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#451 2019-11-20 18:36:53

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,874

Re: Starship is Go...

We have indicated in the past that the handling, storage and use of cyrogenic fuels is not a small issue for the size and quantity of fuels needed for the BFR / Starship combination to be able to get to the moon and even harder for going to mars.
The tanks have been discussed as they have gone from composites now back to metal and with trying to save mass its going to be an issue if they try to cheat with the tanks that store the fuels.

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#452 2019-11-20 19:31:12

louis
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From: UK
Registered: 2008-03-24
Posts: 5,480

Re: Starship is Go...

Clearly something very much amiss. Will be interesting to know if it is something easily resolvable or back to the drawing board.

SpaceNut wrote:

We have indicated in the past that the handling, storage and use of cyrogenic fuels is not a small issue for the size and quantity of fuels needed for the BFR / Starship combination to be able to get to the moon and even harder for going to mars.
The tanks have been discussed as they have gone from composites now back to metal and with trying to save mass its going to be an issue if they try to cheat with the tanks that store the fuels.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#453 2019-11-20 20:12:41

SpaceNut
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From: New Hampshire
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#454 2019-11-20 20:48:08

Oldfart1939
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Registered: 2016-11-26
Posts: 1,800

Re: Starship is Go...

Maybe title of this thread should be "Starship is go...Boom?" wink

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#455 2019-11-20 20:49:52

Oldfart1939
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Registered: 2016-11-26
Posts: 1,800

Re: Starship is Go...

The old time engineering approach is still valid: Build it. Test it. Break it. Fix it. Test it. Break it again. Repeat until it no longer breaks.

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#456 2019-11-20 21:49:57

kbd512
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Re: Starship is Go...

I'm sure they'll fix it and move on.  They always do.

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#457 2019-11-21 04:38:05

louis
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From: UK
Registered: 2008-03-24
Posts: 5,480

Re: Starship is Go...

Lol! I did wonder about starting a new thread! But decided to stay optimistic. smile

Oldfart1939 wrote:

Maybe title of this thread should be "Starship is go...Boom?" wink


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#458 2019-11-21 10:54:10

louis
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From: UK
Registered: 2008-03-24
Posts: 5,480

Re: Starship is Go...

As always Felix is very thorough:

https://www.youtube.com/watch?v=pAjcokd24MU

A good analysis.

This is not a serious set-back...or so the story goes.

Seems like they had already decided Mk 1 was not flight-worthy.

3-4 months delay on a first flight for the Starship. sad

Some mystery regarding the future of Mk 2...will it be "passed over" or will it be the next flight?

I would say it is almost certain now that we will not see a 2024 landing of humans on Mars by Space X. Having previously looked at this, they really needed to get that first serious test flight out of the way by early 2020.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#459 2019-11-21 17:23:43

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,874

Re: Starship is Go...

Based off from the haste that the rocket prototype was built with one can assume that its a failed weld along the top of the tank dome. This would be the likely failure point based off from the fuel cloud. There is quite a bit of the rocket that can be salvaged for making of another.

update:
SpaceX blows the top off first Starship rocket in pressure testing 'to the max'

SpaceX was conducting a test of its first assembled Starship rocket on Wednesday in Texas when immense pressure burst the tank at the top of the spacecraft, sending pieces flying.

"The purpose of today's test was to pressurize systems to the max, so the outcome was not completely unexpected. There were no injuries, nor is this a serious setback,"

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#460 2019-11-21 21:54:16

Oldfart1939
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Registered: 2016-11-26
Posts: 1,800

Re: Starship is Go...

This is typical of the SpaceX engineering approach, which is very "old school;" design it; build it; test it; break it in testing. Learn lessons and repeat process until it DOESN'T break.

This Starship prototype didn't have the 3 Raptors in place, so this was a pressure test to failure. I seriously doubt this will slow SpaceX more than a month or 2. Maybe the Mk. 2 built in Cape Canaveral will be the bird that flies?

