The “Fantasy” of Propellant Depots?

Space Journalist/Blogger Rob Coppinger wrote an article tonight attempting to debunk “The Fantasy of Propellant Depots“, which he makes out to be some sort of religious mantra in the New Space community.  I will admit that depots are finally starting to get a tiny bit of the attention they deserve, but that has only been within the past year or two, so calling it a religious tenet seems like a bit of a stretch.  And while Rob tries to dismiss the claim that propellant depots have the potential to “open up this final frontier”, I stand by my claim that orbital propellant transfer is one of the key technologies required for a truly spacefaring civilization.

Before I get into my rebuttal of Rob’s post though, I had an interesting side note worth mentioning.  In thinking of what to write, I decided to start by trying to figure out where I first became interested in propellant transfer and propellant depots.  I’m pretty sure it was after the Return to the Moon conference in 2004.  Because at that time I was still looking at “tinker-toys” style multiple propulsion module approaches to lunar transfer systems.  So, I did a search on this blog for propellant transfer, and realized that all the way from my very first substantiative post on this blog in June of 2005, it’s a concept I’ve been trying to hammer home.

And quite frankly, I can’t think of a better place to start this discussion than by quoting one of the first things I ever said on this blog about propellant transfer:

After quite a bit of discussion, I realized that your perspective on what constitutes “space development” or “space exploration” will greatly impact your opinion on how to best go about achieving those goals. In fact, this is a fairly valid general point: your focus determines your path.

If you think that having a small McMurdo-on-the-Moon style lunar science base is space development, then your opinion on what is an ideal method to accomplish that will differ quite a bit from someone like me who doesn’t see the moon as settled until there are dozens of settlements and hundreds of thousands of people living and working there.

If you’re only planning on sending a few people a year to a small government camp, with no intention of ever opening the moon up to commercial exploitation, building a big Shuttle Derived Heavy Lift Launch Vehicle may make a perverse amount of sense. If on the other hand you actually want to make money on the moon through say, lunar tourism, you realize that the only way you’ll ever get the costs low enough is if you have some sort of reusability built into your transportation system. Which means biting the bullet with on-orbit rendezvous, docking, propellant transfer, and vehicle assembly.

Ok, with that said, let’s jump into some of my thoughts on Rob’s article:

Missing the Elephant in the Room
In this article, Rob focuses on the economics of a propellant depot, and spends a lot of time trying to make the case that there’s no market for depots.  “But where are the customers?” he asks, all the while missing the most obvious customer for propellant depots: NASA’s manned exploration program.  I’m kind of confused really.  I’m not sure if this is some sort of a strawman–trying to make it look like we think NASA should go away entirely and that with propellant depots, commercial space can do all of the exploration by itself?  Because that’s not what any of us have been suggesting.  We’ve been suggesting that if NASA transitioned to an open exploration architecture, enabled by propellant depots, that it would allow them to do better exploration, while at the same time helping catalyze demand for commercial spaceflight and provide an anchor tenant for the infrastructure that we’ll need if we ever want to get past Apollo reruns.

I guess he could have merely forgotten the comments that started this whole conversation. As I understand it, this whole discussion started with a commenter to his post on space policy recommendations linking to Rand’s article on the same topic, which suggested ditching the NASA-operated HLV approach for a depot-centric commercial launch approach to space exploration.  Rand’s point if I may summarize was that if NASA opened up the lunar architecture to the concept of propellant transfer, not only could they launch the whole thing on existing EELVs (possibly in just two hardware launches), but they would also be opening up the largest launch market in history.  The demand for propellant on orbit for even a modest lunar program would be amazing compared to the current launch markets.

No Such Thing as a Free Launch
Before I go on about other depot markets, there were some other points in Rob’s article that bugged me a bit.  For example, one of them was when Rob goes on about all the costs of a depot.  But instead of listing anything new, he goes and lists a bunch of stuff that are typical costs for any spacecraft.  In fact, he lists several costs that are typically rolled into the cost of launch (like the cost of the launch’s ground support and the cost of shipping the rocket to its launch site).  And then he acts like this is some sort of major news that none of us depot supporters have ever thought of before.  Sure, propellant depots have costs associated with them.  We know that.  Nothing in life is free, but none of that is all that hard in the overall scheme of things.  What matters is whether or not you can keep your costs sufficiently low compared to your revenues to turn a good enough profit.  Unfortunately Rob doesn’t actually go into that at all.

