Abstract:
A process and apparatus for separating element isotopes in space by imparting a velocity and direction to a body of material along a substantially linear path, heating and vaporizing the body and ionizing the material thereof as it flows along the path to produce a first stream comprising ionized material, and then using at least one aperture to separate a first portion of the ionized material having a velocity transverse to the path that exceeds a predetermined transverse velocity limit while a second portion of the ionized material passes through the aperture and can be subsequently collected.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/521,201, filed Mar. 10, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention generally relates to the process of isotope separation, by which atoms of varying molecular weight can be differentiated.  
         [0003]     Commonly-owned U.S. Pat. No. 6,614,018 to Schubert discloses an apparatus and process for continuous isotope separation in microgravity using solar power. Generally, Schubert&#39;s apparatus has axial symmetry and utilizes magnetic beam confinement to perform a continuous process in microgravity environments.  
         [0004]     Several subfields relate to apparatuses and processes of the type taught by Schubert. One subfield is mass spectroscopy, wherein a sample is ionized and sputtered from the matrix being studied through bombardment by another ion such as oxygen or argon. A sample analyzer segregates isotopes through the application of a magnetic field. As ions of charge q, with a velocity v and mass m pass through a magnetic field of strength B, they experience a force perpendicular to the field direction according to the Lorentz force, F=qvxB (F is force vector, a is acceleration, m is mass, q is electron charge, v is velocity vector, B is magnetic field strength, and x is the cross product operator). This force causes an acceleration in a direction normal to the original velocity according to Newton&#39;s law a=F/m (a is acceleration and m is mass). Because different ions have different masses, the acceleration they receive is different. This effect is exploited to separate out the various elements and isotopes of the matrix under study. Suitable collectors monitor the amount of charge impinging at the location associated with various isotopes, providing an indication of their presence, and an approximate indication of their relative abundance. Previous work in the field of mass spectroscopy include U.S. Pat. No. 4,066,895 to Iwanaga, U.S. Pat. No. 4,174,479 to Tuithof et al., U.S. Pat. No. 5,220,167 to Brown et al., U.S. Pat. No. 3,443,087 to Robieux et al., and U.S. Pat. No. 3,772,519 by Levy et al. This technique of magnetic separation is widely used in many fields, as will be discussed below  
         [0005]     In the field of ion implantation, used typically for semiconductor manufacture and for impregnation of specialty materials, a gaseous molecule containing the element of interest is ionized using a radio frequency plasma. The plasma field causes dissociation of the molecule, and causes an excited state of the element to be implanted. All excited species of charge q are then accelerated using electrostatic fields of strength E according to the equation F=Eq. The accelerated ions are collimated and passed through a magnetic field to separate the various isotopes. A suitable shutter system is employed to select the ion of interest, which is then allowed to proceed toward the substrate to be implanted with this ion. However, along the beam path, between the separation magnet and the substrate, dynamic electric fields, oriented typically in two perpendicular directions to the beam axis, are employed to deflect the beam slightly. This deflection is used to cause the beam to be scanned across the substrate, typically with the desire to uniformly cover the substrate area. Once the beam arrives at the substrate, typically with a relatively high velocity and relatively low density, the ions will impinge upon the surface, and penetrate to a distance determined by the beam energy, the ion mass, the angle of incidence, and the atomic mass and crystal orientation of the substrate. Several patents in this area include U.S. Pat. No. 4,841,143 to Tamura et al., and U.S. Pat. No. 5,751,002 to Ogata et al.  
