Experiments
Our experimental research includes propellant accumulation measurement, characterization of surface deposition and surface impact byproducts, electrospray emitter fabrication using nanoscale additive manufacturing, and design of ESI-MS instrument for future planetary science missions.
Measuring Propellant Accumulation In-situ
(PhD Student: Carl Geiger)
Carl works to develop novel techniques for directly measuring neutral particles in electrospray thruster plumes and their effects on key operating surfaces using quartz crystal microbalances (QCMs), secondary charged species emission (SSE), time-of-flight mass spectrometry (TOF-MS), as well as a suite of surface characterization diagnostics. This work will inform accurate lifetime predictions for electrospray thrusters, allowing this technology to be leveraged for longer, cheaper, and more ambitious small satellite missions.
Nanoparticle Ionic Materials
(PhD Student: Stefan Bell)
Stefan is working on operating a new class of electrospray propellants known as Nanoparticle Ionic Materials. Like ionic liquids, these materials can be fluid at room temperature and have negligible vapor pressure. Instead of a molecular anion, however, these fluids have a many-multiply charged nanoparticle. The charge state can vary from 250 to over 10,000 charges, leading to the production of MeV-level kinetic energies for standard electrospray potentials. Despite being large nanoparticles, the m/z of these nanoparticles is comparable to standard molecular species found in traditional electrospray propulsion systems. These fluids represent the ability to tune the thrust and specific impulse directly through propellant design, and are estimated to produce much higher thrusts than traditional electrospray propellants.
Characterizing Surface Impact Byproducts with ESI-MS
(PhD Student: Giuliana Hofheins)
Ionic liquid electrospray thruster lifetimes are limited by the high energy plume impacting downstream surfaces -- including the extractor electrode and vacuum facility surfaces. ASTRAlab has been probing these complex ion-surface interactions through a technique known as secondary ion mass spectrometry (SIMS). These experiments including firing a high energy (> 1 keV), polydisperse molecular ion plume ionic liquid electrospray plume at a surface of interest, where collisions induce the removal of surface atoms and molecules. Through complex collision processes, a portion of the ejecta exist in a charged state. These are known as secondary ions and are particularly interesting as they interact with existing electric fields and disrupt firing characteristics. By establishing a novel electrospray time-of-flight secondary ion mass spectrometry (ESI TOF-SIMS), we have discovered many atomic and molecular secondary ions of both polarities. Through chemical identification, these secondary ions are associated with the surface of interest as well as fragments of the ionic liquid propellant.
Two-Photon Printing of Micro-Architected Electrospray Emitters
(Post Doc: Bryce Kingsley)
Bryce is working on additive manufacturing of electrospray emitters using Two-Photon Polymerization printing. Conventional emitter fabrication techniques, such as chemical etching and micro-machining, often lack the resolution, geometric flexibility, or material compatibility for optimal emitter design and fabrication. Here, we employ an alternative additive technique to fabricate electrospray emitters using Two-Photon Polymerization (TPP) printing, which uses a focused laser beam to print nano-/micro-scale structures in a photocurable resin. TPP printing enables fabrication of highly intricate and complex emitter structures that would be challenging or impossibly to achieve with traditional techniques. We leverage these capabilities by embedding Triply-Periodic-Minimal-Surface (TPMS) lattice structures into the emitter body to create a micro-porous flow network for enhanced propellant transport. With this work, ASTRAlab is building the core framework to the next generation of electrospray thrusters.
Design of ESI-MS Instrument for Future Planetary Science Missions
(Post Doc: Dr. Zach Ulibarri)
Zach Ulibarri earned his PhD in Physics at the University of Colorado studying the 'speed limit' of flyby spacecraft looking for complex organic chemistry with impact ionization, finding that at speeds beyond 7 km/s, amino acids begin to fragment at an accelerated rate. He now works on adapting electric propulsion sources to work as the first stage of a new type of spacecraft electrospray ionization (ESI) mass spectrometer. His work also carries over into electric propulsion, where he is using a new method of aiming emitted ESI plumes to study their angular characteristics.