Quick Notes: Debunking The PLF Volume Argument for HLVs

I noticed during the DIRECT presentation at today’s HSF public meeting, that they were asked why they would need an HLV if they had depots.  Now, I didn’t hear the exact question, since I had a phone call come in just a few minutes earlier (ironically enough from one of my friends in the depot community), but I think the questioner was asking about drylaunching a lunar stack on an EELV and then tanking up at a depot.  The reply given was that while an EELV could loft the mass, it couldn’t handle the volume.

Now, I have a lot of respect for the DIRECT guys, and have to give them kudos for even mentioning depots, but the fact is that this argument for heavy lift isn’t anywhere near as solid as it appears on the surface.  The fact is that there are many ways you could use dry-launch/propellant depot techniques to do ESAS-sized missions without the need of a big fairing or an HLV.  It may be true that you can’t cram the current Altair conceptual design into a Delta-IV fairing, however there are several legitimate alternatives out there to the current Altair concept, that can do the same job without requiring anything bigger than the already massive 5m fairings that come with existing EELVs.  And it’s important to remember that Altair is still in the early conceptual phase, where even fairly significant changes don’t really cost that much yet.

I want to keep this post brief, so I’ll just list a few options out there:

  1. Horizontal landers: I don’t have the latest numbers, but the most recent numbers I’ve found show the LSAM descent stage holding only a little more propellant than a Centaur stage.  A horizontal lander of the type described by ULA in their papers could easily fit within the fairing of an EELV.  Even more so if based on 5m diameter tanking.
  2. Crasher stage landers: It’s possible to split a lander up such that the descent burn is mostly done by a “crasher stage”, which is dropped shortly before the final landing burn (with shortly possibly being over a minute before).  This means that your actual lander stage can be a lot smaller and more compact.
  3. EDS TLI burn: There’s nothing that says the LOI burn has to be done by the LSAM.  An EDS that’s big enough to do the TLI burn can still be fit within an EELV fairing, especially if using a 5m diameter stage like the Common Upper Stage.  With the lander descent stage only having to do the actual descent burn, it can be a lot more tightly packed.
  4. LLO depots: If you have a depot in lunar orbit that is regularly topped off, you can tank up the lander stage after doing the LOI burn and before doing the landing.  This allows for less tankage, since you don’t have to size the lander for both LOI and lunar descent.  Alternately, if you have a reusable lunar lander (ie an SSTO lander designed to work with depots), you can send that lander independently from LEO to to the lunar vicinity.
  5. L2 rendezvous: Having the CEV separate from the lunar stack prior to LOI, and then perform its own powered swingby maneuver greatly reduces the size of the lunar stack that needs to perform the LOI burn.  At this point having either the EDS or the lander do the burn allows for a much smaller lander.

And the list could go on and on.  Basically, so long as you don’t stick to “black aluminum” lander and transfer stage strategies, you can actually use depots to enable ESAS-equivalent landings without needing HLVs or big payload fairings.  There may be other arguments for big fairings (Mars reentry shields if we can’t get hypercones or rocket decelerators to do the trick, other large payloads, who knows), but this isn’t it.

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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

About Jonathan Goff

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

17 Responses to Quick Notes: Debunking The PLF Volume Argument for HLVs

  1. Martijn Meijering says:

    All good suggestions, and I’d like to add my own old favourite: hypergolic landers. And of course, many of these ideas can be combined.

  2. Rand Simberg says:

    This is what I mean by looking at exploration architectures, rather than launch architectures. You have to take a big-picture, systems approach.

  3. MG says:

    Is it fair to suggest that NASA’s launch architecture decision used the “we can’t get a propellant depot in place before our 2020 lunar landing deadline” as a justification for their ARES cr@p?

    Silly me, it would seem that a more thoughtful administrator *might* have returned to the White House and said, “Ya know, if you give us an extra XX years, we can do [insert propellant depot enabled architecture here]”.

    Lost opportunities — whole governments are built on them, and nations die from them.

  4. MG,
    The problem is that in many cases, the “shortcut” is really the longest possible route between two points. Adding a depot into the architecture could very well shorten the time to first lunar landing. Though admittedly, I have to say that the state of propellant depot technology (and more importantly, public knowledge of its status) has improved markedly over the past four years.


