Lunar regolith contains various chemical and mineralogical resources, which can be extracted to build an outer habitat shell using additive manufacturing techniques (a.k.a. 3D printing) by robots. Proof of concept experiments have demonstrated that microwave radiation couples efficiently with lunar regolith resulting in sintering/melting, which could enable resource extraction and the fabrication of 3D structures. However, there still remain major unkowns relating to lunar soil interactions with microwaves that can only be answered through experiments on the Moon surface; for example the effects of nanophase iron (np-Fe⁰), the highly electrostatic nature of the particles, and irregular particle geometries of the real lunar soil. At the Open University (OU), we have embarked on a collaborative project called MARVEL (Microwave heating Apparatus for Regolith Variant Experiments for Lunar ISRU), with Added Value Solutions UK Ltd. and VIPER RF. The team aims to develop a Microwave Heating Demonstrator (MHD) payload which can be deployed on the lunar surface. The ambition is that the MHD will perform pre-defined experiments and be available for selection on future NASA/ESA missions to the Moon. The initial concept of the MHD payload was developed with support from UK Space Agency (UKSA)’s Grants for Exploratory Ideas (GEI) funding under the National Space Technology Programme.