How the heck do you have gas-tight bearings between non rotating and rotating sections?

[KSK]

4 hours ago, SomeGuy123 said:

The reason your idea is still bad and will probably never be done in the history of manned spaceflight actually has to do with design coupling.  You talking about the complexity of electromagnetic bearings - yeah, that's some complexity - but you fail to appreciate that if you take a perfectly good rocket engine and fuel tank design and expect it to take rotational stresses that vary depending on the location on the ship - you end up with immensely complex engineering problems.  The current heat radiators and solar panels they fly are only able to work in microgravity, as a side note.

If the bearings don't have to hold an internal tube that astronauts can traverse, it's just a big bearing in vacuum, that's straightforward engineering.  

I'll take that bet. If we do ever send a crewed vessel to Mars, I say that it won't have a separately rotating habitation section. I think the engineering problems involved in doing so are at least as 'immensely complex' as having the whole vessel spinning and a separately rotating hab section adds all sorts of new and interesting failure modes.

Rotational stresses that vary depending on ship location can be calculated ahead of time and the spacecraft and it's components designed with those stresses in mind. Yes, it's complex, especially to this non-engineer, but no more so (I would think) than building any other air or spacecraft. Having large moving parts that need to  operate in space for months at a time strike me as a far less reliable proposition. It's space - something will go wrong. Nibb's example of the SARJ problems is particularly appropriate. They were 'just a big bearing in a vacuum'. They weren't supposed to have any problems. They did.

Regarding the last point, it would be much easier to dispense with the bearings altogether and just have a tube, pressurised or not.

[fredinno]

16 hours ago, sgt_flyer said:

@SargeRho

 

depends - that would make a lot more rotational inertia to stop when you want to spin down  - so that would be to check about tradeoffs  (as you'll need your fuel tanks for RCS (and maybe main engine too, if you don't want to spin down) to be able to work in both spinning (possible fuel centrifugation) and microgravity situations. having only the hab section rotating would limit the mass you need to stop when spinning down, and you only have to design your fuel tanks to work in for zero g - low linear acceleration situation (as there's no point to keep the spacecraft rotating when it's waiting in earth or mars orbit). 

having only the hab spinning could limit gyroscopic effects (as the mass and spin speed would be limited relatively to the fixed section) - so you could do more easily some manoeuvers without the need to spin down.

- so in the end, what would be the simpler solutions ?  more complex propulsion tankage, or more complex connection to the hab ring ?  (only to keep antennas and solar panels 'fixed')

A HAB ring is more likely to be less complex overall than redesigning EVERYTHING on the ship to work in both micro and partial gravity- in a HAB ring, you only have to redesign the HAB section, and leave everything else roughly intact (aside from maybe structural reinforcements, but you need that for spinning the whole ship too.)

8 hours ago, Nibb31 said:

You can't say that it will never be done.

The stresses aren't anything that can't be designed into the ship. There are plenty of engineering solutions to stress load problems. You could add spring loaded flexible hinges to take up a part of the load like on the Orion solar panels, as previously mentioned.

There are plenty of designs of spin stabilized spacecraft in the past and future concepts too. 

Yes, and these concepts shown here run into the same problem with having rotating hinges...

You might as well be using a HAB ring.

[SargeRho]

34 minutes ago, fredinno said:

Yes, and these concepts shown here run into the same problem with having rotating hinges...

You might as well be using a HAB ring.

Not really. The first one doesn't have constantly rotating hinges, instead it has swivels for the ion engines, which point along the center of rotation when spun up.

The second one, while having hinges, doesn't have much running through them other than electricity.

[cantab]

The simplest approach is probably that of tethering the hab space to a counterweight and tumbling them about each other. That has various benefits, in particular that the artificial gravity is in the same direction as the launch and re-entry forces, and that a light and compact hab space gets a large spin radius to avoid coriolis force problems. The big drawback would I think be complexity when making a manoeuvre, doing it while tumbling really isn't practical. But if you can nail your Earth ejection burn to get your Mars encounter without needing further corrections then the method works great.

[Nibb31]

1 hour ago, fredinno said:

A HAB ring is more likely to be less complex overall than redesigning EVERYTHING on the ship to work in both micro and partial gravity- in a HAB ring, you only have to redesign the HAB section, and leave everything else roughly intact (aside from maybe structural reinforcements, but you need that for spinning the whole ship too.)

Except that you're not redesigning anything. You're designing it from scratch from predetermined requirements that can be easily calculated with pretty much any CAD software, which is something that you would have to do whatever the design. It's Engineering 101.

We're just going to have to disagree on this, because neither you nor I have run the calculations and done the engineering work, so we are basing the argument on assumptions and preconceptions. Someone would need to run an extensive comparative study between the two architectures to make an educated decision.

