Atmospheric Science from Mutual Radio Occulations from Mars Orbiters

J.R. Anderson, S.S. Limaye (UW-Madison), G.L. Tyler (Stanford University)

Radio occultation experiments traditionally are performed using a single spacecraft either in orbit or in a flyby arrangement. A radio source located onboard the spacecraft works in conjuction with Earth-based receivers observing the occultation effects. For Mars and the outer planets, both the flyby and orbital cases, however, are limited geometrically to the terminator region by the need for signal reception on Earth. The use of two or more mutually occulting spacecraft offers a number of advantages over the single spacecraft approach. Proper selection of orbital parameters can enable global coverage and yield many more occultations in a specific period of time than normally would result from a single orbiter. A dense sample of temperature and pressure profiles could be made available. With autonomous spacecraft, some data processing may be conducted and the results cached onboard, reducing the quantity of data that must be returned to the ground and the frequency of ground contact. Eliminating the need to observe each occultation on the ground also frees up Earth-based tracking and data collection resources.

In the near future many spacecraft are likely to be orbited around Mars presenting us an opportunity to determine without any ambiguity the thermal structure of the Martian atmosphere. With a small number of spacecraft equipped with Ultra Stable Oscillators for frequency reference, it is possible to obtain several hundred atmospheric retrievals and surface pressure each day at widely separated latitudes and all local times (assuming appropriate orbits are chosen). This information can serve as a climate indicator and provide useful information on the Martian weather routinely.