Wednesday, September 8, 2010

Dan Adamo On Propellant Depots, Tuesday, 9-7-10

Dan Adamo On Propellant Depots, Tuesday, 9-7-10

Guest: Dan Adamo. Topics: On orbit propellant depots and associated launch and flight dynamics. We welcomed Dan Adamo back to The Space Show to talk about on orbit propellant depots. Please remember that you can post comments, your own material, and even rate this show at the new Space Show blog, "The Space Show's Way Outside The Box Ideas And Plans Blog" at Please use it. Our show was more than two hours and divided into two segments. During our first segment, Dan introduced us to on orbit propellant depots and started out by describing the ISS as a propellant depot. Dan then proceeded to discuss possible depot locations and geometric constraints in servicing and working with depots in various locations. During this first segment, we had lots of email and chat questions from listeners (the phone line only opened up in the second segment), addressing libration point locations, lunar depots, LEO depots, Sun-Earth system depots and more. Dan took us through the orbital and flight mechanics so essential to making a depot location useful and economic. Also in this discussion, Dan talked about launch seasons and launch windows, explained the differences, and told us that for the Earth-Sun system, the launch season and window were essentially the same. He also introduced us to external factors impacting launch windows such as range safety issues and weather, along with launch turnaround issues. As you will hear, understanding the orbital and flight dynamics impacts the location of the depot and can easily make or break it as an acceptable location. Another issue that he brought up was space traffic management for a specific depot, something we have never done and cannot do as of today. Toward the end of this segment, nuclear propulsion was discussed and we asked Dan to prioritize space policy issues were he the man in charge. As we started the second segment, we opened the phone lines to listeners. Our first caller, John from Atlanta, wanted to know more about a lunar oriented depot. In talking about lunar depots as compared to LEO depots, Dan took us through what was involved in the Apollo lunar landings so we could better understand the issues with lunar and other depots. Other listeners had heavy lift questions, suggesting a depot was a better investment than heavy lift rockets. See what you think after listening to Dan on this subject. Regarding LEO depots, Dan talked about the need to be able to predict the orbital plane, a problem for a LEO depot. Lots of questions came up about using the ISS location for depots and the penalty paid to get there. The idea of replication was discussed, for example having 28 ISSs on orbit for lunar access. Dallas called in and talked about depots needing three things, costs, performance, and orbital alignment. Depots were viewed as one possible facilitator for helping to drive up launch rates and other things. At the end, John Jurist phoned in to ask Dan and Dallas to list as a closing statement, their priorities for space policy. Listen to what each said and then John listed his three or four priorities as well. You can ask questions or comment on the blog above or send your comments to me at and I will forward them to Dan Adamo.


  1. I think that it might be useful to listeners to the (9/7/2010) episode of the Space Show to give an outline of general concept I was discussing with Dan Adamo. Because of the format of the show by necessity the listener only gets a snapshot of my concept. Admitted a very important one as if the orbital mechanics don’t work it would be clearly a non-starter.

    First some background. What I’m going to outline isn’t in anyway a truly ideal approach. With larger development budgets no doubt a superior approach could be made that would in the long term benefit space access. The general line of thinking is what we should have done to replace the space shuttle or quite frankly what might we have done instead of it with similar financial constraints. I would like to give a lot of credit to my long term exchanges with “Googlenaut” on the Nuclear Space website on the pros and cons of continuing the current STS. His inputs no doubt led me to the line of thinking I’m going to outline here. What started out to be just a to-LEO shuttle evolved and is still an evolving set of ideas.

    The basic idea was to separate the orbiter from the main propulsion system. The result is an orbiter similar to the Dynasoar, HL-20, and HL-42 vehicles. My thought is that we would want to keep a shuttle bay and it would have the same crew capacity. It would have an OMS system as well as reaction control thrusters. Like the HL concepts it would have high thrust solid rockets in the tail as an abort system. I sized my concept based on a 10 ton payload capacity. I believe that the whole thing would have a GTOW of less than 50 tons. With advances in materials since 1970s we could beat these numbers in my non-expert opinion. It would be good to have some excess capability in order to expand the envelope beyond the most basic LEO objectives.

    To launch this orbiter I propose a 50 ton class launch vehicle. After a variety of tries, I concluded that a two-stage rocket with a first-stage could be thought of as a 40% scale Saturn V first-stage using RP-1/LOx propellant. The second-stage would be a double-sized scale up analog to the S-IVB stage using LH2/LOx. I’m assuming that modern engine designs with the first-stage having an RD-180 performance and the second at the SSME level of vacuum performance. The second-stage engine will also have a J-2 like restart capability for reasons that will become clear later. So we now have a system that can place the orbit into LEO.

