Wednesday, May 25, 2011

Mistakes Were Made

Longtime readers (let's pretend for a moment that such a thing exists) of this blog may recall past posts about Bigelow Aerospace, my excitement about their technologies, and my attempts at creating a Transhab Module Calculator capable of roughly approximating possible Bigelow modules. Today, Bigelow broke it's veil of corporate secrecy and allowed a copy of some charts the founder, Robert Bigelow, presented at the International Space Development Conference to be posted at a few sites. Engineer in Progress was not one of those sites, so I can't present that data, but what I can present is this finely-crafted hyperlink to the presentation on SpaceRef, one of the sites that was allowed to post it.

Naturally, after I got done geeking out about the technical details, one of the first things I considered was the specifications presented for the BA-2100 (now dubbed "Olympus," which I think is appropriate for a module that has greater volume than Skylab, Mir, and the International Space Station added together) and whether they fit my calculator's predictions. The results were troubling: the calculator underestimates the module's volume by almost 300 cubic meters, and overestimates the mass by almost 20 metric tons even on my lowest predicted equivalent density.

This error was pretty significant, and so I decided to double-check the calculator against the provided figures for the BA-330. This module was one of the ones I used to calibrate the calculator when I originally created it, so it was perhaps even more troubling that the predictions were also off for the BA-330: The volume was low by almost 100 cubic meters, an underestimate by almost a third.

Therefore, until I've had a chance to look over the new data and diagrams, re-examine my assumed model parameters, and put everything together, I'm retracting the model. I'm going to have to figure out what to do about the calculator (what's wrong, whether I can fix it, and what to do in the meantime), but I wanted to put this out there.

tl;dr: I've found some mistakes in my model based on new data. It's down until I can fix them to my satisfaction.


  1. I have been looking at the mass numbers Bigelow has been throwing around for the ba2100 it ranges from 65 - 100 tons. I don not believe its a flaw on your part as much as trying to hit a moving target. They can probably make it lighter still.

  2. I'm currently working on two issues I've identified, the first being the equivalent density solution which I'm not sure is quite as good a model as I could have used. On the upper end, if a significant factor of the mass is in the wall, then as the modules get bigger, the mass per volume capacity would go down--classic square-cube law issue. I was aware of this at the time of creating the model, but without solid data on the BA-2100 then, I went with the simpler equivalent density solution. I'm debating a few alternatives, and the BA-2100/Olympus provides a valuable check for the scaling effects since it is well outside the scale of the BA-330 and BA-180/Sundancer.

    The other issue is the volume estimation function and it's more troubling to me; the model is significantly underestimating the volume of every module I've tried so far, so I'm going to be re-examining how I broke the modules down into sections, and then how I related those parameters. The presentation's diagrams should help there as well.

    Both of these issues are being worked on as I have time, and I hope to have the model back up to snuff soon.