Greg Chavers

Validating a Plasma Momentum Flux Sensor to an Inverted Pendulum Thrust Stand

The accuracy of a plasma impact force sensor was compared with that of the more commonly used inverted pendulum thrust stand using a 5 kW Xe Hall effect thruster. An improved plasma momentum flux sensor was designed and constructed based on a previous design. Real-time force measurements were made with both the plasma momentum flux sensor and the inverted pendulum thrust stand. The plasma momentum flux sensor measured the force exerted onto it by the Hall effect thruster exhaust plume with a resolution of 0.1 mN and an average discrepancy of 2 % compared with thrust stand measurements. Experiments were completed using a 9 m by 6 m cylindrical vacuum chamber. The total force from the Hall effect thruster was modulated from 34 to 356 mN by varying both the anode voltage, from 150 to 500 V, and the neutral Xe gas flow rate, from 5 to 15 mg/s.

Physics of Plasma Detachment in a Magnetic Nozzle

The demonstration of plasma detachment from an applied magnetic field is of paramount importance to many future space propulsion designs. Ion engines and Hall thrusters do not produce a magnetized plasma, so the question of plasma magnetization has never bee n raised for these technologies. Several future propulsion technologies, including helicon plasma supplies, do produce a highly magnetized plasma that may or may not break from the applied magnetic field. It has been theorized that a sufficiently energet ic plasma flow will detach from applied magnetic nozzle fields by stretching the magnetic field lines away from the plasma source. Experiments are being conducted at the NASA Marshall Space Flight Center intending to study this type of magnetic detachment . This paper will present preliminary results from that experiment, specifically density measurements that indicate a possibility of detachment occurring in this experiment.

Operational Concept for the NASA Constellation Program's Ares I Crew Launch Vehicle

The Ares I is a shuttle-derived two-stage launch vehicle. The Ares I is comprised of a first stage, which is a five-segment reusable solid rocket booster, and a second stage, or upper stage, which is a liquid oxygen/liquid hydrogen rocket system powered by a single J-2X engine. The operational goal for this launch vehicle is to reduce operating costs and increase system reliability for human missions to the International Space Station and to the Moon. The Ares I will be designed to accommodate efficient operations for the ground and ascent phases of the mission by both the Ground Operations Project and the Mission Operations Project, respectively. This paper provides an overview of the latest Ares I architecture, operations goals, and the operational concepts for both the ground operation and mission operation phases of the launch vehicle. The latest concepts for the Ares I communication and tracking, engineering support, system integration laboratory, operational infrastructure, logistical support, flight and ground operational planning and execution, training, and sustaining engineering are also addressed. The integration of these across the Ares I system, as well as ongoing trades that may impact the design, are examined as well. The operational scenarios for the Ares I element assembly, integration and testing, transportation, prelaunch operations, launch and ascent operations, and post-mission operations are discussed, along with a status of the contingency and off-nominal operations scenarios. Operational concepts drive operations requirements, which drive optimized operations attributes into the design. These operations attributes in the design—‘design for operability’ —ensure that the launch vehicle can be operated in an efficient and cost-effective manner, at minimum risk of loss of crew or mission, and are characterized by high levels of safety, producibility, reliability, maintainability and supportability. The degree to which the design is imbued with the attributes will be manifested in the system readiness, launch availability, and affordability of the integrated vehicle, all of which are governed by Ares I operations requirements.

Simulation and measurement of high-Beta plasma in a magnetic nozzle

The efficient extraction of thrust in a magnetic nozzle is of great importance to many future space propulsion designs. In several high-power EP thrusters, high magnetic fields are required to create and confine a quasineutral plasma. In order to produce thrust, this plasma exhaust must disengage from the applied magnetic fields downstream of the rocket. This paper presents a subset of results from an experiment investigating a high-powered plasma source emitting into a magnetic nozzle. In particular, numerical models and density profiles are presented which suggest that upon reaching high Beta (kinetic pressure > applied magnetic pressure) a flowing plasma will not be confined by the applied magnetic fields. The plasma will propagate as if it were detached from the magnetic fields.

