Neutral Optics Velocity Analyzer, A Novel Method for Measuring Thermospheric Temperatures and Winds

Neutral winds are an under-observed quantity critical for understanding thermospheric dynamics and energetics at planets such as Earth, Mars, and Venus. Neutral wind measurements are a focus of NASA efforts such as Geospace Dynamics Constellation (GDC) and are prominently featured in the Decadal strategy for Solar and Space Physics (Heliophysics) due to their importance in geomagnetic storm response, neutral winds dynamo, and ion-neutral coupling. Neutral winds are also critical to understanding the transport of lighter species and the dynamical heating of the thermosphere. A complementary state variable that is also under-sampled in the terrestrial thermospheres is neutral temperature. What is needed is a way to address the sparsity of neutral wind and temperature data in the temporal and spatial domain. By utilizing increasingly capable swarms of small spacecraft, this goal can be accomplished by placing small, focused, and inexpensive observing platforms in multiple local time planes allowing for the simultaneous deconvolution of temporal, latitudinal, and local time effects at a variety of seasons.

In order to enable thermospheric wind and temperature observations at scale, a breakthrough in sensing technology is needed that reduces the use of expendables such as filaments, reduces power consumption, and increases the ease of instrument and spacecraft integration. The University of Colorado, Boulder is currently developing a novel sensing system that analyzes thermal neutrals without ionization, the Neutral-Optics Velocity Analyzer (NOVA). The NOVA concept is based on previous research done with the scattering of neutral gas at spacecraft velocities from highly-oriented pyrolytic graphite (HOPG) that suggests the use of scattering dynamics alone can determine the energy distribution in the in-track direction. The projection of this energy distribution onto a suitable detector allows for the determination of temperature, in-track velocity, and cross-track velocity. This effort is a collaboration between the Laboratory for Atmospheric and Space Physics and the Smead Department of Aerospace Engineering Sciences.

In this poster, we describe current efforts to design, model, and test the NOVA concept. The concept design occupies approximately 10x10x30cm of volume (3U) and is expected to consume less than 20W of power. Test particle software is used to model the instrument response and predict the observed angular distributions at the detector plane. Initially, the focus is on detecting atomic oxygen distributions due to its scattering properties on HOPG, its abundance in the Earth’s thermosphere, and its presence in the thermospheres of other planets. Preliminary scattering distributions were obtained using a hypersonic beam of neutral atomic oxygen at 5eV (7.8 km/s) kinetic energies at the Molecular Beam Lab in the Smead Department of Aerospace Engineering Sciences. These distributions are used to refine our test particle models of NOVA response to changes in neutral winds and temperatures.