Author Topic: Speculation: Segmented Spin gravity habitat sized for launch in 2017 BFR Cargos  (Read 33020 times)

Offline rakaydos

  • Senior Member
  • *****
  • Posts: 2825
  • Liked: 1869
  • Likes Given: 69
There is an older thread for a "realistic near-term rotating space station".
blerg... I got halfway through the thread before I got fed up with the arguments about NASA, artificial gravity research, and mars programs.

The earlier argument about needing a rigid (compressed) component to dampen oscillation in a tensioned tether was at least useful.

Offline mikelepage

  • Full Member
  • ****
  • Posts: 1218
  • ExodusSpaceSystems.com
  • Perth, Australia
  • Liked: 855
  • Likes Given: 1358
There is an older thread for a "realistic near-term rotating space station".
blerg... I got halfway through the thread before I got fed up with the arguments about NASA, artificial gravity research, and mars programs.

The earlier argument about needing a rigid (compressed) component to dampen oscillation in a tensioned tether was at least useful.

I'm happy to let the older threads die, since BFR seems like a much more likely vehicle (and SpaceX a much more likely partner company) to facilitate spin-gravity habitat research.  I've been somewhat quieter of late because I've been working on Exodus Space Systems, the Australian space startup company I co-founded to deal with exactly these problems.

I'm attaching here an excerpt from our vision/strategy document, which I think provides a good summary of the various considerations that spin gravity proposals should take into account.  Hopefully it should be useful to some of the newer participants, but I'd also appreciate feedback - particularly if you think I've missed anything.
« Last Edit: 11/09/2017 04:16 am by mikelepage »

Offline speedevil

  • Senior Member
  • *****
  • Posts: 4406
  • Fife
  • Liked: 2762
  • Likes Given: 3369
BFR cost to orbit - about $10000/ton. (to make the 'economy ticket' comment for passenger transport work).

SLS program cost - ~$22B out to 2024.

Two million five hundred thousand tons of spinning metal.
There is only one possible station design.




« Last Edit: 11/11/2017 12:12 pm by speedevil »

Offline livingjw

  • Senior Member
  • *****
  • Posts: 2363
  • New World
  • Liked: 5857
  • Likes Given: 2887
There is an older thread for a "realistic near-term rotating space station".
blerg... I got halfway through the thread before I got fed up with the arguments about NASA, artificial gravity research, and mars programs.

The earlier argument about needing a rigid (compressed) component to dampen oscillation in a tensioned tether was at least useful.

I'm happy to let the older threads die, since BFR seems like a much more likely vehicle (and SpaceX a much more likely partner company) to facilitate spin-gravity habitat research.  I've been somewhat quieter of late because I've been working on Exodus Space Systems, the Australian space startup company I co-founded to deal with exactly these problems.

I'm attaching here an excerpt from our vision/strategy document, which I think provides a good summary of the various considerations that spin gravity proposals should take into account.  Hopefully it should be useful to some of the newer participants, but I'd also appreciate feedback - particularly if you think I've missed anything.

One order of magnitude reduction in cost can be expected in the next 5-10 years. Not multiple orders of magnitude. 2 at most a long time from now.

John

Offline rakaydos

  • Senior Member
  • *****
  • Posts: 2825
  • Liked: 1869
  • Likes Given: 69
There is an older thread for a "realistic near-term rotating space station".
blerg... I got halfway through the thread before I got fed up with the arguments about NASA, artificial gravity research, and mars programs.

The earlier argument about needing a rigid (compressed) component to dampen oscillation in a tensioned tether was at least useful.

I'm happy to let the older threads die, since BFR seems like a much more likely vehicle (and SpaceX a much more likely partner company) to facilitate spin-gravity habitat research.  I've been somewhat quieter of late because I've been working on Exodus Space Systems, the Australian space startup company I co-founded to deal with exactly these problems.

I'm attaching here an excerpt from our vision/strategy document, which I think provides a good summary of the various considerations that spin gravity proposals should take into account.  Hopefully it should be useful to some of the newer participants, but I'd also appreciate feedback - particularly if you think I've missed anything.

