SP-473 LDEF

 

Electronics and Optics

 


[152] Holographic Data Storage Crystals for LDEF (A0044)

W. Russell Callen and Thomas K. Gaylord
Georgia institute of Technology
Atlanta, Georgia

 

Background

A compact high-bit-capacity recorder (on the order of 1011 bits) and memory system does not exist at the present time. However, electro-optic holographic recording systems are being developed and appear to be extremely promising.

 

Objective

The objective of this experiment is to test the spaceworthiness of electro-optic crystals for use in ultrahigh-capacity space data storage and retrieval systems.

 

Approach

The experiment approach is to passively expose four holographic data storage crystals, each 10 by 10 by 2 mm in size, to the space environment. Three of the iron-doped lithium niobate crystals contain recorded holograms and one is unrecorded (control sample). Crystal I is heat treated for maximum sensitivity and is blank. Crystal 2 contains a plane wave hologram written with a helium-neon laser (Greek letter lambda = 632.8 nm). Crystal 3 contains a plane wave hologram written with an argon laser (Greek letter lambda = 514.5 nm), and crystal 4 contains a spoke pattern hologram written with an argon laser (Greek letter lambda = 514.5 nm). The crystals containing the holograms were fixed in an atmosphere of lithium carbonate to extend the lifetime of the holograms.

This spectrum of crystals will assure determination of the most suitable crystal treatment for space use. A glass control sample will also be flown.

In crystals 2, 3 and 4, the data will be protected by charge neutrality of combined ion and electron patterns, and the holograms should be directly recoverable upon reexposure to uniform illumination. Two control crystals will remain on the ground, one containing a helium-neon laser hologram and one containing an argon laser hologram.

The crystals for this experiment will be included with the various electro-optical components of LDEF experiment S0050, investigation of the Effects of Long-Duration Exposure on Active Optical System Components, and will be located in the same experiment tray. Figure 64 illustrates the concept of data storage in an optical-phase holographic memory.

 


[
153]

Figure 64.-Data storage concept for an optical-phase holographic memory.

Figure 64.- Data storage concept for an optical-phase holographic memory.

 


[154] Exposure to Space Radiation of High-Performance Infrared Multilayer Filters and Materials Technology Experiments (A0056)

John S. Seeley, R. Hunneman, and A. Whatley
Department of Cybernetics, University of Reading
Reading, Berks, United Kingdom
 
Derek R. Lipscombe
British Aerospace Corporation
Stevenage, Hartfordshire, United Kingdom

 

Background

Infrared multilayer interface filters have been used extensively in satellite radiometers for about 15 years. Filters manufactured by the University of Reading have been used in Nimbus 5, 6, and 7, TIROS N, and the Pioneer Venus orbiter. The ability of the filters to withstand the space environment in these applications is critical; if degradation takes place, the effects would range from worsening of signal-to-noise performance to complete system failure. An experiment on the LDEF will enable the filters, for the first time, to be subjected to authoritative spectral measurements following space exposure to ascertain their suitability for spacecraft use and to permit an understanding of degradation mechanisms.

Additionally, the understanding of the effects of prolonged space exposure on spacecraft materials, surface finishes, and adhesive systems is of great interest to the spacecraft designer. Thus, a series of materials technology experiments will be included with the experiment on infrared multilayer filters,

 

Objectives

The objective of the multilayer filters experiment is to expose highperformance infrared multilayer filters to the space environment and recover them for subsequent analysis and comparison with laboratory control samples. Semiconductors such as PbTe, Si, and Ge will be examined to see if excess free carriers have been generated by exposure, and for evidence of surface contamination or degradation and or decomposition. ZnS and other dielectrics will be examined for evidence of bulk degradation, such as enhanced absorption, color center excess, and reststrahl abnormalities.

The objectives of the materials technology experiments are to evaluate the degradation of spacecraft surface finishes, the outgassing of spacecraft [155] surface finishes, the effect of thermal paints on carbon-fiber-reinforced plastic (CFRP) sheet and the thermal differentiation of expansion between base material and thermal coating, the strength of adhesive-bonded joints (lap shear), the effect of CFRP strength stiffness and interlaminar strength, the dimensions of CFRP curvature, and the effect on bond strength between CFRP-aluminum alloy skins and honeycomb core.

 

Approach

The experiment will utilize one-sixth of a 3-in.-deep peripheral tray and one-fourth of a 3-in.-deep end center tray on the Earth-facing end of the LDEF. Figure 65 illustrates the arrangement of the filters and material samples.

The infrared filters being considered for the experiment are listed in table 17. The samples will be measured on an infrared spectrometer with particular reference to any critical parts of their spectrum (e.g., peak transmission and center wave number of bandpass filters, edge position and steepness in edge filters, and transmission in longwave filters) prior to assembly into the experimental structure. At the same time, the samples will be visually inspected and photographed, and any other testing (for example, adhesion tests) will be carried out. Upon retrieval, the samples will be visually inspected prior to shipment back to the laboratory for postflight testing.

 


[
156]

Figure 65.- Arrangement of infrared multilayer filter and materials technology experiments.

Figure 65.- Arrangement of infrared multilayer filter and materials technology experiments.

 

[157] Table 17.- High-Performance Infrared Filters.

Sample type

Materials (substrate layers)

Function

.

