# Would it be more efficient to build fleets in orbit?

My Dino theme park business didn't end well and I reluctantly fall into depression and decided to go into suspended animation to seek a cure. 200 years later, a lady claims she works with the military woke me up and wants to award a contract of constructing 1000 space ready battleships within 5 years. My depression was instantly cured and promptly agreed to take the offer, after learning everything about spaceship building from many social media I need to look for a suitable site for the construction.

Would it be much faster and economical to do shipbuilding in low gravity region such as orbit compared to on the surface? The contract states that I must deliver the fleet battle ready on Mars surface within 10 years, propulsion engines to be provided by a sub contractor appointed by the client and the only details I received regarding the engine is that it has a specific impulse of 3 million Newton Seconds/Kg. If the economy has remain stagnant ever since fall of 2018, should I put my factories into orbit?

• Do you have a usable and easily accessible space elevator? Otherwise its going to depend a lot on size, resources and purpose. A ship build in orbit might never need to enter the atmosphere or have enough fuel to break free of the atmosphere, but shipping all the parts up one by one is going to be extremely expensive. – Shadowzee Dec 10 '18 at 5:51
• I'm saying the cost would be dependent on the infrastructure you have to get parts into space. If there was already a space elevator, it would be far cheaper than hiring companies to fly small payloads up into space. Depending on how much weight you need to lift up, it might end up being cheaper building them on the ground. – Shadowzee Dec 10 '18 at 6:03
• I thought carbon nanotubes are formed via deposition onto a catalyst material and the Duct tape method was to get a 1 layer thick sheet of graphene(?) – Shadowzee Dec 10 '18 at 6:11
• "[A]fter learning everything about spaceship building from many social media, I need to look for a suitable site for the construction." I'm sure that will end well. Also, I'm not sure how the economy could remain stagnant yet technology has advanced far enough to make space fleets feasible. – jpmc26 Dec 10 '18 at 19:11
• I would say they had you.. You will have to pay huge payments as your fleet will fail like with great success. – Artemijs Danilovs Dec 11 '18 at 0:50

There are several important factors here, like whether or not your space fleet has been designed to also operate in a gravity well, and whether or not you have access to a space elevator.

In general terms, if the answer to the first question is yes, and the second no, then you're far better building on the ground, so as to save the energy cost of getting construction tools and people into orbit. The amount of mass you have to lift is the key factor here and lifting the ship, as opposed to the mass of the ship AND the mass of the construction tools and people, is obviously smaller.

In almost every other scenario, you're better off building in orbit, especially if you have access to raw materials from low gravity locations like the asteroid belt. Being able to build the ship in space is actually essential if it's not designed to lift off a planet, and if you have a space elevator, it's easier and cheaper to lift the mass of the ship components up into space for assembly and launch.

Space is dangerous of course, and building in space means many different things can go wrong, so this may well be the most efficient solution in terms of energy cost, but your staff safety costs are likely to go through the roof, and the pool of people actually rated to build in space is much lower, meaning they'll demand much higher salaries.

In short, there are many considerations, energy cost being only one. I'd factor in (at a minimum) design constraints of the ships, raw material sourcing, availability of space elevators and the like, and whether or not your contract requires you to pay for the energy cost in the first place or fuel etc. is supplied.

• You might try a hybrid approach as well: build small fiddly objects (like computers) or even whole assemblies (like weapons or thrusters) here on Earth, then launch them to orbit for attachment to the space-built frame. – Cadence Dec 10 '18 at 6:27
• If workers are inside a shielded space station, like the ISS, they won't have many issues: space.stackexchange.com/questions/1034/… . If they have to work "in the open", you better shield them, monitor their radiation, look for solar flares, and ensure they work "in the shadow". Radiation accumulats, there is a limit to how long you can live in zero gravity, etc.... – Enric Naval Dec 10 '18 at 10:19
• Based on the contract parameter that they must be delivered battle-ready to the Mars surface, they must be designed to operate in a gravity well at least as big as Mars's. – Nate Strickland Dec 10 '18 at 19:36
• First I thought "yes this is a perfectly reasonable explanation", but why would it be better to build it in space when you have a space elevator? You still need to get all the tools, materials and manpower up to space, and if your space elevator can simply carry the completed space-ship up you have just saved all the time and effort it would take to bring up all the tools and components individually. If you have materials available from space then yes: Build in orbit. But if it comes from the planet and you have all the factories on the planet... Why build it in space? – Demigan Dec 11 '18 at 10:04
• @Derrigan the reason to build in space if you have an elevator is not because of Mass, but because of volume. Even the strongest theoretical designs for a space elevator won't help with something the size of an aircraft carrier in a single go and the centre of gravity for such an object would likely create issues for the climbing systems. On the other hand, many runs containing the raw materials are probably the better way to go because the cost is lower so inefficiency is less of an issue by comparison to logistics in this case. – Tim B II Dec 11 '18 at 11:45

If the economy is 2018 levels, the only place in the solar system with anywhere near the industrial capacity to do this is on the Earth.

