In the spirit of my previous post promoting healthy, competitive industries, I wanted to toss out an idea I’ve had for several years about an alternative to inflatable structures for providing large volume pressurized space facilities. The idea is a derivative of one of the concepts I discussed for dual fluid depots in my paper I did with ULA back in 2009–to make the pressure vessel be integral with the payload fairing walls.
Normally payloads fit inside the fairings, and have to have a sufficiently large gap between them and the fairing that they don’t accidentally vibrate into the fairing during launch. This “dynamic envelope” often cuts the diameter of objects inside a notionally 5m diameter fairing to ~4.5m or less. Building your structure so its cylindrical section is the fairing structure can increase the effective cross-section of your module significantly (~35% more cross sectional area for a 5.1m vs. the 4.39m cross section used for ISS).
Here’s an illustration lifted from that paper I referenced earlier:
Integral Payload Fairing Depot Concept provides ~200m^3 of tank volume fitting within existing Atlas V payload fairings
As you can see, by building a tank that effectively replaces part of the fairing wall, you can fit over 200m^3 of pressurized volume into an existing Atlas fairing (actually closer to 250m^3 once you include that gas buffer tank shown in light blue between the big tank and the Centaur, and add in a docking node fitting into the nosecone area). I haven’t run the numbers on versions flying on Delta-IV or Falcon 9, but figure they’re likely similar since all have ~5m diameter fairings.
In many ways this concept is pretty similar to what was done for Skylab. While NASA originally intended to use a “wet workshop” design for Skylab–where the habitable space would actually be filled with propellant during launch and only converted to warm living space after reaching orbit–in the end they ended up going with a dry-lab that was pre-fitted-out with internal structures, wiring, and a lot of the hardware that would be used on-orbit.
For an Atlas V-launched version, the 5.4m OD of the fairing would work well with the 5.1m OD LH2 tank tooling used for the DCSS upper stage, leaving about 15cm on each side for a variant of Quest Thermal’s MMOD-MLI that could include a thin aeroshell over the outside similar to the LV-MLI. With a tank stretched to fill the available length in the long Atlas V fairing, you’d have somewhere in the 210-220m^3 in the main cylinder, with a pressure vessel and MMOD/MLI dry mass under 4 tonnes.
Quest Thermal MMOD-MLI Test Article
Is this revolutionary? Not really. But I think it’s a reasonable competitor to inflatable modules for a similar job. Some of the benefits of this approach, compared to inflatables:
- Much simpler, lower-risk design, analysis, and fabrication. You’re basically just doing a stretched propellant tank for your pressure vessel. Most of the complexity in a useful hab isn’t in the pressure vessel itself, so making that as simple as possible might not be a bad idea.
- Similar overall volumes. The BA330 would only be about 30-50% bigger (220-250m^3 vs 330m^3 for Bigelow), in spite of the benefits of inflation. This would also be significantly (~50%) bigger than the largest ISS module–Kibo.
- More efficient internal volume utilization. Unlike an inflatable you wouldn’t have a rigid core structure taking up prime real estate down the center of the module, and you also wouldn’t need to have all the volume associated with the inflation pressurization system, as you could launch the module pre-pressurized. If you wanted to have a wide open space for some reason, this would provide it a lot easier than you could get with a comparable inflatable structure.
- If you went with an isogrid aluminum construction like the DCSS tank, you can probably put threaded/helicoiled holes at the repeating nodes where the 6 rib elements come together. This would make it very easy to attach structures or other systems in a reconfigurable manner, whereever you want. With some work, you might even be able to have some set of the node holes done as blind (not thru) tapped holes on the outside for externally mounting hardware.
- Since the structure is rigid, it’s possible to mount items like solar arrays or radiators to the outside of the structure a lot easier than it is with a soft-walled structure. These pieces would have to be stowed somewhere else for launch (maybe back in the gap between the centaur stage and the bottom part of the fairing), and then moved into place using a robot arm, and attached to some form of separable interface. There are some definite details that would need to be sorted out there, but nothing that seems to hard. Plus you wanted a robot arm anyway for delivery vehicle capture/berthing. This may not seem like that big of a deal, but one of the real challenges with a Bigelow module is all of those external pieces have to attach to two fairly narrow pieces of real estate at either end. Being able to attach to the cylinder section gives you a lot less crowded of a space to deal with.
- Adding windows or other local stress points is also a lot easier to do with a rigid structure, as is adding vacuum electrical or fluid pass thrus along the cylinder section if desired.