 

[BananaTime101]

Maybe the rotating sections would be enclosed in a pressured environment?

[fredinno]

6 hours ago, Nibb31 said:

Except that you're not redesigning anything. You're designing it from scratch from predetermined requirements that can be easily calculated with pretty much any CAD software, which is something that you would have to do whatever the design. It's Engineering 101.

We're just going to have to disagree on this, because neither you nor I have run the calculations and done the engineering work, so we are basing the argument on assumptions and preconceptions. Someone would need to run an extensive comparative study between the two architectures to make an educated decision.

 

A design where only the HAB spins only needs that part to be made from scratch. Anything else can use technology from Centaur, ISS, Orion, etc. That's what I meant by redesign.

3 hours ago, BananaIsAFruit said:

Maybe the rotating sections would be enclosed in a pressured environment?

And waste an enormous amount of mass covering a 6m diameter ring? Remember that every gram counts in space, and the leakage rate probably isn't so bad it'd more economical in mass to cover it up.

[sgt_flyer]

i guess that having a mechanical seal big enough to let a man go through it between a fixed section and a rotating section is going to be really annoying to have a reasonable leakage rate. (afterall, needing to have both mating parts so perfectly adjusted over all the circumference) - which is why people are proposing an enclosure  (if you need a fixed habitable section) 

but still  why would we need both a fixed and a rotating section ? having only one of the two entirely removes the need for such a mechanical seal.  so either :

- rotating the whole ship, with the need to get antennas, solar panels, potentially radiators, and maybe engines on a system allowing them to keep pointed in a fixed direction (with their connections to the spaceship needing to take into account the rotation) ,

- having only the habitable section spin (you either only connect to the docking hub when the ring is stopped, or the docking hub is integrated in the hab ring,with the docking port lined up with the axis of rotation (so a docked spacecraft doesn't create an imbalance when the ring is spun) - again, you need a way to interface the rest of the ship with the hab ring, so those connections have to take the rotation into account.

in both cases, you would only have to deal with small connections, much easier to perfectly adjust than one big mechanical seal.

we could also add having the whole habitable structure wholly fit within an enclosed fixed section, which would create it's own engineering problems (additionnal weight for the whole structure notably and such a huge fixed housing structure would surely need to be inflatable to be able to fit in a launcher fairing, then you have to assemble afterwards the rotating hab structure within the inflated housing) 

 

in any of those 3 cases, you'll need to deal with the torque / friction between the rotating and non rotating elements. even if one part has a tiny mass compared to the rest, needing to compensate for friction will still induce opposite movements in both sides  (even with ferrofluid seals - as you still need bearings alongside it, so you have to compensate for that.

on another note, just for ISS, for installing a rotating habitable ring on ISS, didn't they plan to have sets of airtight doors on both sides ? so any leakage occuring in the space between the rotating and fixed sections would be limited to this tiny space between the two doors - and you only open the doors when you need to get from one section to the other, greatly limiting the effects of the increased leakage rates.

Edited February 5, 2016 by sgt_flyer

[fredinno]

6 hours ago, sgt_flyer said:

i guess that having a mechanical seal big enough to let a man go through it between a fixed section and a rotating section is going to be really annoying to have a reasonable leakage rate. (afterall, needing to have both mating parts so perfectly adjusted over all the circumference) - which is why people are proposing an enclosure  (if you need a fixed habitable section) 

but still  why would we need both a fixed and a rotating section ? having only one of the two entirely removes the need for such a mechanical seal.  so either :

- rotating the whole ship, with the need to get antennas, solar panels, potentially radiators, and maybe engines on a system allowing them to keep pointed in a fixed direction (with their connections to the spaceship needing to take into account the rotation) ,

- having only the habitable section spin (you either only connect to the docking hub when the ring is stopped, or the docking hub is integrated in the hab ring,with the docking port lined up with the axis of rotation (so a docked spacecraft doesn't create an imbalance when the ring is spun) - again, you need a way to interface the rest of the ship with the hab ring, so those connections have to take the rotation into account.

in both cases, you would only have to deal with small connections, much easier to perfectly adjust than one big mechanical seal.

we could also add having the whole habitable structure wholly fit within an enclosed fixed section, which would create it's own engineering problems (additionnal weight for the whole structure notably and such a huge fixed housing structure would surely need to be inflatable to be able to fit in a launcher fairing, then you have to assemble afterwards the rotating hab structure within the inflated housing) 

 

in any of those 3 cases, you'll need to deal with the torque / friction between the rotating and non rotating elements. even if one part has a tiny mass compared to the rest, needing to compensate for friction will still induce opposite movements in both sides  (even with ferrofluid seals - as you still need bearings alongside it, so you have to compensate for that.

on another note, just for ISS, for installing a rotating habitable ring on ISS, didn't they plan to have sets of airtight doors on both sides ? so any leakage occuring in the space between the rotating and fixed sections would be limited to this tiny space between the two doors - and you only open the doors when you need to get from one section to the other, greatly limiting the effects of the increased leakage rates.

