Propellant Depot Policy Thoughts

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:

  1. 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.
  2. 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.
  3. 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:

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.

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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.
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52 Responses to Propellant Depot Policy Thoughts

  1. kert says:

    Many NASA probes and its manned exploration programs could be done more cost effectively and accomplish more
    Again, i’d like to see this substantiated with a concrete example. MSR is the current planetary exploration holy grail sought by both ESA and NASA, anyone able to demonstrate how to accomplish it cheaper with propellant depots than current minimum 5-billion dual launch approach, will win a huge support base.

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  3. Habitat Hermit says:

    I like how you listed things not to do (and agree with your reasoning) but there’s one rather big flaw that relates to your “to do” #5 and you kind of say it yourself; one can argue that NASA does not follow current legislation and mandates or at least does everything to bend around it and that Congress does not hold them accountable so why should one expect any different for the future?

    It would depend on Congress and I don’t see them changing their ways.

    In short I think you’re right to be looking for ways to do it without NASA (as you’ve mentioned earlier).

  4. Jonathan Goff Jonathan Goff says:

    HH,
    I think the key is that if there’s a specific and clear law on the books, it’s harder to dodge than a vague one. Right now, that law that requires NASA to buy commercial allows NASA to opt out if the commercial system ‘doesn’t meet their needs’. It’s really easy for NASA to claim any commercial system doesn’t meet some weird and arbitrary need X. On the other hand, with a law that requires them to use orbital propellants, if available (and with only a few exceptions), it’s a lot harder to weasel out. If they’re already carrying the mandated transfer interface, they really don’t have a huge amount of excuses at that point.

    The thing to remember is that NASA isn’t saying “neener, neener, we’re not going to follow this law”. They’re claiming “we fully support this law, but as it says we only have to buy if they meet our needs, and they don’t meet all of our needs, so ah shucks we’ll have to do it ourselves”. I think that if NASA had to break the law in a way that it was obvious they were doing so, they’d be a lot more reticent to cross that line.

    It would still matter how well Congress enforces it, but right now to a non-engineer Congressperson, I imagine they think NASA is actually in compliance with the law.

    ~Jon

  5. Jess Lomas says:

    It will be interesting to see how far the proposed beamed solar power paper gets along, if the power satellite gets built, if we get CATS by an order lower than today – then it WILL suddenly become possible to have propellant depots and space tugs. If it does come about then we will need some sort of Space Traffic Control (that every nation subscribes to, not just currently space faring) to regulate flights…

  6. gravityloss says:

    I guess you might be able to do a bigger Mars sample return mission with just one launch of the hardware if you use a propellant depot since most of the mass is trans Mars injection (TMI) propellants. (And for the people going duh, of course the propellants would still have to be lifted up there to the depot, but that is not directly coupled to the MSR mission anymore and they could be any launchers of any size, which makes the economics and reliabilities very different.)

    I’m not very familiar with the Mars sample return mission concepts out there.

  7. Andrew Swallow says:

    “Many NASA probes and its manned exploration programs could be done more cost effectively and accomplish more
    Again, i’d like to see this substantiated with a concrete example. MSR is the current planetary exploration holy grail sought by both ESA and NASA, anyone able to demonstrate how to accomplish it cheaper with propellant depots than current minimum 5-billion dual launch approach, will win a huge support base.”

    If MSR is like most space missions most of the weight is fuel. The depot becomes the second ‘launch’.

  8. jsuros says:

    Jon,

    I have to disagree with you on your #3 ‘would not like to see’ above; your objection to the idea of “just buy[ing] a bunch of propellant on orbit”.

    If the Federal Government were to take the attitude that rocket propellant in LEO is a strategic resource and would pay to establish a stockpile (as it does for metals, diamonds, etc.) it would become the “anchor tenant” of an expanded spacelift industry. Suppose the stockpile was lifted using EELVs only, 8 tons at a time, using the entire annual capacity for manufacturing CBCs.

