Author Topic: MCT Speculation and Discussion Thread 4  (Read 610827 times)

Online docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #2880 on: 09/25/2016 05:06 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.
>

F9 CRS-1 had an engine fuel dome fail, but unlike N1 Falcon has armor around its engines to protect neighboring engines  from engine failures. The perimeter engine cells also have blowout panels.

CRS-1's avionics shut down the propellant flow to that engine and Dragon continued on its way to ISS. IIRC, it arrived a tad early.

No doubt BFR will get the same engine out capability as it's served them well.
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Offline dror

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Re: MCT Speculation and Discussion Thread 4
« Reply #2881 on: 09/25/2016 07:52 PM »
My unaducated daydream is that the Benjamin Franklin System will be very much like a scaled up Falcon 9:

9 Raptor engines at the ~10m core,
1 Raptor vac seconed stage,
1 XL Dragon2 for the crew variant or payload bay or tanker for cargo and fuel.

The big difference is that the capsule will remain attached to the second stage through the whole flight_refuel_flight_land_refuel_flight_land cycle.
The combined due will EDL at mars retropropulsivly, tail first, like the Falcon 9 core does.
The capsule allows abort throughout the whole cycle, but otherwise remains attached.

I know the stack has a high CG and that it keeps the little people high above the surface, but I try not to think about it too much.
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Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #2882 on: 09/25/2016 07:55 PM »

And announces a >F-1 thrust version of Raptor to keep no. of engines on BFR to no more than 9.

Why do you assume early Sixties engine logic still applies? The base principles of rocketry do indeed move that slowly. The engineering, materials science, and practically everything else, do not.
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Offline Melanchthon

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Re: MCT Speculation and Discussion Thread 4
« Reply #2883 on: 09/25/2016 11:11 PM »
...

1) a) MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft (only)
2) 30 Raptor Engines on BFR (1st stage)
3) 15m Diameter of BFR (1st stage)
4) ~20 Mlbf SL thrust (~2.5x Saturn V)
5) c) BFS contains smaller 'ejection pod' where humans reside during launch
6) c) Cylindrical or biconic - vertical landing
7) a) BFS does direct entry into Mars and Earth atmosphere
8) c) All chemical for now, but plans to incorporate SEP down the road
« Last Edit: 09/25/2016 11:11 PM by Melanchthon »

Online docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #2884 on: 09/26/2016 02:31 AM »
1. b)  Boost phase consists of 2 stages, a BFR booster and integrated S2/BFS
     
2. 30 engines

3. 15 meter BFR, 50% possibility BFS is 16+ meters

4.18 mlbf

5. c) BFS contains upper LAS pod where crew/passengers reside during launch or landing.

6. d) a mix of capsule (LAS pod) and cylindrical which includes a drop cargo section. Side entry & rotation to vertical for landings. LAS pod has its own capsule mode entry heat shield just in case.

7. a) BFS does direct entry into Mars and Earth atmosphere
 
8.  c) All chemical for now, but plans to incorporate SEP/NEP down the road. NEP for beyond Mars: Callisto etc.
« Last Edit: 09/26/2016 02:36 AM by docmordrid »
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Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #2885 on: 09/26/2016 02:54 AM »
But really though, does the number of engines on a stage have any effect on rapid reusability?
« Last Edit: 09/26/2016 03:28 AM by Pipcard »

Offline Oersted

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Re: MCT Speculation and Discussion Thread 4
« Reply #2886 on: 09/26/2016 02:59 AM »
If you want to scale up production and flight rate as much as Musk envisions, it is a great boon to have maximum commonality between engines, both on the first and second stage. Also for purposes of reliability and repair. 

Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #2887 on: 09/26/2016 03:29 AM »
Also for purposes of reliability and repair.
That's what I meant, wouldn't it take longer to repair/inspect 30 engines on one stage compared to 9 or 20? Extra person-hours required for turnaround, etc.
« Last Edit: 09/26/2016 05:48 AM by Pipcard »

Offline MichaelBlackbourn

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Re: MCT Speculation and Discussion Thread 4
« Reply #2888 on: 09/26/2016 05:25 AM »
Here she is!

