Engineering topics

Lazarus, Alan J.

Publications and source records attributed to Lazarus, Alan J..

10 records

NASA NTRS2005

Towards the Development of a Unified Distributed Date System for L1 Spacecraft

The purpose of this grant, 'Towards the Development of a Unified Distributed Data System for L1 Spacecraft', is to take the initial steps towards the development of a data distribution mechanism for making in-situ measurements more easily accessible to the scientific community. Our obligations as subcontractors to this grant are to add our Faraday Cup plasma data to this initial study and to contribute to the design of a general data distribution system. The year 1 objectives of the overall project as stated in the GSFC proposal are: 1) Both the rsync and Perl based data exchange tools will be fully developed and tested in our mixed, Unix, VMS, Windows and Mac OS X data service environment. Based on the performance comparisons, one will be selected and fully deployed. Continuous data exchange between all L1 solar wind monitors initiated. 2) Data version metadata will be agreed upon, fully documented, and deployed on our data sites. 3) The first version of the data description rules, encoded in a XML Schema, will be finalized. 4) Preliminary set of library routines will be collected, documentation standards and formats agreed on, and desirable routines that have not been implemented identified and assigned. 5) ViSBARD test site implemented to independently validate data mirroring procedures. The specific MIT tasks over the duration of this project are the following: a) implement mirroring service for WIND plasma data b) participate in XML Schema development c) contribute toward routine library.

Lazarus, Alan J.↗

NASA NTRS2002

MO and DA on the SWIE Instrument on the Wind Spacecraft

The construction of the Faraday Cup portion of the SWIE instrument on the Wind spacecraft, participation in Mission Operations, and Data Analysis (MO and DA) of observations of the solar wind has been supported by a sequence of grants. This 'final' Report represents work done on Mission Operations and Data Analysis for the Faraday Cup portion of the SWE. The work reported here was supported under NASA Grant NAG5-7359 (OSP 6701100) from June 1998 to October 2001. It should be noted that this work is continuing under NASA Grant NAG-10915, and therefore this report is 'final' only in the sense that the Grant has changed its number; a future report will cover the entire period of work. We have two types of obligations under these contracts: (1) To provide and assure the validity of "Key Parameters" which describe the basic properties of the solar wind on a daily basis. We have provided our 92 second observations daily via plots and parameters available from our Web site: http://web.mit.edu/space/www/wind/wind.html (2). To carry out scientific studies based on our observations. To document the extent of our research, we are including below a list of publications and presentations related to this project. The observations from Wind have made a major contribution to the study of the solar wind, and have every indication of continuing to do so.

Lazarus, Alan J.↗

NASA NTRS2001

Scientific Analysis of Data for the ISTP/SOLARMAX Programs

This Grant supplemented our work on data analysis from the Wind spacecraft which was one of the ISTRIA fleet of spacecraft. It was targeted at observations related to the time of solar maximum in 2000. The work we proposed to do under this grant included comparison of solar wind parameters obtained from different spacecraft in order to establish correlation lengths appropriate to the solar wind and also to compare parameters to explore solar cycle effects.

Lazarus, Alan J.↗

NASA NTRS1995

Radial evolution of the solar wind from IMP 8 to Voyager 2

Voyager 2 and Interplanetary Monitoring Platform (IMP) 8 data from 1977 through 1994 are presented and compared. Radial velocity and temperature structures remain intact over the distance from 1 to 43 AU, but density structures do not. Temperature and velocity changes are correlated and nearly in phase at 1 AU, but in the outer heliosphere temperature changes lead velocity changes by tens of days. Solar cycle variations are detected by both spacecraft, with minima in flux density and dynamic pressure near solar maxima. Differences between Voyager 2 and IMP 8 observations near the solar minimum in 1986-1987 are attributed to latitudinal gradients in solar wind properties. Solar rotation variations are often present even at 40 AU. The Voyager 2 temperature profile is best fit with a R(exp -0.49 +/- 0.01) decrease, much less steep than an adiabatic profile.

Richardson, John D.↗

NASA NTRS1995

Unusual locations of Earth's bow shock on September 24 - 25, 1987: Mach number effects

International Sun Earth Explorer 1 (ISEE 1) and Interplanetary Monitoring Platform 8 (IMP 8) data are used to identify 19 crossings of Earth's bow shock during a 30-hour period following 0000 UT on September 24, 1987. Apparent standoff distances for the shock are calculated for each crossing using two methods and the spacecraft location; one method assumes the average shock shape, while the other assumes a ram pressure-dependent shock shape. The shock's apparent standoff distance, normally approximately 14 R(sub E), is shown to increase from near 10 R(sub E) initially to near 19 R(sub E) during an 8-hour period, followed by an excursion to near 35 R(sub E) (where two IMP 8 shock crossings occur) and an eventual return to values smaller than 19 R(sub E). The Alfven M(sub A) and fast magnetosonic M(sub ms). Mach numbers remain above 2 and the number density above 4/cu cm for almost the entire period. Ram pressure effects produce the initial near-Earth shock location, whereas expansions and contractions of the bow shock due to low Mach number effects account, qualitatively and semiquantitatively, for the timing and existence of almost all the remaining ISEE crossings and both IMP 8 crossings. Significant quantitative differences exist between the apparent standoff distances for the shock crossings and those predicted using the observed plasma parameters and the standard model based on Spreiter et al.'s (1966) gasdynamic equation. These differences can be explained in terms of either a different dependence of the standoff distance on Mach number at low M(sub A) and M(sub ms), or variations in shock shape with M(sub A) and M(sub ms) (becoming increasingly "puffed up" with decreasing M(sub A) and M(sub ms), as expected theoretically), or by a combination of both effects.

