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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Environmental exposure effects on composite materials for commercial aircraft

Activities reported include completion of the program design tasks, resolution of a high fiber volume problem and resumption of specimen fabrication, fixture fabrication, and progress on the analysis methodology and definition of the typical aircraft environment. Program design activities including test specimens, specimen holding fixtures, flap-track fairing tailcones, and ground exposure racks were completed. The problem experienced in obtaining acceptable fiber volume fraction results on two of the selected graphite epoxy material systems was resolved with an alteration to the bagging procedure called out in BAC 5562. The revised bagging procedure, involving lower numbers of bleeder plies, produces acceptable results. All required laminates for the contract have now been laid up and cured. Progress in the area of analysis methodology has been centered about definition of the environment that a commercial transport aircraft undergoes. The selected methodology is analagous to fatigue life assessment.

Hoffman, D. J.↗
NASA NTRS1982

Reconstruction of the 1st Space Shuttle (STS-1) entry trajectory

A discussion of the generation of the best estimate trajectory (BET) of the first Space Shuttle Orbiter entry flight is presented. The BET defines a time history of the state, attitude, and atmospheric relative parameters throughout the Shuttle entry from an altitude of approximately 183 km to rollout. The inertial parameters were estimated utilizing a weighted least squares batch filter algorithm. Spacecraft angular rate and acceleration data derived from the Inertial Measurement Unit were utilized to predict the state and attitude which was constrained in a weighted least squares process to fit external tracking data consisting of ground based S-band and C-band data. Refined spacecraft altitude and velocity during and post rollout were obtained by processing artificial altimeter and Doppler data. The BET generation process is discussed. Software and data interface discussions are included. The variables and coordinate systems utilized are defined. STS-1 mission peculiar inputs are summarized. A listing of the contents of the actual BET is provided.

Findlay, J. T.↗
NASA NTRS1985

Contribution of explosion and future collision fragments to the orbital debris environment

The time evolution of the near-earth man-made orbital debris environment modeled by numerical simulation is presented in this paper. The model starts with a data base of orbital debris objects which are tracked by the NORAD ground radar system. The current untrackable small objects are assumed to result from explosions and are predicted from data collected from a ground explosion experiment. Future collisions between earth orbiting objects are handled by the Monte Carlo method to simulate the range of collision possibilities that may occur in the real world. The collision fragmentation process between debris objects is calculated using an empirical formula derived from a laboratory spacecraft impact experiment to obtain the number versus size distribution of the newly generated debris population. The evolution of the future space debris environment is compared with the natural meteoroid background for the relative spacecraft penetration hazard.

Su, S.-Y.↗
NASA NTRS1987

Deep space network resource scheduling approach and application

Deep Space Network (DSN) resource scheduling is the process of distributing ground-based facilities to track multiple spacecraft. The Jet Propulsion Laboratory has carried out extensive research to find ways of automating this process in an effort to reduce time and manpower costs. This paper presents a resource-scheduling system entitled PLAN-IT with a description of its design philosophy. The PLAN-IT's current on-line usage and limitations in scheduling the resources of the DSN are discussed, along with potential enhancements for DSN application.

Eggemeyer, William C.↗
NASA NTRS1990

When propfans cruise, will LDN 65 fly

The type and extent of response that may be expected from the persons exposed to the noise of propfans cruising overhead is examined. The cruise mode is of particular interest because it appears that it is in this mode that the propfan airplane noise differs substantially from the noise of present jet-powered airplanes. Early test data on propfan engines suggests that noise levels on the ground under the flight track of commercial propfan transports may approach 65 decibels. To explore the reaction of the exposed population to repeated noise levels of this magnitude, it may be helpful to review some of the pertinent literature on the effects of environmental noise.

Mintz, Fred↗
NASA NTRS1993

Analysis of passive acoustic ranging of helicopters from the joint acoustic propagation experiment

For more than twenty years, personnel of the U.S.A.E. Waterways Experiment Station (WES) have been performing research dealing with the application of sensors for detection of military targets. The WES research has included the use of seismic, acoustic, magnetic, and other sensors to detect, track, and classify military ground targets. Most of the WES research has been oriented toward the employment of such sensors in a passive mode. Techniques for passive detection are of particular interest in the Army because of the advantages over active detection. Passive detection methods are not susceptible to interception, detection, jamming, or location of the source by the threat. A decided advantage for using acoustic and seismic sensors for detection in tactical situations is the non-line-of-sight capability; i.e., detection of low flying helicopters at long distances without visual contact. This study was conducted to analyze the passive acoustic ranging (PAR) concept using a more extensive data set from the Joint Acoustic Propagation Experiment (JAPE).