Now, I didn’t mean this post as bashing on Bigelow or inflatable structures. I’m a big fan of what Bigelow is trying to do, and have nothing but respect for a guy willing to put that much of his own money on the line to make a dream happen. That’s balsy. I’m not even necessarily saying that my approach actually is better overall once all factors are taken into consideration. I’m just saying it’s another approach to solving the “large amounts of pressurized volume” problem that’s not particularly high-tech or high barrier-to-entry.
While I definitely want to see Bigelow successful, I’d also love to see him have some successful competition as well, and I just wanted to point out there are other legitimate approaches for solving this problem that I hope someone will try out.
Jonathan Goff
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I wonder how much one charge- how much someone will pay for shadow at EML-1?
5 meter diameter has circumference of 15.7 meters [51.5″].
So one have a 50′ square in space which reflects the sun- creates 50 by 50′ shadow
for miles of distance. And if one is a mile away from the shade, then whatever the heat
of the shade doesn’t matter much in term radiant heat reaching you. So sun’s blocked, but still available to anything sticking out of the shadow. So one the earth about +250,000 km away from it, and Moon about 75,000 km away from it. Neither would be radiating much heat to this location. And if you 100 meters from some other thing
which wants the shade and is is pretty cold- it also would radiate much heat over such a distance.
So telescopes and fuel depots could consider a year of this shade as valuable. Not heated by the sun, but close enough to harvest any solar energy for their needs.
Downside is they would need to able to stay in the shadow- which could use more delta-v for stationkeeping.
Great minds.
gbaikie,
“So one have a 50′ square in space which reflects the sun- creates 50 by 50′ shadow for miles of distance.”
No. The sun has an angular size of half a degree at 1 AU. The shadow from a 50 foot by 50 foot sunshade would drop linearly with distance, petering out entirely by 2900 feet.
–No. The sun has an angular size of half a degree at 1 AU. The shadow from a 50 foot by 50 foot sunshade would drop linearly with distance, petering out entirely by 2900 feet.–
Ok, apparent angular size halves diameter with distance.
Wiki:
“For example, if this circle is 10 cm wide on your monitor, view it from 10.3 m away.”
http://en.wikipedia.org/wiki/Angular_diameter
The 10 cm is the apparent angular size as moon when nearest the Earth- bigger than apparent size sun if 10.3 meters from it.
So, 10.3 meters doubled 4 times is 164.8 meters [540.68′]
10 cm doubled 4 times is 160 cm [16 meters or 59.05′]
So in space something 59′ feet in diameter at 540 feet away would similar to a total ellipse of the sun on Earth. Except the path/footprint of the shadow would *a lot* smaller- it would be about the same size as 59 foot disc rather than being about same size as the Moon’s disc.
Now what would the 50′ square look like at 540′ away with sun between it?
Well within the shadow at that distance which is nearly 50 foot square [or 50′ disk] would resemble an annular solar eclipse and total solar eclipse.
The four corners would completely block sun and rim of sun would extend beyond the flat sides. There would some variation depending actual distance from the Sun. But what important is how much solar flux is reaching you at that distance. So one could easily guess less than 10% of 1414 to 1321 watts per square yearly variation. So less than 141 to 132 watts per square meter. Or about 1/10th of sunlight is about the power of sunlight at Ceres
distance.
So now double the distance again, at 1080 feet away, the 50′ square has halved it’s apparent size. And what does sun look like within that 50 square shadow?
The square will be about half the sun diameter.
So had 2 meter diameter circle, one would 1 meter square box in the middle of it.
2 meter circle has 3.14 meter area, box has 1 square meter. So one only reduces the area by 1/3. So 1/3 1414 is 471 watts. Or one reduce power sunlight to something similar to sunlight on Earth’s surface [about 1000 watts per square meter at noon with sun at zenith. Or roughly, instead of sunlight warming something to 120 C, it warms it to 80 C.
But then we could get complicated- the sun is sphere, and most of energy of sun reaching us come from middle part of that sphere- but we will not do that [mainly because I can’t find a reference which explains it].
Anyway I was wrong to say one would get useful shadow from 50 foot square at a mile distance- it be more like 500 feet away from it. But you could shade more asset within that distance then is needed in short term.
And if put 4 of them together you get about 1000 feet. Or leave 100 foot square hole
in middle and surround by border 12 50 foot squares, get nearly complete shade for 500 feet from it, and solar energy could gotten in the middle or from outer edge.
Or something at 2000 feet from it, would get the donut hole of sunlight [1/4 of solar flux of sunlight if not blocked or “taken” by assets between it.] But even that is not a mile distance of cryogenic useful shade.
