This paper presents the mission concept for Far-infraRed Observation Spectroscopy Telescopes (FROST), a satellite mission dedicated to shedding light on the evolution of protoplanetary disks and planet formation. We target the inner disks around T-Tauri and Herbig Ae/Be stars, similar to the Sun before it reached the main sequence. FROST will be a three-part formation flying interferometer performing far-infrared spectroscopy in the wavelength range 40-200 m. The satellite constellation consists of two light collecting spacecraft and one beam combining spacecraft, where each light collecting spacecraft is equipped with a 2 m mirror. FROST will be equipped with FIR interferometers coupled with a Fourier Transform Infrared spectrometer. From Lagrangian point L2 FROST will observe more than 78 pretargeted disks with an angular resolution of up to 0.003” and a spectral resolution of R = 1000 in order to detect shifts in silicate features in the disks emission spectra. FROST will provide information about the size distribution, structure and chemical composition of grains radially in the disk as well as dynamics and dust growth mechanisms. This paper explores the difficulties involved in such a concept and demonstrates its feasibility by making science-engineering trade-offs with regards to instrumentation and procedure. FROST is the result of a 16-student team effort at the Alpbach summer school of 2017. The main summer school organizers are FFG and ESA.