The Janus Habitat: A Minimal-Mass Rotating Tether System with Recycled PET Counterweight for Mars Transit

This paper presents the Janus Habitat, a novel spacecraft architecture for Mars transit that achieves artificial gravity
through a 200-meter tether system connecting a 50-tonne crew module to a 50-tonne counterweight composed primarily
of terrestrial recycled polyethylene terephthalate (R-PET). The system generates 0.5 g at 2.1 RPM with only ~200 kg of
tether mass, representing a 98.5% mass reduction compared to traditional rotating cylinder designs. The counterweight
utilizes standardized interlocking R-PET blocks manufactured on Earth at approximately 0.1% the cost of launching
dedicated ballast. An optional orbital debris processing system adds value by transforming aluminum space debris into
supplemental shielding. The complete 120-tonne system enables deployment with two heavy-lift launches, providing a
practical path to artificial gravity for long-duration transits while creating terrestrial environmental benefits through space-
based demand for recycled plastics.