LEO Satellite Demand for Depots
Getting back to markets for depots, I think Rob doesn’t really have a good idea of how a depot would likely be used.  It’s really easy to setup strawman markets that don’t make any sense, and then knock them down.  Sure, most satellites aren’t going to go “blast across to a new plane and dock for fuel.”  There are some LEO satellites that could actually use the added flexibility/lifetime that could be had if there were an easy way of refueling themselves on a regular basis (or achieving that goal through alternative means).  Rob dismisses these with the comment:

Telecoms and Earth observation satellite propellant resupply vehicles have been in development but to date, despite an obvious market and claims by developers of anchor purchasers waiting in the wings, nothing has materialised

I think Rob is missing several things here. First off, the capabilities necessary to do such services has only recently been demonstrated by the US. Most of the technology required for doing something like what Orbital Express did wasn’t really that far past what we had in the 1960s, in fact the Russians demonstrated autonomous docking and fuel transfer at around that time. The problem is that while this market is real–most of the people I’ve spoken with in industry agree that there is real need for the added operational responsiveness that tugs and depots could give LEO sats–especially after China’s recent ASAT tests–there are some serious obstacles standing in the way of potential suppliers of these services. For one, no existing US satellite is designed to be refueled on-orbit. There are ways of getting around this (you don’t have to refuel the target satellite per se for the satellite to benefit from the capability of prox ops tugs and orbital refueling), but that provides at least one hurdle that has to be met. Another hurdle is that while there is demand, a lot of it is for government satellites. And while the government can purchase off-the-shelf services, and can set up procurement programs, they can’t typically sign a contingency contract for future delivery. Which means that without the military actually procuring the money to run the development as a typical government contract, potential suppliers would have to build the systems on speculation. And the reality is that most of the big publicly traded aerospace companies have a hard time taking up projects of this size on speculation–it’s just too much risk, and most of them don’t have huge amounts of free cash to invest in such concepts either. On the opposite side of the scale, smaller entrepreneurial firms might be able to handle the risk (and maybe even raise the money), but they face the hurdle that the AF or NRO is unlikely going to let some no-name company get anywhere near one of their “precious national assets” without first making them go through a gauntlet of paperwork. It isn’t impossible, and there may very well be a way of getting around those obstacles, but they are real barriers to entry. But remember: barriers to entry do not mean that there is no market!

Lunar Robotic Explorers
Rob then goes on to unfairly dismiss another market, deep space robotic probes:

The question I raise is this, are there governments around the world that can pay to put together a 20,000kg robotic spacecraft that would also have docking technology (maybe they can buy that off the Russians) and would need the services of an in-orbit propellant depot?

Why do you need to have a 20,000kg robotic spacecraft to take advantage of a depot? Why does the spacecraft itself need to do the docking (or berthing)? The explanation Rob gives in comments is lacking. Right now, there is only one vehicle that can even deliver a payload of 15klb to lunar orbit (that’s about what Delta-IVH can do). If you wanted to send even a 16klb payload to lunar orbit, a depot would be very useful. But more to the point, Delta-IVH’s are extremely expensive. A single Atlas V 401 (or even Falcon IX) could launch the satellite and the transfer state (a refuleing capable upper stage), and then buy propellant from the depot. If the depot is commercial, and in an inclination where it can buy from the cheapest suppliers, you might be able to do such a mission at a far lower cost than you could launching it on a Delta-IVH. With a propellant depot, even stages as small as the Falcon I upper stage can put sizeable payloads into lunar orbit. A single Zenit launched tanker could provide enough propellant for something like five Falcon 1 missions. There’s no reason why customers would have to build super behemoth spacecraft to take advantage of propellant depots.

In fact, some countries, whose launchers are still fairly small (like India for instance) could benefit a lot from propellant depots. The GSLV could launch the biggest GEO sat on the market (minus circularization fuel), and in conjunction with a propellant depot, the upper stage could be refueled could then deliver those satellites to GEO. Without having to develop a new booster to do it. In fact a refueled GSLV could easily deliver even a spacecraft the size of LRO/LCROSS to lunar orbit.

