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2 hours ago, Barzon Kerman said:

Thanks @Ultimate Steve. I was thinking about the planned ISS centrifuge module, and if something like that would be incorporated into the BFR.

There is a better alternative than making a specific centrifuge module. How about we make the BFR itself the centrifuge. They could connect 2 BFR's and connected them via tether to create artificial gravity.

Like this:

bfr_tether_by_zanzalur-dccf7mo.png

The two BFR's could dock and deploy the tether after the transfer burn to Mars, or whatever destination they could be going to. They would simply spin it around to create artificial gravity. No expensive gizmos required other than a special port for the tethers.

This is just a concept however, so far there are no plans for artificial gravity yet for the BFR, and its unlikely it will be favourable over treadmills.

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2 hours ago, Damien_The_Unbeliever said:

Okay, so a thick layer of plastic won't work to make this thing waterproof. You have to come up with a design (as indicated above) that works *both* whilst in use during normal flight regime *and* works during re-entry *and* doesn't significantly degrade through all phases of use and means it's actually reusable. Do you have such a scheme in mind beyond believing that a lot of fairly smart people have ignored common everyday experiences?

My question is, why isn't the Dragon 2 destroyed so quickly by the sea, but the fairing is.  

3 hours ago, sh1pman said:

Even BFR isn't big enough to house a hab ring. 

You could have a four person exercise machine centrifuge thing.  Have one of the decks empty with a pole in the center and spin a treadmill around it.  

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2 minutes ago, DAL59 said:

My question is, why isn't the Dragon 2 destroyed so quickly by the sea, but the fairing is.  

The fairing isn't really designed for seawater unlike the Dragon. Dragon has some protective coating against the salty and critter crawling seawater, while fairings are designed to protect the payload from the aerodynamic stress, and thus, don't have a protective coating.

The fairing also has a higher touchdown speed than the Dragon in order to save mass for the parachute (the faster touchdown speed is also the reason why they want to use a net instead of letting it float) Hitting water at high speed is like hitting a brick wall it full gas, water isn't always a soft cusion.

 

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33 minutes ago, NSEP said:

There is a better alternative than making a specific centrifuge module. How about we make the BFR itself the centrifuge. They could connect 2 BFR's and connected them via tether to create artificial gravity.

Like this:

bfr_tether_by_zanzalur-dccf7mo.png

The two BFR's could dock and deploy the tether after the transfer burn to Mars, or whatever destination they could be going to. They would simply spin it around to create artificial gravity. No expensive gizmos required other than a special port for the tethers.

This is just a concept however, so far there are no plans for artificial gravity yet for the BFR, and its unlikely it will be favourable over treadmills.

As I understand it, elastic forces complicate that setup. There needs to be something rigid to dampen bounce effects between the two.

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2 hours ago, NSEP said:

There is a better alternative than making a specific centrifuge module. How about we make the BFR itself the centrifuge. They could connect 2 BFR's and connected them via tether to create artificial gravity.

Like this:

bfr_tether_by_zanzalur-dccf7mo.png

The two BFR's could dock and deploy the tether after the transfer burn to Mars, or whatever destination they could be going to. They would simply spin it around to create artificial gravity. No expensive gizmos required other than a special port for the tethers.

This is just a concept however, so far there are no plans for artificial gravity yet for the BFR, and its unlikely it will be favourable over treadmills.

I've never thought about having two ships connected like that. It's simple and elegant.

1 hour ago, Rakaydos said:

As I understand it, elastic forces complicate that setup. There needs to be something rigid to dampen bounce effects between the two.

What do you mean by elastic forces? The tether could get into resonance and snap or something? What about having two or three tethers instead of one?

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1 minute ago, Wjolcz said:

I've never thought about having two ships connected like that. It's simple and elegant.

It's an old idea. NASA was proposing it back in the 1970s when they were working on a NERVA mission to Mars. They proposed putting the rocket and reaction mass one one end of the tether and the crewed part of the ship on the other end. Let the tether out for a km or so and then spin both around their common CG. (Of course, if the tether breaks you are doomed.)