Carnes, Benny L.↗
NASA NTRS1992

Efficient geometric rectification techniques for spectral analysis algorithm

The spectral analysis algorithm is a viable technique for processing synthetic aperture radar (SAR) data in near real time throughput rates by trading the image resolution. One major challenge of the spectral analysis algorithm is that the output image, often referred to as the range-Doppler image, is represented in the iso-range and iso-Doppler lines, a curved grid format. This phenomenon is known to be the fanshape effect. Therefore, resampling is required to convert the range-Doppler image into a rectangular grid format before the individual images can be overlaid together to form seamless multi-look strip imagery. An efficient algorithm for geometric rectification of the range-Doppler image is presented. The proposed algorithm, realized in two one-dimensional resampling steps, takes into consideration the fanshape phenomenon of the range-Doppler image as well as the high squint angle and updates of the cross-track and along-track Doppler parameters. No ground reference points are required.

Chang, C. Y.↗
NASA NTRS1994

GRTS operations monitor/control system

An Operations Monitor/Control System (OMCS) was developed to support remote ground station equipment. The ground station controls a Tracking Data Relay Satellite (TDRS) relocated to provide coverage in the tracking system's zone of exclusion. The relocated satellite significantly improved data recovery for the Gamma Ray Observatory mission. The OMCS implementation, performed in less than 11 months, was mission critical to TDRS drift operations. Extensive use of Commercial Off The Shelf (COTS) hardware and software products contributed to implementation success. The OMCS has been operational for over 9 months with no significant problems. This paper will share our experiences in OMCS development and integration.

Rohrer, Richard A.↗
NASA NTRS1994

The application of spaceborne GPS to atmospheric limb sounding and global change monitoring

This monograph is intended for readers with minimal background in radio science who seek a relatively comprehensive treatment of the mission and technical aspects of an Earth-orbiting radio occultation satellite. Part 1 (chapters 1-6) describes mission concepts and programmatic information; Part 2 (chapters 7-12) deals with the theoretical aspects of analyzing and interpreting radio occultation measurements. In this mission concept the navigation signals from a Global Positioning System (GPS) satellite that is being occulted by the Earth's limb are observed by a GPS flight receiver on board a low Earth orbiter (LEO) satellite. This technique can be used to recover profiles of the Earth's atmospheric refractivity, pressure, and temperature using small, dedicated, and relatively low-cost space systems. Chapter 2 summarizes the basic space system concepts of the limb-sounding technique and describes a low-cost strawman demonstration mission. Chapter 3 discusses some of the scientific benefits of using radio occultation on a suite of small satellites. Chapter 4 provides a more detailed discussion of several system elements in a radio occultation mission, including the launch system for small payloads, the LEO microsat, the GPS constellation, the GPS flight receiver payload, the mission operations ground control and data receiving system, the ground-based GPS global tracking network for precision orbit determination, and the central data processing and archive system. Chapter 5 addresses the various technology readiness questions that invariably arise. Chapter 6 discusses the overall costs of a demonstration mission such as GPS/MET (meteorological) proposed by the University Navstar Consortium (UNAVCO). Chapter 7 describes a geometrical optics approach to coplanar atmospheric occultation. Chapter 8 addresses major questions regarding accuracy of the occultation techniques. Chapter 9 describes some simulations that have been performed to evaluate the sensitivity of the recovered profiles of atmospheric parameters to different error sources, such as departure from spherical symmetry, water vapor, etc. Chapter 10 discusses horizontal and vertical resolution associated with limb sounders in general. Chapter 11 treats selected Fresnel diffraction techniques that can be used in radio occultation measurements to sharpen resolution. Chapter 12 provides brief discussions on selected special topics, such as strategies for handling interference and multipath processes that may arise for rays traveling in the lower troposphere.

Melbourne, W. G.↗
NASA NTRS1996

Autonomy metrics

Space missions are currently being designed and developed to rely on increased spacecraft autonomy in order to achieve lower cost operations and to support the fleets of planetary spacecraft with limited deep space network resources. In relation to this, metrics are presented which quantitatively define spacecraft autonomy and will be used to: set measurable autonomy goals for future missions; evaluate and compare the benefits between competing automation technologies, and to compare autonomy between missions. The metrics measure the degree to which spacecraft and space mission designs lead to: longer periods of no-track; shorter track periods; reduced ground-orbit communications, and smaller operations workforces. The results of a survey applying these metrics to historic missions and to planned future missions are reported on, illustrating the differences between the autonomy achieved by previous missions and that predicted for future missions.

