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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Soil Moisture Active/Passive (SMAP) Forward Brightness Temperature Simulator

The SMAP is one of four first-tier missions recommended by the US National Research Council's Committee on Earth Science and Applications from Space (Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond, Space Studies Board, National Academies Press, 2007) [1]. It is to measure the global soil moisture and freeze/thaw from space. One of the spaceborne instruments is an L-band radiometer with a shared single feedhorn and parabolic mesh reflector. While the radiometer measures the emission over a footprint of interest, unwanted emissions are also received by the antenna through the antenna sidelobes from the cosmic background and other error sources such as the Sun, the Moon and the galaxy. Their effects need to be considered accurately, and the analysis of the overall performance of the radiometer requires end-to-end performance simulation from Earth emission to antenna brightness temperature, such as the global simulation of L-band brightness temperature simulation over land and sea [2]. To assist with the SMAP radiometer level 1B algorithm development, the SMAP forward brightness temperature simulator is developed by adapting the Aquarius simulator [2] with necessary modifications. This poster presents the current status of the SMAP forward brightness simulator s development including incorporating the land microwave emission model and its input datasets, and a simplified atmospheric radiative transfer model. The latest simulation results are also presented to demonstrate the ability of supporting the SMAP L1B algorithm development.

Peng, Jinzheng↗
NASA NTRS2012

A Dual-Polarized, Dual-Frequency, Corrugated Feed Horn for SMAP

SMAP will be the first Earth science mission to use a deployable 6m mesh reflector for both radar and radiometric measurements from low Earth orbit. The instrument antenna will spin at about 14 rpm, making the design of both reflector and feed more challenging. While the performance requirements imposed by the radar instrument are relatively benign, those pertinent to the radiometer are more difficult to meet. Extreme care was necessary in designing the feed, especially from a performance stability perspective. Thermal variations due to the spacecraft going in and out of eclipse during orbit and direct solar radiation into the horn are just two of the challenges faced during the design phase. In this paper, the basic concepts behind the design of SMAP's feed will be discussed. Each component of the feed will be analyzed in detail with particular emphasis on its impact on major RF requirements. Overall performance of the feed will also be discussed.

deployable reflector↗
NASA NTRS2009

The Soil Moisture Active and Passive Mission (SMAP): Science and Applications

The Soil Moisture Active and Passive mission (SMAP) will provide global maps of soil moisture content and surface freeze/thaw state. Global measurements of these variables are critical for terrestrial water and carbon cycle applications. The SMAP observatory consists of two multipolarization L-band sensors, a radar and radiometer, that share a deployable-mesh reflector antenna. The combined observations from the two sensors will allow accurate estimation of soil moisture at hydrometeorological (10 km) and hydroclimatological (40 km) spatial scales. The rotating antenna configuration provides conical scans of the Earth surface at a constant look angle. The wide-swath (1000 km) measurements will allow global mapping of soil moisture and its freeze/thaw state with 2-3 days revisit. Freeze/thaw in boreal latitudes will be mapped using the radar at 3 km resolution with 1-2 days revisit. The synergy of active and passive observations enables measurements of soil moisture and freeze/thaw state with unprecedented resolution, sensitivity, area coverage and revisit.

radiometry↗
NASA NTRS2014

Implementation of Active Thermal Control (ATC) for the Soil Moisture Active and Passive (SMAP) Radiometer