         [0006]     Isotope separation, as a field of study, is principally used to enrich uranium with the isotope of atomic weight 235, relative to the much more abundant U 238 . A number of patents in this field demonstrate a wide variety of techniques for achieving isotope enrichment, such as U.S. Pat. No. 3,935,451 to Janes, U.S. Pat. No. 3,940,615 to Kantrowitz, U.S. Pat. No. 4,202,860 to Miyake et al., U.S. Pat. No. 4,726,967 to Arendt et al., U.S. Pat. No. 5,024,749 to Snyder et al., U.S. Pat. No. 4,399,010 to Lyon et al., U.S. Pat. No. 5,422,481 to Louvet, U.S. Pat. No. 4,757,203 to Gil et al., U.S. Pat. No. 5,224,971 to Mukaida et al, and U.S. Pat. No. 3,953,731 to Forsen. Among the various techniques are those which use a linear direction of ion travel, and those which employ a spiral or cyclotron ion movement. In all cases, the uranium, or other element, such as zirconium, is first ionized using one of several different methods. The first broad class of ionization techniques involves first evaporating the material, and then ionizing it using radio-frequency (rf) energy or tuned laser radiation. Evaporation is accomplished with any of several techniques, such as Joule heating, laser bombardment or ion sputtering. Ionization with rf energy will typically excite all isotopes of the element of interest. However, with laser ionization, the frequency of radiation can be selected to preferentially ionize one isotope over another. This appears to be the preferred method in many patents, since it allows separation to be accomplished using electric fields, instead of magnetic fields, although both can be found in the patent records. Once the moving (linear or cyclotron) isotopes are ionized and separated by either electric or magnetic fields, they are collected at surfaces that are temperature controlled to allow condensation.  
         [0007]     The application of very rugged coatings of metal or ceramic is the goal of thermal spray. In each form, the material to be deposited is supplied in a powdered form carried in a stream of gas, such as nitrogen. The small particles of material are plasticized, melted, or ionized, depending on the energy supplied. This energy may be from the combustion of a reactive fuel with oxygen or from an electric arc. The heated particles of metal or ceramic are then carried to the substrate to be coated by the carrier gas, or by the velocity of the exit gasses from combustion. These particles then coat the surface of the substrate, preferably with very little surface reaction, and typically produce a very dense coating. Representative patents in the field of thermal spray include U.S. Pat. No. 3,892,882 to Guest et al., and U.S. Pat. No. 5,71 6,422 to Muffoletto et al.  
         [0008]     The principles of magnetohydrodynamics involve the motion of a charged medium through a magnetic field. In a typical embodiment, the momentum of the moving medium imparts a backward electromotive force which can be used for power generation. In another form, the magnetic field can be used to selectively alter the trajectories of the moving medium, which may be a plasma of ionized isotopes, for example. In this way, magnetohydrodynamics is similar in principle to mass spectroscopy. A patent describing this method is U.S. Pat. No. 4,737,711 to O&#39;Hare. This patent also describes a method of element separation.  
         [0009]     A materials processing environment in a circular orbit around a massive body is essentially in a free-fall, where the effects of static gravity, such as those felt on the surface of such a massive body, are not felt or are very small. Such a microgravity environment has certain advantages for materials processing. The sedimentation or settling of materials of varying densities in a suspension does not occur, allowing the formation of more homogenous materials in orbit than on the surface of a planet or planetoid. The relatively less stringent requirements for fixturing are another feature exploited in some patents on microgravity processing. A sample of microgravity processing patents is U.S. Pat. No. 5,196,999 to Abe.  
         [0010]     Many methods for the separation of chemical elements or molecules in space have been proposed and studied. For the most part, these include the use of reagents, catalysts, and consumable chemicals which must be brought from a planet such as Earth, at great expense. Furthermore, the equipment for these processes tends to be very expensive and intricate, requiring significant maintenance. References to such schemes can be found in U.S. Pat. No. 4,737,711 to O&#39;Hare (noted above), U.S. Pat. No. 5,374,801 to Leung, and U.S. Pat. Nos. 5,096,066 and 5,1 53,838 to Kindig.  