Creating a new industrial capacity using 2018 levels of tech (or, in an economy not much richer than 2018) in 10 years is a non-starter.

So there isn't another place to do it besides the Earth.

The result will be insanely expensive; the effort you require would be extensive enough to cause massive economic disruption to the Earth.

A single aircraft carrier is 4.5 billion dollars today. 1000 of those is 4.5 trillion dollars.

A single battleship cost 100 million dollars back in the 40s. The Apollo program cost 250x as much as a Battleship, and lifted far less.

So building 1000 aircraft carrier sized space ships and launching them out of Earth's gravity well should cost on the order of a quatrillion dollars; world GDP is 78.28 trillion today. So the entire world's economic output over 15 or so years.

Building shipyards capable of constructing these in orbit or elsewhere in the solar system is going to take longer and/or cost more than even that.

Bootstrapping an industrial civilization is a really really long process. It is arguable if we've done it more than once on Earth, as almost all other industrial civilizations relied heavily on trade with the "parent" one during their growth. In every case it took far longer than 10 years. Even Japan's economic miracle after Perry "opened" their ports, leading up to it being a world power, took almost 100 years.

A non-terretrial industrial base wouldn't have Earth's ecology to fall back on, making the problem insanely worse (we rely on it for little things like food, air, wood, lack of vacuum welding, and a million other things).

By far the easiest way to complete your contract is to suborn the government that hired you. Underestimate the difficulty by a factor of 50 or so; if they are earnest that will still get you a budget in-line with the entire world military. Use that to build some your combat capable space battleships, then conquor the Earth with them. Easier than fullfilling the contract.

• The price estimate of 1940's battleship times Apollo cost factor is deeply flawed. First of all, you're not considering technological improvements (and thus cost reductions) between the Apollo program and OP's battleship order, but the two operate in what is clearly an entirely different economy regarding space travel. Secondly, OP never specified a ship size. You're going purely on the word "battleship", of which there are many types and sizes spanning several centuries. – Flater Dec 11 '18 at 10:13
• Thirdly, you're pointing out the added cost of building an orbital shipyard but you're omitting the benefits (cost savings) from constructing the ships in orbit when you have an operational orbital shipyard. – Flater Dec 11 '18 at 10:18
• @flat It doesn't matter if there are benefits if doing it is impossible? 10 years is not going to be enough time to be able to build any non-trivial off-earth industrial base. A real off-Earth industrial chain would have huge benefits, bit huge*0 is still 0. I mean, you could click together things built on Earth (like ISS) but still 99.9% is done on Earth. And yes, we could build 1000 toys and call them battleships. Using moon shot estimates for a mars shot and modern capital ship costs is aimed at finding order of magnitude; when that is beyond entire Earth's GDP, we have a red flag. – Yakk Dec 11 '18 at 12:00
• Clicking together the ISS on Earth and launching it is similarly impossible. The ISS was shipped in parts and the joining of the parts happened in orbit. You're still omitting the implications of being in a universe where building starships is a reasonable request and by no means expected to be a first time feat. – Flater Dec 11 '18 at 12:03
• @Flater No, the OP said "If the economy has remain stagnant ever since fall of 2018". So I'm solving it for the 2018 economy, not for some economy where the problem is practical. – Yakk Dec 11 '18 at 13:03

Judging from the parameters set out in your question, there doesn't seem to have been much change in the last 100 years.

• Economy is roughly at 2018 levels
• Your sub contractor is sticking you with Space Shuttle Booster engines to power your interplanetary warships (or equivalent)
• You have 5 years to build a thousand battleships
• You have to get said battleships to Mars within the next 10 years.

As far as contract terms goes, these aren't great. You may want to consider renegotiating your contract.

