Chromologic (CL) and the California Institute of Technology (Caltech) propose to develop and demonstrate a Multifunctional Environmental Digital Scanning Electron Microprobe (MEDSEM) instrument that transmits high-energy beams of electrons sequentially from a two-dimensional array of miniaturized electron probes into a planetary atmosphere, and these electrons will strike solid or liquid planetary surfaces to simultaneously generate a wealth of spatially-mapped compositional information. MEDSEM will simultaneously measure X-ray Fluorescence (XRF), Backscattered Electron Spectra, Optical Spectra and Mass Spectra. Caltech will transfer to CL the microfabrication technology for vacuum-encapsulating, electron-transmissive SiN membranes, the key enabling component without which MEDSEM would not be possible. Caltech will also transfer the results of electron-optic simulations performed for optimizing the MEDSEM instrument configuration. The 12-month Phase I effort will be aimed at demonstrating the proof-of-principle for MEDSEM via an experimental setup made up of mostly commercial-off-the-shelf (COTS) parts: miniature electron sources, an x-ray detector and a double-chambered test setup. High-energy electrons will be generated in the first, evacuated chamber, and these electrons will pass through the Caltech-fabricated SiN membrane into the second chamber (maintained at Martian ambient pressure), to strike planetary analog samples thereby generating characteristic XRF. The XRF spectra will be captured by a COTS x-ray detector which is present in the second chamber. Contingent on a successful, follow-on, Phase II effort, the proof-of-principle experiment will be expanded to demonstrate the remaining simultaneous measurement modalities, namely the acquisition of Backscattered Electron Spectra, Optical Spectra and Mass Spectra. Microfabrication of the fully-integrated, field-emitter array of miniaturized electron probes will be pursued during Phase II.