With the progress SpaceX has been making with trying to recover their F9R first stage, and their concepts for Mars Colonial Transport, BFRs, and 4000 satellite constellations, a lot of the industry has been fixated on very larger RLVs. I may very well be wrong, but I think there are actually a lot of reasons why smaller RLVs might be even more interesting.
Several years ago during a late night conversation at a Space Access Conference, Jeff Greason made the observation that for a healthy space transportation industry, you really want 2-3 healthy competitors. With only one provider, you get monopolies, two is better, but three is ideal. But for RLVs each provider probably want to maintain a small fleet (at least 2-3 airframes) of RLVs so that they can provide dependable service even if they either have a mishap or have to pull one of the vehicles for maintenance or repair. Having a single vehicle may work during the development phase where you’re transitioning into operations, but once you’re in full operations, you want enough demand for 2-3 companies with probably 2-3 vehicles per year. And for each of those vehicles, in order to get the per flight price in a really good range, you need to fly often–Jeff says 100 times per year, but I’ve heard numbers as low as 30-50 (but any way you slice it, it’s a lot of flights). That comes out to somewhere in the 120-900 flights per year range.
The problem is that there’s no real market that big if your RLVs are F9R/Vulcan class. Big LEO constellations, like what SpaceX is proposing might provide enough demand for higher flight rates, and likely will lead to useful price decreases that should help a lot, but still nowhere near enough to support a healthy RLV-centric launch industry with multiple players. That’s why I’m still intrigued with the idea of small RLVs, and think that the first market segment that ends up with multiple healthy RLV providers will actually be a lot smaller than most people think–probably vehicles in the 300-1000lb to LEO class.
300-1000lb payload class RLVs are interesting for several reasons:
- I think they truly are easier to develop than larger systems. I know that some people disagree, but once you factor in testing, iterations, ground support equipment and everything else, I think that small RLVs will be a lot cheaper to develop than large RLVs. Maybe not proportionally less than large RLVs (ie a 500lb to LEO RLV might not be 10x cheaper to develop than a 5000lb to LEO RLV), but likely enough to make it easier for multiple entrants to make it into the market.
- This is the size range where you could realistically get 1-2 people to LEO (2 would require a vehicle on the higher end of the scale). As I pointed out in Part II of this series, because an RLV by definition carries most of what you need for flying and recovering people, the delta mass needed per person is a lot lower than if you added a capsule on top of a traditional ELV. If you really could get 1-2 paying passengers to orbit, I think that would enable you to address one of the more important RLV markets.
- As I pointed out in Part III of this series, you don’t actually need that high of a flight rate or that low of a price in $/lb to LEO in order to provide a per-seat price in LEO that is near the demand elasticity point1.
- Propellant is also a nice, infinitely divisible payload that could be delivered effectively in 300-1000lb chunks. This payload is more sensitive to $/lb to LEO than people are, but is still a good RLV market. The flight rate would have to get relatively high to get the $/lb lower than a large RLV or semi-RLV flying less frequently, but even one F9R worth of propellant deliveries would provide enough of a flight rate to smaller RLVs to close the case for 1-2 air-frames.
- [Update 5/30/15 at 10:59pm — I forgot to add this point when originally writing the article] Inexpensive propellant from small RLVs could also synergize with big launch vehicles going after traditional beyond-LEO satellite markets. For instance, if you took two “all-electric” satellites, skipped out on the propellant (and excess engine capacity) needed for spiraling out from GTO, and refueled the upper stage they were launched on, you could probably do a direct to GSO delivery that was actually price competitive with the all-electric spiral-out, if the propellant cost for tanking up the upper stage was low-enough.
- Small RLV developers might also be able to take the wet lease or vehicle sales approach instead of making all their money off of selling individual flights–ie more like an airframe manufacturer than an airline. With ELVs or semi-reusable RLVs, this isn’t a practical approach, but it might be for small fully-reusable RLVs. The cost of a TSTO or air-launched TSTO RLV system might not be that much higher than the cost of 1-2 large passenger jets. If you made a system that was reliable, maintainable, and safe to operate in semi-populated areas, how many countries or private entities might want to buy or wet lease one? You might see situation where a space program or even a smallsat provider decided to buy or wet lease their own launch vehicle so they weren’t dependent on others launch manifests. It’s a bit of a paradigm shift for the industry, but XCOR is already doing a little bit of that with their Lynx vehicle.
- “Provisions” or cargo for manned or unmanned space platforms, space parts or materials for orbital construction sites, or satlets/ORUs are also a nice finely divisible market. They care a bit about $/lb to LEO, but there may be benefits to being able to deliver smaller payloads. In many of these cases, there are real benefits to getting a steady stream of smaller deliveries than one big batch per year.
Anyhow, there’s probably many more points that could be made on this topic, but I’m still of the opinion that the small RLV market is a lot more interesting than current popular opinion presupposes.