Author Topic: Nose tethered BFS Spaceships for artificial gravity during the coastal phase.  (Read 100465 times)

Offline CuddlyRocket

Especially as we talk about longer term stays on Mars, the Moon or other bodies, more research is needed into the effects of low gravity. Those experiments should absolutely be done in LEO though.

Whether such experiments should be done in LEO or not, I think that there's little chance that they will be! Missions to the Moon and Mars will be the experiments. They'll rely on volunteers and waivers etc. Nobody wants to spend either the money*, or especially the time, needed to conduct such experiments.

(* Particularly if it's their own money!)
« Last Edit: 11/01/2017 10:28 pm by CuddlyRocket »

Offline intrepidpursuit

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Especially as we talk about longer term stays on Mars, the Moon or other bodies, more research is needed into the effects of low gravity. Those experiments should absolutely be done in LEO though.

Whether such experiments should be done in LEO or not, I think that there's little chance that they will be! Missions to the Moon and Mars will be the experiments. They'll rely on volunteers and waivers etc. Nobody wants to spend either the money*, or especially the time, needed to conduct such experiments.

(* Particularly if it's their own money!)

No one will spend their time and money to find out if this is even helpful, but they will spend the time, money, and danger to do it in route, even though it's unclear that it will have any benefits? I am not following your logic.

Offline KelvinZero

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Mainly I am wondering if we could dismiss a bunch of dragons all at once. Maybe even moon gravity is enough. Maybe we can adapt 4rpm at mars gravity after all.

As for joining two.. maybe the other one would be all cargo but still a crew BFS.

The crane system could be adapted to allow some moderately convenient access to the cargo side. It could also be a complete backup incase the inhabited vehicle develops faults.

Keeping the propellant cool is an issue. Im guessing we don't need to solve it for a LEO experiment. Success of the experiment actually means less need to worry about the actual OP.



Offline mikelepage

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Two ships docked base to base would have a radius in the nose of ~50 meters, only requiring ~2.6 RPM to get Mars gravity. Cargo would only be limited by the tensioned structural strength of the docking mechanisms.

The solar panels would have to be capable of taking the rotation, and would have to be oriented about 90 degrees from the deployment shown (in the same plane as the long axis of the vehicle)

For a LEO test, I think this is a feasible configuration.

Thank you! I haven't wanted to start a new thread talking about the same thing but base-to-base, but I haven't heard any good reasons why base-to-base docking isn't a much more secure configuration to perform spin-G. 

I mean, the presentation actually *showed* two BFS's docking base to base using secure connections, and low-G acceleration was cited as a way to transfer propellents.  You don't need to invent a new attachment point - one already exists, and gives you all the advantages of a much larger spin radius, so lower angular velocity/Coriolis.

Consider: if you attach nose to nose, what would you do with the (mission critical) acceleration couches for crew during the spin-G cruise phase? (risky to pack them away and reinstall before landing, but they'll be in the way otherwise).  If instead, you go base to base, you leave the acceleration couches hard-attached to the "ceiling" and use the same vertical elevators to change between levels - though at Mars G it will be quite possible to jump up or down single floors without hurting yourself.

The downside of tail-to-tail is that it would be harder to move between ships. I think being able to move easily between ships would be an advantage of docking ships together when you're flying multiple passenger ships per mission. It means you can reduce the number of specialists (medical staff, technicians, etc), or having specialists able to work together (instead of being scattered across multiple ships, in order to be available on every ship), or being able to empty one ship while doing major ECLSS repairs, or just for socialising. I could see, in the nose-to-nose configuration, you might have a 4-way docking node (launched and retrieved as cargo by one ship) allowing four BFS's to dock in a pin-wheel formation.

Not necessarily.  Don't forget that there will be at least the same number of cargo craft as crewed craft.  So in the 2 crew + 2 cargo craft scenario, you could have each crewed BFS docked base-to-base to a cargo BFS to form a spin-able unit.  You could then have those two units to form a single assembly if they aligned their dorsal surfaces - and docked using dorsal ports that will be used to access the ground. 