Substrate

CdTe

Longwave blocker

Substrate

Quartz

Shortwave blocker for longwave filter

Substrate

BaF2

Longwave blocker

Substrate

KRSS (TlBrl)

Longwave blocker

Substrate

KRS6 (TlCIBr)

Longwave blocker

Substrate + coating

Germanium with ZnS/PbTe multilayer

Broadband antireflection coating

Substrate + coating

Germanium with ZnS/PbTe/photoresist or PbF2

Broadband antireflection coating

Substrate + coating

Silicon with photoresist

Antireflection coating

Substrates + coatings

Silicon with ZnS, silicon with ZnSe, silicon with CdSe

Longwave reststrahl blockers used in Venus, Pioneer probe

Substrates + coatings

Germanium with ZnS/PbTe multi layers

Bandpass filter on two substrates, 15-µm CO2 band comprising two full blocker edge filters, used in TIROS N Stratospheric Sounding Unit

Substrate + coatings

Silicon with CdSe/PbTe multilayers

Longwave edge filter at 23 µm, fully blocked to shortwave

Substrate + coatings

Germanium with ZnS/PbTe multilayers

10.6-µm narrowband filter, fully blocked to shortwave

Substrate + coatings

Germanium with ZnS/PbTe

15-µm narrowband filter for CO2 band, similar to filters used in Nimbus 5

Substrates + coatings

TlCIBr with ZnSe TlCIBr multilayers + photoresist antireflection coating

Longwave edge for Jupiter missions

Substrate + coatings

Silicon with ZnSe TlCIBr multilayer

Longwave edge for Jupiter missions

Substrate + coatings

Silicon with CdTe TlBrl multilayer

Longwave edge for Jupiter missions

Substrate + coatings

Germanium with ZnS/PbTe multilayer

10.6-µm narrowband filter, fully blocked to shortwave, ZnS spaced

Substrate + coatings

Germanium with ZnS/PbTe mu lti layer with photoresist antireflection layers

Steep-edge filter at approximately 13.5-µm

Mesh filters

Melinex + evaporated Au films

Far-infrared mesh filters

 


[158] Effect of Space Exposure on Pyroelectric Infrared Detectors (A0135)

James B. Robertson, Ivan O. Clark, and Roger K. Crouch
NASA Langley Research Center
Hampton, Virginia
 

Background

NASA's commitment to air pollution monitoring and thermal mapping of the Earth, which includes the remote sensing of aerosols and limb scanning infrared radiometer projects, requires photodetection in the 6- to 20-µm region of the spectrum. The Hg-Cd-Te detectors that are presently used in these wavelengths must be cooled to 50 to 80 K. The cryogenic systems required to achieve these temperatures are large, complex, and expensive.

Pyroelectric detectors can detect radiation in the 1- to 100-µm region while operating at room temperature. This makes the pyroelectric detector a prime candidate to fill NASA's thermal infrared detector requirements.

 

Objective

The objective of this experiment is to determine the effects of long duration space exposure and launch environment on the performance of pyroelectric detectors. This information will be valuable to potential users of pyroelectrics for predicting performance degradation, setting exposure limits, or determining shielding requirements.

 

Approach

In brief, the approach is to measure important detector parameters on a number of detectors before and after flight on the LDEF. Commercially available detectors will be purchased for the experiment. Performance parameters to be measured are responsivity, detectivity, and spectral response. Material properties to be measured are pyroelectric coefficient and dielectric-loss tangent.

After the detectors are returned to the laboratory, all tests and measurements will be repeated to determine the amount and type of damage suffered during launch and exposure.

The detectors for this experiment will be included with the various electro-optical components of experiment S0050, investigation of the Effects of Long-Duration Exposure on Active Optical System Components, and will be located in the same experiment tray.

 


[159] Thin Metal Film and Multilayers Experiment (A0138-3)

J. P. Delaboudiniere and J. M. Berset
CNRS/LPSP
Venieres le Buisson, France

 

Background

It is well known that ultraviolet (UV) and extreme ultraviolet (EUV) experiments suffer degradations during space missions of even I month duration. It is believed that the degradation is due mainly to condensation of outgassing products, followed by solar-induced polymerization. However, penetrating charged particles are also known to produce volume effects. On the other hand, degradation may start immediately after manufacturing of the component due to oxidation, moisture, or chemical corrosion by atmospheric constituents such as CO2 and SO2. Finally, when the filters are used as windows for gas absorption cells or gas filters, or when they define the instrumental bandwidth by themselves (as in photometers and colorimeters), the effects of mechanical degradation by thermal cycling and/or dust impact may be dramatic.

 

Objectives

The objectives of this experiment are to investigate the sources of degradation of both state-of-the-art and newly developed components and to test the usefulness of the concept of storing experiment samples in dry nitrogen under launch and space vacuum conditions during reentry mission phases.

 

Approach

The experimental approach is to passively expose EUV thin films and UV filters to the space environment for postflight measurement and comparison with preflight measurements. The experiment will be located in one of the three FRECOPA boxes in a 12-in.-deep peripheral tray that contains nine other experiments from France. (See figs. 12 and 13.) The FRECOPA box will provide protection for the experiment samples during the launch and reentry phases of the LDEF mission.

All samples will be manufactured at LPSP according to carefully controlled techniques and will be separated into two exactly similar lots, one of which will serve as control samples and will be stored under vacuum conditions in the laboratory. The flight lot will also be divided into two half-lots One will be mounted in the FRECOPA box to see solar illumination and the other will be protected from solar illumination. After LDEF [160] deployment, the FRECOPA boxes will be automatically opened to permit exposure and will be closed prior to LDEF retrieval. After the flight samples are retrieved, their optical properties and the optical properties of the control lot will be remeasured. The control lot will be remeasured to account for intrinsic aging.

