update may 2026:
recommended reading about TLE:
strf file:
LAPAN-A2-18-OKTOBER-2025.dat (2.4 KB)
gpredict tle file:
lapan-a2_2025-10-18.txt (207 Bytes)
ikhnos:
please update to satnogs db
LAPAN-A2
1 40931U 25291.21209780 .00000000 00000-0 -12415-2 0 04
2 40931 6.0006 99.2509 0012733 338.8432 140.9063 14.78961520 08
# 20251018.35-20251018.36, 58 measurements, 0.022 kHz rms
thank you
strf file:
LAPAN-A2-28-OKTOBER-2025.dat (630 Bytes)
gpredict tle file:
lapan-a2_2025-10-28.txt (149 Bytes)
ikhnos:
LAPAN-A2
1 40931U 25301.05483361 .00000000 00000-0 -12415-2 0 07
2 40931 6.0006 45.1217 0012733 338.8432 110.6602 14.79220448 05
gpredict tle file:
lapan-a2_2025-10-30.txt (149 Bytes)
ikhnos:
LAPAN-A2
1 40931U 25303.30778704 .00000000 00000-0 -12415-2 0 05
2 40931 6.0006 9.3579 0012733 338.8432 276.9804 14.79220448 08
gpredict tle file:
lapan-a2_2025-11-01.txt (149 Bytes)
ikhnos:
LAPAN-A2
1 40931U 25305.40850694 .00000000 00000-0 -12415-2 0 07
2 40931 6.0006 0.5114 0012733 338.8432 325.7376 14.79306534 04
LAPAN-A2
1 40931U 25312.07208788 .00000000 00000-0 -12415-2 0 09
2 40931 6.0006 311.2914 0012733 338.8432 261.6692 14.79051654 03
obs-2025-11-08-v1-done.dat (3.4 KB)
sites.txt (12.0 KB)
lapan-a2_2025-11-08_v1.txt (149 Bytes)
LAPAN-A2
1 40931U 25319.07435036 .00000000 00000-0 -12415-2 0 04
2 40931 6.0006 261.8971 0012733 338.8432 202.6862 14.78947778 00
obs-2025-11-15-v1-done.dat (3.4 KB)
sites.txt (809 Bytes)
lapan-a2_2025-11-15_v1.txt (149 Bytes)
LAPAN-A2
1 40931U 25328.63157070 .00000000 00000-0 -12415-2 0 05
2 40931 6.0006 196.8483 0012733 338.8432 101.5677 14.78898168 04
obs-2025-11-24-v1-done.dat (4.9 KB)
sites.txt (809 Bytes)
lapan-a2_2025-11-24_v1.txt (149 Bytes)
LAPAN-A2
1 40931U 25329.67151640 .00000000 00000-0 -12415-2 0 07
2 40931 6.0006 185.7182 0012733 338.8432 257.7856 14.78898168 00
obs-2025-11-25-v3-done.dat (2.6 KB)
sites.txt (3.3 KB)
lapan-a2_2025-11-25_v3.txt (148 Bytes)
LAPAN-A2
1 40931U 25330.68545454 .00000000 00000-0 -12415-2 0 00
2 40931 6.0006 181.5933 0012733 338.8432 267.7950 14.78898168 04
lapan-a2_2025-11-26_v1.txt (149 Bytes)
obs-2025-11-26-v1-done.dat (3.9 KB)
sites.txt (3.3 KB)
LAPAN-A2
1 40931U 25337.49374902 .00000000 00000-0 -12415-2 0 04
2 40931 6.0006 131.0605 0012733 338.8432 257.3957 14.79033923 03
lapan-a2_2025-12-03_v1.txt (149 Bytes)
obs-2025-12-03-v1-done.dat (5.0 KB)
sites.txt (809 Bytes)
LAPAN-A2
1 40931U 25344.45049596 .00000000 00000-0 30000-3 0 06
2 40931 6.0006 76.1618 0012733 338.8432 322.8531 14.79075522 03
obs-2025-12-10-v1-done.dat (3.9 KB)
sites.txt (809 Bytes)
lapan-a2_2025-12-10_v1.txt (149 Bytes)
LAPAN-A2
1 40931U 25355.16637158 .00000000 00000-0 30662-3 0 07
2 40931 6.0006 5.6621 0012733 338.8432 286.2986 14.79075515 03
lapan-a2_2025-12-21_v5.txt (149 Bytes)
obs-2025-12-21-v5-done.dat (3.1 KB)
sites.txt (809 Bytes)
Sorry for this. This holiday xmas new year TLE edition is a bit over the top… please bear with me.
begining from this thread:
This time, I want to share how I found b* drag using a simple method with the existing tools ikhnos and current tle. i use lapan-a2_2025-12-03_v1.txt (149 Bytes) from this post . other tools you can use as alternate is SatNOGS Artifacts - Waterfall Viewer. check here about these tools.
