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At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Solar Cycle Predictions

Solar cycle predictions are needed to plan long-term space missions; just like weather predictions are needed to plan the launch. Fleets of satellites circle the Earth collecting many types of science data, protecting astronauts, and relaying information. All of these satellites are sensitive at some level to solar cycle effects. Predictions of drag on LEO spacecraft are one of the most important. Launching a satellite with less propellant can mean a higher orbit, but unanticipated solar activity and increased drag can make that a Pyrrhic victory as you consume the reduced propellant load more rapidly. Energetic events at the Sun can produce crippling radiation storms that endanger all assets in space. Solar cycle predictions also anticipate the shortwave emissions that cause degradation of solar panels. Testing solar dynamo theories by quantitative predictions of what will happen in 5-20 years is the next arena for solar cycle predictions. A summary and analysis of 75 predictions of the amplitude of the upcoming Solar Cycle 24 is presented. The current state of solar cycle predictions and some anticipations how those predictions could be made more accurate in the future will be discussed.

Pesnell, William Dean↗
NASA NTRS1989

Space Station Freedom solar array panels plasma interaction test facility

The Space Station Freedom Power System will make extensive use of photovoltaic (PV) power generation. The phase 1 power system consists of two PV power modules each capable of delivering 37.5 KW of conditioned power to the user. Each PV module consists of two solar arrays. Each solar array is made up of two solar blankets. Each solar blanket contains 82 PV panels. The PV power modules provide a 160 V nominal operating voltage. Previous research has shown that there are electrical interactions between a plasma environment and a photovoltaic power source. The interactions take two forms: parasitic current loss (occurs when the currect produced by the PV panel leaves at a high potential point and travels through the plasma to a lower potential point, effectively shorting that portion of the PV panel); and arcing (occurs when the PV panel electrically discharges into the plasma). The PV solar array panel plasma interaction test was conceived to evaluate the effects of these interactions on the Space Station Freedom type PV panels as well as to conduct further research. The test article consists of two active solar array panels in series. Each panel consists of two hundred 8 cm x 8 cm silicon solar cells. The test requirements dictated specifications in the following areas: plasma environment/plasma sheath; outgassing; thermal requirements; solar simulation; and data collection requirements.

Martin, Donald F.↗
NASA NTRS1991

Large-scale solar and heliospheric magnetic fields

The magnetic structure of the extended solar corona varies with the changing photospheric field during the solar cycle. A simple potential model of the corona using solar surface observations from 1976 to the present shows how the large-scale coronal field evolves over more than a solar activity cycle. These predictions match well with large stable structures inferred from measurements of coronal electron density and the IMF, though dynamic changes are poorly modeled. The sun's polar field was about 25 stronger at solar minimum in 1986 than in 1976; the heliospheric current sheet was also flatter. In Cycle 21 the coronal and photospheric large-scale long-lived field patterns rotated every 26.9 days in the northern hemisphere; the southern field rotated every 28 days. Similar periods have been present in the IMF and in the occurrence of solar flares during the last several solar cycles.

Hoeksema, J. Todd↗
DOE OSTI2017

Preparation of morphology-controlled TiO{sub 2} nanocrystals for the excellent photocatalytic activity under simulated solar irradiation

Graphical abstract: Morphology-controlled TiO{sub 2} nanocrystals with excellent photocatalytic activity under simulated solar irradiation were successfully synthesized. - Highlights: • TiO{sub 2} nanocrystals (NCs) with different morphologies were synthesized. • The growth mechanism of morphology-controlled TiO{sub 2} NCs was proposed. • The core-shell structured TiO{sub 2} NCs (co-TiO{sub 2}) had a narrow band gap (2.67 eV). • The co-TiO{sub 2} NCs possessed excellent photocatalytic activity and recyclability. - Abstract: A simple synthetic approach based on solvothermal technique and hydrogenation was developed for preparation of TiO{sub 2} nanocrystals with different morphologies such as elongated rhombic, dog-bone, oval and core-shell structured oval. The effect of oleic acid (OA) and oleylamine (OM) as two capping surfactants on the growth of TiO{sub 2} nanocrystals was investigated. The physicochemical properties of the obtained samples were characterized by various techniques including TEM, XRD, UV–vis absorption, Raman, XPS, BET, PL and photocurrent measurement. In photodegradation of RhB under simulated solar irradiation, the oval-shaped TiO{sub 2} nanocrystals with core-shell structure (co-TiO{sub 2}) was superior to other TiO{sub 2} nanocrystals in catalytic activity. Moreover, the co-TiO{sub 2} nanocrystals exhibited well recyclability during multiple photocatalytic tests. These excellent properties of co-TiO{sub 2} were attributed to its special structure, including lattice-disordered surface layer and well-crystallized lattice core, and narrow band gap (2.67 eV).