Each half-lot of the flight samples will contain 12 EUV free-standing "single-layer" thin films (set S1), 24 EUV "single-layer" thin films (set S2), 12 multilayers deposited on glass substrates (set S3), and 4 UV crystals (set S4).

The filters in sets S1 and S2 are thin (1500 to 3000 Å) films of selected metals. Under such thickness, good optical transmission is obtained in wavelength bands approximately 100 Å wide. Selected materials that provide bands in the extreme ultraviolet include Al, Al + C, Sn, and in.

The metallic multilayers in set S3 are new optical components for the EUV region. Interference effects within a stack of alternatively absorbing and transparent materials of appropriate thickness are used to increase the reflecting efficiency within a narrow wavelength range. The number of periods is on the order of 10 to 40. Layers of Si/W and C/W are scheduled to be included if available.

The UV crystal filters in set S4 are relatively thick (2 mm) crystal windows of LiF and MgF2 and are of general use in the far UV range.

For the preflight test program, fabrication controls and preliminary EUV bandpass measurements will be made with a grazing incidence monochromator. The full bandwidth of free-standing filters and multilayers will be measured with a synchrotron light source in several wavelength intervals from 40 to 2000 Å, with emphasis on the interval from 100 to 1000 Å. Optical constants will be measured from deposits on glass substrates.

Preflight measurements will be repeated for the postflight test program, and surface physical and chemical analyses will be made using the samples deposited on glass substrates and some of the free-standing films in cases where drifts have been observed. This will be possible because several filters of each kind will be used (i.e., destructive testing is possible).

 


[161] Vacuum-Deposited Optical Coatings Experiment (A0138-4)

A. Malherbe
Optical Division, Matra S.A.
Rueil Malmaison, France

 

Background

In the past, the Matra Optical Division has developed a wide range of optical components manufactured by vacuum deposition, such as metallic and multidielectric reflective coatings in the UV range, metal-dielectric interference filters in the UV (down to t 100 Å) and IR ranges, narrowbandpass filters in the near-UV and visible ranges, selective metallic mirrors in the range from 1500 to 2500 Å, antireflective and reflective IR coatings, beam splitters in the visible and IR ranges, and optical surface reflection (OSR) coatings. Many of these components, some of which were the first of this type to be manufactured in the world (e.g., interference filters at Lyman Greek letter alpha), have been incorporated into scientific and technical experiments flown on balloons and rockets as well as on Symphonie, Meteosat, OTS, D2-B, TIROS N, and others. These components appear to have operated successfully in flight, but detailed information concerning their long-term behavior is not available.

 

Objective

The objective of this experiment is to analyze the stability of various vacuum-deposited optical coatings exposed to the space environment.

 

Approach

The experimental approach is to passively expose samples of the optical coatings of interest. (See table 18.) Preflight and postflight optical measurements, including visual and microscopic inspections, will be compared to determine the effects of space environment exposure.

The experiment will be located with nine other experiments from France in a 12-in.-deep peripheral tray. The optical coating samples will be located in one of the three FRECOPA boxes located in the tray. (See fig. 12.) The FRECOPA box (fig. 13) will provide protection from contamination for the samples during the launch and reentry phases of the LDEF mission.

Preflight and postflight measurements will include visual and microscopic examination and spectrophotometric analysis. For samples that show changes, microphysical analyses will be performed by experienced laboratories.

 

[162] Table 18.- Optical Coatings Used in Experiment A0138-4.

Sample

Performance a

Application

.

Metallic interference filter made in ultrahigh vacuum, Greek letter lambda= 121.6 nm

T > 10 percent Greek letters delta lambdanear 10 nm

Scientific

Metallic interference filter made in classical vacuum Greek letter lambda = 121.6 nm

T > 8 percent Greek letters delta lambda near 12 nm

Scientific

Metallic interference filter, Greek letter lambda = 130 nm

T > 12 percent Greek letters delta lambda near 15 nm

Scientific

Dielectric interference filter, Greek letter lambda = 500 nm

T > 50 percent Greek letters delta lambda near 5 nm

Scientific

Bandpass infrared filter, Greek letter lambda = 15 µm

T > 5O percent Greek letters delta lambda near 2 µm

Telecommunication,

Earth observation

Al + MgF2 metallic mirror on glass substrate

R > 80 percent at Greek letter lambda = 121 nm

Scientific

Al + MgF2 metallic mirror on Kanigen substrate

R > 75 percent at Greek letter lambda = 121 nm

Scientific

Al + LiF metallic mirror on glass substrate

R > 55 percent at Greek letter lambda = 102 nm

Scientific

Al + LiF metallic mirror on Kanigen substrate

R > 50 percent at Greek letter lambda = 102 nm

Scientific

Platinum mirror

R > 20 percent at Greek letter lambda = 121 nm

Scientific

Au mirror

R > 20 percent at Greek letter lambda = 121 nm

Scientific

Ag + ThF4 metallic mirror on glass substrate

R > 95 percent at Greek letter lambda = 450 nm

Earth observation

Ag + ThF4 metallic mirror on Kanigen substrate

R > 95 percent atGreek letter lambda = 450 nm

Earth observation

Dielectric mirror at Greek letter lambda = 250 nm

R > 9S percent at Greek letter lambda = 250 nm

Scientific

Dielectric mirror at Greek letter lambda = 170 nm

R > 95 percent at Greek letter lambda = 170 nm

Scientific

Metallic selective mirror at Greek letter lambda = 170 nm

R > 80 percent at Greek letter lambda = 200 nm and

R > 20 percent at Greek letter lambda = 300 nm

Scientific

SiO2-TiO2 dielectric mirrors

R > 95 percent in visible

Earth observation

Antireflection coating in 14- to 16-µm region

T > 94 percent at 15µm

Telecommunication

Antireflection coating in 8-to 13 µm region

T > 94 percent at 10 µm

Earth observation, meteorology

Dichrometric separation in visible and infrared region

R > 90 percent in visible, T > 80 percent at 10 µm

Earth observation

a T = transmission, R = Reflectance

 


