To perform such observations on a global basis, a new millimeter- and submillimeter-wave instrument is currently under development with mass, volume and power requirements suitable for deployment on 6U-Class satellites, also known as 6U CubeSats. The Tropospheric Water and Cloud ICE (TWICE) instrument is a wide-band millimeter- and sub-millimeter wave radiometer measuring at 15 frequencies from 118 GHz to 670 GHz. The TWICE instrument is designed to provide observations of upper tropospheric water vapor profiles, temperature profiles and ice particle size distribution in clouds on a global basis at a variety of local times. The TWICE instrument uses 25-nm InP High Electron Mobility Transistor (HEMT) low-noise amplifier-based (LNA) receiver front-ends to provide low-noise and low-power operation in a small form factor at millimeter- and sub-millimeter-wave frequencies. TWICE radiometers will perform conical scanning to preserve the polarization basis. End-to-end calibration will be performed at all 15 frequencies once per scan by viewing both the cosmic microwave background (2.7 K) and an ambient calibration target at a known thermodynamic temperature. TWICE will meet the requirements for operation in a 6U-Class satellite with dimensions of 34 cm x 20 cm x 10 cm and mass up to 12 kg.