This is a revision of a project that I have been working on for a few years now. Oringinally, I started work on it as a concept proposal for a Universal Lander for BuildTheEnterprise (BTE), building off the visual inspiration of the Jupiter 2 from the Lost In Space television series.

At 50m diameter and 12.5m height, the J2 is a very large craft. After having concluded some initial volume studies, I have determined that the loaded wet mass is roughly equivalent to an Apollo Saturn V, when the J2 is configured for SSTO launch from Earth to LEO. The assuptions are that the propellent mass constitues 90% of the wetmass (the requirement for obtaining the effective 9.5 km/s delta-v necessary to transit to LEO), propulsion systems are allocated 2% (coinciding with a very conservative thrust/weight ratio for most rocket thrusters), a target structural mass ratio of 7%, which would allow 1% mass ratio for useful payload. Technically, this means that the craft can only lift about 35 tonnes to LEO, which is less than what the Saturn V was able to deliver to the moon; however, the J2 is a wet workshop platform, and will itself constitue an additional 300 tonnes of payload, with several times more habitable volume than the ISS. The useful payload would allow the J2 to operate with a crew of 5 for well over 2 years... and that is assuming that all closed-loop Environmental Life Support systems break down (leaving only basic filtration systems).

Although fully capable of interplanetary operations (when fitted out with appropriate propulsion and power supply systems), the J2 is intended for more localised operation. The J2 is designed to serve as a functional annex to larger craft on interplanetary missions. Once delivered to a mission destination, it can fill a number of varying roles. Notably, these roles would include bulk deliveries to colonies (normally orbit to surface), and other high mass transports; large capacity personnel transports; as well as long term platform deployments. As an example of the latter group of roles, the J2 could serve as a local command centre for colony development operations. In case of emergencies, the J2 could evacuate 250+ persons to an alternative site, or even into orbit.

The J2 is design for LOX/LH combustive propulsion for Earth operations, but is easily adaptable to LOX/liquid methane propulsion for other locations, where environmental impact is not a major concern. It is equally adaptable to support various propellants for VASIMR, or other, electric drives for space operations. Importantly, with 12 convertable pressure hulls, J2 an support everal different propulsion systems simultaneously. Ideally, J2 would likewise be able to support eventual nuclear power and propulsion operations, but this would be well beyond SpaceDecentral's projected capacities, for various reasons.

J2 would definitely be a long-term project, probably in the 30 year time frame. That said, the concept has been developed around existing materials that are already in, or entering, the mainstream market. Likewise, although the scale will require a considerable amount of testing, the concept has also been developed around production technologies that have been firmly established. On a conceptual level, there is nothing that is reliant on purely theoretical projections of future capabilities and/or properties. In other words, although future technologies could make a better craft, we have everything we need to build the J2 now.