Here is the humor slide I started out with:

We Don’t Need No Steeking Propellant Depots!

My actual presentation:

RLV Friendly Depots

Bernard Kutter’s presentation for ULA:

Near Term Depots

and Dallas Bienhoff’s presentation for Boeing:

Space Transportation Impedance Matching

I haven’t been given a copy of Rand’s presentation yet.

[Edit, here it is, Rand says he'll probably get some annotations up later]

Anyhow, a few quick random thoughts that I don’t think anyone else has really hit upon on the intarwebs:

• One of the concepts out of Dallas’s presentation I liked was the idea of having a space transfer tug that takes landers from EML1 (L2 would also work) to some perilune trajectory, and then returns to EML1.  I’ve been toying with variants of this idea for some time.  With a Centaur-sized trasnsfer tug, fully-tanked-up in EML-1/2, you can actually bring pretty darned big landers most of the way to the lunar surface (ie leaving 1000m/s or less of delta-V for the descent), while still having enough propellant to return to lunar orbit and from there to the L-point station.  That segment is probably one of the easiest in-space segments to start doing reusable stages, since you don’t need an aerobrake, and don’t have to deal with lunar dust, just propellant transfer, and lots of engine relights.
• In a conversation with Jeff Greason late one night at the conference, we got off onto the topic of RLVs and propellant depots.  One of Jeff’s opinions is that in order to really have an industry for some service, you need enough demand to allow for 2-3 healthy competitors.  With only one provider, you get monopolies, three is ideal.  But for RLVs you probably want a small fleet (~3 vehicles) of RLVs so that you can provide dependable service even if you 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 interesting thing that Jeff mentioned was that if you postulated very small RLVs to start with (say 300-500lb to LEO net payload capacity), just one lunar mission per year would be enough to provide enough demand for an entire healthy industry by itself.  Towards the lower ends of that scale, you’d only need one “soyuz around the moon” flight, or 1-3 GEO flights that used a propellant tank-up in LEO (say using a Falcon 1 with a mini-Raptor type LOX/LH2 upper stage?) to provide enough demand for at least the starting of an industry.
  • While 300-500lb to orbit sounds tiny, that’s actually a pretty reasonable size for a first-generation RLV.  The first stage doesn’t end up being that much bigger than existing or planned suborbital vehicles, doesn’t have to have much more capability either.  The upper stage ends up down in the middle of the size range for proposed suborbital vehicles.  While it has a much higher performance requirement, and much nastier reentry environment, it’s on a size that you can realistically work with a lot easier.  Also, a lot of the TPS work can be refined by flying “expendable” upper stages on these first generation commercial suborbital launchers.
  • This would definitely require the sort of RLV-friendly depot setup I described in my presentations–you’d have to have tugs that carry all the rendezvous/docking smarts, and keep the RLV-side of the propellant system as dumb as possible
  • Propellants are a much less demanding payload than people.  Not only does this keep up-front development costs down, but it also reduces the business risk if you happen to lose a vehicle occasionally.  While high flight-rate RLVs should be capable of high reliability, we’re also talking about 1st or 2nd generation systems here, where we’re still learning a lot–and learning can be painful.
• I also liked Bernard Kutter’s graphic of the simple, single-launch, dual-fluid depot concept.  This is a simpler version of the ideas Frank Z and I came up with last year (it uses a stock Centaur-sized tank for the LH2 side of the depot), but is still quite capable–on the order of 30mT capacity is nothing to sneeze at.  With one of those in LEO and one in L2, that’s actually enough to do an ESAS-capacity lunar transportation system without Heavy Lift.
  • One of the really interesting possibilities is that if something like this demonstrator depot were chosen as a part of the money Obama has proposed for orbital refueling technology demonstration (it wouldn’t need anywhere near the full $400M-1B that Obama mentioned per technology area), if the demo system worked, it would actually be operationally useful.  Sure, you’d want to replace it and/or upgrade it down the road with lessons learned, but I’m a fan of pressing technology demos into operational service, as that’s a good way to get a lot more data out of the deal.
• I also liked how Bernard explained a lot of the cryo storage issues.  A lot of this stuff still needs to be proven in space, but they (ULA, LM, and Boeing) have a lot more experience doing related tasks than most people realize.

I probably have some more thoughts on the matter, but I’m home at sick with a cold today, so I’ll leave it at that.

