[Note: While digging through unfinished blog post drafts, I found this one from April 2009. I think this was originally supposed to be the third in the series, but is now the fifth. While the series doesn’t exactly flow, and some of the examples now seem a bit anachronistic, I thought these two provided some interesting points worth consideration.]
The Impact of Divisibility on Flight Rate
One important technical thing about passengers as customers for RLV flights is that while people are not infinitely divisible1, they don’t have to be moved in large batches either. Sure, down the road if you have thousands or tens of thousands of people flying to space every year, having larger transports is eventually going to make sense2. But with realistic near-term demand, even a two-seater RLV might potentially be big enough to be useful. By flying people in smaller batches, the same nominal demand for manned spaceflight can result in a higher number of flights for a smaller vehicle, which counterintuitively could be cheaper than flying a largeer vehicle less frequently. For instance, several years back when Bigelow and LM unveiled some of their original plans for crew vehicles launched on Atlas V, Bigelow was talking about 12-16 flights per year on an Atlas V with a capsule that could sport 8 people (2 crew, 6 passengers)3. That’s somewhere between 70-100 passengers per year. If the launch vehicle instead had 1 crew and 2 passengers, that would result in 35-50 flights right there, instead of the 12-16 for a larger capsule (assuming that doing lots of berthings doesn’t screw up the microgravity for others). If the more frequent visits doesn’t hurt the microgravity too much, 35-50 flights on a tiny RLV may very well be much cheaper than flying 12-16 flights on a large ELV, or even on a partially reusable Falcon 9/Dragon V2 combo. Also more frequent crew flights would mean more opportunities for on-demand cargo deliveries. The place where larger reusable passenger transports shine (relative to small RLVs) is when there is enough demand for them to fly 50+ times per year.
Space Tourism Demand Elasticity
One other point about passengers as an RLV market is that there’s a lot of potential for elasticity of demand. While the old Futron study is now very dated4, there are some common sense reasons to believe that demand for personal spaceflight will rapidly increase if prices can come down. The single biggest factor is the distribution of wealth in the US and the world (note the number of households at each total net asset level is plotted on a logarithmic scale!)5:
The total number of households in the world with greater than $20M in assets according to this several years old data is about 100,000. The total number of households with more than $1M in assets is 7.3 million. Using the rule of thumb that Futron did (that most households won’t spend more than 10% of their value on a space trip), that means that dropping down from the ~$15-20M ticket range to a $1M ticket range would increase the number of eligible households from ~6,000 to nearly 1 million–that’s over two orders of magnitude increase! Basically, assuming that the super wealthy aren’t any more naturally inclined to spend money on space travel than the “just wealthy”, suggests that there’s a lot of potential for demand elasticity for personal orbital spaceflight as the price goes down. This is why I think prices have to come down over an order of magnitude from what even SpaceX is currently proposing before you’re going to pass the elastic point of the demand curve.
The market for flying people into space (and eventually to other destinations) is possibly going to be one of the largest early RLV market segments. Before you can really have any sort of sustained industry in LEO or on the Moon, or anywhere else for that matter, people need to be able to reach there on a regular basis. Existing transportation systems don’t provide an environment very conducive for experimenting with space-based entrepreneurial ventures. However, a transportation system that can safely, reliably, and on a regular and frequent basis transport people to orbit and back is a transportation system that is then on a level that it can enable experimentation with different space venture ideas.
- People tend to be somewhat picky that you transport them in integer quantities
- Building a 50-100 person Super Dragon or Mars Colonial Transport as some suggest seems about as wise to me as trying to build a 737 in the early 1930s
- Note: it’s interesting how far things have changed since I started this blog post 6 years ago…
- It was only a decade old when I started this blog post!
- This data is also a decade old, there are a much larger number of millionaires now then then, partially because inflation means a million dollars isn’t quite what it was worth a decade ago, and also due to increasing wealth in the upper parts of the upper and upper-middle classes.