows what happening to the N-1 and I can't imagine him being that stupid.

We will find out on Tuesday.
Not to disagree with your point, but to nitpick on the phrasing:

Nothing is "happening" to the N-1 for decades

Even if someone, for whatever mystical reason, tried to recreate the N-1 today, for the purpose of producing the same failure, one would have failed miserably.

You'd need the Soviet industrial base, as it were at the time of N-1 production, the Soviet political augmentation of the design process and aerospace engineers with fraction of the knowledge they have today, all of which are pure unobtanium, hopefully, forever.

Edited for clarity
« Last Edit: 09/25/2016 10:17 AM by mfck »

Offline Hauerg

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Re: MCT Speculation and Discussion Thread 4
« Reply #2868 on: 09/25/2016 11:06 AM »
SpaceX may decide to bite the bullet and dev. an F-1 class version of Raptor for BFR to avoid an N-1 type design and to carry over the octaweb design heritage of F9. Raptor is said to be highly scalable so there is no reason whatsoever that several sizes of it for different tasks can be dev. maybe except for dev. cost.

EM did say the plan do use only one size of Raptor throughout the BFR/MCT architecture may change during his AMA in January 2015.

I am sure EM knows what happening to the N-1 and I can't imagine him being that stupid.

We will find out on Tuesday.

If you want/need to go for extreme reusability you might have to go to high number of engines anyway. Engine out & containing engine failures have to be designed as something that WILL be happening during the lifetime of every single stage. And to keep a reasonable production rate for the engines.

Offline Oersted

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Re: MCT Speculation and Discussion Thread 4
« Reply #2869 on: 09/25/2016 11:12 AM »
http://m.imgur.com/a/87OOT
- Was this proposal, by 'Coborop' on Reddit, ever discussed in this thread?

« Last Edit: 09/25/2016 11:12 AM by Oersted »

Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #2870 on: 09/25/2016 11:49 AM »
SpaceX may decide to bite the bullet and dev. an F-1 class version of Raptor for BFR to avoid an N-1 type design and to carry over the octaweb design heritage of F9. Raptor is said to be highly scalable so there is no reason whatsoever that several sizes of it for different tasks can be dev. maybe except for dev. cost.

EM did say the plan do use only one size of Raptor throughout the BFR/MCT architecture may change during his AMA in January 2015.

I am sure EM knows what happening to the N-1 and I can't imagine him being that stupid.

We will find out on Tuesday.

N-1 failed due to fuel system problems that would not exist under present engineering conventions.

Number of engines does not increase risk. Indeed, there's an argument that a high number of engines reduces risk.

It's usually safe to assume that SpaceX isn't "stupid", they're better informed and acting under better data.
« Last Edit: 09/25/2016 11:49 AM by The Amazing Catstronaut »
Resident feline spaceflight expert. Knows nothing of value about human spaceflight.

Offline Oli

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Re: MCT Speculation and Discussion Thread 4
« Reply #2871 on: 09/25/2016 01:24 PM »
http://m.imgur.com/a/87OOT
- Was this proposal, by 'Coborop' on Reddit, ever discussed in this thread?

Looks really cool but...

The sidewall angle of that thing is ~15°, which results in cosine losses of ~3.4%. Too much. In addition, the upper stage engines are used at launch, i.e. at sea level pressure, which would limit their efficiency even further.

Then there's the issue of the center of gravity of the BFS. For a capsule the CoG must be very low, I don't think that's compatible with having most of the payload at the top. The fuel for landing won't make up for that. In a capsule design I would put the tanks at the top and the payload at the bottom, probably with separate tanks at the bottom for the landing fuel.

Edit: Maybe you have seen the Mars ferry design in the attached picture.
« Last Edit: 09/25/2016 01:31 PM by Oli »

Offline DJPledger

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Re: MCT Speculation and Discussion Thread 4
« Reply #2872 on: 09/25/2016 01:24 PM »
SpaceX may decide to bite the bullet and dev. an F-1 class version of Raptor for BFR to avoid an N-1 type design and to carry over the octaweb design heritage of F9. Raptor is said to be highly scalable so there is no reason whatsoever that several sizes of it for different tasks can be dev. maybe except for dev. cost.

EM did say the plan do use only one size of Raptor throughout the BFR/MCT architecture may change during his AMA in January 2015.

I am sure EM knows what happening to the N-1 and I can't imagine him being that stupid.

We will find out on Tuesday.

N-1 failed due to fuel system problems that would not exist under present engineering conventions.

Number of engines does not increase risk. Indeed, there's an argument that a high number of engines reduces risk.

It's usually safe to assume that SpaceX isn't "stupid", they're better informed and acting under better data.
It only takes one engine to explode out of 30 to bring down an LV. I believe this happened to at least one of the N-1's. Anyone including SpaceX even attempting something like the N-1 beggars belief. The more engines you have the greater the risk of one of them exploding causing catastrophic LV failure. 5-9 engines is the optimum no. on a 1st stage to strike a balance between the risk of engine explosion and good engine out capability for benign engine failures. Lets hope that SpaceX have learned the N-1 lesson and the BFR design we should see on Tuesday will have much less than 30 engines on it.

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2873 on: 09/25/2016 01:29 PM »

1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.

