US3177672A - Space simulating apparatus and method - Google Patents

Description

April 13, 1965 7 K. H. SEELANDT SPACE SIMULATING APPARATUS AND METHOD 2 Sheets-Sheet 1 Filed March 31, 1960 April 13, 1965 K. H. SEELANDT SPACE SIMULATING APPARATUS AND METHOD 2 Sheets-Sheet 2 Filed March 31, 1960 diameter spheres.

United States Patent 3 17 7,672 SPACE SIMULATING APPARATUS AND METHOD Karl H. Seelandt, Arlington Heights, IllL, assignor, by mesne assignments, to Martin-Marietta Corporation, Chicago, 10., a corporation of Maryland Filed Mar. 31, 1960, Ser. No. 19,088 2 Claims. (ill. 62-45) This invention relates to a space simulating apparatus and the method for operating it.

The expanding interest in space vehicles, lunar probes, and interplanetary travel increases the importance of having facilities which simulate the lunar-space environment. Such facilities can be used to expedite the development and testing of space vehicles and permit dress rehearsals of men and equipment with maximum effective ness at minimum cost.

Among the conditions which must be met in order to realistically simulate the conditions of outer space are (1) an extremely low pressure, on the order of 1 10 mm. of mercury and below; (2) radiation having an intensity and character accurately simulating that of the sun; and (3) a black-body heat sink at 80 K. corresponding to the heat sink of outer space. Previous space simulating devices have lacked one or more of these essential criteria for comparative evaluation of the simulated conditions and true space conditions.

Generally, the failures arise from the inability to achieve on a large scale the low pressure conditions of outer space. Just as important, however, has been the lack of an ability to produce at the same time selective areas for heating and cooling to conform to the situation in space where one side of an article may be subjected to the intense radiation of the sun and the other side exposed to the temperature of space.

A prerequisite for a successful space-simulating system is that all design parameters shall be feasible and practical for large scale space vehicle test facilities, up to 300 foot The present invention provides such a system, with design criteria which can be applied equally well to small, intermediate, or large scale facilities.

The present invention comprises a system comprising an enclosed zone evacuated to suitably low pressure, said zone having a skin maintained at a low temperature of about 70-l20 K. and provided with a checkerwork of cryoplates maintained at a much lower temperature ad- .jacent the skin and within the evacuated zone, and further provided with means for simulating solar radiation.

In the accompanying drawings:

FIGURE 1 represents an exterior side view of a spacesimulating facility made in accordance with the invention;

FIGURE 2 is a vertical sectional view through the apparatus of FIGURE 1; and

FIGURE 3 is a fragmentary enlarged detail of a portion of FIGURE 2.

The evacuation of a 300 foot diameter space chamber involves the production of high vacuum on a scale never before attempted, and the desired degree of Vacuum (less than 1 l0 mm. Hg) has only been obtained on extremely small laboratory systems. The bulk of air to be removed from such a vessel is approximately 14,000,000 cubic feet plus an almost equal amount of gas dissolved in the three inch steel wall plates which are required.

The bulk of air in the volume of the chamber can be removed in one hour by large mechanical vacuum pumps, or multistage steam ejector vacuum pumps. The real limitation, however, on ultimate vacuum is set by the evolution of dissolved gas through the chamber walls and from the test components, or equipment.

The oil diffusion pumps now available with a speed of 25,000 liters per second at 10" mm. Hg could be used to evacuate the chamber from 0.1 mm. Hg to 10- mm.

Hg after which they will blank off to zero pumping speed at 4 1O mm. Hg. However, it would. take 12,000 of these pumps to maintain a 300-foot chamber at l0- mm. Hg. Power consumption would be in the neighborhood of 200,000 kilowatts.

In view of these considerations and also because some excess capacity will be required to cope with the gas evolved by the equipment under test,.it was apparent that a new approach to the chamber evacuation problem is required. i

This is secured in accordance with the invention by employing a cryopump, which is merely a metal plate refrigerated at a temperature of about 20 K. At this temperature all ordinary gases, with the exception of helium, hydrogen and neon, will be frozen on contact with the cryoplate. The rate at which gas arrives at a given surface is a known function of temperature and molecular weight, and for air at 20 C. this rate is 11.6 liters per second per square cm. This volumetric flow rate is independent of pressure, although the mass flow rate is directly proportional to pressure; the pumping speed of a cryoplate, therefore, is attractively high. i

As an example, at l0 mm. Hg a 12" x 14" cryoplate can match the pumping speed of a 48" diameter diffusion pump which has a speed of 25,000 liters per second. In addition, this pumping speed will be constant down to a pressure of 10* mm. Hg, in contrast to the complete loss of pumping speed at 4 l0' mm. Hg for the diffusion pump. Furthermore, the power consumption of a cryoplate is directly proportional to the heat load on the plate, and therefore, diminishes with the decrease in pressure, whereas the diffusion pump consumes power at a constant rate even after blank off pressure is reached.

