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

Twin Ion Engine Demonstration for Small Spacecraft Applications

Two iodine-fueled, second-generation (Gen-2) “BIT-3” gridded RF ion propulsion systems were successfully demonstrated in proximity. The test units feature a host of upgrades from the flight models delivered to Lunar IceCube and LunaH-Map 6U Cube missions onboard NASA’s SLS Artemis 1. Each Gen-2 BIT-3 system is capable of 1.1 mN thrust, 2,150 sec specific impulse and 31.7 kN-sec total impulse, at 75W maximum power input. The twin engines, separated by a mere 6.5 cm, successfully performed simultaneous startup, sequential startup, and throttling, all without noticeable plasma interference. Onboard telemetry confirms that both thruster and cathode pairs operated nominally, and both ion plumes were stable and properly neutralized by the cathodes in all scenarios. This result should give confidence to microsatellite developers who are looking to fulfill propulsion requirements by multiplexing the BIT-3 - a compact, high-TRL, cost-effective, and readily available propulsion module

LunarCube: A Deep Space 6U CubeSat with Mission Enabling Ion Propulsion Technology

Busek, in partnership with Morehead State University (MSU), is developing a versatile 6U CubeSat platform nicknamed “LunarCube” that can undertake missions beyond LEO. The spacecraft can host a variety of science payloads, and its mission capability is highlighted by \u3e3km/s of delta-V maneuverability with a groundbreaking ion propulsion system heretofore unavailable to CubeSats. Salient features of this propulsion system include innovative use of solid iodine propellant and a 60W class mini RF ion thruster that is capable of 1.3mN thrust and 3250sec specific impulse (Isp). The primary objective of the LunarCube program is to support a deep space CubeSat mission to the Moon from GEO or a translunar trajectory (such as the SLS/EM-1 drop-off) and carry out a lunar science campaign as a technology demonstration of the platform. A secondary objective is to showcase that much of the spacecraft’s miniaturized avionics and power system can survive the harsh radiation environment. The LunarCube concept, especially its ion propulsion element, has received significant attention from the CubeSat user community targeting near-term lunar flights. In fact, the platform has already morphed into an EM-1 CubeSat mission known as “Lunar IceCube”, selected for flight by NASA’s Next Space Technologies for Exploration Partnerships (NextSTEP) program

Numerical modelling of a radio-frequency micro ion thruster

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006.Includes bibliographical references (p. 113-114).A simple performance model is developed for an inductively-coupled radio-frequency micro ion thruster. Methods of particle and energy balance are utilized for modeling the chamber plasma discharge. A transformer model is incorporated in the equations of energy balance for investigating the effect of plasma on the primary circuit and for calculating the absorbed power by the plasma. A simple and one-dimensional ion extraction model is developed based on experimental observation and the result is validated with experimental data. Performance of the RF micro ion thruster is satisfactory with thrust and specific impulse of approximately 2 mN and 2000 seconds, respectively. Comparison is made with a miniature bombardment-type ion thruster, and the RF ion thruster is found to be more efficient when the coupling efficiency is above 80%. Optimization in driving frequency increases power absorption and ionization fraction tremendously. It has a positive but limited effect on propulsive performance as the ion beam current is space-charge limited.by Michael Meng-Tsuan Tsay.S.M

External-Memory Computational Geometry

(c) 1993 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.In this paper we give new techniques for designing e cient algorithms for computational geometry prob- lems that are too large to be solved in internal mem- ory. We use these techniques to develop optimal and practical algorithms for a number of important large- scale problems. We discuss our algorithms primarily in the context of single processor/single disk machines, a domain in which they are not only the rst known optimal results but also of tremendous practical value. Our methods also produce the rst known optimal al- gorithms for a wide range of two-level and hierarchical multilevel memory models, including parallel models. The algorithms are optimal both in terms of I/O cost and internal computation

Optical Property Measurements in Turbid Media Using Frequency Domain Photon Migration

In frequency domain photon migration (FDPM), amplitude-modulated light is launched into a turbid medium, e.g. tissue, which results in the propagation of density waves of diffuse photons. Variations in the optical properties of the medium perturb the phase velocity and amplitude of the diffusing waves. These parameters can be determined by measuring the phase delay and demodulation amplitude of the waves with respect to the source. More specifically, the damped spherical wave solutions to the homogeneous form of the diffusion equation yield expressions for phase (φ) and demodulation (m) as a function of source distance, modulation frequency, absorption coefficient (β), and effective scattering coefficient (Бeff). In this work,we present analytical expressions for the variable dependence of φ and m on modulation frequency. A simple method for extracting absorption coefficients from φ and m vs. frequency plots is applied to the measurement of tissue phantoms. Using modulation frequencies between 5 MHz and 250 MHz, absorption coefficients as low as 0.024cm -l are measured in the presence of effective scattering coefficients as high as 144cm -1. Our results underscore the importance of employing multiple modulation frequencies for the quantitative determination of optical properties