Going with (a)

2) Number of Raptor Engines on BFR (1st stage)

< 30, my best estimate is 25-27 if thrust stays close to 230 tonnes range

3) Diameter of BFR (1st stage)

Range 12.5m-15m, best estimate 15m 1st stage

4) Total Raptor 1st stage thrust (sl)

60 Meganewtons and T/W > 1.3

5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
     d) Other, non-traditional LAS design

Best guess is (a)

6) Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

Going with (c), definitely no horizontal landing

7) Mars and Earth return
    a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod

(a)

8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road

(c) strongly favor

Can anyone think of more/better questions?

Predict Musk will miss 1st crewed landing by >= 3 synods

5-6 Rvacs on BFS stage 2

Raptor sea level will have 10s of tonnes thrust more than the 230 tonnes mentioned by Elon

Entire BFR/BFS GLOW masses under 5.000 tonnes; my estimate ~4,500

Height of BFR/BFS stack under 120m; my estimate <100m

Cargo version, tanker version, crewed version of BFS

1st crewed landing on Mars 8-12 humans planned

Just over 48 hours until Musk makes fools of us

« Last Edit: 09/25/2016 01:38 PM by philw1776 »
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Offline DJPledger

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Re: MCT Speculation and Discussion Thread 4
« Reply #2874 on: 09/25/2016 01:32 PM »

1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.

Going with (a)

2) Number of Raptor Engines on BFR (1st stage)

< 30, my best estimate is 25-27

3) Diameter of BFR (1st stage)

Range 12.5m-15m, best estimate 15m 1st stage

4) Total Raptor 1st stage thrust (sl)

60 Meganewtons and T/W > 1.3

5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
     d) Other, non-traditional LAS design

Best guess is (a)

6) Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

Going with (c), definitely no horizontal landing

7) Mars and Earth return
    a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod

(a)

8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road

(c) strongly favor

Can anyone think of more/better questions?

Predict Musk will miss 1st crewed landing by >= 3 synods

5-6 Rvacs on BFS stage 2

Raptor sea level will have 10s of tonnes thrust more than the 230 tonnes mentioned by Elon

Entire BFR/BFS GLOW masses under 5.000 tonnes; my estimate ~4,500

Height of BFR/BFS stack under 120m; my estimate <100m

Cargo version, tanker version, crewed version of BFS

1st crewed landing on Mars 8-12 humans planned

Just over 48 hours until Musk makes fools of us
And announces a >F-1 thrust version of Raptor to keep no. of engines on BFR to no more than 9.

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2875 on: 09/25/2016 01:36 PM »
http://m.imgur.com/a/87OOT
- Was this proposal, by 'Coborop' on Reddit, ever discussed in this thread?

Up-feed plumbing of propellant to Roc makes this way too complex & heavy.  Cosine losses and reduced engine performance by running stage 2 Roc at sea level for Earth launch a bad tradeoff.   Just add engines on 1st stage Sling until it's big enough to launch upper stage. 
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Online rakaydos

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Re: MCT Speculation and Discussion Thread 4
« Reply #2876 on: 09/25/2016 01:47 PM »
It only takes one engine to explode out of 30 to bring down an LV. I believe this happened to at least one of the N-1's. Anyone including SpaceX even attempting something like the N-1 beggars belief. The more engines you have the greater the risk of one of them exploding causing catastrophic LV failure. 5-9 engines is the optimum no. on a 1st stage to strike a balance between the risk of engine explosion and good engine out capability for benign engine failures. Lets hope that SpaceX have learned the N-1 lesson and the BFR design we should see on Tuesday will have much less than 30 engines on it.
SpaceX has been there and done that.

https://en.wikipedia.org/wiki/SpaceX_CRS-1#Falcon_9_engine_anomaly

Offline Oersted

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Re: MCT Speculation and Discussion Thread 4
« Reply #2877 on: 09/25/2016 02:06 PM »
Up-feed plumbing of propellant to Roc makes this way too complex & heavy.  Cosine losses and reduced engine performance by running stage 2 Roc at sea level for Earth launch a bad tradeoff.   Just add engines on 1st stage Sling until it's big enough to launch upper stage. 

I agree. It looks to me like he just dimensioned the "Sling" too small. Also not too convinced about the weather-vane (or shuttlecock) design. I think SpaceX will go with their tried and tested grid fins. Placed at the top of the first stage, obviously.

Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #2878 on: 09/25/2016 02:31 PM »
I'm not sure, but would having 30+ engines (even if they are on a single core instead of three) result in greater operational complexity? (such as in maintenance, inspection, turnaround time, etc.)

Now, I understand that if the second stage engines need to have a high enough thrust range between getting to LEO without too much gravity losses and landing almost empty (except for payload) in the 38% gravity of Mars (by having a fraction of the engines activated), and have commonalities with the first stage, there would need to be a lot of first stage engines.
« Last Edit: 09/25/2016 04:43 PM by Pipcard »

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #2879 on: 09/25/2016 04:58 PM »
I want to point out that the difference in gravity is not as important for landing as some people may think. Gravity is important if you want to hover. For braking to zero speed however the mass is the important metric and that is still the same. Just gravity losses during braking are smaller.

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