The result of this is that the cryopump becomes very economical at pressures below 10- mm. Hg, particularly for large chambers where it can outperform the diffusion pump by a to 1 ratio. The cryopump has a definite advantage over all other types of vacuum pumps when pumping a large volume at low pressure. This advantage increases rapidly below 10- mm. Hg.

Referring to the drawings, FIGURE l shows a small version of the space simulating apparatus of the invention, substantially in the form of a sphere 10 supported by base 15 and formed of halves 11 and 12 which are joined by a suitableflanged. joint 13 held together by bolts A vertical section through the sphere 10 of FIGURE 1 is shown in FIGURE 2. As can be seen, the equipment comprises an outer spherical shell 10 composed of halves 11 and 12 enclosing a double walled inner sphere 14 joined to the same flanged connection 13 used to join the halves 11 and 12. This double walled inner sphere 1.4 is provided with a porthole system, shown in detail in FIGURE 3, comprising a frame 16 holding a section of plate glass 17 which registers with another frame 18 holding another section of plate glass 19 through which the interior of the. test facility may be viewed.

The halves of the inner sphere 14 are provided with inlet connections (i.e., 21 and 22) and outlet connections (23 and 24) through which a cryogen. such as liquid hydrogen may be supplied, thereby cooling the sphere 14 the inner sphere 14- and outer sphere ill is packed with insulation 26, preferably consisting of sheets of bright aluminum foil loosely distributed within the space. These layers of aluminum foil are brightly finished to afford maximum reflectivity and afford a high degree of thermal insulation while offering only a minimum restriction to evacuation of the zone. The port system consisting of glass plates 17 and 19 is equipped with a suitable screen 27 which prevents displacement of the insulation and thus prevents blocking of the field of view.

The spheres 1i) and 14 are capable of being independently evacuated, sphere 14 through conduit 23 and sphere through conduit 29. Conduits 23 and 29 are connected to suitable diffusion and getter ion pumps (not shown) which permit the establishment within the vessels of vacuums on theorder of 0.1 mm. Hg. The fact that the thermal insulation 26 is also evacuated permits inner sphere 14 to be constructed of relatively thin walled sheet metal, preferably stainless steel. Moreover, the high tensile strength of this metal at extremely low temperatures further permits a reduction in the requisite thickness.

The mouth of conduit 28 leading from sphere M is equipped with a deflector plate 31 supported by. legs 32 which insures a smooth pressure reduction in the vessel and minimizes any disturbance caused by gas flow.

The further reduction of pressure below about (3.1 Hg is accomplished by means of cryoplates or cryopumps 33 and34, shown in greater detail in FIGURE 3. These consist of hollow plate members curve-d to fit the inner sphere adjacent the wall thereof. The construction of the cryopumps is not particularly critical, the only requirement being that it be capable of being cooled to an extremely low temperature on the order of K. A suitable means of accomplishing this cooling is liquid hydrogen which enters through line 36, is distributed throughout the cryopump by means of suitable internal baffles (e.g., 37), and leaves through conduit 3%. Any other convenient method of uniformly cooling the cryoplates to the desired low temperature can also be used, as will be apparent to those skilled in the art.

The shape of the individual cryopumps is not critical. The cryopumps may consist of relatively long narrow plates as shown, or they may have a substantially square shape, or any other convenient shape. The term checkerwor is used herein to describe the system of cryoplates, although it is appreciated that the actual appearance of a particular system may not be aptly described by the term.

The number and location of the cryopumps required in a given installation obviously depends on the size and particular design thereof. It has been found desirable to locate the cryopumps such that the spacing between them is roughly equal to the width thereof.

' In order to reduce the heat load on the cryopumps each of them is provided with a baffle (39 and 46) covering three sides thereof. The battles are cooled in a suitable manner to about the same temperature as the shell 14, i.e., within about 70-120 K. A suitable method of accomplishing this cooling is by supplying liquid nitrogen to the interior of the baffle through line 41, the nitrogen leaving through line 42 (FIGURE 2). These cryopumps function by causing most of the residual gas with the exception of hydrogen, helium, and neon left within the sphere after the mechanical pumps have reached the lower limit of operation to freeze on the cold surface thereof. The gases which do not freeze in this manner (i.e., hydrogen, helium and neon) are removed by the getter ion pump through conduit 28, thus permitting the establishment of a pressure of about 10' mm. Hg or less.

