def _propagate(sat, dt):
'''
True equator mean equinox (TEME) position from `sgp4` at given time. Then converted to ITRS
Parameters
----------
sat : `sgp4.io.Satellite` instance
Satellite object filled from TLE
dt : `~datetime.datetime`
Time
Returns
-------
xs, ys, zs : float
TEME (=True equator mean equinox) position of satellite [km]
'''
# pos [km], vel [km/s]
position, velocity = sat.propagate(dt.year, dt.month, dt.day, dt.hour,
dt.minute,
dt.second + dt.microsecond / 1e6)
if position is None:
raise ValueError('Satellite propagation error')
# I _think_ this is supposed to take time since J2000 in days?
# looking at https://space.stackexchange.com/questions/25988/sgp4-teme-frame-to-j2000-conversion
jd_ut1 = dt - time_J2000
jd_ut1 = jd_ut1.days + jd_ut1.seconds / (3600. * 24)
new_position, new_velocity = sgp4lib.TEME_to_ITRF(
jd_ut1, np.array(position),
np.array(velocity) * 86400)
return tuple(new_position.tolist())
def sgp4Predict(s, t, jd, fr):
satellite = Satrec.twoline2rv(s, t)
jd += 0.5
# get the position and velocity vectors in TEME frame
e, r, v = satellite.sgp4(jd, fr)
# Conversion from TEME to ITRS
r, v = sgp4lib.TEME_to_ITRF(jd + fr, np.asarray(r), np.asarray(v) * 86400)
v = v / 86400
return r * 1000, v * 1000
def plot_sat(Xi, sat, start_time, stop_time, delta, MEOLUT, freq0):
satellite = TLE_read(
sat) #,'sarsat3.txt') - use optional argument to read different TLE
curr = start_time
timelist = list()
posilist = list()
velolist = list()
Rig_list = list()
Ri_list = list()
f_ig_prime_list = list()
f_i_prime_list = list()
f_inv_prime_list = list()
f_inv_ig_list = list()
f_ig_list = list()
while curr < stop_time:
curr += delta
timelist.append(curr)
for times in timelist:
position, velocity = satellite.propagate(times.year, times.month,
times.day, times.hour,
times.minute, times.second)
V_i_TE = [
x * 86400 for x in velocity
] # conversion because sgp4lib.TEME_to_ITRF function expects V in km/day
datetime1 = jday.JD(times)
X_i_ECEF, V_i_ECEF = sgp4lib.TEME_to_ITRF(
datetime1, array(position),
array(V_i_TE)) # get satellite pos and vel
posilist.append(X_i_ECEF)
V_i_ECEF = [x / 86400 for x in V_i_ECEF] # convert back to #km/sec
velolist.append(V_i_ECEF)
Rig = (MEOLUTLocDict[MEOLUT] - X_i_ECEF
) # Rig is vector from MEOLUT to satellite
Rig_list.append(Rig)
Rig_dot = dot(V_i_ECEF, (Rig / norm(Rig)))
Ri = (
Xi - X_i_ECEF
) # Xi is the beacon location, Ri is the vector from beacon to satellite
Ri_list.append(Ri)
Ri_dot = dot(V_i_ECEF, (Ri / norm(Ri)))
inverted = True if str(sat)[0] == '3' else False
freq_down = freq_sband if inverted == True else freq_lband
### this works here
#dF_ig = (Rig_dot/c)*freq_down
#dF_i = -(Ri_dot/c)*freq0 if inverted == True else (Ri_dot/c)*freq0
# testing here
dF_ig = -(Rig_dot / c) * freq0 if inverted == True else (Rig_dot /
c) * freq0
dF_i = (Ri_dot / c) * (freq_down - dF_ig
) #if inverted == True else (Ri_dot/c)*freq0
f_ig_prime = freq0 + dF_i + dF_ig
#f_ig_prime_list.append(f_ig_prime)
#f_i_prime = freq0 + dF_ig # not inverted
f_inv_ig = freq_inv - (f_ig_prime - freq_inv) + freq_shift
#f_inv_ig = f_ig_prime #-freq_inv +freq_shift
f_ig = f_inv_ig if inverted == True else f_ig_prime
f_ig_list.append(f_ig)
alt = [norm(x) for x in posilist]
rangelist = [norm(MEOLUTLocDict[MEOLUT] - x) for x in posilist]
#plotting TLE positional difference below
#fig, ax = plt.subplots()
#plt.plot(timelist, f_i_prime_list, 'g')
#plt.plot(timelist, f_ig_prime_list, 'b-')
#plt.plot(timelist, f_inv_prime_list,c='orange', linestyle = '-', linewidth = 3)
plt.plot(timelist, f_ig_list, c='purple', linewidth=3)
plt.axhline(y=freq0, color='g')
plt.legend(['f_ig'])
#plt.axhspan(406.04e6, 406.05e6)
plt.axhline(y=freq_inv, color='r', linestyle='--')
plt.grid(True)