Anyhow, propellant depots can make a lot of sense for launching planetary/lunar probes, especially if:

  1. It allows you to launch your mission on smaller, cheaper launchers
  2. The depot can buy propellant internationally from the lowest bidder (ie is commercial in a proper orbit)
  3. It gives enough performance that your mission can be launched at all using your existing boosters (existing Atlas V Centaurs modified for refueling can deliver more than 3x what a Delta-IVH can put into lunar orbit without).

Anyhow, enough of that for now.  My key point here is that there are potential users for propellant depots.  Some of them (military LEO sats and possibly the Indian GSLV) that could benefit from the capability sooner rather than later.  Even if NASA decides to continue ignoring propellant depots as Rob suggests, it is a technology that can probably make its way to market.  But the path to commercializing those markets is going to be really tough without a solid anchor tenant.  If NASA did adopt a more depot-centric architecture, it could go a long way towards providing the demand and breathing room for propellant depot operators that would allow them to grow those other markets until they’re ready.  In other words, if NASA actually took seriously its legal mandate to “seek and encourage to the maximum extent possible the fullest commercial use of space”, it could make it a lot easier for propellant depots to come into existence sooner, and survive long enough for the markets to adjust to and adopt those new capabilities.

Heavy Lift
One last thought before I (belatedly) go to bed.  In comments to the post, Rob states that:

A sustained presence on the Moon would help but I still think that building bigger rockets is ultimately more efficient than the entire depot Earth to orbit industry, infrastructure you would have to build to deliver this propellant, that could be on-vehicle using one big booster.

That last bit is the whole point. With depots, you no longer have to fit it all on one booster, which now has to be massive and bloated to deliver even a tiny payload to the Moon. With depots, you have a lot more size flexibility. The same depot that one day allows you to send a small lunar probe into orbit without requiring a huge launcher may on a different day allow you to send a 20-person crew to the Moon or Mars.

There are challenges that will need to be overcome on the way to implementing commercial propellant depots, but they are truly worthwhile, because without them, we’re never going to become a spacefaring society.

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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and is the founder and CEO of Altius Space Machines, a space robotics startup in Broomfield, CO. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
Jonathan Goff

Latest posts by Jonathan Goff (see all)

Jonathan Goff

About Jonathan Goff

Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and is the founder and CEO of Altius Space Machines, a space robotics startup in Broomfield, CO. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
This entry was posted in Commercial Space, International Space Collaboration, Launch Vehicles, Lunar Commerce, NASA, Propellant Depots, Space Development, Space Policy, Space Transportation. Bookmark the permalink.

21 Responses to The “Fantasy” of Propellant Depots?

  1. john hare says:

    The article didn’t seem well done to me at all.

    I wonder if he is setting up the proponents of depots to make stronger arguments. I remember a certain poster on Usenet that championed ELVs for a longtime simply to force RLV proponents to make their arguments coherent.

  2. kert says:

    Anyone care to put forth a simple concrete example that would demonstrate the benefits ? The long sought after Martian sample return is an ideal candidate.
    Currently ESA is baselining two-launch architecture ( Ariane 5 + Atlas V) with Mars orbit rendezvous, and a price tag of 4-8 billion.
    How would a propellant depot in LEO help ?

  3. Bill White says:

    Perhaps the propellant depot advocates should work up budget projections to demonstrate to the U.S. Congress that if they appropriate $X billion on depots starting in 2010 they will save $Y billion in exploration costs by 2018.

    Otherwise, depots appear to be like space elevators – yes they will be terrific in the long run – but how much of the federal budget should we allocate in the upcoming fiscal year to actually implement the idea?

    On a positive note, Rob’s article offer opportunity to answer such questions.

  4. Adam Greenwood says:

    In the 1920s, if the government were developing a combined fighter/bomber/recon/mail delivery aeroplane, you might get some private airplane pioneers arguing that it might make sense for the government to contract out the mail delivery. And it would not make sense for critics to argue that government mail delivery contracts make no sense because there’s no private market for mail delivery. Huh? I mean, Salvador Dali is alive in this time period, so maybe if he’s the critic that’s explicable, but otherwise no.