    The one downside this system has compared to the shuttle is lack of reusability and only 40% of the payload. It was soon obvious to me that the rocket of course could be used without the orbit to place 50 ton payloads into LEO without any additional development. So in some ways we now have superior system. Next, I considered the possibility of making this booster reusable. My current view is that this should be feasible for the first-stage and much more questionable for the second.-stage. For this discussion, I will assume that any reuse of the final stage be in space only. The first-stage would be recovered by a balute, parachutes, and an inflatable landing system to buffer the splashdown. I assume that after engine shut down the tanks would remain pressurized to maintain structural integrity. This is a technical risk area on several fronts.

    see next post

  2. conclusion

    I would estimate that the first-stage would be about 75% of the theoretical first until cost of such a rocket. So if we could reuse this stage perhaps 20 times it would result in a major reduction on the launch costs. The higher volume of the second-stage production would result on reduced unit costs. This should leave these vehicles much more cost-effective that the current space shuttle if a sufficient volume of launches occurs. This will seem a little more reasonable when we consider my suggestion to replace Constellation. You might be wondering at this point what any of this has to do with propellant depots.

    The forgoing is about where my thinking was when the Feb 1, 2010 announcement of new space policy was made. When I focused on potential uses for orbital propellant depots I quickly realized the capability of a refueled second-stage to launch payloads to the Moon. I fact it is far greater than an Ares V. I won’t go into specific details of lunar spacecraft architecture. If development proceed along the line I have suggested it would be somewhat different that Constellation. I’m assuming a modular assemble of the lunar vehicle with a second-stage of my launcher which would be refueled at an appropriate orbital depot for launch to the moon.

    So with the depot we turn a launcher that is below the HLV class into a to-LEO workhorse and a replacement for the Ares V. With the orbiter we have a good-enough shuttle replacement that can do most shuttle missions and regain the ability to bring payloads back to Earth. The depot will greatly expand the demand for launches as at least five would be required to transfer enough propellant to refuel an Earth Departure Stage. So the reusable feature of the launchers first-stage would become cost-effective.

    All of this hangs on the astrodynamics of launch from the depot working out. Dan Adamo indicated that his studies show some significant limitations in launch window due to orbital precession of the depot. However, launch for Earth is also limited a time do to weather conditions which would not be problem from orbit. Other major technological issues must be resolved. The recovery and reuse of first-stages is one issue. Can my proposed landing system return a booster in reusable condition? What can be done to mitigate salt water corrosion? Another big is the transfer of cryogenic propellants in orbit. However, if these challenges can be overcome the reward is great.

  3. I can't see the plus in your launcher idea. It seems to add the worst features of the current shuttle with none of its advantages? The smaller orbiter would not cost less. Adding in the cost of separate expendable boosters roughly doubles the development costs. Also the 25 ton capacity orbiters are needed to lift parts for ISS ect.

    What would make more sense to me would be a biamese orbiter design, or just a bigger orbiter with all the engines needed to lift off on the orbiter, and a big drop tank to lift extra fuel so you don't to develop it as a SSTO. Eiather would be doable for $20B under normal NASA contracting (under a third that much if developed under a more commercial dev contract), saving $50B compared to Ares/Orion or the HLV/Orion currently defined in the proposed NASA budget proposals in work, and use off the shelf systems.

    Given the current interest in returning to the moon. Building such a orbiter as capable of refueling in orbit, and then boosting to Lunar orbit and returning while carrying a fueled Lunar lander would be a quick, low cost, return to the moon program.

  4. During the show the SeaDragon and Star-Raker RLV's were disused. These are very intersting, and ridiculously capable craft, designed by AeroJet and Rockwell international respectively.

    Star Raker, was the Rockwell proposal DOE pretty much baselined their SSPS construction concept on. Big delta wing monster. I have the DOE appendix on it somewhere. The designer was one of the leeds on the Saturn–V dev program. His son tried to get the money to build a downsized 25 ton cargo cap version, but his company folded.

    Low cost, very high flight rate capacity (little to service, so multiple flights per day per ship was considered feasible), limited ground support infrastructure needs, etc. So if you were lifting huge amounts of tonnage to build a fleet of SSPS you could do it for $10-$20 a pound to LEO.

    As to Sea Dragon. It was a monster big dumb rocket designed in the ‘60’s by AeroJet. heavy steel hulls built in ship yards. Simple pressure feed rocket engines. Heavy, highly reusable, and cheap “IF” you can keep the fleet busy. And given they lifted 550 tons cargo to LEO per flight – they’d be hard to use that much capacity.

