RAIDS was conceived and built as a survey experiment with broad capabilities to completely characterize the aeronomically important species in the thermosphere and ionosphere. Nowadays, space science missions are generally expected to have more tightly-focused objectives than those of the original RAIDS mission. Though a global comprehensive thermospheric and ionospheric survey has never been performed, various space experiments over the last 15 years have advanced our understanding of the thermosphere. Yet compelling, fundamental science questions remain concerning (1) the structure of the thermosphere and ionosphere, (2) their responses to solar and geomagnetic forcing, and (3) the effect of tides and gravity waves upon the upper atmosphere. The RAIDS experiment will measure the composition, density, and temperature from which chemical and dynamical effects can be modeled or inferred to address aspects of these questions.
The International Space Station platform is not designed for high latitude (auroral) or ionospheric observations due to its 51.6° orbital inclination and 330‒425 km orbital altitude. Consequently, the ability of RAIDS to address the science questions above will be limited to what can be accomplished in low- to mid-latitudes and in the lower portion of the thermosphere and ionosphere. The new RAIDS objectives tailored for this ISS mission are:
- Primary Objective: Measure the lower thermosphere temperature over altitudes 100-200 km to study the vertical temperature and compositional structure, the thermospheric response to solar UV variability, and the effect of tides and waves on the lower thermosphere.
- Secondary Objective: Measure the O+ initial 83.4 nm emission source in the lower F-region ionosphere separately from the multiple scattering 83.4 nm source near the F-region peak to validate remote sensing of the dayside ionosphere.
- Secondary Objective: Measure the global distribution of minor species in the thermosphere to understand their role in chemical and ionic reactions in the lower thermosphere and ionosphere.
The primary objective of temperature measurements in the lower thermosphere is highly relevant to current community interest in the effects of tides upon the global structure of thermosphere and ionosphere, the development and validation of improved empirical models of the thermosphere, and understanding the heat balance in the thermosphere with respect to global climate change and satellite drag. RAIDS measurements will focus particularly on temperature in the 100-200 km altitude range where a large temperature gradient occurs and which coincides with a temperature data gap between 130-200 km.