Author Topic: MCT Speculation and Discussion Thread 4  (Read 504433 times)

Offline matthewkantar

  • Full Member
  • ****
  • Posts: 693
  • Liked: 440
  • Likes Given: 475
Re: MCT Speculation and Discussion Thread 4
« Reply #1780 on: 02/25/2016 05:29 PM »
Would putting the linens out the airlock and in full sunlight be the ultimate "dry cleaning?" I have no idea if this would work or not, but i love the idea of the MCT strung with clothes lines and festooned with dirty laundry.

Matthew

Offline JasonAW3

  • Senior Member
  • *****
  • Posts: 2434
  • Claremore, Ok.
  • Liked: 384
  • Likes Given: 11
Re: MCT Speculation and Discussion Thread 4
« Reply #1781 on: 02/25/2016 06:59 PM »
Weird thought here;

     Anybody ever consider that the BFR could be an up scaled Falcon 9 configuration, using 9 Raptor engines for the first stage and possibly a couple of BFR's as strap on boosters?  Or even a configuration using six or more Falcon 9 first stages as strap ons as an alternative?
My God!  It's full of universes!

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 27138
  • Minnesota
  • Liked: 7107
  • Likes Given: 4936
Re: MCT Speculation and Discussion Thread 4
« Reply #1782 on: 02/25/2016 07:02 PM »
Weird thought here;

     Anybody ever consider that the BFR could be an up scaled Falcon 9 configuration, using 9 Raptor engines for the first stage and possibly a couple of BFR's as strap on boosters?  Or even a configuration using six or more Falcon 9 first stages as strap ons as an alternative?
A big scaled up Methane Falcon heavy type design was originally the thought of BFR according to Musk in the R*ddit AMA, but in the AMA, Musk said they opted to instead go the single-core route with LOTS of Raptors.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Umbrella

  • Member
  • Posts: 23
  • Liked: 6
  • Likes Given: 24
Re: MCT Speculation and Discussion Thread 4
« Reply #1783 on: 02/26/2016 02:33 PM »
It seems, based on dV requirements, that BFR will likely need to land on a drone ship.  Would the existing drone ships be big enough?  If not, how big would a new drone ship need to be?

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 27138
  • Minnesota
  • Liked: 7107
  • Likes Given: 4936
Re: MCT Speculation and Discussion Thread 4
« Reply #1784 on: 02/26/2016 03:08 PM »
It seems, based on dV requirements, that BFR will likely need to land on a drone ship.  Would the existing drone ships be big enough?  If not, how big would a new drone ship need to be?
What delta-V requirements? Are you thinking BFR is going to launch all the way to Mars? BFR would likely just be launching to LEO. No, return to launch site is much more likely. This way you can have much faster turnaround time of the BFR stage.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline guckyfan

  • Senior Member
  • *****
  • Posts: 6442
  • Germany
  • Liked: 1620
  • Likes Given: 1485
Re: MCT Speculation and Discussion Thread 4
« Reply #1785 on: 02/26/2016 03:17 PM »
It seems, based on dV requirements, that BFR will likely need to land on a drone ship. 

Not only operational aspects are against this. Also the 30% payload loss mentioned by Elon Musk are not laws of nature, they are roughly the result of Falcon 9 design.

More lightweight build, higher ISP of the engines and probably staging even earlier than Falcon 9 will reduce the losses by a lot, making barge landing unnecessary.

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 6413
  • Everyplaceelse
  • Liked: 873
  • Likes Given: 5519
Re: MCT Speculation and Discussion Thread 4
« Reply #1786 on: 02/26/2016 05:07 PM »
Would putting the linens out the airlock and in full sunlight be the ultimate "dry cleaning?" I have no idea if this would work or not, but i love the idea of the MCT strung with clothes lines and festooned with dirty laundry.

Matthew
Interesting idea. Something that should be testable on the ISS.

The joker in the pack is not the vacuum. It's the temperature in the lock. IIRC in full sunlight you're talking c200c, in full shadow -200c.

I think cold would do less damage but I'd still suspect it would do so much damage they would literally crumble in your hands.

But note it's still basically an open loop system and the goal should always be to close the loops.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Offline Umbrella

  • Member
  • Posts: 23
  • Liked: 6
  • Likes Given: 24
Re: MCT Speculation and Discussion Thread 4
« Reply #1787 on: 02/26/2016 05:36 PM »
It seems, based on dV requirements, that BFR will likely need to land on a drone ship.  Would the existing drone ships be big enough?  If not, how big would a new drone ship need to be?
What delta-V requirements? Are you thinking BFR is going to launch all the way to Mars? BFR would likely just be launching to LEO. No, return to launch site is much more likely. This way you can have much faster turnaround time of the BFR stage.