Cairns, Iver H.↗

NASA NTRS1994

Solar wind oscillations with a 1.3 year period

The Interplanetary Monitoring Platform 8 (IMP-8) and Voyager 2 spacecraft have recently detected a very strong modulation in the solar wind speed with an approximately 1.3 year period. Combined with evidence from long-term auroral and magnetometer studies, this suggests that fundamental changes in the Sun occur on a roughly 1.3 year time scale.

Richardson, John D.↗

NASA NTRS1994

Voyager observations of O(+6) and other minor ions in the solar wind

The plasma science (PLS) experiments on the Voyager 1 and 2 spacecraft began making measurements of the solar wind shortly after the two launches in the fall of 1977. In reviewing the data obtained prior to the Jupiter encounters in 1979, we have found that the large dynamic range of the PLS instrument generally allows a clean separation of signatures of minor ions (about 2.5% of the time) during a single instrument scan in energy per charge. The minor ions, most notably O(+6), are well separated from the protons and alpha particles during times when the solar wind Mach number (ratio of streaming speed to thermal speed) is greater than approximately 15. During the Earth to Jupiter cruise we find that the average ratio of alpha particle number density to that of oxygen is 66 +/- 7 (Voyager 1) and 71 +/- 17 (Voyager 2). These values are consistent with the value 75 +/- 20 inferred from the Ion Composition Instrument on ISEE 3 during the period spanning 1978 and 1982. We have inferred an average coronal temperature of (1.7 +/- 0.1) x 10(exp 6) K based on the ratio of O(+7) to O(+6) number densities. Our observations cover a period of increasing solar activity. During this time we have found that the alpha particle to proton number density ratio is increasing with the solar cycle, the oxygen to proton ratio increases, and the alpha particle to oxygen ratio remains relatively constant in time.

Villanueva, Louis↗

NASA NTRS1993

Solar wind conditions in the outer heliosphere and the distance to the termination shock

The Plasma Science experiment on the Voyager 2 spacecraft has measured the properties of solar wind protons from 1 to 40.4 AU. We use these observations to discuss the probable location and motion of the termination shock of the solar wind. Assuming that the interstellar pressure is due to a 5 micro-G magnetic field draped over the upstream face of the heliopause, the radial variation of ram pressure implies that the termination shock will be located at an average distance near 89 AU. This distance scales inversely as the assumed field strength. There are also large variations in ram pressure on time scales of tens of days, due primarily to large variations in solar wind density at a given radius. Such rapid changes in the solar wind ram pressure can cause large perturbations in the location of the termination shock. We study the nonequilibrium location of the termination shock as it responds to these ram pressure changes. The results of this study suggest that the position of the termination shock can vary by as much as 10 AU in a single year, depending on the nature of variations in the ram pressure, and that multiple crossings of the termination shock by a given outer heliosphere spacecraft are likely. After the first crossing, such models of shock motion will be useful for predicting the timing of subsequent crossings.

Belcher, John W.↗

NASA NTRS1991

Magnetopause and cusp observations at Neptune

Plasma and magnetic field measurements in a subsolar cusp region of Neptune are compared with two current models of cusp regions, stemming from earth measurements: (1) a cusp region filled with stagnant plasma separated from the magnetosheath by a tangential discontinuity and (2) a mantle layer of dynamic plasma separated from the sheath by a rotational discontinuity. The plasma observations are more consistent with the mantle-layer interpretation. However, because of the particular trajectory of the Voyager 2 flyby, it was not possible to distinguish the mantle and the stagnant cusp models on geometrical grounds.

Szabo, Adam↗

NASA NTRS1988

IMP 7 (Explorer 47) trajectory, September 26, 1972 to September 25, 1978

The trajectory plots for IMP 7 (Explorer 47) are contained. For each orbit the trajectory is shown in five panels on two pages; each panel is a different representation or projection. The trajectory parameters were obtained from the multi-coordinate ephemeris (MCE) tapes supplied to IMP experimenters by the IMP project. The plots on the right hand pages use a geocentric, solar-ecliptic coordinate system. Distances are in units of earth radii. The plots on the left hand pages use geocentric, solar magnetospheric coordinates with distances in earth radii.

Milligan, Pamela A.↗