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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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Attention is given to the closure of the ATDRSS zone of exclusion (ZOE) utilizing a satellite crosslink whose payload is contained within the FSG. Radio-frequency and optical crosslink approaches are compared in terms of power, volume, and mass. The application considered for the FSG is the ATDRSS ZOE closure utilizing either an optical or an RF crosslink.
The general two-mirror system used at finite conjugates is examined here. Relations for first-order geometric properties and third-order aberrations are given in terms of five design parameters: object distance, image distance, exit pupil size, and the two mirror magnifications. The conditions for aplanatic solutions are derived for conic mirrors. The curvatures of the astigmatic image surfaces are given, and the condition for anastigmatic solutions is derived. The relations are applied to infinite conjugate systems and spherical mirror systems as special cases.
The STGT will provide high availability command and control and improved services to users of NASA's Space Network in the 1990s and beyond. The Space Network, comprising the TDRSS, will be the primary communications gateway for Space Station Freedom and other user's spacecraft and their ground support elements. The STGT will contain a redundant, distributed computer system providing configuration and control of redundant RF to baseband equipment chains for throughput of user data, for user tracking services and for control and monitoring of the TDR Satellites. An interface with NASA's Network Control Center, located at the Goddard Space Flight Center, provides automated scheduling and control of the STGT. A local TDRSS Operations Control Center for local monitoring and back-up control and an interface with the Domestic Satellite for data distribution will be provided by the STGT. This paper describes the STGT, with emphasis on configuration, control and monitoring of those elements providing TDRSS services to user spacecraft.
NASA has taken a stepwise approach to giving high-accuracy, autonomous navigation to TDRSS utilizers. With implementation of the TONS experiment on EP complete, flight demonstration of onboard Doppler extraction and onboard signal acquisition is progressing. Preflight and preliminary inflight analyses show that the flight components are operating within their specifications.
This report documents construction and testing of the Interferometric Tracking System project developed under the NASA SBIR contract NAS5-30313. Manuals describing the software and hardware, respectively entitled: 'Field Station Guide to Operations' and 'Field Station Hardware Manual' are included as part of this final report. The objective of this contract was to design, build, and operate a system of three ground stations using Very Long Baseline Interferometry techniques to measure the TDRS orbit. The ground stations receive signals from normal satellite traffic, store these signals in co-located computers, and transmit the information via phone lines to a central processing site which correlates the signals to determine relative time delays. Measurements from another satellite besides TDRS are used to determine clock offsets. A series of such measurements will ultimately be employed to derive the orbital parameters, yielding positions accurate to within 50 meters or possibly better.
NASA GSFC VNS TSG personnel have proposed the use of TDRSS to obtain telemetry and/or S-band one-way return Doppler tracking data for spacecraft which do not have TDRSS-compatible transponders and therefore were never considered candidates for TDRSS support. For spacecraft with less stable local oscillators (LO), one-way return Doppler tracking data is typically of poor quality. It has been demonstrated using UARS, WIND, and NOAA-J tracking data that the simultaneous use of two TDRSS spacecraft can yield differenced one-way return Doppler data of high quality which is usable for orbit determination by differencing away the effects of oscillator instability.
A scanning system uses a polygonal mirror assembly with each facet of the polygon having an ellipsoidal mirror located thereon. One focal point of each ellipsoidal mirror is located at a common point on the axis of rotation of the polygonal mirror assembly. As the mirror assembly rotates. a second focal point of the ellipsoidal mirrors traces out a scan line. The scanner can be utilized for scanned output display of information or for scanning information to be detected.
Reflectivity measurements from 400 Mc/sec to 10 kMc/sec on 2,200 A thick aluminum deposited on 1/2-mil-thick Mylar film show this material to be a very good reflector of radio waves. Measurements made under conditions of stress and temperature which would be encountered by a communications sphere, such as Project Echo (1960 Iota), showed very little deterioration of the high reflectivity. packaging effects also caused very little reflectivity change. Under conditions of severe temperature cycling, aluminum removal and decreased reflectivity occurred.
Changes in posture can affect the resting length of respiratory muscles, requiring alterations in the activity of these muscles if ventilation is to be unaffected. Recent studies have shown that the vestibular system contributes to altering respiratory muscle activity during movement and changes in posture. Furthermore, anatomical studies have demonstrated that many bulbospinal neurons in the medial medullary reticular formation (MRF) provide inputs to phrenic and abdominal motoneurons; because this region of the reticular formation receives substantial vestibular and other movement-related input, it seems likely that medial medullary reticulospinal neurons could adjust the activity of respiratory motoneurons during postural alterations. The objective of the present study was to determine whether functional lesions of the MRF affect inspiratory and expiratory muscle responses to activation of the vestibular system. Lidocaine or muscimol injections into the MRF produced a large increase in diaphragm and abdominal muscle responses to vestibular stimulation. These vestibulo-respiratory responses were eliminated following subsequent chemical blockade of descending pathways in the lateral medulla. However, inactivation of pathways coursing through the lateral medulla eliminated excitatory, but not inhibitory, components of vestibulo-respiratory responses. The simplest explanation for these data is that MRF neurons that receive input from the vestibular nuclei make inhibitory connections with diaphragm and abdominal motoneurons, whereas a pathway that courses laterally in the caudal medulla provides excitatory vestibular inputs to these motoneurons.
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We present here the functional requirements, design characteristics, and implementational status of the Electra Payload and its role as a telecommunications mode in an evolving Mars orbital infrastructure.
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Cooperative modulation techniques can reduce the energy requirements for the long haul transmission of data from localized sensor networks.
A test using NASA's DSN to mimic the probe's signal was performed in 2000 and uncovered an anomaly that, unchecked, would result in nearly complete loss of the Huygens mission. This led to a suggested modification to the Cassini trajectory that will result in nearly complete data return for Huygens with minimal impact on Cassini.
Currently there is a renewed focus on Mars exploration both by NASA and the international community.
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