One order of magnitude reduction in cost can be expected in the next 5-10 years. Not multiple orders of magnitude. 2 at most a long time from now.

John
Isnt Facon 9 reuse a reduction of costs (not nessesarally prices) of an order of magnitude? And BFR supposed to be another order of magnitude?

Offline speedevil

  • Senior Member
  • *****
  • Posts: 4406
  • Fife
  • Liked: 2762
  • Likes Given: 3369
One order of magnitude reduction in cost can be expected in the next 5-10 years. Not multiple orders of magnitude. 2 at most a long time from now.
I assume this means you don't believe that passenger transport at close to the stated goals will come about ever?

Offline livingjw

  • Senior Member
  • *****
  • Posts: 2363
  • New World
  • Liked: 5857
  • Likes Given: 2887
One order of magnitude reduction in cost can be expected in the next 5-10 years. Not multiple orders of magnitude. 2 at most a long time from now.
I assume this means you don't believe that passenger transport at close to the stated goals will come about ever?

Maybe, a long time from now.  Going from $60,000,000 to $6,000,000 to $600,000 will take time.  That's all I'm saying.

John

Offline lamontagne

  • Senior Member
  • *****
  • Posts: 4270
  • Otterburn Park, Quebec,Canada
  • Liked: 3840
  • Likes Given: 716
Complete station.  48 modules.  About 36 000 m3 of space.
Hi is that based on https://en.wikipedia.org/wiki/BA_2100 or similar?

It looks like you are putting new doors through the inflatable section and including a sizeable new cylindrical join to that section.

IMO you would use the two doors that come at each end of the BA2100, connected to the central rigid part. You would only need a small adaption to one end so that when they joined end to end they formed a curve. Cables to the center could connect to this adaption also.
No its based on a rigid module optimized to fit inside the BFS fairing.


Offline lamontagne

  • Senior Member
  • *****
  • Posts: 4270
  • Otterburn Park, Quebec,Canada
  • Liked: 3840
  • Likes Given: 716
Complete station.  48 modules.  About 36 000 m3 of space.
Hi is that based on https://en.wikipedia.org/wiki/BA_2100 or similar?

It looks like you are putting new doors through the inflatable section and including a sizeable new cylindrical join to that section.

IMO you would use the two doors that come at each end of the BA2100, connected to the central rigid part. You would only need a small adaption to one end so that when they joined end to end they formed a curve. Cables to the center could connect to this adaption also.
This was my inflatable solution  :-)  start with 3 modules, then add and add and add.....
« Last Edit: 11/12/2017 12:52 am by lamontagne »

Offline mikelepage

  • Full Member
  • ****
  • Posts: 1218
  • ExodusSpaceSystems.com
  • Perth, Australia
  • Liked: 855
  • Likes Given: 1358
Complete station.  48 modules.  About 36 000 m3 of space.
Hi is that based on https://en.wikipedia.org/wiki/BA_2100 or similar?

It looks like you are putting new doors through the inflatable section and including a sizeable new cylindrical join to that section.

IMO you would use the two doors that come at each end of the BA2100, connected to the central rigid part. You would only need a small adaption to one end so that when they joined end to end they formed a curve. Cables to the center could connect to this adaption also.
No its based on a rigid module optimized to fit inside the BFS fairing.

Hi Lamontagne, great work, but I'm curious how you figured out how big the BFS payload bay was?

By eyeball it all looks right to me, but Elon did say at 18 minutes into the talk that "that payload bay is eight stories tall, and you could fit a whole stack of Falcon 1s in there".  Looking it up, the Falcon 1 is listed as 21.3m tall. 

In any case, I've been thinking the payload bay must 22-24m long/tall, or just under half the length of the vehicle (48m).  Just wondering how you square that?

EDIT: just looking at your diagrams a little closer and noticed the smaller nose cone section with the little person in there. I suppose you would be able to squeeze in a falcon 1 if you took it right to the tip of the nose.  Makes me wonder if there will ever be a small pressurised section on "cargo" BFSs.
« Last Edit: 11/12/2017 04:51 am by mikelepage »

Offline KelvinZero

  • Senior Member
  • *****
  • Posts: 4286
  • Liked: 887
  • Likes Given: 201
I was just thinking about estimating some values for my telescoping idea.

