Popcorn Mitigation

guest blogger john hare

I noticed an objection to reusing tanks in orbit again that struck me as minor. Insulation popcorning off the tank creates an orbital debris problem that is increasingly unacceptable. It would seem to me that an Echo type balloon much larger than the stage could be used to contain the problem even if it didn’t keep the insulation in place.


A very light balloon structure would seem to be quite sufficient to contain any popcorning problems until permanent solutions could be incorporated. Inflation in vacuum can be done with tiny fractions of an atmosphere of pressure. A drop of water has been used for the purpose for smaller balloons. Think of it as an inflatable hanger.

Using it as a hanger for converting the previous upper stage to living quarters of a propellant depot has other advantages. Lost gloves and tools don’t leave the vicinity, you can get them back without endangering crew or other spacecraft. The balloon can be slightly opaque to cut down on suit heating during the daylight portions of the EVA. The balloon could also re-radiate a bit of heat back to the   EVA personnel during time in shade or night portions of the EVA. Tethers would still be needed, but drifting away from the ships would be less dangerous. Over time, the fractional ton balloon hanger could become a major assembly station as it accumulated tools and supplies from multiple  contracts.

On the downside, drag will cause it to require substantially more station keeping propellant than the tanks it contains would have on their own.

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I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.

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About johnhare

I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.
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14 Responses to Popcorn Mitigation

  1. jsuros says:


    I heard somewhere that you were back, complete with thought experiments and diagrams. Good to hear from you.

    As well as the “loose piece confinement” benefits of an enveloping balloon, I believe some proposals for radiation shielding in space call for a thin and distant outer layer that by itself does not stop much of the radiation, but does convert the really high energy particles into cones of much lower velocity particles that inner shielding of reasonable thickness can stop. Making the outer sphere big means most of the “spalled” radiation misses the habitat due to geometry. I’ll have to dig through my back issues of JBIS to find the reference.


  2. MG says:

    I don’t see how the loss of insulation is much of a problem. It has such a low ballistic coefficient that it will de-orbit quite quickly.

    The utility of an inflatable in LEO is, as you mention, very limited by its own low ballistic coefficient. OTOH, the notion of a cosmic ray mitigator is an interesting one for future long-duration human missions.

  3. Tim says:

    Hi John, good to see you’re back. I have to wonder if the killer app is as a generalised “hangar in space” that you mention at the end of the article rather than simply insulation containment. You could, for instance, inflate the hangar around a satellite that requires EVA maintainence. The similarity to an Echo balloon could also yeild a larger radar signature, which would be useful in tracking the object. Incidentally, do you remember where you heard about the water drop inflation?

  4. Eric Collins says:

    I also think that the orbital hanger idea is going to be a very important piece of infrastructure. You’re balloon idea is good as far as providing confinement on a temporary basis; however the repair or assembly job must still be conducted in full EVA gear.

    For longer duration jobs it may be worthwhile to construct a more robust shipyard using Bigelow’s inflatable habitat material and some minimal scaffolding to anchor it. This shelter could be brought up to a comfortable temperature and pressure to permit a shirt-sleeve environment while working on the repair or assembly of a spacecraft inside. When the job is done, the structure is partially dismantled to allow the spacecraft to leave or wholly dismantled and transported to the next job site.

    I think this is a vital technique to develop, because once you can rapidly assemble these large temporary structures, you’re just a stone’s throw away from being able to construct more robust, longer duration structures of nearly arbitrary size and complexity.

  5. Randy Campbell says:

    Welcome back John, though sorry for the circumstances.

    I’ve actually been thinking along these lines, though not of shuttle-ET tankage but the concept of “modular” tankage that can be “re-purposed” on-orbit.

    I began thinking even more seriously about it once I read Jon’s posting on his thoughts on RLVs. I finally realized there seems to be a slight ‘disconnect’ in the thinking that an RLV has to be COMPLETLY reusable and by that it is meant that everything HAS to come back “home” to be refurbished and readied for the next flight.

    “Anything” else is considered an “ELV” with an RLV component and therefor NOT a “real” RLV. If your don’t bring it “home” then the part is “expended” and useless. But that’s a PERCEPTION problem associated with the (sometimes seemingly eternal :o) argument between ELV and RLV concepts.

    Jon himself commented that he could see “very few” situations where a seperate “compartment” for payload would be economical on an RLV. Specifically he was thinking of a fully self-capable reentry and landing vehicle attached to an RLV orbiter/lander.
    I got and still have the “feeling” that Jon neglected one very important “P” in his listing of “people, propellant, and provisions” because I suppose I’m of the firm belief that “place” is going to be a major factor in orbital travel.

    Jon and Rodrick Reilly discussed the concept of “drop-tanks” and I’ll take a second here to relay that “dropping” things off your vehicle during take off (or anywhere in flight short of orbit) tends to reduce be seen as reducing your E-sub-C due to the assumption that the items you dropped will fall willy-nilly along your flight path.

    Speaking as a 15 year verteran of building, storing, assembling, and using guided munitions if various types I’m quite confident that the technology is well in hand to have any “dropped” objects guided quite accuratly to a designated landing zone with extremly high realiabilabilty for recovery and re-use. There are off-the-shelf RC airplanes that can be programed to fly to specified points using an on-board GPS system for crying out loud!

