Author Topic: MCT Speculation and Discussion Thread 4  (Read 503515 times)

Online AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #2220 on: 06/11/2016 01:06 PM »
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.

BFS is likely designed to reach LEO with little fuel remaining.  Refueling is essential.
This is not one-shot rocketry.
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Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2221 on: 06/11/2016 01:16 PM »
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.

BFS is likely designed to reach LEO with little fuel remaining.  Refueling is essential.
This is not one-shot rocketry.
BFS would necessarily be able to reach LEO with lots of fuel, just not also with a maximum payload. So the point stands.

But refueling will be needed early on.
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Offline linxiaoyi

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Re: MCT Speculation and Discussion Thread 4
« Reply #2222 on: 06/11/2016 01:47 PM »
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.

BFS is likely designed to reach LEO with little fuel remaining.  Refueling is essential.
This is not one-shot rocketry.
I think a BFS with only main rocket systems(tanks, engines, control, etc),can reach a TMI and land on Mars surface by a single launch.
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Online AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #2223 on: 06/11/2016 01:47 PM »
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.

BFS is likely designed to reach LEO with little fuel remaining.  Refueling is essential.
This is not one-shot rocketry.
BFS would necessarily be able to reach LEO with lots of fuel, just not also with a maximum payload. So the point stands.

But refueling will be needed early on.

If payload is 100-200 tonnes, and dry mass is comparable, replacing a large fraction of payload mass with propellant still provides a very low payload mass fraction.  That said, there could easily be conventional second stages and payloads designed for delivering significant Lunar payloads (10-15m fairing?) on BFR.  Just haven't heard any hints taking us in that direction.

Still don't see BFS going much of anywhere without refueling.
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Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2224 on: 06/11/2016 01:59 PM »
Dry mass likely to be much less than the payload. At least for cargo configuration.

There's one area where SpaceX has proven the ability to advance performance WELL beyond the current state of the art, and that's mass fraction.
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Offline linxiaoyi

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Re: MCT Speculation and Discussion Thread 4
« Reply #2225 on: 06/11/2016 02:44 PM »
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.
A BFS with only main rocket systems can reach LLO and back without refueling.But it's not worth.
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Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2226 on: 06/11/2016 03:18 PM »
Dry mass likely to be much less than the payload. ...

Doesn't need to be that much less, a 1:1.35 ratio of dry mass to payload saves enough propellent for TLI. In this case, a 100t ship and nominal 135t payload, for 235t IMLEO.

Forego 99% of the payload and it should reach orbit with enough remaining prop for a 3200m/s burn.

However, that only tests deep space flight and low-mass re-entry. In order to really test interplanetary re-entry it needs an interplanetary payload, so refueling will be implemented quite quickly.

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2227 on: 06/11/2016 04:13 PM »
I ran the #s in my spreadsheet simulator and yes, a lightly loaded BFS can reach LEO with more than enough tons of propellant to do a lunar free return and Earth landing.  Apollo 8 redux!
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Offline docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #2228 on: 06/11/2016 04:32 PM »
As large as its likely to be, and with baked in habitation, could a BFS be considered a lunar "base" if left in place? Guessing it depends on ease of egress/ingress, crew rotation landers and power generation, but still.
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Offline Mongo62

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Re: MCT Speculation and Discussion Thread 4
« Reply #2229 on: 06/11/2016 04:51 PM »
IAC Congress schedule (scroll down):

Friday, September 30 at 8:30 to 10:30 -- Late Breaking News: Elon Musk Space X Title to Be Confirm - Mars

So two hours on the final morning of the congress.
« Last Edit: 06/11/2016 04:54 PM by Mongo62 »

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2230 on: 06/11/2016 04:53 PM »
Newer refined model for BFR/BFS. Spreadsheet attached.

   BFR & BFS MODELS: MCT as 2nd Stage with 100  Metric Tons CARGO   
      BLUE: Enter parameter variable
S1 Avg ISP Sea L to MECO   335   
S2 vac ISP   380   
Raptor sea level thrust KLB & mT   518   235
Rvac thrust KLB & mT   559   254
S1 Dry Wt %    4.5%   
      