    Aerojet did a lot of research on it as far as cost reduction for manufacture and servicing.

    More details available from the chief designer at

  5. One aside. I get annoyed by Dave or others laughing off any proposal as mere "PowerPoint" space craft. Something someone should assume is as realistic as UFO report.

    Now certainly the Alt.Space folks proposals are often laughably unrealistic, and/or completely beyond their capabilities to build even if technologically possible.

    However when major aerospace firms make contract bits for gov contracts or something (like the Star-Raker above). It is a much more seriously researched proposal, by organizations with a long history of developing craft, and a hard won reputation on the line. So it should not be casually laughed off.

  6. A question I mailed Dan Adamo that might be worth discusing:

    I was curious about your Lunar (I presume surface?) depots. Are your assuming Lunar fuel manufacture? If you assume lunar fuel manufacture. The two problems I could see are your tied to a specific surface point to land (you can’t miss by a few miles and still refuel, or explore other areas of the moon. Have you considered operations where you land at a main base, then refuel and hop to another surface point, then fly back to the primary base for refueling for reboost to Earth? I remember a Concept Zubrin thought up where you use nuclear propulsion with a ship that could land no Mars and process the Mars air for more reaction mass – so you can re load your tanks, and hop around several times, before you need to refill and boost back to Earth.

    Have you done cost trade studies comparing the costs of Earth orbit refueling, vrs lunar fuel sources? I looked into that, and the fact you have to have a Earth to LEO RLV for any significant lunar or other space activities, and extra flights of said craft add very little cost per year (shuttles GAO numbs were total program cost per launch of over a billion due to low flight rates, but margin costs per flight was $60 million); flying lots of extra launches carrying fuel up costs a lot less than buying and operating a Lunar to space tanker. It even seemed refueling the Earth to LEO tanker and boosting it to Lunar orbit to refuel a lunar orbital refueling depot to refuel a lunar lander, or really pick up and carry back a Lunar to low lunar orbit shuttle.

    Have you done any cost/complexity trades on this?

  7. Response to Kelly’s comments:

    The advantage of my concept is that it is a lower technology solution. As I pointed out in my preface is not my ideal solution but it is my judgment that it fits in closer to the current NASA philosophy than a technologically advanced RLVs such as the biamese or the Paul Czysz combined-cycle SSTO craft. Biamese craft must have exceptional propellant fractions. Possible using advanced materials but I wonder if NASA is willing be so aggressive. The Czysz NASP-type vehicles are even more technologically challenging and require significant development of enabling technologies first.

    As for the cargo capacity of my orbiter, the basic concept that I started with was a pure crew transport vehicle. It occurred to me that it would be good to keep the idea of a cargo bay and the ability to transport things back down. I also thought that it would be useful to be capable to transporting both people and supplier for the ISS. However, large cargo transport is not the mission of the orbiter. For those missions the booster will be used in an unmanned mode in which it can orbit 50 tons—about twice the shuttles capability. Also, the shuttle is being retired (against my one vote) and at this point it seems that is inevitable. So what I’m proposing it a step ahead on any current program.

    In NASA were to follow something like my idea they might omit the orbiter and just use the Orion spacecraft or whatever capsule based system the chose for near term objectives.

    The other advantage is that with the orbital depots we have a practical replacement for the Ares V. In fact it would be able to send larger payloads to TLI then the now cancelled HLV. Currently NASA and Congress want to start another HLV with undefined objectives. It seems to me that perhaps this new start could be evolved into the medium-heavy booster for that propose. One thing that we agree on is that depots will require a major increase in flight rates which will make lead to lower cost per flight.

    This and my previous proposal (Orion/Delta IV) for the immediate term don’t represent the space program that I would ideally want but rather what I think might be politically possible in the short (next five years) and medium (ten to fifteen years) terms.

  8. John I don't get why you think its lower technology - but certainly its high cost. My Biamese concept - or a single launcher with big strap on tanks - or a SSTO - would require the one orbiter. Which historically would cost less then the Orion capsule/SM, or say a HLV. But you require both the Orion/orbiter class craft AND the HLV to lift it. Hence doubling the cost, and adding more design and servicing complexity and costs.

    I think your assuming the smaller sized orbiter, would be much cheaper to develop - but historically it really isn't. So the 25 ton cargo capacity craft (like the shuttle orbiters) has the same complexity and cost as something like your 10 ton orbiter, or the size of a Orion expendable. So since you are assuming the development of a new orbiter anyway....