    And it would also make no sense to argue that, hey, I have a gut feeling that the fighter/bomber/recon/mail delivery option is going to be cheaper, so lets not even bother putting out mail delivery bids. The fact is that putting out bids costs the government almost nothing. NASA can set a price for a propellant depot that is cheaper than the cost of lifting propellant via its current planned architecture. It would help if NASA were willing to spend a pittance on some of the base technology research. But its probably not necessary. Making a firm commitment to buy propellant at $X/lb will get private people to start doing the work for you.

    The problem with people who want to put their faith in the big, dumb booster is that its faith. We do not know–we cannot know–how any given development path will turn out. We face known unknowns and unknown unknowns. Having a flexible architecture that’s capable of going in lots of different directions makes a lot more sense than putting all your eggs in one kludgy, jobs-program basket.

  5. David Summers says:

    I think this really boils down to a single issue:

    Launch cost scaling

    If you believe that launch costs (per kilogram delivered) go down with larger vehicles, then you want to launch fully loaded vehicles. If you think launch costs will be lower with smaller vehicles, you want to launch dry and fuel in orbit.

    Unfortunately, the only hard data points are those from NASA – and admittedly, NASA vehicles get less expensive per pound as the vehicle gets larger. That places depot proponents in the unenviable position of arguing why it will be different for them – so they argue economies of flight rate, etc. – and these arguments, for the most part, have been destroyed by NASA’s operational history.

    So you are left with either “I believe that free markets will lower the cost of space once a fungible space market exists” or “I believe that space is inherently expensive and nothing can change that.” Both are statements of belief – and are therefor not likely to be changed without extreme levels of proof.

    Personally, I think this is pretty irrelevant really… I think that NASA’s ability to help or hinder space commercialization is far smaller than people think.

  6. Eric Collins says:

    I think this really boils down to a single issue:
    Launch cost scaling

    I was just thinking about scalability. It’s my impression that the ability to scale the mass requirements of a given mission architecture are much less flexible on the big-dumb-booster architecture. Certainly you would eventually hit a ceiling, probably in the 100-150 MT range (including propellant). Beyond that, it would most likely be too expensive or impractical to build bigger-dumber-boosters.

    I think the more pressing concern raised by Mr. Coppinger’s post is one of infrastructure. Right now, on-orbit refueling is facing the same problem as wide-spread adoption of all-electric vehicles. Besides the fact that there are very few existing vehicles that utilize these technologies, there is essentially no infrastructure in place to support them. It’s your classic chicken and egg problem. The thing which makes it so hard to accept is that everybody keeps talking about how much better the newer option is over the status-quo. But until someone bites the bullet and starts establishing the infrastructure, there will be very little adoption of the newer technology.

    The conclusion to which I am inevitably drawn is that someone with deep pockets must place their bets on the market arriving once the infrastructure and services are in place. Robert Bigelow is taking such a gamble right now with his inflatable habitats. Surely, the development and establishment of on-orbit fuel depots would pale in comparison with the effort required to build something as complex as manned space-station modules.

    So, who’s next in line to make the leap from Silicon Valley millionaire to next great space entrepreneur?

  7. Aaron Williams says:

    The problem is that the case for propellant depots is written in the language of commerce, where as it will be read by lawmakers and nasa officials in the language of government. The lawmaker will read it and ask “how will this create jobs for my constituency in the short term to get me elected?” and the answer is that it probably wont in the short term. The nasa official asks “how will this get me more funding from the government?” and the answer is that it wont, it will make things less expensive and the government will say “well done making things cheaper, guess you dont need such a large budget after all.” So to get nasa to implement propellant depots as part of the plan, whats needed is either a suicidal lawmaker hellbent on maliciously cutting thousands of American jobs, or you need a masochistic nasa administrator that wants to cut thousands of his agency’s jobs AND wants a reduced budget. The President can mandate nasa to do whatever he wants, but nobodies going to follow through if it means their own political suicide, specially when the President launches on ‘fire and forget’.