The cryoplates and the bafiles are both preferably made of stainless steel and have a bright surface facing the heat sink to minimize the absorption of radiant energy. The inner face of the bafileas well as the entire heat sink has a black surface, preferably produced by anodizing to prevent the evolution of gases which might result from coatings such as paint.

In order to simulate the radiation conditions of space the test facility is equipped with a source or sources of radiant energy 43 energized in any convenient manner (not shown), equipped with a suitable reflector 4-4 for collimating the beam of radiant energy as required. There is also provided within the test facility an induction heating source of conventional type for producing high frequency inductive flux as desired within a selected area or portion of an object within the enclosure. The interior of the facility is also preferably provided with adjustable platforms or racks (not shown) as required for suitably positioning test objects and materials with relationship to the sources of radiant or inductive energy.

The initial evacuation of the facility is accomplished by a conventional mechanical rotary vacuum pump and an auxiliary roots type blower through conduit 28. An

external vacuum manifold (not shown) is valved to permit simultaneous evacuation of the inner chamber and the insulation space between the vessel shell and the inner refrigerated liner. When the pressure has been lowered to 0.1 mm. Hg or less, refrigerant consisting of liquid hydrogen or helium is introduced to the inner sphere 14 of the vessel to lower its temperature to K. Simultaneously, the pump system is valved off from the inner chamberand permitted to evacuate only the insulation space between the inner and outer shells. At this time the getter ion pump is actuated to getter the remaining inert gases Within theinner chamber, remaining in operation throughout the vacuum pumping cycle. When the temperature of the inner liner has reached a'uniforrn temperature, e.g., 80 K, refrigerant is introduced to the cryoplates 33 and and the cryoplate bafiles 39 and it until temperatures of about 20 K. at the cryoplates and 80 K. at the battles are attained.

In order to avoid unduly stressing the materials of the facility by the sudden introduction of a cryogcn as cold as liquid nitrogen and to eliminate the rapid formation of large volumes of gas which would result if liquid nitrogen, for example, is suddenly supplied to the Warm facility, it is preferred to initiate the cooling cycle in stages. At first the circulating zone, e.g., a cryoplate, is cooled with a gas such as nitrogen which is made progressively colder until the temperature approaches the boiling point of liquid nitrogen. At this point the circulating cryogen (nitrogen) is replaced with cold hydrogen or helium, which is progressively cooled until the temperature on the order of liquid hydrogen is reached, at which time liquid hydrogen is supplied to the cryoplate and the end of the start-up cycle is reached.

The most effective thermal insulation between the outer vessel shell and the inner heat sink liner is accomplished by use of multiple layers of aluminum foil, brightly finished to afford maximum reflectivity. The entire insulation space is evacuated to eliminate transfer of heat by gas convection. Also, the foil type insulation offers only a minimum restriction to evacuation, whereas other types of insulation several restrict gas flow and also by Virtue of their surface-to-surface conduction of heat are not as effective as'thermalinsulation. The effectiveness of solar radiation simulation in the lunar-space facility involves the relationship of the thermal equilibrium of the test specimen. To be factual, the simulator must afiord similar thermal radiation relationships to those experienced in extra-terrestrial space. Solar radiation is energy which is either absorbed or reflected by the object to a black-body heat sink at 80 K. temperature. If the test portion of the spectrum and 943.1 watts per square meter is in the infrared portion of the spectrum. This radiation is readily simulated by concentrated sources of high intensity radiation, such as the tungsten filament and the quartz capillary mercury arc. The proper space relationships and number of such radiators obviously will depend on the size of the facility and can readily be Worked out by those skilled in the art.

Sunlight to the earth is collimated within :05 of angle and ideally the simulated radiation should be collimated in the same way. In the confines of the space chamber, this effect can only be achieved by the use of a parabolic reflector of about the same size as the area to be covered by radiation. Such a reflector blocks the flow of low temperature radiation to the heat sink over an intolerably large area, however, and would therefore cause serious error in the heat shell. As a comprise there can be used an array of small reflectors distributed over an area equal to that covered by radiation but spaced so that only a small percent of the array area is actually covered by reflectors.

Initial evacuation and degassing is accomplished in three phases. Thefirst phase involves the removal of the bulk of air starting at atmospheric pressure and continuing to a pressure of 0.1 to 0.01 mm. Hg. For small chambers this can be done by a mechanical vacuum pump and possibly an auxiliary Roots type pump. For large chambers the pumping speed required makes these types of pumps impractical. Multi-stage steam ejector pumps or possibly turbine pumps are more efficient.

