Using TLEs, vs using SPICE kernels¶

TLE's are generated for Pandora multiple times a day. These capture the instantaneous state of Pandora. TLE's are useful for predicting future positions for Pandora, because they can be propagated forward.

The SPK and CK SPICE kernels that PandoraSpacecraft uses are compressed/interpolated versions of the actual spacecraft bus telemetry, and so capture the "historical truth" of Pandora's state.

You can use PandoraSpacecraft in two modes:

1. Default Mode: This is the mode where PandoraSpacecraft will use the SPICE kernels made from the historical spacecraft bus telemetry. This can only be known in the past, but gives the as measured position, velocity, and pointing.
2. TLE Only Mode: This mode uses only the TLEs for the spacecraft. TLEs are considered "valid" for two days, and the most recent TLE is propagated for 1 year. This means that in this mode you are able to predict the future position of Pandora, but you are unable to access any pointing information.

Below we show how to switch modes, and the different altitudes obtained in the different modes

!!! warning PandoraSpacecraft may be innaccurate

The SPICE kernels for `PandoraSpacecraft` are built from recorded bus telemetry, which in some instances can be misreported or contain outliers/unphysical points. We endeavour to remove those times from the kernels, but some may remain. As such, the SPK and CK kernels are evaluated everywhere, but you should check they are physical in your analysis.

In [2]:

import numpy as np
import matplotlib.pyplot as plt
import pandoraspacecraft as psc

import numpy as np import matplotlib.pyplot as plt import pandoraspacecraft as psc

In [50]:

fig, ax = plt.subplots(dpi=150, facecolor='white')
# Use TLE Mode
ps = psc.PandoraSpacecraft(tles_only=True)
t = Time(np.linspace(ps.start_time.jd + 0.01, ps.end_time.jd - 0.01, 10000), format='jd')
alt = ps.get_altitude(t)
ax.plot(t.jd, alt.value, lw=0.1, c='k', label='TLE Mode')

# Use the default mode
ps = psc.PandoraSpacecraft()
t = Time(np.linspace(ps.start_time.jd + 0.01, ps.end_time.jd - 0.01, 10000), format='jd')
alt = ps.get_altitude(t)

ax.plot(t.jd, alt.value, lw=0.1, c='r', label='Default Mode')
ax.set(ylim=(6950, 7025), xlabel='Time [JD]', ylabel='Pandora Altitude [km]')
ax.legend()

fig, ax = plt.subplots(dpi=150, facecolor='white') # Use TLE Mode ps = psc.PandoraSpacecraft(tles_only=True) t = Time(np.linspace(ps.start_time.jd + 0.01, ps.end_time.jd - 0.01, 10000), format='jd') alt = ps.get_altitude(t) ax.plot(t.jd, alt.value, lw=0.1, c='k', label='TLE Mode') # Use the default mode ps = psc.PandoraSpacecraft() t = Time(np.linspace(ps.start_time.jd + 0.01, ps.end_time.jd - 0.01, 10000), format='jd') alt = ps.get_altitude(t) ax.plot(t.jd, alt.value, lw=0.1, c='r', label='Default Mode') ax.set(ylim=(6950, 7025), xlabel='Time [JD]', ylabel='Pandora Altitude [km]') ax.legend()

Out[50]:

<matplotlib.legend.Legend at 0x169d17940>