According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.  BFR+BFS need to put at least 200 MT in LEO just to cover empty BFS+payload.  And all this has to be done with no more than 4 times FH lift off thrust.

Offline Paul451

  • Full Member
  • ****
  • Posts: 1305
  • Australia
  • Liked: 643
  • Likes Given: 544
Re: MCT Speculation and Discussion Thread 4
« Reply #1788 on: 02/26/2016 07:08 PM »
According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.

Source? That seems incredibly unlikely. 9km/s at staging is enough to carry the fully fuelled ~100 tonne second stage into LEO without firing its engines. That would make the F9 first stage a 110 tonne to LEO SSTO!

(Sorry, a 110 tonne to LEO reusable SSTO.)

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 6413
  • Everyplaceelse
  • Liked: 873
  • Likes Given: 5519
Re: MCT Speculation and Discussion Thread 4
« Reply #1789 on: 02/26/2016 09:39 PM »
According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.

Source? That seems incredibly unlikely. 9km/s at staging is enough to carry the fully fuelled ~100 tonne second stage into LEO without firing its engines. That would make the F9 first stage a 110 tonne to LEO SSTO!

(Sorry, a 110 tonne to LEO reusable SSTO.)
Indeed.

I'd settle for a reusable TSTO.

BTW has anyone mentioned the mass fraction this thing needs?

AIUI people have said a 100 day trip needs 8.8Km/s from LEO. Raptors Isp is suggested at 363secs in Vac, which should be OK in the Mars atmosphere as well, given its pressure.

Putting those into the the rocket eqn gives 11.81:1 or a mass fraction of about 8.5%, giving a gross launch mass (from LEO) is 709 tonnes for a 60 tonne payload IE about 12x the size of the FH. Once again closing the ECLSS loops with an integrated mass efficient ECLSS will pay big dividends on size needed, possibly bigger than getting an extra second of Isp on the engines. Likewise cutting that delta V to 8 Km/s cuts gross mass by 20%.

This is still less than 1/2 the GTOW of the Shuttle stack, so big but not enormous. However that's raw payload, without structure, and I've no real sense what fraction that would be. 10% of payload mass IE 6 tonnes? 10 tonnes?

So cutting delta V, improving ECLSS closure and lowering transit time are all good things, but some are more good than others. for a fully open ECLSS 1 day --> 500Kg of supplies but ISS can already do better, therefor 50 tonnes of supplies is conservative for a 100 day trip (but what'll you eat there & on the way back?)

I think I'm going to have to revise my game a bit more.  :)
« Last Edit: 02/27/2016 09:07 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Offline jsgirald

Re: MCT Speculation and Discussion Thread 4
« Reply #1790 on: 02/26/2016 10:42 PM »
AIUI people have said a 100 day trip needs 8.8Km/s from LEO. Raptors Isp is suggested at 363secs in Vac, which should be OK in the Mars atmosphere as well, given its pressure.

I seem to recall that Tom Mueller said that they aimed for 380 secs of vac Isp.
"For every expert, there is an equal and opposite expert".

Offline DJPledger

  • Full Member
  • ***
  • Posts: 389
  • Liked: 113
  • Likes Given: 2073
Re: MCT Speculation and Discussion Thread 4
« Reply #1791 on: 02/27/2016 07:12 AM »
AIUI people have said a 100 day trip needs 8.8Km/s from LEO. Raptors Isp is suggested at 363secs in Vac, which should be OK in the Mars atmosphere as well, given its pressure.

I seem to recall that Tom Mueller said that they aimed for 380 secs of vac Isp.
363 sec. in vac. for SL Raptor. 380 sec. in vac. for the vac. Raptor.

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 6413
  • Everyplaceelse
  • Liked: 873
  • Likes Given: 5519
Re: MCT Speculation and Discussion Thread 4
« Reply #1792 on: 02/27/2016 09:03 AM »
363 sec. in vac. for SL Raptor. 380 sec. in vac. for the vac. Raptor.
Running with 380sec gives a mass ratio of 10.57:1 and a mass of about 714 tonnes to LEO, IE about 14x the size of the expendable FH.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Offline dror

  • Full Member
  • ****
  • Posts: 556
  • Israel
  • Liked: 128
  • Likes Given: 353
Re: MCT Speculation and Discussion Thread 4
« Reply #1793 on: 02/27/2016 11:41 AM »
According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.