NASA's Earth Observing Soil Moisture Active and Passive (SMAP) Mission is scheduled to launch in November 2014 into a 685 kilometer near-polar, sun-synchronous orbit. SMAP will provide comprehensive global mapping measurements of soil moisture and freeze/thaw state in order to enhance understanding of the processes that link the water, energy, and carbon cycles. The primary objectives of SMAP are to improve worldwide weather and flood forecasting, enhance climate prediction, and refine drought and agriculture monitoring during its three year mission. The SMAP instrument architecture incorporates an L-band radar and an L-band radiometer which share a common feed horn and parabolic mesh reflector. The instrument rotates about the nadir axis at approximately 15 revolutions per minute, thereby providing a conically scanning wide swath antenna beam that is capable of achieving global coverage within three days. In order to make the necessary precise surface emission measurements from space, the electronics and hardware associated with the radiometer must meet tight short-term (instantaneous and orbital) and long-term (monthly and mission) thermal stabilities. Maintaining these tight thermal stabilities is quite challenging because the sensitive electronics are located on a fast spinning platform that can either be in full sunlight or total eclipse, thus exposing them to a highly transient environment. A passive design approach was first adopted early in the design cycle as a low-cost solution. With careful thermal design efforts to cocoon and protect all sensitive components, all stability requirements were met passively. Active thermal control (ATC) was later added after the instrument Preliminary Design Review (PDR) to mitigate the threat of undetected gain glitches, not for thermal-stability reasons. Gain glitches are common problems with radiometers during missions, and one simple way to avoid gain glitches is to use the in-flight set point programmability that ATC affords to operate the radiometer component away from the problematic temperature zone. A simple ThermXL model (10 nodes) was developed to exercise quick trade studies among various proposed control algorithms: Modified P control vs. PI control. The ThermXL results were then compared with the detailed Thermal Desktop (TD) model for corroboration. Once done, the simple ThermXL model was used to evaluate parameter effects such as temperature digitization, heater size and gain margin, time step, and voltage variation of power supply on the ATC performance. A Modified P control algorithm was implemented into the instrument flight electronics based on the ThermXL results. The thermal short-term stability margin decreased by 10 percent with ATC and a wide temperature error band (plus or minus 0.1 degrees Centigrade) compared to the original passive thermal design. However, a tighter temperature error band (plus or minus 0.1 degrees Centigrade) increased the thermal short-term stability margin by a factor of three over the passive thermal design. The current ATC design provides robust thermal control, tighter stability, and greater in-flight flexibility even though its implementation was prompted by non-thermal performance concerns.

Mikhaylov, Rebecca↗
NASA NTRS2017

Modelling the Passive Microwave Signature from Land Surfaces: A Review of Recent Results and Application to the L-Band SMOS SMAP Soil Moisture Retrieval Algorithms

Two passive microwave missions are currently operating at L-band to monitor surface soil moisture (SM) over continental surfaces. The SMOS sensor, based on an innovative interferometric technology enabling multi-angular signatures of surfaces to be measured, was launched in November 2009. The SMAP sensor, based on a large mesh reflector 6 m in diameter providing a conically scanning antenna beam with a surface incidence angle of 40deg, was launched in January of 2015. Over the last decade, an intense scientific activity has focused on the development of the SM retrieval algorithms for the two missions. This activity has relied on many field (mainly tower-based) and airborne experimental campaigns, and since 2010-2011, on the SMOS and Aquarius space-borne L-band observations. It has relied too on the use of numerical, physical and semi-empirical models to simulate the microwave brightness temperature of natural scenes for a variety of scenarios in terms of system configurations (polarization, incidence angle) and soil, vegetation and climate conditions. Key components of the inversion models have been evaluated and new parameterizations of the effects of the surface temperature, soil roughness, soil permittivity, and vegetation extinction and scattering have been developed. Among others, global maps of select radiative transfer parameters have been estimated very recently. Based on this intense activity, improvements of the SMOS and SMAP SM inversion algorithms have been proposed. Some of them have already been implemented, whereas others are currently being investigated. In this paper, we present a review of the significant progress which has been made over the last decade in this field of research with a focus on L-band, and a discussion on possible applications to the SMOS and SMAP soil moisture retrieval approaches.

