Author Topic: Realistic, near-term, rotating Space Station  (Read 978105 times)

Offline RonM

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Re: Realistic, near-term, rotating Space Station
« Reply #1100 on: 08/01/2018 04:30 pm »
"Maybe it's foolhardy, but we're going to do it anyway..."

I mean, surely there's a better way...  ;)

I believe that analysis can apply to a large part of human history.

At Exodus, we're creating a small (washing-machine sized), deployable, "space-origami" structure that can fold up within a long narrow rocket payload bay, and fold out to a segmented, rigid toroid array.  Single launch, no in-space assembly.  I think we've also got some pretty neat mechanisms to control spin orientation and spin rate.

Most importantly, we're looking at all the applications (terrestrial and space-based) where we can start making money from these designs before we even try to scale the concept up to space station size to address the biomedical questions.

Sounds good. Hope you're successful.

Richie-5

Simplified Richie-class ITS Configuration

The initial "Richie-class" options could support concurrent AG tests - for multiple concurrent mission profiles - in low g, Mars g and Earth g.  Each mission crew would switch between AG environments at each simulated mission AG transition: e.g. transition from in-transit low g to Mars surface g, or from Mars surface g to Mars surface centrifuge Earth g.  All system hardware could be returned to Earth for repair or modification between each experimental run, and then repurposed for deep-space missions at the end of AG testing.

To get greater value out of 5 ITS craft, you could tweak that Richie-class config to get 5 different, concurrent AG environments.  This would enable concurrent AG testing of missions to all bodies between Earth and Mars.

The 5 AG environments:

1.  Earth g
2.  Mars g
3.  Lunar g
4.  Deimos g
5.  low g

5 ITS craft for 5 AG environments, with all appreciable g environments located on the ceiling:  "Richie-5", one might say.

4 or 5 BFS is kind of pricey. How would setup an AG station if only 2 BFS were available?

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Re: Realistic, near-term, rotating Space Station
« Reply #1101 on: 08/01/2018 05:49 pm »
Richie-5

Simplified Richie-class ITS Configuration

The initial "Richie-class" options could support concurrent AG tests - for multiple concurrent mission profiles - in low g, Mars g and Earth g.  Each mission crew would switch between AG environments at each simulated mission AG transition: e.g. transition from in-transit low g to Mars surface g, or from Mars surface g to Mars surface centrifuge Earth g.  All system hardware could be returned to Earth for repair or modification between each experimental run, and then repurposed for deep-space missions at the end of AG testing.

To get greater value out of 5 ITS craft, you could tweak that Richie-class config to get 5 different, concurrent AG environments.  This would enable concurrent AG testing of missions to all bodies between Earth and Mars.

The 5 AG environments:

1.  Earth g
2.  Mars g
3.  Lunar g
4.  Deimos g
5.  low g

5 ITS craft for 5 AG environments, with all appreciable g environments located on the ceiling:  "Richie-5", one might say.

4 or 5 BFS is kind of pricey.

In thread context Richie-5 would be pricey only if comparable facilities could be constructed more cheaply another way, plausibly, and also by 2022.

That's not the case, or not yet.

Ideas?

And remember:  leasing is an option with Richie-class systems.   :)

How would setup an AG station if only 2 BFS were available?

It's the premise of yesterday's post, with use as illustrated.  See the schedule.

« Last Edit: 08/01/2018 05:53 pm by LMT »

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Re: Realistic, near-term, rotating Space Station
« Reply #1102 on: 08/01/2018 09:20 pm »
Richie Number

The cost of experiments at these notional Richie-class rotating space stations would be closely tied to the number of ITS craft that must be kept in orbit.  One way to lower cost below that of baseline Richie-5 configuration is to remove ITS craft from orbit when not in use.  The characteristic number of ITS craft used for AG in an experimental run might be called, rather fancifully, the "Richie Number".  It's a metric.

Example:  3 simulated AG missions run concurrently within a Richie-5 system:



The first mission approximates yesterday's single-window Mars mission.  The other 2 missions are theme-and-variation.

At far left the number of ITS craft required for each timeframe (fortnight) is tallied.  Note that all 5 ITS craft are required for only a small fraction of the total experimental run.  Presumably 1 ITS craft could be removed from orbit during other months, reducing cost.

The run's average number of ITS craft is shown at bottom left: i.e., the Richie Number, here calculated as:

3.97

--

Creativity may reduce the Richie Number and cost even further, while producing much the same experimental data.