[163] Ruled and Holographic Gratings Experiment (A0138-5)

Gilbert Moreau
Jobin-Yvon Division, instruments S.A.
Longjumeau, France

 

Background

In the past, several ruled and holographic gratings from Jobin-Yvon with various coatings were successfully flown on rocket experiments from LPSP and other organizations as well as satellites D2-A, D2-B, OSO-I, and some from the U.S. Future utilizations of such gratings are being considered for the Space Telescope and for various Spacelab projects being developed by France, Germany, Belgium, and other countries.

The technique used to replicate gratings can also be used to obtain a wide range of lightweight optical components, including sophisticated aspherical, highly polished mirrors.

 

Objectives

The objective of this experiment is to test the behavior of ruled and holographic gratings with various coatings after extended exposure to the space environments. Specific objectives include examining the coatings for possible changes and differentiating between the influences of vacuum and solar illumination.

 

Approach

The experimental approach is to passively expose samples of the gratings and coatings of interest. Preflight and postflight examination to characterize the optical quality of the gratings will include measurement of wavefront flatness, reflection efficiency, and stray-light level.

The experiment will be located with nine other experiments from France in a 1 2-in. -deep peripheral tray. The grating samples will be located in one of the three FRECOPA boxes located in the tray. (See fig. 12.) The FRECOPA box (fig. 13) will provide protection for the samples from contamination during the launch and reentry phases of the LDEF mission.

The following is a list of the samples to be used in this experiment with a description of each. Type "G" is a replica of a grooved grating with 1200 grooves/mm blazed at 2500 Å (aluminum-coated blank pyrex). Type "H" is an original holographic grating with 3600 grooves/mm and a spectral range of 500 to 1500 Å (platinum-coated blank pyrex). Type "HU" is an ion-etched blazed grating with 1200 grooves/mm blazed at 2500 Å (aluminum-coated [164] blank pyrex). Type "W" is a control mirror on blank pyrex. One half is coated with aluminum and the other half with platinum. Samples will be located on both sides of the mounting plate within the FRECOPA box and will have the shape of a parallelepiped with dimensions 34 by 34 by 10 mm. A set of control samples will also be stored in the laboratory for comparison with those retrieved from space.

Preflight and postflight measurements to be made include the following parameters.

1. Wave surface flatness.-This will separate changes introduced by groove distortion and blank distortion and will be measured on an order of zero for types H, G, and W, and on an order of one for types G, H, and HU. The measurement will be made by photography using a Michelson interferometer.

2. Reflection efficiency.-This is measured with a photogoniometer from 2200 to 6000 Å for types G, HU, and W and with a vacuum photogoniometer from 584 to 1216 Å for types H and W.

3. Stray light level.-For types G and HU, measurements will be made using a continuum spectrum (deuterium lamp) near 2000 Å on a monochromator with a liquid filter. For type HU, measurements will be made using a laser line (6328 Å) on a monochromator. These measurements will help define the limits of utilization for each type of grating. Comparison of the different measurements before and after space exposure will help define the space environment elements that cause degradation of grating optical qualities and the grating components which are damaged by those elements.

 


[165] Optical Fibers and Components Experiment (A0138-7)

J. Bourrieau
CERT/ONERA-DERTS
Toulouse, France

 

Background

Fiber optics are becoming important components in communication systems, optoelectronic circuits, and data links. Space applications are now available with various advantages: weight and size reduction, data transmission rate increase (10 to 102 Mbits), and reduction of electromagnetic susceptibility and power requirements. High sensitivity to ionizing radiations, however, may be a restriction for optic-fiber use on satellites. Presently, in-flight observations of optic-fiber damages are not available, but an increasing number of laboratories are carrying out irradiation tests on these components using neutrons, gamma rays, and X-rays. Radiation damage on optical materials, however, is strongly linked to the test conditions (temperature, dose rate, energy, and nature of the incident particles), and laboratory tests are not as representative as actual space environment exposure.

 

Objectives

The main objective of this experiment is the comparison of fiber optics permanent damages induced by ionizing radiation after a long exposure in space and after laboratory tests. Specific objectives are to validate irradiation tests performed with radioactive sources (Sr90-Y90), to verify computer codes used for the fluence and dose profiles, to determine the performance of fiber optics waveguides in a low-altitude orbit (doses between 10 and 100 Gy are expected), and to determine the origin of transmission losses (e.g., color centers and index variations) in the material.

 

Approach

The experimental approach is to passively expose two optic-fiber waveguides (one step index and one graded index) of some 60 cm in length with connectors. (See fig. 66.) Preflight and postflight measurements of optical properties will be compared to determine the effects of space environment exposure.