Typical Elon style approach: move fast and don't be afraid of mistakes. This Mk. 1 looked pretty "rough" from the construction techniques involved. Building the Mk. 2 with stacked rings looks a lot "prettier."

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#461 2019-11-22 15:48:15

GW Johnson
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From: McGregor, Texas USA
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Re: Starship is Go...

Well,  I finally saw the video of the explosion,  with the forward dome structure of the tank blown clear as a big piece of debris.  It obviously broke at the dome-cylinder joint.

To have a dome separate from the cylindrical section of a pressure tank is prima facie evidence of amateurish design on the part of Spacex. In properly designed pressure vessels,  failure will be a split down the side of the cylindrical portion:  classic hoop stress failure due to overpressure.   

In pressure vessels,  there is a mismatch between induced stress in the dome and cylindrical portions,  which means there is a mismatch between the strain displacements.  That induces bending at the joint,  which gets the stress in the material out of control very quickly. 

There is an easy way to design this kind of dome joint failure mode out of pressure vessels.  Ask any expert on high strength/weight pressure vessels.  There are a couple of populations of them.  They are (1) folks like me who designed cases for solid rocket motors,  and (2) folks who designed boilers to the ASME boiler code.  NASA doesn't qualify,  but some (only some !!!) of their contractors do (the ones who built solid motors cases). 

The ASME boiler code is important,  because there is some 3 centuries of experience behind it.  Lots of people died for us to learn the lessons it embodies.  Very much like the fire codes.  Most of us who built rocket motors cases used the design concepts in that boiler code.  People outside those fields would not be familiar with this failure mode.  So it causes them to break more test articles than needed learning those lessons.  Technical arrogance/technical ignorance does have its costs. 

You basically gradually thicken the cylindrical wall by about a factor of 2 close to the joint with metals (3 or 4 with composites).  You can also thin down the dome far from the joint.  We're talking distances way from the joint that are measured in a single handful of wall thicknesses with metals,  a double or triple handful of wall thicknesses with fiber-reinforced composites.

GW

Last edited by GW Johnson (2019-11-22 15:51:24)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#462 2019-11-22 16:35:35

louis
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From: UK
Registered: 2008-03-24
Posts: 5,480

Re: Starship is Go...

I must say I was surprised at this failure...I would have thought that since we've had big rockets for over 70 years this technology would be well understood and that Space X wouldn't be innovating in this area. It seems not!

GW Johnson wrote:

Well,  I finally saw the video of the explosion,  with the forward dome structure of the tank blown clear as a big piece of debris.  It obviously broke at the dome-cylinder joint.

To have a dome separate from the cylindrical section of a pressure tank is prima facie evidence of amateurish design on the part of Spacex. In properly designed pressure vessels,  failure will be a split down the side of the cylindrical portion:  classic hoop stress failure due to overpressure.   

In pressure vessels,  there is a mismatch between induced stress in the dome and cylindrical portions,  which means there is a mismatch between the strain displacements.  That induces bending at the joint,  which gets the stress in the material out of control very quickly. 

There is an easy way to design this kind of dome joint failure mode out of pressure vessels.  Ask any expert on high strength/weight pressure vessels.  There are a couple of populations of them.  They are (1) folks like me who designed cases for solid rocket motors,  and (2) folks who designed boilers to the ASME boiler code.  NASA doesn't qualify,  but some (only some !!!) of their contractors do (the ones who built solid motors cases). 

The ASME boiler code is important,  because there is some 3 centuries of experience behind it.  Lots of people died for us to learn the lessons it embodies.  Very much like the fire codes.  Most of us who built rocket motors cases used the design concepts in that boiler code.  People outside those fields would not be familiar with this failure mode.  So it causes them to break more test articles than needed learning those lessons.  Technical arrogance/technical ignorance does have its costs. 