    After 5 years there would be something on the order of a thousand tons of propellant in orbit awaiting missions to use it, the EELV development costs would be paid off, and launch operations planning and management would have been streamlined through the implacable force of desperation. All for less than one year of NASAs current budget, too.

    Throw in some details like the launch company can bump any scheduled propellant flight for a higher paying customer so long as the rest of the flight schedule is not delayed, and this plan swallows the existing space launch market without a ripple.

    I’d have congress run this program through the department of the interior (or anything but NASA) just to keep the nonsense to a minimum, but that’s just a happy fantasy. The basic idea is a better jobs program than NASA, for that matter.

  9. Tom D says:

    Jon,

    I agree with most of what you say, but I not sure I understand why congressionally-mandated propellant stockpiling is not a good thing. Although, I can see where NASA might well demand an over-engineered and extremely expensive propellant depot to store the propellant (in fact I’m almost certain that would be their response). Is that your concern?

  10. Jess Lomas says:

    Not sure where Space Island is now but they did have some valid concepts. I agree in using WBCs as a basis for initial tanks, Space Island were going to use ETs, but WBCs or developments thereof would indeed move things forward with regard lunar orbit or even the respective earth orbits.
    Yes, a lot of launches could use EELVs, bumping ‘fuel’ for more valuable cargos.
    What I didn’t mention in my earlier reply is that some company (or companies) could have space tugs in operation to clear LEO/MEO and GEO of dead satellites.
    Most who post may be enthusiasts, some like Jon work and are ‘doing’ – thankfully.

    NASA should NOT be in the job of operating, private corporations who sell should be. Common berthing adapters, common probes and pumping devices, common electrical systems, that all nations use are a must…

  11. James says:

    Hi Jon,

    I think you will need more than just passive interface standardization. I assume the vehicle taking on the propellent will want to know if the depot tank is empty, and there are probably a variety of other such cases. So I think something like the CAN bus standard for automobiles would be required as well. This should not be hard to do, IEEE might be a good venue for standardization.

    jak

  12. Jonathan Goff Jonathan Goff says:

    James,
    Yeah, I figured you would want power, data, and fluid connections.

    ~Jon

  13. corrodedNut says:

    I agree with all but the 2nd #3 of your thesis. It could prove very difficult to get all parties to agree to a common interface; think VHS vs. Beta or BlueRay vs. HD-DVD. It may be hard enough just to reach an agreement on the type of propellent. Why not let the first to orbit a functioning depot dictate the interface? You would only have to require them to license the design. The depot operator will naturally be mindful of their customers’ wishes (i.e. NASA) Winning the “depot race” could be a powerful incentive to speed development.

  14. Jonathan Goff Jonathan Goff says:

    cN,
    I wasn’t suggesting picking just one propellant combo for the standard. I was suggesting that the standard would say that LOX might have one fitting size, storable oxidizers another, storable fuels another, and cryo fuels another (with the cryo fuel interface being designed for LH2, CH4 or propane), and pressurant gasses might be a fifth size/style. Make them so you can’t accidentally hook the wrong thing up to the wrong port. Especially fuels and oxidizers.

    If it turns out that you make the standard and not all propellants end up getting used very much, at least there’s some sort of a standard.

    The thing is that there really isn’t that much to such an interface. It really can be as simple as a panel with some quick disconnect fittings and an electrical connector or two.

    ~Jon

  15. kert says:

    (And for the people going duh, of course the propellants would still have to be lifted up there to the depot, but that is not directly coupled to the MSR mission anymore and they could be any launchers of any size, which makes the economics and reliabilities very different.)
    Again, concrete examples would help. The most recent MSR reference architecture by ESA has Ariane and Atlas for launchers. How could you save significant money over that with a depot ?
    Also note by rough estimation that the launch cost for this is about 1/10th of the mission price.
    It does not seem to me that a convincing case can be made of fuel depot advantages for planetary probes. If you’d consider a series of probes, then perhaps, but they are doing one-offs these days.

