I’ve written a lot about the technical and business implications of propellant depots, and I realized I ought to discuss some of my thoughts on the the public policy side of propellant depots.
On one hand, I think that propellant depots could probably be fielded eventually without any specific government assistance. On many levels I dislike any form of government subsidy or industrial policy, and think that most central planning is doomed to failure (see: current financial situation). While a purely market-driven approach would take a very long time to slowly bootstrap its way up to a full-service depot capability, I do think it is possible, and am currently trying to find ways to attack the problem from that direction.
On the other hand, I think it’s pretty clear that in many cases, there are existing public programs that are spending billions of dollars of taxpayer money that are being done in a less-efficient manner because propellant depots don’t yet exist. Many NASA probes and its manned exploration programs could be done more cost effectively and accomplish more if depots existed. I’ve also seen ways that the military could benefit from the existance of on-orbit refueling services and space tugs.
While I dislike government just giving away handouts, I think that in areas that our representatives have decided to spend our money, investing in ways to make those expenditures more efficient is prudent.
With that in mind, I have some thoughts on things that I think the government could do to help encourage propellant depots, as well as some ideas I’ve heard that I think the government should not do to encourage propellant depots. I’ll start with the things I would not like to see:
- I don’t think NASA should be allowed build or operate a propellant depot. A NASA-run depot is going to be subject to the same political pressures that gave us the current ISS, and will probably end up being a multi-billion dollar megaproject that in the end delivers little of its original promise (but at least keeps lots of people employed at JSC, MSFC, GRC, etc, etc). It’s not that there aren’t talented people at NASA working on technologies like this, it’s just that the institutional incentives NASA faces are probably incompatible with any sort of economically useful depot. People use the ISS as “proof” that microgravity science isuseless, and that we shouldn’t do orbital assembly or build space stations. We don’t need moer “existence proof” like that. Another reason why NASA shouldn’t run a depot is that a NASA-run depot will be a lot more restricted on who it can buy and who it can sell propellant to. While NASA could probably build a propellant depot, it’s just a bad approach all-around.
- I don’t think NASA should have a contractor build and operate a depot either (think “United Space Alliance”).  While I believe Boeing when they say that they could respond to a NASA depot RFP with a $5B depot plan, I also don’t think this is the ideal way. You end up picking winners, there will be a lot more political interference in business operations, and many of the same incentives issues that exist for NASA would exist for a “contractor run” NASA depot.
- I don’t like the idea of Congress setting aside money to “just buy a bunch of propellant on orbit”. Not only do I think it’s a political non-starter, but I hate handouts, and think it would probably end up causing more distortions and more harm than good. NASA has existing and planned projects that can use propellant depots.  There’s no legitimate reason to set up programs to buy propellants not tied to actual needs.
So here’s my thoughts on things the government could/should do to promote propellant depots:
- Continue to invest money into propellant depot research and technology development. NASA is already doing this on a small level with its SBIR program, as well as other small research projects. It would do well to reinstitute the approach O’Keefe took with the H&RT program of providing significant funding for important technology demonstration projects like this. I think such programs should be focused on driving the technology to the level of flight demonstrations as quickly as possible. Proposed cryo fluid management test beds like LM/ULA’s Centaur Test Bed and possible suborbital analogs, should make it possible to actually start reducing more of these ideas to practice with actual flight demonstrations.
- Fund the “Fuel Depot Demonstration” Centennial Challenges (early proposed rules can be found here), or something similar to it. The Centennial Challenges program hasn’t been given a cent other than in its first year. It’s used that money very carefully, and preserved most of the money for actual prizes. But they had several other interesting prizes that they wanted to roll out that they haven’t been able to due to lack of funding. This prize, for $5M nominally (though I think $10M might make it more interesting) was for a system that could store at least a certain amount of LOX and LH2 for at least 120 days. While one can argue with the details of the rules, the idea of offering small prizes for technology demonstrations is important.
