Development Status and 1U CubeSat Application of Busek’s 0.5N Green Monopropellant Thruster

The monopropellant community has been pursuing low-toxicity alternatives to hydrazine for the past two decades. One of such “green” monopropellants, known as AF-M315E, has caught attention of many by offering both improved performance and handling safety. A 0.5N-class, AF-M315E micro thruster was recently developed by Busek that can deliver \u3e220sec vacuum Isp. Both steady-state and pulsed firings were demonstrated. The thruster, when cold, requires a small amount of pre-heating power to start which is no more than 12W or an equivalent of 1.6W-Hr energy input. The thruster is complemented by a novel piezoelectric microvalve that needs less than 200mW to operate and weighs a mere 67g. The valve features an all-welded, all-titanium wetted design for long-term propellant compatibility. It is rated for 1200sccm GN2 max flow and 1.5×10-4sccm GN2 leak rate. The valve passed environmental testing before being integrated into the thruster, and together they demonstrated a minimum impulse bit of 0.036N-sec. Busek is currently developing a 1U CubeSat propulsion system centered on the integrated 0.5N thruster and microvalve. The system is designed to be self-contained and fully loaded with propellant, which allows for simple spacecraft integration and reduced operating cost

Electrospray device

An electrospray device includes an electrospray emitter adapted to receive electrospray fluid; an extractor plate spaced from the electrospray emitter and having at least one aperture; and a power supply for applying a first voltage between the extractor plate and emitter for generating at least one Taylor cone emission through the aperture to create an electrospray plume from the electrospray fluid, the extractor plate as well as accelerator and shaping plates may include a porous, conductive medium for transporting and storing excess, accumulated electrospray fluid away from the aperture

Investigation of a Pulsed Plasma Thruster Plume Using a Quadruple Langmuir Probe Technique

The rectangular pulsed plasma thruster (PPT) is an electromagnetic thruster that ablates Teflon propellant to produce thrust in a discharge that lasts 5-20 microseconds. In order to integrate PPTs onto spacecraft, it is necessary to investigate possible thruster plume-spacecraft interactions. The PPT plume consists of neutral and charged particles from the ablation of the Teflon fuel bar as well as electrode materials. In this thesis a novel application of quadruple Langmuir probes is implemented in the PPT plume to obtain electron temperature, electron density, and ion speed ratio measurements (ion speed divided by most probable thermal speed). The pulsed plasma thruster used is a NASA Glenn laboratory model based on the LES 8/9 series of PPTs, and is similar in design to the Earth Observing-1 satellite PPT. At the 20 J discharge energy level, the thruster ablates 26.6 mg of Teflon, creating an impulse bit of 256 mN-s with a specific impulse of 986 s. The quadruple probes were operated in the so-called current mode, eliminating the need to make voltage measurements. The current collection to the parallel to the flow electrodes is based on Laframboise’s theory for probe to Debye length ratios between 5 and 100, and on the thin-sheath theory for ratios above 100. The ion current to the perpendicular probe is based on a model by Kanal and is a function of the ion speed ratio, the applied non-dimensional potential and the collection area. A formal error analysis is performed using the complete set of nonlinear current collection equations. The quadruple Langmuir probes were mounted on a computer controlled motion system that allowed movement in the radial direction, and the thruster was mounted on a motion system that allowed angular variation. Measurements were taken at 10, 15 and 20 cm form the Teflon fuel bar face, at angles up to 40 degrees off of the centerline axis at discharge energy levels of 5, 20, and 40 J. All data points are based on an average of four PPT pulses. Data analysis shows the temporal and spatial variation in the plume. Electron temperatures show two peaks during the length of the pulse, a trend most evident during the 20 J and 40 J discharge energies at 10 cm from the surface of the Teflon fuel bar. The electron temperatures after the initial high temperature peak are below 2 eV. Electron densities are highest near the thruster exit plane. At 10 cm from the Teflon surface, maximum electron densities are 1.04e20 ± 2.8e19 m-3, 9.8e20 ± 2.3e20 m-3, and 1.38e21 ± 4.05e20 m-3 for the 5 J, 20 J and 40 J discharge energy, respectively. The electrons densities decrease to 2.8x1019 ± 8.9e18 m-3, 1.2e20 ± 4.2e19 m-3, and 4.5e20 ± 1.2e20 m-3 at 20 cm for the 5 J, 20 J, and 40 J cases, respectively. Electron temperature and density decrease with increasing angle away from the centerline, and with increasing downstream distance. The plume is more symmetric in the parallel plane than in the perpendicular plane. Ion speed ratios are lowest near the thruster exit, increase with increasing downstream distance, but do not show any consistent angular variation. Peak speed ratios at a radial distance of 10 cm are 5.9±3.6, 5.3±0.39, and 4.8±0.41 for the 5 J, 20 J and 40 J discharge energies, respectively. The ratios increase to 6.05±5.9, 7.5±1.6, and 6.09±0.72 at a radial distance of 20 cm. Estimates of ion velocities show peak values between 36 km/s to 40 km/s, 26 km/s to 30 km/s, and 26 km/s to 36 km/s for the % J, 20 J, and 40 J discharge energies, respectively

