A hazard to all spacecraft orbiting the earth and exploring the unknown in deep space is the existence of a harsh and ever changing environment with its subsequent effects. Some of these environmental hazards, such as plasma, extreme thermal excursions, meteoroids, and ionizing radiation result from natural sources, whereas others, such as orbital debris and neutral contamination are induced by the presence of spacecraft themselves. The subsequent effects can provide damaging or even disabling effects on spacecraft, its materials, and its instruments. In partnership with industry, academia, and other government agencies, National Aeronautics and Space Administration's (NASA's) Space Environments and Effects (SEE) Program defines the space environments and advocates technology development to accommodate or mitigate these harmful environments on the spacecraft. This program provides a very comprehensive and focused approach to understanding the space environment, to define the best techniques for both flight and ground-based experimentation, to update the models which predict both the environments and the environmental effects on spacecraft, and finally to ensure that this information is properly maintained and inserted into spacecraft design programs. This paper will provide an overview of the Program's purpose, goals, database management and technical activities. In particular, the SEE Program has been very active in developing improved ionizing radiation models and developing related flight experiments which should aid in determining the effect of the radiation environment on modern electronics.

Four Erbium doped fiber optic amplifiers (EDFAs) were irradiated by gamma-rays to dose levels of 40 Krad(Si) and 100 Krad(Si) at dose rates of 0.25 rad(Si) sec^-1 and 1.0 rad(Si) sec^-1, respectively. All EDFAs were observed to incur radiation induced permanent decreases to their pre-irradiated signal gains. The paper will discuss the influence of gamma-ray irradiations on EDFA parameters such as gain, noise figure, and integrated amplified spontaneous emission. A brief discussion of how changes to these parameters evolve is presented.

Since 1993, research concerning CMOS APS (Active Pixel Sensors) has been intensively carried out, in order to offer an alternative to CCDs as an image sensor, particularly in space applications. Many laboratories have demonstrated the feasibility of these new devices and the high level of performances that can be achieved. Nowadays, the first generation of commercial devices becomes available for consumer electronics, and start to be used in many applications such as surveillance micro-cameras, video- conferencing, digital-still cameras. The latest designs have shown that APS is getting closer to the CCD in terms of performance level in scientific applications. APS device offers high potentialities for space applications (low power, low cost, high integration level), and fast improvements will make this sensors available for spacecraft: star tracker, planetary imaging functions, fine guidance sensor... A summary of APS benefits for space applications will be presented in this paper. Recently developed APS image sensors (128 X 128 and 256 X 256 pixels) designed by the Conception d'Imageurs Matriciels Integres (CIMI) group of SUPAERO and jointly tested by CIMI and Matra Marconi Space will be presented. The results demonstrate that standard CMOS process is well suited for image sensors implementation. The trade-off regarding the pixel detector choice (photoMos vs photodiode) will be discussed. Finally, future trends and perspectives for APS applications in space activities will be presented.

Goddard Space Flight Center is conducting a search for space flight worthy fiber optic cable assemblies that will benefit all projects at all of the NASA centers. This paper is number two in a series of papers being issues as a result of this task to define and quality space grade fiber optic cable assemblies. Though to qualify and use a fiber optic cable in space requires treatment of the cable assembly as a system, it is very important to understand the design and behavior of its parts. This paper addresses that need, providing information on cable components shrinkage testing and radiation testing results from recent experiments at Goddard Space Flight Center. This work is an extension of the `lessons learned' reported in the first paper of this series entitled `Fiber Optic Cable Assemblies for Space Flight: Issues and Remedies,' published and presented at the AIAA World Congress in Anaheim CA, on October 15, 1997.

Low-power consumption, high efficiency and high bandwidth surface emitting semiconductor optical sources are critical elements in the development of future photonic systems for space and civil nuclear applications. In this paper, we report on preliminary high total dose experiments performed on two types of recently developed microcavity emitters: VCSELs and microcavity (or resonant cavity) LEDs. We gamma irradiated a total of twelve commercially available packaged VCSELs and two home-made flip-chipped 2 X 2 microcavity LED arrays. For doses between 5(DOT)10⁶ Gy and 1.3(DOT)10⁷ Gy the VCSELs show a threshold current increase lower than 20% and an output power decrease lower than 10%. These values are even smaller if the VCSEL is operated at a higher temperature. At a dose of 3.14(DOT)10⁷ Gy, one VCSEL still showed satisfactory operation. The microcavity LEDs suffered from a burn-in after radiation but recovered quickly when biased. Their output power decrease is comparable to that of the VCSELs, while their quantum efficiency is not much affected. The specifications of both types of devices are not substantially altered by high gamma doses and can therefore be considered for application in enhanced radiation environments.