I think I can work out the basic mass per volume from something like this
https://en.wikipedia.org/wiki/Pressure_vessel#Cylindrical_vessel_with_hemispherical_ends

What is a sensible, non Sci-Fi material choice? What should I use for density and maximum working stress? What should I use for pressure?

Im not asking just for numbers from a table, but also for example what safety margin is it typical to engineer for. Im guessing you don't just engineer for exactly one atmosphere for example. Im guessing those formulae are the theoretical point at which the vessel bursts, ie do not include predefined safety margins. I was thinking there might be some specific guidelines for space, eg engineer for 3x the pressure or such.

Offline speedevil

  • Senior Member
  • *****
  • Posts: 4406
  • Fife
  • Liked: 2762
  • Likes Given: 3369
I was just thinking about estimating some values for my telescoping idea.

I think I can work out the basic mass per volume from something like this
https://en.wikipedia.org/wiki/Pressure_vessel#Cylindrical_vessel_with_hemispherical_ends

What is a sensible, non Sci-Fi material choice? What should I use for density and maximum working stress? What should I use for pressure?
Even using quite modest materials allows really ridiculous volumes.
For example, aluminum as used in scaffolding poles can support ~290MPa of stress.
A 1mm skin can in theory support around 290MPa/75kPa = 3900 times its area = 3.9m. (75kPa chosen as it is the pressure at the first highest city in the USA I'd heard of, Flagstaff).
So, a 1mm skin can (just) support an 8m diameter cylindrical atmospheric load, only considering one axis.

You probably don't in fact want to work close to the limit, and 75% is a sane maximum ever load. Even really, really large structural margins lead to quite large structures. Consider a nesting series of cylinders 8.5m or so in diameter and 8m or so long, 1" thick, for example.
With 150 tons of launch, you get 60m^3 of aluminium, or enough to make a one inch approximately cylindrical structure 8m diameter and 100m long.  (three times the B2100), for something you can order inexpensively constructed tomorrow, with rapid delivery.

This is with a naive safety factor of 25 or so.
Bolting this together will get you at worst 50% safe working cyclic load, with a factor of 12 safety.

The proper design needs to consider launch costs, and if you're at more than double launch costs for your entire construction, you may not be doing things cheaply enough.

It is reasonably arguable that you should for a system like BFR, even for initial launches, you should be aiming to design not for todays launch cost, but tomorrows.

The volume and mass potentially available on orbit means that multiple approaches can be tried on orbit at once, inexpensively.
You don't spend seven years and five billion dollars developing robot arms, you go to the market, and buy the twenty most popular robotic arms for a million or so, lightly modify them so they can probably cope with a vacuum, and try them in orbit.

I am not saying that complex payloads are bad, but that we need to look carefully at the environment that shaped the payloads, and consider carefully if that's what we want to do.

The B2100 is a great example of a payload designed for todays launchers.
It is enormously highly engineered and optimised.
But how much would it cost to buy 50 of them.
It's not optimised for a launch cost of $100/kg, never mind $30 or $10.




Offline tdperk

  • Full Member
  • ***
  • Posts: 369
  • Liked: 152
  • Likes Given: 95
One order of magnitude reduction in cost can be expected in the next 5-10 years. Not multiple orders of magnitude. 2 at most a long time from now.
I assume this means you don't believe that passenger transport at close to the stated goals will come about ever?

Maybe, a long time from now.  Going from $60,000,000 to $6,000,000 to $600,000 will take time.  That's all I'm saying.

John

It will take 5 (+5/-0 years tolerance) for costs to enter the <$100/lb range, R&D amort. neglected.  When prices approach that is a different question.

Offline tdperk

  • Full Member
  • ***
  • Posts: 369
  • Liked: 152
  • Likes Given: 95
I was just thinking about estimating some values for my telescoping idea.

