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Potentially Hazardous Asteroids (Read 4084 times)
Tony
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Potentially Hazardous Asteroids
08/22/07 at 14:36:35
 
Here's a simulation that includes 794 asteroids classified as PHAs.
http://orbitsimulator.com/gravity/simulations/PHA.gsim
 
If you run this from the Beta version, before you open it go to Preferences and change DoEvents Interval from 50 to 1, so your computer doesn't seem jumpy from the large amount of objects.
 
This screenshot shows Earth's crowded neighborhood.  This represents 1 year, from May 2006 to May 2007.  The frame is rotating with Earth's period to keep the Earth / Sun orientation constant.  The Sun is off the image towards the 9 o'clock position.  The asteroids that look like close calls aren't that close.  You can't see the z-axis in this screenshot.
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frankuitaalst
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Re: Potentially Hazardous Asteroids
Reply #1 - 08/24/07 at 11:06:28
 
Nice work ! I guess that you get the data from the NEA-Ephemerides site  a batch . I can't manage this batch type , as I never receive an answer from Nasa . So I have to download each body seperately .  
Is it possible to get a screenshot of the e-mail you use ?
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Tony
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Re: Potentially Hazardous Asteroids
Reply #2 - 08/24/07 at 11:25:53
 
I used the Horizons Automator program described here:
http://www.orbitsimulator.com/cgi-bin/yabb/YaBB.pl?num=1182042588
 
This simulation is very fun to play with.  I wanted to determine how often Earth gets hit by one of these, but it would take too long to directly run the simulation and count.  So I devised a new method.  I increased Earth's size to 100 Earth radii.  Now Earth will get hit 10,000 times as often as it otherwise would.  After running for several hundred years at time step 1024, from 2007 to 2754 I've recorded 46 hits.  This translates into the real-sized Earth being struck about every 50,000 years, assuming that the entire population of PHAs are 2500.  This estimated population varies widely from the web resources I've seen.  There are also varying opinions of how often Earth gets struck by a PHA, ranging from once every 1000 years to every 1000 centuries.  My finding is in rough agreement with the later, especially considering that I used the high-end estimate of the PHA population.
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frankuitaalst
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Re: Potentially Hazardous Asteroids
Reply #3 - 08/24/07 at 13:48:11
 
This sim is fantastic ! Looks like the milky way at first sight , sure if you view side on .
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frankuitaalst
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Re: Potentially Hazardous Asteroids
Reply #4 - 08/25/07 at 10:46:23
 
Heres a animated gif showing the approaches of the asteroids over a timespan of 22 years (2006-2029) .  
The shots are fixed to Earth( non rotating ) . On the average 5-8 asteroids appear in the screen width per year.  
I wonder what happens to the orbit of the moon in the year 2027 , as it is more elliptical than other years .  
Sim was run at about 4000 seconds.
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« Last Edit: 08/25/07 at 14:34:41 by frankuitaalst »  

AsteroidsGsim.gif
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Tony
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Re: Potentially Hazardous Asteroids
Reply #5 - 08/25/07 at 11:55:05
 
I think this is what you meant by the "Milky Way" view.
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frankuitaalst
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Re: Potentially Hazardous Asteroids
Reply #6 - 08/25/07 at 14:33:35
 
indeed !
BTW : I tried to simulate the 805 bodies in the above sim using the Picard Integrator.  
Doesn't work .  
The integrator works fine for a small amount of bodies , giving a high accurancy vs. speed , but if the number of bodies is high the execution speed is very low . I think the speed must be proportional to 1/n^3 .
F.i. 10 times more bodies reduces the speed with 1000 ; 20 times more bodies reduces speed with 8000.
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frankuitaalst
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Re: Potentially Hazardous Asteroids
Reply #7 - 09/23/07 at 10:30:46
 
I have a question about the .gsim files :  
If I want to add a new asteroid in the pha.gsim file , where can I find the exact date and time ?  
The file looks like this .
 
<GrAVITY>
<Distance Boxes>
</Distance Boxes>
<Orbit Boxes>
</Orbit Boxes>
<SData>
 1.52243884034745E-10  
 63319276800
 1  
 0  
 0  
 1  
 205  
False
False
 0  
-10000
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Tony
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Re: Potentially Hazardous Asteroids
Reply #8 - 09/23/07 at 13:32:39
 
In the .gsim file it's the 63319276800 number which represents number of seconds since a particular date (off the top of my head, I forget, but I think its 0/0/0000 00:00:00).  Then you need to do some math to turn it into a time and date.
 
Or... You can let Gravity Simulator do the math for you...
 
pause the simulation, then open pha.gsim and look at the "Date and Time" interface.
 
To get data on a new object from JPL Horizons, send an e-mail to: horizons@ssd.jpl.nasa.gov
Put the word job in the subject line and paste the following code into the body of the e-mail.  Make the necessary changes to the date and the COMMAND line (this example asks for data for 2007 SJ.  If you want, you can put several objects on the COMMAND line.  Put single quotes around them and seperated them by a space.  For example, '1950 DA' '1975 TT2'
 
When you get the return e-mail (one per object), locate this data:
 
 
Code:
!$$SOF
EMAIL_ADDR=''
START_TIME = '2007-May-09 00:00:00'
STOP_TIME = '2007-May-09 00:00:01'
TABLE_TYPE = 'Vector'
REF_PLANE = 'Ecliptic'
CENTER = '@010'
COMMAND= '2007 SJ'
!$$EOF
 


 
When you get the return e-mail (one per object), locate this data:
 
Code:
*******************************************************************************
$$SOE
2453921.502210648 = A.D. 2006-Jul-05 00:03:11.0000 (CT)
   3.357995996678807E+08  1.291245930306552E+08  3.188090989742249E+07
  -8.612795411778024E-01  1.423409492738280E+01  3.058029528049761E+00
   1.204766483547741E+03  3.611799054187939E+08  4.557969944277320E+00
$$EOE
*******************************************************************************
 


Highlight and copy the first 6 numbers after the date:
Code:
3.357995996678807E+08  1.291245930306552E+08  3.188090989742249E+07
-8.612795411778024E-01  1.423409492738280E+01  3.058029528049761E+00
 


Becareful not to include a leading space before the first number, and becareful not to miss a negative sign befor the first number.
 
To add a new object:
Objects > Create Objects
SMA: 1 AU (don't worry about getting it right.  Just give it anything that exceeds the radius of the Sun)
Name and color: give it a name and color
Press Create
 
Object > Edit Object
Choose your object and paste the highlighted data into the "X-Location" box.  It will parse the 6 numbers for you and fill in the rest of the boxes.
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frankuitaalst
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Re: Potentially Hazardous Asteroids
Reply #9 - 09/23/07 at 13:43:21
 
Object > Edit Object  
Choose your object and paste the highlighted data into the "X-Location" box.  It will parse the 6 numbers for you and fill in the rest of the boxes.

Waw ...impressive functionality !  
Many thanks for the reply . I intend to extend the PHA list with some recent discovered NEA .
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