The commercial off the shelf (COTS) twelve channel optical fiber MTP array connector and ribbon cable assembly is being validated for space light use and the results of this study to date are presented here. The interconnection system implemented for the Parallel Fiber Optic Data Bus (PFODB) physical layer will include a 100/140 micron diameter optical fiber in the cable configuration among other enhancements. As part of this investigation, the COTS 62.5/125 micron optical fiber cable assembly has been characterized for space environment performance as a baseline for improving the performance of the 100/140 micron diameter ribbon cable for the Parallel FODB application. Presented here are the testing and results of random vibration and thermal environment characterization of this commercial off the shelf COTS MTP twelve channel ribbon cable assembly. This paper is the first in a series of papers which will characterize and document the performance of Parallel FODB's physical layer from COTS to space flight worthy.

With a greater interest in deep space exploration and space systems in general, the radiation requirement for spacecraft operations has increased considerably. Photonics technology is the future technology that can survive these adverse environmental requirement levels. Companies are investigating the use of photonics for spacecraft system and are also pushing the test criteria for survivable space components to meet these new levels. This paper will address the requirements for space systems in the 21st century and the projected research and development of photonics technology.

Radiation damage from cobalt-60 gamma rays is investigated for TSL235 Light to Frequency Converters. No dose rate effects were observed. the TSL235 is found suitable for use in Low Earth Orbit up to a total dose of 1.5 Krad(Si). Sudden failure of the device is observed at approximately 5 Krad(Si), exhibited by a rapid degradation in performance and a quick rise in device supply current leading to permanent damage (burnout). Annealing at room temperature for 24 hours showed no rebound.

Optical data links are being developed at CERN for use in the tracking system of the Compact Muon Solenoid (CMS) experiment to be operated at the future CERN Large Hadron Collider. The radiation environment will be severe in the CMS tracker; simulations predict hadronic fluences > 10¹⁴/cm² over an experimental lifetime of ten years, consisting of a mixture of neutrons, pions and protons over a wide energy spectrum, plus an ionizing dose of approximately 100 kGy. Candidate optical link components must therefore be qualified for sufficient radiation hardness. Results are presented for commercially available InGaAsP lasers and InGaAs p-i-n photodiodes irradiated with 330 MeV pions up to 5.4 X 10¹⁴ (pi) /cm². The evolution of the laser threshold and efficiency with fluence is presented, in addition to the leakage current and photocurrent in the photodiodes. Comparisons are drawn with previous irradiation tests on identical devices using 6 MeV neutrons and 24 GeV protons, and ionizing damage due to ⁶⁰Co gamma rays.

Several types of commercially available single-mode optical fibers have been irradiated in both gamma and neutron radiation fields to determine the suitability of their use in the readout systems of feature particle physics detectors. A comparative survey of the effect of ⁶⁰Co gammas and neutrons (<E_n> approximately 6 MeV) on different fiber types, including standard germanium doped and pure silica core fibers, has been carried out. Selected fibers were further exposed to gamma radiation at four different dose rates to assess dose rate effects. Results are presented for the dose and fluence levels of interest (100 kGy) and 1 X 10¹⁴ n/cm²), showing induced losses at 1300 nm to be below 0.1 dB/m for both types of field. It has been seen that the damage mechanism is the same for both fields. We conclude that many modern Ge-doped fibers will be suitable for use in future particle physics applications, which gives greater freedom of choice to system designers, and greater immunity from the problems associated with single suppliers of specific fibers.