But a man who dreamed of building a dinosaur theme-park isn't concerned with whether something is practical, so let's get this done. Space-construction is definitely your best option. Lifting anything of a decent size with those engines is going to be expensive, prone to failures and slow. Lifting 1000 battleships and then hurling them towards Mars is near impossible. So we're going to need to get away from earth's gravity well. Earth orbit seems like the most logical location but in terms of large construction projects, it's pretty awful. In 2018 Kessler syndrome was a real risk and I suspect that 200 years haven't improved that by one bit. The last thing we want is for ship #999 to get hit by an old weather satellite, explode into a billion pieces and take out the other 998.
So let's move our operation out a little further. The Earth-Moon L1 Lagrange point seems ideal. It's close, the orbit is stable, not too much gravity and nice and close to the moon. Why close to the moon? because zero-G work is a pain in the ass and lifting parts from the earth is expensive. The solution for that is fairly simple: Build on the moon, launch to our assembly yard from there. And this is where we'll get creative with our contract stipulations.
You see, we need to build the ships in 5 years, but no-one specified that we needed to start right now. So we can spend a little over 4 years preparing. After all, we need to be at mars in 2218. Our engines and orbital mechanics indicate that we're not going to be able to afford a Brachistochrone transfer there, so it's all Hohmann all the the way for the fleet. Back of the envelope math tells us our launch window is mid-september 2227, which puts us on mars in march of 2228.

So:
2218: Hire future-spaceX to life a pile of equipment to the Earth-Moon L1 to build your space-drydock
2218: Build a construction facility on the moon for the heavy work.
2218 - 2222: Mine the ever loving crap out of the moon for raw materials.
2222: Start of contract: Launch partially assembled components to L1 and assemble them there September 2227: Launch
March 2228: Conquer Mars

• Building a moon station is cheap* even: Less than 40 billion USD. Relevant kurzgesagt: youtube.com/watch?v=NtQkz0aRDe8 . (* Cheap in comparison to a thousand space (war) ships anyway.) – Perseids Dec 10 '18 at 12:10
• So, your plan is to bootstrap an industrial civilization on the moon in less than a year, starting mining, and produce industrially significant output in 4 years? Heh. – Yakk Dec 10 '18 at 14:20
• @Yakk Pretty much. Compared to building a thousand warships in 5 years, bootstrapping a decent-sized industrial city on the moon is peanuts. For reference, a single modern aircraft carrier, which can be considered equivalent in terms of effort, is a ~5 Billion dollar project that takes anywhere between 4 and 9 years to complete. Compared to that, bootstrapping the industry needed to do this is peanuts. Besides, think of the jobs created! – Valthek Dec 10 '18 at 14:35
• "Compared to that, bootstrapping the industry needed to do this is peanuts" I assure you, the industry needed to build an aircraft carrier is much less than peanuts. I don't understand how it would be more feasible to build the entire supply chain on the moon, versus using the supply chain that already exists on earth? Yes, there's the issue of getting your materials out of earth orbit, but what about the issue of getting the equipment/resources onto the moon that are needed to manage your supply chain? That's not free, either. – dwizum Dec 10 '18 at 18:30

Based on our current technology, you will want to build the armada on the ground and assemble it in orbit.

Building on the ground allows you to utilize existing industrial and scientific infrastructure. You can also do quality control tests on the factory floor using well known techniques and methodologies, ensuring that the products will be ready to go upon launch and assembly.

The Armada is not going to be following the "rule of cool" once assembled in orbit, every spaceship will resemble an enlarged and weaponized version of the ISS with several powerful engine modules attached. This is a result of the requirement to build everything on the ground using existing infrastructure, but has the benefit that the spacecraft will be highly modular structures which are going to be difficult to disable or destroy.

Space warships have an aesthetic uniquely their own

Continuing on the theme of building on the ground and assembly in orbit, the modules will all have to be of a standard size and mass. Luckily we can contract SpaceX to do the launching into orbit, sizing our modules for Falcon 9 boosters and lofting exceptionally massive pieces using the Falcon Heavy. While SpaceX charges a relatively low price already for launches, the pace of launch and construction should provide additional incentives for the company to provide discounts for the operation.

This also provides the ability to upgrade the fleet during the construction phase. If we imagine that the weaponry is also constrained to 2018, then we can essentially build modules as missile launch packs (similar to Vertical launch cells on a surface warship), or carrying the mechanism and optical train for a 100kW laser. Since the build will take a while, improved weapons can be built into later modules. Enemy ships will have to contend with a variety of weapons, making their use of countermeasures more difficult.

Remove the truck and substitute the spacecraft

The rather unsexy guts of a 100kW laser system

So for any halfway realistic scenario, contract a launch company to provide lift to orbit, and design your spacecraft in a modular fashion to be assembled from standard modules sized for the launch capability you contracted. Build the parts on the ground using existing techniques for ease of construction and quality control, as well as taking advantage of long production runs for economies of scale.

It won't be "pretty", but warfare is about money and logistics, and this is the way to maximize both.