You basically gradually thicken the cylindrical wall by about a factor of 2 close to the joint with metals (3 or 4 with composites).  You can also thin down the dome far from the joint.  We're talking distances way from the joint that are measured in a single handful of wall thicknesses with metals,  a double or triple handful of wall thicknesses with fiber-reinforced composites.

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#463 2019-11-22 19:09:32

SpaceNut
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Re: Starship is Go...

Thats the difference of liquid kerosene and a cryogenic fuel that increase with rising temperature.

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#464 2019-11-22 20:45:44

Oldfart1939
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Registered: 2016-11-26
Posts: 1,800

Re: Starship is Go...

This was obviously a Catch-22 situation; trying to make something BOTH LIGHT and STRONG. GW hit the nail right on the head. Seriously, though: I doubt this will slow development by more than a couple months.

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#465 2019-11-23 10:49:39

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,768
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Re: Starship is Go...

As I said in my post just above,  the populations understanding high-pressure pressure-vessel work are the boiler guys and the solid motor guys.  Solid motors are typically 1000-5000 psia chamber pressures these days.  The entire motor case resists this for the entire firing,  while being heated,  too.  Many superheat boilers fall within this range,  too.

The liquid rocket guys would have no understanding or experience of this,  their tankage holding typically only a few,  to a few dozen psia.  And liquid rocket engine chamber design is not like propellant tank or motor case design,  because of the regenerative double wall.   

What Spacex is facing is a redesign of the dome joint details.  That's not anything fundamental,  but they should seek advice from folks experienced with high-pressure pressure-vessel design to get this done more cost-effectively and quickly.  That means they must abandon technical arrogance in order to eliminate technical ignorance.  Hard for big egos to swallow. 

They need to control which failure mode will occur first when they test to destruction,  in order to document the design's performance.  This is EXACTLY what should be happening with "engineering prototypes".  They are intended primarily for testing-to-destruction to qualify the design for proceeding further. 

Talking about these engineering prototypes as "flight test vehicles" is utter nonsense until the pressure testing (and many other ground test things) has been done successfully. This is the type of early test failure you want to see,  before things get far more expensive in dollars and lives,  later on.

GW

Last edited by GW Johnson (2019-11-23 10:52:19)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#466 2019-11-23 23:27:13

Oldfart1939
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Registered: 2016-11-26
Posts: 1,800

Re: Starship is Go...

GW Johnson wrote:

Talking about these engineering prototypes as "flight test vehicles" is utter nonsense until the pressure testing (and many other ground test things) has been done successfully. This is the type of early test failure you want to see,  before things get far more expensive in dollars and lives,  later on.

GW

Pretty much of the same track in my post #460, above. In agreement about build it, test it, break it.

Last edited by Oldfart1939 (2019-11-23 23:28:01)

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#467 2019-11-24 11:22:10

GW Johnson
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From: McGregor, Texas USA
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Posts: 3,768
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Re: Starship is Go...

Responding to Louis in post 462,  the big rockets of which you speak are all liquids.  The solid boosters some of them use were bought from solid propellant rocket builders as vendors or subcontractors.  My point is that the big liquid rocket guys know nothing about high-pressure pressure-vessel design.  It's the solid guys that truly understand this issue.

Why is that important to Spacex?  Because they are attempting something not commonplace before:  supercooled cryogenics to get higher density.  As those warm while waiting for the next burn,  vapor pressure goes up.  A lot.  Your tankage must hold such pressures.  Unlike anything they did before with LOX-kerosene. 

Now,  you have to understand Spacex's corporate management approach.  They hire no one over about age 40-45,  because older folks do not tolerate working 60+ hour weeks chronically.  It is that overwork scenario that gets them where they go as fast as they do it.  Only younger folks can tolerate that from a health standpoint.

