In this post, I’m going to air three unconventional if not unpopular opinions, then spend a few thousand words explaining my views on them. I will endeavor to use accessible math and be quite clear about which axioms can be altered. My intention is to continue the conversation and to have, in one place, a concise summary of a point of view which can be referred back to as necessary.
Rule 1: There is no problem in space that can’t be most effectively solved by building a bigger rocket on Earth.
In short, big rockets are expensive, but managing interfaces in a vacuum is much, much more expensive. Case in point: The ISS.
Unfortunately there are very few large rocket development programs to use as baselines, but there are a few. The Saturn V, which could launch 110T to LEO, cost about $1.2b to develop in 2016 dollars. The Soviet Energia was considerably cheaper. The SLS has already consumed tens of billions, but it is well understood in the industry that it is not exactly a lean program. SpaceX is developing the BFR using only internal funds, and will probably spend a similar amount to the Saturn V, though with a lower per-flight cost and much higher overall performance.
In contrast, the ISS, which tested the idea of assembling a space station from modular parts launched using a partially-reusable shuttle, has cost $150b, and has taken the better part of 30 years to build, including on-Earth fabrication. And for that cost, a disproportionately high fraction of the overall station mass is consumed by the interfaces: heavy airlocks, narrow connecting passages, and architectural constraints. Further, the station will need to be retired in the next decade or so, as the “sausage link” interfaces are subject to bending fatigue that is gradually weakening them.
Why is this true? The reason is that all large pressurized volumes require assembly from various sub-components. For Boeing jets, this is done in Renton, near Seattle. Even there, in a climate controlled factory, it is a serious headache. It requires a small army of engineers and technicians. But it is still cheaper to do it there, in the factory, than in flight or on the side of a small runway somewhere in the middle of Wyoming.
In short, as much construction and integration as possible should occur on Earth, where labor costs are about a million times lower than in space. Payloads should be launched in the largest possible units, in plug-and-play configuration. And that is why, even though building an enormous rocket is extremely expensive, it is the cheapest way to do business in space.
Are there limits to this? Yes, of course. The largest rockets ever flown delivered about 100T to orbit. It is not clear to me that rockets could efficiently deliver more than about 1000T to orbit in a single shot, with chemical rockets. This is due to fundamental limitations on the strength of materials in pressurized combustion chambers, fuel and material density, and Earth’s gravitational field. But 1000T to LEO is a very, very large chunk of stuff compared to the current model for doing business.
Note: While I personally think that there are all sorts of good reasons to pursue reusable rockets, and that larger rockets in the correct configuration are easier to make reusable due to improved margins, this rule doesn’t imply that reusable rockets are necessary. In particular, the space station would have been much cheaper and faster to build if it were launched on a Shuttle-derived expendable heavy lift stack.
Rule 2: There is no commodity resource in space that could be sold profitably on Earth.
One possible exception: The elixir of life, if it could only be obtained on the Moon.
The usual examples range from water or Helium-3 mined on the Moon, to platinum-rich asteroids, to space-based solar power.
It is important to note that none of these are intrinsically valuable. The illegal drugs are expensive because there’s a high cost to being caught making them. The diamonds are expensive because their market is manipulated. And rare metals are expensive because they’re very hard to chemically extract from rocks, but also because they’re basically never used in industry. That is to say, there is no demand for them.
In particular, of all rare, valuable commodities there isn’t a single one with a high level of baseline usage. This means that if the supply suddenly increased, because of an additional discovery, the price would collapse. Even if there was an asteroid of pure platinum orbiting the Moon, and there most certainly is not, increasing the global supply beyond baseline of about 40T/year would simply reduce the market price.
Finally, let’s consider Helium-3. Helium-3 is a nice example, because it is relatively much more abundant on the Moon, and it is currently very expensive on Earth due to rarity. It is even used in some industrial and scientific processes as a refrigerant. But in order to make a business mining it on the Moon, adequate demand to both keep costs and revenues high must exist. For this, we are told, Helium-3 is a natural fuel for nuclear fusion. There may come a time when lunar Helium-3 fuels fusion-powered interstellar voyages, but I am unable to not put that in the science fiction bucket.
