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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 289 records · Page 16

Tunable Microwave Components for Ku- and K-Band Satellite Communications

The use of conductor/ferroelectric/dielectric thin film multilayer structures for frequency and phase agile components at frequencies at and above the Ku-band will be discussed. Among these components are edge coupled filters, microstripline ring resonators, and phase shifters. These structures were implemented using SrTiO3 (STO) ferroelectric thin films, with gold or YBa2Cu3O7-d (YBCO) high temperature superconducting (HTS) microstrip fines deposited by laser ablation on LaAlO3 (LAO) substrates. The performance of these structures in terms of tunability, operating temperature, frequency, and dc bias will be presented. Because of their small size, light weight, and low loss, these tunable microwave components are being studied very intensely at NASA as well as the commercial communication industry. An assessment of the progress made so far, and the issues yet to be solved for the successful integration of these components into the aforementioned communication systems will be presented.

Miranada, F. A.↗

LITE data processing

The Lidar In-space Technology Experiment (LITE) was a payload onboard the Space Shuttle Discovery as part of the September 1994 STS-64 mission. LITE successfully made both atmospheric and surface measurements at the 355 nm, 532 nm, and 1064 nm wavelengths [Winker et al., 1996]. At mission completion, nearly 45 Gbytes of data had been obtained. As the data were collected they were organized into three data sets. The largest of these data sets contained the single-shot full resolution digitized lidar signals for all three wavelengths. The other two data sets contained the instrument status data block (ISDB) and the quick look science data (QLSD). ISDB information was generated once per second and contained timing parameters and engineering data related to the health, status, and configuration of the instrument. The QLSD are 100shot averages of the 355 nm and 532 nm lidar signals and were generated at ten second intervals. As the LITE data were generated, they were output to low-rate and high-rate telemetry streams. The low-rate data contained the ISDB and QLSD. The lowrate data were transmitted to the ground by the Shuttle S-band system through the Tracking and Data Relay Satellite System (TDRSS). The high-rate data contained the full resolution digitized lidar signals for all three wavelengths, the ISDB, and QLSD. The high-rate data were transmitted in real time by the Ku-band system through TDRSS downlink to the LITE operations center at the Johnson Space Center (JSC). High-rate data were only obtained when the orbiter and TDRSS telemetry link coincided with the real-time operations of LITE. The low-rate data were backed up by a Shuttle recorder during periods when the telemetry link was unavailable, and the entire lowrate data stream was transferred to the ground over the course of the mission. A total of 53 hours of lowrate data and 45.5 hours of high-rate data were acquired. All of the LITE raw telemetry data have been archived at the NASA Langley Research Center (LaRC), and the LITE high-rate data have been processed to the level 1 data product. This paper describes the data processing steps required to convert the LITE raw, high-rate telemetry data to the LITE level 1 data product.

Powell, Kathleen A.↗

RADARSAT Underflights: Comparison of C-band VV and HH Backscatter-Wind Retrieval

The primary objective of this grant was to validate the modified CMOD4 wind speed algorithm used to invert RADARSAT data. We proposed to do the following: TASK 1: Participate in at least two underflights of RADARSAT (collecting backscatter measurements with the UMASS C-band and Ku-band scatterometers, CSCAT and KUSCAT. TASK 2: Process data gathered with CSCAT and KUSCAT into one kilometer along-track pixels with each pixel consisting of seventy-two five degree azimuth bins - each bin containing normalized radar cross section (NRCS) values for that particular azimuth angle and for each of the four incidence angles viewed by CSCAT and KUSCAT. Derive wind speed and direction estimates from each NRCS along-track pixel using CMOD4 and NSCAT models. TASK 3: Compare collocated CSCAT vertically polarized (VV) and RADARSAT horizontally polarized (HH) NRCS data and wind estimates, and based on the comparison, evaluate the performance of the modified CMOD4 wind speed algorithm to invert RADARSAT NRCS measurements. The first two tasks were completed. The third task is still on-going since the RADARSAT data for the underflights has not been released to the University of Massachusetts. We expect that the RADARSAT data will become available in the next few months, and we will complete the third task in a promptly manner once the data has been received. Below the missions flown and the data collected are summarized. Two missions, based out of the NASA Wallops Flight Facility, were flown. The first flight was on 21 September 1997 and the second on 24 September 1997. The time for each mission was approximately 2 hours. Figure 1 plots the flight tracks and marks the location of the NOAA buoys that were in the vicinity.

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Advanced Communications Technology Satellite (ACTS): Four-Year System Performance

The Advanced Communications Technology Satellite (ACTS) was conceived at the National Aeronautics and Space Administration (NASA) in the late 1970's as a follow-on program to ATS and CTS to continue NASA's long history of satellite communications projects. The ACTS project set the stage for the C-band satellites that started the industry, and later the ACTS project established the use of Ku-band for video distribution and direct-to-home broadcasting. ACTS, launched in September 1993 from the space shuttle, created a revolution in satellite system architecture by using digital communications techniques employing key technologies such as a fast hopping multibeam antenna, an on-board baseband processor, a wide-band microwave switch matrix, adaptive rain fade compensation, and the use of 900 MHz transponders operating at Ka-band frequencies. This paper describes the lessons learned in each of the key ACTS technology areas, as well as in the propagation investigations.

