Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/spst/lrpg/mission_planning/leonids/Leonids_2001_Cooke_1.pdf Дата изменения: Wed Sep 11 18:10:29 2002 Дата индексирования: Sun Mar 2 09:53:53 2014 Кодировка: Поисковые слова: meteor shower

A publication of

The Orbital Debris Program Office
NASA Johnson Space Center Houston, Texas 77058 April 2002 Volume 7, Issue 2.

NEWS
Release of ORDEM2000
J.-C. Liou The new orbital debris engineering model ORDEM2000 was released by the NASA Orbital Debris Program Office earlier this year. The model is appropriate for engineering solutions requiring knowledge and estimate of the orbital debris environment (spatial density, flux, etc.) in the low Earth orbit region between 200 and 2000 km altitude. It can also be used as a benchmark for ground-based debris measurements and observations. The highlights of the new model include: (1) a large set of observational data (both in-situ and ground-based), covering the object size range from 10 µ m to 10 m, was incorporated into the ORDEM2000 debris database, (2) a new analytical technique was employed to convert observational data into debris population probability distribution functions - these functions then form the basis of debris populations, and (3) a finite element model was developed to process the debris populations to form the debris environment. In addition, a more capable input and output structure and a user-friendly Graphical User Interface (GUI) are also implemented in the model. ORDEM2000 has been subjected to a significant verification and validation effort. The new model has been tested thoroughly and compared with all available data. Overall, it provides a very good description of the current debris environment. The model is now being used for Space Shuttle and International Space St ation for debris risk assessments. ORDEM2000 is available at the Orbital Debris Program Office website at http://sn-callisto.jsc.nasa.gov/ model/modeling.html. v

The Leonid Storm of 2001
B. Cooke On the night of November 17-18 of this past year, the Leonid meteor shower reached storm level activity over the United States for the first time since 1966. To most, Mother Nature treated them to a spectacular sky show, with meteors appearing every few seconds at the first maximum near 10:30 UT (04:30 CST). To those of us involved in the forecasting and observing of the Leonids, the 2001 storm proved to be a strange mix of excitement and disappointment... It was exciting in that the forecasts proved to be reasonably accurate in terms of the level and duration of the activity and that, of the 6 observation sites manned by MSFC and University of Western Ontario personnel (Eglin AFB, Huntsville, Apache Point, Haleakala, Guam, and Ulan Baator, Mongolia), only Guam experienced cloudy weather, enabling the collection of data over the entire duration of the storm. The disappointment came from the real iz ations that all of the forecasts were wrong in some d etails (mine and P eter Brown's apparently fared the worst), and that a fair amount of work would be needed to locate manpower and funds to reduce the 2+ terabytes o f
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(Continued on page 2 ) (Continued on page 2) Figure 1. 2001 Leonid ZHR profile (IMO, January 2002).

Inside...
Reentry Survivability Analysis of the Upper Atmosphere Research Satellite (UARS)...... 2 Albedo Distributions of Debris ................................ ................................ ............. 4 Meeting Reports ................................ ................................ ................................ . 5
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The Orbital Debris Quarterly News

NEWS
The Leonid Storm of 2001, Continued
(Continued from page 1 )

video data collected by the observing teams. As depicted in figure 1, the 2001 Leonids had two major peaks; the first, mentioned above, reached a maximum Zenith Hourly Rate (ZHR) of around 1600 at 10:35 UT. According to the International Meteor Organization, it is bimodal in nature, with a secondary peak some 24 minutes later, at approximately the same level. The second and larger peak occurred over Asia, at approximately 18:15 UT. It reached a ZHR of 3400, close to the level of the 1999 storm, which peaked at 3700 Leonids per hour. However, unlike the brief outburst of 1999, the 2001 Leonids exhibited significantly elevated activity (ZHRs > 300) for over 12 hours, resulting in a much greater fluence; a current estimate would place it at approximately 4.5 times that of 1999, or about 7 Leonids km-2 down to mass of approximately 10 µg. This is in good agreement with the forecast fluence levels of 5 to 10 Leonids km-2. It is somewhat ironic that satellite operators devoted much more attention to the 1999 shower than the 2001 apparition, where the risk was roughly 5 times greater. While the forecasts did a good job of characterizing the length and overall characteristics of the 2001 Leonids, they fail in the "fine" details. In particular, forecasting the level of the maxima remains problematic, as a glance at figure 2 shows. The Brown/Cooke profile looks particularly disconcordant; this is due to the dy-

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Bill Cooke/MSFC - 11/01/2001

Figure 2. 2001 Leonid forecasts. namical model placing the 1799 stream closer to Earth, resulting in the peak at 13:00 UT, resulting in a much greater contribution to the ZHR profile. It is hoped that the forecasters will take a good look at the 2001 data and use it to revise their models, as storm level Leonid activity is once again projected for 2002. At Marshall, work is progressing in devising an automated method of reducing the video data, the results of which will be used in producing a revised 2002 Leonid forecast. v

Project Reviews
Reentry Survivability Analysis of the Upper Atmosphere Research Satellite (UARS)
W. C. Rochelle and J. J. Marichalar The National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) Upper Atmosphere Research Satellite (UARS), which was launched September 12, 1991 by the Space Shuttle STS-48, will be decommissioned in 2002-2003. It is currently planed to allow the spacecraft to reenter in an orbital decay mode. In accordance with NASA Policy Directive 8710.3, GSFC performed a reentry analysis of the UARS spacecraft using the NASA Lyndon B. Johnson Space Center (JSC) Debris Assessment Software (DAS). The GSFC DAS results showed the UARS spacecraft to be non-compliant with NASA Safety Standard 1740.14 Guideline 7-1, which requires the surviving debris of an uncontrolled spacecraft reentry to produce a risk to ground population no greater than 1:10,000. In response to the results, GSFC requested an analysis be performed using the higher-fidelity Object Reentry Survival Analysis Tool (ORSAT), developed by JSC and Lockheed Martin Space Operations (LMSO). The approximately 5670 kg UARS satellite is providing data on chemistry, dynamics, and energy balance above the Earth's troposphere and coupling between these processes and other atmosphere regions. It also measures ozone and chemical compounds that affect chemistry processes in the ozone layer. The UARS observatory consists of a standard Multi-mission Modular Spacecraft (MMS) coupled to an Instrument Module that includes ten science instruments and various mission-unique components. The starboard view of the UARS space, with the locations of some of the instruments, the MMS, and other elements, is shown in Fig. 1. The UARS will be decommissioned upon completion of its current Science Traceability Mission. There is not enough prop ellant on board or the spacecraft to reenter in a targeted (controlled) entry mode. Eventually the orbital decay of the UARS sp acecraft will cause it to reenter the Earth's atmosphere, resulting in break-up and demise of most of the spacecraft components. However, due to the mass, size, and material properties of some of the comp onents, there is an increased possibility of those components surviving the atmospheric reentry and posing a safety risk to the ground population. In the reentry analysis performed using ORSAT, entry interface for the UARS spacecraft was assumed to be 122 km, with initial break-up occurring at 78 km. This point is the
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