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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Optical Communication Activities Through the Laser-Enhanced Mission Communications Navigation and Operational Services (LEMNOS) Office

The Laser-Enhanced Mission Communications Navigation and Operational Services (LEMNOS) office at Goddard Space Flight Center (GSFC) manages two NASA optical communication related projects, the Orion EM-2 Optical Communications Terminal (O2O) and the Integrated Laser Communications Relay Demonstration (LCRD) Low-Earth Orbit (LEO) User Modem and Amplifier Terminal (ILLUMA-T) projects. The main goal of LEMNOS project is to implement optical communications technologies on NASA missions starting with demonstrations of operational utility on Orion EM-2 and the International Space Station.

Seas, Antonios A.↗
NASA NTRS2020

Space Flight LiDARs, Navigation & Science Instrument Implementations: Lasers, Optoelectronics, Integrated Photonics, Fiber Optic Subsystems and Components

For the past 25 years, the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center's Photonics Group in the Engineering Directorate has been substantially contributing to the flight design, development, production, testing and integration of many science and navigational instruments. The Moon to Mars initiative will rely heavily upon utilizing commercial technologies for instrumentation with aggressive schedule deadlines. The group has an extensive background in screening, qualifying, development and integration of commercial components for spaceflight applications. By remaining adaptable and employing a rigorous approach to component and instrument development, they have forged and fostered relationships with industry partners. They have been willing to communicate lessons learned in packaging, part construction, materials selection, testing, and other facets of the design and production process critical to implementation for high-reliability systems. As a result, this successful collaboration with industry vendors and component suppliers has enabled a history of mission success from the Moon to Mars (and beyond) while balancing cost, schedule, and risk postures. In cases where no commercial components exist, the group works closely with other teams at Goddard Space Flight Center and other NASA field centers to fabricate and produce flight hardware for science, remote sensing, and navigation applications. Summarized here is the last ten years of instrumentation development lessons learned and data collected from the subsystems down to the optoelectronic component level.

Detectors↗
NASA NTRS1993

Lunar rover navigation concepts

With regard to the navigation of mobile lunar vehicles on the surface, candidate techniques are reviewed and progress of simulations and experiments made up to now are described. Progress that can be made through precursor investigations on Earth is considered. In the early seventies the problem was examined in a series of relevant tests made in the California desert. Meanwhile, Apollo rovers made short exploratory sorties and robotic Lunokhods traveled over modest distances on the Moon. In these early missions some of the required methods were demonstrated. The navigation problem for a lunar traverse can be viewed in three parts: to determine the starting point with enough accuracy to enable the desired mission; to determine the event sequence required to reach the site of each traverse objective; and to redetermine actual positions enroute. The navigator's first tool is a map made from overhead imagery. The Moon was almost completely photographed at moderate resolution by spacecraft launched in the sixties, but that data set provides imprecise topographic and selenodetic information. Therefore, more advanced orbital missions are now proposed as part of a resumed lunar exploration program. With the mapping coverage expected from such orbiters, it will be possible to use a combination of visual landmark navigation and external radio and optical references (Earth and Sun) to achieve accurate surface navigation almost everywhere on the near side of the Moon. On the far side and in permanently dark polar areas, there are interesting exploration targets where additional techniques will have to be used.

Burke, James D.↗
NASA NTRS2019

Metric Tracking Services in the Era of Optical Communications

The Space Communications and Navigation program, at the National Aeronautics and Space Administration, is developing free-space optical communications technology to facilitate the next generation of space missions in near-Earth, Lunar, and planetary space. A discussion of optimetric observation performance and hardware-in-the-loop test results are presented. Simulation of orbit-determination for LEO and Lunar spacecraft relying on optimetric tracking extends raw observation accuracy to realizable orbit-determination performance. Potential science and operational applications are reviewed, along with NASA's approach for developing optimetric technology. Current investments in developing optimetric hardware and plans for NASA's future optical communications network define the path for a future operational optimetric capability in the 2020's and beyond.

optimetrics↗
DOE OSTI2024

ReLU, Sparseness, and the Encoding of Optic Flow in Neural Networks

Accurate self-motion estimation is critical for various navigational tasks in mobile robotics. Optic flow provides a means to estimate self-motion using a camera sensor and is particularly valuable in GPS- and radio-denied environments. The present study investigates the influence of different activation functions—ReLU, leaky ReLU, GELU, and Mish—on the accuracy, robustness, and encoding properties of convolutional neural networks (CNNs) and multi-layer perceptrons (MLPs) trained to estimate self-motion from optic flow. Our results demonstrate that networks with ReLU and leaky ReLU activation functions not only achieved superior accuracy in self-motion estimation from novel optic flow patterns but also exhibited greater robustness under challenging conditions. The advantages offered by ReLU and leaky ReLU may stem from their ability to induce sparser representations than GELU and Mish do. Our work characterizes the encoding of optic flow in neural networks and highlights how the sparseness induced by ReLU may enhance robust and accurate self-motion estimation from optic flow.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS2007

