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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system for automatically removing
unwanted films from the surfaces of spacecraft. More specifically, this
invention is concerned with methods and means for removing layers of
organic matter which are tightly bound by the polymerizing action of the
sun's ultraviolet radiation to critically important surfaces of vehicles
in space.
2. Background Information
Once a spacecraft is exposed to the hostile environment beyond the upper
strata of the earth's atmosphere, microscopic substances present in space
as well as particles liberated from the spacecraft itself form occluding
layers over sensitive surfaces which serve as interfaces for the passage
of radiation in and out of the craft. These unwanted substances are
attracted to surfaces by electrostatic forces or are deposited on the
exterior of a vehicle after a random collision as the craft moves along
its course in space. After these particulates adhering to the spacecraft
are irradiated by the sun's ultraviolet rays, they bond together and to
the radiation interface surfaces on the exterior of the satellite. The
sun's energy helps form long chains of organic molecules called polymers
which are difficult to remove from these important sensor and
communication regions of the vehicle.
Once a sensor or radiation aperture is covered with a partially opaque
coating, the efficiency and efficacy of the entire space system is placed
in great jeopardy. The transmission of vital radio, infrared, optical, or
laser signals may be impaired or precluded. The capacity of an orbiting
sensor platform which collects, stores, or analyzes radiation from the
earth's surface or atmosphere in order to help scientists conduct research
may be severely diminished. A satellite which depends upon celestial
navigation techniques to remain on course and at the proper altitude can
become completely useless if the objective lens of its star sensor is
obscured by a shading scale of space debris.
Nearly every craft launched into space suffers from the inevitable
reduction in operational effectiveness that results from the formation of
these contaminant coatings. An increasing number of scientific, military,
and commercial endeavors have begun to reap the benefits of the
exploitation of the regions above our atmosphere. Space-based telescopes
have extended the earthbound limits of astronomical observation. Remote
sensing from orbit is the basis of modern methods of military surveillance
and weather forecasting. Orbital detection systems play a critical role in
studies concerning earthquake detection, agricultural yields, changes in
the world's oceans, and exploration for petroleum and other scarce mineral
resources. The utility of virtually all of these expensive systems is
slowly but inescapably attenuated by the gradual build up of these
unwelcome veneers.
There currently exists no prior methods or devices known to the inventor
which may be employed to automatically clean radiation aperture surfaces
by removing these deleterious organic films from a spacecraft in orbit. If
the particulates clinging to exterior sensors and radiators have never
been exposed to ultraviolet radiation, they are not converted into
stubborn, strongly adhesive polymers and may be dispersed by simple
sublimation if the coated substrate surface can be sufficiently heated.
Since all external areas of a space vehicle in orbit are eventually
illuminated by the sun, the sublimation of contaminants by heating is a
solution which offers few practical advantages.
For space vehicles in low orbits, some cleaning can occur if critical
surfaces are positioned so that they face the direction of motion of the
craft. In this way, traces of atmospheric oxygen which are present sixty
to one hundred miles up may impinge upon the organic films and eradicate
them via oxidation reactions. This technique is only marginally effective
and is limited to vehicles like the space shuttle which are constrained to
operate within a very narrow range of low altitudes. The vast majority of
craft which require sensor and power surface cleaning circumnavigate the
world in far higher orbits, including geosynchronous satellites which
circle the globe over twenty three thousand miles above the earth's
surface.
In terrestrial environments, similar organic materials may be dispersed
using special lamps under laboratory conditions. Atmospheric oxygen can be
converted to its allotropic counterpart, ozone, and atomic oxygen by
stimulation with an ultraviolet lamp. The combined effect of the
interaction of these gases with the polymerized layers and the ultraviolet
energy is the elimination of a few of the uppermost strata of
contaminants. The great bulk of the organic coating is not susceptible to
this method of ultraviolet-ozone treatment, since many layers are simply
re-polymerized by the additional radiation.
