Flyby properties

Search for the closest approach point

The location of the closest approach (CA) point is always computed internally to ensure that the flyby is correctly centered on its lowest altitude with a resolution of 1 sec.

To ensure great performance, the CA location search is performed in a 3-step process:

• 1st step with a coarse resolution (20 min at CA ± 12h)

• 2nd step with a medium resolution (1 min at CA ± 30 min)

• 3rd step with a fine resolution (1 sec at CA ± 2 min)

By default the final sampling temporal steps are irregular with a high resolution only around the CA:

• 1 pt from CA -12 h to CA -2 h every 10 min

• 1 pt from CA -2 h to CA -1 h every 1 min

• 1 pt from CA -1 h to CA -10 m every 10 sec

• 1 pt from CA -10 m to CA +10 m every 1 sec

• 1 pt from CA +10 m to CA +1 h every 10 sec

• 1 pt from CA +1 h to CA +2 h every 1 min

• 1 pt from CA +2 h to CA +12 h every 10 min

fig = plt.figure(figsize=(12, 4))
ax = fig.add_subplot()

ax.plot(flyby.utc, flyby.alt, '.', color='tab:orange')

# Optional labels
ax.set_ylabel('Altitude')
ax.xaxis.set_major_formatter(date_ticks)
ax.yaxis.set_major_formatter(km_ticks)

ax.set_title('Ganymede 1G1 flyby');

List of the available properties

A Flyby object behaves exactly as a Trajectory object but also has additional properties:

• utc_ca: the closest approach UTC time.

• date_ca: the closest approach date.

• lon_e_ca: the sub-spacecraft west longitude at closest approach.

• lat_ca: the sub-spacecraft latitude at closest approach.

• alt_ca: the altitude at closest approach (km).

• inc_ca: the incidence angle at closest approach (degree).

• emi_ca: the emission angle at closest approach (degree).

• phase_ca: the phase angle at closest approach (degree).

• pixel_scale_ca: cross-track iFOV projected on the target body at closest approach (km/pixel).

• t_ca: the relative time to closest approach.

• ca: a Trajectory with only the closest approach point.

Represent one or more flybys on a Map

fig = plt.figure(figsize=(12, 9))
ax = fig.add_subplot(projection=GANYMEDE)

for name, flyby in tour.get_flybys(alt_min=500).items():
    ax.plot(flyby.where(flyby.alt < 20_000), 'inc',
            linewidth=3, vmin=0, vmax=90, cbar=False)

    ax.plot(flyby.ca, 'o', color='lightgrey')

    ax.annotate(f'{name} ({flyby.date_ca})', flyby.ca.lonlat,
                xytext=(0, 10), textcoords='offset points',
                color='lightgrey', ha='center', va='center')

ax.colorbar(vmin=0, vmax=90, label='inc', extend='max')
ax.set_title('Ganymede flybys below 500 km at CA');

Temporal window below a given altitude

You can use the alt_window() function, if you need to find when the flyby is below a given altitude (km):

flyby.alt_window(20_000)

(numpy.datetime64('2032-04-11T03:13:10'),
 numpy.datetime64('2032-04-11T05:16:32'),
 datetime.timedelta(seconds=7402))

You will get, the start and stop times when these conditions are met and the duration of the window.