New Mars Forums

tahanson43206

Moderator

Registered: 2018-04-27

Posts: 19,364

Re: Large Ship Component Manufacture on Earth

For Void re #25

Please ** do ** continue your line of thought!

kbd512 has visions that differ from yours, and this topic is more than large enough for both of you .

There is ** no ** need for anyone to feel pressure to adjust their ideas based upon anything other than Ma Nature, who hands down decisions without partiality.

I personally ** like ** what I understand to be your idea, and I hope you will favor us (the forum plus non-member readers) with your vision of how your idea might be adopted by space architects.

I have adapted your idea slightly, and hope that my version of your idea might be given a bit of breathing room.

Ultimately, the ideas that are best are ** most ** likely to receive funding, and funding is the name of the game.

If your idea is most cost effective for building large structures in space, then it will receive funding.

(th)

Void

Member

Registered: 2011-12-29

Posts: 7,812

Re: Large Ship Component Manufacture on Earth

It is fine, I look forward to what the members do here.  I do not want to be a problem of interference with it.  I just wanted to make sure we understood each other's intentions.

Ending Pending

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tahanson43206

Moderator

Registered: 2018-04-27

Posts: 19,364

Re: Large Ship Component Manufacture on Earth

For Void ... the wording of post #27 seems to imply you will now abandon your idea before it has a chance to sprout, or whatever ideas do.

I hope you will give the idea some nourishment in another topic if not in this one.

(th)

Void

Member

Registered: 2011-12-29

Posts: 7,812

Re: Large Ship Component Manufacture on Earth

No, I have been addressing it in a collection of ideas here: https://newmars.com/forums/viewtopic.php?id=10867&p=2

I just am very interested in getting propellants from the metal of the ships, and then also as a side line structure as well.

The ideas I am working on are a bit too far removed from this topic.

Ending Pending

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kbd512

Administrator

Registered: 2015-01-02

Posts: 7,852

Re: Large Ship Component Manufacture on Earth

tahanson43206,

To be perfectly frank, Void's idea is something that should be pursued first, because if that actually works it means a very simple solution is at hand to travel between planets using bits and pieces of existing flight hardware.  I'm not against Void's idea at all, because I don't care how this vehicle gets built as long as it actually works.  I'm after the end result, not the aesthetics nor personal preferences.  If lopping off the crew compartment of a Starship and welding it up to part of another vehicle actually works, I'll dance a jig over it and move on to the next interesting problem.

tahanson43206

Moderator

Registered: 2018-04-27

Posts: 19,364

Re: Large Ship Component Manufacture on Earth

For kbd512 re #30

It appears that Void will be heading off to other topics, after dropping off the seed of an idea in this one.

I am reminded of Johnny Appleseed, who traveled around the newly formed United States of America to earn a living by distributing apple seeds. 

In this case, the essence of the idea (as I understand it) is to send the second stage of a Starship launch up to LEO to be incorporated into a large structure in assembly there.

The second stage does not have to be round.  Round is a logical shape for an enclosure for round tanks.  However, the second stage could have walls that are flat.  The design has to be strong enough to endure the forces of launch.

And if we grant that the walls could be flat, then it is a small leap to imagine walls that are gently curved to match the exterior of a gigantic Solar System vessel, such as the dual counter rotating habitat vessels described by kbd512 and GW Johnson elsewhere in the forum archive.

Thus, a single Starship designed for this purpose could deliver four panels for the wall of a Large Ship.

The tanks could be used as is for storage of liquids or gases in the large vessel.

What I'm looking for and hope will happen, is that one of the large vessel designers will tackle specification of components to be assembled on orbit to make a useful vessel for inter-planetary service.

Specifications would include (but not be limited to)...

1) Length
2) Width
3) Curvature
4) Thickness
5) Material
6) Mass
7) Specific assigned location on large vessel

At the moment all we have (that I have seen) is broad brush descriptions of large vessels.

Some of the work of RobertDyck can be interpreted as detailed, but we ran out of steam when we tried to imagine how to actually build the unitary rotating habitat design of RobertDyck.

My interpretation is that most of work done to build the single unitary design of RobertDyck could be adapted for the dual counter rotating designs of kbd512 and GW Johnson.

I note that the designs of kbd512 and GW Johnson are vastly different in size.

It seems likely to me that the smaller vessel would be attempted as a precursor for the gigantic one.

On the other hand, the methods developed to build the smaller vessel should be usable for construction of the large one.

What I'm looking for is a plan that could be implemented with funding.

What we have now are visions of what might be done, and those are essential, but by themselves they are insufficient.