High energy beams can be used to bombard surfaces and disband occluding
films through kinetic interactions, but they concomitantly damage and
destroy the sensitive surfaces which they are intended to restore. These
techniques solve the problem by brute force, and are not selective enough
to use on spaceborne surfaces which are often enclosed by delicate,
protective optical coatings.
None of the methods or devices described above provides an effective
solution to the problem of the degradation of spacecraft by organic film
obscuration of their vital radiation apertures. An effective solution to
this problem would satisfy a long felt need experienced by the aerospace
community for over twenty-five years. A truly practical and reliable means
for removing undesirable films would represent a major advancement in
space technology that would enhance the utility of nearly all future space
systems and magnify the opportunities for scientific, military, and
commercial enterprise in space. Such a device would ideally be suited to
operate in cooperation with a wide variety of space systems and to perform
cleaning tasks reliably for a myriad of critical satellite components
without harming the underlying hardware.
SUMMARY OF THE INVENTION
The present invention provides an efficacious, practical, cost-effective,
and straightforward solution to the problem of organic film obscuration of
vital spaceborne radiation interface surfaces. This invention utilizes an
on-board supply of a cleaning reagent capable of being formed into a
stream depolymerizing particles. These particles are aimed at a target
surface bearing an unwanted coating which has been tightly bonded to the
spacecraft by the action of the sun's ultraviolet rays. This molecular,
atomic, ionic, or excited plasma beam is generated within a specific range
of beam energy so that the target surface is not damaged by excessive
kinetic interactions. The cleaning reagent particles interact chemically
with the organic film on the target, which is held at a neutral electrical
potential, in an oxidation reaction. The reactants are then transported
away from the spacecraft as liberated, volatile gases. The cleaning
reagent may alternatively be deployed from a chamber in the spacecraft as
a molecular gas in the vicinity of the target during a period of intense
solar activity. Positive ions formed after the release of the molecular
gas are then accelerated back to the spacecraft, which has accumulated a
net negative charge as a consequence of the solar disturbance, which
occurs, on average, about fifteen percent of any given interval in orbit.
The returning stream of ions accomplishes the same oxidation reaction with
the same result.
It is, therefore, an object of the present invention to provide an
effective means of solving the problem of the degradation of radiation
collection and exchange surfaces as well as other components of spacecraft
which might suffer from the formation of opacifying strata.
It is a further object of this invention to automatically restore and renew
lenses, sensors, laser and radar apertures, windows, reflectors, solar
cells, thermal control surfaces, radiation measurement devices, mirrors,
telescopes, thermal imaging, scanning and staring arrays, detectors,
indicator lamps, and illuminating equipment to their original, unblemished
condition. Other internal and external components in orbit such as
transponders, antennas, actuators, valves, nozzles, rocket parts, docking
assemblies, robotic arms, housings, and cryogenic devices may also be
refitted with equal success. Power generating cells impaired by
nontransmissive, contaminant coatings can be rejuvenated by applying the
method and apparatus of the present invention. This means that the life of
enormously expensive communications, military, and scientific satellites
can be greatly extended by insuring that their means of generating
electricity is not compromised by the devitrification of their light
gathering surfaces.
Yet another object of the invention is to supply a solution to the problem
of satellite maintenance which is compatible with a wide variety of
designs and space system missions. The present invention may be
constructed as a rugged, compact, and reliable subsystem that could easily
be integrated into nearly any spacecraft design.
Another object of the invention is to achieve the desirable result of
spacecraft cleaning without the added weight or complexity of a particle
beam apparatus by exploiting the action of solar storms.
Still another object of the present invention is to clean space vehicles
and other orbiting apparatus without impairing sensitive surfaces and
destroying special coatings which protect space optics and external
surfaces.
Another object of the invention is to provide spacecraft designers with the
freedom to plan and build satellites that can be periodically restored
using the methods and apparatus described in detail below. The ability to
return orbiting components such as second surface, quartz/silver mirrors
which are used for thermal control to their beginning-of-life performance
capability would have a substantial beneficial impact on spacecraft
design, since it would reduce weight requirements and minimize system
constraints.
