Author Topic: Nose tethered BFS Spaceships for artificial gravity during the coastal phase.  (Read 7623 times)

Online Peter.Colin

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Would it be beneficial and practical to create artificial gravity during the coastal phase? It could be done by connecting the two noses of two ships with a long cable, and use the side thrusters to begin spinning to the desired centrifugal force.
How would this effect the radiation shielding of the ship.
How fast would the ships need to spin?, and could this make looking trough a window still pleasant?

Offline Semmel

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Obvious advantages: less medical problems from zero gravity, easier life on board like eating, toilet, washing, etc. Less problems to find zero g solutions for trivial everyday stuff like washing clothes, pumping liquids, probably easier design of the life support system.

Obvious disadvantages: more difficult solar power generation, communication with Earth and Mars, additional mass for the nose connection system, difficult or near impossible to do course corrections, spin up and spin down difficult to Orchestra without introducing oscillations. Oscillations due to mass (people) moving around in both ships.

Indifferent: I don't think radiation shielding is a thing in general, can't get much worse than it is already. Maybe a total mass gain, despite extra mass of the cable system. Would require extensive engineering and tradeoff.

Offline KelvinZero

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Had a fairly over the top thought, certainly not for initial missions

Elon Musk talks about getting to a point of sending many ships in a single launch window. What if these all docked with a lightweight central hub for the flight? The central hub would probably be some sort of cycler. This cylindrical arrangement of ships with engines on the outer side would also provide a fair bit of shielding, should that prove to be an issue.


Online Peter.Colin

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Had a fairly over the top thought, certainly not for initial missions

Elon Musk talks about getting to a point of sending many ships in a single launch window. What if these all docked with a lightweight central hub for the flight? The central hub would probably be some sort of cycler. This cylindrical arrangement of ships with engines on the outer side would also provide a fair bit of shielding, should that prove to be an issue.

I think that's a very good idea!  :)

Would you point the rotational axis of the central hub towards the sun, for easier solar power generation?

Would the central hub make steering corrections or the connected ships?
« Last Edit: 08/06/2017 06:55 AM by Peter.Colin »

Online Peter.Colin

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Obvious advantages: less medical problems from zero gravity, easier life on board like eating, toilet, washing, etc. Less problems to find zero g solutions for trivial everyday stuff like washing clothes, pumping liquids, probably easier design of the life support system.

Obvious disadvantages: more difficult solar power generation, communication with Earth and Mars, additional mass for the nose connection system, difficult or near impossible to do course corrections, spin up and spin down difficult to Orchestra without introducing oscillations. Oscillations due to mass (people) moving around in both ships.

Indifferent: I don't think radiation shielding is a thing in general, can't get much worse than it is already. Maybe a total mass gain, despite extra mass of the cable system. Would require extensive engineering and tradeoff.

In the ITS animation, the tanker is put on the BFR with a crane and a cable on the nose (or at multiples sides), probably the ship has a similar nose cable system already.
« Last Edit: 08/06/2017 08:16 AM by Peter.Colin »

Offline mikelepage

Had a fairly over the top thought, certainly not for initial missions

Elon Musk talks about getting to a point of sending many ships in a single launch window. What if these all docked with a lightweight central hub for the flight? The central hub would probably be some sort of cycler. This cylindrical arrangement of ships with engines on the outer side would also provide a fair bit of shielding, should that prove to be an issue.

I think that's a very good idea!  :)

Would you point the rotational axis of the central hub towards the sun, for easier solar power generation?

Would the central hub make steering corrections or the connected ships?

Keep it simple.  Keep all the intelligence is in the ships themselves - probably much more efficient at first for ships to detach to do course corrections, since burns of a several 100m/s is huge compared to the 20-40m/s of rotation.  What is needed (and I hope Bigelow or similar does this) is a cable-reinforced, inflatable tube module that can take some load.  You cannot just use cables because of the oscillation problem (remember a bridge has both compressive and tensile elements and we're effectively building a suspension bridge in space)

The aim is to get the largest radius of rotation, because this means the rpm can be lower for a given centrifugal acceleration - its the spin which induces vertigo in most people once you get above 4rpm or so.  If you have less than 6 ships/nodes, then you connect directly, or to a dumb central node, but if you have 6 or more ships/nodes in a ring, then the angle between them decreases to 60 degrees or less, and it is a better use of tubes to dispense with the hub and attach the tubes ship to ship, so you get a larger effective radius.

Even for two ITSy ships connected nose to nose, the length of an inflatable tube connector that would fit into an ITSy payload bay could allow on the order of 20m between them, giving an effective radius of at least 30m.  That means that at 4rpm you'd be getting perhaps 0.5 G at the edges, and at least Mars G for much of the crewed area. 

Offline KelvinZero

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Just saw some issues with the cycler idea. With 3 month earth-mars times it probably needs 4 synods to return home. Maybe it can't be a true cycler in which case how does it brake into mars orbit, or maybe this thing passes mars and visits the asteroid belt, and you have 4 of them. Not as simple as it first sounded.