I think I can work out the basic mass per volume from something like this
https://en.wikipedia.org/wiki/Pressure_vessel#Cylindrical_vessel_with_hemispherical_ends

What is a sensible, non Sci-Fi material choice? What should I use for density and maximum working stress? What should I use for pressure?
Even using quite modest materials allows really ridiculous volumes.
For example, aluminum as used in scaffolding poles can support ~290MPa of stress.
A 1mm skin can in theory support around 290MPa/75kPa = 3900 times its area = 3.9m. (75kPa chosen as it is the pressure at the first highest city in the USA I'd heard of, Flagstaff).
So, a 1mm skin can (just) support an 8m diameter cylindrical atmospheric load, only considering one axis.

You probably don't in fact want to work close to the limit, and 75% is a sane maximum ever load. Even really, really large structural margins lead to quite large structures. Consider a nesting series of cylinders 8.5m or so in diameter and 8m or so long, 1" thick, for example.
With 150 tons of launch, you get 60m^3 of aluminium, or enough to make a one inch approximately cylindrical structure 8m diameter and 100m long.  (three times the B2100), for something you can order inexpensively constructed tomorrow, with rapid delivery.

This is with a naive safety factor of 25 or so.
Bolting this together will get you at worst 50% safe working cyclic load, with a factor of 12 safety.

The proper design needs to consider launch costs, and if you're at more than double launch costs for your entire construction, you may not be doing things cheaply enough.

It is reasonably arguable that you should for a system like BFR, even for initial launches, you should be aiming to design not for todays launch cost, but tomorrows.

The volume and mass potentially available on orbit means that multiple approaches can be tried on orbit at once, inexpensively.
You don't spend seven years and five billion dollars developing robot arms, you go to the market, and buy the twenty most popular robotic arms for a million or so, lightly modify them so they can probably cope with a vacuum, and try them in orbit.

I am not saying that complex payloads are bad, but that we need to look carefully at the environment that shaped the payloads, and consider carefully if that's what we want to do.

The B2100 is a great example of a payload designed for todays launchers.
It is enormously highly engineered and optimised.
But how much would it cost to buy 50 of them.
It's not optimised for a launch cost of $100/kg, never mind $30 or $10.

Aluminum should be rejected on account of spallation radiation.  Carbon Fiber is a better match  I think.

The 100$ full density a BFR would carry is what, 11lbs/ft^3 ?  Al is 168.5 lbs /ft^3., CF is half that.

Considering the advantage of using standardized size modules (as opposed to telescoping assemblies which I take to be like matryoshka dolls), I think nesting subassemblies which become modules after assembly are the way to go and have a slight edge over BA style expanding modules -- when assembly on orbit becomes assumed.

Until then BA expanders have an advantage of being first day useful.  I believe they will be the places the people maintaining and operating the assemblers live.

Offline KelvinZero

  • Senior Member
  • *****
  • Posts: 4286
  • Liked: 887
  • Likes Given: 201
Hi, ok I will probably go carbon fibre as a good but non-scifi material that happens to exist in this table:

https://en.wikipedia.org/wiki/Ultimate_tensile_strength#Typical_tensile_strengths
This gives
tensile strength = 1600 for laminates ( I assume the 4137 for fibres alone is just in one direction? )
density = 1.75 g/cm3

I found this inside the link above: https://en.wikipedia.org/wiki/Factor_of_safety

Buildings commonly use a factor of safety of 2.0 for each structural member. The value for buildings is relatively low because the loads are well understood and most structures are redundant. Pressure vessels use 3.5 to 4.0, automobiles use 3.0, and aircraft and spacecraft use 1.2 to 3.0 depending on the application and materials. Ductile, metallic materials tend to use the lower value while brittle materials use the higher values.


( btw, https://en.wikipedia.org/wiki/Basalt_fiber looks really attractive for lunar applications. Strong, fireproof, good elastic strength. No other materials added .. if you are going to do one construction material ISRU on the moon, this sounds great.)

=====

For a carbon fiber cylinder of 8.5m radius and 1atm pressure, I work it out as 50kg/m 12.5kg/m. lets triple it for a lot of safety to 150kg/m 37.5kg/m. A 150 ton BFS cargo could lift 1km ~4km of this cylinder by mass.. which probably means my telescoping idea would have to deal with significant narrowing. I will have to work out the wall thickness and guess the delta width for each segment. It might narrow to an unusable width before it can exploit the BFS launch capability.

