The goal of the proposed effort is to use selective laser melting (SLM, an additive manufacturing technique) to manufacture a hot fire-capable, water-cooled spool piece that features an advanced regenerative cooling technique that combines high heat flux performance with low pressure drop. SLM enables us to "print" the spool piece in days, despite the complexity of the regenerative liner's inherent flow passage complexity. This reduction in manufacturing lead time, combined with the fact that SLM manufacturing costs are driven in large part by the amount of raw powder used during fabrication, results in a substantial cost reduction for future regeneratively-cooled rocket engines. Additionally, the proposed advanced regenerative cooling approach features a heat-pickup efficiency that is at least two orders of magnitude higher than traditional milled channel liners and/or brazed tube bundle chambers. As a result of our Phase I activity and confidence in our commercialization path, we will be making a capital investment to stand up an SLM manufacturing capability in house. We plan to augment that investment with an internally-funded trade study that we will use to derive main combustion chamber performance requirements for a future expander cycle engine. Those requirements will feed into Phase II design requirements and, ultimately, to supporting our commercialization opportunity presented by the Affordable Upper Stage Engine Program.