def generateEphemeris(name, tle1, tle2, time):
"""
Generate ephemeris for the given satellite at given epoch
Parameters
----------
name : str
Name of the satellite (line 0 of 3le)
tle1 : str
First line of the satellite's tle (line 1 of 3le)
tle2 : str
Second line of the satellite's tle (line 2 of 3le)
date_str : str
Desired epoch in format YYYY-mm-ddTHH:MM:SS
Returns
-------
ra :
Raises
------
None
"""
observer = Topos(SITE_LATITUDE, SITE_LONGITUDE, elevation_m=SITE_ELEVATION)
target = EarthSatellite(tle1, tle2, name)
ra, dec, distance = (target - observer).at(time).radec()
return [name, ra.hours, dec.degrees]
def __init__(self, line1, line2, name=None):
"""
Initiates the TLE
Parameters
----------
line1, line2 : str
First and second lines of the TLE
name : str, optional
Name of the object to which the TLE is attributed
"""
self.line1 = line1
self.line2 = line2
if name is not None:
self.name = name[2:]
else:
self.name = 'UNKNOWN'
# ephemeris info
self.obs = TOPOS_LOCATION
self.obj = EarthSatellite(line1, line2, name)
self.ts = TS
# book-keeping
self.norad_id = int(self.line1[2:7])
self.yday = float(self.line1[20:32])
# orbital properties
self.inclination = float(self.line2[8:16])
self.eccentricity = float(self.line2[26:33])
self.raan = float(self.line2[17:25])
self.argperigree = float(self.line2[34:42])
self.mean_anomaly = float(self.line2[43:51])
self.mean_motion = float(self.line2[52:63])
def generate_ephemeris(name, tle1, tle2, date_str):
date = datetime.datetime.strptime(date_str, '%Y-%m-%dT%H:%M:%S')
date = date.replace(tzinfo=utc)
lst = Time(date, scale='utc', location=SITE_LOCATION).sidereal_time('apparent')
print('name', name)
print('tle1', tle1)
print('tle2', tle2)
print('date', date)
observer = Topos(
latitude_degrees=SITE_LOCATION.lat.to(u.deg).value,
longitude_degrees=SITE_LOCATION.lon.to(u.deg).value,
elevation_m=SITE_LOCATION.height.to(u.m).value)
time = load.timescale().utc(date)
target = EarthSatellite(tle1, tle2, name)
ra, dec, distance = (target - observer).at(time).radec()
alt, az, distance = (target - observer).at(time).altaz()
subpos = target.at(time).subpoint()
lat = subpos.latitude.degrees
lon = subpos.longitude.degrees
if lon > 180:
lon -= 360
field = SkyCoord(ra.hours, dec.degrees, unit=(u.hourangle, u.deg))
time2 = load.timescale().utc(date + datetime.timedelta(seconds=5))
ra2, dec2, distance2 = (target - observer).at(time2).radec()
dra = (ra2._degrees - ra._degrees) * 3600 / 5
ddec = (dec2.degrees - dec.degrees) * 3600 / 5
return {
'name': name,
'date': date.strftime('%Y-%m-%dT%H:%M:%S'),
'ra': Angle(ra.to(u.deg)).to_string(unit=u.hourangle, sep=':'),
'ha': (lst - field.icrs.ra).wrap_at(12 * u.hourangle).to_string(sep=':', unit=u.hourangle, precision=2),
'dec': Angle(dec.to(u.deg)).to_string(unit=u.deg, sep=':'),
'dra': round(dra, 3),
'ddec': round(ddec, 3),
'alt': round(alt.degrees, 6),
'az': round(az.degrees, 6),
'latitude': round(lat, 3),
'longitude': round(lon, 3)
}
def predict_doppler_from_tle(tle1, tle2, start_time, gs, base_freq):
end_time = ts.tt_jd(start_time.tt + 1) #predict for 1 day in future
tle_sat = EarthSatellite(tle1, tle2)
times, events = tle_sat.find_events(gs,
start_time,
end_time,