Plasma expansion in a paraxial magnetic nozzle

Summary form only given. Several space propulsion systems have been proposed that could possibly realize mass efficiency gains over prior systems. These propulsion systems utilize magnetic nozzles with strong magnetic fields to shape a plasma flow into a directed jet. The ability of strongly magnetized plasma to break free from the confining field in these systems is critical for efficient momentum transfer to the plasma exhaust. MHD theory and simulation each predict that momentum will be transferred once the flow kinetic energy density WK is greater than WB the magnetic field energy density. An experiment is being conducted at NASA Marshall Space Flight Center which tests this theory. Multiple plasma sources and feed gasses are being used including hydrogen plasma in both a washer gun and helicon source. A paraxial magnetic nozzle guides the plasma with straight diverging field lines to the nozzle aperture. High flow velocities at the nozzle aperture suggest that the flow is super-Alfvenic at this point (WK > WB). Diagnostics used in the experiment to verify the effects of super-Alfvenic detachment include measurements from Hall probes, Langmuir probes, RF interferometer and flux loops

Resource Prospector Lander: Architecture and trade studies

NASAs Resource Prospector (RP) is a multi-center and multi-institution collaborative project to investigate the polar regions of the Moon in search of volatiles. The mission is rated Class D and the duration is approximately 10 days. The RP vehicle comprises three elements: the Lander, the Rover, and the Payload. The Payload is housed on the Rover and the Rover is on top of the Lander. The focus of this paper is on the Lander element for the RP vehicle. The design of the Lander was requirements-driven and focused on a low-cost approach. To arrive at the final configuration, several multi-disciplinary trade studies were conducted. There were several primary trade studies that were instrumental in determining the final design. This paper will discuss six of these trades in further detail and show how these trades led to the final architecture of the RP Lander.

Operational considerations and comparisons of the Saturn, Space Shuttle and Ares launch vehicles

The United States (U.S.) space exploration policy has directed the National Aeronautics and Space Administration (NASA) to retire the Space Shuttle and to replace it with a new generation of space transportation systems for crew and cargo travel to the International Space Station, the Moon, Mars, and beyond. As part of the Constellation Program, engineers at NASAs Marshall Space Flight Center in Huntsville, Alabama are working to design and build the Ares I, the first of two large launch vehicles to return humans to the Moon. A deliberate effort is being made to ensure a high level of operability in order to significantly increase safety and availability as well as reduce recurring costs of this new launch vehicle. It is the Ares Projects goal to instill operability as part of the requirements development, design and operations of the vehicle. This paper will identify important factors in launch vehicle design that affect the operability and availability of the system. Similarities and differences in operational constraints will also be compared between the Saturn V, Space Shuttle and current Ares I design. Finally, potential improvements in operations and operability for large launch vehicles will be addressed. From the examples presented, the paper will discuss potential improvements for operability for future launch vehicles.

Validating A Plasma Momentum Flux Sensor Against an Inverted Pendulum Thrust Stand

The accuracy of a plasma impact force sensor was compared to that of the more commonly used inverted pendulum thrust stand using a 5 kW Xe Hall thruster. A plasma momentum flux sensor (PMFS) was designed and constructed based on a previous NASAMarshall Space Flight Center (MSFC) design. Real-time force measurements were made with both the PMFS and the inverted pendulum thrust stand. The PMFS measured the force exerted onto it from the Hall thruster exhaust plume with a resolution of 0.1 mN, and an average accuracy better than 98% compared to the thrust stand. Experiments were completed at the Large Vacuum Test Facility (LVTF) at the University of Michigan. The total force from the Hall thruster was modulated from 34 mN to 356 mN by varying both the anode voltage, from 150 V to 500 V, and the neutral Xe gas flow rate from 5 mg/s to 15 mg/s. The majority of the force data taken during the experiment campaign was completed as a “blind study” where force measurements from both techniques were disclosed only after the experiment was completed.