Development of Busek 0.5N Green Monopropellant Thruster

The monopropellant community has been actively pursuing low toxicity, green monopropellants for the past two decades. Of the large number of formulations developed, AF-M315E has received the most attention in the U.S. In comparison with hydrazine, AF-M315E offers improved Isp and density-Isp while being extremely stable and easy to handle. Despite the potential benefits, development of AF-M315E thrusters has been slow due to the lack of suitable catalysts. Busek is pioneering an alternative catalytic reactor to address such issue. Busek has developed a 0.5N-class AF-M315E thruster that has demonstrated 20+ minutes of cumulative life and consistently performs at a c* efficiency in the range of 89-93%. A piezoelectric microvalve for the 0.5N thruster has also been developed. It is superior to state-of-the-art solenoid valves of similar flow level as it requires only 0.5W of power and weighs a mere 67 gram. Potential commercial applications for the 0.5N thruster are abundant, including but not limited to primary propulsion for NanoSats and ACS propulsion for SmallSats. Scaling up the thruster is feasible and will create more opportunities to compete with legacy hydrazine thruster systems in the future

Survey of opinions on legalizing bicycling

A study was conducted to determine the opposition and support for implementation of a bicycle path along the lakes of Sortedam and Peblinge found in Copenhagen, Denmark. Surveys of area residents, pedestrians and bicyclists revealed the profiles of advocates and opponents of bicycling. Typically, opponents were 43 years old living directly along the Dosseringen who generally used the area for recreation. The typical supporter was 34 years old, active, and used the Dosseringen for travel and enjoyment of the area

Design and construction of an experimental setup for plume measurements in a large vacuum facility

This project is part of a larger study to characterize pulsed plasma thruster plumes. An understanding of plasma plumes is necessary to determine potential plume/spacecraft interactions. The project's goal was to design and build an experimental setup capable of taking plume measurements of a NASA Glenn pulsed plasma thruster. The setup is based on triple Langmuir probes and is designed for use in a large vacuum facility at NASA Glenn Research Center. A probe support mechanism was designed to be able to move the probe along a straight line downstream of the thruster via the use of a translation table. This probe support was also designed with a servomotor to be able to rotate the probe itself in order to align it with the plume vector. The thruster was mounted on a turntable in order to align the probe along different angles with respect to the center of the Teflon fuel bar. This setup allows probe measurements to be taken on planes perpendicular and parallel to the thruster electrodes at arbitrary plume locations as well as the backflow region. This setup was designed to require a minimum number of pump-downs of the vacuum facilities, with pump-downs occurring only at changes in the plane of measurement

Flight Development of Iodine BIT-3 RF Ion Propulsion System for SLS EM-1 CubeSats

Busek previously developed a 3cm RF ion thruster known as BIT-3 that was the world\u27s first iodinefueled gridded ion thruster. The 60W prototype thruster completed a 500-hour endurance test on iodine and was shown capable of delivering 1.3mN thrust and 3200sec Isp nominally, excluding neutralizer flow. This exceptional performance, combined with the many benefits of iodine propellant, has led to a number of CubeSat flight opportunities on NASA\u27s SLS EM-1 mission. The first confirmed EM-1 mission for the thruster is onboard the 6U Lunar IceCube spacecraft that is being developed by Morehead State University and its partners. This paper will describe the technological advances made to date on the BIT-3 system and the remaining development to flight readiness. Specifically it will include updates on the thruster design and power optimization, measured thruster and Isp performance with an innovative RF cathode neutralizer, and details regarding the flight iodine feed system and power electronics module. In addition, it will include an overview of the BIT-3 system\u27s digital command/control structure and mechanical interfaces in the context of the Lunar IceCube bus. The BIT-3 ion thruster\u27s ability to use iodine as propellant is a huge game-changer for CubeSats, as iodine is stored in high-density solid form (4.9g/cc vs. xenon\u27s 1.95g/cc at 2000psi) devoid of bulky pressure vessels. The solid storage property makes iodine-fueled propulsion systems safe and facilitates compliance with range safety requirements, which is especially important for secondary payloads. The sub-Torr storage vapor pressure also allows for thin-walled, lightweight and conformal tanks that could further reduce the overall volume and mass budget impact without compromising performance. For example, Lunar IceCube\u27s tightly packaged 2U iodine BIT-3 system can provide more than 2km/s delta-V to a 6U/14kg CubeSat for lunar or other deep-space missions. Such unprecedented capability can help increase the practicality and appeal of CubeSats alike, ultimately gaining acceptance within the science community as a viable platform for future robotic exploration missions to destinations currently unachievable with small satellites