Depot-Centric Human Spaceflight: Strengthening American Industry, Creating a Robust Beyond-LEO Exploration Program, and Enabling the Commercial Development of Space

Another common discussion item with RLVs is the chicken and egg problem of high flight rates. The logic typically goes something like this: RLVs tend to have more development costs (and hence higher amortization costs) than ELVs. This means that in order to be profitable, they have to fly more often than a comparably sized ELV. Most studies peg the profitability breakeven point somewhere around 30-50 flights per year–though from what I’ve seen most of those assume “black-aluminum” RLVs designed using “black aluminum” development processes. The chicken and egg problem comes from the fact that at that price point, there’s nowhere near 50 payloads per year worth of demand right now especially if you’re focusing on “existing” ELV markets. Most studies indicate that for existing ELV markets, you don’t see hardly any demand elasticity until you get your vehicle’s $/lb to orbit price below $1000/lb.

The problem is, that for a 1st Generation RLV, being able to both get to the point that you can profitably offer a price of $1000/lb, while simultaneously building up a market of 50 flights per year is extremely daunting. While I think there’s no technical reason, with chemical rockets that you couldn’t eventually get down into the $100-500/lb price range, getting anywhere near those prices for 1st Gen commercial RLVs is going to be tough for several reasons:

1. Regulatory and Insurance Learning Curves: As was pointed out in a paper a few years ago by several of the now Space Cynics, most of the costs associated with an RLV flight are likely going to be things like range costs, insurance costs, regulatory compliance, etc.  While I think many of those costs could be greatly reduced over time, there is going to be a learning curve as groups used to dealing with artillery rockets start understanding that RLVs are different animals, not just ELVs with landing gear.
2. Technology Maturation: While many of the technologies needed for making a successful RLV are more mature than I think most people appreciate, there still are some areas that are poorly developed.  The biggest one being robust, reusable thermal protection systems, and general reentry/recovery techniques.  There have been lots of research done in these areas, and there are tons of good ideas, but very few of them have ever made it even to bench-tests, let alone actual flight demonstration.  Whenever you’re developing something that has an R&D project involved, the costs and timeline can take a big hit.  Government agencies could help a lot by funding some demos of these sorts, but if they don’t, those costs will have to be amortized by that first vehicle.
3. Planning for Iterations: A point Monte Davis has made on several occasions is that one of Shuttles key flaws was that they expected the first attempt at an orbital RLV like that to be a fully operational vehicle.  There was no intention ever to treat it as an attempt, fly it a few times to figure out what needs improvement, and then do another RLV development program.  You can see the same attitude with attempts like Kistler’s K-1.  Part of how they blew so much money is that from the start they were building things up to have three operational vehicles, with no plan of iteration in the middle.  Now, this is a discussion for another post, but intentionally designing a vehicle that you know isn’t likely to be fully up to operational snuff doesn’t mean that you can’t make any revenue off of that vehicle.  But in reality you need to budget probably for more than one development program.  And that is going to make developing a 1st Gen RLV a lot more expensive than later RLVs.

There are probably other reasons beyond these, but it is likely true that a 1st Gen commercial orbital RLV is going to struggle to get their costs low enough to be able to make a profit at a $1000/lb nominal price.  It may actually be possible, but it’s also iffy enough that the industry experts any investor is likely to speak with when doing due diligence are likely to scoff at it.  And that is one of the two or three main reasons we don’t see many attempts at funding/building such vehicles (the other two being lack of a big enough demonstrated market, and the high amount of investment that needs to be raised).

All of that however is probably well-known by anyone who has looked at the problem very much.  Here’s where my counter-intuitive observation kicks in.

How Something More Expensive Can Sometimes Be Cheaper

I had been thinking a lot about these things, when a statement in a post by Tom Olsen (which I otherwise agree with a lot of) started the logical chain that led me to my observation.  Tom made the statement that he didn’t believe that $200/lb to LEO with conventional rockets could be profitable.  While I agree wholeheartedly with him for 1st Gen commercial RLVs, I think you could probably approach that number over time, even without magical new propulsion technologies or structural materials (though those wouldn’t hurt).   More importantly, the $200/lb number doesn’t seem really that relevant to me.   You don’t need to get anywhere near that to start seeing new markets appear, and to see the entire way we do things in space start changing.

This got me thinking though about what price you do need to reach before interesting things start happening.  I happened to be just in the middle of trying to write my big ominbus article about people as an RLV market when Tom wrote his article, and that’s when I made my counter-intuitive discovery:  you might not actually have to get the $/lb price of your RLV much cheaper than existing ELVs to be able to offer a per-seat ticket price low enough to reach the elastic part of the passenger spaceflight demand curve.

