SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Ten months of solar total irradiance data from the Solar Maximum Mission satellite have generated accurate frequencies, amplitudes and linewidths for individual about 5-min solar p-mode oscillations of low degree. The modes can be described as independent and chaotically excited oscillators, and provide no evidence for the fine structure taken to imply rapid internal rotation of the sun.
A review is given of the analysis of new observations of energetic particles and energetic secondary emissions obtained over the solar maxium (approx. 1980) by the Solar Maximum mission, Hinotori, the international Sun-Earth Explorer, Helios, Explorer satellites, and Voyager spacecraft. Solar energetic particle events observed in space, He(3)- rich events, solar gamma rays and neutrons, and solar neutrinos are discussed.
The Solar Maximum Mission (SMM) has operated since 1980 with a package of instruments that cover the solar spectrum from optical to gamma-ray wavelengths. While these instruments were not specifically designed to gather data on flare energetics, the SMM can measure many of the terms in the energy budget of a flare that have not been possible to determine in the past, especially when SMM data are combined with complementary data from other spacecraft and ground-based observatories, as was done as part of the SMY. During the recent SMM workshops on solar flares, the energetics of the gradual phase of several well-observed flares were investigated. The results of these studies are reviewed in this presentation. The advances that have resulted from the SMM flare energetics studies are discussed in context of what still must be done observationally and theoretically to define the complete energy budget of a flare.
Although solar activity prediction uncertainty normally dominates decay prediction error budget for near-Earth spacecraft, the effect of drag force modeling errors for given levels of solar activity needs to be considered. Two atmospheric density models, the modified Harris-Priester model and the Jacchia-Roberts model, to reproduce the decay histories of the Solar Mesosphere Explorer (SME) and Solar Maximum Mission (SMM) spacecraft in the 490- to 540-kilometer altitude range were analyzed. Historical solar activity data were used in the input to the density computations. For each spacecraft and atmospheric model, a drag scaling adjustment factor was determined for a high-solar-activity year, such that the observed annual decay in the mean semimajor axis was reproduced by an averaged variation-of-parameters (VOP) orbit propagation. The SME (SMM) calibration was performed using calendar year 1983 (1982). The resulting calibration factors differ by 20 to 40 percent from the predictions of the prelaunch ballistic coefficients. The orbit propagations for each spacecraft were extended to the middle of 1988 using the calibrated drag models. For the Jaccia-Roberts density model, the observed decay in the mean semimajor axis of SME (SMM) over the 4.5-year (5.5-year) predictive period was reproduced to within 1.5 (4.4) percent. The corresponding figure for the Harris-Priester model was 8.6 (20.6) percent. Detailed results and conclusions regarding the importance of accurate drag force modeling for lifetime predictions are presented.
The scientific objectives and implementation plans and priorities of the Space Science Board in areas of solar physics, heliospheric physics, magnetospheric physics, upper atmosphere physics, solar-terrestrial coupling, and comparative planetary studies are discussed and recommended programs are summarized. Accomplishments of Skylab, Solar Maximum Mission, Nimbus-7, and 11 other programs are highlighted. Detailed mission plans in areas of solar and heliospheric physics, plasma physics, and upper atmospheric physics are also described.
The solar irradiance variations resulting from sunspot deficits and facular excesses in emission have been calculated from 1969 through 1980. Agreement appears to exist between the calculations and the major features seen with the Nimbus 7 cavity pyrheliometer and with both the major and minor features detected by the Solar Maximum Mission ACRIM experiment. The 12-year irradiance variations calculated suggest a larger variance with increased solar activity, and little change in the average irradiance with solar activity. The largest excursions over these 12 years show a 0.4% variation. Removal of the activity influences upon solar irradiance during the numerous rocket experiments observing the solar constant may allow a better value for this quantity to be determined.
The Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission (SMM) spacecraft was used extensively to study the spatial morphology and time variability of solar active regions in the far UV (at approx. wavelength of 1370 A) since July 1985. The normal spatial resolution of UVSP observations in this 2nd-order mode is 10 sec., and the highest temporal resolution is 64 milliseconds. To make a full-field, 4 min. by 4 min. image this wavelength using 5 sec. raster steps takes about 3 minutes. UVSP can also make observations of the Sun at approx. wavelength of 2790 with 3 sec. spatial resolution when operated in its 1st-order mode; a full-field image at this wavelength (a so-called SNEW image) takes about 8 minutes. UVSP made thousands of observations (mostly in 2nd-order) of AR 5395 during its transit across the visible solar hemisphere (from 7 to 19 March, inclusive). During this period, UVSP's duty cycle for observing AR 5395 was roughly 40 percent, with the remaining 60 percent of the time being fairly evenly divided between aeronomy studies of the Earth's atmosphere and dead time due to Earth occultation of the Sun. UVSP observed many of the flares tagged to AR 5395, including 26 GOES M-level flares and 3 X-level flares, one of which produced so much UV emission that the safety software of UVSP turned off the detector to avoid damage due to saturation. Images and light curves of some of the more spectacular of the AR 5395 events are presented.