Acosta, Roberto J.↗

The TRMM Precipitation Radar: Opportunities and Challenges

Although studies on the feasibility of spaceborne weather radar date back to the 1960's, it was only with the launch of the Tropical Rainfall Measuring Mission (TRMM) Satellite in November 1997 that the first weather radar was placed into low earth orbit. The long delay between the initial concept and implementation was caused not only by the demanding requirements of active sensors such as mass, power, and reliability, but because of scientific and technological challenges. For example, the demand for adequate spatial resolution arises from the need to resolve the horizontal structure of convective storm cells and to avoid surface contamination of the rain return at off-nadir angles. To achieve a horizontal resolution on the order of 4 km from low earth orbit with a modest antenna size of 2 m requires the use of a much higher frequency (Ku-band) than those typically used for ground-based weather radars (S- and C-band). Higher frequencies are subject to higher attenuation. As Hitschfeld and Bordan (1954) showed in their classic paper, attenuation correction with a single-wavelength radar is inherently unstable at high attenuations unless the drop size distribution and the radar constant are known precisely. Since these conditions are seldom met, much work over the last decade has been devoted to formulating and testing alternative methods of attenuation correction. The operational method used in the TRMM radar processing is discussed in section 3 of the paper.

Meneghini, R.↗

STS-26: Preparations for Launch

Preparations for launch of STS-26 are shown. They include: (1) VAB to OPF high bay rollover; (2) Main engine unpacking and installation; (3) OMS pod installation; (4) Crew hatch removal; (5) Modified crew hatch installation; (6) Nose cap installation; (7) 17 inch disconnect work; (8) Ku-band antenna stow and deploy; (9) Tile work; (10) Oasis payload installation; (11) Solid rocket boosters arrival, preps and stacking; (13) Modified SRB segments: Arrival via train at KSC RPSF; (14) AFT segment rotation to vertical in RPSF; (15) AFT skirt to AFT segment mating; (16) SRB grain inspection; (17) Lift AFT segment; and (18) Lift and mate external tank.

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STS-103 Crew Activities Report: Flight Day 7 Highlights

Today Discovery's astronauts begin preparing the spacecraft for it's scheduled return to Earth by checking out the flight control system and reaction control jets that support re-entry. Later in the day the astronauts begin stowing equipment used during the past week and start buttoning up on-orbit systems. The Ku-band antenna which provides most of the capacity for data and television relay was stowed around 8:45 p.m. The recently refurbished Hubble Space Telescope moves slowly through it's checkout sequence before resuming science operations. Both the flight control system (FCS) and the reaction control jets (RCS) were without issue, with all systems ready to support Discovery's return to Earth.

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TDRS and the TDRS System

An overview of the Tracking and Data Relay Satellite (TDRS) system is given, including a brief history, the purpose of the TDRS, and who controls the satellite. The S-band and KU-band antennae are described. Footage of the TDRS-E (the fifth TDRS) deployment and images of various spacecraft from space are shown, along with computer simulations of the TDRS's operation.

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Design and Near-Field Measurement Performance Evaluation of the Sea Winds Dual- Beam Reflector Antenna

This paper presents the design and performance evaluation of a lightweight, composite material, elliptical-aperture, parabolic-reflector antenna. The performance characterization is obtained using the cylindrical near-field measurement facility at JPL as shown. The reflector has been designed and calibrated for the SeaWinds spaceborne scatterometer instrument. The instrument operates at Ku-band and is designed to accurately measure wind speed and direction over Earth's ocean surface. The SeaWinds antenna design requires two linearly polarized independent beams pointed at 40 deg.and 46 deg. from nadir as shown. The inner beam, pointed at 40 deg. from nadir, is horizontally polarized with 1.6 in x 1.8 in required beamwidths in the elevation and azimuth planes, respectively. The outer beam, pointed at 46 deg. from nadir, is vertically polarized with 1.4 in x 1.7 in required beamwidths. Noteworthy, the reflector boresight axis is pointed at 43 deg. from nadir. Both beams are required to have the first sidelobe level below -15 dB relative to the peak of the beam.

