Ground deformation measurements obtained with interferometric synthetic aperture radar (InSAR) technologies have the potential to improve short-term forecasting of natural hazards and enable more effective management of natural resources. For maximum impact, InSAR measurements must be precise (sub-cm level) and timely. Frequent acquisitions (sub-weekly) are needed to achieve both requirements. More observations per unit time provide enhanced deformation precision through averaging, and ensure that an event is properly captured and characterized. Yet, single-platform sensors cannot simultaneously achieve frequency and wide-area coverage, and traditional InSAR sensors are too expensive (> $300M) to replicate. We propose to provide high-precision ground deformation measurement capabilities in an affordable package ($1-2M) that can be used to form a constellation of InSAR sensors capable of rapid-repeat (daily) coverage of science targets. Such achievements are made possible through developments in nanosatellite technology, specifically the emergence of the CubeSat standard. We have designed a TRL 2 (TRLin) S-band radar subsystem capable of moderate-resolution (25 m), high-fidelity InSAR performance (sub-cm deformation precision, SNR > 14 dB). The radar fits within 1U of a 6U CubeSat and satisfies the power and thermal requirements of the CubeSat environment. We call this subsystem the SRI CubeSat Imaging Radar for Earth Science (SRI-CIRES). In this investigation, we will develop, build, and test the RF and digital electronic subassemblies of SRI-CIRES over a two-year period to achieve a functional prototype at TRL 5 (TRLout). We will ensure that the SRI-CIRES prototype can meet the science objectives and performance requirements of an operational mission (e.g., can correct atmospheric artifacts and ionospheric effects to achieve sub-cm level accuracy). We will also use funds from this award to thoroughly study and model supporting subsystems, such as power, shielding, and thermal support, as well as the high-gain deployable antenna that SRI-CIRES requires to operate as a full instrument.