This is a 12.5m x 25m "wet-workshop" module currently under development. It is a derivative of an older, purely cylindrical design (an updated version of which I expect to post in the near future... once I have solved a problem that I am having with my CAD programme). As a "wet-workshop" design, the module is intended for conversion to a habitat module following initial service as a propellant tank for a Heavy Lift Launch Vehicle. Given the intended eventual use, it is intentionally rather heavy for a propellant tank, with much greater mass than would otherwise be necessary or desirable. The MH12500A (The "MH" is obviously my initials, but it could also be interpreted as "Module-Heavy"; the number denotes the radius in mm; and, the "A" distinguishes this as a more advanced design) has a mass budget in the range of 80 to 100 tonnes, although it could prove to be much lighter in terms of actual structural mass (the remaining mass would be water added to the voids -I'll explain shortly- to provide extra radiation protection, as well as increased service water reserves). The much of this mass is intended to provide additional insulation / thermal protection, as well as micro-meteoroid and radiation protection. The design is intended to permit up to five of these modules to be stacked in an HLLV configuration, although four modules would be the standard load-out. There would also be a propulsion assembly with at least four independently ejectable thrust assembly modules (to be staged when the added thrust is no longer needed), together with a fifth integral module that places the HLLV in orbit; and a nose-cone fairing... all of which are intended for recovery and reuse. A single module stack is possible, with an estimated 10 tonne useful load capacity (in addition to the converted structure and propulsion mass). The mass allowances assume a mass distribution of 90% propellant (required for an SSTO to achieve LEO with an average Isp of about 400s), 7% structural mass (the STS ET actually achieved a structural mass of just over 3%), 2% propulsion systems (assuming a thrust/mass ratio of 50... normal ratios are closer to 75), and 1% payload. Among some of the more interesting features: * Each module actually has five shell layers, spaced by four 5cm void sections. This layering provides added low-mass insulation (incorporating the voids); as well as a "whipple shield" protection mechanism, enhancing the actual mass/material shielding. * The inner shell is actually composed of three distinct "tanks", incorporating common bulkhead techniques and technologies. The common bulkheads allow for decreased overall insulation requirements (since the common area has a much reduced temperature gradiant), as well as reduced containment mass (since the common area has a much reduced pressure gradiant). The integrated design provides greater mass protection against radiation and micro-meteoroids for the central volume. * The linear (vs stacked) common bulhead tank arrangement greatly reduces the length of plumbing necessary to distribute propellants, which actually reduces added mass considerably. * The modules are designed to "dock" with one another, with multiple docking ports, allowing for propellants to flow directly from tank to tank. Again, this reduces required piping mass. * Intertank modules will be designed to: support the mass of "strap-on" boosters; permit continuous flow-through for the outermost void (which may serve as an added or alternative propellant flow channel, if necessary); serve as load space, directly serving the adjacent modules; and accomodate eventual repurposing as tunnel wall support (etc). Modified intertanks could serve as an alternative propellant configuration (incorporating the flow-through capabilities of the outermost void spaces. The CAD drawings attached (converted to JPEGs) show the general arrangement of the voids, the three tanks of the interior shell, general boundary outlines for the remaining shells, one panel of the exterior end-cap bulkhead, and various construction lines. The parallel construction lines inside the tank space denote centrelines and boundary lines denoting compartment divisions. These latter consist of four lateral decks, themselves divided into a central corridor, two primary living space channels, and two supporting space channels. The outer decks and supporting space channels provide additional radiation shielding for living space areas.