Oh, another thing, the shade would need to go in circle every lunar month- whereas Sun Earth L-1 point would not need to do this. Normally I think of lunar asset rotating
on other axis to not have Moon block the sunlight as much [so to get more time of constant sunlight] though it’s not big problem- Geostationary satellite have the Earth and they are nearer and Earth bigger [though they going about 3 km/sec- at L-1 one stationary to Moon.
Anyways one would have to figure out the best inclination and timing for your circular path.
Could the same thing be done with an in-space vehicle? Likewise, could a fairing (such as on a Falcon Heavy) be stretch aft so that an OTV or lunar lander could be quite large? Could such vehicles retain the upper stage engines such that the combined upper stage and in-space vehicle are one in the same thing?
Jon,
I noticed you still left a nose-cone on your depot-tank. Wouldn’t it be worth having a non-spherical end-cap and skipping the nose-cone entirely? You add mass to the tank due to the slightly less pressure-efficient design, but structurally bi-conics are still pretty strong, I can’t imagine that a bi-conic hybrid end-cap/nose-cone is heavier than a spherical end-cap plus a separate bi-conic nose-cone. (Plus it adds yet more volume.)
(For a hab module, you placed the docking node in the nose, so I realise that’s a different situation.)
Back to faring habs… The Centaur is about 3m diam. The faring is 5m. Giving you a metre each side. Allowing half a metre for the centaur to rattle around in, you could have up to a half metre (of Whipple shield, truss structure, and plumbing) built into that lower faring without interfering with the Centaur. On orbit, the first crew removes the spent Centaur, adds an unpressurised hatch, leaving you with a shielded but unpressurised “garage” to work in. (About 4mx8m internal (100m^3 working volume.))
Much safer than “outside”, meteor/radiation shielded, thermally uniform and stable, no tool loss risk, no drift risk. This should let you work in a pressure-suit, rather than a space-suit, hopefully simplifying long EVAs, reducing prep-time and operational support requirements. It might also allow other cheats, such as a permanent suit-ECLSS built into the walls, so you just plug in a hose for power and life-support. And if that also allows you to produce a full 1atm nitrox pressure-suit more easily, it may allow unscheduled and largely unmonitored EVAs within the garage; reducing operational support to “scuba rules” (buddy up, let someone know when you go out and when you’ll be back.)
[I’m assuming that no matter how much crap you pre-build in the hab, it’s still basically empty space. You’re going to be launching light on anything bigger than a F9, so the garage is essentially a “free” structure.]
If you went with a steel outer shell, perhaps spaced slightly from an aluminum isogrid inner shell, then everything could attach to the outside with super-magnets.
George,
I wonder if you could get a similar result from a thin deposited coating of mu-metal? If ULA ever builds ACES, their plan is to do a DCSS diameter tank using the same seam-welded CRES 201 alloy as Centaur. That material is cold-worked enough to be ferromagnetic. But it wouldn’t have the convenient isogrid mounting properties.
If you did my suggestion of having some of the isogrid tapped holes be ones drilled and tapped from the outside (but not all the way through), you could attach magnetic plates at various key locations…actually there’s probably nearly limitless ways you could do things, but having some sort of separable standardized electromechanical interfaces would make upgrade and repair easier.
~Jon
Paul,
The garage idea is interesting. I had also thought of the idea of having a hatch leading into the LH2 tank of Centaur with your back airlock in the truss that ties the Centaur to the pressure module. If you left that intentionally just as shielded storage, could be interesting. And in that case you would just leave the Centaur attached. If you were really ambitious, you could try to turn the LH2 tank into some extra pressurized space (by welding over some of the various inlet/outlet ports). It would get you up to almost 300m^3 total…but at greatly increased complexity.
All sorts of options.
~Jon
The mu-metal coating sounds good. I wonder if you could do something even stranger and use a regular aluminum shell, but use movable super-magnets on the inside to attract the magnetic base of an attachment on the outside, just like those magnetic aquarium cleaners where the underwater scrubber tracks the handle on the outside?
With a little cleverness, you could reposition external equipment such as sensors, antennas, or solar arrays, without ever going on a spacewalk.
For reference, Skylab was 350M^3.
Could such vehicles retain the upper stage engines such that the combined upper stage and in-space vehicle are one in the same thing?
Brilliant. You want a low mass, high volume (Bigelow?) reusable general purpose ship that once launched never lands again but rendezvous with SSTO landers sent ahead to where ever it goes. You replace the upper stage of a F9R with this 13 ton ship which achieves orbit nearly dry to be refueled. You don’t have to figure out how to recover the second stage. It ain’t coming back, eliminating that challenge.