(th)

Void

Member

Registered: 2011-12-29

Posts: 7,812

Re: Large Ship Component Manufacture on Earth

Well, I like this:

Four Starship Crew Compartments ganged together.

I am looking at nuclear electric propulsion with metal propellants, (Magdrive).

I don't like aerobraking to Mars myself, but each capsule might do it to aerobrake to orbit, but of course you would have to reverse the floor plan so to present convex to the atmosphere, and you would need a heat shield scheme.

The four sections could be reassembled after aerobraking.

For my part I am anticipating the use of nuclear electric (Jetson), with metal propellants, and perhaps the use of ballistic capture.  And with no Aerobraking, the convex floors of the Crew Capsules will not be a problem.

Ending Pending

Jetson: https://www.space.com/space-nuclear-pow … in%20space.
Quote:

The U.S. Air Force Research Laboratory (AFRL) awarded $33.7 million to Lockheed Martin as part of the Joint Emergent Technology Supplying On-Orbit Nuclear (JETSON) effort to "mature high-power nuclear electric power and propulsion technologies and spacecraft design."

JETSON aims to launch a fission reactor that will be started up once in space.

It is possible that the tanks of the Starships might be converted to propellants.  Then at Mars, you might get metals from Phobos or Deimos, should you want to return to Earth, or go somewhere else.

Ending Pending

Last edited by Void (Today 09:06:01)

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kbd512

Administrator

Registered: 2015-01-02

Posts: 7,852

Re: Large Ship Component Manufacture on Earth

tahanson43206,

We're definitely not "granting that the walls could be flat" if the interior of this flat-walled structure will also be pressurized.  ALL propellant tanks are pressurized during launch, to something like 40psi to 70psi.  As a function of basic engineering best practices, no part of a pressure vessel shall ever be "flat", because it concentrates stress into a very small area, which always leads to structural failures in real world pressure vessel designs.  If you make said pressure vessel strong enough to temporarily overcome that stress / force concentration, then it's no longer a flight-weight aerospace structure.

GW can explain why we don't make pressure vessels flat, for like the 5th or 6th time that I'm aware of.  This very idea has been proposed over again and again, and the response from the real aerospace engineer is always the same, each time it's proposed.

The following picture shows a single wedge / donut / section of the ITER Tokamak pressure vessel:

Where the CAD picture is labeled "upper port" or "eq. port" or "lower port", pretend that doesn't exist, or that it's on the opposite side of the structure and pointed inward towards the center barrel section it's attached to.  Pretend all the electromagnetic crap inside the pressure vessel doesn't exist, either.  Roughly speaking, what you're left with is what a "slice" of the toroidal pressure vessel will look like.  The dimensions will be different, wall thickness will be different, and the curvature of the vessel has to be different because it's much larger in diameter than ITER, but that's how the basic concept works.

ITER has an OD of 19.4m and it's 11.4m tall.  It weighs 5,200t because it's trying to resist atmospheric pressure from the outside trying to crush it like an empty beer can.  That wedge is actually hollow, meaning not a solid piece of steel, and IIRC, made from stainless steel.  Coolant water is circulated inside of it to prevent it from melting.  It can't be Mangalloy because it gets too hot and will be pressure cycled like crazy during testing.

We're shipping as many of these slices / wedges of the torus (the giant rotating donut) as will fit in the payload bay of a Starship per trip.  They can either be bolted together if made from CMCs or they can be welded together if made from metals.  If they have to be welded together, then they have to be fixtured in place during welding, and possibly heated up during the welding process using blankets.

tahanson43206

Moderator

Registered: 2018-04-27

Posts: 19,364

Re: Large Ship Component Manufacture on Earth

For kbd512 re interesting mis-reading of text in post #33:

I said:

And if we grant that the walls could be flat, then it is a small leap to imagine walls that are gently curved to match the exterior of a gigantic Solar System vessel, such as the dual counter rotating habitat vessels described by kbd512 and GW Johnson elsewhere in the forum archive.

It is difficult for  me to understand how someone could misread that, but obviously that happened.

The "flat walls" I was talking about were for the proposed Void concept of a Starship intended to deliver components; to LEO.

I have NO idea how that simple idea could have stimulated a rant about flat walls and 5 or 6 times ranting about flat walls.

However, that is clearly what happened.

The lesson is that English is a difficult language to master and obviously I am still a novice.

(th)

tahanson43206

Moderator

Registered: 2018-04-27

Posts: 19,364

Re: Large Ship Component Manufacture on Earth

GW Johnson just sent me an email clarification of the design of Starship. 

I've asked for permission to post the text, but a quick summary is that the hull ** is ** the tank, and not just a wind screen and structure component as I had thought.