So the 4 ships would do their trans Mars injection burns separately, then 2x docking base-to-base, then 2x sets dorsal ports dock (crew-to-crew BFSs, cargo-to-cargo BFSs), then start to spin at Mars G.

Interesting to think how much before EDL you would separate the ships.  4 ships would probably need to be coming in within half an hour of each other if they are to land anywhere near each other, or alternatively you might detach the cargo ships and let them arrive a day earlier. 





Offline KelvinZero

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You might get a bit better than 50m radius with two joined BFS if you can arrange for more mass to be in the nose of the other (cargo carrying) Mars BFS, along with a bit more landing propellant I suppose.

Offline Paul451

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I haven't wanted to start a new thread talking about the same thing but base-to-base, but I haven't heard any good reasons why base-to-base docking isn't a much more secure configuration to perform spin-G.

The main argument is that you have to design around 3 gravity regimes: Earth/Mars down-is-down, zero-g there-is-no-down, and tail-to-tail up-is-down. I don't think it's unviable, but it might make things more awkward to design. (Testing isn't that hard, though, compared to designing for zero-g. You just flip the test-rig.¹)

By contrast, nose-to-nose has the same orientation as on Earth/Mars. So your ECLSS and other plumbing only needs to work on Earth and in orbit.

¹ Aside: This is another reason for spin-g testing before you go to Mars. It's likely that systems that work at Earth-g will work in Mars-g, and probably Luna-g, but it would be nice to spot the inevitable exceptions to the rule before a critical system fails on Mars. And then, once you've got spin-g, why not use it.

I mean, the presentation actually *showed* two BFS's docking base to base using secure connections, and low-G acceleration was cited as a way to transfer propellents. You don't need to invent a new attachment point - one already exists

During tail-to-tail refuelling, the attachments are under compression. During tail-to-tail spin, they are under quite significant tension.

Again, not impossible to design around, and I suspect the thrust frame will be more than capable of handling the loads, it's just not "it already exists".

though at Mars G it will be quite possible to jump up or down single floors without hurting yourself.

Maybe... just use the ladder?

you could have each crewed BFS docked base-to-base to a cargo BFS to form a spin-able unit.  You could then have those two units to form a single assembly if they aligned their dorsal surfaces - and docked using dorsal ports that will be used to access the ground. 
[...] then 2x sets dorsal ports dock (crew-to-crew BFSs, cargo-to-cargo BFSs), then start to spin at Mars G.

Clever idea. But that configuration isn't stable in rotation.

Interesting to think how much before EDL you would separate the ships.  4 ships would probably need to be coming in within half an hour of each other if they are to land anywhere near each other, or alternatively you might detach the cargo ships and let them arrive a day earlier.

During a day, Mars moves a bit over 2 million km in its orbit. If the crew/cargo is on the same trajectory for most of the trip, you might not be able to change the trajectory enough to have a day's difference in arrival. For eg, if you separate the ships a week from Mars, it means the crew ships need about an 8° change in their trajectory, around 3-4km/s burn.

Offline CuddlyRocket

Especially as we talk about longer term stays on Mars, the Moon or other bodies, more research is needed into the effects of low gravity. Those experiments should absolutely be done in LEO though.

Whether such experiments should be done in LEO or not, I think that there's little chance that they will be! Missions to the Moon and Mars will be the experiments. They'll rely on volunteers and waivers etc. Nobody wants to spend either the money*, or especially the time, needed to conduct such experiments.

(* Particularly if it's their own money!)

No one will spend their time and money to find out if this is even helpful, but they will spend the time, money, and danger to do it in route, even though it's unclear that it will have any benefits? I am not following your logic.

People (with the money) want to go to the Moon and/or Mars. They don't want to spend time and money conducting low gravity experiments in LEO. They'll just go to the Moon and Mars and see what effect this has. Which is basically what they've always done. No-one has gone to LEO to conduct low gravity experiments. Astronauts have been put in LEO for other reasons and they've seen what effect their being in LEO has.

