Reusable Launch Vehicles and Lunar Return

I have a new post up at Air & Space with some follow-on thoughts on the the long-term significance of SpaceX’s recent recovery of the Falcon 9 first stage.  Comment here if desired.

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31 Responses to Reusable Launch Vehicles and Lunar Return

  1. Joe says:

    Excellent article.

    Had been thinking about the similarity between Earth suborbital and Lunar Orbit also.

    One point. At the risk of offending SpaceX fans, it is my understanding that the Falcon 9 Merlin engines can not the throttled sufficiently to allow for even a brief hover capability. In fact they can only burn the one Merlin used for descent for a short time to reduce the downward velocity, which is the reason the landing is so high speed. While that makes the successful landing all the more impressive as a technical achievement, it also limits flexibility in landing. Add to that the fact Merlin uses kerosene and its applicability to lunar use is probably limited.

    Blue Origin is another matter. It’s two engines (BE-3 – Hydrogen/LOX and BE-4 – LNG [Methane]/LOX) are both designed to be capable of such throttling and are thus potentially directly applicable for Lunar use. From some things Blue Origin has said about the BE-3, they probably took those uses into account in the engines original design requirements.

  2. billgamesh says:

    In my view the most logical sequence for establishing a long term human presence Beyond Low Earth Orbit (BLEO) is by utilizing a Super Heavy Lift Vehicle with hydrogen upper stage and the Ehricke/von Braun wet workshop concept.

    The first part of the mission being to boost the workshop to escape velocity and send it on it’s way to the Moon. The payload on top of the empty stage would be a methane/oxygen robot lander with a mix of low and hi-thrust engines. The lander would be equipped with a Zero Boil-Off (ZBO) system to maintain the propellants on the trip to the Moon. ULA is developing a piston engine system that could accomplish this and provide power for lunar surface ISRU operations.

    Ideally a future iteration of the SLS will have a pair of reusable pressure-fed boosters that can be recovered at sea in the same manner as the Shuttle boosters. The core stage hydrogen engine module may also eventually separate from the workshop and fly a free return around the Moon and back to a heat shield reentry and ocean recovery for reuse.

    As the workshop approaches the Moon the robot lander’s engines will fire to insert the stack into a lunar polar “frozen” orbit. The lander will then separate and descend on the smaller controllable thrust descent engine/s to a soft landing on an ice deposit.

    The second part of the sequence is for the lander to harvest the lunar ice and using the trapped volatiles manufacture methane as well as liquid oxygen. When the propellant tanks and water tanks are full the powerful ascent engine/s as well as the descent engine/s will fire to send the robot lander back into orbit for docking with the workshop and transfer of the water payload.

    After dozens of missions the workshop water radiation shields will be full and ready for the arrival of astronauts. By connecting two workshops together with a tether system a near-sea-level radiation and one gravity environment will be provided thus allowing unlimited stays. By mating a nuclear propulsion system to such a true space station it becomes a real spaceship capable of multi-year exploration missions to the outer solar system.

  3. I was present at the second launch and successful landing of the DC-X vehicle at White Sands on Sept 11, 1993. That second launch was the exact moment when a large rocket was reused for the very first time. At the time, officials predicted we could have a working orbital vehicle in 6 years. It has actually taken us over 22 years for private companies to duplicate this feat with working rockets carrying payloads, as the government lost interest in the concept.

    While the LOX and methane propellant combination might also be able to be produced by a lunar polar mine, using the same propellants that the DC-X used (LOX and Liquid hydrogen) are much simpler to produce there, as you only need one source component – water.

    For a reusable space vehicle to stay in space and continue to operate, it does need a source of propellant in space, where it operates. A lunar polar mining base is an ideal site for such production. All we have to do is prove that the amount of water ice is sufficient to mine, and we can start work on developing the base and its equipment.

    There are several locations where the propellant can be taken to be used by other spacecraft. Low Lunar orbit does take station keeping fuel or it will drift out of alignment. Others have proposed the Distant Retrograde Lunar orbit, and the EM-L1 and EM-L2 points; I like L1 best since it allows access to all locations on the lunar surface in 12 hours flat without regard for orbital planes, it is high in the Earths gravity well, providing a good departure point, and allows a radio quiet zone on the back side of the Moon. A round trip for a LOX/LH2 powered vehicle to deliver more LOX/LH2 propellant to an L1 base only requires only 3 parts propellant mass for every 1 part delivered as cargo.

