Author Topic: MCT Speculation and Discussion Thread 4  (Read 504239 times)

Offline Zed_Noir

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Re: MCT Speculation and Discussion Thread 4
« Reply #1520 on: 01/30/2016 07:16 AM »
Using a BFS tanker variant for orbital depot is thinking small.

Propose using a slightly modified BFR core as prop depot with one Raptor Vac engine.

Send it up to LEO as upper stage on top of a regular BFR with enough prop to make LEO orbit. Fill the depot core up with many later BFS tanker flights. Docked a combination sunshade, solar arrays, radiator arrays, refrigeration and  refueling structure with austere temporary accommodation to it in travel mode. Move to EML-2 assembly location for the Martian Colonial fleet. Detached the support superstructure and re-docked it in the depot mode with the prop depot core. Fill up to 2 BFS at the same time before the BFSs departed for Mars during a launch window.

Other prop depot cores will ferry more propellants to the EML-2 prop depot as needed.

The prop depot core will be able to land like the regular BFR cores for periodic servicing.

Dubbed this propsal as the BFD (Big F@#king Depot :) )


Also a stripped down expendable prop depot core or BFD could be use as a departure stage for high velocity missions to the outer Solar system from EML-2.

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1521 on: 01/30/2016 07:51 AM »
Using a BFS tanker variant for orbital depot is thinking small.

 :)

I prefer to call it thinking efficiency. It would mainly use existing hardware that has been used to exhaustion for its original purpose. It would mean needing less ullage for fuel transfer. It would mean plenty of depots up there. A small delay in launch and you chose another depot to target. The method would serve well for a few hundred MCT. When it goes into the thousands a bigger depot may become more efficient.

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #1522 on: 01/30/2016 06:08 PM »
We've read elsewhere (Reddit) of really HUGE BFRs.  So large that if you filled even a fraction of their height with propellant way over 50 engines would be needed to lift off. Here, the speculation has mostly centered around BFRs with 25-30ish engines.  Still far larger than Saturn V or Nova class.
IF the optimum Raptor engine thrust size still remains ~230 metric tonnes force, is SX looking at possibly smaller, less engine/plumbing complex BFRs in the high teens to 21ish # of engines for most economical sized launchers?  As long as the BFR can put the 2nd stage dry weight into LEO it's big enough.  Or maybe even a couple launches plus in orbit assembly. Cargo, fuel, etc. could launch on subsequent flights.  Of course these "small" BFRs would have to be so much less expensive to build, maintain and fly that many times more refueling flights per Mars transit launch still makes economic sense.  Arguing against my own question, it seems to me that the largest launcher you can build and fly repeatedly would be the most economical.  Flight operations costs are not zero, plus they would include support of LEO propellant & cargo transfer ops.

Given Elon's Day One focus on economics, I find it difficult to believe that size/complexity/cost tradeoffs aren't fundamental to their ongoing architectural analysis.  September's reveal will be beyond interesting.
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline BSenna

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Re: MCT Speculation and Discussion Thread 4
« Reply #1523 on: 01/30/2016 06:28 PM »
And probably, the BFR 1st stage will not be designed for leaving the upper atmosphere.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #1524 on: 01/30/2016 06:38 PM »
And probably, the BFR 1st stage will not be designed for leaving the upper atmosphere.
If you include the ionosphere in that you are correct, but like an F9 RTLS booster I expect it to go above 200km.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline BSenna

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Re: MCT Speculation and Discussion Thread 4
« Reply #1525 on: 01/30/2016 06:50 PM »
I say, it doesn't have reentry capability. In the first reusable F9 or FH animation, the upper stage was also expected to reenter and landing, but then they decided it doesn't worth.

Offline TomH

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Re: MCT Speculation and Discussion Thread 4
« Reply #1526 on: 01/30/2016 07:18 PM »
We've read elsewhere (Reddit) of really HUGE BFRs.  So large that if you filled even a fraction of their height with propellant way over 50 engines would be needed to lift off. Here, the speculation has mostly centered around BFRs with 25-30ish engines.  Still far larger than Saturn V or Nova class.

