Materials and method of charge dissipation in space vehicles

Details Materials and method of charge dissipation in space vehicles Materials and method of charge dissipation in space vehicles

1999-10-22

2002-03-26

Moore, Margaret G. (Department: 1712)

Stock material or miscellaneous articles

Composite

Of silicon containing

C428S450000, C428S457000, C528S009000, C252S519200, C252S519210, C427S077000, C427S126100, C244S00100R, C244S00100R

Reexamination Certificate

active

06361869

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods of protecting space vehicles and from charge accumulation and arc discharging. More particularly the invention relates to charge dissipation materials for coating, or producing, components used in space vehicles for limiting charge accumulation and arc discharging.
BACKGROUND OF THE INVENTION
Spacecraft in orbit around the Earth are immersed in streams of energetic electrons which are components of the “solar wind” emanating from the sun's surface. These electron streams constitute electrical currents which are sometimes strong enough to perturb the Earth's magnetic field, events which are thus known as “magnetic storms”. Further, these streams of energetic electrons not only sweep past the earth but also are partly trapped In the well-known Van Allen radiation belts which rather inconveniently are concentrated at altitudes much in use by civilian and military communication satellites.
Satellites make extensive use of dielectric materials (mainly polymers). These materials are used on the outside of satellites as “thermal blankets” to limit extremes of temperature, and on the inside as circuit boards and cable insulation. Such polymers are generally very good insulators, so that any injected electrons embedded in them are not quickly conducted away and charge buildup can occur, especially under the magnetic storm conditions described above.
Specifically, dielectric materials such as Mylar, Teflon and Kapton are widely used on spacecraft for thermal control purposes, for example in multilayer thermal blankets and second-surface mirrors. They are also very good electrical insulators, a property that greatly increases the range of their applications to antenna components, antenna covers, single-layer and multilayer circuit boards, integrated circuits, monolithic microwave integrated circuits, cables, solar cells, and supports for solar cell arrays. Unfortunately, this same electrical-insulator property also makes possible the long-term accumulation of electrical charge deposited inside the dielectric by the naturally occurring and deeply penetrating energetic electrons that are especially numerous at altitudes of a few earth radii, altitudes much in use for communications satellites.
If electrical charge accumulates in sufficient quantity, laboratory experiments have shown that the resulting electric field strength can exceed the breakdown level for the material, resulting in high-current electrical discharges which often produce physical damage in the form of microscopic grooves, tunnels and eruptions with signs of local melting. The result of this type of event is primarily the deposition of contaminants over the satellite, the degradation of thermal control material, and the generation of electromagnetic interference that can induce temporary and sometimes permanent failure of electronic circuits.
In principle, charge accumulation and the resulting discharges could be eliminated if the dielectric material had just enough conductivity to drain off the charge faster than it accumulates. Because the incident electron flux is small, the conductivity need not be large, which suggests that the required conductivity could be achieved by mixing in a small fraction of finely ground conducting powder (such as carbon) while the dielectric is in its formative state. However, this solution to the problem requires a significant fraction of the conductive additive in the material since contact among the additive granules is necessary to produce conductivity. With this much additive, there may be degradation in other respects such as thermal properties, mechanical properties, microwave and optical transparency, atomic oxygen erosion, and ultraviolet decomposition. Issues such as these motivate the search for a homogeneous dielectric that acquires conductivity not from being a mixture but rather from its basic electrochemical characteristics.
It would be very advantageous to provide materials either for coating or fabricating various components used in spacecraft and satellites or other applications involving components exposed to charge fluxes for limiting charge accumulation and arc discharging.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and materials for reducing or limiting charge accumulation and the resulting arc discharges in space vehicle or other electronic components prone to charge buildup due to exposure to a charge flux.
In one aspect of the invention there is provided a method of limiting charge accumulation and arc discharging in components exposed to charge fluxes. The method comprises coating the component with a material comprising an effective poly(metallocene).
In this aspect of the invention the poly(metallocene) may include a metallocene unit selected from the group consisting of ferrocene, cobaltocene and ruthenocene.
In this aspect the poly(metallocene) may be a poly(ferrocenylsilane) [Fe(C
5
H
4
)
2
SiRR′]
n
, wherein R and R′ are selected from the group consisting of hydrogen, halogen, short or long chain linear or branched alkyl, cycloalkyl, aryl, aryloxy, alkoxy and amino groups and combinations thereof.
The poly(ferrocenylsilane) may be poly(methylphenylferrocenylsilane) or poly(ferrocenyldimethylsilane).
In another aspect of the invention there is provided a method of charge dissipation in selected components of a space vehicle, comprising:
coating selected components of a space vehicle with a polyferrocene comprising fc-SiRR′, wherein fc is a ferrocene unit C
5
Z
4
FeC
5
Z
4
, and wherein R and R′ are selected from the group consisting of hydrogen, halogen, short or long chain linear or branched alkyl, cycloalkyl, aryl, aryloxy, alkoxy and amino groups and combinations thereof.
In this aspect of the invention Z may be hydrogen.
In another aspect of the invention there is provided a composite dielectric material comprising at least one constituent being an effective poly(metallocene).
In this aspect of the invention the poly(metallocene) may include a metallocene unit selected from the group consisting of ferrocene, cobaltocene and ruthenocene.
In this aspect of the invention the poly(metallocene) may be a poly(ferrocenylsilane) [Fe(C
5
H
4
)
2
SiRR′]
n
, wherein R and R′ are selected from the group consisting of hydrogen, halogen, short or long chain linear or branched alkyl, cycloalkyl, aryl, aryloxy, alkoxy and amino groups and combinations thereof.
In this aspect of the invention at least one of the other constituents of the dielectric material is a polymer such that the dielectric material is a polymer blend.
In another aspect of the present invention there is provided a method of charge dissipation in selected components of a space vehicle, comprising:
producing selected dielectric components of a space vehicle from a composite material, the composite material including an effective poly(metallocene).
In this aspect of the invention the poly(metallocene) includes a metallocene unit selected from the group consisting of ferrocene, cobaltocene and ruthenocone.
In this aspect of the invention the poly(metallocene) is a poly(ferrocenylsilane) [Fe(C
5
H
4
)
2
SiRR′]
n
, wherein R and R′ are selected from the group consisting of hydrogen, halogen, short or long chain linear or branched alkyl, cycloalkyl, aryl, aryloxy, alkoxy and amino groups and combinations thereof.


REFERENCES:
patent: 3847871 (1974-11-01), Stephens et al.
patent: 4705646 (1987-11-01), DuPont et al.
patent: 4873304 (1989-10-01), Rosenblum
patent: 4910050 (1990-03-01), Oldham et al.
patent: 5770269 (1998-06-01), Long et al.
patent: 6037091 (2000-03-01), MacLeod et al.

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