This clarification means I'll have to change my understanding of Void's idea (again).

Aside from the misunderstanding of flat panels that occurred recently this new (to me) information from GW means that any panels that are carried aloft by a Starship as external elements would be released at LEO, and Starship could be returned to Earth as normal.

The curvature of such panels would be specified by the designer of the large structure.  The curvature would be greater for a smaller Solar System vessel such as described by GW, and it would be less for a larger vessel, such as the Large Ship envisioned by RobertDyck.

(th)

Last edited by tahanson43206 (Today 11:47:01)

kbd512

Administrator

Registered: 2015-01-02

Posts: 7,852

Re: Large Ship Component Manufacture on Earth

tahanson43206,

I'm completely willing to concede the point that rockets are very inconveniently shaped for transporting large and bulky cargo items.  If we were able to ship the James Webb Space Telescope to orbit without all the origami work to package it into the cargo bay of a much smaller rocket, that would've made its design so much easier, faster, and cheaper.  The aerodynamic drag and force exerted by pushing an object with the size and shape of a tennis court through the air made that idea a non-starter.

You cannot arbitrarily reshape the upper stage of a rocket powered vehicle because it's convenient for transporting an oversized piece of cargo to orbit.  If the vehicle in question still has to store pressurized propellant and push through a dense atmosphere at supersonic to hypersonic speeds to reach orbit, then how it's sized and shaped must be optimized for that function.

If it was practical to assemble most of the counter-rotating vehicle here on the ground, fill it up with propellant, and launch it to orbit as a single-use upper stage (similar to the original Skylab concept which was ultimately abandoned by NASA), temporarily repurposing its interior volume as very large propellant storage tanks, then we would do that.  Unfortunately, the forces exerted would also greatly exceed those which it would be subjected to on-orbit during the rest of its useful service life.  That means it would have to be much stronger and therefore much heavier, in order to perform both missions.

That's why we're shipping it up in not-so-little pieces and assembling it after it's in space.

The vehicle I proposed has more than double the combined interior pressurized volume of a Starship and its Super Heavy booster, but its actual hull mass is LESS THAN the 375,000kg empty / dry mass of both of those rocket powered vehicles.  The 9mD x 121mL Starship / Super Heavy vehicle would have 7,698m^3 of interior volume if it was a pure cylinder (no "pointy nose").  It's pressurized to about 60psi, IIRC, so the vehicle mass is clearly sufficient to contain that amount of internal pressurization load (hoop stress) trying to make it burst at the weld seams.  The pair of torus structures in my proposed vehicle are 13,300m^3 in total.  The connecting arms and center barrel section push total pressurized volume to greater than double that of an entire Starship Super Heavy launch vehicle.  Somehow, my total hull structural mass is still 25,000kg lighter than a Starship Super Heavy!

How on Earth (or actually, how on-orbit) did I achieve that?

I started by using a steel 2X stronger than stainless, I subjected it to a mere 14.7psi of internal pressurization with a maximum overload of 22psi, and the forces acting on it is highly directional when the torus is rotating.  The directional loads trying to pull the pieces apart while its spinning are resisted by both the shape and steel allocation (varying cross-sectional thickness), plus the fact that it's only subjected to 1g of acceleration when fully assembled.

How does that stack up to a Starship vehicle launch?

Starship is internally pressurized to about 60psi to begin the process of force-feeding propellants into its Raptor engines, and the vehicle acceleration is upwards of 3g after its drained most of its propellant, but the loads imparted to the vehicle are also highly directional in nature, so 375t of stainless is enough to ensure it doesn't disintegrate from the combination of internal pressurization, external aerodynamic loads, and thrust from the engines.

If you tried to do that with the assembled vehicle hull I proposed, it would burst after being internally pressurized to 3X its maximum overload.  A strong gust of wind would act on sufficient surface area to topple the vehicle on the pad, whether empty or full, and it would also crush the booster beneath it from its weight when loaded with 50% more propellant to lift a 50% heavier (350t vs 200t) payload mass to orbit.  The pad launch tower would need to be completely redesigned to accommodate a 50m diameter double toroidal upper stage.  And the list of required changes to survive a launch goes on and on.

Can we still do that if we're really determined to?

I suppose we could, but every bit of the booster underneath it and the launch pad itself would require a complete redesign.  Both the upper stage and the booster would need to be significantly stronger than they presently are.

That's why we're going to ship it to orbit in pieces small enough to fit inside Starship's payload bay, because we don't have to deal with any of those problems which would create significant additional work, slow progress, and become an impediment to building a practical large ship.