Quote from: Coastal Ron on 07/15/2018 08:24 pmWhat humans need to know can only be found out by experimenting on humans. And since setting up colonies on our Moon and on Mars is of HUGE interest, then what we should focus on first is artificial gravity space stations that can provide a minimum of 1/3 G, with the option of operating at 1/6 G too. They also need to be sized in order for humans to actually live and work on them for periods of at least a year, or however long it takes to do studies to see if micro-gravity environments mitigate some or all of the effects of zero-G.Because the goal has to be that we need to find out as soon as possible how humanity will be able to expand out into space while not only surviving, but thriving. Otherwise, why else should we spend money on sending humans to space?All: Gary Hudson over at the Space Studies Institute (SSI) has been beating the drum for the need of artificial-gee for human spaceflight for years now and I totally agree with Gary that before we establish long term colonies on the Earth's Moon and Mars, we had first find out if humans can breed in and live long-term under 1/6 and 1/3 gee gravity fields. A good summary of Hudson's approach to finding the answer to these questions is at the below December 2015 YouTube video URL. In this video Gary lays out a moderately low cost approach to finding the answers to these biological compatibility questions.https://www.youtube.com/watch?time_continue=10&v=xO1Pvtv_A4k Best, Paul M.
What humans need to know can only be found out by experimenting on humans. And since setting up colonies on our Moon and on Mars is of HUGE interest, then what we should focus on first is artificial gravity space stations that can provide a minimum of 1/3 G, with the option of operating at 1/6 G too. They also need to be sized in order for humans to actually live and work on them for periods of at least a year, or however long it takes to do studies to see if micro-gravity environments mitigate some or all of the effects of zero-G.Because the goal has to be that we need to find out as soon as possible how humanity will be able to expand out into space while not only surviving, but thriving. Otherwise, why else should we spend money on sending humans to space?
Quote from: LMT on 08/04/2018 12:55 pmQuote from: rakaydos on 08/04/2018 04:33 amQuote from: LMT on 08/04/2018 01:56 amAs for a single craft, even with full tanks the center of mass is near the mid-point, resulting in a spin radius too short and rpm too high for AG comfort. So you add the mods you need, and extend. Much creativity can go into the design of better mods.Really? Even if the payload doesnt even apprach the 150 ton capacity? I was under the impression that engine mass brings the CoG way back, even without fuel in the tank furthest to the rear. Can you source the CoG being so far foreward?Just consider masses. Dry mass is 85 t, less than any payload. Hence engine mass is much less. LOX tank fills to 860 t, near the center. That prevents shifting of CoM to the tail.To rotate around the tail, you could potentially add a load-bearing mod to the propellant lines / connectors, or perhaps to staging clamps, and rotate while tail-docked.If you look back at my suggestion, I never suggested loading the LOX tank, only the methane tank. (we're not using it for propulsion, just ballast, so we dont need a propulsive mixture) I'm also assuming an expiriment closer to JAXA's module in size, which limits how much the CoM is drawn foreward.
Quote from: rakaydos on 08/04/2018 04:33 amQuote from: LMT on 08/04/2018 01:56 amAs for a single craft, even with full tanks the center of mass is near the mid-point, resulting in a spin radius too short and rpm too high for AG comfort. So you add the mods you need, and extend. Much creativity can go into the design of better mods.Really? Even if the payload doesnt even apprach the 150 ton capacity? I was under the impression that engine mass brings the CoG way back, even without fuel in the tank furthest to the rear. Can you source the CoG being so far foreward?Just consider masses. Dry mass is 85 t, less than any payload. Hence engine mass is much less. LOX tank fills to 860 t, near the center. That prevents shifting of CoM to the tail.To rotate around the tail, you could potentially add a load-bearing mod to the propellant lines / connectors, or perhaps to staging clamps, and rotate while tail-docked.
Quote from: LMT on 08/04/2018 01:56 amAs for a single craft, even with full tanks the center of mass is near the mid-point, resulting in a spin radius too short and rpm too high for AG comfort. So you add the mods you need, and extend. Much creativity can go into the design of better mods.Really? Even if the payload doesnt even apprach the 150 ton capacity? I was under the impression that engine mass brings the CoG way back, even without fuel in the tank furthest to the rear. Can you source the CoG being so far foreward?
As for a single craft, even with full tanks the center of mass is near the mid-point, resulting in a spin radius too short and rpm too high for AG comfort. So you add the mods you need, and extend. Much creativity can go into the design of better mods.
A tighter view of the hub. The center spindle is non rotating.The outer ring and arms turns. There is no rotating seal, there is no direct link between the spindle and the ring.There are two moving airlocks, that are either stionnary on the spindle, or accelerate to become stationnary on the rotating ring.This should eliminate the problem of the rotating seal, substituting the problem of a rotating 'elevator' :-)All the sub elements should fit in the BFR cargo hold of chomper. The most challenging element, IMHO is the spindle.
An whatever magic system keeps the whole thing from failing under various vibration regimes, I expect.
I think limiting the desing to the outer mold of the BFR will be a colossal savings. BFR launches will be an order of magnitude cheaper that a single use booster.
I also expect that redesigning the BFR for a longer or wider shape will be extremely expensive. Much cheaper to design the station to fit. Satellites are designed to fit in fairing, the other way around is much rarer.