Musk via twitter:

SpaceX propulsion just achieved first firing of the Raptor interplanetary transport engine https://t.co/vRleyJvBkx


Online docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #2889 on: 09/26/2016 06:04 AM »
@elonmusk
Production Raptor goal is specific impulse of 382 seconds and thrust of 3 MN (~310 metric tons) at 300 bar

310t = 694,400 lbf.
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Offline malu5531

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Re: MCT Speculation and Discussion Thread 4
« Reply #2890 on: 09/26/2016 06:05 AM »
Raptor design targets;
Quote
Production Raptor goal is specific impulse of 382 seconds and thrust of 3 MN (~310 metric tons) at 300 bar

Will help in modelling MCT if we assume they reach these goal.

Second tweet;
Quote
Chamber pressure is almost 3X Merlin, so engine is about the same size for a given area ratio

Some quick calculations show it's possible to achieve 333s SL Isp in ~same size as Merlin (1.08m diameter) and same area ratio as Merlin, if exhaust pressure is high (1.7x atmosphere) @ 587 klbf and 800 kg/s fuel. (673 klbf @ 382s Isp with Vac nozzle @ 4m diameter). Would improve Isp to go with a bit higher nozzle diameter for exhaust pressure < 1 at SL.

Edit: SL version would be ~334s Isp at 1 atm exhaust pressure with 1.32m diameter nozzle.
« Last Edit: 09/26/2016 06:38 AM by malu5531 »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2891 on: 09/26/2016 07:10 AM »
1 - B, second stage of BFR has 6 engines and will become reusable through repeated trial and error, acts as tanker, propellant depot, TMI booster and sat-launch workhorse.

2 - 31 engines in honeycomb pattern around central landing engine, some engines ungimbaled or on single axis

3 -  10 to 12 m tank manufactured at Mchoud, nearly all carbon fiber, with some wider cowlings around peripheral 1st stage engines similar to Saturn V.

4 - 71MN, 16 million pounds

5 - A, BFS carries minimal propellant at launch and small fast pressure fed or solid boosters give initial push followed by Raptor engines as they come up to full thrust, RTLS for pad abort, water landing for late aborts.

6 - A, BFS will be generally Dragon capsule like in shape and flight plan and employ a radially expanding decelerator at mars to augment it's base heat-shield.  4 Raptor engines peripherally located, low central roll-on-roll-off cargo-hold, tanks above and in flanks.

7 - B, in the sense that the vehicle will be capable of aerocapture if necessary, though direct entry may be nominal flight plan.

8 - C, technically only the BFR design is finalized and when BFS is revealed eventually its mission will use SEP likely as an add on to the BFR 2nd stage tanker which moves it into position for refueling beyond LEO as Earth return will not be direct.



« Last Edit: 09/26/2016 09:17 PM by Impaler »

Offline DJPledger

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Re: MCT Speculation and Discussion Thread 4
« Reply #2892 on: 09/26/2016 11:42 AM »

And announces a >F-1 thrust version of Raptor to keep no. of engines on BFR to no more than 9.

Why do you assume early Sixties engine logic still applies? The base principles of rocketry do indeed move that slowly. The engineering, materials science, and practically everything else, do not.
Looks like crazy EM is going for an N-1 type design for BFR after all judging from the announced Raptor thrust. Lets hope the 1st 4 BFR's don't explode on or just after launch.

Offline malu5531

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Re: MCT Speculation and Discussion Thread 4
« Reply #2893 on: 09/26/2016 11:59 AM »


My best guess

1 - a (BFS 2nd stage is MCT)
2 - 46x raptor on 1st stage, multiple used for landing, for redundancy
3 - 15m
4 - 120 MN SL thrust
5 - Redundant raptors on MCT for LAS / no LAS needed
6 - c
7 - a (or combination with b where there is more than one pass through atmosphere before landing)
8 - a / c

Offline DJPledger

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Re: MCT Speculation and Discussion Thread 4
« Reply #2894 on: 09/26/2016 12:02 PM »


My best guess

1 - a (BFS 2nd stage is MCT)
2 - 46x raptor on 1st stage, multiple used for landing, for redundancy
3 - 15m
4 - 120 MN SL thrust
5 - Redundant raptors on MCT for LAS / no LAS needed
6 - c
7 - a (or combination with b where there is more than one pass through atmosphere before landing)
8 - a / c
Target BFR thrust stated by EM and Raptor announced thrust seems to indicate 25-27 Raptors which is still too many for my liking.

