Author Topic: Getting crew to Mars in 2022.  (Read 15677 times)

Offline aero

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Re: Getting crew to Mars in 2022.
« Reply #100 on: 09/04/2018 01:04 AM »
Big Falcon Hab - That brings up another question, will it really be safe to store prop in the habitat? I guess they do it while in transit from Earth. But as a semi-permanent solution to prop storage?

And BFH brings Falcon Heavy to mind.
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Offline speedevil

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Re: Getting crew to Mars in 2022.
« Reply #101 on: 09/04/2018 10:05 AM »
Big Falcon Hab - That brings up another question, will it really be safe to store prop in the habitat? I guess they do it while in transit from Earth. But as a semi-permanent solution to prop storage?

And BFH brings Falcon Heavy to mind.

If you can't keep gas on one side of a wall, you're already dead.

Online RotoSequence

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Re: Getting crew to Mars in 2022.
« Reply #102 on: 09/04/2018 11:35 AM »
Big Falcon Hab - That brings up another question, will it really be safe to store prop in the habitat? I guess they do it while in transit from Earth. But as a semi-permanent solution to prop storage?

And BFH brings Falcon Heavy to mind.

If you can't keep gas on one side of a wall, you're already dead.

The only probable deal breaker is the exorbitant refrigeration and insulation requirements of the fuel and oxidizer.

Offline speedevil

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Re: Getting crew to Mars in 2022.
« Reply #103 on: 09/04/2018 11:57 AM »
Big Falcon Hab - That brings up another question, will it really be safe to store prop in the habitat? I guess they do it while in transit from Earth. But as a semi-permanent solution to prop storage?

And BFH brings Falcon Heavy to mind.

If you can't keep gas on one side of a wall, you're already dead.

The only probable deal breaker is the exorbitant refrigeration and insulation requirements of the fuel and oxidizer.

They're not very exorbitant.

On the last page of the thread are some references, but if your tanks are comparable to the slightly better commercial ones of this sort of size, they leak out in three years, and will need a kilowatt or so to keep cool. (10kW of electricity).

Commercial 30l dewars have a boiloff rate that if you increase their size twenty fold linearly, you end up with a tenth of this required power. And this is for a whole system that retails for $500/m^2 or so of tank wall shipped.



Online RotoSequence

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Re: Getting crew to Mars in 2022.
« Reply #104 on: 09/04/2018 12:17 PM »
Big Falcon Hab - That brings up another question, will it really be safe to store prop in the habitat? I guess they do it while in transit from Earth. But as a semi-permanent solution to prop storage?

And BFH brings Falcon Heavy to mind.

If you can't keep gas on one side of a wall, you're already dead.

The only probable deal breaker is the exorbitant refrigeration and insulation requirements of the fuel and oxidizer.

They're not very exorbitant.

On the last page of the thread are some references, but if your tanks are comparable to the slightly better commercial ones of this sort of size, they leak out in three years, and will need a kilowatt or so to keep cool. (10kW of electricity).

Commercial 30l dewars have a boiloff rate that if you increase their size twenty fold linearly, you end up with a tenth of this required power. And this is for a whole system that retails for $500/m^2 or so of tank wall shipped.

Boiloff management isn't hard, no; my mind was in the realm of the cryo plant that liquifies the fuel and oxidizer in the first place, so that's my bad for the confusion. The part that concerns me is carbon dioxide frost buildup on the outside of the tanks, which risks significantly increasing the power needs for refrigeration as it freezes on the surface.

Offline speedevil

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Re: Getting crew to Mars in 2022.
« Reply #105 on: 09/04/2018 07:50 PM »
The part that concerns me is carbon dioxide frost buildup on the outside of the tanks, which risks significantly increasing the power needs for refrigeration as it freezes on the surface.
The tanks walls are ~0.2-2C or so cooler than ambient, if you make an attempt at insulating them to a level representative of commercial practice.

Online RotoSequence

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Re: Getting crew to Mars in 2022.
« Reply #106 on: 09/05/2018 03:18 AM »
The part that concerns me is carbon dioxide frost buildup on the outside of the tanks, which risks significantly increasing the power needs for refrigeration as it freezes on the surface.
The tanks walls are ~0.2-2C or so cooler than ambient, if you make an attempt at insulating them to a level representative of commercial practice.

Indeed; with a vacuum flask, that's not a problem, but a BFS isn't a vacuum flask.

Offline speedevil

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Re: Getting crew to Mars in 2022.
« Reply #107 on: 09/05/2018 08:58 AM »
The part that concerns me is carbon dioxide frost buildup on the outside of the tanks, which risks significantly increasing the power needs for refrigeration as it freezes on the surface.
The tanks walls are ~0.2-2C or so cooler than ambient, if you make an attempt at insulating them to a level representative of commercial practice.