Two ships with cables has a lot less question marks, especially if the ship is already designed to be lifted from the nose under 1g like in the animations.

(Off topic, another of my hobby horses is good VR for space travellers. Spin gravity creates a lot of design constraints and you will still be in a cramped spaceship. Good VR, a treadmill and elastic bands could let you jog though expansive fantasy worlds for hours every day.)

Online Peter.Colin

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Just saw some issues with the cycler idea. With 3 month earth-mars times it probably needs 4 synods to return home. Maybe it can't be a true cycler in which case how does it brake into mars orbit, or maybe this thing passes mars and visits the asteroid belt, and you have 4 of them. Not as simple as it first sounded.

Two ships with cables has a lot less question marks, especially if the ship is already designed to be lifted from the nose under 1g like in the animations.

(Off topic, another of my hobby horses is good VR for space travellers. Spin gravity creates a lot of design constraints and you will still be in a cramped spaceship. Good VR, a treadmill and elastic bands could let you jog though expansive fantasy worlds for hours every day.)

Assuming a cycler central hub takes to long.
I think this central rotating hub structure should brake the same way as it's accelerates, with a few Raptor engines.
I know this consumes a lot of fuel, but this amount of fuel/engines could be minimized by pumping from Earth tankers only the required fuel for accelerating.
And for braking at mars pumping fuel from the connected Spaceships.
The central rotating hub structure can also double as a Mars fluids depot in orbit for mars tankers when they're full at the surface. It makes more sense to store the bulk of the liquids in mars orbit, than on the surface.

Spin gravity begins to feel like normal gravity the longer the cable is, so VR would feel similar to VR on earth.

Of topic:
Does anyone have an idea about how much fuel would be left in a fully loaded Mars tanker when it reaches Mars orbit?



Offline Humuku

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How fast would the ships need to spin?, and could this make looking trough a window still pleasant?

Period of tethered movement is proportional to the square root of the radius of the tether.

Offline livingjw

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Just saw some issues with the cycler idea. With 3 month earth-mars times it probably needs 4 synods to return home. Maybe it can't be a true cycler in which case how does it brake into mars orbit, or maybe this thing passes mars and visits the asteroid belt, and you have 4 of them. Not as simple as it first sounded.

Two ships with cables has a lot less question marks, especially if the ship is already designed to be lifted from the nose under 1g like in the animations.

(Off topic, another of my hobby horses is good VR for space travellers. Spin gravity creates a lot of design constraints and you will still be in a cramped spaceship. Good VR, a treadmill and elastic bands could let you jog though expansive fantasy worlds for hours every day.)

Assuming a cycler central hub takes to long.
I think this central rotating hub structure should brake the same way as it's accelerates, with a few Raptor engines.
I know this consumes a lot of fuel, but this amount of fuel/engines could be minimized by pumping from Earth tankers only the required fuel for accelerating.
And for braking at mars pumping fuel from the connected Spaceships.
The central rotating hub structure can also double as a Mars fluids depot in orbit for mars tankers when they're full at the surface. It makes more sense to store the bulk of the liquids in mars orbit, than on the surface.

Spin gravity begins to feel like normal gravity the longer the cable is, so VR would feel similar to VR on earth.

Of topic:
Does anyone have an idea about how much fuel would be left in a fully loaded Mars tanker when it reaches Mars orbit?

Just enough to land after aerobraking.

Offline guckyfan

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Of topic:
Does anyone have an idea about how much fuel would be left in a fully loaded Mars tanker when it reaches Mars orbit?

A cargo ITS would lift 300t to LEO and can land 450t on Mars when loaded with extra cargo in LEO and going on a slow trajectory. A tanker should be able to land at least those 450t in propellant on Mars. If that would make sense. Maybe as a rescue mission for the first crew if sabatier fuel ISRU fails. Enough methane but LOX would still need to be produced from atmospheric CO2. An unlikely string of events.

Online Peter.Colin

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Of topic:
Does anyone have an idea about how much fuel would be left in a fully loaded Mars tanker when it reaches Mars orbit?

A cargo ITS would lift 300t to LEO and can land 450t on Mars when loaded with extra cargo in LEO and going on a slow trajectory. A tanker should be able to land at least those 450t in propellant on Mars. If that would make sense. Maybe as a rescue mission for the first crew if sabatier fuel ISRU fails. Enough methane but LOX would still need to be produced from atmospheric CO2. An unlikely string of events.

Let me clarify my off topic question:
A tanker holds 2500t propelant. But when when this tanker leaves Earth and reaches LEO it only contains 380t of propelant, the rest has been spent to reach orbit. The BFR was also needed to get this propelant into LEO and that contained 6700t of propellant.
So only 4.3% of the original propelant reaches Earth orbit, not much...
I was wondering what part of propelant produced on mars surface reaches mars orbit?