Offline Darkseraph

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Re: MCT Speculation and Discussion Thread 4
« Reply #2895 on: 09/26/2016 12:10 PM »
I'm guessing:

1) The booster stage will have more than 9 engines but less than 22.
2) It will be a fully reusable two stage system not including the ICT spacecraft
3) A variant of the second stage functions as a tanker
4) Booster stage will be 10-12 meters in diameter
5) The Spacecraft itself may be slightly wider than this.
6) Initial crews will be sent to the ICT in orbit, on Dragon2 flights. ICT won't have an escape system.
7) Raptor will first be tested out on an upper-stage for Falcon 9/Heavy.
8 ) This upper stage will be used for scaled tests of docking and refueling in space.
9) Falcon 9 will be eventually phased out and replaced by a raptor based reusable vehicle scaled closer to New Glenn.
10) SEP Barges for cargo are a future growth path for the Mars architecture.
11) The ICT will have an unusual configuration to both protect from radiation and allow easy and safe access to Martian surface.


*This will all be probably horribly wrong when they announce their plans tomorrow. Whatever it is, I hope it is surprising!
 
« Last Edit: 09/26/2016 01:16 PM by Darkseraph »
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Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2896 on: 09/26/2016 01:20 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

May have got one right with Elon's announcement of 310 tonnes thrust for Raptor. 
Not sure if Rvac or Rsea level, believe Rvac with sea level having less thrust.

If this be so, BFR may have ~19-21 engines.
« Last Edit: 09/26/2016 01:22 PM by philw1776 »
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Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #2897 on: 09/26/2016 02:08 PM »
Also for purposes of reliability and repair.
That's what I meant, wouldn't it take longer to repair/inspect 30 engines on one stage compared to 9 or 20? Extra person-hours required for turnaround, etc.
I'm guessing now that this won't be a very huge problem (or will it?), because when Falcon 9's first stage has 9 engines, people aren't talking about how this is harder to maintain than one big engine + at least 2 small engines on the sides for landing; people instead talk about how it is more expensive to maintain production of multiple engine types instead.
« Last Edit: 09/26/2016 02:26 PM by Pipcard »

Offline Mike_1179

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Re: MCT Speculation and Discussion Thread 4
« Reply #2898 on: 09/26/2016 03:25 PM »
Also for purposes of reliability and repair.
That's what I meant, wouldn't it take longer to repair/inspect 30 engines on one stage compared to 9 or 20? Extra person-hours required for turnaround, etc.
I'm guessing now that this won't be a very huge problem (or will it?), because when Falcon 9's first stage has 9 engines, people aren't talking about how this is harder to maintain than one big engine + at least 2 small engines on the sides for landing; people instead talk about how it is more expensive to maintain production of multiple engine types instead.

Like most things that are complicated, the answer is probably "it depends".

If you have fewer engines and you're running chamber temperatures and pressures as high as the materials in the turbo-machinery will allow, you might be a situation where individual components have lower margins or safety factors. This could necessitate higher levels of support to get something in shape to run.

A less powerful engine may have a less extreme environment for its various components, meaning tolerances for some aspects can be larger and require less work.

While not directly applicable to man-hours required, the RS-68 was designed as a less expensive engine than the RS-25. The RS-68 has thrust-to-weight almost 20% lower than the RS-25 and a 10% lower Isp. While the two engines aren't directly comparable because many other design features makes the RS-68 cheaper, you can't assume that because a vehicle has 4x the number of engines, it will take 4x as many hours to get ready for flight.

Offline GORDAP

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Re: MCT Speculation and Discussion Thread 4
« Reply #2899 on: 09/26/2016 04:36 PM »
O.K. I want to change my guess for number of engines from 31 to 27.

And this isn't just because Musk informed us that the thrust is going to be higher than previously hinted at. ;)

It's also because I realized that, while 31 gives a very nice, minimum diameter packing pattern with a single center engine (like the F9), having a single center (landing) engine is probably not appropriate or desired here.  It's unlikely that the BFR could land on a single engine - just too heavy.  3 centralized engines would probably be appropriate.  And the nice symetrical, minimum pattern for 3 center engines comes out to be 27.

We'll know in just over a day (I hope).

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