George Teel

Electric propulsion for small satellites

Propulsion is required for satellite motion in outer space. The displacement of a satellite in space, orbit transfer and its attitude control are the task of space propulsion, which is carried out by rocket engines. Electric propulsion uses electric energy to energize or accelerate the propellant. The electric propulsion, which uses electrical energy to accelerate propellant in the form of plasma, is known as plasma propulsion. Plasma propulsion utilizes the electric energy to first, ionize the propellant and then, deliver energy to the resulting plasma leading to plasma acceleration. Many types of plasma thrusters have been developed over last 50 years. The variety of these devices can be divided into three main categories dependent on the mechanism of acceleration: (i) electrothermal, (ii) electrostatic and (iii) electromagnetic. Recent trends in space exploration associate with the paradigm shift towards small and efficient satellites, or micro- and nano-satellites. A particular example of microthruster considered in this paper is the micro-cathode arc thruster (µCAT). The µCAT is based on vacuum arc discharge. Thrust is produced when the arc discharge erodes some of the cathode at high velocity and is accelerated out the nozzle by a Lorentz force. The thrust amount is controlled by varying the frequency of pulses with demonstrated range to date of 1‐50Hz producing thrust ranging from 1 µN to 0.05mN.

Recent progress and perspectives of space electric propulsion systems based on smart nanomaterials

Drastic miniaturization of electronics and ingression of next-generation nanomaterials into space technology have provoked a renaissance in interplanetary flights and near-Earth space exploration using small unmanned satellites and systems. As the next stage, the NASA’s 2015 Nanotechnology Roadmap initiative called for new design paradigms that integrate nanotechnology and conceptually new materials to build advanced, deep-space-capable, adaptive spacecraft. This review examines the cutting edge and discusses the opportunities for integration of nanomaterials into the most advanced types of electric propulsion devices that take advantage of their unique features and boost their efficiency and service life. Finally, we propose a concept of an adaptive thruster.Miniaturized spacecraft built from advanced nanomaterials are poised for unmanned space exploration. In this review, the authors examine the integration of nanotechnology in electric propulsion systems and propose the concept of self-healing and adaptive thrusters.

Laboratory Modeling of the Plasma Layer at Hypersonic Flight

A simple approach to modeling the plasma layer similar to that appearing in the vicinity of a hypersonic vehicle is demonstrated in a laboratory experiment. This approach is based on the use of a hypersonic jet from a cathodic arc plasma. Another critical element of this laboratory experiment is a blunt body made from a fairly thin foil of refractory material. In experiments, this blunt body is heated by the plasma jet to a temperature sufficiently high to ensure evaporation of surface deposits produced by the metallic plasma jet. This process mimics reflection of gas flow from the hypersonic vehicle in a real flight. Two-dimensional distributions of the hypersonic plasma flow around the blunt body were measured using electrostatic Langmuir probes. Measured plasma density was typically 1012  cm−3, which is close to the values measured for real hypersonic flight. The demonstrated laboratory experiment can be used to validate numerical codes for simulating hypersonic flight and to conduct ground-based tests...

High thrust-to-power ratio micro-cathode arc thruster

The Micro-Cathode Arc Thruster (μCAT) is an electric propulsion device that ablates solid cathode material, through an electrical vacuum arc discharge, to create plasma and ultimately produce thrust in the μN to mN range. About 90% of the arc discharge current is conducted by electrons, which go toward heating the anode and contribute very little to thrust, with only the remaining 10% going toward thrust in the form of ion current. A preliminary set of experiments were conducted to show that, at the same power level, thrust may increase by utilizing an ablative anode. It was shown that ablative anode particles were found on a collection plate, compared to no particles from a non-ablative anode, while another experiment showed an increase in ion-to-arc current by approximately 40% at low frequencies compared to the non-ablative anode. Utilizing anode ablation leads to an increase in thrust-to-power ratio in the case of the μCAT.

Discharge ignition in the micro-cathode arc thruster

The breakdown mechanism in the Micro-Cathode Arc Thruster has been studied to better understand the nature of the discharge ignition and to extend the ignition system lifetime. It has been found that optimal material selection of the insulator is an important factor during breakdown. Two opposite processes have been found to cycle during operation. The processes are degradation of the conductive film from the inter-electrode interface and re-deposition of the conductive film due to cathode spot erosion. Initial resistances were found to vary from hundreds of ohms to thousands of ohms based on the initial connectivity of the film to the electrodes. After initial breakdown however, resistances have been found to stabilize in a typical pattern. Materials capable of withstanding high temperatures, high pressures, and smooth surfaces are shown to be beneficial for extending thruster lifetime.

Enhanced human bone marrow mesenchymal stem cell functions on cathodic arc plasma-treated titanium

Surface modification of titanium for use in orthopedics has been explored for years; however, an ideal method of integrating titanium with native bone is still required to this day. Since human bone cells directly interact with nanostructured extracellular matrices, one of the most promising methods of improving titanium’s osseointegration involves inducing bio-mimetic nanotopography to enhance cell–implant interaction. In this regard, we explored an approach to functionalize the surface of titanium by depositing a thin film of textured titanium nanoparticles via a cathodic arc discharge plasma. The aim is to improve human bone marrow mesenchymal stem cell (MSC) attachment and differentiation and to reduce deleterious effects of more complex surface modification methods. Surface functionalization was analyzed by scanning electron microscopy, atomic force microscopy, contact angle testing, and specific protein adsorption. Scanning electron microscopy and atomic force microscopy examination demonstrate the deposition of titanium nanoparticles and the surface roughness change after coating. The specific fibronectin adsorption was enhanced on the modified titanium surface that associates with the improved hydrophilicity. MSC adhesion and proliferation were significantly promoted on the nanocoated surface. More importantly, compared to bare titanium, greater production of total protein, deposition of calcium mineral, and synthesis of alkaline phosphatase were observed from MSCs on nanocoated titanium after 21 days. The method described herein presents a promising alternative method for inducing more cell favorable nanosurface for improved orthopedic applications.

Applications of Micro-Cathode Arc Thruster as in-space propulsion subsystem for PhoneSat

The George Washington University (GWU) has developed a scalable, efficient and relatively safe electric propulsion device, for small spacecraft applications, called the Micro-Cathode Arc Thruster (μCAT). The first on-orbit demonstration of this thruster subsystem capability is planned in the second half of 2014, as the primary experiment onboard a US Naval Academy BRICSat-P mission, utilizing a 1.5U CubeSat, for validating the performance and design. From December 2012 to September 2013, NASA Ames Research center (ARC) and GWU worked together to increase the Technology Readiness Level (TRL) of the technology by integrating a complete 3-channel μCAT subsystem with the ARC PhoneSat bus. The main objectives of the collaboration were (1) to build a test bench in which a phone, running the PhoneSat firmware and a custom designed Android App could fire several thrusters in a vacuum chamber at the same time and (2) to design a CAD model of a <;3U model that could incorporate the PhoneSat bus, the thruster avionics and the thrusters themselves. At the conclusion of experimental trials, development of embedded applications, and fabrication of compact versions of legacy (2007-2012) laboratory designs, including testing in a controlled environment, the μCAT system achieved TRL 5 equivalent status. This paper presents how the interfaces of these two systems were developed, as well as the results obtained during the testing phase. The μCAT technology has several desirable properties for applications in Space, such as high specific impulse, low energy consumption, and low input voltage range. In particular, it has a compact and simple concentric design with no moving parts for extremely high reliability that yields extended operational lifetime. In this paper, analytical studies are presented to demonstrate its effectiveness for various CubeSat class spacecraft maneuvers. Analyzing the effects of low-thrust is challenging, as small variations of orbital properties should be accurately computed over a long-time period. We present brief, simplified orbital analysis based on the secular change of orbital elements derived from orbital perturbation theory. It is shown that micro-cathode thruster can be effectively used for several phases of a CubeSat mission, including orbital regularization, and inclination changes.

Publisher Correction: Recent progress and perspectives of space electric propulsion systems based on smart nanomaterials

The original PDF version of this Article had an incorrect volume number of ‘8’; it should have been ‘9’. This has been corrected in the PDF version of the Article. The HTML version was correct from the time of publication.

Micro-Cathode Arc Thruster for small sattelites attitude control

Summary form only given. A low-mass, low-volume propulsion subsystems based on electrically activated micro-thrusters that utilize chemically-inert solid propellants are beneficial for small satellite attitude control applications. Micro-thrusters are able to deliver small impulse bits of about several μNs to satellites and characterized by simplicity, scalability, low cost, low weight and high reliability. In this work measurements of the key parameters of micro-Cathode Arc Thruster (μCAT) are presented and μCAT performance compared with other commercially available thruster technologies operating at the same power range.

Laboratory modeling of hypersonic flight conditions

Important issues associated with hypersonic flight include communication blackout, thermal and mechanical loads to the vehicle body etc. Availability of the tools capable to model and predict conditions of hypersonic flight is required to mitigate these issues. Nowadays, conditions of hypersonic flight are primarily modeled using laboratory experiments with hypersonic wind tunnels and numerical codes. However, utilization of wind tunnels is fairly complicated and expensive, and often do not provide complete set of parameters. At the same time, numerical codes require detailed experimental datasets in order to verify and tune the code to achieve adequate prediction accuracy. In this work we propose a novel approach to model the conditions of hypersonic flight in a simple laboratory experiment. The idea of this approach is to utilize hypersonic arc-plasma jet which is being naturally generated in cathodic arc discharge. Utilization of different cathode materials can provide range of plasma jet speeds corresponding to Mach 5-10.