  16. Pingback: Transterrestrial Musings » Blog Archive » How To Implement Prop Depots?

  17. Andrew Swallow says:

    Jonathan Goff wrote
    “If it turns out that you make the standard and not all propellants end up getting used very much, at least there’s some sort of a standard.

    The thing is that there really isn’t that much to such an interface. It really can be as simple as a panel with some quick disconnect fittings and an electrical connector or two. ”

    The interface connector panel does not have to be fully furnished. Unused connectors can be left blank, this happens with the D type computer connectors. If the depot does not sell RP-1 then that connector is not fitted. If the spacecraft does not use LH then it saves the weight by not having a cryogenic connector.

    A few raised pins and holes to automatically align the two connectors and make sure that both spacecraft are pointing in the same direction are a cheap and simple way of designing out a lot of problems.

    During docking radio communication between the depot, spacecraft and tug will probably be needed. The signalling protocols will need publishing. The radio could still be used after docking.

    One of the oldest areas of law are regulations concerning weights and measures – people have too much to gain from cheating. The meters used to measure the propellants sold will need licensing and/or checking by an independent body.

  18. john hare says:

    The first thing is to demonstrate in some manner that propellant transfer is possible and useful. Orbital propellant transfer seems to be in the same place as pre DCX VTVL.

    One possibility is on board transfer of remaining upper stage propellants to the transfer stage or satellite. The 1% or so remaining in the tanks of an upper stage could be quite useful to a GEO transfer or TLI stage. If something this relatively simple could provide any ROI at all, it could be a lever for more aggressive transfers between separate vehicles.

    IMO, the expendable tanker will precede real depots.

  19. Kelly Starks says:

    Propellant depots make a lot of technical and operational sense given certain technical assumptions (for example if you have fleets of RLV’s, launching a tanker on demand vs. no orbit banking makes more sense). They make sense to facilitate development of space. But they don’t make political sense for NASA. They transfer operations out of NASA and dramatically reduce the need for big heavy boosters. That cuts the cost per mission. Which cuts the payments per district per mission. So you undercut public – hence Congressional – support for said missions.

    Votes, not $, are the coin of the realm for a agency like NASA. By cutting costs, you cut the political “affordability” of a mission.

    Like CATS, propellant depots are a big plus for major space colonization or industrialization projects, but not for a agency like NASA.

  20. Randy Campbell says:

    John Hare wrote:
    >The first thing is to demonstrate in some manner that propellant
    >transfer is possible and useful. Orbital propellant transfer seems
    >to be in the same place as pre DCX VTVL.
    Air Force did it last year, automated rendevous and docking along with propellant transfer. Multiple times between the satellites along with other activities. We can put propellant transfer in the ‘demonstrated’ class, however both propellents in this case were non-cryo which still needs demonstration I suppose.

    >One possibility is on board transfer of remaining upper stage
    >propellants to the transfer stage or satellite. The 1% or so
    >remaining in the tanks of an upper stage could be quite useful to
    >a GEO transfer or TLI stage.

    I seem to recall that LM put out something along these lines using the Centaur.

    Randy

  21. Adam Greenwood says:

    #8, JSuros is right. The problem is in thinking about what the government objective should be. If the government objective is merely to continue with its exploration and flags-and-boots program then using the propellant depot merely to accomplish those missions cheaper makes some sense. But offering to buy propellant at a fixed rate societal expansion into space, more than just government forays, much closer to reality. Especially because offering to buy propellant in the future for missions and vehicles that may or may not happen is too much uncertainty for most investors and companies. A fixed rate offered to one and all makes more sense.

    In essence, I’m saying that if Cheap and Reliable Access To Space is your goal, it probably makes sense to offer a prize for repeated successful trips to orbit with a cargo, under a certain cost, and to make it that more than one group can get the prize, and it turns out that offering the “prize” in the form of a fixed payment or fixed bounty for propellant is administratively a lot more efficient than actually running a prize.

    Prizes are a great idea, but sometimes bounties make more sense.

  22. Alan Ladwig says:

    Jon –
    You might consider posting your thoughts on propellant depots on the “Seat at the Table” section of the change.gov sight. We’re looking for new ideas and concepts for consideration.