- Fund the development of an Industry Standard for Passive Orbital Propellant Transfer Interfaces. There’s been a lot of talk over the years of standardizing things like docking interfaces. I think that most of those ideas are premature–docking interfaces are complex enough, and the tradespace has been sufficiently poorly explored that it’s too early to set things like that in stone. Things like a passive propellant transfer interface are ironically probably closer to a point where they could be standardized. By a passive interface, I just mean a set of quick disconnects, power/data transfer hookups, etc that could be added to the outside surface of a tanker or customer that could be connected-to manually, using robot arms, or tugs and hoses/cords. Fund some well-accepted standards group (like ASME/AIAA or someone else) to do a study to see if things really are at a point where the interfaces can be standardized. If they are, have them put together a draft standard, and get industry feedback on it. Creating a simple, publicly available standard for propellant transfer will make it easier for tug developers, tanker developers, propellant depot operators, propellant transfer customers, etc. to develop their systems.
- Once there is an accepted standard, mandate that all government flights beyond LEO be done with stages equipped with those standardized propellant transfer interfaces. A simple passive interface might be able to be used for normal fueling purposes, and might be doable in a way that adds minimal extra weight to a rocket stage, and doesn’t cost a bunch. By requiring all launch providers who want to sell to the government to incorporate that feature, that feature also becomes available to other non-government customers, allowing them to be able to take advantage of that capability without having to foot the bill for that development work by themselves. A mandated standard interface like that also helps make it so prospective depot owners know that there will be stages that can accept transfered propellant for missions where they need the capability.
- Some time after that mandated interface rule has kicked-in, require by law that NASA (and other government agencies if possible) procure propellant from a propellant-depot if available for all stages, satellites, probes, and landers outside of LEO that are too big to launch on a commercial, single-stick (ie no strapons) launch vehicle. The “if available” clause means that if a depot operator doesn’t step-up, NASA isn’t under any obligation. This might also be the case where they want to launch a mission into an inclination where they couldn’t use a depot. But in cases where they could use a depot, it requires them to obey existing laws to procure services commercially when they are available. So, in a way this is just a reaffirmation of existing statutes. It has the benefit that it reduces the risk to a depot startup that NASA would just ignore them and build their own HLVs to launch their own propellant. Lastly, by giving them the option to fly “single-stick” missions without depots, it at least allows the smaller, simpler missions that don’t actually need a depot to work to proceed unchanged.
Now, these are just some thoughts I’ve had over the past several weeks. My goal here is to set up incentives that encourage the private development of depots, reduce the risk to depot operators of NASA ignoring the law and not buying from them if they take the risk to provide that capability, while still not forcing NASA to spend lots of money developing those capabilities and infrastructure itself.
But there may be flaws I’m not seeing. What do you all think? I’d particularly like feedback from people in the Space Policy community.
Jonathan Goff
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> If you do not want to use cryogenic LOX then sulphur could be used as the oxidiser. You would have to design new rocket engines.
Are you referring to the “brimstone rocket” proposed by Vaniman, Pettit, and Heiken? It still uses LOX, the sulphur is the fuel, not the oxidiser. The intriguing advantage is that sulphur is apparently relatively plentiful on the moon, so you could produce both fuel and oxidiser on the moon, instead of importing it all the way from earth. Combined with reusable landers, vasimr cargo transport and orbital infrastructure this could lead to considerable savings in fuel or ,uch more downloaded cargo.
From what I understand ESA, unlike NASA, wants to focus a lot of its attention and lunar activities on building the sort of orbital structures inside the Earth moon system that many people on this blog are interested in…
I was just working from first principles. Sulphur is the element below oxygen in the periodic table so it should perform similar chemical reactions. A quick look at sulphur compounds showed that many were gases, giving a nice expansion = thrust. Examples SO2, H2S and CS2.
The advantage of sulphur was that is a solid over lunar temperature so it does not need refrigeration to prevent boil off. This could simplify both the depot and the rocket.
Unfortunately the Moon (unlike Mars) is short of the normal fuels like carbon, hydrogen and nitrogen. For use as a fuel or oxidiser lunar sulphur may be too rare without major mining. Oxygen is plentiful but only exists in compounds. Common lunar elements are silicon, iron, calcium, aluminium and magnesium – all of which burn when powdered.
Using solar power to extract both oxygen and metal from luna regolith then burning the pair as a propellant is possible, particularly if the mixture is lox rich.