A long time ago, I wrote a blog article about the part of t/Space’s CE&R study where they did a reanalysis of the Futron space tourism study.  While I have some further thoughts on the implications of that study, suffice it for now to say that they found that demand numbers started getting interesting at a ticket price around $5M.

Now, I don’t personally have a lot of background on crewed vehicle design (since Masten is focusing on unmanned science payloads for the current time), so I don’t know exactly how much “payload mass” you would need per passenger to supply all the services that don’t come standard on a well-designed RLV.  But for argument’s sake, let’s say it comes out to in the 500-1000lb/person range.   The higher number is in-line with Dragon theoretically carrying either 7000lb of cargo or 7 crew (1000/lb per person), as well as HMX’s old AAS concept, which would’ve carried about 4000lb of cargo or 4 crew.  In both cases it looks like the crew capacity may be more limited by volume than by payload mass capacity, which might justify the lower 500/lb per person number.

For a $5M per seat price, assuming a two person vehicle, with one pilot and one paying passenger, that comes out to $2500/lb equivalent cargo price if you need 1000lb per person, and a whopping $5000/lb equivalent cargo price if you need only 500lb/person.  The latter price is actually comparable to the current price of an Atlas V 401 (~$4500/lb), and the former price is still higher than a basic Falcon IX (~$1700/lb depending on what the current numbers are).  So, ironically, an RLV could possibly have a lower ticket price than an ELV + capsule in spite of having a higher nominal price in $/lb for payload.

An interesting thought here is that according to t/Space’s analysis, at $5M per seat ticket prices, you could likely get ~20 passengers per year pretty quickly.  If you only initially need to hit a nominal equivalent price target of $2500-5000/lb, you might be able to make a profit at that point only flying 20 times per year at the $5M ticket price.  That’s a pretty low bar compared to needing to hit $1000/lb and 50+ flights per year.

Now, I may be all wet on this.  500-1000lb per person may be way too low.  $2500/lb may still be too hard for a 1st Gen commercial RLV.  $5M per seat may not actually get you enough demand to close your business case.  And for other cargoes like satellite delivery or propellant, the actual nominal price per pound number is going to be a lot more critical.  But it sure seems interesting, because if I’m not off-base, that may make closing the case for an RLV a lot easier.

So am I all wet on this?  Or is this something that has been obvious to everyone else for a while, and I’m only finally getting this?  Or is this as counter-intuitive to you as it was to me?

[Note: Maybe I'm just misunderstanding them, but I think most of the commenters have misunderstood what my counter-intuitive idea was. It is merely that an RLV that would have far too high of a price per pound to be competitive in the satellite launching business may still be far cheaper for launching people than an ELV with a capsule. I wasn't trying to make any statements about the specific size of the manned spaceflight market at various price points, the desirability or undesirability of orbital accommodations or anything else. I was just trying to share that observation. We'll discuss a lot of those other issues in later posts. Patience.]

The key points I previously touched on were why high flight rates are important for RLVs, and that attaining a high flight-rate would require both technology and market development.  While there are many potential markets for launch vehicles that have been discussed over the years, there are three markets–people, propellants, and “provisions”–that I think are particularly suited to early commercial RLV efforts. 

In this article I want to begin making my case for why I think that flying people is one of the most important RLV markets, by sharing an amusing analogy.

The Black Aluminum Analogy
One of the “fun” classes I took as a grad student was on analysis of composite structures. It was interesting, even though most of the class involved lots of matrix math as we worked our way through from first principles till we could understand how multi-layer composite structures behaved. One of the lectures near the end of the course discussed some more qualitative concepts now that we had a mathematical foundation. One of the ideas Professor Eastman drove home during that lecture was that composites weren’t just “black aluminum”. While it is often possible to make a composite that was roughly isotropic (say using chopped fibers in resin) and then use it as a drop-in replacement for an aluminum part, you’d be wasting a lot of the composite’s potential. To truly unlock the potential of composites, you have to understand and take advantage of their anisotropic nature.

For instance, composites allow you to put strength in the areas and directions you need it, while minimizing the strength in directions it isn’t needed. The upshot being that a properly designed composite part for a given application may, and probably should, look drastically different from an aluminum part for the same job. Another upshot is that there are some applications where what you need really doesn’t line-up well with the advantages of composites, and where an aluminum part might have been a much better choice (X33 LH2 tanks anyone?).

