The Nested Inlet for Stratospheric Sampling of Aerosols (NISSA) is an inlet designed to decelerate air from the aircraft true airspeed (~200 m/s) to < 10 m/s to enable accurate aerosol measurements with particle sizing instruments mounted inside the aircraft. Large particles (> ~2 µm in diameter) are not efficiently sampled through existing stratospheric inlets due to losses arising from induced turbulence in the inlet and sharp turns downstream. NISSA is specifically designed to minimize these losses and allow sampling of particles up to 10 µm in diameter. Measuring coarse mode particles in the stratosphere is important for assessing their contribution to the radiative budget and impact on stratospheric chemistry, especially following perturbations such as large volcanic eruptions.
For the SABRE 2025 test flights, NISSA has been instrumented to measure air velocity and turbulence within the inlet, as well as pressures at several locations in the inlet. These measurements will be used to validate the computational fluid dynamics (CFD) simulations of flow around and within the inlet, which allow calculation of particle losses within the inlet and associated tubing. The NISSA was developed at Clarkson University in Potsdam, NY, by Prof. Suresh Dhaniyala and mechanical engineering graduate student Nagarajan Radhakrishnan.
Harvard University's [Dykema] Printed Optical Particle Spectrometer (DPOPS) is an in situ instrument capable of measuring particle number density as a function of size throughout the UTLS (upper troposphere/lower stratosphere). The instrument uses a 405-nm diode laser to count and size individual particles (independent of composition and phase) in the size range 140-3000 nm. The instrument is designed for autonomous operation in flight and requires minimal support between flights. The instrument is commercially available (Handix Scientific, Boulder, CO). Originally modified for use in the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) mission by John Dykema, a custom inlet was mounted in the free stream to sample ambient air - in this case to sample aerosol from NISSA for inlet evaluation purposes.