Source? That seems incredibly unlikely. 9km/s at staging is enough to carry the fully fuelled ~100 tonne second stage into LEO without firing its engines. That would make the F9 first stage a 110 tonne to LEO SSTO!

(Sorry, a 110 tonne to LEO reusable SSTO.)

It was 9000 km/hr:
Quote
It's flying away from the pad in this case at 5000 km/h. In the upcoming flight it'll be going 8 or 9000 km/h, or roughly 5000 mph, in the wrong direction.
http://shitelonsays.com/transcript/postlanding-teleconference-with-elon-musk-2015-12-22
"If we crave some cosmic purpose, then let us find ourselves a worthy goal. "
Carl Sagan, Pale Blue Dot

Offline Umbrella

  • Member
  • Posts: 23
  • Liked: 6
  • Likes Given: 24
Re: MCT Speculation and Discussion Thread 4
« Reply #1794 on: 02/27/2016 11:53 AM »
Apologies, my fault,  the difference was 9000 km/hr down to 6000km/hr.  This was based on a Musk tweet on 1/17/2016.  Still, I think the dV penalty of dry landing of BFR makes drone ship landing worth consideration.

Offline Burninate

  • Full Member
  • ****
  • Posts: 1129
  • Liked: 345
  • Likes Given: 72
Re: MCT Speculation and Discussion Thread 4
« Reply #1795 on: 02/27/2016 03:34 PM »
Yet another lesson in why we should all be using metric, and we should be using m/s.

Online Prettz

  • Full Member
  • *
  • Posts: 144
  • Atlanta, GA
  • Liked: 69
  • Likes Given: 13
Re: MCT Speculation and Discussion Thread 4
« Reply #1796 on: 02/27/2016 03:52 PM »
Apologies, my fault,  the difference was 9000 km/hr down to 6000km/hr.  This was based on a Musk tweet on 1/17/2016.  Still, I think the dV penalty of dry landing of BFR makes drone ship landing worth consideration.
It's not a "penalty" if the first stage is sized to allow for it from the beginning.

Offline philw1776

  • Full Member
  • ****
  • Posts: 894
  • Seacoast NH
  • Liked: 503
  • Likes Given: 254
Re: MCT Speculation and Discussion Thread 4
« Reply #1797 on: 02/27/2016 04:07 PM »
Yet another lesson in why we should all be using metric, and we should be using m/s.

I'll let Elon know!


(I agree wholeheartedly)
« Last Edit: 02/27/2016 04:07 PM by philw1776 »
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline Umbrella

  • Member
  • Posts: 23
  • Liked: 6
  • Likes Given: 24
Re: MCT Speculation and Discussion Thread 4
« Reply #1798 on: 02/27/2016 04:49 PM »
Apologies, my fault,  the difference was 9000 km/hr down to 6000km/hr.  This was based on a Musk tweet on 1/17/2016.  Still, I think the dV penalty of dry landing of BFR makes drone ship landing worth consideration.
It's not a "penalty" if the first stage is sized to allow for it from the beginning.

Even if the BFR is relatively a smaller proportion of the stack, it is hard to see cutoff not being at least a little bit down range.  So, I would claim you can push the design for a somewhat smaller penalty for dry landing - but not penalty free.

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 27138
  • Minnesota
  • Liked: 7107
  • Likes Given: 4936
Re: MCT Speculation and Discussion Thread 4
« Reply #1799 on: 02/27/2016 05:12 PM »
Would putting the linens out the airlock and in full sunlight be the ultimate "dry cleaning?" I have no idea if this would work or not, but i love the idea of the MCT strung with clothes lines and festooned with dirty laundry.

Matthew
Interesting idea. Something that should be testable on the ISS.

The joker in the pack is not the vacuum. It's the temperature in the lock. IIRC in full sunlight you're talking c200c, in full shadow -200c.

I think cold would do less damage but I'd still suspect it would do so much damage they would literally crumble in your hands.

But note it's still basically an open loop system and the goal should always be to close the loops.
200C is actually fine for cotton as long as it's fairly quick. Keep it out there too long and it'd degrade at those temperatures. Anyway, the actual temperature would depend on the color of the cloth and other aspects.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Tags: