Propulsion System Development for the Iodine Satellite (iSAT) Demonstration Mission
No abstract available
Polzin, K.↗
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Iodine Propulsion Advantages for Low Cost Mission Applications and the Iodine Satellite (ISAT) Technology Demonstration
The NASA Marshall Space Flight Center Science and Technology Office is continuously exploring technology options to increase performance or reduce cost and risk to future NASA missions including science and exploration. Electric propulsion is a prevalent technology known to reduce mission costs by reduction in launch costs and spacecraft mass through increased post launch propulsion performance. The exploration of alternative propellants for electric propulsion continues to be of interest to the community. Iodine testing has demonstrated comparable performance to xenon. However, iodine has a higher storage density resulting in higher ΔV capability for volume constrained systems. Iodine's unique properties also allow for unpressurized storage yet sublimation with minimal power requirements to produce required gas flow rates. These characteristics make iodine an ideal propellant for secondary spacecraft. A range of mission have been evaluated with a focus on low-cost applications. Results highlight the potential for significant cost reduction over state of the art. Based on the potential, NASA has been developing the iodine Satellite for a near-term iodine Hall propulsion technology demonstration. Mission applications and progress of the iodine Satellite project are presented.
Dankanich, John W.↗
iSat Surface Charging and Thruster Plume Interactions Analysis
No abstract available
Parker, Linda Neergaard↗
Integrated Thermal Analysis of the Iodine Satellite (iSAT) from Preliminary to Critical Design Review
No abstract available
Mauro, Stephanie↗
Modeling an Iodine Hall Thruster Plume in the Iodine Satellite (ISAT)
An iodine-operated 200-W Hall thruster plume has been simulated using a hybrid-PIC model to predict the spacecraft surface-plume interaction for spacecraft integration purposes. For validation of the model, the plasma potential, electron temperature, ion current flux, and ion number density of xenon propellant were compared with available measurement data at the nominal operating condition. To simulate iodine plasma, various collision cross sections were found and used in the model. While time-varying atomic iodine species (i.e., I, I+, I2+) information is provided by HP Hall simulation at the discharge channel exit, the molecular iodine species (i.e., I2, I2+) are introduced as Maxwellian particles at the channel exit. Simulation results show that xenon and iodine plasma plumes appear to be very similar under the assumptions of the model. Assuming a sticking coefficient of unity, iodine deposition rate is estimated.
Iodine↗
Iodine Propulsion Advantages for Low Cost Mission Applications and the Iodine Satellite (iSAT) Technology Demonstration
No abstract available
Schumacher, Dan↗
Modeling an Iodine Hall Thruster Plume in the Iodine Satellite (ISAT)
An iodine-operated 200-W Hall thruster plume has been simulated using a hybrid-PIC model to predict the spacecraft surface-plume interaction for spacecraft integration purposes. For validation of the model, the plasma potential, electron temperature, ion current flux, and ion number density of xenon propellant were compared with available measurement data at the nominal operating condition. To simulate iodine plasma, various collision cross sections were found and used in the model. While time-varying atomic iodine species (i.e., I, I+, I2+) information is provided by HPHall simulation at the discharge channel exit, the molecular iodine species (i.e., I2, I2+) are introduced as Maxwellian particles at the channel exit. Simulation results show that xenon and iodine plasma plumes appear to be very similar under the assumptions of the model. Assuming a sticking coefficient of unity, iodine deposition rate is estimated.