=====
edit: appended new working 15/Nov/17

I think this works out to about 6 m3 per kg.

That is a very useful figure because you would get the same result regardless of cylinder radius so it can be applied to all the cylinder sections.

That is about 0.7kg/m2 when 8.5m radius. Im getting really thin depth values, under half a millimeter.

That is much thinner than I thought. Does that sound reasonable or have I dropped some decimal places somewhere?

That thin, perhaps you could forget telescoping and send the whole tube rolled up like one of those party whistles.

« Last Edit: 11/14/2017 09:29 pm by KelvinZero »

Offline mikelepage

  • Full Member
  • ****
  • Posts: 1218
  • ExodusSpaceSystems.com
  • Perth, Australia
  • Liked: 855
  • Likes Given: 1358
What's the thinking on maintaining pressure in a telescoping tube?

I'm picturing that each end of each tube segment has some kind of inflatable rubber gasket that abuts the next/previous tube (similar to those on the hatch covers in the ISS cupola), but that kind of arrangement wouldn't be able to hold pressure whilst tubes are sliding against each other. 

I guess it's a related problem to that of trying to hold pressure against a rotating bearing (as in a habitat with rotating and stationary parts).  It's easier if you don't try to hold an atmosphere against moving parts, but parts that move can have several set positions which can hold pressure.  Telescoping tubes will only be used in either contracted or extended forms - i.e. you extend it out first, then you bring it up to pressure.

Offline QuantumG

  • Senior Member
  • *****
  • Posts: 9238
  • Australia
  • Liked: 4477
  • Likes Given: 1108
Human spaceflight is basically just LARPing now.

Offline aero

  • Senior Member
  • *****
  • Posts: 3629
  • 92129
  • Liked: 1146
  • Likes Given: 360
They manage to hold pressure in hydraulic rams so I imagine it could be done on a tube.
Retired, working interesting problems

Offline KelvinZero

  • Senior Member
  • *****
  • Posts: 4286
  • Liked: 887
  • Likes Given: 201
What's the thinking on maintaining pressure in a telescoping tube?

I'm picturing that each end of each tube segment has some kind of inflatable rubber gasket that abuts the next/previous tube (similar to those on the hatch covers in the ISS cupola), but that kind of arrangement wouldn't be able to hold pressure whilst tubes are sliding against each other. 

I guess it's a related problem to that of trying to hold pressure against a rotating bearing (as in a habitat with rotating and stationary parts).  It's easier if you don't try to hold an atmosphere against moving parts, but parts that move can have several set positions which can hold pressure.  Telescoping tubes will only be used in either contracted or extended forms - i.e. you extend it out first, then you bring it up to pressure.

I was thinking something that was not extended by inflation. I was imagining a simple robot, little more than a cog, that extends the innermost section, clicks it into place (whatever that means) then moves to extend the next section.

It only is intended to hold pressure while fully extended, and it is not required to be reversible. The seal has to be very robust even with flexing. I think there is a risk of harmonics building up in this ring, just like with a suspension bridge. Of course we would take all the steps to minimise that. To grow the station and also reduce flexing, multiple rings could be placed side by side. A square grid cross-section might be a bit tidier than a hexagonal one because as one tube narrows its neighbours could widen.

One tricky bit is that we want the extended cylinder to have a slight curve in it. Maybe we could build a slight curve into every single section, but there might be a way to use sections that are straight cylinders and click into place with a 1 degree angle between each section, say. I have no idea which approach would create the least problems.

btw, a full torus is a reasonable pressure vessel, but what about half or quarter torus? Would the pressure attempt to straighten it?
« Last Edit: 11/14/2017 07:27 am by KelvinZero »

Offline speedevil

  • Senior Member
  • *****
  • Posts: 4406
  • Fife
  • Liked: 2762
  • Likes Given: 3369
btw, a full torus is a reasonable pressure vessel, but what about half or quarter torus? Would the pressure attempt to straighten it?
Yes.
However, you can cancel this with a simple rope between the two ends, adding another as you add a segment and moving the old one over.

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
0