36 MATERIALS SCIENCE↗
DOE OSTI2014

Spatiotemporal organization of energy release events in the quiet solar corona

Using data from the STEREO and SOHO spacecraft, we show that temporal organization of energy release events in the quiet solar corona is close to random, in contrast to the clustered behavior of flaring times in solar active regions. The locations of the quiet-Sun events follow the meso- and supergranulation pattern of the underling photosphere. Together with earlier reports of the scale-free event size statistics, our findings suggest that quiet solar regions responsible for bulk coronal heating operate in a driven self-organized critical state, possibly involving long-range Alfvénic interactions.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Solar flares and avalanches in driven dissipative systems

The contention of Lu and Hamilton (1991) that the energy release process in solar flares can be understood as avalanches of many small reconnection events is further developed. The dynamics of the complex magnetized plasma of solar active regions is modeled with a simple driven dissipative system, consisting of a vector field with local instabilities that cause rapid diffusion of the field. It is argued that the avalanches in this model are analogous to solar flares. The distributions of avalanches in this model are compared with the solar flare frequency distributions obtained from ISEE 3/ICE satellite observations. Quantitative agreement is found with the energy, peak luminosity, and duration distributions over four orders of magnitude in flare energy, from the largest flares down to the completeness limit of the observations. It is predicted that the power-law solar flare frequency distributions will be found to continue downward with the same logarithmic slopes to an energy of about 3 x 10 exp 25 ergs and duration of about 0.3 s, with deviations from power-law behavior below these values.

Lu, Edward T.↗
NASA NTRS2009

Predicting the Sunspot Cycle

The 11-year sunspot cycle was discovered by an amateur astronomer in 1844. Visual and photographic observations of sunspots have been made by both amateurs and professionals over the last 400 years. These observations provide key statistical information about the sunspot cycle that do allow for predictions of future activity. However, sunspots and the sunspot cycle are magnetic in nature. For the last 100 years these magnetic measurements have been acquired and used exclusively by professional astronomers to gain new information about the nature of the solar activity cycle. Recently, magnetic dynamo models have evolved to the stage where they can assimilate past data and provide predictions. With the advent of the Internet and open data policies, amateurs now have equal access to the same data used by professionals and equal opportunities to contribute (but, alas, without pay). This talk will describe some of the more useful prediction techniques and reveal what they say about the intensity of the upcoming sunspot cycle.

Hathaway, David H.↗
NASA NTRS2003

Analysis of a Radiation Model of the Shuttle Space Suit

The extravehicular activity (EVA) required to assemble the International Space Station (ISS) will take approximately 1500 hours with 400 hours of EVA per year in operations and maintenance. With the Space Station at an inclination of 51.6 deg the radiation environment is highly variable with solar activity being of great concern. Thus, it is important to study the dose gradients about the body during an EVA to help determine the cancer risk associated with the different environments the ISS will encounter. In this paper we are concerned only with the trapped radiation (electrons and protons). Two different scenarios are looked at: the first is the quiet geomagnetic periods in low Earth orbit (LEO) and the second is during a large solar particle event in the deep space environment. This study includes a description of how the space suit's computer aided design (CAD) model was developed along with a description of the human model. Also included is a brief description of the transport codes used to determine the total integrated dose at several locations within the body. Finally, the results of the transport codes when applied to the space suit and human model and a brief description of the results are presented.

Anderson, Brooke M.↗
NASA NTRS1977

On three-dimensional reconstruction of optically thin solar emission sources

Calculations are given for constructing the three dimensional distribution of optically thin EUV emission sources associated with solar active regions, from two dimensional observations (projections) recorded by the spectroheliograph on the OSO 7 satellite. The relation of the method to other image reconstruction methods is briefly discussed as well as the special requirements imposed in the solar case such as a knowledge of the true solar rotation function. A useful correlation criterion for establishing the physical validity of solutions is given.

