VASIMR Performance Measurements at Powers Exceeding 50 kW and Lunar Robotic Mission Applications

Ad Astra Rocket Company, 77598, Webster, Texas, USA; The University of Houston, 77004, Houston, Texas, USA

ABSTRACT Efficient plasma production and acceleration is observed in a new high power Variable Specific Impulse Magnetoplasma Rocket (VASIMR TM) experiment, the VX-100, using argon propellant. The Radio Frequency (RF) power exceeds 50 kW. A 100 % propellant utilization is achieved with ion fluxes up to 1.7×10 21 /sec. We measure an ionization cost of 80±10 eV per ion-electron pair. Bulk argon ion flow velocities are measured up to 20 km/s. Thrust values based on plasma exhaust measurements exceed 1 N. A 200 kW superconducting device, the VX-200, and 150 m 3 vacuum facility are described. We outline the operations concept for a solar-electric lunar cargo tug whose performance is extrapolated from the VX-100 experiment results. Due to the 5,000 second specific impulse of the VASIMR engine, the fraction of the initial mass in low Earth orbit (IMLEO) that arrives in low lunar orbit (LLO) is approximately double that of a chemical propulsion system that performs at a specific impulse of only 450 seconds. The effect of space photovoltaic power cost on the economic advantage of the solar-electric system is examined.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent progress is discussed in the development of an advanced RF electric propulsion engine: the VAriable Specific Impulse Magnetoplasma Rocket (VASIMR®) VX-200, a 200 kW flight-technology prototype. This device is the only known industrial application of the physics of the aurora borealis. Results are presented from first stage only and first stage with booster stage experiments that were performed on the VX-200 using between 60 mg/s and 150 mg/s argon propellant. The plasma source is a helicon discharge that uses whistler mode waves near the lower hybrid frequency. The booster stage uses electromagnetic ion cyclotron wave absorption to accelerate the ions. Measurements of ion flux, ion energy, plasma density and potential gradients, and force density profiles taken in the exhaust plume of the VX-200 are made within a 150 cubic meter vacuum chamber and are presented in the context of individual stage and total engine performance. Measurements include detailed pitch angle scans of the accelerated ions and plasma parameter maps of the exhaust plume. An emphasis will be given to our ability to probe wave-particle interactions in the exhaust plume. We are now in a position to conduct more detailed auroral simulation studies and are actively seeking collaborators.
    American Geophysical Union, Fall Meeting 2010; 12/2010
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The performance of a 200 kW VASIMR engine has been experimentally measured. The high-power design was developed to test critical technologies and to provide performance measurements at power levels, magnetic field strengths, and configurations applicable to a light unit. The VX-200 demonstrated the capability to operate with a total of 200 kW DC power input into RF generators and coupled to the plasma for a short pulse - proving that the technology does function at high power. The first stage, or helicon stage, generated an argon plasma with a minimum cost to make the ions of 87 eV per ion at approximately 28 kW input power and 107 mg/s argon flow rate. An average ion kinetic energy of 12 eV with only the helicon powered was calculated from plasma flux and force measurements near the thruster exit. The second stage, or ion cyclotron heating (ICH) stage, was operated from zero to 81 kW with the helicon at a fixed power of approximately 28 kW. Extensive measurements of the plasma flux, momentum, and ion kinetic energy in the far-field plume with the ICH stage operating at approximately 135 kW demonstrated a half angle of 24 degrees for 90% of the momentum and 30 degrees for 90% of the plasma flux with the second stage operating. The thrust efficiency and specific impulse increased from approximately 10% and 800 s to 54% and 3500 s, respectively, with increasing ICH power. The data show no saturation in the process that converts ion cyclotron frequency RF waves into ion energy. A semi-empirical model of the efficiency as a function of specific impulse matches the trends of the experimental data and predicts approximately 64% thrust efficiency at 6000 s and 200 kW.
    46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Nashville, TN; 06/2010
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Understanding the physics involved in plasma detachment from magnetic nozzles is well theorized but lacking in large scale experimental support. We have undertaken an experiment using the 150 m 3 VASIMR ® test facility and VX-200 thruster seeking evidence that detachment occurs and understanding of the physical processes involved. It was found that the plasma jet in this experiment does indeed detach from the applied magnetic nozzle (peak field ~ 2 T) in a two part process. The first part involves the ions beginning to deviate from the nozzle field 0.8 m downstream of the nozzle throat. This separation location is consistent with a loss of adiabaticity where the ratio of the ion Larmor radius to the magnetic field scale length (r Li |∇B|/B) becomes of order unity and conservation of the magnetic moment breaks down. Downstream of this separation region the dynamics of the unmagnetized ions and magnetized electrons, along with the ion momentum, affect the plume trajectory. The second part of the process involves the formation of plasma turbulence in the form of high frequency electric fields. The ion and electron responses to these electric fields depend upon ion momentum, magnetic field line curvature, magnetic field strength, angle between the particle trajectories, and the effective momentum transfer 2 time. In stronger magnetic field regions of the nozzle, the detached ion trajectories are affected such that the unmagnetized ions begin to flare radially outward. Further downstream as the magnetic field weakens, for higher ion momentum and along the edge of the plume, the fluctuating electric field enables anomalous cross-field electron transport to become more dominant. This cross-field transport occurs until the electric fields dissipate approximately 2 m downstream of the nozzle throat and the ion trajectories become ballistic. This transition to ballistic flow correlates well with the sub-to-super Alfvénic flow transition (β k). There was no significant change observed to the applied magnetic field. Nomenclature ICH = ion cyclotron heating Rc = radius of curvature [m] Ω c,e,i = generic, electron, ion cyclotron frequency Γ iz = axial ion flux [ions/s] β k,th = kinetic, thermal beta Φ B = axial magnetic flux [Wb] B = magnetic flux density [G] J iz = axial current density [A/m 2 ] D = diffusion coefficient [m 2 /s] f i = ion flux plume fraction μ = mobility [m 2 /V/s] f Φ = magnetic flux plume fraction ν = collision frequency [Hz] r Li = Larmor radius [m] S, L = external ionization sources/losses [ions/s/m 2 ] E = electric field [V/m] u, v i = ion velocity [m/s] q = elementary charge [C] η = plasma resistivity [ohm] E i = ion energy [eV] u de = drift velocity of electrons relative to ions [m/s] ρ = mass density [kg/m 3 ] τ eff = effective momentum transfer time [s] f LH = lower hybrid frequency [Hz] r edge = projected magnetic plasma boundary [m] m e , i = electron, ion mass [kg] V = test particle velocity [m/s] n e = electron density [m -3 ] u⊥ = cross-field electron velocity [m/s] T e = electron temperature [eV] u E = E × B drift velocity [m/s] k B = Boltzmann constant [erg/eV] u D = diamagnetic drift velocity [m/s] ε 0 = permittivity of free space [F/C] ϕ(x) = error function ln Λ = Coulomb logarithm ψ(x) = first derivative of error function θ = pitch, divergence angle [°]
    33rd International Electric Propulsion Conference, The George Washington University, Washington, D.C.; 10/2013

Full-text (2 Sources)

Available from
Jun 1, 2014