Q:  What are some methods that might improve this simple 3-mission case, and what Richie Numbers can be attained by these methods, applied singly or in concert? [pun]

Spreadsheet and image attached.

mikelepage, would you feel like adjudicating this little "challenge", if anyone bothers with it?    8)
« Last Edit: 08/02/2018 06:16 am by LMT »

Offline Paul451

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Re: Realistic, near-term, rotating Space Station
« Reply #1103 on: 08/02/2018 01:46 am »
And remember:  leasing is an option with Richie-class systems.

Not really. To get decent data, you'd need them for at least 2 years, ideally more. That means you're pulling 4 BFSes out of service for that entire time. In addition, you have time on the ground needed for the modifications necessary for your structure. (Two BFSes "upright", two "upside down". The tail-tail mating. Etc.) I think SpaceX would consider it a waste of ships.

So, as I said, you'd be buying the ships. Or leasing on such harsh terms that you are effectively paying their replacement cost over two years.

Offline Paul451

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Re: Realistic, near-term, rotating Space Station
« Reply #1104 on: 08/02/2018 01:48 am »
Best way to get an AG research station built is to convince Elon Musk that SpaceX needs to do the research before going to Mars.

IMO, the best way would be to convince JAXA (and the Japanese government) that their interest in AG research would be better fulfilled by building a small Japanese-owned human-tended AG animal facility, using FH for hardware launches and commercial-crew for people/supplies. (With an option of using New Glenn or BFR for the hardware launches, if either becomes available.) You have to convince them that having their own orbital facility outweighs the "embarrassment" of flying on US launchers.

Then convince the ESA, and their funding nations, that joining the Japanese would let them further pursue their own, smaller but present, AG interest.

And then convincing Musk that it's a good deal for him.

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Re: Realistic, near-term, rotating Space Station
« Reply #1105 on: 08/02/2018 03:19 am »
And remember:  leasing is an option with Richie-class systems.

Not really. To get decent data, you'd need them for at least 2 years, ideally more. That means you're pulling 4 BFSes out of service for that entire time. In addition, you have time on the ground needed for the modifications necessary for your structure. (Two BFSes "upright", two "upside down". The tail-tail mating. Etc.) I think SpaceX would consider it a waste of ships.

So, as I said, you'd be buying the ships. Or leasing on such harsh terms that you are effectively paying their replacement cost over two years.

Oh, you've considered how and why big-ship leasing works?  Cool.  Do give us some case studies, and compare/contrast.
« Last Edit: 08/02/2018 03:30 am by LMT »

Online Coastal Ron

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Re: Realistic, near-term, rotating Space Station
« Reply #1106 on: 08/02/2018 04:12 am »
So, as I said, you'd be buying the ships. Or leasing on such harsh terms that you are effectively paying their replacement cost over two years.

Oh, you've considered how and why big-ship leasing works?  Cool.  Do give us some case studies, and compare/contrast.

Oh, you've considered how and why big-ship leasing works?  Cool. Why do you think Musk will be leasing out lots of BFS?

And more importantly, who will be making the lease payments, and why?
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline mikelepage

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Re: Realistic, near-term, rotating Space Station
« Reply #1107 on: 08/02/2018 04:18 am »
How would setup an AG station if only 2 BFS were available?

It's the premise of yesterday's post, with use as illustrated.  See the schedule.



This is nice.  The tail-to-tail configuration en route to and from Mars is what I've imagined would be the absolute minimum effort way for SpaceX to generate some partial G data.  With a radius of 28-48m they would be able to simulate Mars G or higher at low spin rates which should be well within the tolerances of the interstage docking clamps, and without any of the potential dynamic issues of nose-to-nose tethered connections.

Also a small correction - there's no need to depict refueling of BFR in low Mars orbit - one full tank on Mars surface is enough to get all the way home so it should just launch directly to the interplanetary transit back to Earth.

Some notes on nomenclature:
I think everyone at SpaceX has settled on Big Falcon Rocket, made up of BFS and BFB.  Not even with a wink and a nudge.  That's what we're calling it now.