  5. MG says:

    Other than pretty graphics of LM concepts, I haven’t dug into the details of current depot proposals. However, seeing how nothing is magical about a specific landing date, it seems a no-brainer to go back to the authority to get a change in the date, if it provides big advantages in the out years.

    There IS the small matter of it being impolitic in some extremely uptight circles, or if it violates what the administrator is already predisposed towards.

  6. Chris says:

    If your launch vehicles are cheap enough, you could also switch the EDS and lander fuel to propane, an alcohol or kerosene. That would save a huge amount of volume.

    Sure it’s 50% higher launch mass, but if you’re pumping out the vehicles like Camrys who cares? If you were really bold you would subcontract fuel delivery to Zenit and CZ-5 and launch the mission critical gear on more reliable American launchers.

  7. Martijn Meijering says:


    Dense propellants are indeed nice, although their Isp is typically significantly lower than LOX/LH2. If they’re storable as well, it gets even better, because you can take low-energy routes to transport your propellant. This allows you to recover some of the lost performance. Alcohol and kerosene are of course storable, but LOX isn’t (yet). If you use a storable oxidiser (H2O2 or NTO), you can eliminate that drawback, again at some performance penalty.

    You would have to develop new engines of course, because AFAIK there are no operational deeply throttleable alcohol/H2O2 engines. This is the big advantage of MMH/NTO, there’s an enormous amount of experience with it. It’s even hypergolic which is very nice for safety and very useful for reusable systems. It’s also very toxic, carcinogenic and corrosive, but NASA and ULA have a lot of experience dealing with these substances safely. In the longer term using gelled propellants would reduce the safety risk and increase density even further. Metal loading would increase density yet further and also improve Isp.

    To put the performance loss into perspective, here are some numbers:

    By my calculations (no warranty!), under current Constellation plans every kg of landed mass (including the lander itself, residuals etc) on the moon requires 4.04 kg IMLEO. Using a hypergolic lander (and assuming the same dry mass for the lander) you need 4.35 kg IMLEO. That’s a performance penalty of less than 10%, for which you get a lot of safety, eliminate the need for a large EDS and get to introduce depots early, since hypergolic fluid transfer has been demonstrated in orbit for years and is currently being used on the ISS.

    Still, at some point you would likely want to switch to a different propellant because of the handling costs of MMH/NTO. LOX/LH2 is an obvious choice, especially once propellant depots are operational and doubly so with lunar ISRU. Higher silanes + H2O2 are also very interesting ISRU propellants: they are less toxic than MMH/NTO, have better Isp, have good density, are hypergolic and can be mostly sourced from ISRU.

  8. Pete says:

    Since it will be some time before any of this happens anyway…

    So apparently there is this ~4kW/kg thin film solar suggested for solar power satellites. This could also make some pretty effective solar powered high ISP stages using far less of a perhaps easier to store propellant. This does not have the power density to get to and from the lunar surface – though a hybrid system might (perhaps one reusable stage all the way there and back to LEO).

    Will higher ISP solar powered systems be possible by the time propellant depots arrive? Or by the time anyone gets back to the moon? Should they be developed and planned on now?


  9. Martijn Meijering says:

    Shannon also used the Altair volume argument in his Not-Shuttle-C presentation to the Augustine commission yesterday.

  10. Chris says:

    LH2 isn’t storable, but LOX, methane and other mild cryogens are plenty storable for an almost infinite duration with a cryocooler and a minimum of insulation. Going with mild cryogens means an extra 30s isp and low cost ground handling compared to hypergolics.

    There is a cost trade, between low complexity hypergols and existing engines, and moderate complexity cryo storage and a billion dollar engine development program that needs to be made. If we are launching hundreds of rockets with fuel for a lunar program, and particularly if we are pulling that fuel using high isp electric tug to lunar orbit, at some point going with more complex mild cryogens like lox/methane or lox/propane may make sense.

    If we are going with hypergolics we most certainly should be going with what the russians use, UDMH and N2O4, because we can take fuel transfer hardware, fuel lines, valves, engines, etc used with zvezda, soyuz and progress straight off the shelf with zero development.

