Cold Gas Jets Research Articles

Dynamics and control of a spacecraft with a moving pulsating ball in a spherical cavity

A model with two interacting bodies, for a spacecraft with liquid, has been developed. The spacecraft without liquid is the ‘tank’ and is characterized by its inertial properties and the location and size of a spherical cavity. In the cavity is located the ‘slug’, a sphere of uniform density with a variable radius. At the point of contact between slug and tank the interaction force and torque are prescribed as a function of liquid properties and state variables. The model is named SMS, for Sloshsat Motion Simulator. Its initial objective is to support the development of control laws for the Sloshsat spacecraft, presently under development and scheduled to be launched in 1998. Sloshsat is to perform a series of experiments for the validation of CFD models of spacecraft with onboard liquid. The SMS parameters are to be predicted by CFD simulations and finally to be validated by Sloshsat results. The special feature of SMS is the variable size of the slug. It provides a degree of freedom for the modelling of the variable shape of onboard liquid. The dynamic behaviour of SMS is illustrated and discussed for some particular cases, including a PAM-D nutation model. Control of SMS is evaluated for commanded uniform rotation about its intermediate principal axis and stabilized by a cold-gas jet system with 12 nozzles. The cavity centre is on the axis of rotation but not at the centre of mass of the tank. Although the tank is easily stabilized by its reaction control system, a very small friction between slug and tank causes angular momentum to accumulate in the slug motion and results in large oscillations of Size.

Results of the early orbit manoeuvres of the ampte-uks

The Active Magnetospheric Particle Tracer Explorers (AMPTE) program consists of three satellites which were launched on 16th August 1984. The scientific aim of the mission is to inject lithium and barium tracer ions inside and outside the Earth's magnetosphere and to detect and monitor these ions as they diffuse through the inner magnetosphere. The first of these three satellites, the U.S. Charge Composition Explorer (CCE) was launched into an elliptical orbit of apogee 8 R e . The other two satellites are the West German Ion Release Module (IRM) and the U.K. Subsatellite (UKS), both of which were launched on the same vehicle into a highly elliptical orbit of apogee 18 R e . At discreet intervals during the mission the IRM will release ions into the solar wind, and the movement of these ions will be monitored by the UKS. Depending on the particular scientific requirement, the UKS has to be positioned accurately at a given distance behind the IRM. Initially the UKS has to be located 100 km behind the IRM, and held there for ∼9 months. It will then be moved a distance of ∼1 R e behind the IRM. In order to manoeuvre the UKS around its orbit, a cold gas jet system is incorporated on the satellite, allowing impulses to be applied both along and perpendicular to the orbit velocity vector. The orbit control system also has to cater for relative orbit changes due to air drag at perigee, as the IRM and the UKS have different area mass ratios. This paper presents an account of the orbit control system implemented on the UKS, together with the mathematical approach adopted, and results from manoeuvres made in the first weeks of the mission.

Exospheric density measurements from the drag-free satellite Triad

The Triad satellite is maintained within 1 mm of its proof mass (a small metal ball) in a purely gravitational orbit, using a drag-free control system, named Discos, as the disturbance compensation system. The Discos proof mass is surrounded by an outer shell which holds fuel tanks and cold gas jets. The shell shields the proof mass from such nongravitational forces as radiation pressure, atmospheric drag, and micrometeorite impact. Whenever these forces displace the outer shell relative to the proof mass, an error signal is generated by a capacitive bridge sensor, and the satellite is propelled by gas jets to remain centered on the proof mass when the error reaches 1 mm. Local atmospheric densities near 800 km were measured, using ball position data, and the observed accelerations were corrected for the effects of solar radiation pressure. The measured densities reveal a greater dependence on latitude than that indicated by balloon satellites, and also a dependence on longitude. Only a small dependence on Kp, however, was observed in the region where the measurements were made.

Analysis of noise produced by jet impact near the trailing edge of a flat plate

The sound field produced by the interaction of a subsonic cold gas jet with the trailing edge of a large flat plate is analyzed. The jet issuing from a 2-in.-diameter convergent nozzle impacted the plate seven nozzle diameters downstream from the nozzle exit and one diameter from the plate's trailing edge. The plane of the plate intersected the nozzle axis at 60°. Data analysis was performed to obtain a better understanding of the dominant noise source and the mechanism governing the peak frequency of the broad-band spectra. Results indicate that noise from the plate emanates from two principal sources: first, the impact of the jet on the plate and, second, the flow over the plate's trailing edge. Above a jet Mach number of 0.5, the dominant noise as detected on the impingement side of the plate results from the jet impact (eighth power of the velocity dependence) rather than a trailing edge disturbance (fifth or sixth power of the velocity dependence), which is generally assumed dominant. Also, the frequency of the peak SPL may be governed by a feedback phenomenon, resulting in periodic formation and shedding of ring vortices from the nozzle.

Calculation of Obstruction Effects on Rarefied Particle Streaming through Short Tubes

A numerical technique has been developed to study the behavior of the flow conductance through a cylindrical channel for various types of rarefied particles. The present method has the characteristics of being accurate and more efficient than the conventional Monte Carlo. In comparison with Clausing and DeMarcus's approaches of solving integral equations, the method is superior by being both versatile and flexible. The channel obstruction effects are characterized by a dimensionless parameter K which is computed in TUBNOF code. Some of the effects investigated are the specular reflection, adsorption, and absorption. The finite molecular mean free path effect on the rarefied particle flow is also considered. The technique can be very useful in studies involving sublimation, molecular beams, cold gas jets, and radiation streaming.

電子衝撃型イオンエンジンの研究(1)

Station keeping and attitude control are required to make a communication satellite stationary in a 24-hour orbit against various perturbations. An electrical micro-thruster is considered to be more suitable for a long life operation because the exhaust velocity of propellant easily reaches about 100 times higher than that in the cold gas jets and so the propellantconsumption becomes negligible. This paper deals with preliminary experiments on an electron-bombardment-type ion engine and represents some available informations for designing future engines. The magnetic field has been found to be efficient not only for the ionization of propellant but for the ion extraction from the ionization chamber of the engine. Plasma boundaries in the ionization chamber seem to change positions depending on the intensity of the magnetic field. The influence of the teststand pressure and the effect of the neutralizer are discussed in detail.

A determination of Earth equatorial ellipticity from seven months of Syncom 2 longitude drift

The 24-hour Syncom 2 satellite has been under periodic observation by range and range rate radar and Minitrack Radio Interferometer stations since mid-1963 [Wagner, 1964b]. Seven months of longitude drift in the vicinity of two momentarily stationary configurations were analyzed for sensitivity to hypothetical longitude components of the earth's gravity field which would be in ‘resonance’ on such a satellite [Blitzer et al., 1962; Wagner, 1964a]. This drift, in the region 54°W to 64°W (over Brazil), was derived from orbits calculated at the Goddard Space Flight Center. From mid-August 1963 to late November 1963, the figure-eight ground track of Syncom 2 drifted from 55°W to 59°W, with a mean acceleration of The average growth of the semimajor axis for this period was estimated as 0.0093±0.0042 km/day. The figure-eight configuration was momentarily stationary at about 54.76° on September 6, 1963, at which time the semimajor axis was 42166.0±0.2 km. On November 28, 1963, the westward drift of Syncom 2 was stopped by ground command firing of tangentially oriented cold gas jets on the satellite.