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Sign upadded atmospheric drag + tests #343
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nikita-astronaut
added some commits
Apr 10, 2018
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codecov
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Apr 10, 2018
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Codecov Report
@@ Coverage Diff @@
## master #343 +/- ##
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+ Coverage 81.55% 81.68% +0.13%
==========================================
Files 31 31
Lines 1496 1507 +11
Branches 115 115
==========================================
+ Hits 1220 1231 +11
Misses 248 248
Partials 28 28
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Juanlu001
requested review from
Juanlu001
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AunSiro
Apr 10, 2018
Juanlu001
requested changes
Apr 12, 2018
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Overall this looks good, but I asked for more comments, your opinion on a minor API change, and some more details about the approximation. I didn't do the pen-and-paper myself, just looks like a big leap. |
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| # parameters of a circular orbit with h = 10 km | ||
| h = 250 # km | ||
| r0 = np.array([R + h, 0, 0]) # km |
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| k : float | ||
| gravitational constant, (km^3/s^2) | ||
| B: float | ||
| ballistic coefficient B = C_D[] x A[m^2] / m[kg], (m^2 / kg) |
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| B: float | ||
| ballistic coefficient B = C_D[] x A[m^2] / m[kg], (m^2 / kg) | ||
| H0 : float | ||
| the e-times density decay heigth, (km) |
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Juanlu001
Apr 12, 2018
Member
Perhaps "atmospheric scale height" is more descriptive? (from utexas website)
| C_D = 2.2 # dimentionless | ||
| A = ((np.pi / 4.0) * (u.m**2)).to(u.km**2).value # km^2 | ||
| m = 100 # kg | ||
| B = C_D * A / m |
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Juanlu001
Apr 12, 2018
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What do you think as having C_D and m as input instead of B? So we compute B inside the function
| v0 = np.array([0, np.sqrt(k / (R + h)), 0]) # km/s | ||
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| # parameters of a body | ||
| C_D = 2.2 # dimentionless |
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Juanlu001
Apr 12, 2018
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Do these parameters matter for the test itself? Or any value would do?
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| orbit = Orbit.from_vectors(Earth, r0 * u.km, v0 * u.km / u.s) | ||
| tof = 100000 # s | ||
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| dr_expected = -B * tof * rho0 * np.exp(-(norm(r0) - R) / H0) * np.sqrt(k * norm(r0)) |
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Juanlu001
Apr 12, 2018
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This is related to the approximation trick you mention in the first comment I guess. Can we move that comment next to this line, and put * tof at the end?
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| def test_atmospheric_drag(): | ||
| # http://farside.ph.utexas.edu/teaching/celestial/Celestialhtml/node94.html#sair (10.148) | ||
| # given the expression for \dot{a} / a, aproximate \Delta a \approx F_a * \Delta t |
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nikita-astronaut
added some commits
Apr 12, 2018
Juanlu001
approved these changes
Apr 13, 2018
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The math checks out :) (leaving this here for future reference, as it was not obvious for me)
Going to merge this manually. |
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Merged in 35a2c34. Thanks @nikita-astronaut! |
nikita-astronaut commentedApr 10, 2018
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edited
Added atmospheric drag perturbation and tests. For links, see comments to the functions.