A Carbon Nanotube (CNT) ultracapacitor capable of operating from the extreme low temperature of -110°C, up to 80°C will be developed. Traditional ultracapacitors exhibit limited operating temperature ranges due to use of high melting point and volatile electrolytes, and activated carbon electrodes. During Phase I, we will demonstrate a new low melting point ionic liquid based electrolyte and engineered CNT electrodes for high power and energy density retention at temperature extremes. The proposed ultracap will enable significant improvements in spacecraft avionics, launch vehicles, rovers and landers - reducing weight, volume and complexity while improving performance and relaxing design constraints on traditional battery technologies. At the end of Phase II, this device will deliver a high peak power density of (10kW/kg and 14kW/L) and an energy density of (8Wh/kg and 11Wh/L) over this broad temperature range. The prototype will have a cycle life of 1,000,000 cycles at room temperature and below, and more than 100,000 cycles at 80°C. Further, the device will be engineered to withstand high shock (up to a 1000Gpeak) and vibration (up to 60 Grms) conditions. In applications where long-lived energy storage devices are critical, dramatic reductions in total weight and volume can be achieved by pairing batteries with the proposed ultracap technology.