  11. Martijn Meijering says:

    I wasn’t aware that LOX would be that easy. If that’s really the case, then kerolox sounds very interesting. Mixing in some silane with the hydrocarbons might be enough to get back hypergolicity, I vaguely remember reading something to that effect. Hypergolicity is very nice for reuse and reliability.

    You could also use higher silanes instead of hydrocarbons, which are supposed to be less toxic than MMH and have slightly better Isp and combustion properties than the corresponding hydrocarbons. They also have better ISRU potential.

    In the short run, I would still prefer MMH/NTO since that’s what’s being planned for Orion and Altair and I would like both to be refuelable. Propellant gels and metal loading also decrease handling risks and improve Isp and ISRU potential. Toxicity and low Isp with MMH/NTO is clearly an issue, but the more I read about it, the more it appears there are good ways to mitigate that.

    And there’s also the issue of reusability. I think that for the near term LOX/LH2 is going to be much harder to make reusable than MMH/NTO which has been used and reused for ages with OMS. I have no idea how difficult it would be to make kerolox engines that are reusable in space.

    On UDMH/MMH/hydrazine and NTO/MON I’m told by knowledgeable sources that the required modifications are minimal.

    Of course there’s also HAN and other green propellants. If you can find a propellant that is dense, hypergolic, completely non-cryogenic and non-toxic that would be great. Higher silanes + H2O2 might be that combinations, especially with metal loading. For certain applications high up in the Earth’s gravity well, or other circumstances where delta-v’s are small you may not need very high Isp.

  12. Rick Boozer says:

    Proponents of DIRECT that I know have thrown up the argument to me about the diameter restrictions of EELVs requiring HLVs for beyond Earth orbit missions. Now I can send them to this web page.

    I am really looking forward to reading your article about how to use dual-launched EELVs for manned missions, when you are able get around to it.

  13. Fred Willett says:

    The elephant in the room with the Augustine panel is the jobs currently supporting the shuttle. Jobs that will go with any sensible architecture.
    Atlas V, Delta IV, Falcon 9, Taurus II all have their own work forces.
    making any of these a prime LV for NASA dooms most of the shuttle workforce.
    Ares 1,V is designed to keep as much of the shuttle workforce in place as possible. Mike admitted as much.
    That inevitably means that Ares I,V is an expensive program as costs relate very closely to jobs.
    Augustine’s problem is that budgets are going to be tight going forward due to the economy. But to do the sensible thing and move to an existing (or soon to be existing) EELV would be to doom Ares 1,V. Doom shuttle jobs, upset loads of senators and congressmen (and women).
    Logic has nothing to do with it. It’s all about the elephant.
    And it’s pretty big.

  14. kert says:

    Jon has probably seen this, as he frequents the NSF forums, but here goes anyway:

    However, they are sufficient to show that an L2 rendezvous mission can be accomplished with two launches of a vehicle capable of sending 25 tonnes to TLI. This is less than half the capacity of the baseline Ares V, and opens up a range of more cost-effective launch vehicle options.

    Well written letter.

  15. Martijn Meijering says:

    I agree about the jobs issue, although I wonder to what degree someone like senator Nelson cares about people losing their jobs compared to net job losses or even just the amount of federal money spent in Florida.

    Shuttle extension and building new pads for Atlas and Delta (preferably at LC-39 to make return of the shuttle or an SDLV more difficult) would be a good way to direct pork to Florida in the short term. The same goes for increasing Orion’s budget, accelerating work on Altair and work on new hardware, say – my favourite – a hypergolics depot. COTS-D would work in the slightly longer term.

  16. Fred Willett says:

    It ought not to be about jobs in that infrastructure per the original vision; Depots, tug, reusable lunar lander etc could generate a lot of jobs plus money freed up from an overly expensive launch architecture could free up $$$ and jobs to go into more exploration/science/R&D.
    It’s just that NASA seems fixated on the Ares i,V as the only way to keep jobs and I can’t see anything that will change that.

  17. Andrew Swallow says:

    The lunar Orion + Ares I is probably a never fly combination. Run them for a few more years and the Shuttle will have gone, taking the launch and repair jobs with it. The restrictions these jobs place on NASA will also have gone. There are better ways of removing the restrictions but they require management rather than being automatic.

    If you want a propellant depot and space tug architecture get small ones operating and allow NASA to come to you. The DoD may be willing to pay for some of this.

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