SMOS↗
NASA NTRS2015

Soil Moisture Active and Passive (SMAP) White-Painted Expanded Polystyrene (EPS) Radome Survivability Test

NASA's SMAP Mission launched in January 2015 into a 685 km near-polar, sun-synchronous orbit. The SMAP instrument architecture incorporates an L-band radar and radiometer which share a common feedhorn and mesh reflector. The instrument rotates about the nadir axis at approximately 15 rpm, thereby providing a conically scanning wide swath antenna beam that is capable of achieving global coverage within three days. The radiometer and its associated electronics have tight thermal stability requirements in order to meet the required surface emittance measurement precision from space. Maintaining the thermal stabilities is quite challenging because the radiometer is located on a spinning platform that can either be in full sunlight or eclipse, and thus exposed to a highly transient environment. Stability requirements were met by integrating a light-weight Expanded Polystyrene (EPS) radome into the design to prevent solar illumination of the feed horn interior. The radome was painted white since the thermo-optical properties of bare sunlit EPS degrade rapidly over the three-year mission. Milling of the EPS and solvent within the white paint created cavities on the EPS surface which may introduce localized hot spots possibly violating the EPS glass transition temperature of 96degC and leading to structural integrity concerns. A three-day thermal test was conducted in a vacuum chamber to verify survivability of the radome during a simulated non-spin fault condition at end of mission. A portable solar simulator illuminated the test article and the beam irradiance was kept nearly constant during the entire 50 hour test, except during the first hour which simulated the expected 79degC on-orbit surface temperature of the radome. The test article survived based on the established pass criteria for three separate metrics: dimensional, optical property, and color. If any hot spots exist locally, they did not cause any observable permanent deformation when compared to pre- and post-test images. The test results increase confidence that there is a high probability that the radome will survive the worst-case scenario of a no-spin fault condition at the end of mission.

Mikhaylov, Rebecca↗
NASA NTRS2016

A GNC Perspective of the Launch and Commissioning of NASA's SMAP (Soil Moisture Active Passive) Spacecraft

The NASA Soil Moisture Active Passive (SMAP) spacecraft was designed to use radar and radiometer measurements to produce global soil moisture measurements every 2-3 days. The SMAP spacecraft is a complicated dual-spinning design with a large 6 meter deployable mesh reflector mounted on a platform that spins at 14.6 rpm while the Guidance Navigation and Control algorithms maintain precise nadir pointing for the de-spun portion of the spacecraft. After launching in early 2015, the Guidance Navigation and Control software and hardware aboard the SMAP spacecraft underwent an intensive spacecraft checkout and commissioning period. This paper describes the activities performed by the Guidance Navigation and Control team to confirm the health and phasing of subsystem hardware and the functionality of the guidance and control modes and algorithms. The operations tasks performed, as well as anomalies that were encountered during the commissioning, are explained and results are summarized.

Brown, Todd S.↗
NASA NTRS2016

Soil Moisture Active Passive Mission Mass Properties Optimization and Analysis

The Soil Moisture Active Passive (SMAP) mission creates global soil moisture measurements every 2-3 days by spinning a lightweight, ~6 meter diameter deployable mesh reflector. This represents the largest spinning antenna ever to be used on a NASA satellite. The paper discusses the mass properties challenges that were overcome in implementing the mission, including the definition of a combined imbalance term called the Effective Product of Inertia, the selection of an optimum Spun Instrument focal length and edge offset that fostered a reduced mass properties sensitivity, the inclusion of late game Spun Instrument configuration flexibility, the use of balance mass locations that leveraged the large moment arm provided by the reflector, and a subassembly measurement campaign that reduced mass properties uncertainties on testable components.

Hendry, Morgan L., IV↗
NASA NTRS2019

NISAR flight feed assembly measurement campaign

NISAR (NASA ISRO SAR, National Aeronautics and Space Administration, Indian Space Research Organization, Synthetic Aperture Radar) is an Earth science project currently in its final development phase at NASA Jet Propulsion Laboratory (JPL) and at ISRO. Due for launch in 2022, it will assess how our planet changes overtime by measuring differences in the Earth’s solid surface due to factors like climate change, movement and melting of glaciers, earthquakes, land-slides, deforestation, agriculture and others. The enabling instrument for this mission is a dual band radar (L-Band and S-Band) that feeds a 12m deployable mesh reflector. This paper describes the antenna measurement campaign of the L-Band feed array developed at JPL. The SBand feed array is developed by ISRO and is not part of this paper. While Measurements of the Engineering Model have been published before, this paper focuses on the first measurements done with the Flight Model.

