On the effect of considering more realistic particle shape and mass parameters in MMOD risk assessments

One of the primary mission risks tracked in the development of all spacecraft is that due to micro-meteoroids and orbital debris (MMOD). Both types of particles, especially those larger than 0.1 mm in diameter, contain sufficient kinetic energy due to their combined mass and velocities to cause serious damage to crew members and spacecraft. The process used to assess MMOD risk consists of three elements: environment, damage prediction, and damage tolerance. Orbital debris risk assessments for the Orion vehicle, as well as the Shuttle, Space Station and other satellites use ballistic limit equations (BLEs) that have been developed using high speed impact test data and results from numerical simulations that have used spherical projectiles. However, spheres are not expected to be a common shape for orbital debris; rather, orbital debris fragments might be better represented by other regular or irregular solids. In this paper we examine the general construction of NASA’s current orbital debris (OD) model, explore the potential variations in orbital debris mass and shape that are possible when using particle characteristic length to define particle size (instead of assuming spherical particles), and, considering specifically the Orion vehicle, perform an orbital debris risk sensitivity study taking into account variations in particle mass and shape as noted above. While the results of the work performed for this study are preliminary, they do show that continuing to use aluminum spheres in spacecraft risk assessments could result in an over-design of its MMOD protection systems. In such a case, the spacecraft could be heavier than needed, could cost more than needed, and could cost more to put into orbit than needed. The results obtained in this study also show the need to incorporate effects of mass and shape in mission risk assessment prior to first flight of any spacecraft as well as the need to continue to develop/refine BLEs so that they more accurately reflect the shape and material density variations inherent to the actual debris environment.     

Normalized ionization yield function for various nuclei obtained with full Monte Carlo simulations

Several recent results important for production of ion pairs in the Earth atmosphere by various primary cosmic ray nuclei are presented. The direct ionization by various primary cosmic ray nuclei is explicitly obtained. The longitudinal profile of atmospheric cascades is sensitive to the energy and mass (charge) of the primary particle. In this study different cosmic ray nuclei are considered as primaries, namely Helium, Oxygen and Iron nuclei. The cosmic ray induced ionization is obtained on the basis of CORSIKA 6.52 code simulations using FLUKA 2006 and QGSJET II hadronic interaction models. The energy of the primary particles is normalized to GeV per nucleon. In addition, the ionization yield function Y is normalized as ion pair production per nucleon. The obtained ionization yield functions Y for various primaries are compared. The presented results and their application are discussed.     

Ionization effect of solar protons in the Earth atmosphere – Case study of the 20 January 2005 SEP event

The cosmic ray ground level enhancement on January 20, 2005 is among the largest recorded events in the history of cosmic ray measurements. The solar protons of MeV energies cause an excess of ionization in the atmosphere, specifically over polar caps following major solar disturbances. The ionization effect in the Earth atmosphere is obtained for various latitudes on the basis of solar proton energy spectra, reconstructed from GOES 11 measurements and subsequent full Monte Carlo simulation of cosmic ray induced atmospheric cascade. The estimation of ionization rates is based on a numerical model for cosmic ray induced ionization. The evolution of atmospheric cascade is performed with the CORSIKA 6.52 code using FLUKA 2006b and QGSJET II hadron interaction models. The atmospheric ion rate ionization is explicitly obtained for 40°N, 60°N and 80°N latitudes. The time evolution of obtained ion rates is presented. It is demonstrated that ionization effect is negative for 40°N and small for 60°N, because of accompanying Forbush decrease. The ionization effect is significant only in sub-polar and polar atmosphere during the major ground level enhancement of 20 January 2005.     

Investigation into impact of tropical cyclones on the ionosphere using GPS sounding and NCEP/NCAR Reanalysis data

Ionospheric response to tropical cyclones (TCs) was estimated experimentally on the example of three powerful cyclones – KATRINA (23–31 August 2005), RITA (18–26 September 2005), and WILMA (15–25 October 2005). These TCs were active near the USA Atlantic coast. Investigation was based on Total Electron Content (TEC) data from the international network of two-frequency ground-based GPS receivers and the NCEP/NCAR Reanalysis data. We studied the spatial–temporal dynamics of wave TEC disturbances over two periods of ranges (02–20 min and 20–60 min). To select the ionospheric disturbances which were most likely to be associated with the cyclones, maps of TEC disturbances were compared with those of meteorological parameters.     