Storing most propellant in mars orbit minimizes the amount of storage volume needed, this could be done in the central rotating hub.
« Last Edit: 08/06/2017 10:32 PM by Peter.Colin »

Offline darkenfast

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If the ship can reach Mars in under six months, why in the world would you spend so much mass and added complexity to provide artificial gravity?  We know that crews can be walking on Earth within a day or two of return from the ISS (with some restrictions), and in an emergency can get themselves out of a Soyuz unaided after a bad landing.  The gravity on Mars is one fourth of ours.  They don't have to leap out of their couches and start heavy lifting immediately after touchdown. 

Spending years going to Saturn?  Then maybe we need something.  But not for Mars. 

Offline KelvinZero

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If the ship can reach Mars in under six months, why in the world would you spend so much mass and added complexity to provide artificial gravity?  We know that crews can be walking on Earth within a day or two of return from the ISS (with some restrictions), and in an emergency can get themselves out of a Soyuz unaided after a bad landing.  The gravity on Mars is one fourth of ours.  They don't have to leap out of their couches and start heavy lifting immediately after touchdown. 

Spending years going to Saturn?  Then maybe we need something.  But not for Mars.
The nose-tethered option is not that extravagant.

The other options only make sense with much greater scale but they don't add much mass,  proportionally. They even have the possibility of saving mass if you are preaccelerating fuel ahead of time, or packing more people into your ITS like sardines because they will have more volume during the trip. The argument against them is definitely about complexity. This could grow to be a whole new vehicle that (if not a true cycler) also needs to aerobrake.

A nose tethered option for a mission to Saturn is also an interesting suggestion IMO. Maybe we should be using that as our primary justification for a discussion of two nose tethered ITS.

Online Peter.Colin

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If the ship can reach Mars in under six months, why in the world would you spend so much mass and added complexity to provide artificial gravity?  We know that crews can be walking on Earth within a day or two of return from the ISS (with some restrictions), and in an emergency can get themselves out of a Soyuz unaided after a bad landing.  The gravity on Mars is one fourth of ours.  They don't have to leap out of their couches and start heavy lifting immediately after touchdown. 

Spending years going to Saturn?  Then maybe we need something.  But not for Mars.


Because it would start to smell, washing clothes washing yourself, going to the toilet is not easy without gravity.

And I wouldn't want to drink my glass of champagne out of a bag, that can explode because of the bubbles...  ;)

If a tether can prevent these and more inconveniences, and if the ship (the tanker we know) is allready lifted on the BFR by a nose tether. Why not do it like this.


« Last Edit: 08/07/2017 04:01 PM by Peter.Colin »

Online docmordrid

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>
Because it would start to smell, washing clothes

Supercritical CO2 laundry. Dry, isolated, works & COTS.

Quote
washing yourself, going to the toilet is not easy without gravity.

There was a shower on Skylab, and space potties are obviously on ISS.
DM

Offline intrepidpursuit

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The ship would have to spend at least several days in microgravity before such a contraption could be assembled, so there still have to be zero g facilities for everything (I think three months of laundry is still easier to carry than something that can clean the laundry in space). Three months isn't long enough to cause major damage to the passengers. They are heading to a reduced gravity environment so they won't need as long to acclimate anyway.

Artificial gravity for mars is WAY more trouble than it is worth.

I hope one day there will be a ship with centripetal gravity, but early mars settlement ships don't need that development burden.

Offline KelvinZero

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I hope one day there will be a ship with centripetal gravity, but early mars settlement ships don't need that development burden.
This is why I suggested maybe moving the goalposts to the saturn mission. (Actually someone else suggested it)

What I mean is, I think it is better to just discuss it as a technical problem. It is after you have sorted out how difficult it is that you have the basis to argue where it could be useful and where it is not worth the bother.

A lot of things we will not know for sure until we have moved a lot of people. We only have a small sample set at the moment. Same with radiation. Im convinced we have enough info on both to not be afraid to just begin, but I don't think anyone can be confident of what we will decide is optimal by the time we are shipping hundreds of thousands of people of all ages to Mars.. so just treat it as a technical problem.

Offline guckyfan

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I hope one day there will be a ship with centripetal gravity, but early mars settlement ships don't need that development burden.
This is why I suggested maybe moving the goalposts to the saturn mission. (Actually someone else suggested it)

I did. Not claiming I was the only one.

What I mean is, I think it is better to just discuss it as a technical problem. It is after you have sorted out how difficult it is that you have the basis to argue where it could be useful and where it is not worth the bother.

As such it is an interesting argument.

Offline Paul451

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If the ship can reach Mars in under six months, why in the world would you spend so much mass and added complexity to provide artificial gravity?

What "mass and added complexity"? At Mars gravity and 4-6 RPM, AG is almost free. The only reason not to do it would be out of spite.

We know that crews can be walking on Earth within a day or two of return from the ISS

We also know that that is a meaningless measure of their actual health, and that astronauts experience random orthostatic hypotension episodes for weeks after their return due to a suppressed baroreceptor reflex. According to flight surgeons and works published by long-duration astronauts, typical recovery is 1 day on the ground for 1 day in orbit.

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