    The two main technical areas that remain to be demonstrated at the scale needed are the transfer of cryogenic liquid propellants between tanks without requiring motion (rotation or ullage) and cryo-coolers to keep the propellant from boiling away (Zero Boil-Off condition (ZBO). There are slightly more complicated ways around both of these problems.

    The combination of a lunar polar mining base and a refueling base in space near the Moon will open up the Moon, Cis-lunar space and the inner solar system to routine operations without outrageous expense.

    John Strickland

    • billgamesh says:

      “(LOX and Liquid hydrogen) are much simpler to produce there, as you only need one source component – water.”

      Simpler to produce but not simple to store or transfer. I am always surprised at how those who claim expertise in space technology use the word simple where it simply does not apply. Storing hydrogen is a far more difficult proposition than methane because of the temperature and exothermic form- and transferring it requires pre-cooling the lines with liquid helium. Hydrogen is not “simple” unless there is a full fledged fuel farm available to handle and transfer it into the vehicle. Until some city sized lava tubes are found there will be no such handling facilities forthcoming.

      As for “Low Lunar orbit does take station keeping fuel or it will drift out of alignment”, that problem is not significant. Definitely not significant enough to open the propellant depot can of worms. A “refueling base in space” is actually the “outrageous expense” that must be avoided.

      “For the gravity field of the moon, the present analytical study demonstrates the existence of
      low-eccentricity frozen orbits in all the range of inclinations. These frozen orbits are generally
      stable, and may enjoy very low eccentricities at a handful of specific inclinations.”

      The most efficient path initially is for a robot lander to harvest surface or just-beneath-the-surface ice deposits and using the volatiles trapped in the ice to manufacture oxygen and methane for propulsion. The main requirement for astronauts in a deep space habitat is several hundred and most likely well over a thousand tons of water-as-radiation shielding. Using ISRU derived propellants the robot can ascend from the lunar surface and descend back for more water, and also use it’s engine/s for workshop orbital corrections when docked.

      Without a large human-rated lander (like Altair) and the location of lava tubes to provide ready-made radiation sanctuaries the best plan for establishing a long term presence Beyond Low Earth Orbit (BLEO) is with robot landers ferrying lunar ice products to a wet workshop space station.

      • Warren Platts says:

        “Simpler to produce but not simple to store or transfer. I am always surprised at how those who claim expertise in space technology use the word simple where it simply does not apply. … transferring it requires pre-cooling the lines with liquid helium. … Until some city sized lava tubes are found …”

        @ Gary Church: John did not discuss storage or transfer of LH2, but you vastly overestimate the difficulty. In fact LH2 has been used as a fuel for internal combustion engines (ICE) in ordinary cars, such as the BMW H7 series, in addition to the ULA ICE (it is imprecise to call this a “piston engine” as some space probes also make use of Stirling engines that also use pistons). Liquid H2 does not require transfer lines to be precooled with liquid helium, and in fact it is typically transferred via pressure–no pumps or compressors are required. Truck drivers deliver it every day over the nation’s highways. Moreover, most hydrogen fueling stations in the USA are mom ‘n’ pop-sized operations where the H2 is made onsite. Indeed, if you had bothered to read the Spudis and Lavoie proposal, their plan was to ship water to an orbital facility where the water would be cracked into rocket propellant. “City sized” lava tubes are absolutely not required. You are spreading FUD.

  4. The ULA claims that the hydrogen engines (BE3U/RL-10/XCOR) that it will use for it future ACES upper stage system will have unlimited engine restarts. The RL-10 was supposed to be the descent engines for the Altair landing vehicle.

    ACES IVF technology is supposed to be inherently reusable with the capability of being utilized with LOX/LH2 propellant depots. So it looks like there are a few American companies (ULA: Boeing, Lockheed-Martin, Blue Origin, etc.) ready to do the job of designing a single stage reusable LOX/LH2 lunar shuttle– if NASA decides it wants one.

    Such a LOX/LH2 lunar shuttle, IMO, should have the capability of traveling to and from the lunar surface from the Earth-Moon Lagrange points on a single fueling. A lunar shuttle with that capability would also be capable of taking off from the martian surface (landing on Mars will only require a delta-v of less of than 600 m/s using ADAPT or HIAD deceleration shield technology). Using propellant depots at LEO and EML1, such a lunar shuttle would also be capable of transporting passengers between LEO and EML1 without the need of the Orion MPCV.


    • Joe says:

      ” The RL-10 was supposed to be the descent engines for the Altair landing vehicle.”