A feasibility study for the detection of the diurnal variation of tropospheric NO2 over Tokyo from a geostationary orbit

We have conducted a feasibility study for the geostationary monitoring of the diurnal variation of tropospheric NO₂ over Tokyo. Using NO₂ fields from a chemical transport model, synthetic spectra were created by a radiative transfer model, SCIATRAN, for summer and winter cases. We then performed a Differential Optical Absorption Spectroscopy (DOAS) analysis to retrieve NO₂ slant column densities (SCDs), and after converting SCDs into vertical column densities (VCDs), we estimated the precision of the retrieved VCDs. The simulation showed that signal-to-noise ratio (SNR) ? 500 is needed to detect the diurnal variation and that SNR ? 1000 is needed to observe the local minimum occurring in the early afternoon (LT13–14) in summer. In winter, the detection of the diurnal variation during LT08–15 needs SNR ? 500, and SNR ? 1000 is needed if early morning (LT07) and early evening (LT16) are included. The currently discussed sensor specification for the Japanese geostationary satellite project, GMAP-Asia, which has a horizontal resolution of 10 km and a temporal resolution of 1hr, has demonstrated the performance of a precision of several percent, which is approximately corresponding to SNR = 1000–2000 during daytime and SNR ? 500 in the morning and evening. We also discuss possible biases caused by the temperature dependence of the absorption cross section utilized in the DOAS retrieval, and the effect of uncertainties of surface albedo and clouds on the estimation of precisions.     

Seasonal variation of surface refractivity over Nigeria

The seasonal variation of surface refractivity over Nigeria was studied using two years in-situ meteorological data from eight locations over Nigeria. The result shows that the surface refractivity generally has higher value during rainy season than dry season at all location studied. The results also show that the value of surface refractivity increases from arid region in the north to the coastal area in south. The results also show that local meteorology plays a very important role in refractivity variation.     

Pre-storm behaviour of NmF2 and TEC (GPS) over equatorial and low latitude stations in the Indian sector

The pre-storm behavior of NmF₂ and TEC over an equatorial station, Trivandrum (8.47°N, 76.91°E, dip 0.6°S) and a low latitude station, Waltair (17.7°N,83.3°E, dip 20°N) has been studied for a total of 18 strong geomagnetic storms with DST ? −100 nT. The simultaneous measurements of GPS-TEC and NmF₂ over Trivandrum and Waltair during the period 2000–2005 have been considered for the present study. It is found that there is a substantial increase in NmF₂ and TEC before the onset of the storm over Waltair, while the increase is not present at Trivandrum. The origin of pre-storm enhancements in electron density still remains unresolved owing to several conditions in their potential sources and occurrence mechanisms. In the present study an attempt is made to identify the possible mechanisms responsible for such enhancements in electron density of the F-region.     

Intelsat's next generation satellite for the Americas

In order to meet the growing demand for high performance C- and Ku-Band services in the Americas, INTELSAT contracted with Astrium in February 2000 to procure a high capacity communications spacecraft for its 310°E operational location. The spacecraft platform is based on Astrium's next generation platform, the Eurostar 3000. Several new technologies such as integrated Data Handling System, Plasma Propulsion System, etc. are integral features of this platform. The communication payload comprises 36 C-Band and 20 high power Ku-Band transponders. The beam coverages are tailored for the 310°E orbital location and are implemented using a hybrid shaped antenna design approach, where multiple C-Band coverages are generated from a single shaped reflector utilizing a pair of Tx/Rx feed horns for each coverage. The Ku-Band coverages are generated by the classical dual Gregorian shaped reflector antenna design approach. With a total dry mass on the order of 2650 kg and a separated launch mass of 5400 kg, the spacecraft is compatible with most of the available launch vehicles providing mission life of greater than 13 years. The paper will provide technical details of the spacecraft.