Offline KelvinZero

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I haven't wanted to start a new thread talking about the same thing but base-to-base, but I haven't heard any good reasons why base-to-base docking isn't a much more secure configuration to perform spin-G.
The main argument is that you have to design around 3 gravity regimes: Earth/Mars down-is-down, zero-g there-is-no-down, and tail-to-tail up-is-down. I don't think it's unviable, but it might make things more awkward to design.
This is another reason to just start with my original one-BFS suggestion. All the rocket plumbing end would experience gravity in the same direction as on the pad. Only passenger area would be inverted.

I suspect the weight of the BFS is mainly around the tail, and this imbalance could be increased by filling the tanks. This would increase the radius of the spin of the passenger portion.

This experiment could give some critical answers that determine if you need to go further.

----
Idea 2:
A stretched variant of the BFS that weighs ~150t and has no tanks or engines. This is launched as the 150 payload on top of a BFR+BFS cargo, and it stays in space. It is pushed on it's way by a tanker BFS on a trajectory that skims the origin planet, allowing the tanker to aerobrake into low orbit and be reused within days. The passenger portion aerobrakes into orbit at the destination.

The real goal of the above was that only the passenger portion could not be reused frequently. The advantage for spin gravity is that this thing could be at least twice the length of a normal BFS. By putting as much mass as possible at the tail end, including LS, cargo, consumables and storm shelter, you could get significantly higher radius at the passenger end.

This is a thought for the fairly far future of course. It implies you have BFS tankers being serviced at mars and never returning to earth.

Offline mikelepage

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I mean, the presentation actually *showed* two BFS's docking base to base using secure connections, and low-G acceleration was cited as a way to transfer propellents. You don't need to invent a new attachment point - one already exists

During tail-to-tail refuelling, the attachments are under compression. During tail-to-tail spin, they are under quite significant tension.

Again, not impossible to design around, and I suspect the thrust frame will be more than capable of handling the loads, it's just not "it already exists".

Dry mass of BFS listed as 85 ton, most of which will be very close to the centre of rotation and as light as possible if tail-to-tail, or it will be the furthest from centre of rotation and as heavy as possible if nose-to-nose.  However robust the join has to be for tail-to-tail, it has to be more robust for nose to nose... 

Rough guessing at numbers: If spinning tail-to-tail at Mars G, (two crew BFS) the weight on the join will come from the 150 ton payload in each ship + ~30 ton for the frame of each BFS body that's away from the centre of rotation + ~50 ton from each BFS's lot of landing prop x 0.4g? So what, call it 200 ton in tension...

You've got an attachment joint designed to hold a 1300+ ton ship securely to the booster while being accelerated at 3+ G.  That's a weight of 4000+ tons in compression, whilst dealing with all the aerodynamic stresses of launch, including going through max Q.  I can't believe that attachment joint can't take ~200 ton in tension. 

Quote
I haven't wanted to start a new thread talking about the same thing but base-to-base, but I haven't heard any good reasons why base-to-base docking isn't a much more secure configuration to perform spin-G.

The main argument is that you have to design around 3 gravity regimes: Earth/Mars down-is-down, zero-g there-is-no-down, and tail-to-tail up-is-down. I don't think it's unviable, but it might make things more awkward to design. (Testing isn't that hard, though, compared to designing for zero-g. You just flip the test-rig.¹)

By contrast, nose-to-nose has the same orientation as on Earth/Mars. So your ECLSS and other plumbing only needs to work on Earth and in orbit.

Fair point, but designing how everything is oriented is going to be an interesting/complex problem anyway.  It looks like they are designing the BFS crewed area around modular "crew cabin" boxes which are wedge-shaped prisms and can be installed circumferentially around the core.  Problem I see is that the orientations of the cabins will all be different, yet everyone has to be oriented the same way head up for the belly-down portion of EDL. 

Attached: I had a bit of fun with imagining a "swivel door" to each cabin which has the acceleration couches installed and could close to allow for privacy.  That way you could just mass-produce the cabin units and install them in place.

