SDP4 tests
Scott Wilson (wilson@scuch8.psc.sc.edu)
Tue, 1 Apr 1997 14:35:53 -0500 (EST)
I read with interest Rob Matson's posts on a flaw in some implementations of
the SDP4 orbit model. I decided to try his test cases to see if my system
showed the flaw. I run OrbitTrackFPU 2.1.5 from BEK Developers of St.
Petersburg Florida on a Mac Quadra 610 with 16 Meg.
I used the Ariane element set:
Ariane V.22 Deb F
1 19220U 88051F 97079.11485035 +.00000856 +00000-0 +43713-3 0 07948
2 19220 009.9715 304.0187 5734345 315.9233 010.5502 04.37227961086454
at two time intervals: 13:43 to 13:53 UTC and 14:40 to 14:45 UTC. The flaw
shows up as a discontinuity in the latitude and longitude of the subsatellite
point. As a check, you can compare to the SGP orbit model, in which there have
not been any flaws reported.
Case 1: 13:43 to 13:53: <<SDP4>>
OrbiTrack Position - 04/01/97 1336:30
Pass - From: Fri 01/17/97 13:43:00 UTC
To: Fri 01/17/97 13:53:00 UTC
Ariane V.22 Deb F
Time UTC Height North West Satellite
DOW MM/DD/YY HH:MM:SS km Lat Long Visibility
Fri 01/17/97 13:43:00 928.3 2.99 159.92 In Darkness
Fri 01/17/97 13:43:30 864.7 2.63 157.96 In Darkness
Fri 01/17/97 13:44:00 804.2 2.27 155.96 In Darkness
Fri 01/17/97 13:44:30 747.0 1.90 153.94 In Darkness
Fri 01/17/97 13:45:00 693.2 1.52 151.88 In Darkness
Fri 01/17/97 13:45:30 643.1 1.13 149.78 In Darkness
Fri 01/17/97 13:46:00 596.6 0.74 147.66 In Darkness
Fri 01/17/97 13:46:30 554.0 0.34 145.51 In Darkness
Fri 01/17/97 13:47:00 515.3 -0.07 143.33 In Darkness
Fri 01/17/97 13:47:30 480.7 -0.48 141.13 In Darkness
Fri 01/17/97 13:48:00 450.2 -0.90 138.91 In Darkness
Fri 01/17/97 13:48:30 424.0 -1.31 136.66 In Sunlight
Fri 01/17/97 13:49:00 402.1 -1.73 134.40 In Sunlight no jump
Fri 01/17/97 13:49:30 384.6 -2.14 132.12 In Sunlight
Fri 01/17/97 13:50:00 371.6 -2.56 129.83 In Sunlight
Fri 01/17/97 13:50:30 363.0 -2.97 127.54 In Sunlight
Fri 01/17/97 13:51:00 359.0 -3.37 125.23 In Sunlight
Fri 01/17/97 13:51:30 359.5 -3.77 122.92 In Sunlight
Fri 01/17/97 13:52:00 364.5 -4.17 120.61 In Sunlight
Fri 01/17/97 13:52:30 374.0 -4.55 118.31 In Sunlight
Fri 01/17/97 13:53:00 388.0 -4.93 116.01 In Sunlight
The same time interval for SGP also has no jump
Case 2: 14:40 to 14:45: <<SDP4>>
OrbiTrack Position - 04/01/97 1331:59
Pass - From: Fri 01/17/97 14:40:00 UTC
To: Fri 01/17/97 14:45:00 UTC
Ariane V.22 Deb F
Time UTC Height North West Satellite
DOW MM/DD/YY HH:MM:SS km Lat Long Visibility
Fri 01/17/97 14:40:00 8806.7 -6.07 14.06 In Sunlight
Fri 01/17/97 14:40:30 8896.2 -6.00 13.71 In Sunlight
Fri 01/17/97 14:41:00 8985.2 -5.93 13.36 In Sunlight
Fri 01/17/97 14:41:30 9073.7 -5.87 13.01 In Sunlight
Fri 01/17/97 14:42:00 9161.7 -5.80 12.68 In Sunlight
Fri 01/17/97 14:42:30 9249.3 -5.73 12.34 In Sunlight
Fri 01/17/97 14:43:00 9336.4 -5.67 12.02 In Sunlight-> no jump
Fri 01/17/97 14:43:30 9423.0 -5.60 11.69 In Sunlight
Fri 01/17/97 14:44:00 9509.2 -5.54 11.38 In Sunlight
Fri 01/17/97 14:44:30 9594.9 -5.48 11.06 In Sunlight
Fri 01/17/97 14:45:00 9680.1 -5.41 10.76 In Sunlight
The same time interval for SGP also has no jump:
OrbiTrack Position - 04/01/97 1331:16
Pass - From: Fri 01/17/97 14:40:00 UTC
To: Fri 01/17/97 14:45:00 UTC
Ariane V.22 Deb F
Time UTC Height North West Satellite
DOW MM/DD/YY HH:MM:SS km Lat Long Visibility
Fri 01/17/97 14:40:00 8923.8 -5.15 7.86 In Sunlight
Fri 01/17/97 14:40:30 9012.6 -5.08 7.51 In Sunlight
Fri 01/17/97 14:41:00 9101.0 -5.01 7.17 In Sunlight
Fri 01/17/97 14:41:30 9188.9 -4.94 6.84 In Sunlight
Fri 01/17/97 14:42:00 9276.3 -4.87 6.51 In Sunlight
Fri 01/17/97 14:42:30 9363.2 -4.80 6.18 In Sunlight
Fri 01/17/97 14:43:00 9449.7 -4.73 5.86 In Sunlight-> no jump
Fri 01/17/97 14:43:30 9535.7 -4.67 5.55 In Sunlight
Fri 01/17/97 14:44:00 9621.2 -4.60 5.24 In Sunlight
Fri 01/17/97 14:44:30 9706.2 -4.53 4.93 In Sunlight
Fri 01/17/97 14:45:00 9790.8 -4.47 4.63 In Sunlight
>From these tests, I was relieved to see that OrbitTrack appears to handle SDP4
correctly. Are there any other useful diagnostic tests that anyone has that
would point out any other similar flaws in sat tracking programs?
Scott Wilson
Dept of Physics
Univ of South Carolina
Columbia, SC, USA
President, Midlands Astronomy Club