# Going to Jupiter with Python using Jupyter and poliastro¶

Let us recreate with real data the Juno NASSA Mission. The main objectives of Juno spacecraft is to study the Jupiter planet: how was its formation, its evolution along time, atmospheric characteristics…

First of all, let us import some of our favourite Python packages: numpy, astropy and poliastro!

```
[1]:
```

```
import numpy as np
import astropy.units as u
from astropy.time import Time
from astropy.coordinates import solar_system_ephemeris
from poliastro.bodies import Sun, Earth, Jupiter
from poliastro.twobody import Orbit
from poliastro.maneuver import Maneuver
from poliastro.plotting import StaticOrbitPlotter
from poliastro.util import norm
solar_system_ephemeris.set("jpl")
```

```
[1]:
```

```
<ScienceState solar_system_ephemeris: 'jpl'>
```

All the data for Juno’s mission is sorted here. The main maneuvers that the spacecraft will perform are listed down:

- Inner cruise phase 1: This will set Juno in a new orbit around the sun.
- Inner cruise phase 2: Fly-by around Earth. Gravity assist is performed.
- Inner cruise phase 3: Jupiter insertion maneuver.

Let us first define the main dates other relevant parameters of the mission.

```
[2]:
```

```
## Main dates
date_launch = Time("2011-08-05 16:25", scale="utc")
date_flyby = Time("2013-10-09 19:21", scale="utc")
date_arrival = Time("2016-07-05 03:18", scale="utc")
# Atlas V supplied a launch energy
C_3 = 31.1 * u.km ** 2 / u.s ** 2
```

With previous dates we can create the different orbits that define the position of the Earth along the mission.

```
[3]:
```

```
# Initial state of the Earth
ss_e0 = Orbit.from_body_ephem(Earth, date_launch)
r_e0, v_e0 = ss_e0.rv()
# State of the Earth the day of the flyby
ss_efly = Orbit.from_body_ephem(Earth, date_flyby)
r_efly, v_efly = ss_efly.rv()
# Plot initial Earth's position
plotter = StaticOrbitPlotter()
plotter.plot(ss_e0, label="Initial Earth's position", color="blue")
```

```
/home/lobo/Github/poliastro/src/poliastro/twobody/orbit.py:393: TimeScaleWarning:
Input time was converted to scale='tdb' with value 2011-08-05 16:26:06.183. Use Time(..., scale='tdb') instead.
/home/lobo/Github/poliastro/src/poliastro/twobody/orbit.py:393: TimeScaleWarning:
Input time was converted to scale='tdb' with value 2013-10-09 19:22:07.182. Use Time(..., scale='tdb') instead.
/home/lobo/Github/poliastro/src/poliastro/twobody/orbit.py:1095: UserWarning:
Frame <class 'astropy.coordinates.builtin_frames.icrs.ICRS'> does not support 'obstime', time values were not returned
```

```
[3]:
```

```
[<matplotlib.lines.Line2D at 0x7f4a1fa62cf8>,
<matplotlib.lines.Line2D at 0x7f4a2013ff28>]
```

Since both Earth states have been obtained (initial and flyby) we can now solve for Juno’s maneuvers. The first one sets Juno into an elliptical orbit around the Sun so it apply a gravity assist around the Earth.

```
[4]:
```

```
# Assume that the insertion velocity is tangential to that of the Earth
dv = C_3 ** 0.5 * v_e0 / norm(v_e0)
# We create the maneuver from impulse constructor
man = Maneuver.impulse(dv)
```

If we now apply previous maneuver to the Junos’s initial orbit (assume it is the Earth’s one for simplicity), we will obtain the orbit around the Sun for Juno. The first inner cruise maneuver is defined just till the ahelion orbit. While Juno is traveling around its new orbit, Earth is also moving. After Juno reaches the aphelion it will be necessary to apply a second maneuver so the flyby is performed around Earth. Once that is achieved a final maneuver will be made in order to benefit from the gravity assist. Let us first propagate Juno’s orbit till the aphelion.

```
[5]:
```

```
# Inner Cruise 1
ic1 = ss_e0.apply_maneuver(man)
ic1_end = ic1.propagate_to_anomaly(180.0 * u.deg)
# We solve for Earth's position when Juno is at aphelion
ss_e_ic1 = Orbit.from_body_ephem(Earth, epoch=ic1_end.epoch)
# We can check new bodies positions
plotter = StaticOrbitPlotter()
plotter.plot(ss_e_ic1, label="Earth's position at flyby", color="blue")
plotter.plot_trajectory(ic1_end.sample(min_anomaly=0*u.deg, max_anomaly=180*u.deg),
label="Inner cruise 1 full orbit",
color="orange")
```

```
/home/lobo/Github/poliastro/src/poliastro/twobody/orbit.py:1095: UserWarning:
Frame <class 'astropy.coordinates.builtin_frames.icrs.ICRS'> does not support 'obstime', time values were not returned
```

```
[5]:
```

```
[<matplotlib.lines.Line2D at 0x7f4a1fb56828>]
```