  23. Jonathan Goff Jonathan Goff says:

    Alan,
    Good idea. I’ll try taking care of that tonight when I get off work.

    ~Jon

  24. john hare says:

    If propellant transfer has been demonstrated on orbit, then the next step is to demonstrate usefulness (profitable). Send up the first Falcon 9 with a propellant payload instead of a dummy or expensive one. Then modify Falcon 1 upper stages for extended operations after it tanks up from the 9 tanker. Several serious lunar, GEO, or deep space missions could fly off of that one tanker load. If successful, that should set the ball rolling.

  25. Andrew Swallow says:

    Using a demo depot to put a payload launched on a Falcon-1 into lunar orbit should make a good demonstration.

  26. jsuros says:

    John,

    I take your point about expendable tankers preceding depots, but until the state of the art in launch rate operations goes up enough that a mission could count on getting the tankers up in a short time I think staging fuel ahead of a vehicle is safer.

    Interesting idea about a Falcon 9 refueling a falcon 1 upper stage. How much fuel does the falcon 1 upper stage hold, anyway?

  27. Will McLean says:

    The enormous challenge of making a propellant depot work for comsat launches is the depot must be able to offer the launch firm propellant for less than their own *marginal* cost per kg to LEO. Letting Sealanch put up the same number of satellites for three launches instead of six saves them a lot less than what they charge a customer for three launches. However, the vehicle delivering the propellant must recoup its average cost, and the depot operator must recoup their costs as well.

    Refueling the mauevering propellant of comsats from a depot near GEO makes more sense, but that’s a small market: the refueling propellant is a lot less mass than a new satellite, and a lot of them will fail for other reasons before they run out of fuel, or have so little usefull life left that they aren’t worth refueling.

  28. Eric Collins says:

    Of course it wouldn’t make sense to buy a Falcon 9 fuel tanker launch if you were only going to refuel a single Falcon 1 upper stage. You might as well just buy the Falcon 9 for your payload. Rather, if you could sell the propellant in the tanker to multiple Falcon 1 payloads, then you might be talking about a potential business.

    Just taking a quick look at the Falcon data sheets, I see that for $36.75 million dollars, a Falcon 9 could put up a 12500 kg payload into LEO. I also see that the usable propellant load for the Falcon 1 upper stage is about 8900 lbs (4045 kg). So, one F9 tanker could theoretically refuel three F1 upper stages. (possibly more if the F1 stages do not need to be completely topped off, possibly less if the mass of the tanker cuts too far into the payload mass).

    Assuming some ballpark figures for propellant mass to orbit (~11000 kg) and cost of the tanker plus launch and operations overhead (~$40 million), then we get a price point of around $3600 per kg of fuel in LEO. Does this sound right? Anybody else wanna check my numbers?

  29. john hare says:

    Eric,

    I was thinking of using the test flights of the Falcon 9 as demonstrations of the depot concept. If 3 or more Falcon 1 missions were seriously enhanced in the process, then there would be some serious evidence for the concept. It would be considerably harder to convince congress that it was too hard and dangerous if SpaceX was doing it routinely.

    From a pure economics standpoint, skipping the tanker in favor of straight Falcon 9 vehicles would be more cost effective for the small missions I suggested. If there is some doubt that the 9 will reach orbit on the first try though, it would be worth a shot. It is almost certainly too late for them to change to this configuration, even if they wanted to.

    One thing that would be enabled early is responsive enhanced light missions. With a 9 tanker in place, 1s could do target of opportunity launches to NEOs and other objects of interest at a distance.

  30. jsuros says:

    Sure, a fun late friday time waster! taking all numbers from the SpaceX site:

    The kestrel engine delivers 6900 pounds of force with an Isp of 320s and so requires 21.5625 pounds of propellant per second. This engine fires for 378 seconds (from T-174 to T-552) and so will require a total of 8150.625 pounds of propellants to complete the flight profile.

    Close enough to your number, Eric. Were you working from the volume of the second stage or something?