Taking it one step further, the "back wall" of each cabin could have another rotational joint (perpendicular to the swivel door, axis pointing towards the centre of the craft), which could be flipped for use either on the ground or in tail-to-tail spin G.  On it would be a "fluids management unit" which could hold each cabin's water supply (for radiation shielding), plus a sink and toilet/bathing facilities.   Fluids could be pumped for reclamation/filtering, but solids would most likely still have to be disposed of separately.

Offline Aussie_Space_Nut

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What about a 4 ship configuration.

2 Cargo ships docked tail to tail.

Then dock a crewed ship nose to nose with each of the cargo ships.

Then when spun up orientation of liveable areas need only be designed for 1g to 0g.

Offline FutureSpaceTourist

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twitter.com/tobyliiiiiiiiii/status/1412847354412032001

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Has SpaceX ever considered tethering two crew Starships to create artificial gravity enroute to Mars?

https://twitter.com/elonmusk/status/1412864246719737856

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Yes

Offline Dave G

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I remember reading a paper several years ago that seemed to suggest 0.2g was adequate.
They also mentioned that small differences in gravity between your head and feet could cause issues over time.
So they seemed to be recommending a lower spin rate, longer cable, and 0.2g.
That may be enough for a few months.

In any case, it's obvious to me that we need some real data on this.
We have lots of experience with microgravity, but I don't know of any real experience with low gravity.

Offline GHogan

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I think Elon stated that the nose would be pointing towards the Sun during flight. I expect for a couple of reasons 1 so solar array could get most energy 2) to limit the effects of solar energy on fuel required for landing. Also if you spin up the ships would mean the solar arrays would then need to withstand partial G forces. Great idea but probably not realistic

The opposite, keeping the rockets pointed toward the sun at all times, gives you several layers of radiation shielding at no additional mass cost. So is zero g or radiation the bigger danger?

Offline Robotbeat

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I think Elon stated that the nose would be pointing towards the Sun during flight. I expect for a couple of reasons 1 so solar array could get most energy 2) to limit the effects of solar energy on fuel required for landing. Also if you spin up the ships would mean the solar arrays would then need to withstand partial G forces. Great idea but probably not realistic

The opposite, keeping the rockets pointed toward the sun at all times, gives you several layers of radiation shielding at no additional mass cost. So is zero g or radiation the bigger danger?
Not quite. Solar radiation is actually fairly isotropic as it's spiraling around the interplanetary magnetic field (IMF) and bouncing back and forth a bit. There's some anisotropy, but not a ton, and you want to point at an angle to the Sun, not directly at it.
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Offline Paul451

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I remember reading a paper several years ago
They also mentioned that small differences in gravity between your head and feet could cause issues over time.

Can you find the paper? This is the opposite to what I've seen. Spin-table experiments seem to suggest that there's no effect from even major g-load differences between head/feet.

Online edzieba

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I remember reading a paper several years ago
They also mentioned that small differences in gravity between your head and feet could cause issues over time.

Can you find the paper? This is the opposite to what I've seen. Spin-table experiments seem to suggest that there's no effect from even major g-load differences between head/feet.
Spincalc has several listed under 'references'.

Offline Paul451

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I remember reading a paper several years ago
They also mentioned that small differences in gravity between your head and feet could cause issues over time.
Can you find the paper? This is the opposite to what I've seen. Spin-table experiments seem to suggest that there's no effect from even major g-load differences between head/feet.
Spincalc has several listed under 'references'.

None of those reflect Dave's claim.

Offline michcies

I think there are several strong arguments in favour of coupling Starships together and generate a little gravity.
My proposal is to have docking adapter in the nose of a Starship and couple several (i.e. 6) Starships to a central hub with docking ports at the circumference.
There are several positive aspects with this approach.

1) The medical aspect
It is clear that 1g is what we are used to and also that a 0g environment is problematic.
What we do not know is how much g we need for our health and if it is more than 0.38g it will be a problem on Mars.
I expect that 0.38g is sufficient - either with training for return to Earth or without when you plan to stay on Mars.

2) Comfort
Even a little g (like 0.1g) will allow to drink from a glass, eat from a plate, use a toilet or a washing machine. It is a long journey to Mars and the comfort that even a little g provides will be very welcome.

