Liquid Oxygen Magnetohydrodynamics

In the cryogenic realm, liquid oxygen (LOX) possesses a natural paramagnetic susceptibility and does not require a colloidal suspension of particles for practical application as a magnetic working fluid. Commercial ferrofluids have performed well in industrial applications, but expanding their workable range to low temperatures requires a suitable selection of the carrier fluid, such as LOX. In this chapter, the equation of motion for the pure fluid is derived and applied to a slug of LOX being displaced by a pulsed magnetic field. Its theoretical performance is compared to actual experimental data with discussion on empirical parameters, sensitivity to measurement uncertainty, and geometric similarity. The 1.1 T pulse of magnetic flux density produced oscillations in the slug of 6-8 Hz, generating up to 1.4 kPa of pressure change in a closed section when the slug acted like a liquid piston. The experiments and theoretical model demonstrate that LOX could be used as a magnetic working fluid in certain applications

Cryogenic Experimentation on the Magnetohydrodynamics of Liquid Oxygen

The increasing demands of the small satellite industry are forcing the development of subsystems with increased reliability and robustness while maintaining harsh mass and volume constraints. Basic research has begun on the cryogenic magnetohydrodynamic properties of liquid oxygen to determine its feasibility as a working fluid in a magnetic system void of mechanically moving parts. A 1D finite-differenced numerical algorithm verified experimental data on the dynamics of a liquid oxygen slug propagated by pulsed magnetic fields. Up to 1.4 T was induced by electrically-sequenced solenoids wound with 30 gauge copper wire. The test section consisted of two solenoids and a 0.075 inch quartz tube and was completely submerged in liquid nitrogen. Because of this, visual confirmation of the slug size was difficult, and the algorithm was also used to determine its length. Using data obtained from upstream and downstream pressure sensors, the lengths were predicted as 3.75 inches for an oscillating slug test and as 2.2 inches for a propagating slug test. The maximum pressure differential obtained was 0.24 psi, which is comparable to ferrofluid-based experiments. The experiment resulted in the most detailed information to date on the paramagnetic susceptibility of liquid oxygen. It is anticipated that this basic research will eventually lead to the development of small satellite subsystems with significantly longer lifetimes

Spin-torque driven magnetization dynamics in a nanocontact setup for low external fields: numerical simulation study

We present numerical simulation studies of the steady-state magnetization dynamics driven by a spin-polarized current in a point contact geometry for the case of a relatively large contact diameter (D = 80 nm) and small external field (H = 30 Oe). We show, that under these conditions the magnetization dynamics is qualitatively different from the dynamics observed for small contacts in large external fields. In particular, the 'bullet' mode with a homogeneous mode core, which was the dominating localized mode for small contacts, is not found here. Instead, all localized oscillation modes observed in simulations correspond to different motion kinds of vortex-antivortex (V-AV) pairs. These kinds include rotational and translational motion of pairs with the V-AV distance d ~ D and creation/annihilation of much smaller (satellite) V-AV pairs. We also show that for the geometry studied here the Oersted field has a qualitative effect on the magnetization dynamics of a 'free' layer. This effect offers a possibility to control magnetization dynamics by a suitable electric contact setup, optimized to produce a desired Oersted field. Finally, we demonstrate that when the magnetization dynamics of the 'fixed' layer (induced only by the stray field interaction with the 'free' layer) is taken into account, the threshold current for the oscillation onset is drastically reduced and new types of localized modes appear. In conclusion, we show that our simulations reproduce semiquantitatively several important features of the magnetization dynamics in a point contact system for low external fields reported experimentally.Comment: 26 pages, 12 figures, submitted to Phys. Rev.