The latter option is most likely, but would likely be preceded by a few Nautilius-X ISS things before we can build these large enough to make humans live in them for long periods of time. So it's going to be A WHILE.

[RocketSquid]

If you have a ship that: A) spins along its thrust axis or B) Spins like a bola, it will have some fairly serious logistics problems as well. The first is docking, since docking is complicated enough without incorporating unequal spin rates. Meanwhile, it would be fairly difficult for astronauts onboard to help with docking, or much else, since they would be on a spinning platform. Also, if it spins like a bola, thrust could be a problem, since the engines would no longer be inline with the center of mass.

[sgt_flyer]

@RocketSquid

in interplanetary spaceship cases, docking events (especially on a mars mission) basically occurs only before departure and after arrival so i guess you can allow a spin down of the spaceship / hab ring at these occasions (besides, while the crew is down there on mars, there's supposed to be nobody inside the ship, so you can let your ship without rotation). the same for 'important' burns, you can allow a spin down too it won't kill the astronauts to be in weightlesness for the duration of a planned burn

sidenote, for 'supply' crew only before departure, they are only there to unload stuff, and for a short duration stay only - so they most likely won't need artificial gravity.

[DerekL1963]

1 hour ago, RocketSquid said:

Also, if it spins like a bola, thrust could be a problem, since the engines would no longer be inline with the center of mass.

The engines don't have to be inline with the center of mass - the thrust vector has to be through the center of mass.  (Real life example:  the Shuttle after SRB jettison, the SSME's gimbal to maintain thrust through the center of mass even though it's inside the ET for most of that period.)

[RocketSquid]

1 hour ago, DerekL1963 said:

The engines don't have to be inline with the center of mass - the thrust vector has to be through the center of mass.  (Real life example:  the Shuttle after SRB jettison, the SSME's gimbal to maintain thrust through the center of mass even though it's inside the ET for most of that period.)

That was what I meant, but even so that would be very, very hard to do with a bola-type design.

[fredinno]

11 hours ago, sgt_flyer said:

@RocketSquid

in interplanetary spaceship cases, docking events (especially on a mars mission) basically occurs only before departure and after arrival so i guess you can allow a spin down of the spaceship / hab ring at these occasions (besides, while the crew is down there on mars, there's supposed to be nobody inside the ship, so you can let your ship without rotation). the same for 'important' burns, you can allow a spin down too it won't kill the astronauts to be in weightlesness for the duration of a planned burn

sidenote, for 'supply' crew only before departure, they are only there to unload stuff, and for a short duration stay only - so they most likely won't need artificial gravity.

Exactly, only thing is that you're looking at adding a lot more RCS to do each spin up and down manuver.

[KSK]

On 5 February 2016 at 1:38 AM, fredinno said:

A design where only the HAB spins only needs that part to be made from scratch. Anything else can use technology from Centaur, ISS, Orion, etc. That's what I meant by redesign.

Why on earth would we do that? By the time you've bodged, futzed and otherwise compromised your design for the sake of incorporating mismatched technology that was never intended for the purpose and modules that were never intended to be part of anything other than a LEO space station, I'm betting it would have been cheaper, safer and more efficient to have started from scratch. Besides, unless you're seriously intending to dismantle ISS and build it's parts into your new ship, you'd need to build your ISS-a-like parts from scratch in any case.

Building a spacecraft out of ISS era parts in The Martian was a nice visual clue that the Ares program was set in the near future. Doing it in real life would be a waste of time and money.

Edited February 6, 2016 by KSK

[fredinno]

4 hours ago, KSK said:

Why on earth would we do that? By the time you've bodged, futzed and otherwise compromised your design for the sake of incorporating mismatched technology that was never intended for the purpose and modules that were never intended to be part of anything other than a LEO space station, I'm betting it would have been cheaper, safer and more efficient to have started from scratch. Besides, unless you're seriously intending to dismantle ISS and build it's parts into your new ship, you'd need to build your ISS-a-like parts from scratch in any case.

Building a spacecraft out of ISS era parts in The Martian was a nice visual clue that the Ares program was set in the near future. Doing it in real life would be a waste of time and money.

I'm not the one suggesting using ISS and Cygnus parts for HAB use.  http://spacenews.com/spending-bill-to-accelerate-nasa-habitation-module-work/

I'm pretty sure OrbitalATK, LockMart, and Boeing know what they are doing. 