The second phase of the initial evacuation is accomplished by the cryoplates and is concerned with the removal of the retained air in the chamber down to a pressure of mm. Hg, where the evolution of gas from the walls becomes a dominant factor. This phase, it the cryoplates could be brought to temperature instantly, would last only a few seconds, the time being determined by thethermal capacity of the cryoplates and the number present in the chamber.

The third phase of the initial evacuation is best accomplished through the use of anion gettering pump, such as a Vac-Ion or Evapor-Ion gettering pump, in conjuction with the cryopump. The ion pump is used to remove the remaining helium, hydrogen and neon in the chamber, as these gases will not condense on the cryoplate.

When the mechanical pumps evacuate the chamber to a pressure of 0.1 mm. Hg, the partial pressures of the atmospheric components are reduced in the same ratio since the mechanical pumps are not selective to gas composition. The pressure of the non-condensible gases is then approximately 10* mm. Hg. The cryopump, therefore, having started at 0.1 mm. Hg, blanks off at 10- mm. Hg, unless provisions are made to remove the non-condensible gases with a getter-ion type pump. Since the initial pressure of the inert gases is already down to 10- mm. Hg, and it is not necessary to provide for rapid exhaust, a nominal size getter-ion pump will be sufficient. The cryopump can then reduce the chamber pressure down to a value of 10- and possibly lower, depending upon the evolution of gas from the test components and the chamber walls.

Further improvements of vacuum can be realized by purging the gas source of its dissolved gas by heating it to a high temperature (900 C.) in vacuum, and by installing an inner liner of thin sheet metal within the chamber, as previously described, as an airtight shell which is then heated to outgassing temperature. Since this shell is airtight, the space between it and the chamber wall can be exhausted by a separate pump, thereby preventing collapse of the liner. The inner liner is also used as a black-body heat sink by refrigerating it to 80 K. Thermal insulation consisting of multiple aluminum foil between the liner and the chamber wall reduces the thermal load on the heat sink. The heat sink, in turn, reduces the thermal load on the cryoplate, thereby improving pumping efi'iciency. Also, since gas diffusion rate through metals is very sensitive to temperature, a reduc tion of temperature of the inner liner to K. results in a reduction of gas evolution from the wall by a factor of 10- This means thatthe gas will be essentially trapped and will not escape.

Black-body heat sink requirements can be met by the aforementioned chamber inner liner refrigerated to 80 K. This temperature can be obtained with liquid hydrogen, helium, or nitrogen circulation around the sheet metal liner. The most favorable thermodynamic ef-. ficiency can be realized with liquid hydrogen or liquid helium.

Thermal insulation between the refrigerated inner liner and the chamber walls is preferably provided by multiple layers of high emissivity aluminum foil. This space is evacuated, further reducing the thermal heat transfer by eliminating gas convection of heat. A total heat loss of only 3 10- B.t.u./hr.-ft. F./ft. can be realized with this type of thermal insulation. Aluminum foil also permits simplified assembly and a minimum of weight to be retained in position. 7

The inner'liner can be fabricated of thin gauge stainless steel because of the increase in tensile strength at 80 K. Refrigerant cooling channels may be silver soldered to the inner side of the liner and the inner side anodized to simulate a black-body condition. The outer side facing the radiation shields can be polished to achieve maximum reflectivity.

The radiation of the sun in the infrared, visible and ultraviolet range as measured above the earths atmosphere is very closely approximated in intensity and spectral distribution by radiation from a black-body at a temperature of 5830 K. Since the moon has essentially no atmosphere, this same level of radiation would also be encountered on the moons surface. The spectral distribution of the solar radiation cannot be matched by simulation with an actual black-body source at 5 830 K., however, since all known solids are vaporized at this temperature. The spectral distribution must, therefore, be synthesized approximately by combining the radiation from several reliable sources. The very practical combination for simulating this spectral distribution can be obtained through use of mercury arc lamps or xenon arc lamps of the proper intensity for the blue and ultraviolet portion of the solar spectrum and bare tungsten filaments for the red and infrared portion of the spectrum.

The surface of the moon is under a continuous bombardment of high energy particles which cover the entire range from electrons and protons of moderate velocity to the most energetic cosmic rays ranging up to energies of 1000 Bev. Simulation of electrons, protons, and other ions with velocities up to 100,000 volts or more can readily be provided by available electron and ion sources combined with simple electrostatic acceleration systems.