altitude_degrees=0.0)
#Find events where the satellite sets below 10 degrees, and use this to split the times array up into individual passes
sat_passes = []
start = -1
end = -1
for i, event in enumerate(events):
if (event == 0):
start = i
if (event == 2) and (start > end):
end = i
sat_passes.append([times[start], times[end]])
for sat_pass in sat_passes:
p_start = sat_pass[0]
p_end = sat_pass[-1]
#Split pass timeframe into 1000
time_points = ts.tt_jd(np.linspace(p_start.tt, p_end.tt, 1000))
sat_range_rate = tle_sat.at(time_points).velocity.km_per_s - gs.at(
time_points).velocity.km_per_s
sat_range = tle_sat.at(time_points).position.km - gs.at(
time_points).position.km
#Take the range rate's component in the direction of the range
radial_velocity = np.array([np.dot([a[b] for a in sat_range], [a[b] for a in sat_range_rate]) \
/ np.linalg.norm([a[b] for a in sat_range]) for b in range(1000)])
shifted_freqs = base_freq / (1 + radial_velocity / c)
plt.plot(time_points.tt, shifted_freqs, markersize=1)
plt.xlabel("Time (Julian Days)")
plt.ylabel("Shifted frequency (Hz)")
plt.show()
def test_appendix_c_satellite():
lines = appendix_c_example.splitlines()
sat = EarthSatellite(lines, earth)
jd_epoch = sat._sgp4_satellite.jdsatepoch
three_days_later = jd_epoch + 3.0
offset = JulianDate(tt=three_days_later)._utc_float() - three_days_later
jd = JulianDate(tt=three_days_later - offset)
# First, a crucial sanity check (which is, technically, a test of
# the `sgp4` package and not of Skyfield): are the right coordinates
# being produced by our Python SGP4 propagator for this satellite?
rTEME, vTEME, error = sat._position_and_velocity_TEME_km(jd)
assert abs(-9060.47373569 - rTEME[0]) < 1e-8
assert abs(4658.70952502 - rTEME[1]) < 1e-8
assert abs(813.68673153 - rTEME[2]) < 1e-8
assert abs(-2.232832783 - vTEME[0]) < 1e-9
assert abs(-4.110453490 - vTEME[1]) < 1e-9
assert abs(-3.157345433 - vTEME[2]) < 1e-9
def test_appendix_c_satellite():
lines = appendix_c_example.splitlines()
sat = EarthSatellite(lines, earth)
jd_epoch = sat._sgp4_satellite.jdsatepoch
three_days_later = jd_epoch + 3.0
jd = JulianDate(tt=three_days_later)
jd.ut1 = array(three_days_later)
# First, a crucial sanity check (which is, technically, a test of
# the `sgp4` package and not of Skyfield): are the right coordinates
# being produced by our Python SGP4 propagator for this satellite?
rTEME, vTEME = sat._position_and_velocity_TEME_km(jd)
assert abs(-9060.47373569 - rTEME[0]) < 1e-8
assert abs(4658.70952502 - rTEME[1]) < 1e-8
assert abs(813.68673153 - rTEME[2]) < 1e-8
assert abs(-2.232832783 - vTEME[0]) < 1e-9
assert abs(-4.110453490 - vTEME[1]) < 1e-9
assert abs(-3.157345433 - vTEME[2]) < 1e-9
def test_iss_altitude_computed_with_gcrs(iss_transit):
dt, their_altitude = iss_transit
cst = timedelta(hours=-6) #, minutes=1)
dt = dt - cst
t = api.load.timescale(delta_t=67.2091).utc(dt)
lines = iss_tle.splitlines()
s = EarthSatellite(lines, None)
lake_zurich = api.Topos(latitude_degrees=42.2, longitude_degrees=-88.1)
alt, az, d = lake_zurich.at(t).observe(s).altaz()
print(dt, their_altitude, alt.degrees, their_altitude - alt.degrees)
assert abs(alt.degrees - their_altitude) < 2.5 # TODO: tighten this up?
