Atmospheric Breathing Electric Thruster for Planetary Exploration

The objective of this phase of the program was to show feasibility of a Martian atmosphere breathing Hall effect thruster (MABHET). To accomplish this objective, we set out to demonstrate that: 1) a Busek Hall effect thruster could operate on the Mars atmospheric gases, 2) the atmospheric conditions and orbital parameters required for the MABHET were indeed achievable, 3) further advancement of the inlet concept held credible, and 4) continued investigation into the remaining vehicle components including the cathode, power generation, size/mass and science remained feasible. We achieved all of these goals during the first phase of this program. One major achievement during this phase was the operation of a Busek HET with simulated Mars atmosphere. Two goals included an overall efficiency of at least 20% and a maximum thrust to power ratio since the vehicle would likely be power limited. The HET was operated over a wide range of mass flow, applied anode voltage and overall power, simulating various potential altitudes and size of the thruster. Definitive thrust measurements prove that 20% efficiency is indeed possible and likely on the low end of expected performance. The thrust to power ratio peaked around 30mN/kW with an efficiency around 22-25%, depending on the operating conditions. This measured performance with be discussed in more detail below. Sizing of the vehicle, propulsion system and Mars atmosphere conditions also need to be confirmed that such a concept is feasible. The major drivers of this analysis are the vehicle drag and solar flux/collection. Utilizing current technology for spacecraft drag and solar arrays, the MABHET concept is right on the edge of feasibility. However, solar arrays are becoming more efficient on a study pace and drag in rarefied atmospheres is also becoming better understood. Minor improvements, in either or both of these areas, will confirm credibility to MABHET feasibility for future missions. The atmospheric inlet or propellant collector is a critical component for the MABHET concept to work. We chose to further our investigation of the inlet numerically utilizing DSMC and we found that shrinking the inlet proportionally for a smaller thruster/vehicle design also held performance, thus the focus on a lower power, smaller vehicle was also feasible. The inlet is the lead critical path component and needs to be investigated early in future programs. Finally, analysis and some experiments on the remaining propulsion system components and spacecraft design were initialized during phase I. This included some radio frequency cathode tests performed by Colorado State University. Though these tests were unsuccessful, rational for the failure and a path to success has been determined. We also began looking at the science made possible by this concept and who in the science community might be interested. Solar array advances and possible low drag surfaces are discussed.