    Yes propellant depots are the future, but not for nasa. Maybe we need a startup to just go out and develop them, didnt Richard Garriot just leave gaming to pursue interests in space? Maybe somebody should send him an email…

  8. Karl Hallowell says:

    If you believe that launch costs (per kilogram delivered) go down with larger vehicles, then you want to launch fully loaded vehicles. If you think launch costs will be lower with smaller vehicles, you want to launch dry and fuel in orbit.

    That’s not the correct characterization of scaling. As I see it, the two not necessarily exclusive scaling choices are 1) larger payload per launch, and 2) more frequent launches. Every mode of transportation has gone through the “bigger is better” phase, but eventually reaches (and sometimes repeatedly over history) a point of diminishing returns.

    My take is that in the US we’re pretty much reached it economically with the EELVs. Aside from NASA, there’s no one interested in payloads above 25 metric tons or so at current costs. In fact, a lot of payloads are already split payloads, two or more packages.

    OTOH, all these rockets launch at horrifically slow rates. There’s very few platforms that launch more than six times a year. The only experiences we have with mass produced rockets are the ballistic missiles. There, it appears that one can obtain substantial savings in production costs from producing hundreds or thousands of rockets. As is well known, the only mass produced rocket that has also been mass launched is the V-2, produced by Nazi Germany during the Second World War. Again we see signs that the launch frequency has resulted in substantial reductions in cost.

    There are other benefits to higher launch frequency. The key ones are knowledge and reliability. A higher launch frequency means that you have more flight data, more opportunities to test vehicle modifications, more experience in your workforce from design through to the pad crew, and insuring launches becomes more viable and predictable.

    High reliability just doesn’t make sense for a low frequency launch vehicle. If you have a manned vehicle that launches six times a year, it’s unlikely that it can maintain a failure rate of 1 in 200. That would mean a single accident on average every 30 years. The problem is that it’s unlikely that your prep and launch crews can stay on top of things for that length of time. You’d probably have the entire crew replaced over that time. Subcontractors would come and go. How do you maintain reliability when you can’t get enough information from your launches to determine whether your changes are hurting your reliability.

    OTOH, if you launch 50 times a year, then every four years, you’d launch 200 times. Thus, for a failure rate of 1 in 200, you’d expect one accident every 4 years. So your workforce would soon have the experience of hundreds of successful launches and several failures under their belt.

  9. David Summers says:

    Karl, you are just arguing that launching often is cheaper than launching a single, take it all, rocket. I may agree, but the data strongly suggests otherwise. Looking at currently commercially available rockets, the price per kg goes down with increasing GLOW. You can’t really dispute that – so NASA goes with the largest GLOW that the taxpayers will bear…

    You are saying that if we leave current experience, the cost structure will change dramatically. (And, be sure, I believe that also) But that is a belief – a leap of faith. There is very little data to support it. (The V2 data is probably the best – but there were a lot of exceptional circumstances with that…)

  10. Jonathan Goff Jonathan Goff says:

    David,
    That’s only true if you ignore development costs. Once you factor that in, you quickly find that you’re probably out into the late 2040s (if ever) before there’s even a theoretical chance that a big Shuttle Derived booster will be cheaper. The costs for the development are not sunk yet so you can’t use that argument. Starting from today, what will give us more bang for the same buck, development costs included? My bet is strongly on commercial launch vehicles.

    ~Jon

  11. David Summers says:

    Jon, you can’t use shuttle in a costing model! Shuttle is a welfare program with wings, not a spacecraft. I was thinking more of pegasus, delta series, saturn, etc.

    Presumably, the Pegasus and Delta prices include any development costs – though you can never be too sure about government programs. Even development costs scale only weakly with size, though. Pegasus was cheaper to develop than the Delta IV, perhaps – but was it 1/50 the cost? That is the ratio of payloads – so if the Pegasus development was more than 1/50 the cost of the Delta IV development program then it will never catch up in cost per kg delivered. Of course, these were very different programs, which makes the numbers not that comparable – but, like I say, to NASA they have pretty strong evidence that bigger is better.