An appreciation of other aims and objects of the present invention and a
more complete and comprehensive understanding of the this invention may be
achieved by studying the following description of a preferred embodiment
and by referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of the present invention showing apparatus
for generating a beam of oxygen ions or excited plasma which is directed
at an optical surface bearing a contaminant layer that is volatilized by a
chemical reaction.
FIG. 2 is a perspective view of a satellite exposed to the energy of a
solar storm which presents an opportunity to clean the spacecraft surfaces
by deploying molecular oxygen and allowing positive oxygen ions formed by
the solar disturbance to accelerate back toward the negatively charged
spacecraft under the influence of electrostatic forces. This alternative
method obviates the need for the beam generating apparatus shown in FIG.
1.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIG. 1, apparatus for atomic beam irradiation 10 is shown
including a particle beam generator 12 which is supplied with molecular
oxygen from supply 14 that is controlled by a valve 16. A control unit 18
coordinates the flow of oxygen to the beam generator 12 by sending an
electrical signal over cable 17 to valve 16, which is opened and closed
electrically. Oxygen gas flows from supply 14 into the evacuated
acceleration chamber 22 of the particle beam generator 12 through conduit
20. A filament 24 heated by passing current through it from power supply
26 initiates a thermionic process that liberates electrons which
accelerate toward a plate 28 held at a high electrical potential. The
electrons that boil off the filament 24 and migrate toward plate 28
collide with the oxygen dimers and form oxygen ions. Various charged
surfaces in the path of the oxygen ions such as control grid 30 are
employed to attract and accelerate the positively charged oxygen ions 40
across the generator chamber 22 and out beam nozzle 38.
The oxygen ions 40 are directed at a target comprising a contaminant
organic coating, which will be referred to as an episubstrate layer 42,
and a radiation aperature surface. This surface below the episubstrate 42
is depicted in FIG. 1 as a lens substrate 44 mounted on a portion of a
spacecraft schematically illustrated as 46. Lens 44 is electrically
grounded in order to obtain the full effect of the positively charged ions
40 which bombard the unwanted organic layer 42 without damaging the
optical coating 43 which protects lens 44. When the ions 40 impinge upon
layer 42, an oxidation reaction occurs and the organic materials in layer
42 break down, combine with the oxygen 40, and are dispersed as volatile
gases 50 away from the spacecraft 46. The compounds formed by this
chemical interaction usually comprise carbon monoxide, ammonia, methane,
and water. The beam generator 12 can be mounted on a spacecraft so that it
is permanently aimed at a critcal radiation aperture surface such as lens
44, or may be adapted to move by remote control on a hinge or gimbal in
order to enhance its range and clean more than one fixed area of a
spacecraft.
FIG. 2 reveals an alternative embodiment of the present invention which
avoids the use of the beam generator 12 shown in FIG. 1. A satellite 52
includes a chamber of oxygen 14 connected by a valve 15 operated by
electrical signals dispatched over cable 19 from control unit 18 (shown in
FIG. 1). The chamber is connected to oxygen jet 58. During a period of
intense solar activity, the satellite is bombarded with photons 54 which
impose a negative charge on its hull (shown by negative signs 56). When
molecular oxygen is released through valve 15 to jet 58, the same solar
radiation ionizes a significant portion of the oxygen dimers released in
ambient space and creates both positively and negatively charged oxygen
ions 60 and 62 which move away from satellite 52. Due to the Debye Effect,
a negative charge 56 is imposed on the craft's hull. The positive ions 60
are electrostatically attracted and accelerated back toward the
spacecraft. As they collide with the satellite's exterior, they mimic the
technique employed by the beam generator 12 described above and
illustrated schematically in FIG. 1. This technique may be performed by
commanding the control unit 18 to open valve 15 via radio signal from
personnel on the earth when they have detected a solar storm.
Alternatively, a sensor (not shown) coupled to control unit 18 may be
installed permanently on the spacecraft 52 to monitor solar radiation 54
and perform the cleaning operation automatically when a threshold level of
radiation is detected.