We discuss radiation test results on 1.55 micrometers , polarization maintaining fiber from two sources. One fiber employs stress induced birefringence, the other is an elliptical waveguide that achieves birefringence through a geometrical shaping of the core. Testing was conducted in accordance with FOTP-64 at the SEGIT Facility at the Defense Microelectronics Activity, Sacramento, CA. Overall dose rate was approximately 10.5 kilorads/min (SiO₂) for a total dose of 10 Megarads (SiO₂) at temperatures of -55, +23 and +125 degree(s)C.

The use of fiber optics to distribute UHF signals has been the topic in several studies. Some advantages of this approach are weight and volume savings compared with the use of waveguides and coaxial lines. We have developed a prototype fiber-optic system that modulates ultrastable time and frequency signals over fiber-optic lines. Some performance limitations of this technique are single sideband phase noise and signal-to-noise degradation. This paper will present experimental results including single sideband noise measurements and a discussion on the system's limitations.

This paper describes the design, fabrication, surface characterization, and adaptive optics simulation of advanced surface micromachined micromirror devices. Design considerations and fabrication capabilities are presented. Various shapes and array distributions of unique Flexure- Beam Micromirror Devices are simulated for adaptive optics performance against several typical optical aberrations. These devices are fabricated in the state-of-the-art, four- level, planarized, ultra-low-stress polysilicon process available at Sandia National Laboratories known as the Sandia Ultra-planar Multi-level MEMS Technology (SUMMiT). This enabling process permits the development of micromirror devices with near-ideal characteristics that have previously been unrealizable in standard three-layer polysilicon processes. The advanced capabilities of this process along with customized layout tools have permitted the fabrication of highly advanced and often irregular shapes of mirror surfaces that can be uniquely distributed to minimize wavefront error across the pupil.

Surface polysilicon micromachined micromirrors require ultra-flat surfaces for advance optical applications such as adaptive optics. This paper details the planarization of micromirrors using chemical-mechanical polishing. We show that the increase in topography is due to a high temperature anneal step downstream for the CMP process itself. Two process alternatives were investigated: (1) perform a CMP step after the high temperature anneal step, and (2) perform a CMP step on a final polysilicon mirror surface. Both process alternatives produced acceptable flatness requirements for micromirror applications.

In some of the future laser communication satellites, it is plausible to assume that tracking and communication receivers will be using the same array of detector. The reason for such detector dual use is to design simpler and cheaper satellites. Satellites vibrate continually due to operation of their subsystems and environmental sources. The vibrations cause non-uniform spreading of the received energy on the detector array. In view of this, we use the information from the tracking system in order to adapt individually the communication signal gain of each of the detectors in the array. This adaptation of the gains improves communication system performance. It is important to emphasize that the communication performance improvement is achieved by only gain adaptation. Any additional vibrations decrease the tracking and laser pointing system performances, which decrease the return communication performances (two-way communication). A comparison of practical communication systems is presented. The novelty of this research is the utilization of natural satellite vibrations to improve the communication system performance.

Free space optical communication between satellites networked together can make possible high speed communication between different places on earth. The basic free space optical communication network includes at least two satellites. In order to communicate between them, the transmitter satellite must track the beacon of the receiver satellite and point the information optical beam in its direction. The pointing systems for laser satellite communication suffer during tracking from vibration due to electronic noise, background radiation from interstellar objects such as sun, moon, earth and stars in the tracking field of view, and mechanical impact from satellite internal and external sources. Due to vibrations the receiver receives less power. This effect limits the system bandwidth for given bit error rate. In this research we derive an algorithm to maximize the communication system bandwidth using the transmitter telescope gain as a free variable based on the vibration statistics model and the system parameters. Our model makes it possible to adapt the bandwidth and transmitter gain to change of vibration amplitude. We also present an example of a practical satellite network which includes a direct detection receiver with an optical amplifier. A bandwidth improvement of three orders of magnitude is achieved in this example for certain conditions, as compared to an unoptimized system.

Several new types of absolute optical encoders of both rotary and linear function are discussed. The means for encoding are complete departures from conventional optical encoders and offer advantages of reliability, compact form, immunity to damage-induced dropouts of position information, and about an order of magnitude higher sensitivity over what is commercially available. Rotary versions have sensitivity from 0.02 arcseconds down to 0.003 arcsecond while linear models have demonstrated sensitivity of 10 nm (0.01 micrometers ) with higher sensitivities possible.