    Back to my original subject: The concept of using “drop-tanks” has appeared numerous times for RLV launch concepts usually to allow ‘fudging’ of the vehicle mass-ratio to allow it to achieve orbit. Some of the concepts dropped the tank(s) as early as possible once they became empty, but a majority seem to have kept the tanks almost till they reached orbit to allow maximum payload to orbit. Dropping the tanks short of orbit achieves two tasks; one it achieves a higher payload to orbit since the orbital vehicle only has to use a small amount of propellant to ‘finish’ reaching orbit without the drag of the tank mass, two it ensures the dropped tank is destroyed so as not to add orbital debris.

    The idea of taking the tanks all the way to orbit to be ‘re-used’ though it has come up again and again runs into several “real-world” problems though. For one thing it reduces the payload to orbit of your launch vehicle concept and while the penalty may not be ‘much’ on larger vehicles such as the Shuttle the effect hurts a lot more on smaller vehicles. You also run into the issue that a “good” fuel tank does not usually translate well into even an ‘adequate’ habitat or laboratory module on-orbit unless one can do a lot of on-orbit labor to re-purpose the module. Lack of adequate space suits designed to actually be used for labor in space make this a daunting if not impossible task. I’ll finish with a most major issue; there is no demand or need for on-orbit modular tankage that is going to take effort and probably expense to convert to usable storage, habitat, vehicles, etc.

    All of these ‘problems’ are solvable, and with proper design of the tank ‘modules’ I believe that a launch program that includes such designs will have huge advantages in flexability and economics. But then again, I could be all wet and having a fever dream :o)

    (As a note, my “insperation” for this combines the original InterOrbital Systems 1.5 stage to orbit launch vehicle/space station, a now non-op website on modular construction which had paper .pdfs that you could build of the various modular pieces {http://www.geocities.com/codex34/paper/pdf2/pdf.html and if anyone can get me the name of the author of those pages I’d appreciate giving credit where credit is due} and many suggestions and ideas from folks that frequent this and other blogs and cyber space. Thanks :o)


  6. Pete says:

    Yes welcome back!

    Micro meteoroid holes might be an issue with regards inflation, though it would add significant extra shielding. One possibility is to leave the front fully open – like a big bag, and use ram air inflation to keep it inflated – have that drag work for you.

    I wonder at what orbital height it would become viable to also use this for atmosphere skimming – vacuum pump plus high ISP drive to keep it in orbit.

  7. john hare says:

    An orbital hangar will certainly be a seriously useful thing when it happens. My thought was for a simple and cheap (relatively) stepping stone on the way. The problem with an orbital hangar has the same problem as the orbital propellant depot though, since it doesn’t yet exist, there is no demonstrated market, which means it doesn’t get financing, which means nobody will figure one into their plans, which means……………………………….

    Some people are seriously worried about loose insulation, which makes it a problem of potential liability even if it is a non-problem problem. At orbital velocities a gram of foam can have the impact energy of a 50 caliber bullet. Somebody loses a solar array and blames it on our carelessness, it could be a legal problem even with no proof at all.

    I seem to recall that the water drop inflation was in the Echo program. While used tank modules or upper stages may not be good for reuse as depots or living quarters, solving individual problems can change the usefulness and value of various commodities.

    Thanks for the welcome back everybody. My circumstances are actually better than a few months ago.

  8. Chris says:

    Here’s an idea, deorbit the tank. And if you’re building a propellant depot, lets spend an extra ten tonnes on lifting insulation that stays firmly attached to the tank.

    This is really very simple, it’s the principle of not leaving your crap in orbit. You put a satellite in space, you leave enough deltav in the tank to move it out of the road.

  9. jsuros says:

    I found the reference to an outer layer of radiation shielding in the January 2009 JBIS, but it doesn’t really apply to this case. The idea was that a thin “heavy ion trap” would turn cosmic rays into a spray of muons that convert to lower energy elementary particles after a short time. The problem is that cosmic rays are really fast so the gap between your outer layer and the standard shielding on your station has to be more that 2 kilometers. The math works out to better protection than earth’s atmosphere.

    Useful for really big habitats in deep space, but not for an early orbital station. Never mind.

  10. jsuros says:


    You remind me of a story I heard once about SpaceLab, in which serious thought was given to launching the station flooded with Liquid oxygen and then refitting the empty “tank” in orbit as a station. SpaceLab was just a big aluminum can, after all.

    I wonder if a scheme like this would work to lift sections of a large station or vehicle, where the “launch vehicle” sacrifices all payload to internal bulkheads and airlocks. The soap, spam, and toilet paper get sent up on separate cargo vehicles before or after. This gives you an easy way to deliver engines to orbit, too. Just put them to work on the way up and switch nozzles for vacuum work.

  11. Mike Puckett says:

    How about a form-fitting Kevlar blanket ala a beer Coozie that covers and traps the insulation?

    A tank-condom?!?

  12. john hare says:


    Makes more sense than my idea.

  13. Wesley Johnson says:

    Wouldn’t standard MLI do the trick? The one problem would be if the foam popcorned with enough energy to penetrate the blanket, but I don’t think that would happen once you got to orbit. Another problem is that the MLI probably couldn’t survive ascent without protection. But that protection might actually weight less than the foam, therefore you wouldn’t need the foam because you could purge the MLI. But if you are going to use Kevlar or some type of RTV, you might as well make it the insulation.

  14. john hare says:

    I’m sure there are many ways to do it, this just happened to be the one I found most interesting. Keeping the insulation in place was supposed to be just part of the idea. The partial protection assembly area was the other.

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