Carraway, John B.↗
NASA NTRS2004

Autonomous Navigation Results from the Mars Exploration Rover (MER) Mission

In January, 2004, the Mars Exploration Rover (MER) mission landed two rovers, Spirit and Opportunity, on the surface of Mars. Several autonomous navigation capabilities were employed in space for the first time in this mission. ]n the Entry, Descent, and Landing (EDL) phase, both landers used a vision system called the, Descent Image Motion Estimation System (DIMES) to estimate horizontal velocity during the last 2000 meters (m) of descent, by tracking features on the ground with a downlooking camera, in order to control retro-rocket firing to reduce horizontal velocity before impact. During surface operations, the rovers navigate autonomously using stereo vision for local terrain mapping and a local, reactive planning algorithm called Grid-based Estimation of Surface Traversability Applied to Local Terrain (GESTALT) for obstacle avoidance. ]n areas of high slip, stereo vision-based visual odometry has been used to estimate rover motion, As of mid-June, Spirit had traversed 3405 m, of which 1253 m were done autonomously; Opportunity had traversed 1264 m, of which 224 m were autonomous. These results have contributed substantially to the success of the mission and paved the way for increased levels of autonomy in future missions.

autonomous↗
NASA NTRS2006

Challenging Implementation and Operations Traditions

The Deep Space Network (DSN) that provides for the communications link between the deep space missions and the science users currently consists of a small set of very large monolithic tracking antennas. This ground-based network includes a total of 12 antennas located in three roughly equidistant longitudes around the earth and utilizes a decentralized approach to it operations. Recently, however, studies have suggested that the number, complexity, and data throughput of the future set of space probes will be increasing dramatically. This demands more performance from the DSN than is currently available. In identifying the architecture for the future DSN required to support this mission set, one concept that proves promising is one that consists of a great many number of much smaller antennas configured in an array. This concept has been supported by the developments in antenna manufacturing technology and the consistent decrease in the cost of electronics required to receive, amplify, and combine signals from deep space probes. Furthermore, it is clear that past developments in the DSN have not benefited from the applications of economies of scale.

ANTENNA ARRAYS↗
NASA NTRS2004

Effect of Clouds on Optical Imaging of the Space Shuttle During the Ascent Phase: A Statistical Analysis Based on a 3D Model

Clouds are highly effective in obscuring optical images of the Space Shuttle taken during its ascent by ground-based and airborne tracking cameras. Because the imagery is used for quick-look and post-flight engineering analysis, the Columbia Accident Investigation Board (CAIB) recommended the return-to-flight effort include an upgrade of the imaging system to enable it to obtain at least three useful views of the Shuttle from lift-off to at least solid rocket booster (SRB) separation (NASA 2003). The lifetimes of individual cloud elements capable of obscuring optical views of the Shuttle are typically 20 minutes or less. Therefore, accurately observing and forecasting cloud obscuration over an extended network of cameras poses an unprecedented challenge for the current state of observational and modeling techniques. In addition, even the best numerical simulations based on real observations will never reach "truth." In order to quantify the risk that clouds would obscure optical imagery of the Shuttle, a 3D model to calculate probabilistic risk was developed. The model was used to estimate the ability of a network of optical imaging cameras to obtain at least N simultaneous views of the Shuttle from lift-off to SRB separation in the presence of an idealized, randomized cloud field.

FROM↗
NASA NTRS2013

Orbital Debris: Past, Present, and Future

In the early days of spaceflight, the gBig Sky h theory was the near universally accepted paradigm for dealing with collisions of orbiting objects. This theory was also used during the early years of the aviation industry. Just as it did in aviation, the gBig Sky h theory breaks down as more and more objects accumulate in the environment. Fortunately, by the late 1970 fs some visionaries in NASA and the US Department of Defense (DoD) realized that trends in the orbital environment would inevitably lead to increased risks to operational spacecraft from collisions with other orbiting objects. The NASA Orbital Debris Program was established at and has been conducted at Johnson Space Center since 1979. At the start of 1979, fewer than 5000 objects were being tracked by the US Space Surveillance Network and very few attempts had been made to sample the environment for smaller sizes. Today, the number of tracked objects has quadrupled. Ground ]based and in situ measurements have statistically sampled the LEO environment over most sizes and mitigation guidelines and requirements are common among most space faring nations. NASA has been a leader, not only in defining the debris environment, but in promoting awareness of the issues in the US and internationally, and in providing leadership in developing policies to address the issue. This paper will discuss in broad terms the evolution of the NASA debris program from its beginnings to its present broad range of debris related research. The paper will discuss in some detail current research topics and will attempt to predict future research trends.