The experiment will be located with nine other experiments from France in a 12-in. -deep peripheral tray. The optical fibers will be located in one of the three FRECOPA boxes in the tray. (See fig. 12. ) The FRECOPA box (fig. 13) [166] will provide protection for the optical-fiber waveguides from contamination during launch and reentry phases of the LDEF mission. The in-flight absorbed dose profile will be measured with five thermoluminescent dosimeters shielded by various aluminum thicknesses.

Irradiation of the selected optic fiber waveguides will be carried out in the laboratory with an Sr90-Y90 beta ray source in order to simulate the in-flight dose. Before and after flight and laboratory simulation, measurements of the optic-fiber waveguide light transmission will be made with a spectrophotometer. Four sets of samples will be manufactured, one for ground test and the others for control, flight, and space flight sets.

 


Figure 66.- Optical-fibers experiment configuration.

Figure 66.- Optical-fibers experiment configuration.

 


[167] Passive Exposure of Earth Radiation Budget Experiment Components (A0147)

John R. Hickey and Francis J. Griffin
The Eppley Laboratory, inc.
Newport, Rhode island
 

Background

Earth Radiation Budget (ERB) experiments require accuracies on the order of fractional percentages in the measurement of solar and Earth flux radiation. In order to assure that these high-accuracy devices are indeed measuring real variations and are not responding to changes induced by the space environment, it is desirable to test such devices radiometrically after exposure to the best approximation of the orbital environment.

 

Objective

Since the Earth Radiation Budget experiment was operational on Nimbus 6 and is operational on Nimbus 7, and since in-flight calibration is difficult for the solar and Earth flux channels, the objective of this experiment is to expose ERB channel components to the space environment and then retrieve them and resubmit them to radiometric calibration after exposure. Subsequently, corrections may be applied to ERB results and information will be obtained to aid in the selection of components for future operational solar and Earth radiation budget experiments.

 

Approach

Passive exposure of solar and Earth flux channel components of the ERB radiometer is the basis of the approach. Three Earth flux channel types of ERB will be mounted in one-fourth of a 3-in.-deep end center tray on the Earth-viewing end of the LDEF. (See fig. 67.) Prior to delivery, these channels will undergo complete radiometric and spectrophotometric examination. These tests will be repeated after retrieval to evaluate changes in orbit. The solar-channel components will be mounted in one-sixth of a 3-in.-deep peripheral tray near the leading edge of the LDEF (in the direction of the velocity vector) to view the Sun in the manner most like the ERB experiment on Nimbus. Solar-channel components to be tested include thermopiles, interference filters, and fused silica optical windows. (See fig. 68.) Additionally, some state-of-the-art vacuum-deposited interference....

 


[
168]

Figure 67.- Earth flux channel components.

Figure 67.- Earth flux channel components.

 


Figure 68.- Solar-channel components.

Figure 68.- Solar-channel components.

 

[169] ....filters have been included to examine space environment effects on these components. The two thermopiles will have different black paint on the receivers. The cavity unit will be similar to that proposed for future solar constant measurement missions. Vacuum bakeout will be performed on all elements as prescribed and performed for Nimbus prior to delivery. Radiometric testing and weighing will be performed on the thermopile and cavity devices. Spectrophotometric testing will be performed on filters and fused silica components.

 


[170] Effects of Solar Radiation on Glasses (A0172)

Ronald L. Nichols
NASA George C. Marshall Space Flight Center
Huntsville, Alabama
 
Donald L. Kinser
Vanderbilt University
Nashville, Tennessee

 

Background

The deterioration of glass when subjected to solar radiation has been scientifically observed. Since the molecular structure of glass is considered to be in a metastable state, this lack of stability is not an unexpected event; the glass would achieve a lower state of energy if its atoms were rearranged in a long-range repetitious lattice structure. Changes in the properties of a glass are commonly associated with exposure to solar radiation. Because of insufficient test data for glasses exposed to actual space radiation, the materials engineer must attempt to extrapolate from data for artificial solar radiation exposure in order to select glasses for use in hardware that will be exposed to the space environment for long periods of time. This limitation severely degrades the confidence level for the performance of glasses utilized in space.

 

Objective

The objective of this experiment is to determine the effects of solar radiation and space environment on glasses in space flight by exposing glass specimens to the space environment and analyzing the optical, mechanical, and chemical property changes that occur. The property changes of samples receiving differing cumulative solar radiation exposure will be compared.

 

Approach

This experiment will be conducted by passively exposing glass samples to the space environment. Glass samples occupying one-sixth of a 3-in.-deep tray will be located near the trailing edge of the LDEF so that they will be exposed to a maximum amount of incident solar radiation. This location will contain 68 cylindrical disc samples 1.25 in. in diameter. (See fig. 69.) Another group of 52 samples occupying one-fourth of a 3-in.-deep tray will be located on the Earth-facing end of the LDEF and will receive minimum exposure to solar radiation. The properties of each sample will be measured....

 


[
171]

Figure 69.-Solar radiation on glasses experiment.

Figure 69.- Solar radiation on glasses experiment.

 

[172] ....prior and subsequent to exposure to the space environment. Several samples of each glass composition selected for flight will be evaluated to allow a statistical analysis of the data obtained. Candidate compositions include aluminosilicates, fused silica, titanium silicate, lead silicates, borosilicates, soda potash lime, potash borosilicate, and soda lime silica glasses.

 


[173] Study of Factors Determining the Radiation Sensitivity of Quartz Crystal Oscillators (A0189)

John D. Venables and John S. Ahearn
Martin Marietta Laboratories
Baltimore, Maryland
 

Background

It has long been known that radiation increases the acoustic absorption of quartz crystal oscillators and produces shifts in their resonant frequency which may be as large as 400 parts per million. The need for high-precision quartz oscillator clocks (and filters) in communication satellites, missiles, and space probes makes it necessary to improve the radiation stability of materials used for these applications.