    Agree by the way that with on-orbit refueling you don't need HLV's. Course right now Congress probably needs a HLV program to keep the space launch industry of the US from dieing -- and they probably believe Griffin and Bolden's inane claims that HLVs are needs for beyond LEO exploration.

    Personally, I'ld like to see congress dump Orion and the HLV, and take Orions systems and use off the shelf stuuff to build a Biamese, or something like a LOCKHEED “STARCLIPPER”

    Not likely to be asked of course....


  9. However when major aerospace firms make contract bits for gov contracts or something (like the Star-Raker above). It is a much more seriously researched proposal, by organizations with a long history of developing craft, and a hard won reputation on the line. So it should not be casually laughed off.

    It's not a question of laughing it off, it's a question of realizing what typically goes into a proposal, even those by reputable individuals and firms.

    All proposals that seriously push the state of the art have to make many, many assumptions, some explicit, but many more implicit. A lot of these assumptions in retrospect are seen to be clearly unrealistic. No one today serious believes that von Braun's 3 stage reusable ferry rocket could have been built (in the 1950s or today) because the assumptions built into it were in retrospect unrealistic even though von Braun was possibly the most qualified man in the world to design such a vehicle. The same applies to his space station and "Mars Project" schemes.

    Speaking of Star-Raker specifically it is instructive to note that Rockwell was same organization that could not meet the weight targets on the Space Shuttle orbiter, even when serviceability features were abandoned, a very much less ambitious project than Star-Raker.

    Most, possibly all, of the various RLV proposals over the past 50 years were (and are)unbuildable for a variety of reasons, which is why we don't have RLVs.

  10. Jim, SeaDragon didn't really push the state of the art. The only really innovative issues were the sea launch, which they actually demonstrated with real hardware. As always, the issue with SeaDragon was changing winds of political favor - and a lack of a commercial market to replace it.

    To summarize Dan's argument in regards to LEO propellant depots: if you don't get to choose the inclination and the longitude of the ascending node, then all you can vary is the argument of periapsis - and that means you have a limited launch season to the Moon or other destinations. He didn't go into as much detail on this show as he did in previous shows (which is a shame, really) but the operational effect is that *missing* a launch window almost certainly means a multi-day delay while you wait for another window. If you're at the end of the launch season, the delay could be even longer.

    The key point to keep in mind is whether or not this is a show stopper or just another operational wrinkle to iron out. For example, how much fuel does it take to "dogleg" to the Moon in a suboptimal way? Is that penalty reasonable for an abundant propellant situation?

  11. I really enjoyed the show. The fuel depot idea is intresting but doesn't seem feasible for LEO. We probably should concentrate on Heavy Lift. I can't imagine getting the funding for the project.

  12. I followed up with Dan on the launch window issue. His analysis is that a suitable LEO orbital depot would have a launch window to TLI approximately every nine days. That is forty windows per year. When you consider that weather is clearly the leading cause of launch aborts from KSC the orbital window issue probably isn’t a show stopper. (Dan admittedly favors another idea, i.e., prepositioning propellant at the objective.)

    I don’t see any major human space flight projects beyond LEO in the next few years. So I can agree that a LEO depot to the moon and a heavy lift vehicle to the moon are unlikely until the current economic situation is resolved. Why should we limit ourselves to such short term issues? Some of the best original work leading to our current space capabilities was done during the great depression. Now is the time to get our planning together so that when the opportunity comes we will make better choices that before.

    My problem with heavy lift is that we just had that program and cancelled it. So if that was the way to go when not just continue with Constellation? All that Constellation would have given us would be the ability to make an occasional trip to the Moon and the ability to stay longer, etc. It wouldn’t support an enduring presence. Propellant depots in one form or another are central to a space program that will be more that an exotic demonstration of capabilities, i.e. first on the Moon, etc.

    While other people have different concepts for the exact for the vehicles could take (Kelly’s comments for example), what I’m pointing out is that a 50 ton to LEO vehicle with about 3 million pounds of takeoff thrust coupled with the LEO depot could provide a superior capability to an Ares V. The other key is to add reusability of the first stage to make this concept affordable.

  13. The whole idea now that you need HLV to go beyond LEO is nuts. You can debate where to put a depot - but I think the need of RLV with a big improvement in serviceability, flight rate, and safety - is undeniably.

    As for constellation vs. new HLV -- basically they are shedding the redundant Ares-I and downsizing Ares-V to a cheaper initial config. Past that, I just think they figured if they didn't have some development program going - they'ld lose all the capability to ever do anything. As is NASA technical development ability is way down from what it was a decadeor two ago. US aerospace is way down to.