Black Aluminum and RLV Markets
I think this analogy is relevant to the discussion of how to use RLVs. It’s possible to use RLVs as though they were ELVs that just happen to be cheaper, or that just happen to come home from work at the end of the day. Most experienced ELV people I know who look at RLVs treat them that way. They talk about how “there aren’t enough payloads to justify developing an RLV today”, usually followed by a comment that “maybe in 20-30 years there might be”. By payloads, they tend to be thinking of satellites–because that’s one of the only things ELVs are any good for. And for a satellite, especially the way they’re done today, reusability is just a nuisance, unless it happens to make the flight cheaper. It’s just that much less payload available.

Now, this isn’t to say that the only thing RLVs have to offer is the potential of lower launch prices. Eventually, I think you’ll see satellites that take advantage of intact abort capabilities, the ability to do on-orbit checkout before release, etc. I’m just saying that for satellites most of the reusability stuff is of only secondary importance.

People though are different.

People more often then not will be flying round trips. For them, the recovery system isn’t some extraneous feature that is only useful if it makes things cheaper–it’s a fundamental part of the service. Being able to make it back home in one piece even when something goes wrong also tends to be more highly valued by breathing cargo.  The interesting thing is that the needs of the personnel transport market actually turn some of the main “drawbacks” of RLVs into strong benefits.  That recovery system is no longer “parasitic mass” that can’t be used for payload–Now it’s services already provided by the launch vehicle that don’t have to be deducted from the payload.   Of course, it is possible for a manned RLV to carry its crew in a separate capsule just like an ELV, in which case you’d lose a lot of these benefits, but it’s never been obvious to me why that that approach makes any sense.

One corollary of this is that a manned RLV doesn’t need to be able to carry anywhere near as much nominal cargo capacity to carry people as an ELV would.   Depending on the details, instead of needing 10-20klb worth of payload capacity for a 4-8 person capsule on an ELV, you might be able to fly a 2-3 person compliment with an RLV that has only 1000-3000lb worth of cargo capability.  In fact, you could consider the Falcon 9/Dragon stack to actually be a ~6klb to orbit 3STO RLV, just as readily as a 20klb to orbit TSTO with a capsule on top. Of the systems you need for a manned spacecraft, most of them already need to exist for an RLV stage–TPS, landing systems, avionics, RCS, power systems and radiators, abort recovery systems, and possibly even some basic life support hardware (if you’re shipping pressurized/biological cargoes like some of the stuff Dragon will be shipping to ISS).

While it’s outside of the scope of this blog post, before I go on, it is worth mentioning that there are two technologies/techniques that accentuate the advantages of RLVs even further–tugs and fast rendezvous techniques. But that’s a discussion for a different day. It’s also worth mentioning that the “black aluminum” treatment of RLVs extends not just to how people think about using them, but also in how people think about developing them. But that is also a discussion for another day.

In my next post in this series, I’m going to discuss a counter-intuitive result that this line of thinking led me to.

Why Flight Rate Matters: Fixed and Marginal Costs
A common conclusion found in many studies on reusable space transportation is that RLVs need at least 50 flights per year to make economic sense.  While there are a lot of assumptions that go into the specific number, the basic idea is that there’s some minimum number of flights you need to make the economics work for RLVs.  RLVs typically have higher development and fixed costs, but much lower marginal costs than a similarly sized ELV.  The more often you can fly an RLV, the lower your overall flight cost will be because each flight’s percentage of your fixed cost goes down as flight rate goes up.

Fixed costs are those things you have you have to pay for on a monthly or yearly basis regardless of how often you fly.  Stuff like facilities, payroll, overhead, capital equipment amortization (including the air frames), etc.  Marginal costs on the other hand are what it costs to add one more flight to your manifest.  This is stuff like the cost of replacing any expendable components, maintenance and refurbishment costs for the vehicle, launch insurance, mission specific engineering, propellants/consumables, any touch labor not covered under fixed costs, etc.

The fewer flights per year you have, the larger each flight’s share of the fixed costs will be.  In fact, at a low enough flight rate, reusable vehicles can sometimes end up costing more per flight than a similarly sized ELV. See the Shuttle as an example of this situation.

Terrestrial airlines are also in a similar situation.  They also have high enough fixed costs that they are only able to stay economical is by keeping their vehicles flying as often as possible.

Now, the exact number of flights necessary for a specific RLV to start running in the black will vary a lot depending on the details.  The commonly quoted magic number of 50 flights per year mentioned above depends on a lot of assumptions, not all of which may be valid.  One typical assumption that may not be valid is that the development cost for an RLV will be much higher than an ELV.  This may be true if you develop an RLV using the same processes you would use for an ELV, but there are arguments that there may be ways to use the fact that the vehicle is reusable to actually make development cheaper.  Regardless of how the numbers come out though, the fundamental reality is that RLVs need larger flight rates than most existing ELVs see in order to make economic sense.