But there is a cost,  a downside,  to that approach.  Older guys are more experienced,  with a wider knowledge base,  than youngsters fresh out of school.  This has hurt them multiple times,  the first being the teething problems with Falcon-1 that nearly killed the enterprise.  Knowing how to build a rocket engine says nothing about knowing how to fly a supersonic flight vehicle,  especially one with staging.  And THAT was their teething problem!   

They have to get outside advice from experienced people when those bad things happen,  and there is a management preference not to do that,  or at least to hide it when they do.  It's as much an ego thing as anything else.  Many companies suffer from it.

So,  bear in mind that Starship Mark 1 and probably Mark 2 are nothing but PR stunts and destructive-test articles.  It'll be a while yet before we see anything fly.  Probably faster than anything NASA and its highly-favored contractors Boeing and Lockheed-Martin would do,  but not as fast as the tweets and presentations indicate. 

And you should be very happy to see more of these explode or otherwise fail in ground tests!  What that really means is that fewer people will be killed later,  when one of these actually flies.  Sorry,  but the "usual public perception" of test failures is just wrong.  Way to hell-and-gone wrong.  You want to uncover the failures early,  while still testing on the ground. 

GW

Last edited by GW Johnson (2019-11-24 11:26:52)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#468 2019-11-24 11:32:32

louis
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From: UK
Registered: 2008-03-24
Posts: 5,480

Re: Starship is Go...

Interesting post, GW.  Well I hope they do tap into some outside expertise in this area.

GW Johnson wrote:

Responding to Louis in post 462,  the big rockets of which you speak are all liquids.  The solid boosters some of them use were bought from solid propellant rocket builders as vendors or subcontractors.  My point is that the big liquid rocket guys know nothing about high-pressure pressure-vessel design.  It's the solid guys that truly understand this issue.

Why is that important to Spacex?  Because they are attempting something not commonplace before:  supercooled cryogenics to get higher density.  As those warm while waiting for the next burn,  vapor pressure goes up.  A lot.  Your tankage must hold such pressures.  Unlike anything they did before with LOX-kerosene. 

Now,  you have to understand Spacex's corporate management approach.  They hire no one over about age 40-45,  because older folks do not tolerate working 60+ hour weeks chronically.  It is that overwork scenario that gets them where they go as fast as they do it.  Only younger folks can tolerate that from a health standpoint.

But there is a cost,  a downside,  to that approach.  Older guys are more experienced,  with a wider knowledge base,  than youngsters fresh out of school.  This has hurt them multiple times,  the first being the teething problems with Falcon-1 that nearly killed the enterprise.  Knowing how to build a rocket engine says nothing about knowing how to fly a supersonic flight vehicle,  especially one with staging.  And THAT was their teething problem!   

They have to get outside advice from experienced people when those bad things happen,  and there is a management preference not to do that,  or at least to hide it when they do.  It's as much an ego thing as anything else.  Many companies suffer from it.

So,  bear in mind that Starship Mark 1 and probably Mark 2 are nothing but PR stunts and destructive-test articles.  It'll be a while yet before we see anything fly.  Probably faster than anything NASA and its highly-favored contractors Boeing and Lockheed-Martin would do,  but not as fast as the tweets and presentations indicate. 

And you should be very happy to see more of these explode or otherwise fail in ground tests!  What that really means is that fewer people will be killed later,  when one of these actually flies.  Sorry,  but the "usual public perception" of test failures is just wrong.  Way to hell-and-gone wrong.  You want to uncover the failures early,  while still testing on the ground. 

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#469 2019-11-27 20:44:07

louis
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From: UK
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Posts: 5,480

Re: Starship is Go...

Starship might still be go...

Progress on the Mk 3...

https://www.youtube.com/watch?v=ajtqX8RrSxM


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#470 2019-11-28 15:17:02

louis
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From: UK
Registered: 2008-03-24
Posts: 5,480

Re: Starship is Go...