Kastner, S. O.↗
NASA NTRS1983

Observations of hydromagnetic turbulence in the solar wind

MHD turbulence is studied by analyzing magnetic field and plasma observations from Helios-1 and -2 at minimum solar activity. The steady conditions in the plasma flows and the magnetic field sector structure in 1975/1976 facilitate an investigation of the radial evolution of the turbulence from 0.29 to 1AU. In high speed streams the fluctuations in the solar wind velocity v and the magnetic field b are highly correlated (the correction coefficient almost being one), which indicates that the turbulence is mainly Alfvenic in high speed plasma. While some general fluctuation properties remain essentially unchanged from 0.29 to 1AU, power spectral analysis reveals a different frequency composition of the Alfvenic turbulence at different heliocentric distances. At 0.3AU much more 'high' frequency fluctuations contribute to the total power in the magnetic field and velocity fluctuations than at 1AU. The contributions of field magnitude fluctuations are found to be distance and frequency dependent. Magnetic field spectra with an extended frequency range up to 470Hz show certain frequency bands, where the steepness of the spectra is independent of the helicocentric distance.

Denskat, K. U.↗
NASA NTRS1990

NOAA/TIROS and GOES Observations of Galactic and Solar Cosmic Rays over a Solar Cycle

Correlations between solar activity and atmospheric processes have been investigated for more than 30 years, and the reality of the strong correlations found has been well accepted. However, it remains problematic to establish mechanisms capable of coupling the physical manifestations of solar variability to the lower atmosphere. There has been to date a lack of long-term satellite measurements of particles of sufficient energy to penetrate the Earth's atmosphere. The NOAA Space Environment Laboratory has maintained energetic particle detectors on board the NOAA/TIROS and GOES series of satellites. These instruments monitor the flux of energetic protons to energies greater than about 800 MeV. Measurements of particles above 350 MeV began October 1978, and continue to date. The instruments are briefly described, along with the current program to reduce the data. The goal is to provide a data base that will help to assess the significance of variations of atmospheric and ionospheric properties due to energetic particle precipitation.

Sauer, Herbert H.↗
NASA NTRS2000

Natural Hazards of the Space Environment

Spacecraft in Low Earth Orbit (LEO) are subject to numerous environmental hazards. Here I'll briefly discuss three environment factors that pose acute threats to the survival of spacecraft systems and crew: atmospheric drag, impacts by meteoroids and orbital debris, and ionizing radiation. Atmospheric drag continuously opposes the orbital motion of a satellite, causing the orbit to decay. This decay will lead to reentry if not countered by reboost maneuvers. Orbital debris is a by-product of man's activities in space, and consists of objects ranging in size from miniscule paint chips to spent rocket stages and dead satellites. Ionizing radiation experienced in LEO has several components: geomagnetically trapped protons and electrons (Van Allen belts); energetic solar particles; galactic cosmic rays; and albedo neutrons. These particles can have several types of prompt harmful effects on equipment and crew, from single-event upsets, latchup, and burnout of electronics, to lethal doses to crew.All three types of prompt threat show some dependence on the solar activity cycle. Atmospheric drag mitigation and large debris avoidance require propulsive maneuvers. M/OD and ionizing radiation require some form of shielding for crew and sensitive equipment. Limiting exposure time is a mitigation technique for ionizing radiation and meteor streams.

Evans, Steven W.↗
NASA NTRS1993

The magnetic state of the lower ionosphere during Pioneer Venus entry phase

During the entry phase of the Pioneer Venus Orbiter (PVO), defined as that period at the end of mission in 1992 when the periapsis fell below 185 km, the magnetometer made repeated measurements throughout the post midnight ionosphere until about 0430 LT. In this region the magnetic field is generally stronger at comparable altitudes than it was earlier at times of higher solar activity. This increase combined with a decrease in electron density causes the ratio of the magnetic pressure to thermal pressure to approach unity at altitudes above 200 km, whereas it was much lower than unity at these altitudes during solar maximum. From 160-200 km the magnetic field pressure exceeds that of the ionospheric plasma quite unlike the usual conditions seen at the beginning of the mission. At lowest altitudes below 150 km, however, the field becomes weaker and hence no evidence for a planetary magnetic field is found.

Russell, C. T.↗
NASA NTRS1993

The Magnetic State of the Lower Ionosphere During Pioneer Venus Entry Phase

During the entry phase of the Pioneer Venus Orbiter, defined as that period at the end of mission in 1992 when the periapsis fell below 185 km, the magnetometer made repeated measurements throughout the post midnight ionosphere until about 0430 LT. In this region the magnetic field is generally stronger at comparable altitudes than it was earlier at times of higher solar activity. This increase combined with a decrease in electron density causes the ratio of the magnetic pressure to thermal pressure to approach unity at altitudes above 200 km, whereas it was much lower than unity at these altitudes during solar maximum. From 160-200 km the magnetic field pressure exceeds that of the ionospheric plasma quite unlike the usual conditions seen at the beginning of the mission. At lowest altitudes below 150 km, however, the field becomes weaker and hence no evidence for a planetary magnetic field is found.