We can check that the period of the orbit is similar to the one stated in the mission’s documentation. Remember that in previous plot we only plotter half of the orbit for Juno first maneuver and the period is the time that would take Juno to complete one full revolution around this new orbit.

```
[6]:
```

```
ic1.period.to(u.day)
```

```
[6]:
```

Notice in previous plot that Earth’s position is not the initial one since while Juno is moving Earth also does. We now solve for the Lambert maneuver in order to perform a flyby around the earth when it is at flyby date.

```
[7]:
```

```
# Let's compute the Lambert solution to do the flyby of the Earth
man_flyby = Maneuver.lambert(ic1_end, ss_efly)
imp_a, imp_b = man_flyby.impulses
print("Initial impulse:", imp_a)
print("Final impulse:", imp_b)
```

```
Initial impulse: (<Quantity 0. s>, <Quantity [0.88693809, 0.56813305, 0.2473722 ] km / s>)
Final impulse: (<Quantity 34658187.19869139 s>, <Quantity [-911111.20112242, -502306.17344648, -217608.72240858] km / d>)
```

```
[8]:
```

```
# Check the initial delta-V
dv_a = imp_a[-1]
norm(dv_a)
```

```
[8]:
```

We can now solve for the flyby orbit that will help Juno with the gravity assist. Again, the inner pahse 2 maneuver is define till Juno reaches Earth’s position for the flyby date although the full orbit is plotted.

```
[9]:
```

```
# Let us apply the maneuver
ic2, ss_flyby = ic1_end.apply_maneuver(man_flyby, intermediate=True)
# We propagate the transfer orbit till the flyby occurs
ic2_end = ic2.propagate(date_flyby)
plotter = StaticOrbitPlotter()
plotter.plot(ss_efly, label="Earth's position at flyby", color="blue")
plotter.plot_trajectory(ic1.sample(max_anomaly=180*u.deg),
label="Inner cruise 1",
color="orange")
plotter.plot_trajectory(ic2_end.sample(min_anomaly=180*u.deg, max_anomaly=400*u.deg),
label="Inner cruise 2 full orbit",
color="green")
```

```
/home/lobo/Github/poliastro/src/poliastro/twobody/orbit.py:1095: UserWarning:
Frame <class 'astropy.coordinates.builtin_frames.icrs.ICRS'> does not support 'obstime', time values were not returned
```

```
[9]:
```

```
[<matplotlib.lines.Line2D at 0x7f4a20110828>]
```

We can now start solving for the manuever that will take Juno to Jupiter. Another Lmabert maneuver is required but first let us solve for Jupiter position on arrival.

```
[10]:
```

```
# And now, go to Jupiter!
ss_j = Orbit.from_body_ephem(Jupiter, date_arrival)
```

```
/home/lobo/Github/poliastro/src/poliastro/twobody/orbit.py:393: TimeScaleWarning:
Input time was converted to scale='tdb' with value 2016-07-05 03:19:08.184. Use Time(..., scale='tdb') instead.
```

```
[11]:
```

```
# Solving for maneuver to Jupiter
man_jupiter = Maneuver.lambert(ic2_end, ss_j)
imp_a, imp_b = man_jupiter.impulses
print("Initial impulse:", imp_a)
print("Final impulse:", imp_b)
```

```
Initial impulse: (<Quantity 0. s>, <Quantity [-7.72107629, 2.07530268, 3.69516973] km / s>)
Final impulse: (<Quantity 86342221.001597 s>, <Quantity [ 1237.29016567, -447386.11128413, -146581.52932187] km / d>)
```

Again, we apply the maneuver.

```
[12]:
```

```
# Apply the maneuver
ic3, ss_target = ic2_end.apply_maneuver(man_jupiter, intermediate=True)
ic3_end = ic3.propagate(date_arrival)
```

Finally, we can plot all the different phases of the mission. This shows the whole power of *poliastro* package, since a beautiful image is created showing the whole maneuvering process.

```
[13]:
```

```
# Final plot for the whole mission
plotter = StaticOrbitPlotter()
plotter.plot(ss_efly, label="Earth's position at flyby", color="blue", trail=True)
plotter.plot_trajectory(ic1.sample(max_anomaly=180*u.deg),
label="Inner cruise 1",
color="orange")
plotter.plot_trajectory(ic2.sample(min_anomaly=180*u.deg, max_anomaly=400*u.deg),
label="Inner cruise 2",
color="green")
plotter.plot_trajectory(ic3.sample(min_anomaly=10*u.deg, max_anomaly=180*u.deg),
label="Inner cruise 3",
color="red")
plotter.plot(ss_j, label="Jupiter's position at arrival", color="purple", trail=True)
```

```
[13]:
```

```
[<matplotlib.collections.LineCollection at 0x7f4a1f88bd68>,
<matplotlib.lines.Line2D at 0x7f4a1f88b940>]
```