       BRIEF SUMMARY OF INVENTION  
       [0011]     According to the present invention, there is provided a process and apparatus that achieves separation of multiple isotopes simultaneously using a pulsed, batch-type operation, and powered primarily using solar energy. The process entails separating element isotopes in space by imparting a velocity and direction to a body of material along a substantially linear path, heating and vaporizing the body and ionizing the material thereof as it flows along the path to produce a first stream comprising ionized material, and then using at least one aperture to separate a first portion of the ionized material having a velocity transverse to the path that exceeds a predetermined transverse velocity limit while a second portion of the ionized material passes through the aperture and can be subsequently collected. The apparatus includes means for imparting a velocity and direction to a body of material along a substantially linear path within an apparatus, means for heating and vaporizing the body and ionizing the material thereof as it flows along the path to produce a first stream comprising ionized material, and at least one aperture configured to separate a first portion of the ionized material having a velocity transverse to the path that exceeds a predetermined transverse velocity limit while a second portion of the ionized material passes through the aperture. According to certain aspects of the invention, heating and vaporizing of the body and ionization of the material thereof can be performed using concentrated sunlight and ionizing radiation, followed by electric field separation and collection of the desired isotopes in appropriate receptacles.  
         [0012]     The process and apparatus of this invention allow flexibility of implementation, very high separation efficiency, and minimal waste when simultaneously collecting a multiplicity of isotopes, and can greatly reduce the cost of producing purified finished materials in space. This capability makes economical the fabrication of complex and large structures for space-based industry and habitation. The output stream of pure isotopes can be directed, focused, and shuttered to allow the creation of composite materials, superlattices, or three-dimensional structures of almost any atomic and spatial configuration.  
         [0013]     Other objects and advantages of this invention will be better appreciated from the following detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  represents an embodiment of the present invention, in which kinetic energy is imparted to a slug that is then vaporized, ionized, separated and finally collected.  
         [0015]      FIG. 2  is a more detailed depiction of an aperture design exemplifying the restriction of beam velocities to achieve greater purity of the separated elements; and re-use of the aperture material to reduce waste.  
         [0016]      FIG. 3  represents an embodiment of the invention using multiple apertures that are positioned to avoid cross-contamination between the separated output from each aperture.  
         [0017]      FIG. 4  represents the present invention as a component of a system architecture for energy production, materials handling and human habitation in a low or microgravity environment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The present invention involves a process in which a body or slug of material, such as cored rock or formed minerals, is given a velocity and directed on a substantially linear path. This velocity may come from an electromagnetic catapult (also called a rail gun or a mass driver), or from a device employing stored mechanical energy such as a sling or catapult, or from a device using the rapid expansion of materials such as a cannon. Once the slug is given a velocity, it is heated very quickly to vaporize the material, a state in which molecular bonds within the matrix are broken to liberate individual elements as atoms. The heat for vaporization may come from concentrated sunlight or laser irradiation. The vaporized elements are now ionized using radio-frequency ionization and/or laser irradiation to form a plasma. Though the linear velocity of the slug is conserved by the ionized elements, the thermal expansion of the vaporization process will cause radial spreading of the material relative to the original direction of motion. One or more apertures are then used to narrow the cross section of the stream of vaporized materials.  
         [0019]     The vaporized elements exiting the aperture may then pass through an electric field formed transverse to the direction of the motion of the particles. As the charged elements pass through the electric field, they experience a transverse velocity proportional to their charge and inversely proportional to their mass. This transverse velocity, when added to the initial linear velocity, deflects the various elements to a differing degree. Additional electric fields, oriented longitudinally to the direction of the beams of separated elements may be used to reduce their velocity. Appropriately placed collection receptacles collect the separated and purified elements, the primary output of the current invention. Thermal control of the receptacles removes the waste heat.  
         [0020]     A sufficient vacuum environment is needed for the operation of the present invention. Upon collection of the separated elements, and allowing for possible re-charging of the power sources for the vaporization, ionization and separation, the process is repeated with another slug of rock or material. Through this method of pulsed operation, the necessity for beam confinement is reduced or eliminated. Further advantages of pulsed operation are that there is no requirement to accelerate the ions electrically in a longitudinal direction, and this process can be used either in orbit or on the surface of a planetoid with sufficient vacuum.  
