← Back to NASA Technology Projects
Completed TRL 2 (started at 2, targeting 5)
The increasing use of nanosatellites, colloquially "CubeSats," necessitates the development of new micro-propulsion technologies. NASA's 2015 Technology Roadmap specifically mentions several candidates, including electrospray propulsion (TA 2. 2.1.5). Research into this technology has produced propulsion systems that have been successfully demonstrated on orbit, but work remains to be done in optimizing both hardware design and propellant selection.
UTSI has developed novel femtosecond laser based microfabrication processes capable of forming emitters with nano-scale dimensions. UTSI has invested in the development of this capability and sees a synergistic application of this core capability (manufacturing, materials, etc) to the fabrication of micro-electric propulsion thrusters for CubeSat applications. UTSI has already begun development of an electrospray thruster, called the Micro Scalable Thrusters for Adaptive Mission Profiles in Space (µSTAMPS). The proposed system has emitter pitch that is an order of magnitude smaller than current state of the art thrusters, increasing thrust density by a factor of ~100 and has ultra-sharp emitter tips reducing applied voltages by a factor of~ 10. UTSI is in the process of fabricating these µSTAMPS devices.
Ionic liquids (IL) are green propellants that enable the electrospray devices that UTSI is committed to develop. Through UTSI's early research effort a gap has been identified in the range of available ionic liquids and their pertinent properties related to propulsion systems. Since MSFC has a leading role in NASA's IL development, we are proposing a collaborative effort to concurrently develop novel propellants for microelectrospray thrusters. The outcome of the proposed activity will not only provide a systematic compatibility characterization of IL for this application, it will also enable a green micro-electrospray thruster that supports MSFC's efforts to develop propulsion systems for small satellites .
It is envisioned that these micro-propulsion thrusters offer a reduced volume propulsion solution for CubeSats by being inserted into the walls/structures of cubesats/smallsats, as well as reducing operation voltage and interference with other electronics. If the proper IL is developed, longer thruster lifetime will result , enabling longer missions. The proposed activity will also demonstrate the application of UTSI's advanced microfabrication capabilities toward the development of a micro-propulsion system. What is proposed includes a modest investment by MSFC to support the IL propellant development and in-kind contribution by UTSI.
The µSTAMPS thruster technology is based on well-known electrospray concepts. When a conductive fluid is in the presence of a strong electric field, the surface deforms from the spherical shape associated with surface tension and forms a Taylor cone that generates a jet of charged liquid droplets at the tip of the cone. These droplets are accelerated by the field produced between an array of needles, around which the cones form, and extractor and accelerator grids to produce thrust. A notional concept of the µSTAMPS thruster emitter and extraction grid. The subcomponents of the µSTAMPS thruster, namely the array of needles and the extractor and accelerator grids, as well as propellant storage and delivery microfluidics, can all be patterned via direct-write femtosecond laser microfabrication (FLM) methods developed at UTSI. Unlike conventional photolithography, FLM methods allow designs containing microscopic features to be etched directly, in a single step, on virtually any material (metals, ceramics, glass materials and polymers), without a photomask. Compared to picosecond and nanosecond laser based methods, femtosecond lasers provide superior materials ablation efficiency, as well as superior quality in terms of attainable minimum
feature sizes and part finish. With femtosecond lasers, one can attain smaller and sharper features, with virtually no heat-induced artifacts (such as melt spatters, cracks, burrs) that are commonly observed with longer pulse laser technologies. Such attributes make femtosecond lasers the best suited technology for applications involving microfabrication. With this technology, emitters exhibiting 100 nm radius tips, and arranged in arrays of several millions within a square centimeter are routinely fabricated. Grids of 5 um OD through-holes in 1-to-2 mil thick metal sheets have been demonstrated. And complex microfluidics for lab-on-a-chip devices have been reported. Emitters, grids, and microfluidics prepared using FLM methods have all been demonstrated using the state of the art facility located at the UTSI Center for Laser Applications.
The selection of an appropriate propellant is an important part of designing electrospray thrusters. The propellant must be conductive in order to form Taylor cones that produce charged droplets that are accelerated by an electrostatic field. As propellant is ejected from the needle tip, it is replenished by capillary action, so high surface tension and low viscosity are required properties. Additional desirable properties are similar anion and cation masses, low electrical permittivity, low hygroscopicity, low vapor pressure , and high materials compatibility. ILs are well suited for use in electrospray thrusters. Being entirely composed of ILs are naturally conductive. The presence of both positively and negatively charged species allows for the thruster to be sequentially operated at opposite polarities, which prevents charging of the spacecraft and removes the need for neutralizers. !Ls can have almost no vapor pressure, enabling them to be stored on spacecraft without the use of heavy pressure vessels. !Ls also have high electrochemical stability, allowing greater electrostatic potential to be applied and generally have wide liquidus ranges that exceed the temperature regime imposed on spacecraft. Despite these attractive properties, only two ILs, 1-ethyl-3-methyimidazolium tetrafluoroborate (EMI BF4) and 1-ethyl-3- methyimidazolium bis(trifluoromethylsulfate)imide (EMI TFSI) have been widely studied for use as propellants. Of these ILs, (EMI BF4) readily hydrolyzes in the presence of water which produces HF which corrodes thruster hardware. State of the art micro-propulsion systems are expected to be particularly sensitive to HF corrosion given the extensive use of materials such as Silicon, Silicon Dioxide, and metals in their fabrication. We propose conducting a systematic study to optimize hardware geometry and propellant selection. This effort will advance electrospray propulsion by furthering our understanding of hardware design and propellant selection.
Listed on TechPort itself — the most direct way to ask about this specific project.
This is early/mid-stage (TRL 2) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.
None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.