ion Electrospray Propulsion System for CubeSats (iEPS)



Objective of the Research

The objective of this project is to evaluate the use of electrosprays for propulsion in nano and pico-satellites. CubeSats are 10x10x10 cm, 1 kg satellites that currently do not feature high specific impulse and compact propulsion. Our team is currently developing a MEMS-based propulsion system for CubeSats that will provide attitude control and main propulsion with specific impulse between 2000 and 3500 seconds in a system that will not occupy more than 10% to 30% of the size of a 1U CubeSat. The anticipated delta-V produced by these devices depends on the amount of propellant carried on board. For instance less than 150 g of propellant would be required by a 1U CubeSat to reach earth's escape velocity from LEO and explore interplanetary space.

           

Engineering Team:


- Natalya Brikner (Ph.D. Candidate): Compatibility of thruster materials
- Chase Coffman (Ph.D. Candidate): Porous material and extractor fabrication
- Hanqing Li (Research Scientist/MTL): Device and process design
- Fernando Mier-Hicks (Ph.D. Candidate): Electronics, thrust balance and CubeSat integration
- Louis Perna (Ph.D. Candidate): Silicon MEMS fabrication and packaging
- Steven Arestie (Ph.D. Candidate): Porous material development and fabrication


Science Team:


- Tom Coles (Ph.D. Candidate): Atomistic simulation of ion emission and ion stability
- Carla Perez-Martinez (Ph.D. Candidate): Ion beam spatial distribution and ion optics

Undergraduate Researchers (UROPs):


- Grace Krusell
- Filip Twarowski
- Kelly Mathesius
- Da-Yeon Kim


Principal Investigator:


Prof. Paulo Lozano



Approach

The propulsion system is based on the extraction and acceleration of heavy molecular ions using strong electric fields at the interface between the propellant (zero vapor pressure ionic liquids) and vacuum. The process of field evaporation to produce the charged particles does not require any appreciable volume for ionization. Furthermore, the propellant does not need to be pressurized and flows exclusively by capillarity forces. The lack of valves, pipes, pumps and pressurization enables very compact designs, compatible with CubeSat limitations and requirements.

Fig 1. Conceptual view of an iEPS thruster module (Dan Courtney, courtesy)

Maximum compactness is achieved through the use of MEMS techniques, similar to those used in the fabrication of microchip components. A crucial part in the process is the monolithic integration of silicon with micro-fabricated porous metal substrates containing the ion emitting structures. Designing the new generation of compact ion thrusters is a challenging task. Essentially, we have a very small thruster (10x10x2.5 mm) which is literally soaked in a conductive liquid and includes all required elements to provide outstanding electrical and hydraulic isolation at voltages of about 1000 V when operating for long times at high performance.

Fig 2. Left: iEPS modules fabricated in silicon (SPL). Right: Electron microscope images of ion emitting structures micro-fabricated in porous metal (Dan Courtney, courtesy)

The goal is to integrate iEPS thrusters in different CubeSat configurations. For example, having 4 thruster modules in a 1U CubeSat would be the minimum configuration to provide basic attitude control and main propulsion.

Fig 3. Graduate student Natalya Brikner holds a 1U CubeSat prototype with 4 iEPS thruster modules and PPU electronics (SPL)

Our laboratory is currently developing a magnetically-levitated balance for CubeSats that allows for a complete characterization of thruster performance through controlled slew maneuvers. This facility will also allow our team to study the performance of iEPS thrusters in high precision attitude control down to the arc-second range.

Fig 4. Prototype of a magnetically levitated CubeSat balance to study thruster performance. The setup will be mounted inside a vacuum chamber to replicate the conditions encountered in space. The small satellite is completely untethered thus allowing testing of fully-integrated CubeSat systems (Fernando Mier-Hicks, courtesy)

    There are a number of CubeSats missions that would benefit from iEPS technology, for example:

- Removal of orbital debris
- Formation flying: collaborative architectures
- Servicing missions: inspection, docking, assembly and repair
- Satellite de-orbit at the end of mission
- 3-axis attitude control (including ultra-precise pointing)
- Desaturation of reaction wheels
- Change orbital elements
- Counteract atmospheric drag at LEO
- Interplanetary exploration: thrusting to the moon, asteroids and beyond


Fig 5. CAD illustration of a 3U CubeSat using 32 iEPS thruster modules for high-precision attitude control and main propulsion. The iEPS thruster assemblies are under development in a NASA SBIR Phase II program with Espace Inc (Rebecca Jensen-Clem, Francois Martel, courtesy)