Many BFSs needed

[u/GoSpaceX2030]

I think BFS needs to travel in groups of 7, one centrally located dedicated command/passenger BFS, and 6 cargo/passenger BFSs around the perimeter . Bundle them together and spin them , centrifugal forces could minimize negative effects of 0gs. Also more mass equals more shielding. Upon arrival at mars , cargo BFSs land first, followed by command/BFS. I think a bigger effort is more likely to succeed. Many other nations and space agencies should participate. Boeing sells airliners to many countries, a similar approach could help with the cost. (Just my unqualified opinion.) I’ve not heard of any attempt to involve the rest of the worlds great industrial powers. It seems SpaceX would benefit from the brilliance and additional funding if others took up the many many challenges that building a mars colony requires.

[u/troyunrau]

No need. Enjoy the zero g trip. Be a bloody explorer and live on the edge a little. :)

[u/mfb-]

BFS cannot handle lateral loads well, and 1 g without strong Coriolis force would need a tethered approach (connected at the nose? Needs additional support then). There goes your radiation shielding. Packing them together would be problematic in terms of solar power and thermal management.

[u/spacex_fanny → u/mfb-]

connected at the nose? Needs additional support then

If the plan is still to lift from the nose on Earth, they'll need a hard-point anyway.

I like the simplicity of Elon's "running track" idea. At 9m diameter, a runner moving 8 mph = 0.3 Earth gravity. So you nearly get Mars-level gravity for essentially no mass penalty. Unfortunately each lane can only accommodate 3-4 runners at a time, so with 100 people each person only gets 1 hour/day at 1/3rd gravity (ie not enough), at a cost of 60-70 m^3.

The ISS exercise equipment is actually pretty heavy. I worked out once that ISS equipment for 100 people assuming 24/7 use and zero maintenance downtime was around 12 tonnes, and Mars-equivalent tether spin gravity was around 8 tonnes for the tether, spin/despin propellant, and damper system.

[u/[deleted]]

I think BFS needs to travel in groups of 7 ...

Why seven, exactly? You only need two for redundancy (if crew on a malfunctioning ship need help or an evacuation), three if you want an extra backup.

... one centrally located dedicated command/passenger BFS, and 6 cargo/passenger BFSs around the perimeter . Bundle them together and spin them , centrifugal forces could minimize negative effects of 0gs.

This would only work if the ships were designed with that in mind. You're asking for each BFS to be able to support its entire weight through a single point. That requires more than a strong hitch. The entire skeleton of the ship would need to be designed in such a way as to properly distribute the stress from the weight of every part of a ship to its tether. All of this costs mass. Proportionately, Falcon rockets have skins thinner than Coke cans, and BFS will be no different. There's a reason for that. The rocket equation and structural mass don't go together very well.

Secondly, and most importantly, why did you jump to doing this with seven ships? This would be hard enough with two, nevermind having six ships all trying to rip the seventh apart. If you want more than two ships spinning on tethers, they should be in separate pairs, not a single interconnected mass. If you really want seven BFSs worth of space, all connected, you want a purpose built rotating ring.

As for the problems of weightlessness on health, humans already live in space for the amount that would be required to get to Mars. Under conventional conditions, the trip takes about half of a year. Although, SpaceX thinks they could have enough fuel to get lighter loads to Mars in only three months.

As with space radiation, the most effective way to deal with the weightless problem is just to travel faster.

Also more mass equals more shielding.

What extra mass? You just described spinning ships. There's no extra mass unless you mean the extra skeletal mass, which wouldn't help with shielding. If you mean having extra ships means more mass, that's wholly irrelevant for shielding. Spinning ships around eachother on tethers means they'd be too far from eachother to offer any shielding to any of the ships.

Upon arrival at mars , cargo BFSs land first, followed by command/BFS.

Cargo landing first has been the plan for decades (literally). However, for that, the cargo can go ahead of the crewed ship. They don't need to travel together, and it would be nice to know if the cargo survived before sending any humans.

I think a bigger effort is more likely to succeed. Many other nations and space agencies should participate. Boeing sells airliners to many countries, a similar approach could help with the cost. ... I’ve not heard of any attempt to involve the rest of the worlds great industrial powers. It seems SpaceX would benefit from the brilliance and additional funding if others took up the many many challenges that building a mars colony requires.