def test_appendix_c_satellite():
lines = appendix_c_example.splitlines()
sat = EarthSatellite(lines, None)
ts = api.load.timescale()
jd_epoch = sat._sgp4_satellite.jdsatepoch
three_days_later = jd_epoch + 3.0
offset = ts.tt(jd=three_days_later)._utc_float() - three_days_later
t = ts.tt(jd=three_days_later - offset)
# First, a crucial sanity check (which is, technically, a test of
# the `sgp4` package and not of Skyfield): are the right coordinates
# being produced by our Python SGP4 propagator for this satellite?
rTEME, vTEME, error = sat._position_and_velocity_TEME_km(t)
assert abs(-9060.47373569 - rTEME[0]) < 1e-8
assert abs(4658.70952502 - rTEME[1]) < 1e-8
assert abs(813.68673153 - rTEME[2]) < 1e-8
assert abs(-2.232832783 - vTEME[0]) < 1e-9
assert abs(-4.110453490 - vTEME[1]) < 1e-9
assert abs(-3.157345433 - vTEME[2]) < 1e-9
def test_iss_altitude_computed_with_gcrs(iss_transit):
dt, their_altitude = iss_transit
cst = timedelta(hours=-6) #, minutes=1)
dt = dt - cst
jd = JulianDate(utc=dt, delta_t=67.2091)
lines = iss_tle.splitlines()
s = EarthSatellite(lines, earth)
lake_zurich = earth.topos(latitude_degrees=42.2, longitude_degrees=-88.1)
alt, az, d = lake_zurich.gcrs(jd).observe(s).altaz()
print(dt, their_altitude, alt.degrees, their_altitude - alt.degrees)
assert abs(alt.degrees - their_altitude) < 2.5 # TODO: tighten this up?
def create_ground_track(out_path, sat, tle=None, start=None, delta_min=1, num_steps=1440, min_sun=None, sensor_angle=None, check_swath=False):
"""
Compute the ground track and sensor swatch for Globals and then write to GeoJSON
"""
# get globals tles from Celestrak if TLE not passed in
if tle is None:
tle = get_globals_tle(sat)
timescale = load.timescale(builtin=True)
times_dt = generate_time_array(start, delta_min, num_steps)
times = timescale.utc(times_dt)
sat_obj = EarthSatellite(line1=tle[0], line2=tle[1])
subsat = sat_obj.at(times).subpoint()
lat = subsat.latitude.degrees
lon = subsat.longitude.degrees
track = np.concatenate([lon.reshape(-1, 1), lat.reshape(-1, 1)], axis=1)
track_list = filter_sun_elevation(track, times_dt, min_sun)
track_list = correct_rollover(track_list)
properties = {"sat": sat, "start_time": str(times_dt[0]), "stop_time": str(times_dt[-1]), "time_step_minutes": delta_min}
write_track_geojson(out_path, track_list, properties)
if sensor_angle is not None:
swath_list = get_sensor_swath(track_list, sensor_angle, GLOBALS_ALTITUDE_KM[sat])
swath_out_path = os.path.splitext(out_path)[0] + "_swath" + os.path.splitext(out_path)[1]
write_track_geojson(swath_out_path, swath_list, properties)
if check_swath:
swath_check_out_path = os.path.splitext(out_path)[0] + "_swath_test" + os.path.splitext(out_path)[1]
check_swath(swath_check_out_path, track_list, sensor_angle, 1000*GLOBALS_ALTITUDE_KM[sat])
def test_iss_altitude_computed_with_bcrs(iss_transit):
dt, their_altitude = iss_transit
cst = timedelta(hours=-6) #, minutes=1)
dt = dt - cst
jd = Timescale(delta_t=67.2091).utc(dt)
lines = iss_tle.splitlines()
s = EarthSatellite(lines, None)
earth = api.load('de421.bsp')['earth']
lake_zurich = earth.topos(latitude_degrees=42.2, longitude_degrees=-88.1)
# Compute using Solar System coordinates:
alt, az, d = lake_zurich.at(jd).observe(s).altaz()
print(dt, their_altitude, alt.degrees, their_altitude - alt.degrees)
assert abs(alt.degrees - their_altitude) < 2.5 # TODO: tighten this up?
