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# Strange error during propagation using sgp4_array

See original GitHub issue

Hi Brandon First of all, great library!

I have the following problem (in versions 2.12 and 2.16) and I don’t seem to be able to find a solution for it: `sgp4_array` throws some NaNs at time 2459026.2 whereas `sgp4` does not.

Here is a working example that I found.

``````from sgp4.api import Satrec, jday
import numpy as np

tle = (
"1 44160U 19006AX  20162.79712247 +.00816806 +19088-3 +34711-2 0  9997",
"2 44160 095.2472 272.0808 0216413 032.6694 328.7739 15.58006382062511"
)

s = Satrec.twoline2rv(*tle)

jd0, jd1 = jday(2020, 6, 10, 19, 7, 51.381408)
``````

Here is the part for `sgp4`, which works as expected if you run it:

``````for i in range(0, 50):
r = s.sgp4(jd0+i, jd1)
print(i, r[0], np.linalg.norm(r[1]), r[1])
``````

And here using `sgp4_array`:

``````jd0_ = jd0 + np.arange(0, 50, dtype="f")
jd1_ = np.ones_like(jd0_) * jd1
res = s.sgp4_array(jd0_, jd1_)
ier = res[0]
r = res[1]
v = res[2]
for i in range(len(ier)):
print(i, jd0_[i] + jd1_[i], ier[i], r[i], v[i])
``````