From February 1980 - February 1982, the Gamma Ray Spectrometer on the Solar Maximum Mission satellite observed the impulsive phases of sixteen western hemisphere flares that were associated with prompt solar proton events. Six of these flares had a detectable excess in the 4-8 MeV window and four others had detectable continuum emission above 300 keV. As indicated in earlier studies based on fewer events, a lack of correlation is found between the peak 10 MeV near-earth proton fluxes and prompt gamma-ray-line fluences. The two largest proton events in the sample did not have detectable emission above 300 keV. For the 9 December event, an upper limit for the density of the ion acceleration region of 8 billion/cu cm or less is obtained for an acceleration time constant of 1500 s.
User cost for three satellite services were assessed. The three missions are: advanced X-ray astrophysics facility (AXAF) revisit; upper atmosphere research satellite (UARS) revisit: and solar maximum mission (SMM) Earth return. Service scenarios for the missions to identify service equipment needs and on orbit usage were developed. The AXAF revisit is a service mission involving a contamination sensitive satellite. Following servicing and checkout, the spacecraft is redeployed from the orbiter. The total user charges for revisit missions is from 5 to 10% less than the cost to build and relaunch a replacement satellite. It is indicated that satellite servicing from the Orbiter is cost effective.
All work performed on the Ku-band rendezvous radar performance computer simulation model program since the release of the preliminary final report is summarized. Developments on the program fall into three distinct categories: (1) modifications to the existing Ku-band radar tracking performance computer model; (2) the addition of a highly accurate, nonrealtime search and acquisition performance computer model to the total software package developed on this program; and (3) development of radar cross section (RCS) computation models for three additional satellites. All changes in the tracking model involved improvements in the automatic gain control (AGC) and the radar signal strength (RSS) computer models. Although the search and acquisition computer models were developed under the auspices of the Hughes Aircraft Company Ku-Band Integrated Radar and Communications Subsystem program office, they have been supplied to NASA as part of the Ku-band radar performance comuter model package. Their purpose is to predict Ku-band acquisition performance for specific satellite targets on specific missions. The RCS models were developed for three satellites: the Long Duration Exposure Facility (LDEF) spacecraft, the Solar Maximum Mission (SMM) spacecraft, and the Space Telescopes.
The historical development of U.S. space technology is examined as a basis for future programs planned in the field of astrophysics, meteorological and land sciences, and planetary exploration. The background of the NASA space station project is described, as well as other current programs: Voyager II for Uranus and Neptune exploration, Galileo mission for sending probes into the Jovian atmosphere, Venus Radar Mapper, Mars Geochemistry and Climatology Orbiter, and the International Solar Polar mission. Recent advances in in-orbit assembly, refurbishment and repairs are discussed through the example of the Solar Maximum mission spacecraft repair in 1984 and the use of the RMS tool. The U.S. space observatory project with a 20-meter reflector telescope, currently in the early definition stage, is also discussed. Finally, the Soviet Salyut and Soyuz missions, together with the Soviet Union's study of long term flight conditions are mentioned as possible comparison with the NASA work.
The variations of the total solar irradiance is an important tool for studying the Sun, thanks to the development of very precise sensors such as the ACRIM instrument on board the Solar Maximum Mission. The largest variations of the total irradiance occur on time scales of a few days are caused by solar active regions, especially sunspots. Efforts were made to describe the active region effects on total and spectral irradiance.
The Solar Maximum Mission (SMM) spacecraft has provided high time resolution observational data regarding the soft X-ray emission from solar-flare plasma during 1980. The present investigation is concerned with the characteristics of a soft X-ray flare and the energetics of the impulsive phase on the basis of the data collected with the aid of two of the instruments on board the SMM, taking into account the Hard X-ray Burst Spectrometer (HXRBS) and the Bent Crystal Spectrometer (BCS). Attention is given to an analysis of soft X-ray flare spectra, the relative motion of the soft X-ray sources, the phenomenology of the soft X-ray flare, energy and mass transport during the impulsive phase, and energy deposition in the chromosphere during evaporation.
