I have a piece up at Popular Mechanics about the AIAA conference this week, and ULA’s non-heavy-lift architecture. Hell hath no fury like a rocket company scorned.
Meanwhile, it looks like there may be a battle in Congress to preserve the Ares pork. At some point, though, they’re going to have to confront budgetary and programmatic reality.
[Noon update]
Here is the permalink.
[Another update a few minutes later]
Paul Spudis has a longish essay on the history of the VSE, how NASA mangled it, and what we need to do going forward.
I have often found a basic understanding of inflated structures to be somewhat limited – even among those who should know better. Unfortunately people tend to design inflated structures as if they were rigid ones – which is kind of to be expected. I can not speak for the design of the Human Lunar Return Surface Inflated Habitat shell, I have not looked into this one in detail – I hope it is not designed like the Transhab module.
Practical minimum gauge constraints for rigid materials might be in the 0.5-1mm range, though at that I would want to maybe add an isogrid (which almost comes standard with inflated structures). Minimum gauge constraints for inflated materials can get below 0.1mm and their material densities are typically much less, fabric weights of 40g/m^2 are quite standard. So inflated structures might enable about an order of magnitude reduction in minimum gauge constraints. This is actually the key to designing inflated structures, unless the application is within this range then an inflated structure is probably not worth doing (unless packing or surface robustness is also an issue, etc.) An inflated structure can be more robust that a rigid one, especially if it has an additional fiber net over it. They can deflect large amounts without breaking and the flexible net prevents “crack” propagation.
Like sheet metal, fabrics come in a wide range of weights off the shelf, also, fabrics allow the use of multiple layers stacked together. However a serious inflatable construction system might consist of a loose net of woven fibers (Spectra, Vectran, carbon, Kevlar, PBO, etc) with an impermeable fabric/film beneath it. The 3DL sail making system, for example, basically sandwiches specifically placed fibers between to very thin layers of Mylar. In practice one would go for multiple shells – to increase robustness, including a human proof one on the inside. Above 10-20 meters in diameter rigid is still probably better, unless packing is a constraint.
Some materials are more UV resistant than others, but if memory serves a surface coating of around 50g/m^2 can give pretty comprehensive UV protection. External thermal insulation and micro meteor protection probably gives you UV protection, assuming it is needed. Radiation shielding on the lunar surface really favors covering “the tent” with regolith – completely different design to one in space.
Like sheet metal, fabrics come in a wide range of weights off the shelf, also, fabrics allow the use of multiple layers stacked together. However a serious inflatable construction system might consist of a loose net of woven fibers (Spectra, Vectran, carbon, Kevlar, PBO, etc) with an impermeable fabric/film beneath it. The 3DL sail making system, for example, basically sandwiches specifically placed fibers between to very thin layers of Mylar. In practice one would go for multiple shells – to increase robustness, including a human proof one on the inside. Above 10-20 meters in diameter rigid is still probably better, unless packing is a constraint.
Some materials are more UV resistant than others, but if memory serves a surface coating of around 50g/m^2 can give pretty comprehensive UV protection. External thermal insulation and micro meteor protection probably gives you UV protection, assuming it is needed. Radiation shielding on the lunar surface really favors covering “the tent” with regolith – completely different design to one in space.
Again, I think we may be talking at cross-purposes. My remarks about inflatables were meant to be applied only to the discussion of the design of a vehicle for transport of humans and valuable/oversized cargo betwen EML and the lunar surface. I have no idea why one would want to consider covering the lunar lander crew enclosure with regolith.
Here’s how Edward originally estimated the mass of a crew enclosure for a reusable lander:
Although he doesn’t state his assumptions, he seems to be scaling down the Surface Inflated Habitat — about the size of a small bedroom — to about 40 percent in each dimension to get that factor of 22.5 in volume. He didn’t say where he got that factor of 22.5, though. I don’t know the original height of the habitat volume, but I’d assume it would be a bit taller than the size of a standing person wearing a spacesuit; it seems unlikely to me that you’d want to scale that dimension down to 40 percent of its original value. Anyway, somehow Edward seems to be claiming that he can scale down a room-sized enclosure that masses 332 kg down to a smaller enclosure for two astronauts on the lander that masses only 15 kg, which seems implausibly small. And that’s why I made the comment about surface area versus volume.
If that’s not what he was trying to do, he sure wasn’t very clear about it.
The inflatable habitat masses I gave are kind of minimum mass ones – one can of course design them heavier. Unfortunately there are so many assumptions and accessories rolled into inflatable habitat masses that it really pays to look at the raw numbers.
I also just checked some numbers for a lunar lander, dry mass might only be around 10-15% of payload, so even a 25 ton payload lunar lander might only mass around 3 ton empty – not a huge cost. Maintaining a reasonable flight rate and fleet size is probably the real size constraint – and propellant will cost.
Looking more generally at inflatable habitats, a 20 meter diameter by 50 meter long inflated habitat could be launched on a Falcon IX heavy. Another launch would be required to fill it with air and many more to furnish it. This would be some thirty times the volume of the ISS and would enable some fifteen stories and 5000m^2 of living space. Similarly a 5 meter diameter by one kilometer long farming habitat could be launched that could feed around a hundred people. And yes inflatable habitats can be modular or easily assembled from smaller pieces if need be.
My point is habitat volume is cheap, this time round I hope those who go will be given the elbow room to actually do stuff – like build things. Whether it be on the moon or in LEO – there is no need to be cramped. All the systems necessary for life support may be heavy, but actual habitable volume is not. Large low cost inflatable habitats in space or on the moon could greatly inspire people as to the possibilities of space.