Experiments performed at Martin Marietta Laboratories demonstrate that the technique of transmission electron microscopy (TEM) provides a powerful method for studying the effect of radiation on crystalline quartz. When suitably thin samples of a-quartz are examined by TEM, it is observed that defect clusters form at a rapid rate within the material even when the incident electron energy is as low as 40 keV. Studies of this phenomenon indicate that the clusters are formed from atoms that have been displaced by electrons in the incident beam, that the clusters nucleate at impurities (because the cluster concentration appears to be impurity dependent), and that the clusters induce large strain fields in the lattice surrounding them, as evidenced by their paired black-dot images, which are characteristic of "strain field contrast."

Two factors suggest that the observed clusters may be responsible for the radiation-induced frequency drift and acoustic-absorption effects associated with irradiated quartz resonators. First, the clusters are expected to be very effective in modifying the piezoelectric properties of quartz because of the large strain fields associated with them. Second, both phenomena appear to be sensitive to the impurity concentration. If this conclusion is valid, it suggests that TEM can be used to classify grades of quartz according to their suitability for use in radiation-hard resonators. Moreover, using this technique it may be possible to identify the impurities that are responsible and thereby effect an improvement in the stability of quartz oscillators.

 

Objective

The objective of this experiment is to determine whether there is a correlation between defect cluster concentrations observed for different [174] grades of quartz examined by TEM and the electrical stability of quartz resonators exposed to the complex radiation associated with an orbital LDEF environment.

 

Approach

To accomplish the objectives, several grades of single-crystal a-quartz containing a wide range of impurity concentrations have been examined by TEM to determine differences in their susceptibility to cluster formation during electron irradiation. Based on the sensitivity of the quartz materials to radiation as determined by TEM, two grades of quartz have been selected for fabrication into resonators. The selection has been made to maximize the differences in radiation sensitivity of the chosen materials. The electrical properties of the resonators are being established by measuring their resonant frequency as a function of time to establish the natural frequency drift of the resonators before insertion into orbit. After exposure to the LDEF environment, a second series of electrical measurements will be made on the resonators to determine variations from the preflight data. Changes in the electrical data will then be compared with TEM results to determine whether TEM observations are relevant to the study of the stability of quartz resonators in an outer-space environment.

The experiment hardware consists of one-sixth of a 3-in.-deep peripheral tray with 14 5-MHz fifth-overtone. At-cut resonators mounted on an aluminum plate, as shown in figure 70. The resonators have been fabricated from two materials (synthetic swept premium Q and Brazilian natural quartz) selected because the TEM technique indicates large differences in their radiation sensitivity. Four resonators (two from each grade of material) will be used as controls and shielded from radiation. The remaining ten resonators (five from each grade) will be exposed to the space radiation. In addition, two resonators (one from each grade) will be kept in the laboratory as additional controls. By determining the frequency drift of the resonators before and after the LDEF flight, as well as the frequency offset occurring during the flight, it will be possible to separate the natural frequency drift from that induced by the space radiation and to determine whether the radiation damage observed by TEM correlates with the space radiation environment of an orbital LDEF flight.

 


[
175]

Figure 70.-Quartz crystal oscillator experiment.

Figure 70.- Quartz crystal oscillator experiment.

 


[176] Investigation of the Effects of Long-Duration Exposure on Active Optical System Components (S0050)

M. Donald Blue, James J. Gallagher, and R. G. Shackelford
Engineering Experiment Station, Georgia institute of Technology
Atlanta, Georgia

 

Background

In the future, electro-optical systems will find increasing applications in space-based systems. The successful flights of interplanetary probes dating back to Mariner 11 in 1962 have demonstrated the ability of optical systems to operate in the interplanetary space environment over periods of many months. Current and planned Earth resources and meteorological satellites are indicative of the complexity being achieved in such systems, and the planned laser intersatellite communication links show a new level of sophistication being developed for future electro-optical systems.

The environmental hazards peculiar to space include radiation-induced discoloration, electrically active flaws, and changes in index of refraction. These problems may arise from sublimation, outgassing, and decomposition effects as well as from deposition of such products and other debris onto component surfaces. Other hazards are abrasion or cratering of surfaces, which are caused by meteoroids and cosmic dust.

Optical and electro-optical components must survive this environment. Assurance of survival is typically provided by ground-based testing to simulate those aspects of the space environment which are considered most serious. The availability of the LDEF permits exposure of electro-optical components to a true space environment at a reasonable cost.

 

Objectives

The objectives of this experiment are to determine quantitatively the effects of long-duration space exposure on the relevant performance parameters of lasers, radiation detectors, and selected optical components, to evaluate the results and implications of the measurements indicating real or suspected degradation mechanisms, and to establish guidelines, based on these results, for selection and use of components for space electro-optical systems.

 

Approach

The experiment includes a representative sample of sources, detectors, and passive components typical of basic elements in electro-optical systems.

[177] These components are mounted in a 6-in.-deep peripheral tray in a manner that simulates their likely surroundings in an operational system. Figure 71 shows the construction and assembled appearance of one of the six subtray panels making up the experiment. Careful attention to surface coatings is required to maintain component temperatures below levels at which deterioration can occur. The arrangement shown in the figure uses a sunscreen, black paint, and anodized coatings to achieve a temperature range of -50° to 68°C.