Although oxygen is the preferred cleaning agent, any member of the halogen
family will perform the film removal task. Any beam of particles which
will remove organic films by a chemical reaction which disperses the
unwanted patina from surfaces in a low pressure environment is suitable as
a cleaning agent for this invention. Although the inventor currently
expects the best mode of the invention to require oxygen ions, any
molecules, atoms, ions, sub-atomic particles, photons, or plasma that are
capable of implementing the essential idea embodied by the present
innovative methods and apparatus may be employed.
Similarly, although particles exhibiting a broad range of energies may be
selected to practice the invention, each individual application may call
for a specific energy range in order to avoid initiating a sputtering
reaction that would damage the substrate beneath the unwanted contaminant
layer. Recently performed laboratory tests suggest that the best spectrum
of beam energy for this task is one to ten electron volts (eV) when oxygen
is utilized. Some of the cleaning action of the invention is accomplished
by the kinetic interaction of the beam and the film. If a particular film
is known to be susceptible to dispersal by selective collisions with a
particle stream having a precisely controlled energy level, that film may
be abraided from a surface without the necessity of inducing a chemical
interaction.
As described in detail above, the particles may be conveyed to the target
using any instrumentality which will create the opportunity for the
desired physical or chemical reaction. Although the preferred embodiment
incorporates an ion gun that develops a cleaning agent flux by
thermoionically cleaving molecular oxygen supplied from an on-board
supply, any means for realizing the deployment of particles or energy
fields that would bring the inventor's concept to fruition could be
successfully exploited. Ion beams may be generated using well-known
electron gun techniques or may be formed using less conventional microwave
or radio frequency excitation circuitry which create plasma jets. A laser
beam could be employed to selectively remove unwanted films by bombarding
surfaces with photons bearing precise quantities of energy capable of
liberating contaminants kinetically.
The invention need not be circumscribed by the constraints of a limited,
exhaustible supply of oxygen or other cleaning agent. Gathering means
mounted on a spacecraft may be adapted to work in concert with one of the
embodiments explained above which could collect suitable particles from
ambient space as a craft flies its course. These collected particles could
be stored for automatic cleaning at regular intervals or could be expended
on demand.
The beam generating means may be activated by radio commands from a ground
control station on earth, by astronauts in a nearby space vehicle, or may
be programmed using circuitry well known to those skilled in the
electronics arts to clean sensitive surfaces periodically as regularly
scheduled maintenance. The invention may also be adapted to operate in
response to signals from a sensor which is mounted on or in the spacecraft
to observe the build up of contaminant layers on crucial regions or
components of the craft. A photoconductive sensor may be positioned to
measure the degree of scattering or absorption of a laser beam from a tiny
semiconductor laser installed adjacent to a solar cell or objective lens
of a detector array. This information could comprise the input to a
microprocessor which could, in turn, instruct the beam generator or other
cleaning agent deployment means when to commence operation.
The methods and apparatus described in this application are not limited to
cleaning surfaces on the exteriors of spacecraft. Although the inventor
presently expects that the primary use of this invention will be to clean
optics, sensors, and solar cells on the outside of the spacecraft which
may be generically referred to as radiation exchange apertures, interior
components of satellites can also suffer from the formation of unwanted
residue layers. Cryogenic cooling systems within a spacecraft which enable
radiation detectors to perform complex thermal imaging operations from
orbit may also be cleaned and refurbished using these methods and
apparatus. Any terrestrial environment which calls for the same
contaminant film removal objectives can benefit from the application of
the methods and apparatus of the present invention. Manufacturing
processes which rely upon the fabrication or modification of substances or
devices in substantially evacuated chambers may benefit from the
opportunities presented by the important invention claimed in this patent
application.
Although the present invention has been described in detail with reference
to a particular preferred embodiment, persons possessing ordinary skill in
the art to which this invention pertains will appreciate that various
modifications and enhancements may be made without departing from the
spirit and scope of the invention.
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