    To me, the real advantage of a propellant depot is that it introduces competition. Competition quickly brings about optimizations / design space searches – I think the price would come down dramatically, and I don’t have to know how that would happen. Free markets just do that sort of thing… but anything involving NASA cannot be a free market. So I have to admit, I am not that excited about NASA developing a propellant depot. If NASA did it, they would think a long time, come up with the “best way” to do a depot, and build that. Any vessel that didn’t pass design reviews and inspections would not be allowed to dock at such an important national installation. Only approved vendors and customers can use the fuel, etc.

    The way this really works: build it, and NASA will be forced to use it in future vehicles as a cost saving device. But be ready to wait a while before they buy from you…

  12. Karl Hallowell says:

    David, I argue that for the current state of launch vehicles, launching more frequently gives better return (that is, cheaper cost per kg) than increasing the size of the vehicle. Further, I don’t see the “strong suggestion” you refer to. Even for the current feeble launch rates, every launch platform has high fixed costs. It is obvious that there’s significant benefit to higher launch frequency when you are launching, for example, two to three vehicles a year.

    Moving on, there’s also a huge body of evidence from the manufacture sector as a whole that increasing the life time production of a manufactured good results in a decline in the cost per unit of the good. I forget what the name of the rule of thumb is (I see it termed “learning curve” or “experience curve” in wikipedia for what that’s worth), but a doubling in the amount produced results in at least a 10% decline in price per unit.

  13. David Summers says:

    Well, I’m having trouble arguing too much, Karl, because I personally agree with you. I just think that the difference between those for and against depots can be summed up with the question of how launch costs scale… which is essentially the difference between new space and old space, in my opinion.

  14. Rand Simberg says:

    Launch cost scale much more steeply with flight rate than with vehicle size. Every space transportation architecture study ever performed abundantly confirms this.

  15. Monte Davis says:

    David @9: The V2 data is probably the best – but there were a lot of exceptional circumstances with that…

    Most significantly, people who cite “A Rocket a Day” for its tempting figure of $43K per V2 (or $13K marginal cost, both WWII $USD) rarely go on to acknowledge that even at a production run of 6,240, the $2B development cost works out to about $350K per V2.

    For comparison, a Sherman tank cost $33K; a Mustang fighter $51K; a B-17 $140K.

    To me, “we could get great economies of scale if our space access efforts followed the example of an increasingly desperate dictator with no more judgement about bang/buck than a bratwurst” has never been a terribly compelling argument.

  16. Monte Davis says:

    So you are left with either “I believe that free markets will lower the cost of space once a fungible space market exists” or “I believe that space is inherently expensive and nothing can change that.”

    You’re excluding the middle. I have no reason to doubt that free markets will lower the cost — but it will happen slowly, by small percentages per decade rather than by multiples or orders of magnitude, because they’re starting in a zone of much higher real startup cost and much narrower market drivers than any previous new domain of transportation. That, rather than space per se, is what’s “inherently expensive.”

    To use the well-worn comparisons with Columbus and the Wright brothers: by “much higher real startup cost” I mean that Columbus’ expedition happened in a world in which thousands of ships just like his, from hundreds of shipyards, were already routinely making money in European, Mediterranean and North Atlantic waters. The Wright brothers’ innovations were financed by the spare cash of a two-man bicycle shop. Neither situation is remotely like that we face in space.

    By “narrower market drivers” I mean that within a few decades after Columbus — and with little technological advance in ships — gold was pouring in from the Americas, gold and slaves from West Africa, spices and other luxuries from the Indian Ocean and East Indies… with sugar and tobacco in the wings. I mean that within 15 years of Kitty Hawk, governments bought tens of thousands of aircraft during WWI. A couple of years after that, scheduled commercial point-to-point air transport was beginning — because large numbers of people had already long been traveling from London to Paris, Berlin to Vienna, etc., paying extra for speed, so air travel was a no-brainer extension. (Even then, it should be noted, direct and de facto government subsidy was important to the expansion of commercial air transport.)

    Again, space is very different: unless you’re a believer in the wonders of He3, or in mass hypersonic transport just around the corner, the only near-term drivers are science, national prestige, and extreme tourism (which is a very different thing from point-to-point travel to run colonies, do business, or visit Aunt Agnes). Yes, I do believe in SSP, other space resources, and eventually flourishing colonies as long-term drivers — but it’s the relatively modest near-term drivers, and their relatively modest returns, that have to bootstrap us to where those become feasible.