   BFR 1   
BFR DIA   15.0   m
MCT BFS Dry Wt & Cargo   225   mT
S2 Dry Mass   125   mT
Propellant for S2 BFS Landing   30   mT
Total Mass to LEO   255   mT
1st Stage Propellant Tank Length   18.0   m
S1 Propellant Volume   3179   m3
Propellant Mass   3371   mT
S1 Dry Wt %    4.5%   
S1 DRY Weight   159   mT
S1 Total Weight mT   3529   mT
S! Dry Wt Delta V (No 2nd stage)   10.2   Km/sec Rocket Equation
Stage One Full Load Delta V    3.35   Km/sec Rocket Equation
RTxx Propellant   70   mT
RTxx Delta V @Minimum Load   1.20   Km/sec Rocket Equation
Est S1 Gravity Loss    0.9   Km/sec
Est S1 Velocity @ Burnout   2.45   Km/sec
2nd Stage Propellant Tank Length   7.5   m
Propellant Volume   1,325   m3
Propellant Mass   1,404   mT
S2 Mass w/MCT   1,629   mT
S2 Mass w/MCT   3.6   Million LBS
Calc # Rvac Raptor Eng   5.01   0.78
Stage 2 Thrust mT   1271   
Stage 2 Thrust   2.8   Million LBS
Stage 2 Km/sec    6.91   Km/sec Rocket Equation
Stage 2 Wet to Dry Mass Ratio   12.2   
S1 + S2  Total Delta V   9.4   Km/sec
TOTAL WT mT   5,159   mT
TOTAL WT LBS   11.4   Million LBS
THRUST Needed LBS   14.0   Million LBS
THRUST Needed mT   6345   
THRUST Needed MegaNewtons   62   
1st Stage T/W @ Takeoff   1.23   
1st STAGE # ENG    27   
LEO Mass Fract   4.4%    %
LEO Wet to Dry Mass Ratio   23    F9 v1.1 25/1 Musk
MCT Cargo Hold length   10   m
MCT Cargo Vol m3   1766   m3
   Eng 16+8+3=27   
   Outer Ring, Inner Ring, Central Engs   
   NOTE 1:   S1 Km/sec + S2 Km/sec must ~9Km/sec for LEO with grav losses
   NOTE 2:   Rocket Equation   
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Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2231 on: 06/11/2016 05:40 PM »
As large as its likely to be, and with baked in habitation, could a BFS be considered a lunar "base" if left in place? Guessing it depends on ease of egress/ingress, crew rotation landers and power generation, but still.
If Tiangong can be considered a space station, then sure, why the heck not?
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Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2232 on: 06/11/2016 06:06 PM »
As large as its likely to be, and with baked in habitation, could a BFS be considered a lunar "base" if left in place? Guessing it depends on ease of egress/ingress, crew rotation landers and power generation, but still.
If Tiangong can be considered a space station, then sure, why the heck not?
I doubt the hab will be baked in, which probably helps. Thermal control during the month long day/night cycle is an issue though.

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Re: MCT Speculation and Discussion Thread 4
« Reply #2233 on: 06/11/2016 06:27 PM »
As large as its likely to be, and with baked in habitation, could a BFS be considered a lunar "base" if left in place? Guessing it depends on ease of egress/ingress, crew rotation landers and power generation, but still.
If Tiangong can be considered a space station, then sure, why the heck not?
I doubt the hab will be baked in, which probably helps. Thermal control during the month long day/night cycle is an issue though.
According to Musk, it will be.
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Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2234 on: 06/11/2016 06:55 PM »
Musk said the life support will have to be very light, and that everything would be reused with nothing discarded. That's not incompatible with the hab being modular. Nor is it incompatible with the hab being left somewhere to be reused.

Offline pobermanns

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Re: MCT Speculation and Discussion Thread 4
« Reply #2235 on: 06/11/2016 06:56 PM »
Musk quoted in the Washington Times article:

"Being a product scheduling professional, my mind started backing off that date all of the physical tasks that needed to happen in just 6 short years.  …...

And if we're talking MCT, we have to assume the BFR will also be under development.  That is a lot.  I would imagine we'll get a sense of the schedule of events when Musk unveils more details in September, and as he says in the article:

I think that lots of guys have shared your skepticism about the timeline. But do you think that slippage of one synod would not be OK for this grand plan? Meaning, that he's shooting for the 2022 synod but expects the next one to be achievable.

From a leadership standpoint, it seems that this plan might be very effective to motivate the "true believers" to put in their 100%. He's got a real strong cadre with world-class skills, but they need a clear goal. If he sets a goal for 2022, they'll bust their a**es to make it happen. If that comes to pass, GREAT, but if it slips for whatever technical reasons, won't this still be a winning situation? All of them will understand why thy didn't *quite* make it for that synod, and they'll be stoked to make it happen for the next  one.
« Last Edit: 06/11/2016 06:59 PM by pobermanns »

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2236 on: 06/11/2016 07:00 PM »
I would definitely bet that SpaceX is unlikely to meet the 2025 window for crew. Musk said 2025 is the date if everything went according to plan. You and I and Musk know that not everything goes according to plan. So yeah, I'd say 2027 is more likely for crew. But yeah, they'll probably have to be working on MCT realsoonnow. Break ground on launch site by 2018/2019.
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Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #2237 on: 06/11/2016 07:12 PM »
Break ground on launch site by 2018/2019.

