The Leonid
Fluence Calculator has been updated to incorporate results from 1997 observations of the
Leonids. In particular, the mass index has been changed to 1.8, the cutoff mass has been
lowered to 5x10-8 grams, and the shower duration has been adjusted so that the
ZHR is 0.5 maximum one hour from the peak. The new changes give results that match the
1966 Pegasus satellite observations to better than 20%. If you have version 1.0b, you only
need to replace the eol.exe file (located in the Leonids directory) with a new one.
Otherwise, you need to uninstall your current program and obtain the new binary as before
(you DO NOT need to download the Sun JRE again).
To get the new eol.exe, please contact Sopo Yung at sopo.yung@msfc.nasa.gov.
I have also just completed a paper describing the physics behind the program.
Introduction:
Very strong Leonid meteor showers are expected to occur in November of 1998, 1999, and perhaps 2001 as a result of the recent passage of the generating comet, Tempel-Tuttle. These showers consist of extremely high velocity meteoroids which may produce mechanical damage due to impact and, more importantly, electromagnetically induced damage due to plasma arcs. The consensus opinion of the technical community is that the integrated fluence of each shower will probably be less than the yearly fluence of high speed meteoroids. However, the situation is very poorly defined and it is possible that the actual fluence will be much greater. Given this uncertainty and the high public visibility of these events, it is prudent to plan operations for science missions and technology demonstrations that will mitigate the environment effects.
Mitigation efforts should be planned on a case by case basis with a view toward minimizing mission risk, loss of science, and operations costs. Systems with robust designs from meteoroid impact and spacecraft charging, electromagnetic interference points of view should experience little difficulty. Most likely problem areas include:
- Low inclination, low Earth orbit satellites designed for a benign plasma environment.
- Spacecraft with high surface electric potentials.
- Spacecraft operating in the vicinity of the L1 point.
Note that the high speed meteoroids comprise only a small fraction of the normal environment, so a minimum of 10 years flight experience is needed to demonstrate robustness on that basis alone.
Description:
The MSFC Leonid Storm Fluence Calculator is a JAVA/FORTRAN-based tool designed to help the satellite engineer or operator evaluate the vulnerability of existing or future satellites to the upcoming Leonid meteor storms. Given the orbital elements of the satellite on the day of the storm, the program is capable of calculating the total impacting Leonid fluence for meteoroids above 5x10-8 grams or the penetrating fluence, given the equivalent thickness of the spacecraft's skin in centimeters of aluminum. It does this for surfaces of the spacecraft facing in the following directions: spacecraft ram and wake, radially towards and away from Earth, towards the north and south poles of the orbital plane, and sunward. To complete the information, the application also calculates the percentage of time that the spacecraft is shielded from the Leonids by the Earth.
System Requirements:
It was our hope that the use of JAVA would enable the use of this tool on any platform capable of running Internet Explorer or Netscape Navigator. However, the differences in the various JAVA virtual machines and runtime environments have forced us to make the initial release for Sun SPARCstations running Solaris, Windows 95/NT or OS/2 4.0 users only. We are currently working on a Macintosh port. Running the code locally requires a Pentium 100 or higher, though users of 486-based computers can still make use of the tool by the Remote Compute button, provided they have an Internet connection .
Installation Instructions (Windows 95 or NT, others see Getting Help below):
Obtain application forms from http://see.msfc.nasa.gov/ModelDB/ModelDB.htm.
Running the Application:
After installation, the application may be executed by selecting the NASA-MSFC Leonids Fluence Calculator group from the Programs section of the Windows 95 Start menu and then choosing Leonids.bat. This will invoke a DOS batch file, which will start the application. The user need only fill in the information on the left-hand side of the window and then click on the Local Compute or Remote Compute button. After a few seconds (10 to 30, depending on the speed of the computer), the results will be returned and displayed. The bar chart and the text box at the upper right display the fluences (number of Leonids per m2) striking or penetrating each spacecraft surface, whereas the circular plot in the middle graphically depicts the percentage of time that the spacecraft is shielded from the Leonids by the Earth. A sample run is shown in the picture below...
Usage Notes:
- It is HIGHLY recommended that you install the application to the recommended default directory. If you do not, then the file Leonids.bat will have to be edited to reflect the location of the installed program.
- The default value of the Predicted ZHR is the current best estimate for the 1998 Leonid storm.
- To get the total Leonid fluence, set the skin thickness to 0 cm.
- The values of the fluences in the upper-right text box may be copied to the clipboard by highlighting them and pressing Ctrl-c. These may then be pasted into other Windows applications by the Paste item under the Edit menu, or by pressing Ctrl-v.
- It is recommended that the user check this page frequently, as we will be updating the FORTRAN code to reflect the latest information concerning the Leonids.
Known Bugs:
1) The Uninstall script assumes that your windows directory is located on C: drive. If not, you must perform the following before attempting to uninstall the calculator:
- Go to your Windows directory
- Copy the jre.exe file to java.exe (Do not rename it!)
This should allow you to uninstall the application.
Getting Help:
Help may be obtained by sending e-mail to William.J.Cook@nasa.gov.