Random Thoughts: Integral Payload Fairing Habitats As a Potential Alternative/Competitor to Inflatables?

2009 was a busy year for me. Around the same time that we were slogging away at getting Xombie and Xoie prepped for the Lunar Lander Challenge at Masten, and around the time that the Augustine Committee was trying to prepare yet another study on NASA’s future that Congress would immediately ignore, I was also working on a propellant depot paper with some friends from ULA and Boeing to present at the AIAA SPACE 2009 conference. This was back in the relatively good old days when a ULA engineer could actually coauthor a paper with the word “depot” in the title without getting in trouble with Boeing or Lockheed execs.*

The paper was focused on near-term options for propellant depots that could be fielded for relatively low cost, and one of the important ideas we discussed was how much LOX/LH2 depot capacity could you launch on a single EELV. We wanted to know if there were any ideas that could enable a “dual-fluid” (ie LOX and LH2) depot with sufficient capacity to be interesting for manned missions beyond LEO.

One of the creative ideas that one of the ULA folks suggested was simultaneously bleedingly obvious, yet profound enough that I had never heard anyone suggest it before: build a tank whose walls are integral with the launcher’s payload fairing. Typically, when you launch a payload inside a fairing, you end up wanting to give it some healthy clearance between the payload and the walls of the fairing–because launch vibrations can cause the cantilevered payload to vibrate back and forth and if you don’t leave enough clearance, you could hit the inside of the fairing with your typically fragile payload. So in many cases, payloads inside a 5m diameter EELV fairing might only be 4.5m in diameter (about the same diameter as the existing ISS modules). But if you make the wall of your pressure vessel double as part of the barrel section of the payload fairing, that problem goes away, and you can now fit a much bigger volume onto the same vehicle–just going from 4.5m to 5m diameter increases cross sectional area by 25%! By going with an integral payload fairing design for the Atlas-launched dual-fluid depot, we could fit a LH2 tank of a bit over 200m^3, enabling (with a few tweaks) a dual fluid depot with 75mT propellant capacity.

In case you’re having a hard time visualizing it, here’s Figure 9b from that paper:

Integral Payload Fairing Depot Concept provides ~200m^3 of volume fitting within existing Atlas V payload fairings

Provides ~200m^3 of LH2 tank volume fitting within existing Atlas V payload fairings


The cool thing is that the same idea can be interpolated for any pressure vessel, probably including habitat modules.

The conventional wisdom says that the only way to put up spacious pressurized volumes is to use inflatable habitats like what Bigelow is doing, or to launch on an HLV that has an oversized fairing. But in an existing EELV fairing, you can fit a pressure vessel with somewhere around 200-220m^3 of pressurized volume, and since the fairing diameter is similar to the tank diameter on the Delta-IVH upper stage LH2 tank, there’s existing fabrication tooling for making lightweight cylindrical tanks in those dimensions. Some additional ideas/benefits include:

  • If you used some of the Launch-Vehicle MLI and MMOD-IMLI concepts that Quest Thermal has been developing with Ball Aerospace (previously discussed on Selenian Boondocks here), you can provide lightweight thermal insulation and excellent MMOD protection that can be launched on the external skin of the pressure vessel without requiring any on-orbit deployment, and without changing the outer-mold-line of the payload fairing.
  • Since it’s not an inflatable structure, you can have all of your structural attachments, cable harnesses, and cooling systems pre-installed on launch, and you also don’t have to have a central core structure or inflation systems.
  • The outer structure can be made as solid as you want it, making it possible to have interfaces allowing you to plug-in external structures such as solar arrays, radiators, robotic manipulators, and communications systems anywhere on the outside surface–unlike inflatable modules that have to fit most of their hardware at the two endcaps.
  • It might even be possible to integrate flexible solar cells into the LV-MLI if the external sheet was both robust and transparent.
  • Also, if you ever lose pressure, the structure retains its shape.

Admittedly it’s not quite as big as you can do with a Bigelow module (something like 2/3 the volume), but it should be cheap, low technical risk, and easily doable, especially if having a large amount of pressurized volume was a key concern. It’s also not entirely a new idea, as it’s more or less how Skylab was done, just in this case using existing, commercially available launch vehicles. Now I’m not saying that this is the only way things ought to be done–there are probably many situations where inflatable structures would be as or more preferable. But if the goal is to create large open volumes in space, affordably, and soon, it seems like the kind of idea makes a lot of sense. And with how bleedingly obvious it is, I’m somewhat baffled it isn’t discussed more. Am I missing some hidden flaw in this concept?