• Note that the question states a specific impulse of 3Mm/s, which is a lot more than the 4.4km/s that we can achieve with liquid hydrogen/oxygen rockets. With 3Mm/s engines, reusable rockets with relatively small tanks and serious payloads will be the norm. The falcon line will look like a steam car by comparison: Huge, inefficient, and powerless... The reasoning about building parts on earth, and assembling in space is gold, though. – cmaster Dec 10 '18 at 23:05
• Since the technological restraints are 2018, I chose to go with the Falcon, It also was not clear from reading the question if the engines being referred to were for space (like ion engines) which have high ISP but very low thrust. – Thucydides Dec 11 '18 at 12:56

In general, construction in orbit is more efficient - under certain conditions.

The most important being, do you have manufacturing capabilities for the materials in space? I don't mean just shaping armor plating or something like that, but actually smelting, refining and in general turning ores into the various alloys you use.

If you have that, then you can tow asteroids into orbit or use existing asteroid mining supply chains to build ships without having to transfer mass from the planet to the orbit, which saves huge amounts of energy/fuel/money.

An aircraft carrier weighs around 100'000 metric tons. A rocket can carry around 20 metric tons, so it would take 5'000 flights to lift enough material to build one of them in orbit. A space battleship might weigh from ten to a thousand times as much, because aircraft carriers have fairly thin armor and battleships probably need to be much tougher. Carry capacity of rockets might improve in the future, but you'll probably still need a lot more launches. It will still take a lot of flights to lift stuff and for everything you lift, you need to lift the fuel required to lift it, too. Imagine as well what 5'000 flights per battleship would do to the environment.

If you can avoid all that ground-to-orbit transfer of material by using resources from space or maybe lower-gravity wells like the moon or mars, the costs for building your fleet will drop a lot. You can even import hydrogen as fuel from Jupiter. However, establishing such an industry in space takes a lot of time, so you definitely will miss your deadline if it doesn't exist already.

That means if the industry doesn't exist in space, you'll either have to transfer the mass or the completed ship into space. Which option you should take depends on the design of the ships.

Space propulsion is fairly different from atmospheric flight, so a space battleship might not be able to produce the thrust required to leave orbit. It might also break apart due to the stresses from acceleration and speed against air pressure. Building the ships in a way that they could do the launch would add additional costs and make the designs more complex for a feature that would probably never be required. After all, if you want to shoot surface things, you don't have to be in the atmosphere and if you want to shoot space things, the atmosphere just gets in the way. If that feature is required, however, you might as well build it on the ground and let it fly up.

If surface launch capabilities are not required nor desired, your only real option is orbital construction. Of course you could strap rockets to the finished battleships and reinforce them with some scaffolding so they survive the launch, but by that point you might as well just launch an orbital construction facility and lift up everything it needs instead.

The only advantage of building in orbit is that, if you lack the capacity of lifting a huge load, you can send many small loads in space and create the huge there. Moreover if your assembly doesn't have to fly through the high Q region of atmosphere, you have more versatility with the design.

That is basically what has been done with the ISS.

For all the rest building in space with present level of technology is a real pain in the back: it is expensive, it's hard to hide, it's highly risky.

Is it better to build in space or on the ground is a question of technologies, existing infrastructure and ship design.

If you have the infrastructure to build the ship parts in space from in orbit existing resources - aka asteroids - then build in space. Escpecially if the rescources on earth are as scarce as they are today. That way, you dont possibly dont even need a real shipyard. On earth, you need a place for each and every ship to be build, assembled and start. In space, literally anywhere you can start to build your ship, assemble it and you dont even have to start it. Only problem would be, that you need a habitat or something similar in a close proximity for the workers. But hey, depending on the ship design you could even use drone satellites and automate the build process, just like a assembly line for cars.

If you dont have this infrastructure, do you have the technologies to easily put stuff into space? Like antigrav or even space elevator? If yes, you should still build in space, but maybe even better start building the infrastructure mentioned above.

If you dont even have that, you could, as you mentioned, send part for part into space and assemble them there. If even that isnt possible (Parts to big to send up), then maybe it would even be more useful to do start building infrastructure in space.

First, leave town, NOW there is no way of completing in the time allotted.

So the engine people probably had decades while you slept, and now after the engines are mostly done you have to complete the ship in 5-8 years. You were really taken advantage of here.

I am going to assume technology kept its current pace, either that or you have a major plot point to explain. This means our technology should be 70-100 doubling faster or better than what we have today.

So your first bit of good news is 3D printers and/or replicators should be amazing by then. Probably able to print molecules.

