Modeling transient dynamics of a fiber laser with application to deep space optical communications
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Controlling Laser Spot Size in Outer Space
Three documents discuss a method of controlling the diameter of a laser beam projected from Earth to any altitude ranging from low orbit around the Earth to geosynchronous orbit. Such laser beams are under consideration as means of supplying power to orbiting spacecraft at levels of the order of tens of kilowatts apiece. Each such beam would be projected by use of a special purpose telescope having an aperture diameter of 15 m or more. Expanding the laser beam to such a large diameter at low altitude would prevent air breakdown and render the laser beam eyesafe. Typically, the telescope would include an adaptive-optics concave primary mirror and a convex secondary mirror. The laser beam transmitted out to the satellite would remain in the near field on the telescope side of the beam waist, so that the telescope focal point would remain effective in controlling the beam width. By use of positioning stages having submicron resolution and repeatability, the relative positions of the primary and secondary mirrors would be adjusted to change the nominal telescope object and image distances to obtain the desired beam diameter (typically about 6 m) at the altitude of the satellite. The limiting distance D(sub L) at which a constant beam diameter can be maintained is determined by the focal range of the telescope 4 lambda f(sup 2) where lambda is the wavelength and f the f/number of the primary mirror. The shorter the wavelength and the faster the mirror, the longer D(sub L) becomes.
Bennett, Harold E.↗
Project LOCOST: Laser or Chemical Hybrid Orbital Space Transport
A potential mission in the late 1990s is the servicing of spacecraft assets located in GEO. The Geosynchronous Operations Support Center (GeoShack) will be supported by a space transfer vehicle based at the Space Station (SS). The vehicle will transport cargo between the SS and the GeoShack. A proposed unmanned, laser or chemical hybrid orbital space transfer vehicle (LOCOST) can be used to efficiently transfer cargo between the two orbits. A preliminary design shows that an unmanned, laser/chemical hybrid vehicle results in the fuel savings needed while still providing fast trip times. The LOCOST vehicle receives a 12 MW laser beam from one Earth orbiting, solar pumped, iodide Laser Power Station (LPS). Two Energy Relay Units (ERU) provide laser beam support during periods of line-of-sight blockage by the Earth. The baseline mission specifies a 13 day round trip transfer time. The ship's configuration consist of an optical train, one hydrogen laser engine, two chemical engines, a 18 m by 29 m box truss, a mission-flexible payload module, and propellant tanks. Overall vehicle dry mass is 8,000 kg. Outbound cargo mass is 20,000 kg, and inbound cargo mass is 6,000 kg. The baseline mission needs 93,000 kg of propellants to complete the scenario. Fully fueled, outbound mission mass is 121,000 kg. A regeneratively cooled, single plasma, laser engine design producing a maximum of 768 N of thrust is utilized along with two traditional chemical engines. The payload module is designed to hold 40,000 kg of cargo, though the baseline mission specifies less. A proposed design of a laser/chemical hybrid vehicle provides a trip time and propellant efficient means to transport cargo from the SS to a GeoShack. Its unique, hybrid propulsion system provides safety through redundancy, allows baseline missions to be efficiently executed, while still allowing for the possibility of larger cargo transfers.
Dixon, Alan↗
Neutron radiation hardness of aluminum gallium nitride UV LEDs at various wavelengths
Radiation hard diagnostics are critical to the success of nuclear fusion at National Ignition Facility, Z, ITER, and prolonged space explorations. We have first demonstrated the exceptional proton radiation hardness of initial GaN devices and qualified their space flight and deployment for missions such as the Laser Interferometer Space Antenna and International Space Station. We have further conducted neutron radiation hardness experiments at Los Alamos Neutron Science Center by opening a new high fluence beam station. During 2014–2016, we irradiated multiple Aluminum Gallium Nitride (AlGaN) LEDs with a maximum fluence of 2.4 × 1013 neutrons/cm2 in 3 years and generated 54 161 current–voltage (I–V) scan traces. Our data processing program analyzes each and all I–V traces. In addition, we retrieved local temperature records to analyze and remove temperature effects in the outdoor environment. The I–V curve families of AlGaN UV LEDs with emitting wavelengths of 265, 275, and 310 nm were compared. The I–V curves of 265 nm AlGaN UV LEDs have the smallest deviations from the average value, while the I–V curves for 310 nm AlGaN LEDs showed the largest deviations from the average value. We have reached another important recommendation for the optimal use of multiple AlGaN optoelectronic devices or imaging arrays for inertially confined fusion diagnostics: Shorter wavelength devices at 265 nm exhibit more consistent radiation hardness performance than the 310 nm devices. Higher aluminum content LEDs or AlxGa1–xN devices with higher mole fraction x for generating shorter wavelengths have better radiation hardness for fusion diagnostics.