Who's Richie?  ;D Is that your name LMT? I always assumed you were Matthew. (I'm just Mike fyi, Le Page is my last name)

mikelepage, would you feel like adjudicating this little "challenge", if anyone bothers with it?    8)

Sorry LMT, no can do.  You're doing your hijacking thing again btw.  The proper forum for expanded brainstorming like this is to write a paper and submit it to a journal for publication, or set up a website like Al Globus did.  Here at NSF you really need to get a proper nibble before you spend too much effort going on tangents like this.  If you don't, you're at risk of getting into a passive-aggressive war of sarcasm  ::) and then moderated.  :P

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Re: Realistic, near-term, rotating Space Station
« Reply #1108 on: 08/02/2018 05:35 am »
With a radius of 28-48m they would be able to simulate Mars G or higher at low spin rates which should be well within the tolerances of the interstage docking clamps, and without any of the potential dynamic issues of nose-to-nose tethered connections.

Has SpaceX given any specs on those clamps, and their use during propellant transfer?  I hadn't seen, so I proposed a mod to the lines instead.

Also, yes, you'd want to avoid tethers if possible in this application, for dynamics and perhaps just for simplicity.  An adaptation of the James Webb telescoping mast system seemed plausible for the larger, 1 g system.  It could be rock-solid in operation, and easily stowed.

Some ITS Richie-class mods 1, 2, 3; and mod implementation as "safety features".

Also a small correction - there's no need to depict refueling of BFR in low Mars orbit - one full tank on Mars surface is enough to get all the way home so it should just launch directly to the interplanetary transit back to Earth.

Actually that seemed to be needed in this case due to Handmer's "closing edge of the return window".  His tight free-return mission timing is specific; it encounters a return shortfall of some hundreds of m/s (see chart), which he meets with SEP.  But ITS-2 would have extra propellant in LMO.  Why not share it with ITS-1, and thereby avoid the $ of giant SEP?

The proper forum for expanded brainstorming like this is to write a paper and submit it to a journal for publication, or set up a website

Oh, it's just brainstorming - nothing like the rigors of real phys/eng published work of course - and on-topic.  Now, if brainstorming best station $/value doesn't interest thread readers, that's curious given thread subject, but of course no one dictates interest.  Notions come and go; small thought experiments, too.

Facts sometimes return. 

Who's Richie?

« Last Edit: 08/02/2018 06:12 am by LMT »

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Re: Realistic, near-term, rotating Space Station
« Reply #1109 on: 08/03/2018 03:04 am »
Scheduling

An AG experimental schedule could run 2022-2025.  1+ year of AG testing would precede the first single-window Mars mission; 3+ years of testing would precede the first long-stay mission.

Ideally experiments would inform a comprehensive AG flight reference (presumably NASA's), providing AG recommendations for missions to any body between Earth and Mars, for missions lasting up to ~ 3 years.  The notional experimental schedule would sync with SpaceX's notional Mars schedule, wherein we might infer a long-stay mission launching no earlier than late 2026.

Inference:

This AG experimental schedule would not hinder the SpaceX Mars launch cadence.  Spacecraft would exit the experiment as their launch windows approached.  For this reason there's no schedule pressure to justify the sort of daredevil thinking mikelepage characterized as, "Maybe it's foolhardy, but we're going to do it anyway..."  It just takes some forethought.

Experimental efficiency:

It would also take careful structuring of the experimental work.  How best to "pack" experiments to get comprehensive data in least time and with fewest test subjects?  For that matter, how many test subjects are really needed, to meet the required confidence level for each AG flight reference recommendation?  (Qs for casual brainstorm, directed mainly at mikelepage and HMXHMX, and any others with AG lab experience)

Hardware efficiency:

And of course you'd want to minimize the experimental hw in LEO.  With most AG designs, the hw is fixed in LEO; whereas the notional ITS Richie-class systems could be reconfigured at each AG transition to minimize hw in LEO, dynamically.

If it's of interest, I tried the example case from previous post, applying several methods to minimize LEO hw, or lower the Richie Number.   Methods were at least arguable.  For example I inserted a few weeks of extra mission time into one simulated mission plan, so that two missions could sync their Earth-return AG cadence and thereby minimize the number of ITS craft required to simulate the return in LEO.

Result:

Richie Number drops from 3.97 to:

« Last Edit: 08/03/2018 03:06 am by LMT »

Offline mikelepage

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Re: Realistic, near-term, rotating Space Station
« Reply #1110 on: 08/03/2018 06:58 am »
With a radius of 28-48m they would be able to simulate Mars G or higher at low spin rates which should be well within the tolerances of the interstage docking clamps, and without any of the potential dynamic issues of nose-to-nose tethered connections.