* I wish I was kidding

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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.
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16 Responses to Random Thoughts: Integral Payload Fairing Habitats As a Potential Alternative/Competitor to Inflatables?

  1. ken anthony says:

    Great article. I wrote something vaguely related about a week ago.

    Skylab was a great success. Why can’t we do even better today and at relatively low cost?

  2. ken anthony says:

    I meant to add. Keep the upper stage integrated with your habitat and now you have a potentially refuelable ship just add more light weight fuel bladders that feed the existing tankage.

  3. mike shupp says:

    Also, keep the payload fairing in place and you’ve got a shield against micrometeorites and orbital debris damage, Okay, you’ve got to kick loose a panel or two to allow access to the ports in your tank or to let astronauts in or out of the habitat, but that shouldn’t be much of a challenge — you’re just separating a portion of the fairing, rather than the whole thing. So you remove some small charges, which gives you another couple pounds for payload, and maybe allows for a simpler fairing design, which is also virtuous…..

  4. Mike,
    Keeping the fairing doesn’t actually work, because for most of the exposed surface area of the facility, the pressure vessel wall *is* the fairing. You could still keep the fairing at the nose cone, and over the rocket stage, but in both cases I can think of better uses for that volume that would better suited by just dumping those parts–stuff like a docking port, and/or solar panel arrays.


  5. Ken,
    Yeah the benefit of this approach over the “trailer pop-outs” one is that a metal pressure vessel is really high TRL, and enables adding all sorts of integral features, and you’re already up to pretty respectable volumes with just one such integral fairing habitat.

    But I do like the idea of keeping the Centaur stage attached, possibly with a few additional “top-off” tanks added…

    And I know just the way to enable it to inexpensively get into low circular orbits around planetary bodies with atmospheres, but that’s a blog post for another day.


  6. Krishna Kattula says:

    Interesting you should mention this idea. AIUI, NASA’s preferred architecture for a DSH is now a repurposed upper stage LH2 tank. ‘dry lab’. For many of the same reasons. Of course their intended upper stage is an 8m diameter SLS US.

    Just goes to show how right the Skylab designers got it.

  7. Jonathan Goff Jonathan Goff says:

    8.4m obviously gives you more volume, I was looking at this more as a way of competing on the commercial side where costs and ever-happening-ability matter more.


  8. ken anthony says:

    to inexpensively get into low circular orbits around planetary bodies with atmospheres

    I have some idea where you may be going with this involving dual use… I am definitely looking forward to reading the post when you do it.

  9. Redchrome says:

    One factor in favor of inflatable habitats is that they can be made small enough in diameter to be transported by road or rail. A 5m-diameter cylinder (if not builr right next to the launch facility) needs to go on a transport aircraft, a ship, or a very troublesome and tedious road journey.

    Not that this invalidates your idea at all, it’s just a cost factor worth considering. One could easily build a fairing-capsule/tank 3m in diameter and thereby be road-transportable, and there’s plenty of reason to build inflatable habitats 10m in diameter when collapsed which would have to be transported by barge.

  10. Redchrome,
    Interesting point–I hadn’t thought of that one. Though my gut intuition tells me that arranging for “odd shipping” on the earth may not be such a big deal compared to other considerations (the ability to preinstall wiring, HVAC “plumbing”, structural mounts, etc), but it does give at least one additional advantage to inflatables.


  11. ken anthony says:

    Please forgive if I’m straying from the topic (I’m blaming Redchrome for causing my mind to stray… it takes very little.)

    If we want to use our spaceship we have to keep the rocket equation in mind. Regardless of inflatable or not, at the present stage of the game we don’t need to wait for larger launch vehicles because what we have will already launch a vehicle we will have difficulty in financing operations.

    If we built for the F9 (13,150 kg to LEO) integrating the upper stage as part of the ship so that it arrives in orbit dry. Crew (3 to 8), Volume (50 to 200 m3) and consumables for a mission would bring the dry mass up to perhaps 30 mt. (I’ve been using a ref mission at 100 mt. previously.)

    We could actually afford to send a 30 mt someplace but even that would cost at least $300m in fuel for a mission. Add $200m for a Mars One lander and you’ve got a mission we can afford to do more than once.

    That’s a heck of a lot cheaper than the $6b Mars One intends to spend.

