#The MIT License (MIT)

#Copyright (c) 2012-2019 Juan Luis Cano Rodríguez and the poliastro development team

#Permission is hereby granted, free of charge, to any person obtaining a copy

#of this software and associated documentation files (the "Software"), to deal

#in the Software without restriction, including without limitation the rights

#to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

#copies of the Software, and to permit persons to whom the Software is

#furnished to do so, subject to the following conditions:

#The above copyright notice and this permission notice shall be included in all

#"copies or substantial portions of the Software.

import numpy as np

from numpy.linalg import norm

import matplotlib.pyplot as plt

from astropy import units as u

from astropy.time import Time, TimeDelta

from astropy.coordinates import solar_system_ephemeris

from poliastro.twobody.propagation import propagate, cowell

from poliastro.ephem import build_ephem_interpolant

from poliastro.core.elements import rv2coe

from poliastro.constants import rho0_earth, H0_earth

from poliastro.core.perturbations import atmospheric_drag_exponential, third_body, J2_perturbation

from poliastro.bodies import Earth, Moon

from poliastro.twobody import Orbit

from poliastro.plotting import OrbitPlotter3D

import plotly.io as pio

pio.renderers.default = "notebook_connected"

#Atmospheric drag

#The poliastro package now has several commonly used natural perturbations. One of them is atmospheric drag! See how one can monitor decay of the near-Earth orbit over time using our new module poliastro.twobody.perturbations!

R = Earth.R.to(u.km).value

k = Earth.k.to(u.km ** 3 / u.s ** 2).value

# parameters of a body

#C_D = 2.2 # dimentionless (any value would do)

#Min kommentar: ändrade från den betämda luftmotståndskonstanten C_D = 2 till att testa olika värden(värdena 1.02 till 2.0) i en vektor.

#Min kommentar: Dessutom lade jag till en for-loop för att programmet skulle ge mig svar för olika värden på C_D.

#C_D = np.array([1.22, 1.44, 1.66 ])

C_D = np.arange(1.50, 1.6, 0.1) #Min kommentar: Jag bytade från np.array till np.arange(börjar:1.5,slutar2.0,hoppar0.1)

for x in C_D:

A_over_m = ((np.pi / 4.0) * (u.m ** 2) / (100 * u.kg)).to_value(u.km ** 2 / u.kg) # km^2/kg #Min kommentar: Här tror jag vi antar att föremålet väger 100kg, men jag förstår inte area-beräkningen?

B = x * A_over_m #Min kommentar: Skrev in x istället för C_D

# parameters of the atmosphere

rho0 = rho0_earth.to(u.kg / u.km ** 3).value # kg/km^3

H0 = H0_earth.to(u.km).value #Min kommentar: Ändras atmosfärens egenskaper ju högre radien är i det här programmet?

#[<matplotlib.lines.Line2D at 0x7ffb5f511048>]

#Orbital Decay

#If atmospheric drag causes the orbit to fully decay, additional code is needed to stop the integration when the satellite reaches the surface.

#Please note that you will likely want to use a more sophisticated atmosphere model than the one in atmospheric_drag for these sorts of computations.

orbit = Orbit.circular(Earth, 230 * u.km, epoch=Time(0.0, format="jd", scale="tdb")) #Min kommentar: Här tror jag att jag kan ändra på värdet hos radien på omloppsbanan

tofs = TimeDelta(np.linspace(0 * u.h, 100 * u.d, num=200))#Min kommentar: Här tror jag deltatiden beskrivs, att den mäter mellan noll timmar till ett max antal dagar, samt att den mäter 2000 gånger.

from poliastro.twobody.events import LithobrakeEvent

lithobrake_event = LithobrakeEvent(R)

events = [lithobrake_event]

rr = propagate(

orbit,

tofs,

method=cowell,

ad=atmospheric_drag_exponential,

R=R,

C_D=x, #Min kommentar: Här ändrade jag från C_D till x på högra sidan likhetstecknet

A_over_m=A_over_m,

H0=H0,

rho0=rho0,

events=events,

)

print('{0} {1:.2f} {2}'.format('orbital decay seen after', lithobrake_event.last_t.to(u.d).value, 'days'))

plt.ylabel("h(t)")

plt.xlabel("t, days")

plt.plot(tofs.value, rr.norm() - Earth.R)

#[<matplotlib.lines.Line2D at 0x7ffb5f53f898>