The surface of the moon can be considered a semismooth reflector. It has a permittivity of 9.5 10 f./m., and a mean conductivity of 4.8 10 mho/m., characteristics roughly equivalent to dry sand. A processing plant will be required to remove absorbed gas from the lunar soil-simulating material prior to placing it in the space chamber. A properly selected soil material will also act as a getter for inert gases in the chamber, thereby improving the ultimate high vacuum which can be attained.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. A space simulating vessel comprising in combination an outer skin, an inner skin insulated therefrom and enclosing an evacuable volume, means associated with the inner skin for cooling said skin with a first cryogen to a uniform temperature of about 70 to K., a checker- Work system of cryogenically cooled plates adjacent to but Spaced apart from said inner skin, a shield for each of said plates provided interiorly thereof, means associated with said shield for cooling said shield by means of said first cryogen, means for circulating a second cryogen through said checkerwork system of plates to cool said plates to a temperature of the order of 20 K., means for evacuating the volume enclosed by said inner skin, and means for flooding at least a portion of said enclosed volume with radiation, said inner skin, said plates and said shields being made of metal and finished so that the interior-facing surfaces of said inner skin and said shields are blackened and the exterior-facing surfaces ofsaid shields and all the surfaces of said plates are bright finished.

2. A vessel as in claim 1 wherein the means for evacuating the volume enclosed by the inner skin includes means for gettering non-condensible gases.

8 References Cited in the file of this patent UNITED STATES PATENTS 2,130,306 Lintern Sept. 13, 1938 2,858,972 Gurewitsch Nov. 4, 1958 2,897,657 Rupp Aug. 4, 1959 2,927,437 Rae Mar. 8, 1961) 2,939,316 Beecher et al June 7, 1960 2,985,356 Beecher May 23, 1961 3,010,220 Schueller Nov. 28, 1961 FOREIGN PATENTS 119,726 Australia Apr. 12, 1945 ROBERT A. OLEARY, Primary Examiner.

GEORGE HYMAN, JP, LEO SMILOW, EDWARD J.

MICHAEL, Examiners.

UNITED ST T S PATENT OFFICE CERTIFICATE OF CORRECTION Patemt No. 3 ,177,,672 April is, 1965 Ka'rlH. Seelandt I I It is hereby certified that error aopear's in -the above numbered pat-- en't reqiiring correction and that the said Letters Patent should read as correctedbelow. i e

Column 4 line 57 for "several" read severely column. 5 line 17 for "comprise" read compromise line 41, for "anion" read an ion 'same column 5 lines 42 and 43 for "conjuction" read conjunction Signed and sealed this 24th day off-August 1965.

- (SEAL) Attest: 'ERNEST- w. SWIDER EDWARD, J. BRENNER I Auk-sting Officer V Commissioner of Patents".

Claims (1)

1. A SPACE SIMULATIN VESSEL COMPRISING IN COMBIANTION AN OUTER SKIN, AN INNER SKIN INSULATED THEREFROM AND ENCLOSING AN EVACUABLE VOLUME, MEANS ASSOCIATED WITH THE INNER SKIN FOR COOLING SAID SKIN WITH A FIRST CRYOGEN TO A UNIFORM TEMPERATURE OF ABOUT 70* TO 120*K., A CHECKERWORK SYSTEM OF CRYOGENICALLY COOLED PLATES ADJACENT TO BUT SPACED APART FROM SAID INNER SKIN, A SHIELD FOR EACH OF SAID PLATES PROVIDED INTERIORLY THEREOF, MEANS ASSICIATED WITH SAID SHIELD FOR COOLING SAID SHIELD BY MEANS OF SAID FIRST CRYOGEN, MEANS FOR CIRCULATING A SECOND CRYOGEN THROUGH SAID CHECKERWORK SYSTEM OF PLATES TO COOL SAID PLATES TO A TEMPERATURE OF THE ORDER OF 20*K., MEANS FOR EVACUATING THE VOLUMNE ENCLOSED BY SAID INNER SKIN, AND MEANS FOR FLOODING AT LEAST A PORTION OF SAID ENDLOSED VOLUME WITH RADIATION, SAID INNER SKIN, SAID PLATES AND SAID SHIELDS BEING MADE OF METAL AND FINISHED SO THAT THE INTERIOR-FACING SURFACES OF SAID INNER SKIN AND SAID SHIELDS ARE BLACKENED AND THE EXERIOR-FACING SURFACES OF SAID SHIELDS AND ALL THE SURFACES OF SAID PLATES ARE BRIGHT FINISHED.

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