def __init__(self, line1, line2, name=None):
self.line1 = line1
self.line2 = line2
if name is not None:
self.name = name[2:]
self.obs = TOPOS_LOCATION
self.obj = EarthSatellite(line1, line2, name)
self.ts = TS
self.norad_id = int(self.line1[2:7])
self.yday = float(self.line1[20:32])
self.inclination = float(self.line2[8:16])
self.eccentricity = float(self.line2[26:33])
self.raan = float(self.line2[17:25])
self.argperigree = float(self.line2[34:42])
self.mean_anomaly = float(self.line2[43:51])
self.mean_motion = float(self.line2[52:63])
def __init__(self, line1, line2, name=None):
"""
Initiates the TLE
Parameters
----------
line1, line2 : str
First and second lines of the TLE
name : str, optional
Name of the object to which the TLE is attributed
"""
self.line1 = line1
self.line2 = line2
if name is not None:
self.name = name[2:]
else:
self.name = 'UNKNOWN'
# ephemeris info
self.obs = TOPOS_LOCATION
self.obj = EarthSatellite(line1, line2, name)
self.ts = TS
from datetime import datetime
from astropy.table import Table
import numpy as np
import time
from st.site import Site
EPHEM_PATH = '/Users/jblake95/GitHub/tlemcee/ephem_astra_1m_20180618_LaPalma.csv'
TS = load.timescale()
ephem = Table.read(EPHEM_PATH)
line1 = '1 33436U 08057A 18170.03521762 .00000104 00000-0 00000+0 0 9996'
line2 = '2 33436 0.0136 355.3865 0004990 118.0808 185.6030 1.00271245 35197'
obj = EarthSatellite(line1, line2)
site = Site('LaPalma')
# test 1 - without arrays
times = []
for t in ephem['UTC']:
times.append(datetime.strptime(t, '%Y-%m-%dT%H:%M:%S.%f'))
times = np.array(times)
print('Computing for {} positions'.format(len(times)))
from astropy.coordinates import SkyCoord
from astropy import units as u
t0 = time.time()
ra, dec = np.zeros((2, len(times)))
for t, dt in enumerate(times):
def test_epoch_date():
# Example from https://celestrak.com/columns/v04n03/
s = appendix_c_example.replace('00179.78495062', '98001.00000000')
sat = EarthSatellite(s.splitlines(), None)
assert sat.epoch.utc_jpl() == 'A.D. 1998-Jan-01 00:00:00.0000 UT'
def unpackElements(tle):
"""
Unpack TLE input
Parameters
----------
tle : st.tle.TLE
TLE object to unpack
Returns
-------
None
"""
tle.checksums = []
# line 1 elements
if tle.line1 is not None:
tle.norad_id = Norad_ID(tle.line1)
tle.designator = Designator(tle.line1)
tle.epoch = Epoch(tle.line1)
tle.mmdot = Mmdot(tle.line1)
tle.mmdot2 = Mmdot2(tle.line1)
tle.drag = Drag(tle.line1)
tle.setnumber = SetNumber(tle.line1)
tle.checksums.append(CheckSum(tle.line1))
else:
tle.norad_id = Norad_ID()
tle.designator = Designator()
tle.epoch = Epoch()
tle.mmdot = Mmdot()
tle.mmdot2 = Mmdot2()
tle.drag = Drag()
tle.setnumber = SetNumber()
tle.line1 = EmptyTLE.line1.format(tle.norad_id.entry,
tle.designator.entry,
tle.epoch.entry, tle.mmdot.entry,
tle.mmdot2.entry, tle.drag.entry,
tle.setnumber.entry)
# compute checksum
tle.checksums.append(CheckSum(tle.line1))
tle.line1 = '{}{}'.format(tle.line1[:-1], tle.checksums[0].entry)
# line 2 elements
if tle.line2 is not None:
tle.inclination = Inclination(tle.line2)
tle.raan = RAAN(tle.line2)
tle.eccentricity = Eccentricity(tle.line2)
tle.argperigee = ArgPerigee(tle.line2)
tle.meananomaly = MeanAnomaly(tle.line2)
tle.mm = Mm(tle.line2)
tle.revnumber = RevNumber(tle.line2)
tle.checksums.append(CheckSum(tle.line2))