Russell, C. T.↗
NASA NTRSDate not supplied

Shielding Considerations for CubeSat Structures During Solar Maximum

The purpose of this lessons learned is to communicate the utility of shielding in small spacecraft planning for the support of mission assurance and reliability. Numerous SmallSats have been flying in polar low earth orbit for scientific, communications, technology demonstrations, and imaging with academic, commercial, and government interests. Shielding has been part of mission assurance and reliability from the advent of long duration spacecraft missions. The Shields-1 CubeSat has been operating in polar low earth orbit since 16 December 2018 with atomic number (Z)-grade radiation shielding and demonstrates shielding effectiveness. Shields-1 has collected a representative example of solar minimum data in 2019 with 8 Teledyne dosimeters over varying shielding effectiveness. It serves as current experimental data and has been compared with NOVICE Shielding estimates using the AP8 –AE8 trapped radiation model with the Shields-1 CAD and generic CubeSat 3 unit (U) models. Using NOVICE model radiation analysis coding, the shielding effectiveness's, based on a generic CubeSat 3U structure with 4 electronic boards, were estimated for aluminum wall thicknesses ranging from 0.204 cmto4.44 cm (0.550 g/cm2–12.0 g/cm2) thick aluminum. For modeled polar orbiting spacecraft, solar maximum total ionizing dose (TID)increases by nearly a magnitude for thin-walled aluminum 0.550g/cm2-0.686 g/cm2(0.204 cm –0.254 cm) typical CubeSat structures. The shielding effectiveness by NOVICE Sigma estimates, which is a shielding sphere approximation around a detector, showed a linear relationship with wall thickness, which increased over the wall thickness by a ratio of 1.43 determined by linear regression analysis. Using NOVICE Adjoint Monte-Carlo Modeling of solar minimum and solar maximum with the inclusion of a worst-case solar particle event over a one year mission without geomagnetic shielding, the TID for minimum and maximum conditions for a generic 3U with a wall thickness of 0.254 cm is 158 RAD and 1540 RAD, respectively. The modeled total solar maximum TID is over estimated, because at low orbital latitudes a spacecraft will have shielding from Earth's magnetic field. However, TID will still be significant at high latitudes over the poles, where a spacecraft is exposed in a solar particle event. In contrast, to a thin walled generic 3U CubeSat, Shields-1 electronics enclosure has a shielding effectiveness of 21.3 g/cm2from NOVICE Sigma modeling and is expected to show reduced total ionizing dose increases during the present active Solar Cycle 25 period. Because solar particle events during solar maximum increase TID on electronic parts with thin-walled shielding in short periods of time, it is a mission assurance and reliability consideration on the spacecraft’s mission value versus adding shielding for risk reduction of premature spacecraft or instrument payload loss. Since the volumes of many instruments and system electronics have reduced with small spacecraft, shielding material costs and weight penalties have diminished. A small spacecraft project budget and schedule may limit traditional radiation-hardened part use and radiation testing requirements, where shielding can contribute to mission assurance and reliability with reduced costs.

Shields-1↗
DOE OSTI2015

DOES THE VARIATION OF THE SOLAR INTRA-NETWORK HORIZONTAL FIELD FOLLOW THE SUNSPOT CYCLE?

The ubiquitousness of the solar inter-network horizontal magnetic field has been revealed by space-borne observations with high spatial resolution and polarization sensitivity. However, no consensus has been achieved on the origin of the horizontal field among solar physicists. For a better understanding, in this study, we analyze the cyclic variation of the inter-network horizontal field by using the spectro-polarimeter observations provided by the Solar Optical Telescope on board Hinode, covering the interval from 2008 April to 2015 February. The method of wavelength integration is adopted to achieve a high signal-to-noise ratio. It is found that from 2008 to 2015 the inter-network horizontal field does not vary when solar activity increases, and the average flux density of the inter-network horizontal field is 87 ± 1 G, In addition, the imbalance between horizontal and vertical fields also keeps invariant within the scope of deviation, i.e., 8.7 ± 0.5, from the solar minimum to maximum of solar cycle 24. This result confirms that the inter-network horizontal field is independent of the sunspot cycle. The revelation favors the idea that a local dynamo is creating and maintaining the solar inter-network horizontal field.

79 ASTRONOMY AND ASTROPHYSICS↗