|Does this really show a 100-ton 2100 cubic meter module?|
I've been working on a calculator for the size and mass of Bigelow modules of certain parameters. I first got interested when I noticed that there's some fairly consistent information about Bigelow's modules, and it plays a role here. The diagram below shows some dimensions relevant to TransHab-derived modules.
|Reference Dimensions of Bigelow Inflatable Modules|
Model and image created by Rob Davidoff
So, anyway, at ISPCS, Bigelow was showing off a model of what they claimed to be a 2100-cubic-meter, 100-ton module capable of being launched in an 8-meter fairing. They also said they have a similar design for a module that would weigh 70 tons and be 1150 cubic meters when deployed. How do these claims compare to the math, and does the model they were showing off actually represent what they claim?
First, the density check. Do the volumes cited match the masses? At 100 tons, the 2100 cubic meter module would have a density of 47.6 kg/m^3, which is in the range mentioned above. At 70 tons, the 1150 cubic meter module would have a density of 60.8 kg/m^3, so that may actually be a conservative value for how much volume could be contained by a 70-ton module; something more like 1250 cubic meters is possible if you use 55 kg/m^3. So the figures for what really matter, the mass and volume on orbit, seem right, if maybe even a bit conservative for the 70-ton module.
However, the volume they claim for the model module doesn't seem to reflect these figures. The launch diameter of the BA-2100 showed at ISPCS was supposed to be something like 7 meters (figure some clearance for an 8 m fairing), so I worked up a model of the module in AutoCAD Inventor using the observations from above and images of the model. Have a look at the figure below, which compares the ISPCS display model and a similar image of the CAD model I created.
|Left: Bigelow "BA-2100" Model at ISPCS 2010. Right: AutoCAD Inventor Model Approximating Model to Left|
The difference becomes even clearer when an actual 2100 cubic meter, 7.6 meter module is compared to the modeled monster module. Below is an image showing representations of a Sundancer and a BA-330 docked to a pair of nodes modeled after Nodes 2 and 3 of the International Space Station. Also docked are the BA-1150 and BA-2100 models I created with accurate volumes, and the monster module they were showing off at ISPCS. All modules have inflated diameters and a launch mass (estimated from density in the case of monster module) noted.
|Comparison image of AutoCad Inventor models of various Bigelow inflatable modules|
Models and Image by Rob Davidoff
I care about this because Bigelow is one of the leaders in private spaceflight, maybe even one of the top five or so key companies in my mind. Unlike most entrants to the field, they aren't focusing on the launch vehicles; they're focusing on the payloads and what we'll do when the launch market exists. That's a big deal and a major part of making sure there's someplace to go when the vehicles come into being. The fact that this is possible is a major reason why I am so astounded with the work they do. I am amazed with what they do because it is indeed now possible for a private company to talk about selling space stations for about $500 million on delivery and contemplate building new stations larger than any currently in existence, funded not by governments but paying for themselves. However, I hope that next time they come to an event like this, they can make sure that the models they bring of the cool stuff they're doing are current, or that they at least make clear where the model and the current vision differ. Images of this BA-2100 went all over the place in the space community, from Popular Mechanics to the NASAspaceflight.com forums. I even talked about it here on Engineer in Progress last month, and there's already plenty of misinformation out there stemming from just the actually correct parts.Some people missed the distinction between the 70-ton BA-1150 and the 100-ton BA-2100, and ended up confusing the two. It'd be nice if all those images actually matched what Bigelow is really capable of, rather than a payload for a now-cancelled rocket.
I'm kind of busy today, so your closing link is just a music video for Weird Al Yankovic's great song Everything You know Is Wrong.Why? Because it's a fun song. Enjoy.