         [0021]     Perceived inefficiencies in the operation of the present invention can be used to advantage. For example, the apertures may be formed of other slugs of rock or mineral, so they collect waste material which can be fed again into the process. As another example, the un-ionized portion of the material stream, which does not experience a transverse velocity, may be collected as a hard slag. The slag can be collected on a movable working surface so that the shape of the slag can be controlled. These bricks of slag material can be used for construction of habitats and other structures, and have the benefit of providing radiation shielding to any human occupants of those habitats.  
         [0022]     In view of the above, significant advantages of this invention include the capability of separating materials without the use of reagents, catalysts, consumable chemicals, or reaction vessels, and using an apparatus that can require very little maintenance. Furthermore, the present invention makes use of heating, ionization, and collection techniques that can be used in combination with known processing techniques, such as magnetic separation and dynamic scanning to select specific isotopes.  
         [0023]     Also in view of the above, the present invention provides numerous benefits for space-based manufacturing of in-space materials as well as waste materials from spacecraft and human habitation. Any material can be fed into the apparatus for separation into purified elements. Every element can, in theory, be separated from every other to make the present invention a nearly universal recycling device. The purified raw materials from the collection receptacles can be further processed to fabricate many of the components of the present invention, thus approaching a von Neumann machine which can replicate itself. A near-geometric growth in output can be used advantageously to lower initial launch costs, thereby making the process more economically attractive than competing methods of in-space materials separation. The lack of requirements for externally supplied reagents, the reliance upon power from the Sun, and the lack of moving parts provide for very low operating costs and low maintenance costs. Pulsed operation make this process suitable as a flexible component of an integrated raw material extraction system. It is expected that the realization and implementation of the apparatus and process will greatly facilitate advances in human utilization and colonization of space.  
         [0024]      FIGS. 1 through 4  represent an apparatus  10  and process for isotope separation in accordance with the above, by which atoms of varying molecular weight are differentiated. The apparatus  10  and process use a pulsed operation capable of separating one or more elements, and potentially all elements, contained in a slug of input material. The process and apparatus  10  is particularly adapted for use in space applications, typically in low-gravity environments (e.g., the Moon) and microgravity environments (e.g., orbital), though uses in higher gravity environments are also within the scope of this invention. With reference to  FIG. 1 , the principle of operation of the apparatus  10  is to first impart a velocity to a slug  12  of material. The slug  12  may be cored from a rocky body such as an asteroid or the Moon. The slug  12  may also be formed by pressing regolith into a given shape, or it may be water materials that have been pre-processed and formed into a given shape. The shape of the slug  12  is preferentially a sphere or cylinder. The slug  12  should have sufficient structural integrity that it will survive the acceleration process of imparting a velocity. Velocity may be imparted to the slug  12  using, for example, an electromagnetic rail launcher  14  (also called a mass driver or electromagnetic catapult, or a rail gun) depicted in  FIG. 1 . In a typical rail launcher design well known in the art, a body to be launched (such as the slug  12 ) is placed within a holding device or fixture attached to a conductive bar. The bar forms a moveable fourth side of a rectangular loop of conductors, and when a current is passed through the loop, the bar is pushed out of the rectangular loop. As the bar exits the rectangular loop, the holding device becomes detached from the slug  12 . Through inertia, the slug  12  will continue in a substantially linear direction out from the rail launcher  14 . Other means of imparting velocity are also envisioned, for example, a spring-loaded catapult can be used to throw the slug  12  with a linear velocity. Such a mechanical catapult may be linear, or it may be radial, in which case the slug  12  is thrown at a tangent. Another means of imparting velocity is to use the acceleration of gravity by dropping the slug  12 . A number of other means by which a body can be accelerated and given a velocity are also within the scope of the present invention.  