Sun, K. -X. (ORCID:0000000224659235)↗
Laser propulsion for orbit transfer - Laser technology issues
Using reasonable near-term mission traffic models (1991-2000 being the assumed operational time of the system) and the most current unclassified laser and laser thruster information available, it was found that space-based laser propulsion orbit transfer vehicles (OTVs) can outperform the aerobraked chemical OTV over a 10-year life-cycle. The conservative traffic models used resulted in an optimum laser power of about 1 MW per laser. This is significantly lower than the power levels considered in other studies. Trip time was taken into account only to the extent that the system was sized to accomplish the mission schedule.
Horvath, J. C.↗
Direct solar pumping of semiconductor lasers: A feasibility study
The primary goals of the feasibility study are the following: (1) to provide a preliminary assessment of the feasibility of pumping semiconductor lasers in space directly focused sunlight; and (2) to identify semiconductor laser structures expected to operate at the lowest possible focusing intensities. It should be emphasized that the structures under consideration would provide direct optical-to-optical conversion of sunlight into laser light in a single crystal, in contrast to a configuration consisting of a solar cell or battery electrically pumping a current injection laser. With external modulation, such lasers may prove to be efficient sources for intersatellite communications. We proposed to develop a theoretical model of semiconductor quantum-well lasers photopumped by a broadband source, test it against existing experimental data where possible, and apply it to estimating solar pumping requirements and identifying optimum structures for operation for operation at low pump intensities. This report outlines our progress toward these goals. Discussion of several technical details are left to the attached summary abstract.
Anderson, Neal G.↗
Residual mode filters and adaptive control in large space structures
One of the most difficult problems in controlling large systems and structures is compensating for the destructive interaction which can occur between the reduced-order model (ROM) of the plant, which is used by the controller, and the unmodeled dynamics of the plant, often called the residual modes. The problem is more significant in the case of large space structures because their naturally light damping and high performance requirements lead to more frequent, destructive residual mode interaction (RMI). Using the design/compensation technique of residual mode filters (RMF's), effective compensation of RMI can be accomplished in a straightforward manner when using linear controllers. The use of RMF's has been shown to be effective for a variety of large structures, including a space-based laser and infinite dimensional systems. However, the dynamics of space structures is often uncertain and may even change over time due to on-orbit erosion from space debris and corrosive chemicals in the upper atmosphere. In this case, adaptive control can be extremely beneficial in meeting the performance requirements of the structure. Adaptive control for large structures is also based on ROM's and so destructive RMI may occur. Unfortunately, adaptive control is inherently nonlinear, and therefore the known results of RMF's cannot be applied. The purpose is to present the results of new research showing the effects of RMI when using adaptive control and the work which will hopefully lead to RMF compensation of this problem.
Davidson, Roger A.↗
Direct solar pumping of semiconductor lasers: A feasibility study
This report describes results of NASA Grant NAG-1-1148, entitled Direct Solar Pumping of Semiconductor Lasers: A Feasibility Study. The goals of this study were to provide a preliminary assessment of the feasibility of pumping semiconductor lasers in space with directly focused sunlight and to identify semiconductor laser structures expected to operate at the lowest possible focusing intensities. It should be emphasized that the structures under consideration would provide direct optical-to-optical conversion of sunlight into laser light in a single crystal, in contrast to a configuration consisting of a solar cell or storage battery electrically pumping a current injection laser. With external modulation, such lasers could perhaps be efficient sources for intersatellite communications. We proposed specifically to develop a theoretical model of semiconductor quantum-well lasers photopumped by a broadband source, test it against existing experimental data where possible, and apply it to estimating solar pumping requirements and identifying optimum structures for operation at low pump intensities. These tasks have been accomplished, as described in this report of our completed project. The report is organized as follows: Some general considerations relevant to the solar-pumped semiconductor laser problem are discussed in Section 2, and the types of structures chosen for specific investigation are described. The details of the laser model we developed for this work are then outlined in Section 3. In Section 4, results of our study are presented, including designs for optimum lattice-matched and strained-layer solar-pumped quantum-well lasers and threshold pumping estimates for these structures. It was hoped at the outset of this work that structures could be identified which could be expected to operate continuously at solar photoexcitation intensities of several thousand suns, and this indeed turned out to be the case as described in this section. Our project is summarized in Section 5, and information on publications resulting from this work is provided in Section 6.