Operations at the JPL OCTL Telescope

The JPL Optical Communications Telescope Laboratory (OCTL) is a 200 sq-m located at 2.2.km altitude in Wrightwood California and houses a state-of-the-art 1-m telescope. The OCTL team is involved in the development of operational strategies for ground-to-space laser beam propagation for future NASA optical communications missions. Strategies include safe beam propagation through navigable air space, line of sight optical attenuation monitoring, adaptive optics, and multi-beam scintillation mitigation. This paper presents the results of recent operations at the OCTL facility including telescope characterization data and laser beam propagation experiments to Earth-orbiting retro-reflecting satellites; experiments that validate the telescope's tracking and blind-pointing performance and safe laser beam transmission procedures for propagating through navigable airspace.

optical communications↗
NASA NTRS1984

Comparison of NAVSTAR satellite L band ionospheric calibrations with Faraday rotation measurements

It is pointed out that interplanetary navigation at the Jet Propulsion Laboratory (JPL) is performed by analyzing measurements derived from the radio link between spacecraft and earth and, near the target, onboard optical measurements. For precise navigation, corrections for ionospheric effects must be applied, because the earth's ionosphere degrades the accuracy of the radiometric data. These corrections are based on ionospheric total electron content (TEC) determinations. The determinations are based on the measurement of the Faraday rotation of linearly polarized VHF signals from geostationary satellites. Problems arise in connection with the steadily declining number of satellites which are suitable for Faraday rotation measurements. For this reason, alternate methods of determining ionospheric electron content are being explored. One promising method involves the use of satellites of the NAVSTAR Global Positioning System (GPS). The results of a comparative study regarding this method are encouraging.

Royden, H. N.↗
NASA NTRS1993

NASA's first in-space optical gyroscope: A technology experiment on the X ray Timing Explorer spacecraft

A technology experiment on the X-ray Timing Explorer spacecraft to determine the feasibility of Interferometric Fiber Optic Gyroscopes for space flight navigation is described. The experiment consists of placing a medium grade fiber optic gyroscope in parallel with the spacecraft's inertial reference unit. The performance of the fiber optic gyroscope will be monitored and compared to the primary mechanical gyroscope's performance throughout the two-year mission life.

Unger, Glenn↗
NASA NTRS1992

Autonomous planetary landing guidance by optical correlation

We describe our planned use of optical correlation in landmark navigation associated with planetary landing. Standard correlation provides 'pointing-to' information, giving the vector to the landmark from the spacecraft in the spacecraft frame. The synthetic estimation filter (SEF) provides 'pointing-from' information, estimating the vector from the landmark to the spacecraft. Digital and optical SEFs were constructed and compared using a Martian-like 3D modelboard to provide test images. The digital SEF worked reasonably well, but the optical SEF did not perform as expected. The optical SEF was implemented with a liquid crystal television (LCTV) correlator that had been used successfully in previous SEF experiments using a spacecraft model. The results suggest the SLM model for the LCTV needs further refinements. Both the digital and optical filter provided good pointing-to results. We did not plot the correlation surface for the digital SEF response, and though it is less sharp than the POF, it had only a one-pixel variation in the peak location. Surface plots for the conventional optical phase-only filter produced a correlation peak that was sharp enough to be located within two pixels.

Knopp, Jerome↗
NASA NTRS2007

Development of Laser Beam Transmission Strategies for Future Ground-to-Space Optical Communications

Optical communications is a key technology to meet the bandwidth expansion required in the global information grid. High bandwidth bi-directional links between sub-orbital platforms and ground and space terminals can provide a seamless interconnectivity for rapid return of critical data to analysts. The JPL Optical Communications Telescope Laboratory (OCTL) is located in Wrightwood California at an altitude of 2.2.km. This 200 sq-m facility houses a state-of- the-art 1-m telescope and is used to develop operational strategies for ground-to-space laser beam propagation that include safe beam transmission through navigable air space, adaptive optics correction and multi-beam scintillation mitigation, and line of sight optical attenuation monitoring. JPL has received authorization from international satellite owners to transmit laser beams to more than twenty retro-reflecting satellites. This paper presents recent progress in the development of these operational strategies tested by narrow laser beam transmissions from the OCTL to retro-reflecting satellites. We present experimental results and compare our measurements with predicted performance for a variety of atmospheric conditions.

optical communications↗
NASA NTRS1986

Orbit determination for the Voyager II Uranus encounter

The Voyager II flyby of Uranus in January 1986 was the most distant planetary encounter ever attempted, and presented unique challenges to the process of orbit determination. Long light-times and spacecraft receiver difficulties hampered the collection of two-way radiometric data and helped bring about the maturation of a Very Long Baseline Interferometry navigational data type during the long cruise from Saturn. Planet and satellite ephemeris uncertainties necessitated the use of the onboard spacecraft optical system for Uranus-relative navigation. During the close approach phase, these optical data were combined with radiometric data to drive the Uranus system-relative uncertainties down to the level of a few tens of kilometers. This paper contains qualitative and quantitative results and conclusions based on orbit determination experience during Uranus cruise and encounter. Topics include an overview of the navigation-related mission events and requirements, and a review of the salient orbit determination results.