Has SpaceX given any specs on those clamps, and their use during propellant transfer?  I hadn't seen, so I proposed a mod to the lines instead.

Must admit I've not seen any actual specs, but IIRC Elon Musk has said it's the same interface that connects BFB to BFS that allows two BFS to dock tail to tail, which implies it is a uni-directional, rather than male-female type connection.

My assertion that it can probably take it, is based on the fact that prior to stage separation (if the falcon 9 flight profile is anything to go by), those clamps are stabilising some 1335 tons of BFS under 3x gees of compressive force.  So on the order of 40 x 10^6 N.  But most of that mass is propellant which is used during the second stage burn, so during cruise phase, you only have 235 ton of BFS, plus landing propellant of maybe ~100 ton.  Even if you were to spin that up to 1G (4.3 rpm at r=48m), the centre of mass of BFS at that stage is well down towards the engines (perhaps 16m or 1/3 of the radius away from the clamps), so the tensile force on the clamps would be on the order of 1.1 x 10^6N.

Basically I find it hard to believe that clamps built to take 40 MegaNewton in compression wouldn't be able to take 1 MegaNewton in tension.

***

Totally missed the Lionel Richie reference above (skimming), but I suppose that's as good a reason for naming something as any.

***

Edit: I've also remembered that keeping the landing propellant cool is going to be the main reason the BFS wants to stay pointed at the sun, and not engage in any spin G experiments.  Having said that EM has mentioned the tankage for the landing prop could be subject to redesign.
« Last Edit: 08/03/2018 07:02 am by mikelepage »

Offline J-V

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Re: Realistic, near-term, rotating Space Station
« Reply #1111 on: 08/03/2018 07:10 am »

Edit: I've also remembered that keeping the landing propellant cool is going to be the main reason the BFS wants to stay pointed at the sun, and not engage in any spin G experiments.  Having said that EM has mentioned the tankage for the landing prop could be subject to redesign.

Just leave the tanks as empty as possible and refuel once the spinning part of the flight has ended.

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Re: Realistic, near-term, rotating Space Station
« Reply #1112 on: 08/03/2018 09:21 am »

Edit: I've also remembered that keeping the landing propellant cool is going to be the main reason the BFS wants to stay pointed at the sun, and not engage in any spin G experiments.  Having said that EM has mentioned the tankage for the landing prop could be subject to redesign.

Just leave the tanks as empty as possible and refuel once the spinning part of the flight has ended.

Veering off topic now, but that's not actually an option.  The only reason BFR can get away with so little landing fuel as it is, is that it goes directly into atmospheric entry from interplanetary velocities.  There's nowhere to refuel from, between cruise phase and atmospheric entry.

Therefore, spin gravity tests during interplanetary transits will only be possible if SpaceX decides to implement some kind of active cooling of its landing fuel, which is possible, but not currently planned.

Offline Paul451

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Re: Realistic, near-term, rotating Space Station
« Reply #1113 on: 08/03/2018 09:41 am »
My assertion that it can probably take it, is based on the fact that prior to stage separation (if the falcon 9 flight profile is anything to go by), those clamps are stabilising some 1335 tons of BFS under 3x gees of compressive force.

Compression <> tension.

Basically I find it hard to believe that clamps built to take 40 MegaNewton in compression wouldn't be able to take 1 MegaNewton in tension.

Because you're assuming the clamps themselves (rather than rest-plates) are taking the entire force.

Edit: I've also remembered that keeping the landing propellant cool is going to be the main reason the BFS wants to stay pointed at the sun, and not engage in any spin G experiments.

It's not hard to keep your spin-axis pointed at the sun, even when orbiting Earth. The hard part is the reflection from Earth. It's about a third the sun's direct heat, IIRC.

But, if you're in Earth orbit, then it's relatively simple to buy an orbital refuelling for the landing fuel. One tanker should be able to refuel all 4 of them with enough to land.

My issue remains that it's a waste of BFSes. Musk wants to use them. Having four sitting around in a paddock full of rats (from his point of view) is a waste. He is going to charge you appropriately. I suspect somewhere around the replacement value over two years. And no mysterious funder is going to pay that.

Offline J-V

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Re: Realistic, near-term, rotating Space Station
« Reply #1114 on: 08/03/2018 10:01 am »

Edit: I've also remembered that keeping the landing propellant cool is going to be the main reason the BFS wants to stay pointed at the sun, and not engage in any spin G experiments.  Having said that EM has mentioned the tankage for the landing prop could be subject to redesign.

