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Aceshigh wrote:I remember some speculation years ago, here at TP, that the ideal design for a ME Spaceship would be somewhat like... a flying saucer?
I've considered this now for many hours over the years and I don't think there is one design that meets a "best" criteria. I think there are several answers for several different kinds of needs.
For making space travel as ubiquitous as possible, one wants to build the equivalent of a Ford Model T or DC-3. IMHO, the best way to make space travel "
safe, quick, convenient and economical" is to go immediately for economies of scale, by producing a basic assembly line that can build many different kinds of craft by fitting together modules of various different sorts. The skin of the craft seems at this time best made of composite, because composite's high moisture content aids in protecting from space weather (radiation), and because unlike metals, it does not convert gamma into far more dangerous forms of radiation. You don't want to use metal.
When it comes to composites, by far the most cost effective means, and the one that produces by far the highest strength to weight is either dry or wet-filament winding. Wet filament was the preferred method 10 years ago, but new resins have been created in the last decade that make dry winding a legitimate option. Both have made advances that no longer require an autoclave, nor baking in a vacuum. In both cases, you are winding a thread around a mandrel that gives the shape to what is wound, and you want that shape to be common for as many spacecraft modules as possible. Also note you can't wind concave surfaces this way. You need a convex surface. The simplest is the cylinder. This is the most basic module. If you want to give a head nod to some aerodynamic concerns, you might make a truncated cone instead of a cylinder for one end. The other end you would want your docking/air lock module. So the simplest form would be one pointy end module and one docking module gives a space taxi. Put a cylinder with rows of seats between and you have a bus. I've noted 16 different kinds of modules to this sort of assembly that can easily yield millions of different configurations, each owner ordering what they want from this group of choices. You have communications rings that can turn an antenna assembly to any point on the circumference of the craft so the deck always stays normal to the direction of travel, and sleeping quarters, galleys, science facilities, medical, etc. I'm sure the list will grow longer. Basically though, you are looking at a cigar shape for the vast majority of craft.
For larger assemblies like this, it makes sense to have a "T" connector module available so all your builds don't require linear progression, and force people to walk through every module to get from one end to another. This is really just for the bigger craft. A pair of T connectors in a pair of linear progressions makes it possible to join two linear fuselages in parallel. It also makes it possible to dock at other than one end. A very complex arrangement of these relatively cheap modules can have as many docking rings as one likes, so the lines between spaceship and space station begin to blur. Note though, that every module has as many systems in common as is useful. So propulsion can be distributed for example, throughout the entire ship; say under the flooring for easy access should you need to replace ceramic drive units. Power can be in the ceiling. Life support can be in the walls. Common power busses can link modules so that if a single section takes an asteroid impact, the airtight doors at each end of every module can seal it off, and redistribute power and the ship automatically uses its redundancies to continue to fly. BTW, the doors in Star Trek make good sense if you can make them airtight, since they don't take up floorspace where they have to swing open. With two doors in every module, this makes a huge difference.
This is all cheap to build, but modular construction has one down side--it replicates systems in an inefficient manner such that it is not nearly as high performance as something built as a single unit. There are reasons to build other shapes. For instance, suppose you want to build a Hilton on the Moon, Mars or Titan (or all three). The most efficient method is surely to build hotel rooms on Earth, fly them to their homes and snap them together like Legos. Each room is similar to the modular construction above except there is now utility in a square or rectangular cross section, and you don't need things like propulsion systems. You can filament wind these rooms too, and you can even wind them with a trapezoidal cross section for assembly into ring-cities in the sky. These aren't spacecraft though they would likely have their own life support, but the point is to move them economically, you need an external cargo carrier like the S-64 Skycrane or even resembling a tractor trailer. You design the rooms so your transport can pick them up from the parking lot at the factory, fly them straight to their destination and snap them into place. If you want to fly them with people aboard, at one Gee it's 9 days to Titan. If you want to fly them robotically, you can choose any plausible acceleration in vacuum to get shorter travel times for each hauler. If you can make it to Mars in a few hours, all the better to optimize your transport ship's scheduling. Keep it flying fast and cheap. No pilots required. Especially since you'd expect the return trips to all be empty, why limit the travel accelerations to those a person can endure comfortably? Pull 10 Gees on the homeward trip while the ship is unladen. That saves money.
All of these shapes--cylinders, truncated cones, rectangles and trapezoidal cross sections--can be manufactured on the same equipment and this is important to driving down tooling costs such that this stuff gets done. It is when pie-in-the-sky engineering ignores things like tooling and infrastructure costs that we get these proposals for stuff no one in their right mind would ever invest in. If we take these shapes and assign them standard hotel room like dimensions, 12' wide and 8' high cross sectional area for all ships and living quarters; then a filament winding gantry needs to be able to wind 14' diameters plus some extra for radiation protection. The McClean Anderson Raptor can wind 16' diameters up to 70 meters long, so this one machine can build millions of different kinds of spacecraft, hotel rooms and sky born cities. It's just sensible to order half a dozen.
http://www.mccleananderson.com/index.cf ... tle=Raptor
When it comes to special needs that you can't serve with modular construction, perhaps the best need to represent that class is any ultra-high performance ship, such as what the military sails and flies. The military is one of the few groups who could have a pressing need to fly fast in atmo so they might prefer a triangle or saucer shaped ship. While these shapes can move through atmo fast on edge, its when they're in vacuum the shape really comes into its own. You want the largest cross sectional area to be normal to travel so there's room for lots of thrusters, so short and wide makes good sense. Also saucers are a good shape for fitting a wormhole generator should you take the technology that far. In Nembo Budrini's depiction on the cover of Woodward's book, The Journey Home; you see a ring generator fitted around the ship, but there is really no reason to have empty space inside the ring at all. If you fill that space with spacecraft, and make it thin on edge for atmo, and as wide a cross section as possible for fitting the most thrusters as possible, you get a saucer geometry and the best way to construct it, is as a single unit--not modularly. If you stay with filament wrapping for this, this would require a much larger machine than a McClean Anderson Raptor. I don't know if there is such a machine commercially available. I believe Lock-Mart has a machine they use to wrap X-47b's, but that is not nearly large enough for real spacecraft of this type. I think a custom built gantry is certainly called for in this instance, but McClean Anderson does that too.
Cigars, triangles and saucers--pretty much your best options save for the robotic trucks that one supposes might resemble the S-64 Skycrane, though even that presumes a need to extend the ship below the top of the external cargo and that might not be necessary at all. Depends how you grapple the cargo. Might look closer to the Eagle Transporter in Space 1999, or the entire heavy hauler might be smaller than the dimensions of a standard hotel room, just so the ship itself does not get in the way of placing modular pieces. It you can get sufficient grasp of a module by a set of grapple points build into the roof of a module, keeping the entire hauler smaller than the dimensions of that module will make it easy to fit the modules in place. Lastly and a separate case is any hypersonic dabbling you'd like to do--then you need to look at wedges (which can also be done on a winding gantry), but this is not an especially useful nor practical type of travel as the thermal stresses are so severe, you're not then looking at useful maintenance schedules.