Anderson, Neal G.↗
Retrievals of Thick Cloud Optical Depth from the Geoscience Laser Altimeter System (GLAS) by Calibration of Solar Background Signal
Laser beams emitted from the Geoscience Laser Altimeter System (GLAS), as well as other space-borne laser instruments, can only penetrate clouds to a limit of a few optical depths. As a result, only optical depths of thinner clouds (< about 3 for GLAS) are retrieved from the reflected lidar signal. This paper presents a comprehensive study of possible retrievals of optical depth of thick clouds using solar background light and treating GLAS as a solar radiometer. To do so we first calibrate the reflected solar radiation received by the photon-counting detectors of GLAS' 532 nm channel, which is the primary channel for atmospheric products. The solar background radiation is regarded as a noise to be subtracted in the retrieval process of the lidar products. However, once calibrated, it becomes a signal that can be used in studying the properties of optically thick clouds. In this paper, three calibration methods are presented: (I) calibration with coincident airborne and GLAS observations; (2) calibration with coincident Geostationary Operational Environmental Satellite (GOES) and GLAS observations of deep convective clouds; (3) calibration from the first principles using optical depth of thin water clouds over ocean retrieved by GLAS active remote sensing. Results from the three methods agree well with each other. Cloud optical depth (COD) is retrieved from the calibrated solar background signal using a one-channel retrieval. Comparison with COD retrieved from GOES during GLAS overpasses shows that the average difference between the two retrievals is 24%. As an example, the COD values retrieved from GLAS solar background are illustrated for a marine stratocumulus cloud field that is too thick to be penetrated by the GLAS laser. Based on this study, optical depths for thick clouds will be provided as a supplementary product to the existing operational GLAS cloud products in future GLAS data releases.
Yang, Yuekui↗
Ten point six micron laser communications system experiment for ATS-F and ATS-G
Optical space communication laser for applications technology satellites
Mc Avoy, N.↗
Direct Global Measurements of Tropspheric Winds Employing a Simplified Coherent Laser Radar using Fully Scalable Technology and Technique
Innovative designs of a space-based laser remote sensing 'wind machine' are presented. These designs seek compatibility with the traditionally conflicting constraints of high scientific value and low total mission cost. Mission cost is reduced by moving to smaller, lighter, more off-the-shelf instrument designs which can be accommodated on smaller launch vehicles.
Kavaya, Michael J.↗
Thermoelectronic laser energy conversion for power transmission in space
Long distance transmission of power in space by means of laser beams is an attractive concept because of the very narrow beam divergence. Such a system requires efficient means to both generate the laser beam and to convert the light energy in the beam into useful electric output at the receiver. A plasma-type device known as a Thermo-Electronic Laser Energy Converter (TELEC) has been studied as a method of converting a 10.6 micron CO2 laser beam into electric power. In the TELEC process, electromagnetic radiation is absorbed directly in the plasma electrons producing a high electron temperature. The energetic electrons diffuse out of the plasma striking two electrodes with different areas. Since more electrons are collected by the larger electrode there is a net transport of current, and an EMF is generated in the external circuit. The smaller electrode functions as an electron emitter to provide continuity of the current. Waste heat is rejected from the large electrode. A design for a TELEC system with an input 1 MW laser beam was developed as part of the study. The calculated performance of the system showed an overall efficiency of about 42%.
Britt, E. J.↗
Independent Reliability Assessment of the NASA GSFC Laser Transmitter for the LISA Program
The Laser Interferometer Space Antenna (LISA) is a partnership between the European Space Agency (ESA) and NASA to build a Gravitational Wave (GW) observatory. The observatory, which consists of a three-spacecraft constellation with a nominal separation of 2.5 million km between each spacecraft, provides a tool for scientists to directly detect gravitational waves generated from various astronomical phenomena in a waveband that is not accessible from Earth. NASA is developing laser transmitters as one of the potential US contributions to LISA. The NASA laser design leverages lessons learned from previous flight missions and included the latest technologies in photonics packaging and reliability engineering to ensure a laser lifetime of >16 years covering integration and test through a possible extended mission phase. As part of the laser development process, NASA’s Goddard Space Flight Center (GSFC) requested support from the NASA Engineering and Safety Center (NESC) to independently assess the Technology Readiness Level (TRL) of the LISA Laser System (LS). The independent assessment included the following tasks: (a) assess the design for weaknesses and suggest improvements to mitigate risks, (b) assess the laser reliability plan for weaknesses and suggest improvements to mitigate risks and improve effectiveness, and (c) assess the current redundancy plan on laser subsystems for weaknesses and suggest improvements to mitigate risks and improve effectiveness. The NESC team comprised of a team of subject matter experts (SMEs) and performed a 12-month review of every aspect of the laser design. We present the assessment findings and the current development progress of the LISA laser to meet the mission requirements with a delivery of a form, fit, and functional TRL6 laser to the LSIA mission by late 2023.