So what would a space resource have to look like, quantitatively, to make a business selling it on Earth? My interest here is to be inclusive, so I will underestimate fixed costs as much as possible on the first pass. Let’s say that although currently it costs about $3000/kg to launch something to LEO on a reusable F9 flight, SpaceX’s BFR reduces that further to $100/kg. Let’s suppose that further the cost of delivering cargo to the Moon using hardware based on the BFR is $1000/kg and the cost of returning cargo from the Moon $10,000/kg, which assumes at least local oxygen propellant production. By comparison, the cost of shipping a container half way around the world is about $0.10/kg.
The question, then, is what commodity is relatively much more available on the Moon than the Earth to make up for the fact that shipping it is 100,000 times as expensive. I am not aware of any physical matter, short of the elixir of life, that would make this worthwhile. Yes, a tiny number of high net worth individuals may want to travel there for tourism, but that doesn’t approach a billion dollar industry.
But what about space-based solar power, popularized by Gerard O’Neill in The High Frontier? While shipping matter to and from space is enormously expensive, it is much cheaper to beam microwaves as they have no intrinsic mass.
Gerard O’Neill’s book was written in the early 1970s, when it seemed as though the world was headed for a Malthusian crisis of population and energy consumption. This is not the case anymore. Indeed, the fundamental challenge with space solar power is that although the solar resource in space is about 3 times as good as the best places on Earth, the transmission losses from space are comparable in magnitude. Economically, it is much cheaper to deploy solar photovoltaic panels on Earth than in space, where at best the delivery costs are 1000 times higher, the maintenance costs a million times higher, and the environment much more difficult to deal with.
As Elon Musk has concisely pointed out, the fundamental problem with space solar power is that it’s obtaining a commodity, power, somewhere where it’s expensive and selling it somewhere where it’s cheap. This is not a good business. Indeed, it would make more sense to beam power from Earth to space stations, if they needed it. And, more generally, the same goes for supply chains for any other product.
That’s not to say that microwaves have intrinsically low value. The trick is to use them for something other than carrying power, namely, information. And indeed, the majority of the space industry, and almost all of the non-military space industry, is dominated by microwave communications. The dispatching of information, through space, from specialized satellites made in factories on Earth. And SpaceX has a play in this market too, with their StarLink internet constellation. The right kinds of information, at the right place and time, are very valuable indeed.
Note: This rule doesn’t necessarily apply to Earth-based manufacturing with a step performed in zero-G LEO. There are a number of companies pursuing niche products that exploit zero-G processes to make stuff, and at a potential level of revenue adequate to cover the cost of launch and recovery. These products however, do not necessarily lead to a generic space industrial capacity, or generalize in any particular way. There is no good reason, for instance, to extract material precursors from a passing asteroid instead of launching them from Earth.
Rule 3: Self-replicating robots and matter compilers do not exist.
In answer to the previous two rules, some proponents of space settlement argue that it’s not necessary to launch giant payloads from Earth. All that needs to occur is the launch of a small, robotic egg to a convenient asteroid. Once there, it will process the raw materials to produce whatever it needs, build thrusters, antennas, copies of itself, habitats, food, televisions, whatever. This asteroid will then be a glorified robot and can be steered back to the Earth in preprocessed, highly valuable form to be used as a mine or space station or interstellar spaceship or whatever.
This idea sounds great, and variations of it have been kicking around since at least the time of the ancient Greeks. The fundamental problem is that such a compact universal factory, or egg, simply does not exist.
Indeed, the reason that there are so few countries capable of heavy industry, and all of them are very large, wealthy countries, is that industry is big. Why must industry be so big? The self-replicating machine that is modern industry requires about a million different kinds of specialists. Specialists train for years to be sufficiently efficient at their given tasks, without which the final product, such as an iPhone or fighter jet, may well take infinite time to complete.
There are numerous theoretical approaches to matter compilers, or rapid, atomic-level 3D printers, but I am not aware of any that pose a credible threat to the current industrial status quo. It would be cool, but as far as I’m concerned, we’re more likely to have a vibrant lunar Helium-3 mining industry in 50 years than access to universal matter compilers.
What does this mean? There is no way to do advanced industry in space without thousands to millions of humans. There are no miracle shortcuts. We just have to find a way to support thousands to millions of humans in space, probably on a planet with a diverse array of natural resources.