Add launchtle.py

examples/irvine01.txt

@@ -0,0 +1,3 @@
+IRVINE01
+1 70002U 18599A   18315.16151858  .00000000  00000-0  00000-0 0    07
+2 70002  85.1205  90.1568 0012705 292.5520 107.9249 15.20792276    04

python/README.md

@@ -21,3 +21,14 @@
   ```
   ./pass.py ../examples/sathyabamasat.txt $ST_DATADIR/sites.txt -s 7300 --starttime 2019-11-06T19:30:00
   ```
+
+- Adjust a TLE to a new launch time
+  ```
+  # Data from https://community.libre.space/t/electron-its-business-time-launch-this-weekend-irvine-01-amateur-payload/2819/4
+  $ ./launchtle.py ../examples/irvine01.txt 2018-11-11T03:00:00 2018-11-11T04:05:00
+  New TLE for a launch delay of 1:05:00h :
+
+  IRVINE01-delayed
+  1 70002U 18599A   18315.20665747  .00000000  00000-0  00000-0 0    09
+  2 70002  85.1205 106.4513 0012705 292.5520 107.9249 15.20792276    05
+  ```

python/launchtle.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+
+import argparse
+from datetime import datetime, timedelta
+
+from sgp4.io import twoline2rv
+from sgp4.earth_gravity import wgs84
+
+from astropy.coordinates import Longitude, Angle
+from astropy import units as u
+from astropy.time import Time
+
+
+
+def gmst(t):
+    return Time(t).sidereal_time('mean', 'greenwich')
+
+def fractional_days(t):
+    d = t - datetime(t.year, 1, 1)
+    return t.timetuple().tm_yday + (d.seconds + d.microseconds/1e6)/(60*60*24)
+
+def print_tle(tle, new_epoch, new_nodeo):
+    def checksum(proto_tle):
+        s = 0
+        for c in proto_tle:
+            if c.isdigit():
+                s += int(c)
+            if c == '-':
+                s += 1
+        return s%10
+
+    tle0,old1,old2 = tle
+    tle1_proto = '{} {:2d}{:.8f} {}'.format(old1[:17],
+                              abs(new_epoch.year)%100,
+                              fractional_days(new_epoch),
+                              old1[33:-1])
+    tle2_proto = '{} {:>8.4f} {}'.format(old2[:16],
+                                   Angle(new_nodeo*u.radian).degree,
+                                   old2[26:68])
+            
+    return (tle0,
+            tle1_proto + str(checksum(tle1_proto)),
+            tle2_proto + str(checksum(tle2_proto)))
+
+def launch_tle(tle, launch_date, new_launch_date):
+    sat = twoline2rv(tle[1], tle[2], whichconst=wgs84)
+
+    # New Epoch
+    new_epoch = sat.epoch - launch_date + new_launch_date
+
+    # New Right ascension of ascending node in radians
+    new_nodeo = (gmst(new_launch_date) - gmst(launch_date) + Longitude(sat.nodeo * u.radian)).rad
+    
+    return print_tle(tle, new_epoch, new_nodeo)
+
+
+if __name__ == "__main__":
+    # Parse arguments
+    parser = argparse.ArgumentParser(
+        description="Adjust a TLE to a new launch time")
+    parser.add_argument('TLEFILE', help="reference tle file", type=str)
+    parser.add_argument("OLD",
+                        help="Reference (old) launch time (YYYY-MM-DDTHH:MM:SS)",
+                        type=str)
+    parser.add_argument("NEW",
+                        help="New launch time (YYYY-MM-DDTHH:MM:SS) [default: now]",
+                        default=datetime.utcnow().strftime("%Y-%m-%dT%H:%M:%S"),
+                        type=str)
+
+    args = parser.parse_args()
+
+    with open(args.TLEFILE, 'r') as f:
+        tle = f.readlines()
+    tle = [l.strip() for l in tle]
+ 
+    launch_date_ref = datetime.strptime(args.OLD, '%Y-%m-%dT%H:%M:%S')
+    new_launch_date = datetime.strptime(args.NEW, '%Y-%m-%dT%H:%M:%S')
+    
+    new_tle = launch_tle(tle, launch_date_ref, new_launch_date)
+    
+    print('New TLE for a launch delay of {}h :\n'.format(new_launch_date - launch_date_ref))
+    print(new_tle[0].strip()+'-delayed')
+    print(new_tle[1])
+    print(new_tle[2])

python/test_launchtle.py

@@ -0,0 +1,28 @@
+from datetime import datetime
+from launchtle import launch_tle
+
+
+launch_date_ref = datetime(2018, 11, 11, 3, 0)
+tle_ref = ["1 70002U 18599A   18315.16151858  .00000000  00000-0  00000-0 0    07",
+           "2 70002  85.1205  90.1568 0012705 292.5520 107.9249 15.20792276    04"]
+
+# Testing the Implementation against 'launchtle' from sattools
+# launchtle -c irvine.txt -i 70002 -t 2018-11-11T03:00:00 -T 2018-11-11T03:00:00 -I 70002 -d 18599A
+fixtures = [(datetime(2018, 11, 11, 3, 0),
+            ["1 70002U 18599A   18315.16151858  .00000000  00000-0  00000-0 0    07",
+             "2 70002  85.1205  90.1568 0012705 292.5520 107.9249 15.20792276    04"]),
+            (datetime(2018, 11, 11, 3, 5),
+            ["1 70002U 18599A   18315.16499080  .00000000  00000-0  00000-0 0    09",
+             "2 70002  85.1205  91.4102 0012705 292.5520 107.9249 15.20792276    02"]),
+            (datetime(2018, 11, 11, 4, 0),
+            ["1 70002U 18599A   18315.20318525  .00000000  00000-0  00000-0 0    08",
+             "2 70002  85.1205 105.1979 0012705 292.5520 107.9249 15.20792276    07"]),
+            (datetime(2018, 11, 12, 3, 0),
+            ["1 70002U 18599A   18316.16151858  .00000000  00000-0  00000-0 0    08",
+             "2 70002  85.1205  91.1424 0012705 292.5520 107.9249 15.20792276    06"])]
+
+def test_launchtle():
+    for new_launch_date, tle_correct in fixtures:
+        tle = launch_tle(['DUMMYSAT', *tle_ref], launch_date_ref, new_launch_date)
+        assert(tle_correct[1] == tle[2])
+        assert(tle_correct[0] == tle[1])