Do you know how big some Nova designs were? There were dozens and dozens of them.
http://astronautix.com/lvs/novamm1c.htm

Nova MM 1C:
Gross mass: 11,516,800 kg (25,390,100 lb).
Payload: 444,000 kg (978,000 lb).
Height: 119.00 m (390.00 ft).
Diameter: 21.00 m (68.00 ft).
Thrust: 144,157.50 kN (32,407,895 lbf).
And this wasn't some internet amateurs' fantasy. It was a study by Martin Marietta.
The F-1A engine was actually built and developmental work done on the M-2.
« Last Edit: 01/30/2016 07:36 PM by TomH »

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1527 on: 01/30/2016 07:45 PM »
We've read elsewhere (Reddit) of really HUGE BFRs.  So large that if you filled even a fraction of their height with propellant way over 50 engines would be needed to lift off. Here, the speculation has mostly centered around BFRs with 25-30ish engines.  Still far larger than Saturn V or Nova class.
IF the optimum Raptor engine thrust size still remains ~230 metric tonnes force, is SX looking at possibly smaller, less engine/plumbing complex BFRs in the high teens to 21ish # of engines for most economical sized launchers?  As long as the BFR can put the 2nd stage dry weight into LEO it's big enough.  Or maybe even a couple launches plus in orbit assembly. Cargo, fuel, etc. could launch on subsequent flights.  Of course these "small" BFRs would have to be so much less expensive to build, maintain and fly that many times more refueling flights per Mars transit launch still makes economic sense.  Arguing against my own question, it seems to me that the largest launcher you can build and fly repeatedly would be the most economical.  Flight operations costs are not zero, plus they would include support of LEO propellant & cargo transfer ops.

Given Elon's Day One focus on economics, I find it difficult to believe that size/complexity/cost tradeoffs aren't fundamental to their ongoing architectural analysis.  September's reveal will be beyond interesting.
Shotwell mentioned about BFR a few months ago at the South Summit 2015 (Oct 7-9), in Madrid, " [Falcon Heavy] This one is about 4M pounds of thrust, and the mock... the vehicle that takes us to Mars will be three or four times that size"

https://www.youtube.com/watch?v=omBF1P2VhRI?t=10m46s

(original video, mostly Spanish-language conference proceeding, but Shotwell's voice still appears beneath a title graphic for the first ten minutes, though not her face.  The video I linked above seems to have been created a while after this one was promoted, and does a proper cut to her presentation alone)

I also vaguely remember her mentioning offhand that they were developing a 180-210t to LEO superheavy launcher.  I've been trying to find the interview, but can't turn anything up.

There's still some play in those words if you stretch it - is the "vehicle" the stage 1 BFR?  the stage 2 MCT?  Is she referring to thrust or mass?  With that said... a reasonable interpretation is that BFR stage 1 will start out with 24 to 40 500klbf Raptors, with maybe a few extra if they don't start out operations at full thrust.
« Last Edit: 01/30/2016 07:50 PM by Burninate »

Offline kch

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Re: MCT Speculation and Discussion Thread 4
« Reply #1528 on: 01/30/2016 07:49 PM »
We've read elsewhere (Reddit) of really HUGE BFRs.  So large that if you filled even a fraction of their height with propellant way over 50 engines would be needed to lift off. Here, the speculation has mostly centered around BFRs with 25-30ish engines.  Still far larger than Saturn V or Nova class.

Do you know how big some Nova designs were? There were dozens and dozens of them.
http://astronautix.com/lvs/novamm1c.htm

Nova MM 1C:
Gross mass: 11,516,800 kg (25,390,100 lb).
Payload: 444,000 kg (978,000 lb).
Height: 119.00 m (390.00 ft).
Diameter: 21.00 m (68.00 ft).
Thrust: 144,157.50 kN (32,407,895 lbf).
And this wasn't some internet amateurs' fantasy. It was a study by Martin Marietta.
The F-1A engine was actually built and developmental work done on the M-2.

