From: vince@offshore.ai (Vincent Cate)
Newsgroups: sci.space.science
Subject: Re: Drag at Orbital Altitudes
References: <5dcb47db.0311190511.68203dac@posting.google.com> <9186edb5.0311192354.e0f9d34@posting.google.com> <5dcb47db.0311210440.7eb53e3f@posting.google.com>
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cray74@hotmail.com (Mike Miller)
> Next question: how much worse is the radiation environment at 600km vs 400km?
There is an online version of the AP-8/AE-8 model for the Van Allen belt
radiation at:
http://nssdc.gsfc.nasa.gov/space/model/models/trap.html
But as of 11/22/03 the online version would not run for me, so I downloaded:
http://nssdcftp.gsfc.nasa.gov/models/radiation_belt/radbelt/fortran_code/
Documentation related to these is at:
http://nssdc.gsfc.nasa.gov/space/model/magnetos/radbelt.html
http://nssdc.gsfc.nasa.gov/space/model/magnetos/aeap.html
Key terms are:
L-value: equatorial distance to a geomagnetic field line measured in
earth radii
B/Bo: magnetic field strength normalized to the equatorial val
Bo: magnetic field strength at the magnetic equator (minimum value)
So:
L-value = 1 + altitude/EarthRadius
EarthRadius: 6378000 meters
L-value for 400 km is about 1.06272
L-value for 600 km is about 1.09407
So running the Fortran code (online version is similar but less options):
1) I select: AP8MIN
2) I want to look at range of energy values so I put in:
6, then 0.1,2,8,32,64,128
3) For L-values I enter: 0 then 1.03,1.33,0.03
To get the range: 1.03,1.06,1.09,1.12,1.15,1.18,1.21,1.24,1.27,1.30
4) For B/Bo I enter: 10 then 1,2,3,4,5,6,10,15,20,50
Though I only use "1" for the table below:
5) For output I enter "1" for "E * L TABLE - integral"
Then I pick the B/Bo value of 1 (equatorial).
And I get the table:
integral flux [PROTONS /cm*cm*sec]
L \ E/MeV 0.10 2.00 8.00 32.00 64.00 128.00
------\--------------------------------------------------------------
1.03 I 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00
1.06 I 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00
1.09 I 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00
1.12 I 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00
1.15 I 4.004E+02 3.563E+02 3.198E+02 1.473E+02 6.786E+01 2.048E+01
1.18 I 2.023E+03 1.931E+03 1.829E+03 1.492E+03 1.179E+03 7.216E+02
1.21 I 4.728E+03 4.629E+03 4.445E+03 3.748E+03 3.093E+03 1.911E+03
1.24 I 9.318E+03 9.038E+03 8.342E+03 6.131E+03 4.848E+03 2.853E+03
1.27 I 1.836E+04 1.765E+04 1.566E+04 1.003E+04 7.599E+03 4.260E+03
1.30 I 3.660E+04 3.483E+04 2.969E+04 1.654E+04 1.200E+04 6.403E+03
So this model predicts that at 600 km (L-value 1.09) you are still not
getting significant radiation. But you don't want to get much above
800 km (L-value 1.12). Using AP8MAX gives a similar result.
If you are not at the magnetic equator (can't orbit there as the Earth
rotates) the above is not going to be exactly right. But if you are
over the Earth's equator, I don't think it is far off. However, if your
orbit passes through the South Atlantic Anomaly you will get some
radiation.
-- Vince