which yields:

``````0 2459011.2 0 [ 2.41464418e+02 -6.64590746e+03 -9.37349881e-04] [-0.71720095  0.07212463  7.78138163]
1 2459012.2 0 [   15.03351833  6027.73284644 -3390.25230116] [ 0.77844336 -3.6607103  -6.50959084]
2 2459013.2 0 [ -377.07198181 -2826.33161405  6005.14918003] [-0.74454705  7.00476588  3.35620303]
3 2459014.2 0 [  713.26199209 -1398.96601871 -6596.62261048] [ 0.39554425 -7.42643673  1.77509584]
4 2459015.2 0 [-812.07032448 6133.95588683 2928.11093856] [ 0.32314368  3.39799364 -6.76611198]
5 2459016.2 0 [  283.86827906 -5757.08079769  3252.33603352] [-1.00843474  3.75610953  6.79958794]
6 2459017.2 0 [  636.67442201  -125.60519267 -6726.66503702] [ 0.83879049 -7.60551209  0.36376957]
7 2459018.2 0 [-974.5974261  6641.97494784 1343.34308475] [ 0.47602838  1.6133775  -7.37717825]
8 2459019.2 0 [ -327.85325328 -1881.15256086  6397.04807578] [-1.2398994   7.31677442  2.21843553]
9 2459020.2 0 [ 1114.44467976 -6353.52536393 -1407.6566936 ] [-0.43957567 -1.73643171  7.62815489]
10 2459021.2 0 [  688.99011615  -418.90939529 -6636.08980865] [ 1.21001573 -7.5926442   0.73137065]
11 2459022.2 0 [ -594.46126229  5363.24756229 -4083.1575965 ] [ 1.38096894 -4.51862535 -5.99049808]
12 2459023.2 0 [-1342.69683985  6628.66687018   486.75886791] [ 0.57768626  0.66032168 -7.55960087]
13 2459024.2 0 [-1505.65682385  5722.9420058   3265.55435086] [-0.16961905  3.77357815 -6.62302689]
14 2459025.2 0 [-1544.65886896  5264.33269643  3911.40748805] [-0.42613438  4.49864644 -6.15839203]
15 2459026.2 0 [nan nan nan] [nan nan nan]
16 2459027.2 0 [nan nan nan] [nan nan nan]
17 2459028.2 0 [           nan  1629.73053961 -6359.26714453] [        nan -7.30785055 -1.71837043]
18 2459029.2 0 [ 1830.86002598 -6116.31950075 -1211.36493712] [-0.27242591 -1.6447351   7.69790257]
19 2459030.2 0 [-1217.10693282  2134.17843527  6130.69042289] [-1.80142179  6.99452779 -2.73978104]
20 2459031.2 0 [  415.81175295   653.71934763 -6426.14143211] [ 2.36881928 -7.47994795 -0.53940074]
21 2459032.2 0 [-933.97608025  972.58220555 6397.59652987] [-2.23826422  7.30730719 -1.39034781]
22 2459033.2 0 [ 2100.3959201  -5417.40160538 -2678.09076348] [ 0.46061982 -3.39534964  7.14922145]
23 2459034.2 0 [  -73.40993402  1881.99639952 -6096.93392467] [ 2.73384426 -7.10778407 -2.16512776]
24 2459035.2 6 [-1260.63037181  4538.03783856 -4287.29405378] [ 2.37166984 -4.88132249 -5.76033957]
25 2459036.2 6 [ -449.3236561   2622.83077916 -5715.49135764] [ 2.89530936 -6.6768767  -3.232872  ]
26 2459037.2 6 [ 2259.53093091 -4812.09284893 -3289.99918448] [ 1.0144526  -4.18615237  6.75142538]
27 2459038.2 6 [-1423.49775387  2031.02535631  5770.20555676] [-2.56387682  6.8606897  -3.04606812]
28 2459039.2 6 [ 2344.47321672 -4638.22520069 -3302.79592151] [ 1.17409842 -4.25893347  6.74553816]
29 2459040.2 6 [ -119.61572571  1582.19771137 -5885.02581612] [ 3.39151538 -7.09062735 -1.95217819]
30 2459041.2 6 [  331.71510733   591.80969861 -5995.17916219] [ 3.48217555 -7.3377898  -0.52306885]
31 2459042.2 6 [ 2566.91618932 -5402.9400998    488.12194128] [-0.9425547   0.2425601   8.09309346]
32 2459043.2 6 [-2419.07007367  5155.33312615 -1621.47614793] [ 1.6713446  -1.72512795 -7.8527453 ]
33 2459044.2 6 [-2102.27613075  3157.38677818  4472.16623278] [-2.46876391  5.8075733  -5.28247854]
34 2459045.2 6 [-2764.7477027   5017.49192579   676.2090556 ] [ 0.21310201  1.1986892  -8.22718653]
35 2459046.2 6 [ 2684.85009962 -4375.26876465 -2435.73400242] [ 1.15837161 -3.50793088  7.51834434]
36 2459047.2 6 [   -8.41152467  1027.48213038 -5481.28392598] [ 4.25781663 -7.17334209 -1.35522187]
37 2459048.2 6 [ 2472.64414183 -3566.8460297  -3365.71481695] [ 2.15239042 -4.83436008  6.67257159]
38 2459049.2 6 [-2832.04167605  4417.15356683  1212.18217604] [-0.35928872  2.05602928 -8.3523955 ]
39 2459050.2 6 [-2830.8138051   4266.09738206  1272.76281745] [-0.4729579   2.19371765 -8.40371125]
40 2459051.2 6 [ 2621.09805586 -3579.18983068 -2650.23358753] [ 1.89396784 -4.16807436  7.48959022]
41 2459052.2 6 [ 1986.80969801 -2294.17509988 -4030.39849466] [ 3.56962523 -6.1838674   5.27220465]
42 2459053.2 6 [-1312.61798841  1155.72800504  4582.79954527] [-4.57779313  7.11187117 -3.09588977]
43 2459054.2 6 [-1338.0608939   1174.44953571  4426.28061058] [-4.69842052  7.10502408 -3.29357285]
44 2459055.2 6 [ 2373.44146937 -2783.62864033 -2862.29783253] [ 2.85649023 -5.00594776  7.24109556]
45 2459056.2 1 [0.00000000e+000 6.90385107e-310 3.95252517e-321] [0.00000000e+000 2.08928597e-076 1.69759663e-313]
46 2459057.2 1 [9.88131292e-324 9.88131292e-324 6.57818695e-313] [1.90979621e-313 1.21223444e-099 6.95333864e-310]
47 2459058.2 1 [4.94065646e-324 6.95333864e-310 6.90370111e-310] [8.09244594e-153 1.17847856e-047 8.98330940e-096]
48 2459059.2 1 [6.90385569e-310 9.88131292e-324 5.41495948e-321] [6.95333864e-310 6.95333864e-310 7.10600469e-038]
49 2459060.2 1 [1.48219694e-323 6.36598737e-314 6.95314361e-310] [8.48798317e-314 2.12199579e-313 3.32903893e-090]
``````

### Issue Analytics

• State:
• Created 3 years ago
• Comments:6 (4 by maintainers)

#### Top GitHub Comments

1reaction
daluarcommented, Feb 18, 2021

Wow! This was quick Thank you 😉

0reactions
brandon-rhodescommented, Feb 17, 2021

First of all, great library!

Oh, and: thanks for the kinds words! I’m glad you’re enjoying it.

I have just started the release of 2.17 that makes this fix available. Hopefully the build will complete within the next half-hour or so, making the fix available for all users.

Read more comments on GitHub >

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