Current Research Projects

Last Updated: January 2017

Multiphase Monopropellant Micropropulsion Concepts

 The next generation of miniaturized spacecraft (“nanosats”) being developed by NASA, the Department of Defense, European Space Agency (ESA), and similar agencies will have masses less than 10 kg and have unique  propulsion requirements. The propulsion systems must be capable of providing extremely low levels of thrust and impulse (~1-100 μN-sec) while also satisfying stringent demands on size, mass, power consumption and cost.  Our sponsored work has been targeted at developing computational and experimental models for MEMS-based monopropellant micro-thruster concepts; in particular, concepts utilizing hydrogen-peroxide, a so-called “green propellant”.  Successful catalytic decomposition of the monopropellant fuel on these small length scales and low Reynolds numbers calls for non-traditional  approaches to achieving flow mixing with the catalyst.   Our current efforts have focused on multi-phase flow approaches to enhance mixing and to also throttle flows to levels commensurate with the target impulse levels.


Catalysis of H2O2 Micro-Scale Slug


 

Micro-Scale Aerospike Nozzles for Micropropulsion

Another key component in micro propulsion systems is the supersonic micro-nozzle use to convert the thermal energy into kinetic energy.  Owing to the low Reynolds numbers, viscous effects on the nozzle expander walls can significantly impact nozzle efficiency.  Our past work has extensively examined the performance of conical micro-nozzles under these flow conditions, demonstrated in the movie below: 

Transient Micro-Thruster Firing

 
We are currently investigating the use of "aerospike" nozzle geometries - usually associated with large hypersonic flight vehicles - as a means for mitigating viscous flow effects on the micro scale: 



 

Evolutionary Computing Approaches for Orbital Trajectory Design & Optimization 


The planning of orbital maneuvers and/or trajectories for spacecraft represents a design optimization problem that is associated with multiple engineering constraints (e.g., time of flight, fuel consumption, and positional accuracy). Aside from the inherently nonlinear equations of classical orbital motion, modern problems of practical interest are further complicated by various sources of perturbations such as planetary oblateness, atmospheric drag for low Earth orbits (LEO), and solar radiation pressure among others. With the emergence of satellite formation-flying mission concepts, additional constraints are often required in order to achieve satisfactory performance. 

Owing to the multiple objectives and system complexity, analytical approaches to trajectory optimization are generally not available and numerical optimization is required. To this end, various evolutionary approaches for trajectory optimization have been explored over the past decade.  Our current efforts are focused on the use of the evolutionary algorithm of "Differential Evolution" for trajectory optimization for spacecraft under realistic non-Keplerian flight conditions associated with low Earth and near Earth orbits subject to multiple sources of perturbations.  

An example of our current work is depicted below, motivated by NASA's MMS project, wherein a group of four satellites are required to assume a tetrahedron shape around apogee for measurement requirements.