3) Safety / Redundancy
Coupling Starships together will increase safety by having redundant hardware in the form of the other Starships. Consider you have a problem with air supply in one ship, you can just go into another ship until the problem is fixed.
If you get a decompression problem, it might be the only solution.
Another form of redundancy comes with the critical skills of the people on board. What will you do if you have only one doctor and he/she gets sick?
By coupling Starships together you increase the headcount of the community and make it much easier to have multiple redundancies across all the essential skills.

4) Social Aspects
It is a long journey and it happens that people start quarrelling. With coupled Starships it is possible that these persons will go to different Starships and do not need to see each other.

I think if we want to attract a lot of people to settle on Mars we should make the journey as safe and comfortable as possible.
The proposed docking adapter in the nose is a small mass penalty for all the benefits you gain and could possibly be used as an anchor point for stacking as well.
The central hub could stay in orbit and be used only for transportation to and from Earth to Mars. This way it would need no TPS. It could also contain the solar cells and heat reflector to protect starship fuel from sunlight.

At 4rpm you need 21m lever arm to create the Martian acceleration of 3.69m/s^2.
The upper ~20m of Starship are the living quarters, so in the last 7m an average Martian gravitation is created at 4rpm.

With a center of gravity 35m away from the nose the speed of this COG is 16.5m/s, so only 33m/s is needed for going in and out of rotation.

I think this is not a big price to pay for all the benefits of having some artificial gravity.

« Last Edit: 08/18/2021 04:36 pm by michcies »

Online steveleach

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I think there are several strong arguments in favour of coupling Starships together and generate a little gravity.
My proposal is to have docking adapter in the nose of a Starship an couple several (i.e. 6) Starships to a central hub with docking ports at the circumference.
To get SpinCalc to go all-green you need 85m radius for 0.38g, and I'm guessing the max habitable radius in your setup is maybe 20m?

Obviously SpinCalc isn't authoritative, and hopefully SpaceX will be able to experiment with this in Earth orbit to actually get some real data on the subject, but until they do I think they'll have to rely on long tethers rather than direct attachment.

The nice thing about tethers, of course, is that you can change the radius easily. Start long, reel them in slowly until people start to feel the effects, then back off a bit. If you comfortably get the radius down enough to make direct attachment work then maybe start planning for that approach 26 months later.

Offline michcies

I think there are several strong arguments in favour of coupling Starships together and generate a little gravity.
My proposal is to have docking adapter in the nose of a Starship an couple several (i.e. 6) Starships to a central hub with docking ports at the circumference.
To get SpinCalc to go all-green you need 85m radius for 0.38g, and I'm guessing the max habitable radius in your setup is maybe 20m?

Obviously SpinCalc isn't authoritative, and hopefully SpaceX will be able to experiment with this in Earth orbit to actually get some real data on the subject, but until they do I think they'll have to rely on long tethers rather than direct attachment.

The nice thing about tethers, of course, is that you can change the radius easily. Start long, reel them in slowly until people start to feel the effects, then back off a bit. If you comfortably get the radius down enough to make direct attachment work then maybe start planning for that approach 26 months later.
I think SpinCalc is overly conservative. It is for shure true that you will not feel any effects at 1rpm.
But it is easy to get used to much higher rpm values. A value of 4rpm should be no problem for nearly all people after a day or so and you can test people for this on Earth before the flight.
In space you can slowly ramp up the rpm so people can adapt.

But in my view the main benefit of coupling Starships is the hatch that allows you to from one ship into another. This increases safety a lot. Just think about a micro-meteorite punches a hole in the hull and the ship is loosing atmosphere. The passengers can just crawl in another ship and be safe. If the hole cannot be found it is possible to abandon the ship but the passengers are safe.
Also essential skills like a doctor. You don't need 2% doctors but you want to be redundant in case the only doctor gets sick.

The central ship could be equipped to provide shelter in case of a solar storm. In this case it would be packed with people but only for a short time.
« Last Edit: 08/18/2021 07:17 pm by michcies »

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