  12. Pingback: Low-Cost Propellant Depots | Transterrestrial Musings

  13. gbaikie says:

    Suppose you thought it was a good idea to put gas station in the middle of the Pacific. Probably quite dissimilar to fuel depot in Space,
    but maybe some things are similar.
    The biggest difference is though a lot fuel is used for cargo ships, the fuel needed doesn’t represent a significant fraction compared to tonnage of cargo. Perhaps it become more of the case if one used natural gas, rather than bunker fuel.

    I know US navy ships are refueled, but not aware of civilian ships doing this. It seems that one would want to refuel while the ship is moving. Or it seems the advantage of refueling at a port is loading other stuff in the ship and you can refuel at the same time.
    So generally you have depot mid way of transportation route, and have smaller refueling ships meeting up with a cargo ship and refueling it while it going to it’s destination. And returning to depot
    to be refuel, so it can go out refuel other cargo ships.
    And having the stationary depot which is refueled weekly or monthly or whatever.
    Anyways it seems the ocean depot would be something like “floating production, storage and offloading (FPSO) ”
    “As an example, the Sanha LPG FPSO, which operates offshore Angola, is the first such vessel with complete onboard liquefied petroleum gas processing and export facilities. It can store up to 135,000 cubic meters of LPG while awaiting export tankers for offloading.”
    So these things could merely store and/or process fuel. They design to withstand severe weather. A problem is the crew is stuck out in the Pacific [though one limit the amount crew needed by some degree of automation/teleoperation].
    But anyhow, if we assume such things don’t already exist, how you go about starting such a market?

  14. great paper Jon,

    Another idea that might be germane to a middle ground between spaceX and ULA
    space depots
    in space stages
    modification off existing LH2?LO2 Engines
    Cross feeding between CBC’s

    is this white paper; http://www.grc.nasa.gov/WWW/Fuels-And-Space-Propellants/GELLED.htm

    This gelling of LH2 with crystals of Methane seems like an intermediate step to all of the above,My idea of cross feeding LH2/Methane into a LH2?LO2 central core should be traded with an all LH2/Methane system.
    At what point in a density mix could you not have to modify existing existing engines?
    “Existing” methane engines, the paper claims that a 5% Methane ISP is higher than LH2/LO2 ! I suspect you folks who are experts would say higher density would be more important?
    How much of a density would allow us not to modify an “Existing” Methane engine ( Raptor!)

    This paper claims that Methane at 70%WT has an ISP just below 400! so I would love to have experts such as yourselves engage me in this thought experiment; If we had a LH2/Methane/L02 Delta IV or an SLS how would this look in the trade spaces?

    a year ago I was looking for a LH2/Methane CBC to the SLS with out having to modify the SSME’s (crossfeed the Methane into the unmodified SLS core) VS the F1 powered proposal. I thought, well no not competitive but then my thoughts turned to the Delta IV and then later the proposed Raptor and LH2/Methane fuel depots.
    LH2/Methane powered RL-10’s powered “giddy” thoughts followed close behind :):):)

    see! maybe I now see why Jon is a “recovering rocket plumber”

    I have a secret method to cross feed LH2/Methane into the LH2 central core, but I wont tell!

  15. Paul451 says:

    While I understand the point is to strip away complexity and mass, I’m wondering if it would be possible to build a module from each half of the fairing, with an inflatable module built in between (inflating on orbit, spreading the modules apart.) Essentially turning the Bigelow configuration inside-out. Two hard shelled sub-modules instead of the internal frame.

    I figure since the inflatable portion is pressurised, the inner (hard) walls of the fairing-modules can be flat. So those walls could carry the experiment racks. And the outer walls (the fairing halves) can support utilities, inside and out. The inflatable volume would presumably serve as the main habitat and storage area. Couple of hatches built into in the inner walls would allow passage between the three spaces, and allow isolation when necessary.

    Taken to an extreme, start with the proposed flared fairing from SLS Block II, 10m x 18m, halved and joined by a centre portion on the scale of a BA2100 (12m diam when inflated)… Enough station for any reasonable man, put up on a single launch.

  16. Jonathan Goff Jonathan Goff says:

    Sure, you could likely do something like that, but as you point out, you’re back to something low-TRL with lots of development work. I was just trying to point out that if it looks like there’s demand for private space facilities (maybe if/when commercial crew vehicles start flying), then someone could possibly compete in that sector with an approach that requires no real tech development, just the spacecraft systems integration.


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