Spacecraft Interaction with Plasma Environments

 

Natural space plasmas occur almost everywhere in the universe: examples for plasmas are the hot interior of the sun and other stars, their atmospheres, most of the interstellar medium, the solar wind and the Earth's ionosphere. In fact, most of the matter in the universe is in the plasma state. The plasma in the near-Earth space is of special interest, as it interacts with artificial satellites used for communications and research. The near-Earth plasma also interacts with low-altitude rockets used for ionospheric research.

Space plasma environments in near-Earth space can be roughly divided into two categories: those at low altitudes (100km - 1000km, also called "low-Earth orbit" for satellites) and those at high altitudes, i.e. around geosynchronous orbit (6.6 Earth radii or 35000km altitude). The first range of altitudes is roughly the altitude range of the Earth's ionosphere where the plasma is dense, cool and fairly steady with the maximum density around 300 km. Here collective effects dominate and the plasma is anisotropic due to the Earth's magnetic field. At geosynchronous orbit however the plasma is hot and tenuous and highly variable, depending strongly on solar activity.
 
 
 


     
 

Sheath waves at low altitudes

When a conducting structure is immersed in a plasma there exists a region of low electron density, the ion sheath which is a few Debye lengths thick, surrounding its surface. This sheath can act as a waveguide where surface waves, the so-called sheath waves, can propagate over long distances. A frequency range of special interest is the one below the plasma frequency where the plasma is cut off for uniform plane waves. The existence of sheath waves has two effects. First, in the case of an antenna they make a significant contribution to the antenna impedance thus affecting its performance. Second, they provide a mechanism for locally generated electromagnetic waves to propagate between widely separated points on ionospheric spacecraft. This has been shown in the tethered sounding rocket experiment OEDIPUS-A, which demonstrated strikingly the propagation of sheath waves along a thin, cylindrical conducting tether oriented nearly parallel to the ambient magnetic field.

The objectives of our research are theoretical modeling of sheath waves, experimental studies of sheath waves in magnetized and isotropic laboratory plasmas as well as data analysis from the OEDIPUS-A and OEDIPUS-C experiments.
 
 

Selected Publications

James, H.G., K.G. Balmain, C.C. Bantin, and G.W. Hulbert, `Sheath waves observed on OEDIPUS-A', Radio Sci., 30(1), 57-73, 1995.

Morin, G.A. and K.G. Balmain, `Plasma sheath and presheath waves: Theory and experiment', Radio Sci., 151-167, 1993.

Balmain, K.G., D.A. Baker, and C.C. Bantin, `Sheath wave propagation in a magnetoplasma', Proc. Workshop Phys. Charged Bodies in Space Plasmas, Eds. M. Dobrowolny and E. Sindoni, Varenna, Italy, 1991, 223-230.

Morin, G.A. and K.G. Balmain, `Hydrodynamic radio-frequency model of an ion sheath near a conductor in a plasma, Radio Sci., 26(2), 459-467, 1991.

Laurin, J.-J., Morin, and K.G. Balmain, `Sheath wave propagation in a magnetoplasma', Radio Sci., 24(3), 289-300, 1989.
 
 

Spacecraft charging in geosynchronous orbit

In geosynchronous orbit which is occupied by communication satellites the collective effects that are dominant in low-Earth orbit are weak and individual particle effects are dominant. Electron energies here range from several keV up to the MeV range. This altitude (6.6 Earth radii) lies in the magnetosphere, which is the part of near-Earth space dominated by the Earth's magnetic field. During magnetic storms which accompany high solar activity the incidence of high-energy particles originating from the solar wind increases significantly. The energetic electrons collide with spacecraft in geosynchronous orbit, building up charge which can eventually lead to electrical breakdown, arc discharge and physical damage.

The charging phenomena are divided into two categories: surface charging which occurs in exposed surface dielectrics such as thermal blankets and internal charging which affects insulating material inside the satallite such as circuit boards. Discharges interfere with control signals and in the worst case can destroy circuits. Consequences of discharges range from temporary operational anomalies to permanent failure of entire satellites. It is believed that the recent failure of the ANIK E1 satellite was caused by unusually high rates of high-energy electrons during the week preceding the problem. ANIK E1 and E2 previously experienced operational difficulties during a similar situation in January 1994.

The objective of our research is the laboratory simulation of surface and internal charging of spacecraft dielectrics in two specially designed vacuum chambers using an electron gun for electron energies up to 25 keV and a Sr90 source for electron energies up to 2 MeV.
 
 

Selected Publications

K.G. Balmain, `Arc propagation, emission and damage on spacecraft dielectrics: a review', J. of Electrostatics, 20, 95-108, 1987.

K.G. Balmain, `Surface arc discharges on spacecraft dielectrics', IEEE Trans. Elect. Insulation, 21(3), 427-430, 1986.

K.G. Balmain, M. Gossland, and K. Karia, `Spacecraft fiberglass strut charging/discharging and EMI', IEEE Trans. Nucl. Sci., 32(6), 4438-4440, 1985.

K.G. Balmain, A. Battagin, and G.R. Dubois, `Thickness scaling for arc discharges on electron-beam-charged dielectrics', IEEE Trans. Nucl. Sci., 32(6), 4073-4078, 1985.

G. McKeil and K.G. Balmain, `Analysis of the ion spot phenomenon on beam-charged dielectrics', IEEE Trans. Nucl. Sci., 33(6), 1396-1401, 1986.
 

[Back]


[Top] [Electromagnetics Home] [ECE Department]