 

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11 hours ago, mikegarrison said:

It's an old idea. NASA was proposing it back in the 1970s when they were working on a NERVA mission to Mars. They proposed putting the rocket and reaction mass one one end of the tether and the crewed part of the ship on the other end. Let the tether out for a km or so and then spin both around their common CG. (Of course, if the tether breaks you are doomed.)

 

Yeah, I knew about this one. It's just that it never occurred to me that you could have two spaceships connected by tether. And I guess there's not much difference what's on the other end but having two autonomous ships that can do everything on their own (apart from generating artificial gravity) and connecting them like that would be a really smart and relatively simple thing to do +you get twice the payload/crew in one go and always in proximity in case something goes horribly wrong on one of the ships.

Edited by Wjolcz
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1 hour ago, HebaruSan said:

Howso? Are you alluding to the difference between standing at the bottom of a craft versus floating anywhere within it?

He may be referring to the fact that one of the benefits of 0g is that you can use every surface for something, including the ceiling.

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4 hours ago, mikegarrison said:

Of course, if the tether breaks you are doomed.)

Not at all, you just would lose the convenience of art-g and have to make a minor course correction.  

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1 hour ago, DAL59 said:

Not at all, you just would lose the convenience of art-g and have to make a minor course correction.  

Not if you have the rocket at one end of the tether and the living quarters at the other end. How are you going to catch up to that rocket that is now flying away from you?

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1 hour ago, mikegarrison said:

Not if you have the rocket at one end of the tether and the living quarters at the other end. How are you going to catch up to that rocket that is now flying away from you?

RCS? What sort of delta V would be needed for such a rendezvous maneuver?

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7 minutes ago, mikegarrison said:

I don't know. Yeah. OK, so "doomed" is an overstatement. But it wouldn't be trivial.

Ackchually...:sticktongue:

Going back to the original diagram of two identical ships tethered together, it becomes far less serious if they get separated... 

*pokepoke*

Spoiler

giphy.gif

 

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9 hours ago, Ultimate Steve said:

He may be referring to the fact that one of the benefits of 0g is that you can use every surface for something, including the ceiling.

There's that, but there's also the sudden need for stairs and things like that. I don't know how much space that would take, but I imagine it's a lot.

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22 minutes ago, Lukaszenko said:

There's that, but there's also the sudden need for stairs and things like that. I don't know how much space that would take, but I imagine it's a lot.

Stairs? Why not ladders?

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Spoiler
4 hours ago, CatastrophicFailure said:

two identical ships tethered together, it becomes far less serious if they get separated... 

One will go back and deorbit, another will get additional delta-V.
Pure double profit.

 

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50 minutes ago, Lukaszenko said:

There's that, but there's also the sudden need for stairs and things like that. I don't know how much space that would take, but I imagine it's a lot.

The BFS pressurized compartement should have stairs/ladders, without a doubt. Remember, the BFS is going to land and stay on Mars for several months or years, and you have to bring the people down and back from their cabins somehow when you are on Mars. The BFS will probably house people, and/or cargo even after the bases have been built, as extra room. If i had a giant spaceship with the internal volume of a big airliner, i wouldn't waste that space on nothing.

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1 hour ago, NSEP said:

The BFS pressurized compartement should have stairs/ladders, without a doubt. Remember, the BFS is going to land and stay on Mars for several months or years, and you have to bring the people down and back from their cabins somehow when you are on Mars. The BFS will probably house people, and/or cargo even after the bases have been built, as extra room. If i had a giant spaceship with the internal volume of a big airliner, i wouldn't waste that space on nothing.

2 hours ago, Wjolcz said:

Stairs? Why not ladders?

Yeah, maybe, but it's tall and ladders aren't the safest things. 

But indeed, it will be on Mars anyway. Perhaps I overanalyzed. Still, if there is a big open common area, having space in 3d would be, well, more space.

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I read a book called MARS by Ben Bova in the 90s.  It had a depiction of a reasonably realistic Mars mission in which they used a "two spaceship on a tether" gravity system.  The advantage was that everything for the mission was doubled for safety purposes.

I suspect that the weight of cable is a big DV downside.

 

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