  31. Eric Collins says:

    John@29: The payloads for the Falcon 9 test flights are going to be Dragon capsules. Trying to prove out these two systems is probably more than enough to worry about without adding the further complexity of on-orbit refueling to the mix. Though I think it would be awesome if they could demonstrate the ability to transfer excess LOX from the upper stage into a storage tank on the Dragon module after the desired orbit is obtained. Think of it as a backup to the on-board life-support, or as a commodity which could be delivered to the ISS.

    The tanker would be more mass effective if it were integrated with the second stage so that it could take advantage of the existing tanks. However, I do not think the current tank layout would be optimal for storing the cryogenic oxygen for very long. For one thing, the tanks are the primary structure for the upper stage. Thus, the tank walls would be directly exposed to solar heating. Boil-off would likely happen very quickly. Using a dedicated tanker as a payload decouples the development requirements for a long term fuel depot/tanker from that of an upper stage propulsion system. For the Centaur, they appear to have already done alot of this development work, but for a new system like Falcon, it’s probably best to keep things simple.

    jsuros@30: I got the propellant mass from the Falcon 1 User’s Guide. There’s a nice table on page 8 with the specs for the each of the stages. Thanks for double checking.

    Now, the interesting question should be: What kinds of missions become enabled with a tanked up Falcon 1 upper stage for a given amount of propellant. In other words, how much fuel would you have to buy at $3600/kg if you wanted to take a Falcon 1 payload to GEO, the Moon, or Mars?

  32. Andrew Swallow says:

    To reuse the Falcon 1’s upper stage as a mini Earth Departure Stage (mini-EDS) the helium will probably also need refuelling. Although since helium is cryogenic fitting larger helium tanks at the same time as the refuelling interface may be simpler.

    The advantages of fitting a refuelling interface are the entire launch vehicle is several tonnes lighter and simpler than one with a third stage. The second stage’s parachute and heat shield are no longer needed.

    According to http://en.wikipedia.org/wiki/Delta-v_budget the delta V from LEO (Kennedy) are:
    LEO-GEO 4.33 km/s
    LEO-LLO 4.04 km/s
    LEO-EML2 3.43 km/s
    LEO-Low Mars orbit 6.1 km/s (via C3 without air breaking)

    LLO-lunar surface 1.87 km/s

    This should permit estimation of the amount of payload that can be sent to the above destinations.

  33. Eric Collins says:

    Ok, for those of you who may be curious, I did some BOE calculations regarding how much additional propellant would be required to reach certain destinations beyond LEO.

    For these calculations, I’m once again using the Falcon 1 User’s Guide. The Isp of the Kestrel is given as 317s, which gives an exhaust velocity of 3107 m/s. The dry mass of the second stage is 545 kg (1200 lbs). The payload masses for the Falcon 1 and 1e are given on the SpaceX website as 420 kg and 1010 kg, respectively. If your initial mass is m0 = (second stage drymass + payload mass + fuel) and your final mass is m1 = m0 – fuel, then for a given delta-v you can back out the fuel mass from the rocket equation.

    For LEO to GEO, the delta-v requirement is around 4330 m/s. So, to put a Falcon 1 payload into GEO, you would need at least 2282 kg of additional propellant. At $3600 per kg (to use the figure I came up with earlier), that comes to around $8.2 million. On top of the $7.9 million for the Falcon 1 launch to LEO, that comes out to roughly $16 million dollars to put a 420 kg payload into GEO. For a Falcon 1e, you’ll need about 4710 kg of fuel for $16.9 million. That would get your 1010 kg payload to GEO for around $26 million, except for the fact that the upper stage can only hold 3900 kg of propellant. You would have to trade a little bit of payload mass to make it to GEO on a Falcon 1e with on-orbit refueling.

    Now for something a little more interesting: A logistics/resupply mission to L1 using a Falcon 1e. Delta-v is around 3770 m/s, so you’ll need around 3677 kg of propellant at $13.2 million, for a total mission cost of about $22 million. So, whatever you’re sending to L1 better be worth about $22000 per kg.