Gradio: Project proposal for satellite gradiometry

A gradiometric approach, rather than the more complicated satellite to satellite tracking, is proposed for studying anomalies in the gravitational fields of the Earth and, possibly, other telluric bodies. The first analyses of a gradiometer based on four of ONERA's CACTUS or SUPERCACTUS accelerometers are summarized. it is shown that the obstacles to achieving the required accuracy are not insuperable. The device will be carried in a 1000 kg lens shaped satellite in a heliosynchronous orbit 200 to 300 km in altitude. The first launching is planned for the end of 1987

Perform a gyro test of general relativity in a satellite and develop associated control technology

The progress accomplished in the Stanford Gyro Relativity program during the period November 1974 to October 1975 was described. Gyro developments were continued in the main laboratory dewar, concentrating on the operation of a three axis gyro readout and on improvements to the methods of canceling trapped fields in the rotor; these efforts culminated in the first successful observation of the London moment in the spinning gyro rotor in March 1975. Following a review meeting at that time, a new goal was formulated for the next 12 to 18 months, namely to operate a gyroscope in the new ultra-low field facility with readout resolution approaching 1 arc-second. The following other tasks were also completed: (1) sputtering work, (2) magnetometry, (3) construction and installation of the North Star simulator, (4) analysis of torques on the gyro, especially in inclined orbits, (5) equivalence principle accelerometer, and (6) analysis of a twin-satellite test of relativity

Unclassified information list, 12-16 September 1966

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Attitude motion of a non-attitude-controlled cylindrical satellite

In 1985, two non-attitude-controlled satellites were each placed in a low earth orbit by the Scout Launch Vehicle. The satellites were cylindrical in shape and contained reservoirs of hydrazine fuel. Three-axis magnetometer measurements, telemetered in real time, were used to derive the attitude motion of each satellite. Algorithms are generated to deduce possible orientations (and magnitudes) of each vehicle's angular momentum for each telemetry contact. To resolve ambiguities at each contact, a force model was derived to simulate the significant long-term effects of magnetic, gravity gradient, and aerodynamic torques on the angular momentum of the vehicles. The histories of the orientation and magnitude of the angular momentum are illustrated

The Development of LOX-Based Magnetic Fluid Technology and its Impact on Small Satellites

A magnetic fluid system could potentially replace mechanically moving parts in a satellite as a means of increasing system reliability and mission lifetime, but rather than a standard ferrofluid with magnetic particles, liquid oxygen (LOX) may be a more adequate working fluid. As a pure paramagnetic cryogen, LOX is already heavily used in space, but still requires basic research before being integrated into system development. The objectives of the research conducted were to verify LOX as a magnetic working fluid through experiment and establish a theoretical model to describe its behavior. This paper presents the theoretical, experimental, and numerical results of a slug of LOX being pulsed by a 1.1 T solenoid in a quartz tube with an inner diameter of 1.9 mm. The slug oscillated about the solenoid at 6-8 Hz, producing a pressure change of up to 1.2 kPa. System efficiency based on the Mason number was also studied for various geometric setups, and, using a one-dimensional, finite-differenced model in Matlab 2008a, the numerical analyses confirmed the theoretical model. The research provides groundwork for future applied studies using Comsol Multiphysics 3.5a with complex designs

Quasi-geostrophic modes in the Earth's fluid core with an outer stably stratified layer

Seismic waves sensitive to the outermost part of the Earth's liquid core seem to be affected by a stably stratified layer at the core-mantle boundary. Such a layer could have an observable signature in both long-term and short-term variations of the magnetic field of the Earth, which are used to probe the flow at the top of the core. Indeed, with the recent SWARM mission, it seems reasonable to be able to identify waves propagating in the core with period of several months, which may play an important role in the large-scale dynamics. In this paper, we characterize the influence of a stratified layer at the top of the core on deep quasi-geostrophic (Rossby) waves. We compute numerically the quasi-geostrophic eigenmodes of a rapidly rotating spherical shell, with a stably stratified layer near the outer boundary. Two simple models of stratification are taken into account, which are scaled with commonly adopted values of the Brunt-V{\"a}is{\"a}l{\"a} frequency in the Earth's core. In the absence of magnetic field, we find that both azimuthal wavelength and frequency of the eigenmodes control their penetration into the stratified layer: the higher the phase speed, the higher the permeability of the stratified layer to the wave motion. We also show that the theory developed by Takehiro and Lister [2001] for thermal convection extends to the whole family of Rossby waves in the core. Adding a magnetic field, the penetrative behaviour of the quasi-geostrophic modes (the so-called fast branch) is insensitive to the imposed magnetic field and only weakly sensitive to the precise shape of the stratification. Based on these results, the large-scale and high frequency modes (1 to 2 month periods) may be detectable in the geomagnetic data measured at the Earth's surface, especially in the equatorial area where the modes can be trapped