      Interesting Historical point. The engines intended for use on the Altair First Stage were directly derived from the RL-105A’s developed for the DC-X. Perhaps the first direct link between reusable rocket research and Lunar Activity.

      • billgamesh says:

        The RL-10 was tested with methane but I am not sure if a deep throttle capability with methane was ever tested.

        • Joe says:


          Since, at least to the best of my knowledge, the RL-105A was the only RL-10 variant to have the “deep throttle” capability; it is doubtful it was tested with methane.

          However, the Blue Origin BE-4 is an LNG/LOX engine and, again to the best of my knowledge, it has been designed for “deep throttle” capability;

          The BE-4 has been developed to test stand level and Blue Origin and ULA have a Billion dollar contract to produce a flight qualified engine.

          Sometimes progress is made in spite of the best attempts by our political “leaders” to prevent it.

          • billgamesh says:

            Well Joe, that is all well and good but in my view the best benchmarks are all from the 1960’s and when compared none of the present efforts bode well for the future.

            Concerning solid fuel, studies were done on 15 million pound thrust monolithic boosters.
            Concerning pressure-feds 2.2 million pound thrust shuttle boosters were studied.
            Concerning hydrogen engines the M-1 would have produced upwards of 3 million pounds.
            The up-rated F-1A was ready to fly at 1.8 million.

            It was realized that these thrust ranges were what would be necessary to send worthwhile payloads Beyond Earth Orbit to the Moon. That has not changed in the slightest; multi-million pound thrust boosters are still the basic prerequisite.

            The new engines may be cheap to manufacture and perfect for lofting GEO satellites but they are woefully inadequate for Human Space Flight needs. Somewhere along the line the basic lessons learned at the dawn of the space age have been forgotten.

            At 3.6 million pounds the 5 segment SRB is not in the same class as the half-size monolithics test-fired in the 60’s but they are still the only thing available to get a starter SLS off the ground. Four of them would have been better to start with. At 800,000 pounds in a vacuum the RS-68A is not bad but has a rather low Isp for a hydrogen burner. Unfortunately because of the ablative nozzle features it was found to be incompatible with the SLS.

            Much larger engines are required for future iterations of the SLS- and there are none on the drawing board.

            But we are of course talking about lunar lander engines and not launch vehicles. The BE3 seems to me to have too much thrust (surprised?). But if a lander big enough to utilize it can be sent on it’s way to the Moon I will not complain. How do you think that could be made to work?

          • Joe says:

            “But we are of course talking about lunar lander engines and not launch vehicles. The BE3 seems to me to have too much thrust (surprised?). But if a lander big enough to utilize it can be sent on it’s way to the Moon I will not complain. How do you think that could be made to work?”

            Three Points:

            (1) The important point is the technology development. If you want a less capable version of the BE-3 or BE-4 the existence of the BE-3/BE-4 makes that much easier. Note that I am not trying to rule out use of a new variant of the RL-10, but now there are new options. The BE-3/BE-4 have been designed from the start to be compatible with Additive Manufacturing (3D Printing) and thus may be the best progenitors of engines manufactured on the Moon.

            (2) If a BE3/BE4 lander is too big for a single launch of a Block I SLS, it could be launched and assembled in LEO. That should be no more complicated than the LEO rendezvous/docking contemplated in Constellation Systems for each lunar mission and would give you a reusable lander good for multiple missions.

            (3) Absent a specific design study it is not really known what the dry mass of a BE3/BE4 Lunar Lander would be. It might not exceed the capabilities of the Block I SLS.

  5. Vladislaw says:

    “Many unanswered questions remain about the true economics of Falcon 9 reusability, including the reliability of reused stages, the costs in money and time for refurbishing and preparation for re-launch, and the flexibility of manipulating manifests and schedules to make a workable space transportation system.”

    Musk just reported they did a static test fire of the engines from the recovered 1st stage. All engines were good but one showed a thrust fluctuations

    • Paul Spudis says:

      Fine. But my original comment is still valid.

    • Joe says:

      “All engines were good but one showed a thrust fluctuations”

      That statement is self contradictory. An engine that shows “thrust fluctuations” is by definition not “good”.

      From the linked article:

      “Conducted hold-down firing of returned Falcon rocket. Data looks good overall, but engine 9 showed thrust fluctuations. Maybe some debris ingestion. Engine data looks ok. Will borescope tonight. This is one of the outer engines.”

      There could be many causes, including (but not limited to) kerosene residue in the lines. So the “kick the tires and light the fires” approach Musk has been selling is already showing signs of strain after a single flight (not 100’s or even 1,000’s of flights).