Hussein, Z.↗

Dichroic Design for the Orbiting VLBI Earth Station Antenna

In this paper the design and performance of a single screen frequency selective surface with gridded square loop patch elements are described for diplexing the X-and Ku-band signals in an Orbiting Very Long Baseline Interferometer (OVLBI) earth station reflector antenna system.

gridded square element resonant frequency drift Or↗

Summary Report of Mission Acceleration Measurement for STS-87, Launched November 19, 1997

Two accelerometer systems, the Orbital Acceleration Research Experiment and the Space Acceleration Measurement System, were used to measure and record the microgravity environment of the Orbiter Columbia during the STS-87 mission in November-December 1997. Data from two separate Space Acceleration Measurement System units were telemetered to the ground during the mission and data plots were displayed for investigators of the Fourth United States Microgravity Payload experiments in near real-time using the World Wide Web. Plots generated using Orbital Acceleration Research Experiment data (telemetered to the ground using a tape delay) were provided to the investigators using the World Wide Web approximately twelve hours after data recording. Disturbances in the microgravity environment as recorded by these instruments are grouped by source type: Orbiter systems, on-board activities, payload operations, and unknown sources. The environment related to the Ku-band antenna dither, Orbiter structural modes, attitude deadband collapses, water dump operations, crew sleep, and crew exercise was comparable to the effects of these sources on previous Orbiter missions. Disturbances related to operations of the Isothermal Dendritic Growth Experiment and Space Acceleration Measurement Systems that were not observed on previous missions are detailed. The effects of Orbiter cabin and airlock depressurization and extravehicular activities are also reported for the first time. A set of data plots representing the entire mission is included in the CD-ROM version of this report.

Rogers, Melissa J. B.↗

SCADA Application for ACTS Technology

A satellite and earth terminal systems study was initiated by the NASA Advanced Communication Technology Satellite (ACTS) Project Office and was performed by Hughes Network Systems. The purpose of the study was to investigate the potential of a specialized Ka-band spot beam satellite to reduce the cost of supervisory control and data acquisition (SCADA) communications. The study showed that the technology exists to build a system that could be priced less than 77permonthperRTU(remoteterminalunit),includingearthstationequipment.TheRTUearthstation,orUSAT,wouldcost a quantity level of 500000. SCADA systems which poll RTU's rapidly will not be as economical to serve by satellite. A parallel study initiated by Southern California Edison and performed by Weber State University found similar satellite economics at Ku-band, but did not address earth station manufacturing cost. Market size estimates support a phased development approach. The first phase would be prototype system development at both Ku- and Ka-bands. NASA is currently sponsoring an additional study that would develop more detailed specifications.

B. Fairbanks↗

41-G Mission Report - Summary

Challenger's sixth flight launched from KSC at 6:03 CDT October 5, 1984. It returned to Kennedy eight days later, landing on October 13th. Since 41-G was a planned EVA flight, two prime EMUs and one backup short EMU were stowed in the Airlock. No MMUs were carried. Astronaut A and Astronaut B successfully accomplished their 3 l/2 hour EVA on October 11th, Flight Day 7 of the mission. This EVA took place the day after the EMU Checkout and Maintenance Recharge activities. During this time Astronaut A and Astronaut B completed the planned installation of the Orbital Refueling System Ball Valve mod kit as well as an unplanned activity of locking the gimbals on the Ku-Band antenna. They each performed quite well in their EMUs.

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Results of Airborne Backscatter Measurements During the Surface Wave Dynamics Experiment

Ocean backscatter data over a wide variety of oceanic and atmospheric conditions were obtained by the Jet Propulsion Laboratory NUSCAT Ku-band scatterometer during the Surface Wave Dynamics Experiment (SWADE). Thirty hours of backscatter data were collected in ten flights by NUSCAT on the NASA Ames C130 aircraft during an intensive observation period (IOP) of SWADE in the winter of 1991. The SWADE experimental area, off the coast of Virginia and Maryland, was deployed with an array of buoys providing appropriate in-situ measurements to correlate with the radar backscatter for incidence angles from 10ø to 60ø at both horizontal and vertical polarizations.

Airborne↗

Design of Dual Frequency Interferometric SAR

Using a spaceborne interferometric SAR, it is possible to produce a high resolution global topographic map with a height accuracy of several meters. However, frequency selection of the interferometric SAR is rather complicated due to interferometric phenomenology and atmospheric effects. In this paper, we propose a dual frequency interferometric SAR to achieve better understanding of interferometric height (especially for penetrable medium) and corresponding calibration and to remove the atmospheric effects. The selected frequencies are L- and Ku-bands. We also present a radar design and show that a light weight and efficient SAR can be designed using new technologies and dual frequency advantages even with two frequency radars in a single spacecraft.

Interferometric↗

Arctic Sea Ice Extent and Melt Onset from NSCAT Observations

Arctic sea ice extent and the timing of melt onset are important parameters in the study of polar processes and climate changes. NSCAT Ku-band active microwave observations of the Arctic sea ice cover are described in this article with emphasis on their potential use for estimating ice extent and detection of spring melt.

Arctic↗

Optimal Estimation of Rain Rate Profiles from Single-Frequency Radar Echoes

It is well-documented (Hitschfeld and Bordan 1954, Meneghini 1978, Haddad et al 1993) that there are significant ambiguites inherent in the determination of a particular vertical rain intensity profile from a given time profile of radar echo powers measured by a downward-looking (spaceborne or airborne) radar at a single attenuating frequency.

stochastic constraints Ku-band Precipitation Radar↗