         [0025]     After leaving the launcher  14 , the moving slug  12  is heated to break the molecular bonds which may exist within the matrix of the slug material and then vaporize the individual elements to form a cloud  18  of vaporized material. Concentrated sunlight, through the use of concentrating mirrors or lenses  16  (one of which is represented in  FIG. 1 ) can be used to vaporize the moving slug  12 . Alternatively, a plurality of energetic lasers may be used to vaporize the slug  12  either alone or in tandem with the concentrated sunlight from the mirrors or lenses  16 . Other means of vaporizing material, such as plasma etching, irradiation, electromagnetics or mechanical impact may be used instead of concentrated sunlight or lasers. In the preferred embodiment, the mirror or lenses  16  generate concentrated sunlight with a focal line co-linear with the path of the moving slug  12 . A focal line may also be formed through the concentrating action of a mirror with a half-cylinder cross section, or an extruded parabolic shape. It is preferred that the sunlight or laser irradiation be substantially radially symmetric, to the extent practical through the fixturing of the mirrors or lasers.  
         [0026]     Vaporization of the slug  12  causes an expansion of the volume of the material. However, the individual atoms within the vapor cloud  1   8  will still retain the substantially linear momentum of the initial velocity of the slug  12 . The vaporized atoms within the expanding cloud  18  will continue moving in the initial direction of the slug  12 , so that the volume occupied by the vaporized cloud  18  forms a cone. It is believed that some fraction of the slug  12  material may not vaporize fully. Whether through insufficient heat of vaporization from concentrated sunlight, or imperfect heating with lasers, there may exist intact molecules within the vapor cloud  18 . To maximize the efficiency of the process, it is desired to vaporize as much of the slug material as possible. However, increasing the solar or laser energy to vaporize minerals with especially high heats of vaporization also increases the expansion of the vapor cloud  18 . There exists a family of operating curves which trade off the percent vaporization and the rate of expansion of the vapor cloud  18 . Considered together with the initial velocity of the slug  12 , there may be various operating conditions which maximize certain metrics, such as purity of the separated elements or throughput flux.  
         [0027]     Simultaneously with, or shortly after, the vaporization of the slug  12 , the individual atoms within the vapor cloud  18  are ionized. As known in the art, ionization is the process of stripping away one or more of the electrons from the outer shell of the atom or molecule. While the vaporization process will likely ionize a fraction of the elements, a further ionization step is preferred to increase the ionization percentage.  FIG. 1  depicts a radio-frequency (rf) source  22  of electromagnetic energy as being used to ionize the atoms within the vapor cloud  18 , forming a plasma cloud  20 . The rf source  22  may have a single frequency (such as 13.56 MHz), or a broad spectrum of frequencies designed to preferentially ionize certain elements such as silicon, iron, aluminum and oxygen. Laser energy can also be used for ionization, where the laser frequency is tuned to preferentially ionize certain elements. Either or both rf and laser ionization may be used.  
         [0028]     Ionization of the vapor cloud  18  to create the plasma cloud  20  creates even more expansion of the material through such processes as thermal diffusion, self-scattering, electrostatic repulsion, and self-induction. As with the vaporized atoms within the expanding vapor cloud  18 , the ionized atoms within the plasma cloud  20  continue moving in the initial direction of the slug  12 , so that the volume occupied by the plasma cloud  20  forms a cone. Increasing the ionization frequency and energy will increase the percentage of ionization of the elements, but will also cause the cone of material to expand even more rapidly. There exists a tradeoff between ionization energy and frequency with the spread of material. Similar to the discussion regarding vaporization, there may exist several operation points which optimize different metrics such as purity of the finished product or throughput capacity of the process.  
