Mars Radiation Environment and Water-ice Prospecting through a Distributed Swarm of Tumbleweed Rovers

The Tumbleweed mission aims to revolutionize Mars exploration by leveraging the unique capabilities of wind-driven, spheroidal rovers. The use of modular design strategies, off-the-shelf components, and mass production will significantly reduce costs, making Mars exploration more accessible. Designed for rapid and extensive surface exploration, Tumbleweed rovers offer an affordable and efficient method for gathering crucial data across large areas of the Martian terrain. By deploying a swarm of more than 90 rovers equipped with various scientific instruments, this mission will significantly enhance our understanding of Mars, facilitating future human exploration and settlement.

The search for water in various forms is the common thread that binds the science goals of Mars exploration missions over the past few decades. For large scale water extraction (aimed at producing propellant and potable water in sizable quantities), a coordinated prospecting and characterisation campaign is required to arrive at maps of exploitable reserves.

Unfortunately, current architectures rely primarily on large, complex, and expensive rovers. While these platforms provide invaluable data, they are limited in their spatio-temporal coverage. Consequently, optimal Exploration Zones (EZs) for human exploration of Mars are yet to be defined.

Based on current priorities in Mars science and exploration, as well as the technical constraints of the Tumbleweed rover, a preliminary list of instruments was drafted. Exploring the synergies amongst these instruments, we arrived at the opportunity to use radiation-focused instrumentation to simultaneously achieve high-resolution mapping of hydrogen in the near-surface environment. Measuring the flux of epithermal neutron emissions is one of the best approaches towards estimating water equivalent hydrogen (WEH) abundance. Thermal and epithermal neutron measurements from instruments such as FREND, HEND and DAN have indicated the presence of WEH in the near-surface. This would represent the prime target for ISRU operations in the near future. However, the resolution of existing orbital maps of water ice is insufficient to direct and execute robotic/human operations on ground. 

This suite of radiation detection instruments will be consolidated in the future through the addition of a miniaturized Gamma Ray Spectrometer, providing the ability to perform elemental mapping along the rover traverse. Beyond neutron spectrometers, patch permittivity sensors may also be deployed on the Tumbleweed Rovers, enabling cross-confirmation of WEH mapping.

This instrumentation and our mission architecture enable high-resolution mapping of Martian environments, combining radiation scouting with WEH prospecting, thus identifying low-radiation and high-WEH regions ideal for crewed missions.

To aid further maturation and design of the mission, a conceptual study is proposed herein. Starting from a simulation of the individual rover’s trajectories on the surface of Mars, we shall geospatially compute the probable intersections with the already identified EZs on Mars. Based on these intersections we can infer thresholds for the controlled navigation of individual rovers (assessing intersections per trajectory buffer size) and classify candidate EZs according to known topography and available WEH mapping. This classification would enable more precise GEANT4 modelling of individual rovers and their instrumentation, resulting in probable neutron counts and dose/flux readings, leading to mission-specific requirements for our spacecrafts and their payloads.