The scientific justification for an observing campaign to study the quantitative magnetic and plasma properties of coronal loops in active regions is presented. The SOHO (Solar and Heliospheric Observatory) instruments of primary relevance are CDS (Coronal Diagnostic Spectrometer), EIT, SUMER (Solar Ultraviolet Measurement of Emitted Radiation), and MDI. The primary ground based instruments would be the VLA (Very Large Array), the Owens Valley Radio Observatory, and vector and longitudinal field magnetographs. Similar campaigns have successfully been carried out with the Solar Maximum Mission x-ray polychromator and the Soft X-ray Imaging Sounding Rocket Payload (CoMStOC '87), the Goddard Solar EUV Rocket Telescope and Spectrograph, the Lockheed Solar Plasma Diagnostics Experiment rocket payload, and the Soft X-ray Telescope in Yohkoh (CoMStoc '92). The scientific payoff from such a campaign is discussed in light of the results from these previous campaigns.
Total solar irradiance observations by the Active Cavity Radiometer Irradiance Monitor (ACRIM) on the Solar Maximum Mission, the Nimbus 7/Earth Radiation Budget (ERB), the NASA/Earth Radiation Budget Satellite (ERBS), and NOAA 9/Earth Radiation Budget Experiment (ERBE) are combined to demonstrate the characteristics of the variation of solar luminosity over the solar cycles 21 and 22 between 1978 and 1990. Observations of solar Lyman Alpha and 10.7 MHz fluxes are used to demonstrate a total irradiance variability asymmetry relative to the maximum of solar activity.
Solar physics and the effects of emanations from the Sun on communications and Earth's weather and climate are discussed. Scientific interest in the solar system from the old Stone Age to the present is reviewed with particular emphasis on the objectives sought and information obtained by Explorer satellites, Pioneer satellites, Skylab, Helios, ISEE, the solar maximum mission, and the Dynamics Explorer. The goals of missions planned for the 1980's are discussed including those using space shuttle, Spacelab, the Solar Mesosphere Explorer, the solar optical telescope, the upper atmosphere research satellite, and the solar probe. The objectives of the international solar polar mission and of the Origin of Plasma in Earth's Neighborhood mission are also delineated. Other missions being considered are reviewed and the prospect of taming the fusion process to provide clean, harmless electrical energy like that obtained from the Sun is entertained.
The exact nature of the solar flare process is still somewhat a mystery. A key element to understanding flares if the relationship between the hard x rays emitted by the most energetic portions of the flare and the soft x rays from other areas and times. This relationship was studied by comparing hard x ray light curved from the Hard X-Ray Burst Spectrometer (HXRBS) with the soft x ray light curve and its derivation from the Bent Crystal Spectrometer (BCS) which is part of the X-Ray Polychrometer (XRP), these instruments being on the Solar Maximum Mission spacecraft (SMM). Data sample was taken from flares observed with the above instruments during 1980, the peak of the previous maximum of solar activity. Flares were chosen based on complete coverage of the event by several instruments. The HXRBS data covers the x ray spectrum from about 25 keV to about 440 keV in 15 spectral channels, while the BCS data used covers a region of the Spectrum around 3 angstroms including emission from the Ca XIX ion. Both sets of data were summed over their spectral ranges and plotted against time at a maximum time resolution of around 3 seconds. The most popular theory of flares holds that a beam of electrons produces the hard x rays by bremsstrahlung while the soft x rays are the thermal response to this energy deposition. The question is whether the rate of change of soft x ray emission might reflect the variability of the electron beam and hence the variability of the hard x rays. To address this, we took the time derivative of the soft x ray light curve and compared it to the hard flares, 12 of them showed very closed agreement between the soft x ray derivative and the hard x ray light curve. The other five did not show this behavior but were similar to each other in general soft x ray behavior. Efforts to determine basic differences between the two kinds of flares continue. In addition the behavior of soft x ray temperature of flares was examined.
Five flight instruments for high resolution X-ray spectroscopy are described. They include one- and two-dimensionally collimated solar rocket X-ray spectrometers, a 1-23 A X-ray polychromator for the Solar Maximum Mission, a collimated crystal spectrometer for cosmic X-ray studies, and a grating spectrometer/spectrograph with paraboloidal telescope for 10 to 50 A solar X-ray research. The discussion includes factors motivating design and use, examples of results for those already flown, and potential for future studies.