Just leave the tanks as empty as possible and refuel once the spinning part of the flight has ended.

Veering off topic now, but that's not actually an option.  The only reason BFR can get away with so little landing fuel as it is, is that it goes directly into atmospheric entry from interplanetary velocities.  There's nowhere to refuel from, between cruise phase and atmospheric entry.

Therefore, spin gravity tests during interplanetary transits will only be possible if SpaceX decides to implement some kind of active cooling of its landing fuel, which is possible, but not currently planned.

Oh. I missed the part where the thread moved from space stations to Mars-Earth transits. Please carry on...

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Re: Realistic, near-term, rotating Space Station
« Reply #1115 on: 08/03/2018 12:15 pm »
First Tourist Station

I missed the part where the thread moved from space stations to Mars-Earth transits. Please carry on...

But that's how you get your very first realistic, near-term, rotating space station - even for tourists.

Noodling:

On that notional schedule the era of AG experiment ends circa 2026.  Long-duration operations begin.

Also by 2026 SpaceX would have begun mass-production of ITS, not just for Mars but also for Earth operations (point-to-point flights).  How to improve the profitability of those terrestrial flights?  One possibility:  give passengers a high-value destination - a rotating space station, with great features such as:

- Mars gravity
- Mars Environmental Test Facility, (2), with real Mars rock and Mars base hw (and O2 ambient atmosphere for tourists, presumably)
- Fine dining, stylish quarters, etc.

A Richie-2 configuration would be adequate, requiring only 2 ITS craft.  Build more to match demand.

Circa 2028, on the notional schedule.

That should be a profitable run, don't you think?  How to improve it?



« Last Edit: 08/03/2018 01:55 pm by LMT »

Offline mikelepage

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Re: Realistic, near-term, rotating Space Station
« Reply #1116 on: 08/03/2018 12:49 pm »
My assertion that it can probably take it, is based on the fact that prior to stage separation (if the falcon 9 flight profile is anything to go by), those clamps are stabilising some 1335 tons of BFS under 3x gees of compressive force.

Compression <> tension.

Basically I find it hard to believe that clamps built to take 40 MegaNewton in compression wouldn't be able to take 1 MegaNewton in tension.

Because you're assuming the clamps themselves (rather than rest-plates) are taking the entire force.

Fair call, compression is not the key factor, my mistake. 

What I was intuitively driving at was the vibrational loads at Max Q that those clamps must be able to safely contain.  Looking up the falcon 9 payload guide, any payload is required to be able to take up to 0.5-0.6xg laterally (attachment is screenshot from page 23).  Presumably the interstage clamps must be capable of this too, and I'm not sure whether building bigger rockets does anything to change this issue.

Clamps that are able to resist 0.5-0.6xG force vibrations, laterally on a 1335 ton BFS during Max Q, I would have imagined would be capable of taking as much as 1xG in tension on a much lighter (~335 ton) BFS in a much more benign space environment.

Quote
Edit: I've also remembered that keeping the landing propellant cool is going to be the main reason the BFS wants to stay pointed at the sun, and not engage in any spin G experiments.

It's not hard to keep your spin-axis pointed at the sun, even when orbiting Earth. The hard part is the reflection from Earth. It's about a third the sun's direct heat, IIRC.

I thought the point of keeping the BFS pointed at the sun was to keep the engine (and associated structures) shaded, as these are what will conduct heat into the landing prop tanks.  Keeping your spin axis pointed at the sun doesn't necessarily shade the engines.

Quote
But, if you're in Earth orbit, then it's relatively simple to buy an orbital refuelling for the landing fuel. One tanker should be able to refuel all 4 of them with enough to land.

My issue remains that it's a waste of BFSes. Musk wants to use them. Having four sitting around in a paddock full of rats (from his point of view) is a waste. He is going to charge you appropriately. I suspect somewhere around the replacement value over two years. And no mysterious funder is going to pay that.

I tend to agree re in-orbit use of BFS's.  If I was proposing spin G with BFS's to Musk, it would be to do this as an experiment whilst in transit to and from Mars, which he's said will include BFS's travelling in pairs.  As long as you're not compromising the spacecraft in any way, this could be a minimum effort method of getting some partial G data, and increasing passenger comfort.

