SNAP: Small Next-generation Atmospheric Probe Concept

We present a concept for a small, atmospheric probe that could be flexibly added to future missions to a giant planet as a secondary payload, which we call the Small Next-generation Atmospheric Probe (SNAP). SNAP's main scientific objectives are to determine the vertical distribution of clouds and cloud-forming chemical species, thermal stratification, and wind speed as a function of depth. As a case study, we present the advantages, cost and risk of adding SNAP to the future Uranus Orbiter and Probe flagship mission; in combination with the mission's main probe, SNAP would perform atmospheric in-situ measurements at a second location, and thus enable and enhance the scientific objectives recommended by the 2013 Planetary Science Decadal Survey and the 2014 NASA Science Plan to determine atmospheric spatial variabilities.

Out study demonstrates that the science objectives can be achieved with a 30-kg entry probe, 0.5m in diameter (less than half the size of the Galileo probe) that reaches 5-bar pressure-altitude and returns data to Earth via the carrier spacecraft. As the baseline instruments, the probe will carry an Atmospheric Structure Instrument (ASI) that measures the temperature, pressure and acceleration, a carbon nanotube-based NanoChem atmospheric composition sensor, and an Ultra-Stable Oscillator (USO) to conduct a Doppler Wind Experiment (DWE). We also catalog promising technologies currently under development that will strengthen small atmospheric entry probe missions in the future. The cost estimate for such a mission is about $80 Million (in FY18 dollars), including 30 percent reserve. The current estimate for the total atmospheric entry mass is 20.5 kg. The total mass including a 30 percent mass-growth allowance is 26.6 kg, which leaves 13 percent margin in our 30 kg target design. With the 30 kg design target (accounting for the 30 percent mass-growth allowance and 13 percent mass margin), the TPS mass fraction is 21 percent, and the instrument mass fraction is 19 percent.

The project has been supported by NASA Planetary Science Deep Space SmallSat Studies Program grant NNX17AK31G.