Relevance of ASPEN-Mars to Mission Development and Planning

The completeness of the ASPEN-Mars parameter space means that instrument concepts can be tested using the ASPEN-Mars model output. For example, ASPEN-Mars can provide reasonable estimates of temperatures, winds, and composition and their distribution with latitude, longitude, and local time, together with their variation as a function of season and solar cycle. Such studies are vital for remote sensing instruments, which must be designed for both benign and extreme conditions. In particular, gradients in the parameter to be measured can degrade the performance of the remote sensing instrument. ASPEN-Mars provides 3-D distributions, with vertical and horizontal gradients that can be fed into remote sensing algorithms and used to guide instrument design, and to define performance expectations with error bars before the instrument leaves the drawing board. This is applicable to all wavelengths from IR to UV, and to both occultation and emission measurements.

An important part of mission design is to anticipate the different phases of the mission, and to define a minimum set of success criteria. The ASPEN-Mars model provides global distributions of density and other parameters for any conditions, which can be used to define aerobraking and later phases of the mission. It can also provide guidance on where certain measurements can be expected to be successful, versus where signals may be too weak, either from lack of sunlight, or small concentrations of emitting species. Using the model, different mission scenarios can be explored well in advance, thus reducing risk to the mission success.

Temperature, Winds and Composition
The ASPEN-Mars model simulates all of the atmospheric parameters to be measured by a typical aeronomy mission through most of the altitudes of interest (above 14 km). These include temperatures, winds and composition. For example, a mission might measure CH4, H, H2O, CO, CO2, O, OH, Na, NO) from 20-130 km. All of these species are simulated by ASPEN-Mars, and our understanding of the measurements will be enhanced by the ability of ASPEN-Mars to provide a complete chemical analysis combined with fully coupled thermal and dynamical terms affecting the species distribution. Of particular interest is our ability to simulate the methane distribution and its transport by winds.

Aerobraking and Density
The ASPEN-Mars model can also be used in aerobraking studies. In Mars Data Analysis we briefly described comparisons between ASPEN-Mars simulations and density measurements from MGS and Mars Odyssey. Thus, ASPEN-Mars has been tested in the aerobraking regime, and performed well, capturing global thermospheric structures.

Gravity waves, Planetary waves, and Tides
Another important aspect of Mars is the effects of gravity waves, planetary waves, and tides on the variability of the atmosphere. The global 3-D ASPEN-Mars model includes the ability to force the lower boundary of the model to investigate the effects of tides and gravity waves as they propagate upwards in the atmosphere. An aeronomy mission would likely provide measurements of some tidal, planetary, and gravity wave components, and ASPEN-Mars would be available to study their contributions to temperature, wind and compositional variations at altitudes between 14 km and the exobase near 250-300 km.