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Re: Realistic, near-term, rotating Space Station
« Reply #1117 on: 08/03/2018 02:16 pm »
Even if you were to spin that up to 1G (4.3 rpm at r=48m), the centre of mass of BFS at that stage is well down towards the engines (perhaps 16m or 1/3 of the radius away from the clamps), so the tensile force on the clamps would be on the order of 1.1 x 10^6N.

Something like that, yes.  Also the base Richie-4 config (symmetric 1 g) increases station radius and adds 150 t of water; hence the suggested 3 MN rating.  Clamps or lines could accommodate the load, if AG were planned for.

re: water:  During long-duration AG tests, I think you'd want the full 150-t, 40+ cm water shield to control against radiation effects.

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Re: Realistic, near-term, rotating Space Station
« Reply #1118 on: 08/03/2018 02:39 pm »
Basically I find it hard to believe that clamps built to take 40 MegaNewton in compression wouldn't be able to take 1 MegaNewton in tension.
Because you're assuming the clamps themselves (rather than rest-plates) are taking the entire force.
[...] Clamps that are able to resist 0.5-0.6xG force vibrations, laterally on a 1335 ton BFS during Max Q, I would have imagined would be capable of taking as much as 1xG in tension on a much lighter (~335 ton) BFS in a much more benign space environment.

Just for clarity, this might better illustrated what I was trying to say:



Those 9 plates take up most of the forces, both compression and vibration loads. By design, very little load would be on the latches (of which only one is so-far mounted, at the top.) I would assume BFR would have similar kind of set-up. Are the latches alone strong enough to hang from under 1g? Or 0.38g? Even at the reduced mass.

It's not hard to keep your spin-axis pointed at the sun, even when orbiting Earth.
Keeping your spin axis pointed at the sun doesn't necessarily shade the engines.

Oops, I went back to thinking of a single BFS spinning on its long-axis.

If I was proposing spin G with BFS's to Musk, it would be to do this as an experiment whilst in transit to and from Mars

Yeah, I missed that part, sorry.
« Last Edit: 08/03/2018 02:48 pm by Paul451 »

Online Coastal Ron

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Re: Realistic, near-term, rotating Space Station
« Reply #1119 on: 08/03/2018 02:50 pm »
Fair call, compression is not the key factor, my mistake. 

...Presumably the interstage clamps must be capable of this too, and I'm not sure whether building bigger rockets does anything to change this issue.

Clamps that are able to resist 0.5-0.6xG force vibrations, laterally on a 1335 ton BFS during Max Q, I would have imagined would be capable of taking as much as 1xG in tension on a much lighter (~335 ton) BFS in a much more benign space environment.

What Musk has said is the transferring of propellant between two BFS would be done by docking them and then the ship to gain propellant would gently accelerate against the ship with propellant - the propellant would "run down hill". One would imagine that the ship being pushed against could also use their thrusters to push back to a lesser amount to maintain stability.

In such a method no clamps would be needed, and I'm not sure we've seen evidence of clamps on the notional 3D models SpaceX has shown.

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I thought the point of keeping the BFS pointed at the sun was to keep the engine (and associated structures) shaded, as these are what will conduct heat into the landing prop tanks.  Keeping your spin axis pointed at the sun doesn't necessarily shade the engines.

I'm glad you remembered this topic since Musk did say that the BFS would not keep propellant pressurized, that it would in fact be open to space. And the only way to do that is to keep the BFS tank area shaded as much as possible.

Based on that, no matter how you orient two BFS spinning while connected at their nose, a side of the BFS will be exposed to direct sunlight 50% of the time. For the BFS as described by Musk, that doesn't sound like it will work.

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I tend to agree re in-orbit use of BFS's.  If I was proposing spin G with BFS's to Musk, it would be to do this as an experiment whilst in transit to and from Mars, which he's said will include BFS's travelling in pairs.  As long as you're not compromising the spacecraft in any way, this could be a minimum effort method of getting some partial G data, and increasing passenger comfort.

Musk did mention artificial gravity as a potential feature, but we don't know if that would just be spinning a BFS along the axis so that it can still keep it's nose pointing at the sun for shading the propellant tanks.

As with trying to utilize Bigelow modules and other structures designed for non-artificial gravity uses, it would appear that the BFS have a number of critical issues that limit their use for artificial gravity.

Which doesn't mean artificial gravity with spaceships and space stations should be hard, just that a design without so many compromises will likely need to be a clean-sheet design.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

 

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