Numerical Simulation↗
The Iodine Satellite (iSAT) Propellant Feed System - Design and Development
The development, modeling, and testing of components and subsystems required to feed iodine propellant to a 200-W Hall thruster and cathode are described. This work aims to address design deficiencies and issues associated with the propellant feed system that were revealed by an integrated thruster-cathode-feed system test. The feed system design is modified to use materials that are more resistant to the highly-reactive nature of iodine propellant. Dynamic modeling indicates that the inclusion of additional constraints on feed system tubing will reduce the vibrationally-induced stresses that occur during launch. Full spacecraft thermal modeling show that the feed system heater power levels are sufficient to heat the tank and propellant lines to operating temperatures, where iodine in the tank is sublimed to supply propellant for operation and the tubing is elevated in temperature to keep propellant from redepositing to block the flow. Experiments are conducted to demonstrate that is it possible through the application of heating to clear an iodine deposit blocking the flow. Deposits in the low-pressure portion of the system near the exit to vacuum are shown to be relatively easy to remove in this manner while blockages forming upstream nearer to the higher-pressure propellant tank require significantly more effort to remove. Fluid flow modeling of the feed system is performed, exhibiting some qualitative agreement with experimental data. However, the highly viscous nature of the fluid flow and the dependence of the component flow coefficients on the Reynolds number are likely causes of the generally-poor quantitative agreement between the modeling results and experimentally-measured fluid flow properties.
Polzin, Kurt A.↗
The Iodine Satellite (iSat) Propellant Feed System - Design and Demonstration
CUBESATS are relatively new spacecraft platforms that are typically deployed from a launch vehicle as a secondary payload, providing low-cost access to space for a wide range of end-users. These satellites are comprised of building blocks having dimensions of 10x10x10 cm3 and a mass of 1.33 kg (a 1-U size). While providing low-cost access to space, a major operational limitation is the lack of a propulsion system that can fit within a CubeSat and is capable of executing high Delta V maneuvers. This makes it difficult to use CubeSats on missions requiring certain types of maneuvers (i.e. formation flying, spacecraft rendezvous). Work has been performed investigating the use of iodine as a propellant for Hall-effect thrusters (HETs) that could subsequently be used to provide a high specific impulse path to CubeSat propulsion. One of the systems under development to support such a technology is the propellant feed system, which must be capable of storing solid iodine propellant, applying heat to sublime the stored solid into the vapor phase, and then control the flow of low-pressure gaseous iodine to both the thruster and cathode. In a test conducted in 2016, a first-generation iodine propellant feed system was integrated with a cathode and Hall thruster. While this test had to be terminated, the feed system in this first test was able to support both cathode and integrated cathode and thruster operation prior to the termination of the test. In the present paper, we describe work performed since that initial integrated test. The effort uses lessons learned from the previous integrated test, retiring risk associated with the iodine propellant feed system, answering open design-space questions, and demonstrating iodine flow control in an integrated system. The work is undertaken at both the component level and then at the integrated subsystem level to systematically improve the feed system design, improving the hardware fidelity so the appearance and operation of the system are as flight-like as possible. At the component level, the work focuses on the propellant tank, the feed system tubing, the valves used to control the flow to the cathode and thruster, and the heaters that maintain the temperature of the flowpaths and keep iodine from redepositing and clogging the system. Work on the propellant reservoir focuses on fabricating a tank that matches the geometry of the flight design, which allows for the identification of flight tank fabrication issues that may arise and permits thermal testing of a tank possessing the same size and thermal mass as the flight design, which can be used to anchor thermal modeling of the component. This is critical for finalizing the tank heater power requirements that feed into the heater design. All metallic materials in the feed system are hastelloy or Inconel, as these materials are resistant to chemical attack by the highly-reactive iodine vapor. The tubing in the iodine feed system must possess ports to permit a neutral gas purge of the system that clear impurities after iodine is loaded into the propellant tank. A procedure is discussed whereby these ports are crimped and sealed after the purge process is completed so as to not re-expose the iodine system to air. The valves are a critical component for control of the flow to the thruster and the cathode. Significant effort has gone into upgrading the materials of the valves to make them more resistant to chemical attack and into developing an understanding of the use of these valves during the startup and operation of the cathode and thruster. The heaters that line the entire feed system are designed to draw minimal power from the power processing unit (PPU) while still having the capacity to maintain all the feed system components at the temperatures required to discourage iodine deposition inside components downstream of the propellant tank exit. The heaters possess two separate resistive traces, giving the design redundancy should a failure occur in the primary heater circuit of one of the heater zones. The task of operating a feed system in conjunction with a thruster and cathode is undertaken in a series of sub-steps. The system is first assembled and operated on xenon gas, using the valves for cathode startup and thruster control based on measurement of the discharge current. After startup and control on xenon are demonstrated, the thruster will be transitioned to iodine operation, demonstrating thruster startup and feed system control while using a xenon-fed cathode. Finally, the last step is to integrate an iodine-compatible cathode with the system, demonstrate autonomous cathode start-up with open-loop control and thruster start-up with closed-loop control for multiple cycles.