      Additionally an evaluation of the structural fatigue to entire stage must be done. Etc., Etc., Etc.

      • billgamesh says:

        “-the “kick the tires and light the fires” approach Musk has been selling is already showing signs of strain-”

        They will borescope the engine tonight huh? How about all nine? And examining just about every inch of the stage structure for stress and damage? This is pretty much a replay of the 1950’s when someone stated something to the effect that rocket science is not about flying in space- it is about cracks.

        It may turn out, like the shuttle SRB’s, that reusing the Falcon first stage does not quite break even. I doubt that- in my view it will cost far more to reuse than to simply drop in the ocean and make a new one. Only the engineers at SpaceX know what is really going on- whether this is all just a publicity stunt or if their boss is really serious about trying to make this scheme worth the time and trouble.

        The “simple truth” is that scale is the most important factor in launch vehicle design in terms of Human Space Flight Beyond Low Earth Orbit (HSF-BLEO). The falcon is nowhere near large enough to be useful. It is essentially a hobby rocket.

        The present SLS design is just a start and future iterations will have to be much more powerful for any kind of timely cislunar infrastructure development. As I have commented several times the critical missing piece of technology is not a hobby rocket first stage flying a couple times before failing- it is multi-million pound thrust pressure-fed boosters recovered at sea in the same manner as the shuttle SRBs.

        An appropriate pair of methane rocket engines- a variable low thrust and a higher thrust model- are in my view the topic that needs to be discussed here. How powerful these two engines should be for what size lander is the question. Again, scale is the most important consideration and the largest size lander possible is the way to go. Just how large a lander could be realized using a dual SLS launch scenario?

      • Vladislaw says:

        Joe, I believe this is the first time engines have been fired like this from a previous flight? Wasn’t it just more of a “let see what happens” kind of test? I would imagine the testing regime will dig in when they return more of them to play with. From what I have read, sounds like it will destined for a museum.

        • Joe says:


          Not the first time a rocket engine has been re-fired. The SSME’s from the Space Shuttle were reused many times (with refurbishment). But they were Hydrogen/LOX

          To the best of my knowledge, this is the first time a Kerosene/LOX engine has been even re-fired after an actual flight. However in repeated test stand firings, residue build up has been noted.

          Hydrogen and Methane are both cleaner burning than kerosene. That is one of the reasons Blue Origin is using LNG for the BE-4 Engine and the Russians are using it for the engines on their recently approved Soyuz 5 rocket.

    • As the Space Shuttle found out, the economics of reusable spacecraft is highly dependent on the demand for space launch services. Right now there are too many types of launch vehicles for too little launch demand.

      The real economic advantage for reusable– extraterrestrial vehicles– will be in the transport valuable commodities such as lunar water needed for drinking, washing, growing food, air production, propellant production, and radiation shielding.

      Both terrestrially launched reusable– and expendable– vehicles and reusable extraterrestrial vehicles could benefit from a surge in demand for passengers from space tourism. At least 50,000 people are currently wealthy enough to be able to afford a trip to a private space station– if any existed:-)


    • The engine that is having the difficulty was not one that was used for the stage return. S some sort of deposit occurring for the firing of its siblings is the most likely culprit. If that is indeed the case then the engine bell and especially the TC’s will need to have the deposits cleaned out between flights. A problem due to the use of RP-1.

      The BE-3 will not have that problem.

      Also other recent events brings the likely hood of a SSTO large Lunar lander closer. The funding of work for a BE-3U engine variant, the very variant required not only by Upper Stages but by a reusable Moon Lander as well. This engine on a ~150t wet stage could transport a combined crew and cargo of ~50t to and back from the surface with fueling only at one point in the round trip.

      • billgamesh says:

        If the BE-3 can throttle down to ten tons of thrust then 16 times that number is what will hover on the Moon. Correct me if I am wrong.

        It is probable the engine can be throttled down even further though- if I recall the RL-10 worked at 11-1 ratio after some “chugging” problems had been solved.

  6. Joe says:

    “A problem due to the use of RP-1.”

    Check. That is one of the reasons Blue Origin is using LNG for the BE-4 Engine and the Russians are using it for the engines on their recently approved Soyuz 5 rocket.

  7. Mark R. Whittington says:

    FYI, NASA has tinkered with reusable landers in its Morpheus and Mighty Eagles projects,

    • Paul Spudis says:

      NASA has tinkered with reusable landers in its Morpheus and Mighty Eagles projects

      Yes, I know about both of those projects, but both use storable propellants, not cryogenics.