         [0029]     The expanding cloud  20  of ionized material will contain a plurality of elements, with a wide range of velocity components perpendicular to the original direction of motion of the slug  12 . To achieve good separation of the materials, it is desired that the perpendicular expansion rate of the ionized elements be small compared to their linear velocity from the original slug  12 . As this may be a practical challenge in certain operating conditions, it is advantageous to limit the dimensions of the cloud  20  of material in at least one direction. This limiting can be accomplished by a slit or aperture within or between some solid material. In the embodiment of  FIG. 1 , the cloud  20  of ionized plasma encounters a rectangular-shaped aperture  24  defined by two panels  26 , so that the material exiting the aperture  24  is an ion beam  28  limited in the direction of the short dimension of the rectangular shape of the aperture  24 . While the use of a single aperture  24  is represented in  FIG. 1 ,  FIG. 3  represents an embodiment in which a plurality of slits or apertures  24  are used to maximize the usage of ionize materials and achieve greater throughput. The multiple apertures  24  of  FIG. 3  are shown spaced appropriately to the separation of elements, to prevent cross-contamination between ionized materials that have passed through adjacent apertures  24 .  
         [0030]     Downstream of the aperture(s)  24 , the rectangular cross-section beam  28  is passed between substantially parallel plates  30  of a conductive material. With a voltage applied from one plate  30  with respect to the other, an electric field is formed in the space between the plates  30 . As the charged, ionized elements encounter the electric field, they experience a force proportional to the field strength, proportional to the charge state of the ion, and inversely proportional to the mass of the element. With a uniform electric field, the force on each atom is directly proportional to the charge-to-mass ratio of the atom. The orientation of this electric field is oriented with the long dimension of the aperture  24 , so that the force upon each ion is transverse to the direction of motion of the original slug  12 . With this new component of velocity, the ions are deflected to different extents according to their charge-to-mass ratio. The differing degrees of deflection now allow the ion beam  28  to be separated into a plurality of ion beams  32 , each having a different element in a different charge state.  
         [0031]     The thermal energy of these separated ion beams  32  will be high. To remove some of this energy, the present invention allows for a second electric field, shown in  FIG. 1  as being produced by transverse electric field plates  34 . The plates  34  is arranged so that the second electric field is oriented in a reverse direction to the direction of the separated ion beams  32 , and thus works to decelerate the ions, effectively cooling them and slowing their velocity.  
         [0032]     Collection receptacles  38  are shown in  FIG. 1  as placed at appropriate places in the path of the plurality of ion beams  32 . The receptacles  38  may be simply planar substrates of metal or ceramic that collect the desired elements from the separated beams  32 . Pre-coating each receptacle  38  with the element to be collected will reduce interaction between the beam  32  and its receptacle  38 . A wide range of collection receptacle technologies are envisioned by this invention, including but not limited to cryogenic cooling, direct-write ion beam technology, ion implantation, mass spectroscopic analysis, cyclotron separation for even greater purity refinement, oblique angle collection to distribute heat, dissolvable substrates, and prepared thin films for creation of superlattices or composite materials. A further preferred feature of this invention is to provide goniometer and translation stages in the collection process, allowing for rotational and translational movement of the collection receptacles  38 . Through appropriate movement, direct writing of elements can be effected onto any conceivable surface. By combining such movement with further apertures (not shown) nearly any conceivable structure, device or component can be created with the invention.  
         [0033]     Cooling of the ion beams  32  with the reverse electric field facilitates the collection of gaseous components of the slug matrix, such as oxygen and nitrogen which are best stored as a liquid. Reducing the thermal energy of the separated ions beams  32  also reduces the requirements for heat dissipation from the receptacles  38 , providing greater flexibility in the design of the receptacles  38 .  
         [0034]     While it is desired to have complete vaporization of the slug  12 , and complete ionization of the vapor cloud  18 , in practice these fractions will be less than 100%. The portion of the slug  12  material which is not vaporized or ionized, having no net electric charge, will pass undeflected through the transverse electric field plates  34 . This material will generally be in the form of a slag stream  36  containing a mix of elements. The material within the slag stream  36  may be formed into useful shapes through the movement of one of the receptacles  38 , designated as a slag collection receptacle  40 . Bricks, slabs, and other components needed to build structures may be formed from the slag. For human habitats, these slag bricks can be used both for structural integrity as well as radiation shielding.  