 


Figure 71.-Active optical system components experiment.

Figure 71.-Active optical system components experiment.

 

[178] A total of 171 components have been acquired, of which 136 will be mounted in the tray and 35 will be maintained in the laboratory as controls. A brief listing of these components is presented in table 19.

The analysis procedure involves careful measurement of the operational characteristics of the components before and after space flight. It may be necessary to analyze surface debris or coatings of condensed materials on optical surfaces, although the extent and nature of such effects cannot be anticipated at this time. The analysis techniques available include scanning electron microscopy, electron and X-ray fluorescence spectroscopy, and X-ray diffraction.

Duplicate components will be stored in a laboratory environment and will be available for comparison purposes in most cases. The experiment will be passive and no electrical power will be employed. Components normally operated at cryogenic temperatures will not be cooled. For this reason, the....

 

Table 19. - Electro-Optical Components.

 

Passive components

Active components

Detectors

.

Black paint, EccoSorb
CR-110
Black paint, 3M black
(101-C10)
Black paint, IITRI bone lack D-111
Black paint, 3M CR-110 on EccoSorb
Black paint, Chemglaze
Z-306 flat
Neutral-density filter
Narrowband filters
Hot mirror
Dielectric mirrors
Optical glasses
Window, MgF2
Window, Al2O3
Window, CaF2
Window, LiF
Window, SiO2
Mirror, Al + MgF2
Mirror, UV laser
Filter, Lyman Greek letter alpha
Filter, 1600 Å
35mm canister, shortwave radiation film
Black polyethylene
Modulator, ammonium
dihydrogen phosphate
Channeltron array
Laser diode, Al1-yGayAs
Laser diode array
GaAs LED
YAG: Nd rod
CO2 waveguide laser
HeNe laser
Holographic crystals
Flash lamps
Silicon PIN
Silicon photovoltaic
Silicon gamma ray detector
PbSnTe photovoltaic planar arrays
GaAsSb photovoltaic
InSb photovoltaic
PbS photoconductive
PbSe photoconductive
HgCdTe photoconductive
HgCdTe photovoltaic
Pyroelectric LiTaO3
Ultraviolet photomultiplie tube
UV Si
Pyroelectric:
Strontium
barium niobate
Triglycine sulfate
LiTaO3

 

[179] ....experiment will serve to establish a baseline for the effects of degradation of components at ambient temperature. Future experiments on the effects of exposure at normal cryogenic operating temperatures can be combined with the ambient-temperature data to separate degradation effects that are speciflcally temperature related.

 


[180] Fiber Optic Data Transmission Experiment (S0109)

Alan R. Johnston and Larry A. Bergman
Jet Propulsion Laboratory
Pasadena, California

 

Background

Application of fiber optic technology to data transmission on a spacecraft will yield several benefits in comparison to conventional copper wire transmission. Probably the most important advantage is that fiber links are inherently insensitive to pickup, electromagnetic interference, and ground loops. Also, fibers are roughly two orders of magnitude smaller and lighter than their copper wire equivalent, and ultimately it is anticipated that a fiber link will become cheaper than copper. The same components, once installed, could handle the wide range of signal bandwidths, from telephone rates (tens of kilobits) up to tens of megabits. In addition, there is a largely unexplored relationship with the developing microcircuit technology, suggesting other applications that are presently unknown. Therefore, early verification of fiber optic technology in the spacecraft environment should have a broad-based interest in the future, and this experiment will provide an opportunity to test representative types of fiber links in an actual space environment.

 

Objective

The objective of this experiment is to test fiber optic components in the space environment to determine their ability to operate over long periods of time without degradation of performance.

 

Approach

The experiment occupies a 6-in.-deep peripheral tray and consists of approximately 10 state-of-the-art fiber cable samples and three candidate connector types which will be passively exposed to the space environment. Figure 72 shows the flight hardware.

Four fiber cable samples will be mounted in a planar helix coil on thermally isolated mounting plates attached at the tray surface. Six or more additional cable samples will be mounted on the bottom surface of the tray. Each of the cable samples will be terminated in connectors mounted on brackets. These will be located on the back surface of the upper plates, or on the base plates for the internally mounted samples.

 


[
181]

Figure 72.-Fiber optic data transmission experiment shown during receipt and inspection activity.

Figure 72.- Fiber optic data transmission experiment shown during receipt and inspection activity.

 


[182] Space Environment Effects on Fiber Optics Systems (M004)

Edward W. Taylor
Air Force Weapons Laboratory, Kirtland Air Force Base
Albuquerque, New Mexico

 

Background

Although the application of fiber optic technology in ground-based data links is becoming commonplace, the technology advancement for aerospace military application has not yet developed to the extent that full utilization is a reality. Although fiber optic technology offers advantages such as reduction of system susceptibility to electromagnetic pulse (EMP), electromagnetic interference (EMI), system-generated EMP (SGEMP), ground loop, and inadvertent discharge phenomena, the undesirable response of optical fibers exposed to ionizing radiation is presently of concern to military aerospace system designers. Functional improvements, such as weight and power reductions, realized through the use of fiber optic technology certainly appear attractive at this time, particularly in aerospace communication systems. However, since optical waveguide electro-optic technology has yet to be used in space-borne applications, issues such as link life expectancies, power consumption, sensitivity, and radiation hardening are of primary concern.