      • Mark R. Whittington says:

        I thought Morpheus used a LOX Methane burner. Am I confused?

        • Paul Spudis says:

          I thought Morpheus used a LOX Methane

          You are correct — I was mistaken. Morpheus does use LOX-methane and was conceived as a way to deliver payloads autonomously to the cislunar localities. Mighty Eagle does not utilize cryogenics but uses a monoprop hydrogen peroxide system. It was primarily designed to validate hazard avoidance software for robotic landers.

  8. billgamesh says:

    “Their dream is that this event heralds a new age of cheap access to space, whereby reusable launch vehicles will continuously deliver various payloads to orbit, and in time, we will proceed to colonize the universe.”

    It is a wonderful fantasy that Musk has taken full advantage of. He promises much but has in reality delivered little. SpaceX has taken cargo to the ISS at more cost per pound than the shuttle and is now launching satellites for profit (subsidized by those taxpayer dollars intended for a “cheap astronaut taxi.” ) Landing back the first stage is not such a remarkable achievement compared to the space shuttle that landed back the second stage engines, fully equipped space labs, and up to 8 astronauts.

    “The greatest value to be realized from a reusable cryogenic space vehicle would come from developing a version that is permanently based in space, one that is not subjected to the extreme thermal environments of Earth orbital re-entry.”

    In my view the main difficulty in building such a cycler-type vehicle is this recurring theme of transferring propellants from some kind of miraculous gas station in space. Such a scheme is a mess any way you look at it. I submit launching propulsion modules consisting of propellant tanks and engine/s from the Moon as the likely solution. A lunar lander would lift such a module from the Moon and deliver it to the vehicle while taking on an empty module (and eventually passengers) for return to the lunar surface- where the module would likely be very slowly and meticulously refueled from an ISRU facility. Such a module might be pressure-fed which would make for a much longer and more trouble free service life than a turbopump fed system (for a significant penalty in performance).

    • Paul Spudis says:

      the main difficulty in building such a cycler-type vehicle is this recurring theme of transferring propellants from some kind of miraculous gas station in space.

      There is nothing “miraculous” involved in it; it is simply a technology that we need to mature. The fact is that in space vehicles since Apollo, cryogens have been moved from storage tanks to fuel cells. This indicates that no physical principles are violated by such transfer. We need to be able to move propellant, store it, tank it and use it throughout cislunar space and eventually, this skill must be mastered and become a part of the infrastructure of a space transportation system.

  9. Grand Lunar says:

    Nice to see a reasonable representation of what reusable systems mean, as opposed to seeing the media force feed talk of “Could this be the end of United Launch Alliance” after a single success.
    The recent return at sea that ended in a cracked leg (and the destruction the stage) also gives reason for pause.

    I’ve seen footage of DCX in action and it seemed quite the vehicle. The thing was made to fly horizontal at times, IIRC. How nice it would be to resurrect that project for a sort of universal lander (as it seems it ought to be able to operate in both atmosphere and vacuum).

    In addition to a DCX based concept for a reusable single stage lunar lander, how about a dual thrust axial lander?

    • Paul Spudis says:

      how about a dual thrust axial lander?

      For the Moon? I guess I don’t know what the advantages of such a system are.

      • Grand Lunar says:

        Here’s what I’ve found on it.
        This is from a 2009 study done by ULA (or so it says).
        Seems it makes use of an ACES.

        “The lateral propulsion system provides highly responsive, multi-axis control with maximum reliability but with inherently low, throttleable thrust. This lateral propulsion system can be a pressure fed, hypergolic system derived from existing robust engines. If technology matures sufficiently, a LO2/LH2 system could be utilized for enhanced performance. The throttleable lateral landing thrusters allow precision control of the final descent and translation rates. Since nearly all the work of descent will be performed using the high-efficiency RL10 engines, the system has a low gross weight. Even substantial hover and final descent durations using the lateral thrusters do not demand onerous propellant burdens.
        The ability to rapidly maneuver is a clear advantage enabling selection of an optimal landing site. The distribution of lateral thrusters around the lander enables management of widely varying centroid locations which occur from mission to mission. It also permits control over residual propellant slosh behaviors as the vehicle maneuvers. The loss of a single thruster has minimal impact on system behavior, providing increasing system reliability.”

        Another item of note is that it makes surface access easier, since they are closer to the ground. And it also allows for an unobstructed view of the surface when landing.

        Not sure if the design could allow for lift off as well, though I figure if it can allow for hovering capability, lift off isn’t too much of a stretch.

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