    At that price, would it make it more or less economical to do the Propellant depot at L1? Would it make much of a difference if you were to top off a Falcon 9 upper stage/tanker to make the delivery instead?

    That’s all I have time for now. Let me know if I messed up on any of these calculations. If I get the chance, I’ll run the numbers on the Falcon 9 tanker later.

  34. Andrew Swallow says:

    To make a profit and cover development costs a commercial propellant depot will probably charge more than $3600 per kg. It is likely to be 2 or 3 times that.

    Depots at LEO and Lagrange points are not mutually exclusive, although the further from Earth the more expensive the fuel. Some missions may refuel at both depots.

    L1 and L2 are good points to transfer from capsules to lunar landers and ascent stages. A reusable lander may even be parked there between missions.

    L2 is a good point to launch “large” payloads to Mars, Venus and beyond – the spacecraft can use gravity assist from both Earth and the Moon. Doubly so if electric propulsion is being used for the interplanetary stage.

    Mars transfer vehicles can return to L2, since they can pause there.

    Example mission. Samples are returned to L2 using the same VASIMR transfer vehicle that carried the lander to Mars. The samples are then placed inside say a DragonLab for splash down on Earth. This may require several launches but the extra ones are at off the shelf rather than made-to-measure prices.

  35. Eric Collins says:

    My figures were just back of the envelope calculations. As such, they could be considered very rough estimates. Economic realities may force the price up higher, or perhaps clever engineering and/or low-delta-v transfers could reduce the price even further.

    The question I’m asking of Jon, or whomever, is if these prices would be considered attractive enough to get people interested in depot enabled architectures? Or would prices need to be brought down further before anyone would give it any serious attention? This assumes, of course, that the principal objections to depots are financial rather than technical. I have a better feeling for the technical aspects than I do for the financial concerns, which is why I’m asking.

  36. Andrew Swallow says:

    If a VASIMR transfer vehicle weighing 10 tonnes is used to transfer a 10 mT Mars lander from EML2 to Mars orbit and return 100 kg of samples it will need about a tonne of Argon propellant. This assumes a delta-V of 1.2 km/s each way, a 5000 sec ISP and a thrust of about 5 Newtons.

  37. Andrew Swallow says:

    When marketing a product there are three important financial
    questions to be asked:
    (a) How much can we make and distribute the product for?
    (b) How much can we sell the product for?
    (c) Is the sale price higher than the manufacturing and distribution
    cost?

    Eric Collins produces an estimate for the manufacturing and
    distribution cost of propellant from a depot in space. As for the a
    possible sales price on 15 November 2005 NASA Administrator
    Michael D. Griffin said on record to the American Astronautical
    Society’s 52nd Annual Conference

    “There are several ways in which the value of this extra capability
    might be calculated, but
    at a conservatively low government price of
    $10,000/kg for payload in LEO, 250 MT of fuel for
    two missions per
    year is worth $2.5 B, at government rates. If a commercial provider
    can supply
    fuel at a lower cost, both the government and the
    contractor will benefit.

    See Page 8 of
    http://www.nasa.gov/pdf/138033main_griffin_aas1.pdf

  38. Andrew Swallow says:

    If the upper stage of an Atlas V or Delta IV can be refuelled then the EELV only has to get the payload to LEO. This may allow a much heavier lander and ascent stage.

    A depot in Mars orbit may permit the ascent stage to be used to bring the samples back to LEO or L2.

  39. Jonathan Goff Jonathan Goff says:

    Andrew,
    Exactly. 20klb is actually a lot of hardware, if you can launch the propellants (and the transfer stage propellant) separately.

    But at least so far, the big areas where depots make commercial sense are:

    1-manned transportation beyond LEO (the only way to do that commercially or without HLVs)
    2-allowing otherwise impossible missions (missions that would be too heavy to launch on existing vehicles for a given country, such as JIMO for the US, or India wanting to launch the biggest GEO sats using their existing GSLV)
    3-when combined with tugs it can also allow more orbital servicing type missions that are currently impossible without propellant transfer (but most of those use non-cryo propellants).