         [0035]     In  FIG. 2 , the panels  26  and their aperture  24  are shown in greater detail in order to demonstrate certain features of the invention. The purpose of the aperture  24  is to provide a beam  28  of roughly rectangular cross section having one relatively narrow dimension for the purposes of improving the purity of the separated elements. If the beam  28  were an ideal beam, with the narrow dimension approaching a line, the particles within the beam  28  would have equal velocities which are co-linear. When these charged particles encounter the transverse electric field of the plates  30 , they will experience a transverse acceleration from the electric field in the amount of a=qE/m (a is acceleration vector, E is electric field strength vector, and m is particle mass). For a length of travel L through the transverse electric field, the transverse velocity component dv will be dv=qEL/mv, where v is the original velocity. The linear separation of the ion beams  32  will then increase according to this velocity.  
         [0036]     In a practical beam, the dimension of the aperture  24  is finite and larger than zero, and the particle velocities will have a distribution of values. Furthermore, because of the vaporization and ionization processes, some of the beam particles will have velocities at random angles to the primary beam direction. The polar plot on the left side of  FIG. 2  illustrates this two-dimensional distribution of velocity. The circle indicates angle to the primary beam direction, traveling to the right in all the figures. At the origin of the circle is a dot representing zero velocity. The circumference of the circle represents a large velocity. The shaded region indicates the approximate distribution of velocities and angles in a practical beam just after the ionization step in the process. Upon encountering the aperture  24 , particles having a velocity with angle far from the primary beam direction will be stopped, and removed from the beam  28 . The second polar plot indicates this narrowing of the distribution of velocities, where the shaded region is limited in the angular component.  
         [0037]     The importance of limiting the angular components of the ion beam  28  can be understood by considering the separation of each isotope beam  32 . Consider two particles which are different elements, for example Si (silicon having atomic weight of 28) and Fe (iron having atomic weight of 52). Assuming both exist in a singly-ionized state for simplicity of the description, the Si particle will be deflected approximately twice as much as the Fe particle because of its smaller mass. However, if the Fe particle already possesses a transverse velocity from processing of the beam  28 , it may travel in the transverse direction an amount equal to the deflection of a Si particle having an initial velocity co-linear with the primary beam direction. In this example, both particles will arrive at the receptacle  38  designated to collect silicon. The Fe particle will be an unwanted contaminant.  
         [0038]     A small aperture  24  will minimize this cross-contamination of the isotopes. However, a small aperture  24  will, in general, have a lower throughput than a larger aperture  24  which can support a larger flux. Therefore, an engineering tradeoff exists between purity and throughput. For the purposes of this invention, either end of the spectrum of purity versus throughput may be desirable depending on the purposes to which the output is being produced. Silicon solar cells demand high purity, while structural metals may be more tolerant of contaminants but favor high throughput to keep per-unit costs low. The entire spectrum of this tradeoff is considered covered by the present invention.  
         [0039]     Also shown in  FIG. 2  is the use of undersized slugs  42  placed in front of each aperture panel  26 . These undersized slugs  42  collect the stopped beam elements having large transverse velocities. The addition of this material will increase their dimension, so they can be used in subsequent processing as input to the entire process. These slugs  42  can also be used as structural components, as has been described for the slag in  FIG. 1 .  
         [0040]      FIG. 3  shows a further adaptation of the invention intended to increase the throughput of the process. As discussed above,  FIG. 3  depicts the use of multiple apertures  24  instead of a single aperture  24 . Each aperture  24  is spaced apart by a gap  44  that prevents cross-contamination of ion beams  28  coming through adjacent apertures  24 . The use of multiple apertures  24  is not likely to double the throughput, since the bulk of the material should be substantially co-linear with the primary beam direction. The slag stream  36  of un-ionized material will travel through a primary aperture  24 , shown as the bottom aperture  24  in  FIG. 3 . However, for beam components with a substantial transverse velocity, the second aperture  24  may allow separation and collection of additional components.  