Your biggest problem is going to be raw materials, another person said 100,000 metric tons for an aircraft carrier so 1000 is 100,000,000 tons and you have to get it into space.

I would suggest building in outer space.

1. No pesky borders to respect, no you can't just steal russia's resources
2. No governments to deal with
3. You don't have to mine miles deep and risk cave-in's
4. Mine's usually wreck a great deal of the surrounding area.
5. The materials have to be in orbit anyway.
6. It makes lifting heavy parts easier
7. Lots of room to spread out with conflict with neighbors

So we are going to have to mine a great deal of the Kuiper belt. And your going to need vast fleets of 3D printers in space. Each one mass producing certain parts, and then lego'ing them together later. You will also need a vast mining fleet sending resources back to the shipyards at a steady pace.

Your best bet is if humanity has mastered E=mc^2 by then. Wherein, we can disassembly any matter and turn it in to any other matter with more/less produced depending on the density of the source and destination materials. This way you won't have to waste any time searching for certain types of minerals.

All matter is converted to energy and the 3D printers use the energy, not only to print but power itself. So now as long as you have a stream of matter, your 3D printers will spit out parts.

Your going to have to send up a bunch of parts to get the process started. Especially 3D printers and robots we can control from earth to assemble the printed parts. Also mining robots to capture and bring back the asteroids.

You probably need to assemble a 3D printer which can manufacture a larger 3D printer in space. Until you have one that can 3D print a whole ship at once, or large pieces of it. Any manual assembly is going to slow you way down.

So you need a 1000 ship sized printers so you can be printing them all separately. In the meantime teams of people will be needed on Earth to control all of the automation. Also more teams to get the blueprints ready for the ships so you can begin printing the moment the printers are ready.

The idea you can get your ideas on how to build a battleship from socials is a bad idea. Probably one of the reasons your Dino business failed, and why your fleet of ships could turn out horribly wrong.

Instead, if you team up with the scientific and construction communities there will be plenty of good ideas. However, each ship will have 1000's of moving parts and will all have to be tested here on Earth before they are printed in outer space.

In order to meet your economic requirements things will have had to change radically on earth. Given current economic condition 1000 battleships could and would never be paid for in time. However, if things change to a Star Trek like universe regular money would be only a fraction of the currency. Also, if you were provided a house(3d printed/replicated to your design),transportation, food, education, and probably a few other things I forgot for free (or a greatly reduced price) then you would need significantly less money.

Say everyone is given a base amount of compensation, and depending on your job you will go up a little or a lot. Engineers get a lot, floor sweep a little extra. The future might be based on energy credits where you use energy at a replicator to produce the things you need/want. Using e=mc^2 that energy is turned into matter.

In our Star Trek like universe where people acted for the common good, the problem becomes a lot easier. Say the population had some sort of voting system, and if ##% approve it is done. Costs are meaningless because things are just done. You need a crane the crane company delivers a crane, but no money is exchanged because no one is directly being paid and no one needs money. Want a steak walk up to a 3D printer/replicator, select steak and there you go.

Yes, there are people doing jobs, but they all volunteer to do their jobs because all of their other needs are met. They all enjoy doing what they are doing because they were screened by computers and your perfect job is automatically known.

We struggle on with jobs because we need to pay bills. We only need money because other people expect money from us. In my world, this simply doesn't happen, only as an exception to rule. Lets say you want 100 room mansion, you will have to perform some task(s) that provide enough value to the community to earn it and the land because it is a huge luxury and not a need. As a scientist, lets say you invent or help invent warp drive, clearly you have earned it.

It depends if your ships need to be able to enter atmosphere or not.

If they do, then you might as well build them on Earth and just fly them up.

If they don't, they will be much cheaper and simpler to build but you need to be able to assemble them in space. The question then is it easier to build the parts on Earth and fly up, mine asteroids and do the whole thing in space or use somewhere with low grav, such as the moon, to build the parts and them assemble in orbit.

The answer to that is what tech you have. Currently we really lack the tech to manufacture in space but if AI gets created and automated robots asteroid miners built, building in space would be far cheaper.

On land is cheaper for humans but more expensive to get into space. Building in space is cheaper for building but more expensive for humans. The moon is a middle ground for both.

With your timeframe, space is the only option. Tech wise you need self replicating robots, it's the only way you'd get a workforce large enough, quickly enough to complete on time.

1000 ship in five years means you need a ship complete every 1.8 days. America builds an aircraft carrier every four years.

Automated self replicating robots in space is the only option. Self replicating nanites that build the ships out of themselves would be really cool. They eat an asteroid and form ships.