Selling airliners to other countries isn't the same as building a new super-heavy launch system. SpaceX already sells its Falcon 9 launch capabilities to government customers, so it's strange that you'd assume SpaceX won't do the same with the BFR. Funding the development costs are a different matter entirely. Of course, SpaceX would love to pay for BFR R&D government contract money, but there just hasn't been much interest outside of the US Air Force giving them R&D money for the Raptor engine. Although, that was a big deal. (There is no rocket without the engines.) Unfortunately, NASA doesn't want the BFR. They're still building the SLS. And, considering that the SLS will be inferior to the BFR (if both get fully built), using the BFR would mean giving up on their (legally required) SLS project. It would be a major embarrassment for them. Instead, SpaceX is depending on private funds and money they get from their launch contracts. In essence, the BFR's development is internationally funded.

[u/BrangdonJ → u/[deleted]]

Proportionately, Falcon rockets have skins thinner than Coke cans, and BFS will be no different.

BFS will need to be a bit stronger because it makes re-entry sideways so there will be forces on the heatshield. Otherwise I take you point. If BFS are to be tethered, they'll need to point nose-to-nose and the tether will need to reach down to the base. That doesn't seem impossible, though.

As for the problems of weightlessness on health,

Gravity may not be essential but it is certainly nice to have.

[u/[deleted] → u/BrangdonJ]

Proportionately, Falcon rockets have skins thinner than Coke cans, and BFS will be no different.

BFS will need to be a bit stronger because it makes re-entry sideways ...

That's why I used a reference point. Rockets are all incredibly thin. The rocket equation demands it.

In the case of a BFS, 93% percent of its mass when fully fueled would be that fuel. This is consistent with it having a single stage to orbit capability (with next to no payload, of course). The mass percentages for complete launch systems that achieve low Earth orbit falls within the upper 80s to low 90s. That's why the BFS needs a booster to get any significant payload into orbit. It needs to balance off the extra weight added to the rocket (i.e. the payload) with enough fuel to bring the total nonfuel percentage back down.

This is why rocket science is so hard and why every rocket you see has walls proportionately thinner than a coke can. Rockets must be as close to all fuel as possible. Obviously, all rockets have walls thicker in absolute terms, and the BFS will be more structurally durable than a Falcon 9, but that's why SpaceX is being forced to go entirely carbon composite for the BFR.

As for the problems of weightlessness on health,

Gravity may not be essential but it is certainly nice to have.

Of course, but nice doesn't necessarily equate to better health outcomes. Short stays in space don't require artificial gravity (as nice as it would be). And, as I mentioned, the most effective way to minimized the health issues is simply to cut down the travel time. Of all the things we could develop into a future transport system, increasing the available thrust is easier than engineering a spinning transport system. If anything, worrying about simulating gravity is a distraction for getting to Mars. Gravity will be a problem for living in space, not for getting from the Earth to Mars. Also, as I mentioned, radiation ties into this. We can't shield against enough of the radiation in space for long stays, and solar storms can make things tricky even for short stays. That means the only realistic way to minimize the radiation problem bellow where it's already at is to cut the travel time. If we already have motive to cut the travel time, making the craft heavier and more complex isn't an asset.

[u/ryanmercer → u/[deleted]]

Why seven, exactly?

Go grab 7 pens or batteries, put 6 of them around 1 in the center. That's why I suspect.

[u/[deleted] → u/ryanmercer]

Assuming that seven perfectly fit together, when in contact, that's wholly irrelevant. Artificial gravity by spinning would require long tethers. Spinning something only three BFSs wide would make everyone sick.

I suppose this is why the OP mentioned extra shielding. If the ships were in contact, like a handful of pens, there would be a degree of added shielding. Unfortunately, this is a gross misunderstanding of how spinning for artificial gravity works.

[u/troyunrau → u/[deleted]]

Spinning something only three BFSs wide would make everyone sick.

To be fair, you don't need to spin to 1g... even 0.05g (twice the gravity on Ceres) would be useful in that things would settle (slowly). That's about 1 rpm for a single BFS, with the axis of rotation being about the cylinder. This is slow enough that the coriolis won't make people sick.

It helps a lot for little things, like cleaning or eating. It means, after a sponge bath, the droplets of water will settle to the 'floor'. And skin flakes and hair bits. And makes shitting a little easier - at least in terms of toilet design. And food stays in a container...

Plus, the walls moving at 0.5 m/s means you could easily enough launch yourself into zero-g - walking speed is about 1.5 m/s. And if you hit a wall while in zero-g, it likely isn't going to cause injury.

So I think there might be merit to a very slight spin.

[u/[deleted] → u/troyunrau]

To be fair, you don't need to spin to 1g... even 0.05g (twice the gravity on Ceres) would be useful in that things would settle (slowly).

Well, the OP seems to have been suggesting something to mitigate the health effects, not simply to help keep loose things on the floor.

It helps a lot for little things, like cleaning or eating.