Harrell, Jefferson A.↗
NASA NTRS2017

In-flight pointing accuracy assessment and GNC commissioning overview for the dual-spinning SMAP (Soil Moisture Active Passive) spacecraft

NASA’s new SMAP (Soil Moisture Active Passive) spacecraft is a radar and radiometer- based climate monitoring mission that, for an earth-orbiting satellite, presented an uncommonly large engineering challenge for the spacecraft designers at NASA’s Jet Propulsion Laboratory. The primary engineering challenge of this mission was to design a three-axis stabilized dual-spinning spacecraft with the largest spinning flexible mesh reflector of any known spacecraft. This paper reports on the attitude control performance of this duel-spinning conicalscanning system during the first 18 months of science operations, and provides an overview of the Guidance, Navigation, and Control (GNC) subsystem performance for this climate monitoring asset.

Sung, Tina S.↗
NASA NTRS2020

NISAR flight feed passive antenna measurements

NISAR (NASA ISRO SAR, National Aeronautics and Space Administration, Indian Space Research Organization, Synthetic Aperture Radar) is an Earth science project currently in its final development phase at NASA Jet Propulsion Laboratory (JPL) and at ISRO. Due for launch in 2022 it will assess how our planet changes over time by measuring differences in the Earth’s solid surface due to factors like climate change, movement and melting of glaciers, earthquakes, land-slides, deforestation, agriculture and others. The enabling instrument for this mission is a dual band radar (L-band and S-band) that feeds a 12m deployable mesh reflector. This paper describes the measurement campaign of the L-band flight feed in its passive configuration. Further measurements will be done using the antenna with the active radar components but they are not part of this paper.

Harrell, Jefferson A.↗
NASA NTRS2022

NISAR Flight Feed Passive Antenna Measurements

NISAR (NASA ISRO SAR, National Aeronautics and Space Administration, Indian Space Research Organization, Synthetic Aperture Radar) is an Earth science project currently in its final development phase at NASA Jet Propulsion Laboratory (JPL) and at ISRO. Due for launch in 2022 it will assess how our planet changes over time by measuring differences in the Earth’s solid surface due to factors like climate change, movement and melting of glaciers, earthquakes, land-slides, deforestation, agriculture and others. The enabling instrument for this mission is a dual band radar (L-band and S-band) that feeds a 12m deployable mesh reflector. This paper describes the measurement campaign of the L-band flight feed in its passive configuration. Further measurements will be done using the antenna with the active radar components but they are not part of this paper.

Harrell, Jefferson A.↗
NASA NTRS2022

Evolution of the NISAR Feed Antenna Design due to Environmental Requirements

NISAR (NASA ISRO SAR, National Aeronautics and Space Administration, Indian Space Research Organization, Synthetic Aperture Radar) is an Earth science project currently in its final development phases at NASA Jet Propulsion Laboratory (JPL) and at ISRO. Due for launch in 2023 it will assess how our planet changes over time by measuring differences in the Earth’s solid surface due to factors like climate change, movement and melting of glaciers, earthquakes, land-slides, deforestation, agriculture and others. The enabling instrument for this mission is a dual band radar (L-Band and S-Band) that feeds a 12m deployable mesh reflector. Given the extreme accuracy needed to perform these measurements from Low Earth Orbit (LEO) some of the most stringent requirements were pushed onto the antenna subsystem to control phase and gain stability over time. In this paper we describe how environmental requirements affected the antenna design and what techniques were used to meet these requirements.