... and then there's this wee beastie:

http://astronautix.com/lvs/novagde.htm

:)

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1529 on: 01/30/2016 07:53 PM »
"There's always a bigger fishrocket"

There have been studies of all sorts of things, but the Nova we're talking about is the one that LC39a and b were sized for.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline TomH

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Re: MCT Speculation and Discussion Thread 4
« Reply #1530 on: 01/30/2016 08:49 PM »
...the Nova we're talking about is the one that LC39a and b were sized for.

My reply was not to you. It was to philw1776, re. his "Nova class":

...Nova class...
"
The stuff he's talking about is the stuff of internet fantasy and he claimed it's "way" bigger than anything of Nova class. It isn't. And these were studies done by aerospace companies, not amateur crowdsourcing.
« Last Edit: 01/30/2016 08:59 PM by TomH »

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #1531 on: 01/30/2016 09:38 PM »
Class was a bad choice of wording on my part.  To clarify, I intended to refer to the Nova that Robotbeat was referring to that NASA sized LC39a and b for.
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline Umbrella

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Re: MCT Speculation and Discussion Thread 4
« Reply #1532 on: 01/31/2016 03:00 PM »
Since Shotwell has said BFR will be 3x - 4x FH (at most 2x Saturn V) and Musk describes tanker refueling in orbit in the Vance book, that looks like the way they will go.  However, this is going to require many tanker flights for each BFS transit.  Some people have estimated as few as 3-4 tanker flights, but when I run numbers 8 or more seems more realistic.  This means some significant cryocooling equipment to capture boil off for the 80% of propellant that is LOX.  This equipment has not been needed before since up to now cryo propellants have been burned shortly after liftoff.  Cryocooling has been used in orbit for the smaller amounts of cryo liquids used to cool sensitive instruments, but will it scale up very well to handle about 1,000 MT of LOX for a BFS ?
« Last Edit: 01/31/2016 03:12 PM by Umbrella »

Offline BSenna

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Re: MCT Speculation and Discussion Thread 4
« Reply #1533 on: 01/31/2016 03:23 PM »
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

Offline Umbrella

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Re: MCT Speculation and Discussion Thread 4
« Reply #1534 on: 01/31/2016 03:29 PM »
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

BTW, note the cryocooling requirement kicks in with just about any orbital refueling architecture, probably even for just 1 tanker flight and propellant transfer.

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1535 on: 01/31/2016 03:31 PM »
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

That has been speculated a lot a while back. But Elon Musk has explained that 100t it usable payload, not vehicle mass.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #1536 on: 01/31/2016 04:04 PM »
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

BTW, note the cryocooling requirement kicks in with just about any orbital refueling architecture, probably even for just 1 tanker flight and propellant transfer.

Which argues strongly for a depot from my point of view along with the idea that in the early days when only a few BFRs exist having a depot could allow for a significant increase in the number of BFSs that can launch in one window.

It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Umbrella

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Re: MCT Speculation and Discussion Thread 4
« Reply #1537 on: 01/31/2016 04:17 PM »
Which argues strongly for a depot from my point of view along with the idea that in the early days when only a few BFRs exist having a depot could allow for a significant increase in the number of BFSs that can launch in one window.

An orbital depot is probably a requirement just because it would be very inefficient for BFS and/or the tankers to have to lug around the cryocooling equipment. 

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1538 on: 01/31/2016 04:29 PM »
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.

« Last Edit: 01/31/2016 04:31 PM by Burninate »

Offline Ionmars

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Re: MCT Speculation and Discussion Thread 4
« Reply #1539 on: 01/31/2016 04:29 PM »
In regards to the MCT Depot, I think we are in the early planning stages where general issues can be discussed before any commitments will be made. I am trying to devise a few tools to help the discussion.

Attached is an simple Excel spreadsheet that calculates some data for this purpose. The inputs are the number of berths (Line 2), the assumed diameter of MCT (line3), and the minimum acceptable gravity force at the tank location closest to the depot center (line15). Some of the data of interest to me are depot diameter, the  highest gravity force that will be recorded at the outermost edge of each tank, and the rotational acceleration required to achieve these gravity forces. These are just a few of the factors to be considered. Please check it out.
« Last Edit: 01/31/2016 04:35 PM by Ionmars »
* Mars' orbit: a convenient service station for an asteroid-sized spaceship en-route to Ceres. *

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