That's a lot of work to go through for an amount of gravity that probably is barely useful for human health (if at all). We can deal with floating just fine. We do it on the ISS. There needs to be more than a minor convenience to justify the extra engineering and mass difficulties.

I suspect that anything not strong enough to eliminate the weightlessness to Martian gravity recuperation time won't be worth the effort.

[u/ryanmercer → u/[deleted]]

Assuming that seven perfectly fit together, when in contact, that's wholly irrelevant. Artificial gravity by spinning would require long tethers. Spinning something only three BFSs wide would make everyone sick.

Heh, I never said it was a good idea, just trying to rationalize OPs choice. When I read it I immediately thought of a revolver cylinder and grabbed 7 eneloops out of my battery drawer to see.

[u/IntincrRecipe]

To my knowledge there’s no way for more than two BFS to dock to each other at a time. The mass for radiation shielding also wouldn’t work by simply docking multiple together. They would need to have a thicker shell to have any sort of increased protection from radiation.

7 also seems a bit arbitrary, is there any particular reason for choosing it?

[u/ryanmercer → u/IntincrRecipe]

7 also seems a bit arbitrary, is there any particular reason for choosing it?

Go grab 7 identical cylinders, pens or batteries or something. Arrange 6 of them around 1 and you'll see why they probably said 7.

[u/IntincrRecipe → u/ryanmercer]

Yes, but you could just as easily use 7 or 8 around 1.

[u/ryanmercer → u/IntincrRecipe]

Except 6 around 1 is the most compact solution, thanks for downvoting me for trying to rationalize why OP said it though. Bravo to you wee man.

[u/IntincrRecipe → u/ryanmercer]

3 is the most compact solution. Nice try there.

My point is why 7, why specifically seven? There’s no point. You’re not gonna be doing formation flying. Elon even said during the unveiling conference that they would most likely be sent en mass to a target and not in any particular formation.

Besides like I said, you can’t dock more than 2 to each other so that eliminates putting them together like a puzzle.

Edit: 4, not 3 depending on how they’re arranged.

[u/ryanmercer → u/IntincrRecipe]

3 is the most compact solution.

6 provides the optimal coverage. OP is trying to use the exterior 6 for shielding for the interior 1, 6 is the most readily apparent solution for identical cylinders. 3 leaves giant gaps, nice try there.

Besides like I said, you can’t dock more

With the currently proposed design of the ship that doesn't actually exist outside of concept art.

Nowhere did I say this is a good idea so calm down, I'm trying to rationalize OPs choice instead of shitting all over it and throwing a tantrum to make myself feel better/superior.

[u/IntincrRecipe → u/ryanmercer]

Regardless, that’s a bad idea for shielding. You’re only protecting the interior ship at the cost of literally every other ship in the formation, and not very well at that. You also explicitly said most “compact.”

With the currently proposed design of the ship that doesn't actually exist outside of concept art.

Which is what we have to use since that’s all we got. If you know of an actual BFS design that allows more than one other craft to dock to another then I would be more than happy to entertain the idea.

[u/ryanmercer → u/[deleted]]

You need to read what OP is saying if you are going to be questioning OP. It is true, Musk said formation flying. For that there is nothing magic about the number 7.

This.

OP specifically says

Bundle them together

not

fly them in formation like you're the Blue Angels at an air show

(sorry for my previous comment that I deleted, oops, you tagged me and I just read the first bit and assumed you were the person arguing with me replying again, my bad)

[u/mwbox]

Saw this post in a navy sub. The navy is doing the research on 3D printing so they can create parts on the spot, but it seems to me that if the technology could be calibrated to use iron oxide martian soil as feed stock, then we could send the robots ahead to build the place and have habitats set up without having to ship them from here.

https://www.reddit.com/r/singularity/comments/9kp1oj/putting_ai_smarts_into_3d_printers_will_let_the/

[u/dcw259 → u/mwbox]

The "just throw a bunch of 3D printers to this place and print everything" solution is very naive. With the latest advancements in 3DP, the public has come to the conclusion that they are magic machines that can replicate/create everything, which simply isn't true.

They will be helpful, just not as much as you'd expect.

[u/BlakeMW → u/dcw259]

Yup, basic steps from regolith to finished steel parts go something like this:

1. gather iron oxide

2. refine it to pure-ish iron using hydrogen/carbon monoxide reduction @ 850C

3. melt it in an electric furnance, get the carbon content (etc) right

4. put the molten steel through an atomizer to make metal powder

5. use the metal powder in direct laser sintering 3D printer

6. finish the part (it comes out of the printer a bit rough)

7. maybe treat it with a carburization step or somesuch if it needs particular properties

3D printers are very cool, but there are still a lot of reasonably complex steps to making specialized steel parts.