Which would require start of a EIS tomorrow I would guess. Unless there is a site with a special deal for EIS, is there? At the cape, anywhere?

Offline Coastal Ron

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Re: MCT Speculation and Discussion Thread 4
« Reply #2238 on: 06/11/2016 07:25 PM »
I think that lots of guys have shared your skepticism about the timeline. But do you think that slippage of one synod would not be OK for this grand plan? Meaning, that he's shooting for the 2022 synod but expects the next one to be achievable.

I will cheer them on regardless, since despite any inevitable slips to their schedule they will likely be far ahead of anyone else, and it won't be costing me any of my tax dollars.  This is free entertainment as far as I'm concerned.

Quote
From a leadership standpoint, it seems that this plan might be very effective to motivate the "true believers" to put in their 100%. He's got a real strong cadre with world-class skills, but they need a clear goal. If he sets a goal for 2022, they'll bust their a**es to make it happen. If that comes to pass, GREAT, but if it slips for whatever technical reasons, won't this still be a winning situation? All of them will understand why thy didn't *quite* make it for that synod, and they'll be stoked to make it happen for the next  one.

I think Musk is very good at keeping his employees and followers motivated, and no doubt setting challenging goals is part of that.  Doable, but challenging.

Also, there are other aspects to his plan that we don't see yet, and I think part of that is assembling funding partners.  And according to the plan he's announced, they will need a lot money upfront to do everything he wants to do, so I think he's announcing these dates as part of his fundraising efforts.
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Online MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2239 on: 06/11/2016 09:05 PM »
Newer refined model for BFR/BFS. Spreadsheet attached.

   BFR & BFS MODELS: MCT as 2nd Stage with 100  Metric Tons CARGO   
      BLUE: Enter parameter variable
S1 Avg ISP Sea L to MECO   335   
S2 vac ISP   380   
Raptor sea level thrust KLB & mT   518   235
Rvac thrust KLB & mT   559   254
S1 Dry Wt %    4.5%   
      
   BFR 1   
BFR DIA   15.0   m
MCT BFS Dry Wt & Cargo   225   mT
S2 Dry Mass   125   mT
Propellant for S2 BFS Landing   30   mT
Total Mass to LEO   255   mT
1st Stage Propellant Tank Length   18.0   m
S1 Propellant Volume   3179   m3
Propellant Mass   3371   mT
S1 Dry Wt %    4.5%   
S1 DRY Weight   159   mT
S1 Total Weight mT   3529   mT
S! Dry Wt Delta V (No 2nd stage)   10.2   Km/sec Rocket Equation
Stage One Full Load Delta V    3.35   Km/sec Rocket Equation
RTxx Propellant   70   mT
RTxx Delta V @Minimum Load   1.20   Km/sec Rocket Equation
Est S1 Gravity Loss    0.9   Km/sec
Est S1 Velocity @ Burnout   2.45   Km/sec
2nd Stage Propellant Tank Length   7.5   m
Propellant Volume   1,325   m3
Propellant Mass   1,404   mT
S2 Mass w/MCT   1,629   mT
S2 Mass w/MCT   3.6   Million LBS
Calc # Rvac Raptor Eng   5.01   0.78
Stage 2 Thrust mT   1271   
Stage 2 Thrust   2.8   Million LBS
Stage 2 Km/sec    6.91   Km/sec Rocket Equation
Stage 2 Wet to Dry Mass Ratio   12.2   
S1 + S2  Total Delta V   9.4   Km/sec
TOTAL WT mT   5,159   mT
TOTAL WT LBS   11.4   Million LBS
THRUST Needed LBS   14.0   Million LBS
THRUST Needed mT   6345   
THRUST Needed MegaNewtons   62   
1st Stage T/W @ Takeoff   1.23   
1st STAGE # ENG    27   
LEO Mass Fract   4.4%    %
LEO Wet to Dry Mass Ratio   23    F9 v1.1 25/1 Musk
MCT Cargo Hold length   10   m
MCT Cargo Vol m3   1766   m3
   Eng 16+8+3=27   
   Outer Ring, Inner Ring, Central Engs   
   NOTE 1:   S1 Km/sec + S2 Km/sec must ~9Km/sec for LEO with grav losses
   NOTE 2:   Rocket Equation

Pretty much what I think the the BFS/MCT will be, with a few minor changes:
1. larger (longer) cargo hold.
2. slightly better mass fractions (but maybe not on the first MCT).
3. slightly less delta-v required to reach orbit, difference from your figures gives margin.


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