Taylor, T. H.↗
NASA NTRS1989

An onboard navigation system which fulfills Mars aerocapture guidance requirements

The development of a candidate autonomous onboard Mars approach navigation scheme capable of supporting aerocapture into Mars orbit is discussed. An aerocapture guidance and navigation system which can run independently of the preaerocapture navigation was used to define a preliminary set of accuracy requirements at entry interface. These requirements are used to evaluate the proposed preaerocapture navigation scheme. This scheme uses optical sightings on Deimos with a star tracker and an inertial measurement unit for instrumentation as a source for navigation nformation. Preliminary results suggest that the approach will adequately support aerocaputre into Mars orbit.

Brand, Timothy J.↗
NASA NTRS1972

Estimating trajectory correction requirements for multiple outer planet missions.

General approach to the problem of estimating trajectory correction requirements for multiple outer planet flyby missions when the navigation system uses onboard optical measurements made during approach to each target planet to complement the ground-based radio measurements. The accuracy and reliability of the onboard measurement system plays a critical role in sizing the trajectory correction capability required. An illustration of the combined use of radio and optical measurements is provided for the particular case of a Jupiter-Uranus-Neptune mission. Use of the statistical technique developed for computing the trajectory correction margin required to account for uncertainties in subsystem performance, permits trajectory correction savings of 100 to 20 m/sec over 'worst case' designs. This represents weight savings of about 50% of the science payload. For the example case trajectory correction requirements are estimated for two candidate optical systems and the radio alone case. The use of onboard measurements allows a trajectory correction savings of approximately 140 m/sec.

Friedman, L. D.↗
NASA NTRS1979

To the solar foci

Earlier authors showed that the sun is likely to act as a lens for gravitational radiation, with focui in the outer solar system. They suggested that missions to these foci have the potential of directly measuring the density structure of the sun. Other applications include gravitational wave astronomy and tests of general relativity. This idea is reexamined, concentrating on the engineering aspects of focal missions; primarily spacecraft design and performance. Other topics studied include solar optics, gravitational wave detectors, navigation, and the design of missions for different purposes. Specifically, it is shown that shuttle launched chemical rockets have a substantial capability for reaching some foci; and that all can be reached with large payloads using nuclear isotope-electric propulsion.

Sonnabend, D.↗
NASA NTRS2008

Optical Communications from Planetary Distances

Future planetary campaigns, including human missions, will require data rates difficult to realize by microwave links. Optical channels not only provide an abundance of bandwidth, they also allow for significant size, weight, and power reduction. Moreover, optical-based tracking may enhance spacecraft navigation with respect to microwave-based tracking. With all its advantages, optical communications from deep space is not without its challenges. Due to the extreme distance between the two ends of the link, specialized technologies are needed to enable communications in the deep space environment. Although some of the relevant technologies have been developed in the last decade, they remain to be validated in an appropriate domain. The required assets include efficient pulsed laser sources, modulators, transmitters, receivers, detectors, channel encoders, precise beam pointing technologies for the flight transceiver and large apertures for the ground receiver. Clearly, space qualification is required for the systems that are installed on a deep space probe. Another challenge is atmospheric effects on the optical beam. Typical candidate locations on the ground have a cloud-free line of sight only on the order of 60-70% of the time. Furthermore, atmospheric losses and background light can be problematic even during cloud-free periods. Lastly, operational methodologies are needed for efficient and cost effective management of optical links. For more than a decade, the National Aeronautics and Space Administration (NASA) has invested in relevant technologies and procedures to enable deep space optical communications capable of providing robust links with rates in the order of 1 Gb/s from Mars distance. A recent publication indicates that potential exists for 30-dB improvement in performance through technology development with respect to the state-of-the-art in the early years of this decade. The goal is to fulfill the deep space community needs from about 2020 to the foreseeable future. It is envisioned that, at least initially, optical links will be complemented by microwave assets for added robustness, especially for human missions. However, it is expected that as optical techniques mature, laser communications may be operated without conventional radio frequency links. The purpose of this paper is to briefly review the state-of-the-art in deep space laser communications and its challenges and discuss NASA-supported technology development efforts and plans for deep space optical communications at JPL.

Laser Communications↗