Achieving Higher Flight Rates: Launch Supply and Demand
In order to achieve higher flight rates, you need both a vehicle capable of high flight rates and enough demand to buy all those flights.  You need both parts of the equation in order to make the business case close.  The Shuttle is a good example of what happens when you try to do an RLV that doesn’t meet either of those criteria.  The Space Shuttle fleet was incapable of coming anywhere near the 50-100 flights a year they needed to get to be economical, and there also weren’t 100 flights per year worth of payloads that the Shuttle could fly.  The end result was a very expensive RLV system that flew as infrequently as ELVs and ended up costing several times as much.

Attacking the supply side of the problem mostly involves technology development and maturation.  Operability is one key to economical RLVs–If it takes you more than a week to turn around your vehicle, there’s probably something on it that isn’t really robust enough for prime time.  If your TPS system for instance takes hundreds of people weeks to inspect, maintain, repair, and qualify for reflight, it’s probably too dangerous and marginal to use on an operational system.  It is unclear if the technology we have currently is up to this task, but this is an area where suborbital RLVs are having an important impact.  The key will be finding technologies or combinations of technologies that allow you to make engines, TPS, and other systems robust and low-maintenance while still maintaining enough performance to make the rest of the design close.

Now, while us rocket nerds love debating things like the technical aspects of making a low-cost, robust RLV, the demand side is probably even more important.  One of the common refrains you hear from industry veterans about RLVs is “where’s the money going to come from to pay for enough payloads?”  As Rand Simberg used to say in his usenet tagline back when I was first getting into the whole space thing “Extraordinary launch vehicles require extraordinary markets”.  While focusing on the technology side of the problem, and using an “if you build it they will come” approach to handling demand might be a great deal for those who end up buying your company’s bankrupt corpse, it’s probably not the route that ought to be taken if you actually want to make a profit for your original investors.

So, what kind of payload types are best suited for RLVs? Why don’t I start out first by talking about an important payload type that probably isn’t.  Satellites–at least as they are done today–are probably not a good fit, for several reasons:

• Not very many satellites are launched per year
• Many of them are going to higher altitude destinations (high LEO, MEO, or even GEO), which most RLVs would have a hard time reaching without an expendable kick stage
• Satellites tend to go into a wide variety of orbits, including a wide range of inclinations, apogees, and perigees.  This requires more mission-specific engineering, more time for regulatory compliance such as getting launch licenses (especially if the RLV is using an inland spaceport as may well be the case), and all of this generally means a lot more time between an order and a flight.  This may result in a higher margin for satellite flights, but the lead times will be longer
• Satellites tend to require a lot of handholding.  Lots of testing and unique integration work that may be not be applicable to any other satellite.
• Most existing satellite developers are very conservative.  While price is a factor, perceived risk and insurance costs are also very important.
• Satellites don’t start showing significant demand elasticity with lower prices until the prices have dropped substantially from existing levels.
• Even if the demand does pick up, it will still take several years for that demand to ramp up, since satellite design/build/test programs can often last a long time.

Now, these problems aren’t impossible to solve.  Given enough time, the market will adjust to new capabilities, and there may be ways to get higher launch demand out of existing satellite customers, using techniques like the ones Dave Salt has proposed for GEO launches (launch the propellant for the GTO and GEO insertion burns separately from the satellite itself using multiple launches and orbital rendezvous/propellant transfer).  But the reality is that for the near future, satellites really aren’t that great of a market for reusable launch vehicles.

When thinking of what the ideal payloads would be for RLVs, I could think of a couple of possible criteria:

• Doesn’t need a lot of handholding, integration work, or mission-specific engineering
• Doesn’t cost tons more than the flight would
• Provides good demand price elasticity
• Is divisible into chunks small enough to be carried by light RLVs (less than 5000lb payload)
• Provides demand for flights on a regular and consistent schedule
• Provides demand for many flights to the exact same destination (for example a station in a resonant orbit).
• Is sufficiently self-similar to allow for many flights reusing the same interfaces, and the same operating procedures
• Is tolerant of risk
• Doesn’t require several years lead-time to develop the payload

As I see it, there are three main types of “RLV Friendly Markets” that I think meet these criteria: people, propellants, and “provisions” (ie light cargo that aren’t self-contained spacecraft or satellties).  I’ll give a few thoughts of each of those in the following parts of this series.