LISA↗
Effect of atmospheric turbulence on the bit error probability of a space to ground near infrared laser communications link using binary pulse position modulation and an avalanche photodiode detector
The effect of atmospheric turbulence on the bit error rate of a space-to-ground near infrared laser communications link is investigated, for a link using binary pulse position modulation and an avalanche photodiode detector. Formulas are presented for the mean and variance of the bit error rate as a function of signal strength. Because these formulas require numerical integration, they are of limited practical use. Approximate formulas are derived which are easy to compute and sufficiently accurate for system feasibility studies, as shown by numerical comparison with the exact formulas. A very simple formula is derived for the bit error rate as a function of signal strength, which requires only the evaluation of an error function. It is shown by numerical calculations that, for realistic values of the system parameters, the increase in the bit error rate due to turbulence does not exceed about thirty percent for signal strengths of four hundred photons per bit or less. The increase in signal strength required to maintain an error rate of one in 10 million is about one or two tenths of a db.
Safren, H. G.↗
Sensitivity Limits of Space-Based Interferometric Gravitational Wave Observatories from the Solar Wind
Space-based interferometric gravitational wave instruments such as the ESA/NASA Laser Interferometer Space Antenna (LISA) observe gravitational waves by measuring changes in the light travel time between widely separated spacecraft. One potential noise source for these instruments is interaction with the solar wind, in particular the free electrons in the interplanetary plasma. Variations in the integrated column density of free electrons along the laser links will lead to time-of-flight delays which directly compete with signals produced by gravitational waves. In this paper we present a simplified model of the solar plasma relevant for this problem, anchor key parameters of our model using data from the NASA Wind/solar wind experiment instrument, and derive estimates for the effect in the LISA measurement. We find that under normal solar conditions, the gravitational wave sensitivity limit from the free-electron effect is smaller than other noise sources that are expected to limit LISA’s sensitivity.
Oliver Jennrich↗
Laser rocket system analysis
Potential national space transportation budget savings offered by laser rocket systems are considered. Orbital payload transportation costs, requiring 16 MW laser power space based or 37.5 MW ground based, are reduced by a factor of 2.4. The SPS orbital transportation costs, requiring 490 MW laser power space based or 1000 MW ground based, are reduced by factors up to 7. Technology advancement is indicated for the laser, thruster, large lightweight adaptive mirror, and pointing and tracking.
Source record↗
An antenna for laser gravitational-wave observations in space
Progress during the past two years on a proposed Laser Gravitational-Wave Observatory in Space (LAGOS) is discussed. Calculated performance for a 10 to the 6th km sized antenna over the frequency range of 10 to the -5th to 1 Hz is given. The sensitivity from 0.001 to 0.1 Hz is expected to be 1 x 10 to the -21st/Hz exp 0.5. Noise sources such as accelerations of the drag-free test masses by random molecular impacts and by fluctuations in the net thermal radiation pressure will limit the sensitivity at lower frequencies. The scientific objectives are the observation of CW gravitational waves from large numbers of binary systems and the detection of pulses which may have been emitted during the period of galaxy formation.
Faller, J. E.↗
Microthrust Propulsion of the LISA Mission
We present the most recent propulsion requirements for the Laser Interferometer Space Antenna (LISA) Mission and describe potential microth ruster technology that can meet these requirements. LISA consists of three spacecraft in heliocentric orbits, forming a triangle with 5x l 0 (exp 6) km sides that are the arms of three Michelson-type interferometers. Reflective proof masses provide the reference surfaces at the end of the interferometer arms as part of the Gravitational Referenc e Sensor (GRS) designed to detect gravitational waves. The microthrus t propulsion system will be part of the Disturbance Reduction System (DRS), which is responsible for maintaining each spacecraft position w ithin approximately 10 nm around the proof masses. To provide the nec essary sensitivity, the GRS must not experience spurious acceleration s >15 (exp -10) m/ s(exp 2) in the 0.1 mHz to 1 Hz bandwidth, requiring precision formation flying and drag-free operation of the LISA spa cecraft. This leads to the following microthruster performance requir ements: a thrust range of 2-30 Micro N, a thrust resolution < 0.1 Mic ro N, and thrust noise <0.1 Hz(exp -1/2) over the LISA measurement bandwidth. The microthruster must provide this performance for 5 years c ontinuously, contain 10 years worth of propellant, and not disrupt th e science measurements. Potential microthruster technologies include Colloid, Field Emission Electric Propulsion (FEEP), and precision cold gas microthrusters. Each of these technologies is described in detai l with focus on the NASA microthruster development of the Busek Collo id Micro-Newton Thruster (CMNT).
Field Emission Electric Propulsion (FEEP)↗