Does anyone know of a paper that analyses vibrations in large rotating structures?As there is no air or water medium, vibration will not be dampened by the media but need to be handled entirely by the vehicle, that needs to cancel them out by inducing counter vibrations, or damping them out as heat.Any cyclical behaviour may induce energy, in the forms or waves in the elastic structure, than will amplify if they are not handled in some way. Wobble and waves can be very bad, is my guess. And the structure will have motors, moving people, moving liquids and gases, the transfer rings, sun pressure, differential gravity and even atmospheric drag that can all induce vibration and instability.
Maybe I'm missing something, but in order to have vibration you need an energy source. For instance, when you're on a ship you feel the thrum of the engines, and vibration from the waves that is made possible by the energy from the engines. Same for other transportation system, as well as stationary structures.What is the energy source on your station that is creating the vibration?Also, modern design software can anticipate resonant frequencies of structures, and they can be dealt with by either changing the design or changing material in the design. Your design seems pretty straightforward, so I have a hard time imagining that it has a HUGE design flaw that needs to be addressed with regard to vibration.
Quote from: Coastal Ron on 08/04/2018 07:30 pmMaybe I'm missing something, but in order to have vibration you need an energy source. For instance, when you're on a ship you feel the thrum of the engines, and vibration from the waves that is made possible by the energy from the engines. Same for other transportation system, as well as stationary structures.What is the energy source on your station that is creating the vibration?Also, modern design software can anticipate resonant frequencies of structures, and they can be dealt with by either changing the design or changing material in the design. Your design seems pretty straightforward, so I have a hard time imagining that it has a HUGE design flaw that needs to be addressed with regard to vibration.The station is provided with a large solar power system. This system is used to power a number of systems, some of which are rotating and mobile. Although most of the solar power will become heat pretty fast, some of it will become vibration modes in the system. Some of which might be harmful.The station will be a very flexible structure, at least the ones illustrated here. Therefore it will not have all that much mass to flex, heat and dissipate energy. So it's important to think about vibration. I agree it should be a controllable problem, but if one of the six pods shown started vibrating, for some reason, and if there were not the structures tying it to the other pods, how would it behave?TBH I expect the large spoked bicycle wheel would be much more rigid and perhaps proof against this problem. But you might want to have some electric turnbucles, for example, or shock absorbers on the lines.
The station is provided with a large solar power system. This system is used to power a number of systems, some of which are rotating and mobile.
Although most of the solar power will become heat pretty fast, some of it will become vibration modes in the system. Some of which might be harmful.
The station will be a very flexible structure, at least the ones illustrated here. Therefore it will not have all that much mass to flex, heat and dissipate energy. So it's important to think about vibration.
I agree it should be a controllable problem, but if one of the six pods shown started vibrating, for some reason, and if there were not the structures tying it to the other pods, how would it behave?
TBH I expect the large spoked bicycle wheel would be much more rigid and perhaps proof against this problem. But you might want to have some electric turnbucles, for example, or shock absorbers on the lines.
Iwas thinking of motors and fans, perhaps compressors, but I must admit most of the power will probably go to lighting, so i'll stop worrying about rotation of relatively small items. Factor in controls and some kind of mass balancing.
What might be the development cost of a module, and could we integrate life support systems developed for the BFR? I'm thinking of a carbon fiber walled tanks, with lightweight floors. Perhaps water filled walls for radiation protection? Seems simpler than all that fabric required for Bigelow modules.
As there is no air or water medium, vibration will not be dampened by the media
and if they are made out of composite material they will have no resonant frequency that they will respond to.
Quote from: rakaydos on 08/04/2018 04:17 pmQuote from: LMT on 08/04/2018 12:55 pmQuote from: rakaydos on 08/04/2018 04:33 amQuote from: LMT on 08/04/2018 01:56 amAs for a single craft, even with full tanks the center of mass is near the mid-point, resulting in a spin radius too short and rpm too high for AG comfort. So you add the mods you need, and extend. Much creativity can go into the design of better mods.Really? Even if the payload doesnt even apprach the 150 ton capacity? I was under the impression that engine mass brings the CoG way back, even without fuel in the tank furthest to the rear. Can you source the CoG being so far foreward?Just consider masses. Dry mass is 85 t, less than any payload. Hence engine mass is much less. LOX tank fills to 860 t, near the center. That prevents shifting of CoM to the tail.To rotate around the tail, you could potentially add a load-bearing mod to the propellant lines / connectors, or perhaps to staging clamps, and rotate while tail-docked.If you look back at my suggestion, I never suggested loading the LOX tank, only the methane tank. (we're not using it for propulsion, just ballast, so we dont need a propulsive mixture) I'm also assuming an expiriment closer to JAXA's module in size, which limits how much the CoM is drawn foreward.OK. Drop LOX and your CoM remains somewhere within the LOX tank, unfortunately. Effective spin radius just over 20 m. What g levels do you want in your experiment?
...However, because you have a rotating/non-rotating part joined at a hub, you must have extensive mass-balancing to ensure the centre-of-mass remains precisely at the centre-of-rotation, ie, that the centre of rotation remains precisely at the centre of the hub. Failing to perfectly and continuously balance the mass (including the moving mass, people/cargo/fluids/elevators/etc) will induce horrific vibration in both structures.IMO, when you add a non-rotating section, you drastically amplify your engineering issues (not just because of the design of a pressurised and/or utility-connecting hub either.)
That is why in my proposed system, I included tanks and pumps to move oil between modules, side to side and across to other side of ring where the elevators are.
Note that off-balance will "vibrate" at rotational rate so while it needs to be dealt with, I don't think the response has to be instantaneous and the vibration will not be horrific.