    Free markets are powerful and important, but they’re not magic.

  17. Monte Davis says:

    oops… intended after that first “already” 🙁

  18. Dave Salt says:

    Hi Jon,

    I think Rob’s analysis is somewhat disingenuous because it implies that people are arguing for orbiting propellant depots because they would make sense with respect to the current space paradigm. Obviously they don’t and all his article does is set out the basic reasons why this is so.

    Now, maybe there are some “enthusiasts” out there who are arguing this way but, from my experience, most present the case in a somewhat different manner: they recognise the constraints imposed by the current paradigm and try to figure out ways in which it could be changed. In my opinion, this is what NewSpace is all about.

    Most see the cost of space access (i.e. launch costs) as being the greatest constraint, though many also site things like launcher availability and reliability as well as the demanding design and operational requirements they place upon payloads. Reusable launchers are considered the best way to reduce most of these constraints but current market demands are either too small or too conservative (e.g. comsats) to justify their development. So, this raises the question: what can be done to increase/evolve current markets and, more importantly, develop new ones?

    Unfortunately, there is *no* easy answer to this question; no single solution that could change things, though some regard space tourism as one such a “killer app”. However, many consider the vast sums spent on government programmes as having the potential to tip the balance towards a new paradigm by fostering the development of new markets that encourage the development of new launch systems. Employing orbiting propellant depots within future human space exploration architectures would be one way of doing this because the majority of the “payload” launched into orbit would most likely be propellant (i.e. assuming no propulsion breakthroughs like gas-core fission or fusion engines). As such, it which would be amenable to launch by a wide range of systems and, more importantly, it could be utilised by other future government programmes and/or commercial ventures, once its utility has been demonstrated.

    Concepts such as orbiting propellant depots therefore represent ways in which government resources (i.e. technology, credibility… cash!) can be used to foster a paradigm shift in the way we explore and, more importantly, exploit space for the benefit of all human kind. Nevertheless, many still consider the current paradigm as the best or only way to achieve this goal. Based upon his article, I assume Rob believe this too.

    Dave

  19. Exploration Fan says:

    “Rand’s article on the same topic, which suggested ditching the NASA-operated HLV approach for a depot-centric commercial launch approach to space exploration. Rand’s point if I may summarize was that if NASA opened up the lunar architecture to the concept of propellant transfer, not only could they launch the whole thing on existing EELVs (possibly in just two hardware launches), but they would also be opening up the largest launch market in history. The demand for propellant on orbit for even a modest lunar program would be amazing compared to the current launch markets.”

    This has got to be one of the major game changing opportunities in the whole concept of space access. In one swoop we triple the annual launch requirement from the current ~300 klb/year, to ~900 klb/year. This has the likely effect of encouraging mass competition and reduced launch costs not only for space exploration but commercial and national security needs as well.

  20. Jonathan Goff Jonathan Goff says:

    Exploration Fan,
    “This has got to be one of the major game changing opportunities in the whole concept of space access. In one swoop we triple the annual launch requirement from the current ~300 klb/year, to ~900 klb/year. This has the likely effect of encouraging mass competition and reduced launch costs not only for space exploration but commercial and national security needs as well.”

    It’s even more of a game changer than if that was another 600klb of satellites. Propellant is an easy first market for RLVs. Low-risk, simple interface, not as much mission-specific engineering, and it can be divided down into much smaller chunks if you want to do a small RLV. A 1klb to LEO RLV could easily get past the 50-100 flights a year worth of demand minimum feasibility point, while still only taking 1/6th of that market.

    ~Jon

  21. Exploration Fan says:

    “It’s even more of a game changer than…”

    I fully agree with you. I have no idea what form of transportation will prove to be the most cost effective and robust: high flight rate with small payload; medium flight rate, medium payload; or infrequent launches of very massive rockets. Using propellant depots you don’t have to bet on the answer to this. The competitive launch market will determine the true answer. The depot will enable space utilization/exploration to win regardless of the answer.

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