In the space industry miniaturization has been a trend for decades, with satellite masses ranging from 0.1-10kg for pico- and nano-satellites. Propulsion subsystems for these satellites have not kept up with this trend performance-wise. They are often limited by safety regulations requiring inert propellants and power budget constraints of the satellite. Vaporizing Liquid Microthruster (VLM) are a type of resistojet considered for pico- and nano-satellites and are currently in development at Space Engineering (SE) department of the Technical University of Delft (TUD). VLM expel an electrically heated (inert) propellant, which is stored in the liquid phase. Currently, VLM are inefficient and design tools are needed to find more optimal designs. In this research such a design tool is developed, and applied to thrusters with water as a propellant. A distinction with earlier research on VLM is that specific attention was paid to the field of microchannel flow boiling, so that knowledge from this discipline could be applied in the heat transfer model of the VLM heating channels. The design tool was successfully developed, and is extendible with novel heat transfer and pressure drop relations when required for future research. When applied to 15 mN thrust range, the outcome is that the chamber temperature can be increased without increasing the total power consumption significantly. Heating chamber design also tends to be more optimal if more and smaller channels are used than in earlier published VLM designs. The optimal wall temperatures were about 40 K higher than the chamber temperature. The optimal channel width and wall thickness were constrained by structural limitations, at 20 and 50 micron, respectively. The optimal number of channels increased with thrust from 3-4 channels at 1 mN to 8-9 at 5 mN.