Stansbery, Gene↗
NASA NTRS2014

Partial Automated Alignment and Integration System

The present invention is a Partial Automated Alignment and Integration System (PAAIS) used to automate the alignment and integration of space vehicle components. A PAAIS includes ground support apparatuses, a track assembly with a plurality of energy-emitting components and an energy-receiving component containing a plurality of energy-receiving surfaces. Communication components and processors allow communication and feedback through PAAIS.

Kelley, Gary Wayne↗
NASA NTRS2014

Imagery Integration Team

The Human Exploration Science Office (KX) provides leadership for NASA's Imagery Integration (Integration 2) Team, an affiliation of experts in the use of engineering-class imagery intended to monitor the performance of launch vehicles and crewed spacecraft in flight. Typical engineering imagery assessments include studying and characterizing the liftoff and ascent debris environments; launch vehicle and propulsion element performance; in-flight activities; and entry, landing, and recovery operations. Integration 2 support has been provided not only for U.S. Government spaceflight (e.g., Space Shuttle, Ares I-X) but also for commercial launch providers, such as Space Exploration Technologies Corporation (SpaceX) and Orbital Sciences Corporation, servicing the International Space Station. The NASA Integration 2 Team is composed of imagery integration specialists from JSC, the Marshall Space Flight Center (MSFC), and the Kennedy Space Center (KSC), who have access to a vast pool of experience and capabilities related to program integration, deployment and management of imagery assets, imagery data management, and photogrammetric analysis. The Integration 2 team is currently providing integration services to commercial demonstration flights, Exploration Flight Test-1 (EFT-1), and the Space Launch System (SLS)-based Exploration Missions (EM)-1 and EM-2. EM-2 will be the first attempt to fly a piloted mission with the Orion spacecraft. The Integration 2 Team provides the customer (both commercial and Government) with access to a wide array of imagery options - ground-based, airborne, seaborne, or vehicle-based - that are available through the Government and commercial vendors. The team guides the customer in assembling the appropriate complement of imagery acquisition assets at the customer's facilities, minimizing costs associated with market research and the risk of purchasing inadequate assets. The NASA Integration 2 capability simplifies the process of securing one-of-a-kind imagery assets and skill sets, such as ground-based fixed and tracking cameras, crew-in the-loop imaging applications, and the integration of custom or commercial-off-the-shelf sensors onboard spacecraft. For spaceflight applications, the Integration 2 Team leverages modeling, analytical, and scientific resources along with decades of experience and lessons learned to assist the customer in optimizing engineering imagery acquisition and management schemes for any phase of flight - launch, ascent, on-orbit, descent, and landing. The Integration 2 Team guides the customer in using NASA's world-class imagery analysis teams, which specialize in overcoming inherent challenges associated with spaceflight imagery sets. Precision motion tracking, two-dimensional (2D) and three-dimensional (3D) photogrammetry, image stabilization, 3D modeling of imagery data, lighting assessment, and vehicle fiducial marking assessments are available. During a mission or test, the Integration 2 Team provides oversight of imagery operations to verify fulfillment of imagery requirements. The team oversees the collection, screening, and analysis of imagery to build a set of imagery findings. It integrates and corroborates the imagery findings with other mission data sets, generating executive summaries to support time-critical mission decisions.

Calhoun, Tracy↗
NASA NTRS2016

NASA Near Earth Network (NEN) and Space Network (SN) Support of CubeSat Communications

There has been a historical trend to increase capability and drive down the Size, Weight and Power (SWAP) of satellites and that trend continues today. NASA scientists and engineers across many of NASAs Mission Directorates and Centers are developing exciting CubeSat concepts and welcome potential partnerships for CubeSat endeavors. From a Telemetry, Tracking and Command (TTC) Systems and Flight Operations for Small Satellites point of view, small satellites including CubeSats are a challenge to coordinate because of existing small spacecraft constraints, such as limited SWAP and attitude control, and the potential for high numbers of operational spacecraft. The NASA Space Communications and Navigation (SCaN) Programs Near Earth Network (NEN) and Space Network (SN) are customer driven organizations that provide comprehensive communications services for space assets including data transport between a missions orbiting satellite and its Mission Operations Center (MOC). This paper presents how well the SCaN networks, SN and NEN, are currently positioned to support the emerging small small satellite and CubeSat market as well as planned enhancements for future support.

Satellite↗