         [0041]      FIG. 4  shows the architecture of a system oriented towards human habitation, spacecraft fabrication, and energy production based on the present invention. Beginning on the left side of  FIG. 4 , raw materials are extracted from a planetary body or a planetoid, or eventually from waste materials. Slugs  12  of this raw material are fed into the pulsed isotope separator  10  of this invention (e.g.,  FIG. 1 ). Outputs of the isotope separation process are purified elements like silicon, iron, aluminum (Al), and oxygen (O), un-ionized slag  36 , and waste heat. The purified silicon can be further processed to make solar cells. Aluminum can be used as a structural material for habitats, spacecraft and antennae, and can also be evaporated onto surfaces to make high-quality mirrors for concentrating sunlight, such as might be used in the vaporization portion of the present invention. A further use of aluminum is in wiring, which might be needed for electrical connections among the solar cells. Iron can be used as a structural material, or as components of a rail gun, such as that used as the velocity-imparting mechanism of  FIG. 1 . Oxygen is an important component of a safe, breathable atmosphere within habitats or spacecraft, and can also be used as an oxidizer in chemical processes such as fuel cells.  
         [0042]     Slag  36  produced by the process of this invention can be used to make bricks or structural elements, as explained above. Waste heat taken from the collection receptacles  38  will be considerable, and can be utilized to realize further benefits. The Sterling engine is a reciprocating device which can use a difference in the heat of two environments to produce useful work. With the waste heat from the present invention as the high-temperature environment, and a suitable thermal mass exposed to the ambient temperature of space, for example, a Sterling engine could find great many uses within a human habitation. Waste heat can also be used directly for heating the habitat.  
         [0043]     Using all these products as applied to a habitat or spacecraft fulfills many of the essential requirements for supporting humans in space or on the surface of a planetary body. By making it easier and more convenient for humans to live in space, they can in turn operate and maintain the isotope separator  10  and its associated infrastructure. With the advantages realized by the present invention, and further utilization of its outputs, human activities in space can approach the point of self-sustainability.  
         [0044]     In view of the preceding description, it can be appreciated that the present invention differs from the teachings of commonly-owned U.S. Pat. No. 6,61 4,018 to Schubert. For example, the operation of the present invention is inherently pulsed or periodic, and not continuous, as a result of the processed material being in the form of bodies or slugs that are individually launched into the apparatus  10 , as opposed to a continuous stream of particulate material. Also, the present invention is intended for use in environments of any gravity field, not just a microgravity environment. Another distinction is that the present invention relies on time-of-flight and apertures  24  to restrict the beam cross section, and while a magnetic beam confinement technique may be used, this is not a requirement. Another notable characteristic of the present invention is the lack of an axis of symmetry. These distinctions are believed to make the present invention more suitable for operation on the surface of a planetary body, such as the Moon, Mars, etc.  
         [0045]     The description above, related to the pulsed isotope separation apparatus  10  and its associated process in the vacuum of space explains in detail the theory, operation, and design of this invention. In the text above, numerous additional improvements, options, and embodiments are referred to for the purpose of improving various facets of the useful application of this invention. The technologies involved in this invention span a wide range of human endeavor, and as such draw upon the excellent prior work of many others. It is hoped that anyone skilled in one or more of these various arts will be encouraged to test the combinations and alternatives enumerated and suggested in the detailed description. The lack of figures for every possible alternative in no wise implies that these are not considered part and parcel of this invention. Rather the intent is to present the basic concepts, key features and design considerations.  
         [0046]     Therefore, while the invention has been described in terms of a preferred embodiment, it is apparent that other forms could be adopted by one skilled in the art. Accordingly, the scope of the invention is to be limited only by the following claims.