Indeed; with a vacuum flask, that's not a problem, but a BFS isn't a vacuum flask.

I am assuming this is a solved problem, as you absolutely can't do ISRU with naked uninsulated tanks on Mars, the heat gains murder you, so it must have been included in the designed mass originally.

Either the tank would need to be part of the payload, which raises issues of getting it out of the BFS and setting it/them up on the surface, or it is a tank-in-tank construction in the main tanks as a later variant, or they are doing something odder.

Online RotoSequence

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Re: Getting crew to Mars in 2022.
« Reply #108 on: 09/05/2018 09:09 AM »
I am assuming this is a solved problem, as you absolutely can't do ISRU with naked uninsulated tanks on Mars, the heat gains murder you, so it must have been included in the designed mass originally.

Either the tank would need to be part of the payload, which raises issues of getting it out of the BFS and setting it/them up on the surface, or it is a tank-in-tank construction in the main tanks as a later variant, or they are doing something odder.

Since header tanks are part of the BFS design, I don't think they have solved it for the regular ships. Maybe they have a dedicated, one way ISRU tanker in work, because I don't know how else you'd do it.

Offline Donindacula

Re: Getting crew to Mars in 2022.
« Reply #109 on: 09/05/2018 06:09 PM »
This is my first post  so let me know if I get it wrong. 

My understanding is that SpaceX would launch cargo ships in 2020 with enough supplies, habitats, farms, equipment to drill/mine for water/ice, and anything else for the first crews to survive for a couple of years.   If those ships land safely a small crew of 10-15 would then launch in 2022 with a full cargo bay and probably other cargo ships too.

That crews main tasks would be to get water and start making oxygen, build the farms and start farming, build the habitats and get everything ready for the next crew of 100 other settlers landing two years later . 

They won't need to worry about fuel for awhile. They'll need to use their own landing ship as a habitat for several months while they get everything else done. 


So if the BFR cargo ships aren't ready by 2020 would the FH be able to launch enough supplies (over several launches) to make that work?

Offline envy887

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Re: Getting crew to Mars in 2022.
« Reply #110 on: 09/05/2018 06:35 PM »
The part that concerns me is carbon dioxide frost buildup on the outside of the tanks, which risks significantly increasing the power needs for refrigeration as it freezes on the surface.
The tanks walls are ~0.2-2C or so cooler than ambient, if you make an attempt at insulating them to a level representative of commercial practice.

Indeed; with a vacuum flask, that's not a problem, but a BFS isn't a vacuum flask.

It plausibly could be, with a cryogenic polymer sheet bladder inside a LOX-safe aerogel insulation layer bonded to the CRFP hull. The aerogel can be purged with CO2, then sealed, and as cryogens are added inside the tank (sealed by the bladder), the CO2 will condense out leaving a vacuum, as described in this patent for a cryogenic insulation system. The aerogel is strong enough to support itself against tank pressure on the vacuum.

You basically get a LOX-capable vacuum flask, and conduction through 10 cm of the aerogel is less than 5 kW for a whole BFS, about 1% of the total power needed for propellant production to return that BFS to Earth once per synod.
« Last Edit: 09/05/2018 06:37 PM by envy887 »

Offline philw1776

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Re: Getting crew to Mars in 2022.
« Reply #111 on: 09/05/2018 08:04 PM »
This is my first post  so let me know if I get it wrong. 

My understanding is that SpaceX would launch cargo ships in 2020 with enough supplies, habitats, farms, equipment to drill/mine for water/ice, and anything else for the first crews to survive for a couple of years.   If those ships land safely a small crew of 10-15 would then launch in 2022 with a full cargo bay and probably other cargo ships too.

That crews main tasks would be to get water and start making oxygen, build the farms and start farming, build the habitats and get everything ready for the next crew of 100 other settlers landing two years later . 

They won't need to worry about fuel for awhile. They'll need to use their own landing ship as a habitat for several months while they get everything else done. 


So if the BFR cargo ships aren't ready by 2020 would the FH be able to launch enough supplies (over several launches) to make that work?

Welcome.
Just to clarify.  This thread is talking about a hypothetical 2022 crewed mission.
SpaceX's aspirational schedule is Cargo launch in 2022 and humans in 2024.
FH has no way of landing supplies on Mars as Red Dragon is cancelled.  In any case Red Dragon would be a single digit # of tons vs 100+ tons per BFS landing so, No. FH would need way way too many launches and again has no lander.
« Last Edit: 09/05/2018 08:05 PM by philw1776 »
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Offline Donindacula

Re: Getting crew to Mars in 2022.
« Reply #112 on: 09/05/2018 11:36 PM »
philw1776 ,  Thanks for the reply 8)

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