Space qualification of materials unique to fiber optic technology (i.e., bonding and potting agents) over a typical temperature range from - 65°C to 125°C under vacuum conditions is an immediate need for satellite applications. In essence, then, fiber optic space application must begin with early spaceflight assessment of the influence of launch and orbital extremes. This Air Force Weapons Laboratory (AFWL) investigation, although primarily concerned with the survivability and vulnerability of fiber optic systems exposed to the space radiation environment, is also cognizant of the entire space qualification requirement.

 

Objectives

The objectives of this experiment are to assess the performance survivability of hardened fiber optic data link design for application in future spacecraft systems and to collect, analyze, and document the effects of space environmental conditions on link performance. Particular attention will be directed toward the integration and operation of new fiber optic link components exhibiting increased hardening to radiation environments. The opportunity to expose operational fiber optic data links to an actual space environment for 6 months or longer and to retrieve the data links for analysis [183] is expected to impact future Air Force design of space-qualified fiber optic systems. Data from the experiment, along with data from previous AFWL material and component radiation response studies, will be used to form reliable design criteria for future spacecraft applications, particularly relative to the long-term low-dose space radiation effects as a function of temperature.

 

Approach

This investigation is composed of nine distinct experiments consisting of both active and passive data links or components. Certain links or components will be preirradiated in order to assess the effects of the long-term low-dose space radiation environment on link performance. The data rate for the active fiber optic links was selected to be 10 Mbits/sec. Shown in figure 73 is a photograph of the fiber optics systems experiment, which will be installed in a 6-in.-deep peripheral tray. In all instances, emitters, detectors, and all connectors, couplers, and electronic components are tray shielded. Experimental measurements to be performed and recorded on magnetic tape will include bit error loss (BER) burst errors and fiber attenuation losses for the data links, in addition to fiber temperature and tray volume temperature.

 


Figure 73.- Fiber optics systems experiment.

Figure 73.- Fiber optics systems experiment.

 

[184] Thermoluminescent devices will be used within the tray volume in order to measure incident radiation. An experiment power and data system (EPDS) will be used to satisfy the data recording requirements.

 

Active Experiments

Active data links. - Four active links will be exposed to space. One of these links will consist of 45 m of cabled glass fiber incorporating a hermetically sealed emitter and detector operating at a wavelength of 1.3 µm. The remaining active links will consist of three cabled plastic-coated silica fiber links using LED's and PIN photodiodes operating at a wavelength of 830 nm. Two of these links will be 20 m long and the remaining link will be 48 m long. Optical waveguides, connectors, and other experimental equipment will consist of components selected according to recent results of Air Force studies.

One-m temperature data link. - A 1-m optical data link will be used for recording the relative temperature of the tray inner volume.

Passive Experiments

Ten-m data links. - Three 10-m data links will be located within the tray volume. The links have been preirradiated and will be evaluated upon LDEF retrieval for increased radiation damage. These links will serve primarily as comparison links and will be evaluated upon LDEF retrieval for comparison to the active-link experiments.

Components experiment. - This experiment will contain preirradiated and nonirradiated LED's and photodiodes rigidly mounted within a section of the tray volume. As in the case of the active and passive links previously discussed, each component will be characterized prior to launch and will be tested functionally upon mission completion in order to assess any degradation effects from the launch or orbit conditions.

 


[185] Space Environment Effects (M0006)

Joseph A. Angelo, Jr., and Richard G. Madonna
Air Force Technical Applications Center
Patrick Air Force Base, Florida
 
Lynn P. Altadonna
Perkin-Elmer
Danbury, Connecticut
 
Michael D. D'Agostino and Joseph Y. Chang
Grumman Aerospace Corp.
Bethpage, New York
 
Robert R. Alfano and Van L. Caplan
The City College
New York, New York

 

Objectives

The primary purpose of this experiment is to examine the effects of long-term exposure to the near-Earth space environment on advanced electro-optical and radiation sensor components. A secondary objective involves an exobiology experiment to observe the effect of long-duration spaceflight on the germination rate of selected terrestrial plant seeds.

 

Approach

The approach of the main experiment is to measure the optical and electrical properties of the electro-optical and radiation sensor components before and after exposure to the space environment. The selected components being tested are hard mounted in an experiment exposure control canister (EECC) which occupies one-third of a 6-in.-deep tray, which is then sealed. (See fig. 74.) The sealed EECC prevents contamination of the test components during ground transportation to and from the launch site, payload processing at the launch complex, and launch and landing. The EECC is programmed to open 2 weeks after deployment and close I week prior to anticipated retrieval. The EECC will not be reopened until the experiment has been returned after the flight to the investigator's laboratory.

The electro-optical and radiation sensor components include a variety of semiconductor materials (e.g., CdSe, p-GaAs, n-GaAs, and n-GaAs), mirrors (including fused silica and beryllium), a Nd+ :glass laser rod, a fiber optics cable, and a variety of polymeric materials.

 


[
186]

Figure 74.- Space environment effects experiment.

Figure 74.- Space environment effects experiment.

 

[187] The secondary exobiology experiment involves a variety of terrestrial plant seeds enclosed in a benign environment (dry air) aluminum alloy tube. Postflight germination rates of these seeds will be compared to the germination rates of control seed samples kept on Earth. Lithium fluoride (LiF) radiation dosimeters are also included in the seed capsule to provide an approximate measure of total space radiation exposure within the capsule. The experiment is housed in an aluminum alloy tube and involves seeds of hybrid 3358 corn, sugar pumpkin, giant gray-striped sunflower, garden bean (Tennessee green pod and bush Romano #14), Henderson's bush lima bean, and Alaska pea.

 
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