else:
tle.inclination = Inclination()
tle.raan = RAAN()
tle.eccentricity = Eccentricity()
tle.argperigee = ArgPerigee()
tle.meananomaly = MeanAnomaly()
tle.mm = Mm()
tle.revnumber = RevNumber()
tle.line2 = EmptyTLE.line2.format(
tle.norad_id.entry, tle.inclination.entry, tle.raan.entry,
tle.eccentricity.entry, tle.argperigee.entry,
tle.meananomaly.entry, tle.mm.entry, tle.revnumber.entry)
# compute checksum
tle.checksums.append(CheckSum(tle.line2))
tle.line2 = '{}{}'.format(tle.line2[:-1], tle.checksums[1].entry)
# name
if tle.name is not None:
# remove line number if from 3le
if tle.name[0] == '0':
tle.name = tle.name[2:]
else:
tle.name = 'UNKNOWN'
tle._object = EarthSatellite(tle.line1, tle.line2, tle.name)
return None
def modifyElements(tle, checksum, norad_id, designator, epoch, mmdot, mmdot2,
drag, setnumber, inclination, raan, eccentricity,
argperigee, meananomaly, mm, revnumber):
"""
Modify elements of a TLE object
Parameters
----------
tle : st.tle.TLE
TLE object in need of modification
checksum : bool
Toggle to recalculate checksum
See descriptions above for suitable inputs for args
(set to None for no modification)
Returns
-------
None
"""
if norad_id is not None:
tle.norad_id = Norad_ID(norad_id)
tle.line1 = '{}{}{}'.format(tle.line1[:2], tle.norad_id.entry,
tle.line1[7:])
tle.line2 = '{}{}{}'.format(tle.line2[:2], tle.norad_id.entry,
tle.line2[7:])
if designator is not None:
tle.designator = Designator(designator)
tle.line1 = '{}{}{}'.format(tle.line1[:9], tle.designator.entry,
tle.line1[17:])
if epoch is not None:
tle.epoch = Epoch(epoch)
tle.line1 = '{}{}{}'.format(tle.line1[:18], tle.epoch.entry,
tle.line1[32:])
if mmdot is not None:
tle.mmdot = Mmdot(mmdot)
tle.line1 = '{}{}{}'.format(tle.line1[:33], tle.mmdot.entry,
tle.line1[43:])
if mmdot2 is not None:
tle.mmdot2 = Mmdot2(mmdot2)
tle.line1 = '{}{}{}'.format(tle.line1[:44], tle.mmdot2.entry,
tle.line1[52:])
if drag is not None:
tle.drag = Drag(drag)
tle.line1 = '{}{}{}'.format(tle.line1[:53], tle.drag.entry,
tle.line1[61:])
if setnumber is not None:
tle.setnumber = SetNumber(setnumber)
tle.line1 = '{}{}{}'.format(tle.line1[:64], tle.setnumber.entry,
tle.line1[68:])
if inclination is not None:
tle.inclination = Inclination(inclination)
tle.line2 = '{}{}{}'.format(tle.line2[:8], tle.inclination.entry,
tle.line2[16:])
if raan is not None:
tle.raan = RAAN(raan)
tle.line2 = '{}{}{}'.format(tle.line2[:17], tle.raan.entry,
tle.line2[25:])
if eccentricity is not None:
tle.eccentricity = Eccentricity(eccentricity)
tle.line2 = '{}{}{}'.format(tle.line2[:26], tle.eccentricity.entry,
tle.line2[33:])
if argperigee is not None:
tle.argperigee = ArgPerigee(argperigee)
tle.line2 = '{}{}{}'.format(tle.line2[:34], tle.argperigee.entry,
tle.line2[42:])
if meananomaly is not None:
tle.meananomaly = MeanAnomaly(meananomaly)
tle.line2 = '{}{}{}'.format(tle.line2[:43], tle.meananomaly.entry,
tle.line2[51:])
if mm is not None:
tle.mm = Mm(mm)
tle.line2 = '{}{}{}'.format(tle.line2[:52], tle.mm.entry,
tle.line2[63:])
if revnumber is not None:
tle.revnumber = RevNumber(revnumber)
tle.line2 = '{}{}{}'.format(tle.line2[:63], tle.revnumber.entry,
tle.line2[68:])
if checksum:
calculateCheckSums(tle)
tle._object = EarthSatellite(tle.line1, tle.line2, tle.name)
return None