[KSK]

2 hours ago, fredinno said:

I'm not the one suggesting using ISS and Cygnus parts for HAB use.  http://spacenews.com/spending-bill-to-accelerate-nasa-habitation-module-work/

I'm pretty sure OrbitalATK, LockMart, and Boeing know what they are doing. 

Perhaps, but unless I'm missing something, the article made no mention of repurposing current hardware. The closest thing I could find was a mention that Bigelow have been awarded a study contract for a next generation hab module - and that one of their inflatable modules is due to be tested on the ISS.

Besides, if ISS hardware reuse is a serious proposal, I have absolutely no doubt that Boeing et al know exactly what they're doing, particularly if building this thing is done under a costs plus contract. Reusing ISS sounds like a lovely money saver, letting them put in a lovely lowball bid. Conveniently that lowball bid also has enormous potential for all sorts of unanticipated problems cropping up, thus lots of lovely cost overruns. And if by some miracle, hardware reuse does actually go smoothly (unlike the farcical efforts at saving money by repurposing Shuttle hardware), then Boeing or whoever can extract the maximum amount of government money for the minimum amount of effort.

Total win-win for them. A decent habitation module happening as a result would be a happy side benefit.

 

Edit. This is not meant to disparage the actual people working on the project. I have no doubt that they'll be deeply committed to it and want to see it enable the kind of deep space missions that I think most folks on this forum would want to see too.

I just don't think the companies as a whole give much of a rats behind about space exploration except as a previously mentioned method of extracting government money.

Edited February 6, 2016 by KSK

[fredinno]

8 hours ago, KSK said:

Perhaps, but unless I'm missing something, the article made no mention of repurposing current hardware. The closest thing I could find was a mention that Bigelow have been awarded a study contract for a next generation hab module - and that one of their inflatable modules is due to be tested on the ISS.

Besides, if ISS hardware reuse is a serious proposal, I have absolutely no doubt that Boeing et al know exactly what they're doing, particularly if building this thing is done under a costs plus contract. Reusing ISS sounds like a lovely money saver, letting them put in a lovely lowball bid. Conveniently that lowball bid also has enormous potential for all sorts of unanticipated problems cropping up, thus lots of lovely cost overruns. And if by some miracle, hardware reuse does actually go smoothly (unlike the farcical efforts at saving money by repurposing Shuttle hardware), then Boeing or whoever can extract the maximum amount of government money for the minimum amount of effort.

Total win-win for them. A decent habitation module happening as a result would be a happy side benefit.

 

Edit. This is not meant to disparage the actual people working on the project. I have no doubt that they'll be deeply committed to it and want to see it enable the kind of deep space missions that I think most folks on this forum would want to see too.

I just don't think the companies as a whole give much of a rats behind about space exploration except as a previously mentioned method of extracting government money.

Whoops, that one lacked the stuff the Boeing and etc were working on. This has more information:http://forum.kerbalspaceprogram.com/index.php?/topic/129421-nasa-accelerates-deep-space-hab-work/

And re-purposing Shuttle hardware for SLS has actually proven to be cheaper than not doing so for NASA's rockets. Look at Constellation Ares V VS SLS Block I. Ares V was a nightmare in implementation compared to SLS, and making the new 10m diameter cores, J2-Xs (which were dragging behind in development) and RS-68s (huge amounts of heating- too much) would almost certainly cost more to fix. Skylab also cost very little for what it was due to using leftover Apollo hardware. And why wouldn't Boeing get contracts from a completely new rocket?

[Lead boots]

This all sounds like an engineers approch to a problem of biology. Let your friendly pharmaceutical industry settle this one. 

 

https://www.nibr.com/stories/discovery/mice-space

Sclerostin Modulating drugs for musculoskeletal wasting. Cardiovascular drugs. 

Vallium if the long trip gets a bit dull. 

I'm sure cold storage of a few drugs weights less that generating artificial gravity.

Side effects incude.... can't be obtained without prescription. 

[Archgeek]

Please forgive the necro, but there's an easy-mode solution here if you quite want a pressurized, rotating hab on non-rotating superstructure -- dont' pressurize the bearing.

Keep your propulsion and service modules, your docking astrogation nice and steady, and have your rotating hub include its own, internal airlock to a non-pressurized interface section where astronauts and supplies can come in and out, around which the bearing goes, nice and evacuated.  A few hand-holds to match apparent rotation when entering or exiting, with the rest of the non-presurized portion of the ship abaft.  Power from the service modules can transfer via an induction interface in the bearing hub, and the hab can have its own darn cooling system, with friendly company, and gambling.

Edited August 18, 2016 by Archgeek
I should really preview post more, two entire words were missing.