Vacchione, Joseph D.↗
NASA NTRS1993

Electrical performance of wire mesh for spacecraft deployable reflector antennas

Mobile satellite communications systems require large, high gain antennas at the spacecraft to minimize the antenna gain and power requirements for mobile user elements. The use of a deployable reflector antenna for these applications provides a lightweight system that can be compactly stowed prior to deployment on orbit. The mesh surface material is a critical component in the deployable reflector antenna design. The mesh is required to provide the desired electrical performance as well as the mechanical properties that are necessary to deploy and maintain the reflector surface on orbit. Of particular interest in multi-channel communications applications is the generation of Passive InterModulation (PIM) products at the reflector surface that can result in interference in the receive band. Wire mesh was specifically identified by some as having a high potential for PIM generation based solely on the existence of nonpermanent metal to metal contacts at the junctions that are inherent in the mesh design. There are a number of other factors, however, that reduce the likelihood of PIM occurring at the mesh reflector surface. Experimental data presented demonstrate that mesh PIM generation is not significant for typical applications. PIM and reflectivity performance of wire mesh composed of gold plated molybdenum wire in a tricot knit are described. This type of mesh was successfully used for the deployable Single Access Antennas of the Tracking and Data Relay Satellite System.

Turner, Greg↗
NASA NTRS1982

RF verification tasks underway at the Harris Corporation for multiple aperture reflector system

Mesh effects on gain and patterns and adjacent aperture coupling effects for "pie" and circular apertures are discussed. Wire effects for Harris model with Langley scale model results included for assessing D/lamda effects, and wire effects with adjacent aperture coupling were determined. Reflector surface distortion effects (pillows and manufacturing roughness) were studied.

Gutwein, T. A.↗
NASA NTRS1983

The effects of mesh reflecting surfaces upon radiometric measurements

Reflector antennas with mesh surfaces have been used in ground and space applications primarily for communication systems. How the requirements for mesh surface reflectors are different for microwave radiometric applications is indicated, a method of measuring the anticipated small dissipation losses of gold-plated mesh using a radiometer system is proposed.

Crosswell, W. F.↗
NASA NTRS1979

Surface accuracy measurement system deployable reflector antennas

Conceptual optical sensor configurations for measuring the surface deformations of large, deployable space antennas are described. These antennas include precision deployable reflectors up to 30 meters diameter and 1000 GHz frequency and mesh deployable reflectors up to 100 meters diameter and 30 GHz frequency. For each representative antenna configuration, the surface deformation sensor provides continuous, real-time measurements at a sufficient number of sample points to be compatible with active surface control. Moreover, the sensor system does not interfere with the mechanical or microwave characteristics of either the antenna surface or the feed. For the applications considered, the sensor system consists of a central receiver ring containing six to ten long focal length, angle measuring instruments, each viewing a dedicated set of bright point targets at the antenna. The targets, either light emitting diodes or illuminated retroreflectors, are modulated to eliminate errors from spurious backgrounds. Very preliminary performance estimates indicate that the sensor system, using commerical grade components, can produce a 20th to a 30th wavelength accuracy (3 sigma).

Neiswander, R. S.↗
NASA NTRS1983

Phased arrays for satellites and the TDRSS antennas

The design and performance of satellite phased-array systems are examined by considering several specific antennas built for spacecraft use. Particular consideration is given to: (1) the JARED (Jammer Reduction Antenna System) antenna, and adaptive phased array which can be used to null jammer signals while providing coverage to specific user areas; (2) the algorithm used in the JARED antenna; and (3) a technique that can be used to detect and locate jammers. The antennas used by the Tracking and Data Relay Satellite System (TDRSS) are then described. A significant aspect of the TDRSS is the multiple access antenna which is a 30-element phased array, providing a single steered beam on transmit and the ability to receive data from 20 simultaneous users. Also included on the TDRSS is a mesh deployable reflector and a C-band and K-band communications system.

Imbriale, W. A.↗