LAPAN-A2
1 40931U 25337.49374902 .00000000 00000-0 -12415-2 0 04
2 40931 6.0006 131.0605 0012733 338.8432 257.3957 14.79033923 03
as you can see, the current b* drag value is -12415-2 . This is a bad number. A negative value means that the drag is very fast, making the TLE become outdated in just a few days. However, this satellite is at an altitude of over 600 km, which means the drag should be slow.
so what i do is i just try positive number around 11000 to 70000 (1.1e-4 or 0.11e-3 to 7.0e-4 or 0.7e-3)
for example, i try 70000e-3
so the new tle will like this:
LAPAN-A2
1 40931U 25337.49374902 .00000000 00000-0 70000-3 0 02
2 40931 6.0006 131.0605 0012733 338.8432 257.3957 14.79033923 03
and then i copy paste all second line to online TLE checksum, like this:
and then replace 02 with correct crc number 08, so the tle become like this:
LAPAN-A2
1 40931U 25337.49374902 .00000000 00000-0 70000-3 0 08
2 40931 6.0006 131.0605 0012733 338.8432 257.3957 14.79033923 03
i hope you understand
and i repeat above task with another numbers between 11000-3 and 70000-3
the next step is test each of this tle with real observation. I choose observation with a date that is much newer than the TLE date, deliberately selecting observations where the center frequency is no longer centered. in this example i choose obs 13022563
the next step is create waterfall image for each tle set using ikhnos, the command like this:
./ikhnos.py -r 24 -f 0.8 -t lapan-a2_2025-12-03_DRAG.txt 13022563
-r 24 = sample rate 24khz
-f 0.8 = The default is 0, but I set it to 0.8 because this station likely has a ppm error. The goal is to ensure the signal in the waterfall is positioned in the center.
-t = the tle set file name.
13022563 = satnogs observation id
here the result:
as you can see and compare, the best waterfall (the red line follow the signal), is when b*drag value 12800e-3
so the best tle become:
LAPAN-A2
1 40931U 25337.49374902 .00000000 00000-0 12800-3 0 02
2 40931 6.0006 131.0605 0012733 338.8432 257.3957 14.79033923 03
So what’s next? I will use this b* drag value 12800e-3 as a reference for the next TLE of Lapan IO-86
LAPAN-A2
1 40931U 25360.30710720 .00000000 00000-0 12800-3 0 00
2 40931 6.0006 332.5373 0012733 338.8432 8.1437 14.79075515 01
lapan-a2_2025-12-26_v4.txt (149 Bytes)
obs-2025-12-26-v4-done.dat (2.2 KB)
sites.txt (1.0 KB)
LAPAN-A2
1 40931U 26032.24206106 .00000000 00000-0 12837-3 0 08
2 40931 6.0006 58.4313 0012733 338.8432 291.7537 14.79136711 06
# 20260131.08-20260201.24, 131 measurements, 0.158 kHz rms
lapan-a2_2026-02-01_v1.txt (208 Bytes)
sites.txt (485 Bytes)
lapan-a2_2026-02-01_v1.txt (208 Bytes)
LAPAN-A2
1 40931U 26051.50840545 .00000000 00000-0 12837-3 0 09
2 40931 6.0006 282.0515 0012733 338.8432 194.8877 14.79136711 05
# 20260216.01-20260220.65, 86 measurements, 0.243 kHz rms
lapan-a2_2026-02-20_v1.txt (207 Bytes)
lapan-a2_2026-02-20.dat (2.9 KB)
sites.txt (593 Bytes)
LAPAN-A2
1 40931U 26116.46610613 .00000000 00000-0 12837-3 0 07
2 40931 6.0006 182.4770 0012733 338.8432 335.8502 14.79220230 03
# 20260425.31-20260426.47, 107 measurements, 0.125 kHz rms
lapan-a2_2026-04-26.dat (3.7 KB)
lapan-a2_2026-04-26_v1.txt (208 Bytes)
sites.txt (593 Bytes)
LAPAN-A2
1 40931U 26135.94719338 .00000000 00000-0 12837-3 0 05
2 40931 6.0006 41.0271 0012733 338.8432 315.3302 14.79243689 03
# 20260510.08-20260516.09, 134 measurements, 0.066 kHz rms
# 14017786_14029557_14057284_14058775_14070024_14070025.dat (total: 6 obs) (duration: 144 hours) (magic key: 256sfefef)
# generated using: https://github.com/hobisatelit/satno2tle (v0.02)
lapan-2026-05-16.zip (23.9 KB)
lapan-a2_2026-05-15_v1-tle.txt (396 Bytes)
LAPAN-A2
1 40931U 26152.38749123 .00000000 00000-0 12837-3 0 07
2 40931 6.0006 283.2690 0012733 338.8432 257.5946 14.79252685 05
# 20260524.49-20260601.46, 83 measurements, 0.074 kHz rms
# 14143010_14168786_14197041_14209627.dat (total: 4 obs) (duration: 191 hours) (magic key: 256sfefef)
# generated using: https://github.com/hobisatelit/satno2tle (v0.02)
lapan-a2_2026-06-01_v1-tle.txt (377 Bytes)
lapan-a2_2026-06-01_v1.zip (23.9 KB)
LAPAN-A2
1 40931U 26165.13411713 .00000000 00000-0 77536-4 0 03
2 40931 6.0006 190.4965 0012733 338.8432 279.4005 14.79261912 01
# 20260511.02-20260614.20, 290 measurements, 0.104 kHz rms
# 14297204_14297225_14297203_14297202_14250190_14244582_14231996_14209627_14197041_14089676_14070024_14057284_14029557.dat (total: 13 obs) (duration: 0 hours) (magic key: manual)
# generated using: https://github.com/hobisatelit/satno2tle (v0.03)
lapan-a2_165_v9.zip (34.5 KB)
LAPAN-A2
1 40931U 26172.08518624 .00000000 00000-0 77536-4 0 04
2 40931 6.0006 143.4652 0012733 338.8432 312.0802 14.79263831 03
# 20260615.50-20260621.16, 96 measurements, 0.051 kHz rms
# 14341487_14341446_14309771_14309768.dat (total: 4 obs) (duration: 0 hours) (magic key: manual)
# generated using: https://github.com/hobisatelit/satno2tle (v0.03)
lapan-a2_172_v1-tle.txt (372 Bytes)
lapan-a2_172_v1.zip (21.8 KB)