    ~Jon

  40. Andrew Swallow says:

    A depot can sell non-cryo propellants, just leave off the zero boil off technology, or simplfy it for LOX and argon.

  41. Andrew,
    Of course! In fact depending on how things go, the first depots may very well be non-cryo ones. It sucks having to take detours like that along the way, but the business case for non-cryo depots closes a lot easier (since it doesn’t require NASA HQ to act in a non-retarded fashion).

    ~Jon

  42. kert says:

    Actually, for a cheapish demo, you’d want to refuel your Falcon I upper stages with something like Dnepr. IIRC they charge around $15M for it.

  43. Yup,
    And for propellant deliveries, Dnepr’s reliability isn’t as much of a liability. Plus, you’re ridding the world of some more ICBMs, which is a definite good thing.

    ~Jon

  44. Andrew Swallow says:

    If you are supplying propellant to Falcon-1 and Falcon-9 upper stages then both use non-cryo kerosene (RP-1). See page 8 of SpaceX’s User Guide.
    http://www.spacex.com/Falcon1UsersGuide.pdf

  45. Martijn Meijering says:

    Would it make sense to start with nitrous oxide instead of oxygen as an oxidiser to reduce cryogenic problems? I can’t find the specific impulse of N2O/kerosene, but apparently N2O/propane is on the order of 220 s. This isn’t great, but perhaps doable. Then you’d have both fuel and oxidiser that were non-cryogenic.

  46. Eric Collins says:

    I still think that the ISS would make a great place to start testing out propellant depot technologies. They already have almost everything they need on orbit to start manufacturing propellants. All that they are missing is some cryo-tanks, liquefiers, and possibly a Sabatier reactor if they wanted to throw in methane as a additional propellant choice. Plumbing might be a non-trivial task, though.

    Does anybody have any idea what it would cost to pitch this idea to NASA?

  47. Ian Smith says:

    Where would they get the raw materials?

  48. Andrew Swallow says:

    Would it make sense to start with nitrous oxide instead of oxygen as an oxidiser to reduce cryogenic problems?

    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.

  49. Eric Collins says:

    The ISS already possesses several electrolysis units, both U.S. and Russian. The raw materials are water (usually waste water or condensate), and carbon-dioxide (produced by the crew). Currently, the water is split with the oxygen being vented into the cabin and the hydrogen being dumped overboard. The plumbing already exists to connect a Sabatier reactor to the hydrogen stream, and if I’m not mistaken, one was supposed to fly with Node 3. This reactor would pull carbon-dioxide from the air and combine it with the hydrogen to form methane (CH4) and oxygen.

    For the purposes of demonstrating the key technologies required for propellant depots, only small amounts of hydrogen, oxygen, and methane need to be set aside for testing the handling properties of cryogenic fluids in micro-gravity. If the tests are successful, then perhaps a pilot plant could be established. In addition to providing fuel for reboosting the station, the depot might also be able to support a handful of ISS-servicing tugs.

  50. Chuck2200 says:

    kert: Also note by rough estimation that the launch cost for this is about 1/10th of the mission price. It does not seem to me that a convincing case can be made of fuel depot advantages for planetary probes.

    The value of depots (notice the plural) is not necessarily in the cost of the launch, but will find its greatest utility by being an “enabler”. There are only a few nations capable of launching rockets large enough to actually participate in a meaningful way in space exploration. But there are many more with decent launch capability to LEO that could participate if they were able to dedicate their lift capacity to the spacecraft, and not to the mission propellant. Remember that in some cases up to 80% of the spacecraft mass is propellant. Being able to “gas up” once in orbit before setting off on the mission would enable many more players from around the globe to participate and would enable vastly superior probes from all nations, even the big boys, to head into the solar system. A 20 ton spacecraft that is actually 20 tons of spacecraft and not 4 tons of spacecraft and 16 tons of propellant at launch is a far more useful probe.
    -Chuck

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