Latest from Felix. Encouraging signs of progress on Mk 3. They may retain the nose cone from Mk 1. Mk 3 is a much higher spec than Mk 1.

https://www.youtube.com/watch?v=gh8fcfJqlSw


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#471 2019-12-01 18:05:07

louis
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From: UK
Registered: 2008-03-24
Posts: 5,480

Re: Starship is Go...

Felix has some v. interesting news.

Seems like the Cocoa Beach facility is being retired.

Mk 2 prototype being junked essentially.

https://www.youtube.com/watch?v=LAXo1FdywLE

Just a thought on all this...when Columbus sailed to the New World (what he thought was China) he produced a fake ship log (for the crew, to allay their fears that they were travelling too far from home) as well as a genuine one. Maybe Musk is the new Columbus...

Last edited by louis (2019-12-02 16:55:10)


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#472 2019-12-02 06:30:38

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 333

Re: Starship is Go...

Supercooling a liquid propellant would tend to lower vapour pressure.  Presumably SpaceX are thinking of using helium for tank pressurisation.  I seem to remember that being standard for cryogens anyway.

Using cryogens as propellants would seem to make tank design more difficult, as many common pressure vessel materials (alloy steels) become brittle at those temperatures.  So you are left with austenitic stainless steel (which has poor strength-weight) or aluminium alloys (which have fatigue life problems).  I can remember Arthur Schmit's minimum cost design article discussing room temperature propellants and hypergols to get around problems like this.


Interested in space science, engineering and technology.

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#473 2019-12-02 17:15:42

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,768
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Re: Starship is Go...

The choice of materials for a cryogenic propellant tank is subject to many constraints.  Not all tank design problems are the same,  not by a long shot. 

Spacex used helium pressurization in Falcon,  but my understanding is that they are deleting that in favor of self-pressurization as the liquids absorb heat in Starship/Superheavy.  I cannot confirm that,  it's just my impression. 

Spacex started out with carbon-epoxy composite tank designs for Starship,  even tested one to destruction in California.  They used aluminum in Falcon.  Neither can take full orbital re-entry heating successfully,  much less harsher entries. 

The Starship must do Earth entries well above escape velocity coming back from Mars.  And THAT is why they had to go to stainless steel.  Only it can take both cryogenic temperatures,  and entry heating (just with no propellant in contact with the exposed shell). 

That last is really why there are so-called "header tanks" nested within tanks in the Starship design.  Otherwise,  your propellant would get vaporized,  even at super high pressures,  during entry.

GW

Last edited by GW Johnson (2019-12-02 17:17:40)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#474 2019-12-02 17:37:31

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,874

Re: Starship is Go...

The real issue is we have little data for the Liquid CH4 and the tanks that hold it best when of the magnetude of BFR and Starship.
https://en.wikipedia.org/wiki/Methane_(data_page)
Triple point: 90.67 K (−182.48 °C), 0.117 bar Critical point: 190.6 K (−82.6 °C), 46.0 bar Std enthalpy change of fusion..

https://webbook.nist.gov/cgi/cbook.cgi? … pe=TTRIPLE

I am thinking the time to put the fuel in the tank is causing the issue for the high pressure that is seen as its not cold enough to make it stay liquid as the tank is fueled. What if the tank is prechilled with liquid nitrogen so as to allow for the initial fueling to stay cold enough to allow for the tank to fill. Or create a nitrogen outer shell tank to keep the fueling colder.
The starship is already got inner tanks for mars boil off so adding more mass for the tanks to keep them from bursting, so what.as thats what rocket science is.

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#475 2019-12-24 16:35:35

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,874

Re: Starship is Go...

https://www.thespacereview.com/article/3479/1
Engineering Mars commercial rocket propellant production for the Big Falcon Rocket (part 1)

https://www.thespacereview.com/article/3484/1
Engineering Mars commercial rocket propellant production for the Big Falcon Rocket (part 2)

Lots of energy details and what a system might need

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