Polzin, Kurt A.↗
In Space Assembled Telescope (ISAT) Study Preliminary Findings
“When is it advantageous to assemble telescopes in space rather than deploying them from launch vehicle fairings”? This question forms the crux of the objectives of a NASA study we have been conducting in collaboration with colleagues from different NASA centers, industry and academia. In this study, we have engaged a broad cross section of experts from the various fields of optics engineering, that is, telescope design and instrument design, structure and thermal engineering, robotics, launch system engineering, orbital mechanics, integration and testing, astrophysics, and NASA programmatics among others. Initial efforts began with a quick review of the current state of art of the component technologies that contribute towards an in-space assembled telescope. Then, leveraging the collective expertise of the diverse group of experts, we formulated a reference telescope design and attempted to develop a baseline approach to modularize the telescope into components amenable for robotic assembly. The group identified different trades associated with modularization and also developed a set of criteria to discern between the different options as revealed by the trades. Based on the modularization of the telescope, we will assess the impact of various launch vehicles, orbits for assembly and operation, robotic systems and operational approaches, and other related variables. From this, a concept to assemble the reference telescope in space from modular components will be developed. Based on this concept, and definition of the modules, we will develop a mission lifecycle plan for an assembled telescope over different phases of preliminary design, detailed design, assembly-test-and-integration, and in space operations. The mission lifecycle plan will be used to evaluate cost and risk implications of in-space assembly toward answering our fundamental question of the advantages, if any, of assembling a telescope in space as compared to self-deployment. In this paper, we summarize the objectives of the study, a review of the status of the underlying component technologies, a description of the methodology, including three different multi-day technical interchange meetings (TIMs), summary of findings from the TIMs and other related activities. In addition, a detailed description of the various factors that impact in-space assembly, their interplay and criteria for discerning among them, a preliminary description of the life cycle plan, including the test and integration plan, and initial observations on cost and risk implications will be included in the paper.
Mukherjee, Rudranarayan↗
Tessellation and Numerical Simulation of the in-Space Assembled Telescope (iSAT) Reflector
A novel tessellation method has been developed to allow the use of uniform truss modules to form curved or doubly curved surfaces. To illustrate the method, the structural support for the doubly curved in-Space Assembled Telescope primary reflector is developed. The method intentionally leaves gaps at the nodes between identical connecting modules; the gaps are relatively small, on the order of 0.5% of the lattice characteristic cell size. Uniquely shaped nodal connectors called multi-nuts are generated to fill in the nodal gaps and connect adjacent modules. With optimization techniques, the size of these nodal gaps can be minimized to thereby minimize the incurred structural efficiency losses. Finite element analyses of the primary reflector were performed, and the structural efficiency losses amounted to a natural frequency reduction of 5%. The benefits of having uniform truss modules outweigh the structural penalties as it will greatly simplify assembly and lower manufacturing costs.
Tessellation↗
Tessellation and Numerical Simulation of the in-Space Assembled Telescope (iSAT) Reflector
A novel tessellation method has been developed to allow the use of uniform truss modules to form curved or doubly curved surfaces. To illustrate the method, the structural support for the doubly curved in-Space Assembled Telescope primary reflector is developed. The method intentionally leaves gaps at the nodes between identical connecting modules; the gaps are relatively small, on the order of 0.5% of the lattice characteristic cell size. Uniquely shaped nodal connectors called multi-nuts are generated to fill in the nodal gaps and connect adjacent modules. With optimization techniques, the size of these nodal gaps can be minimized to thereby minimize the incurred structural efficiency losses. Finite element analyses of the primary reflector were performed, and the structural efficiency losses amounted to a natural frequency reduction of 5%. The benefits of having uniform truss modules outweigh the structural penalties as it will greatly simplify assembly and lower manufacturing costs.
Tessellation↗