#!/usr/bin/env python3

# -*- coding: utf-8 -*-

"""

NH_TEST_KEM_ATS -- test some trajectory files

This is just a simple one-off program to do some tests on YPG's KEM flyby trajectories.

Concl of this problem: She used one NAIF ID for MU69, and the earlier trajectory I had was using a different one.

Created on Tue Jun 27 22:14:44 2017

@author: throop

"""

import math # We use this to get pi. Documentation says math is 'always available'

# but apparently it still must be imported.

import os.path

from astropy.utils import data

from astropy.wcs import WCS

import astropy

import matplotlib

import matplotlib.pyplot as plt # pyplot

from matplotlib.figure import Figure

import numpy as np

import spiceypy as sp

# HBT imports

import hbt

sp.furnsh('kernels_kem_ats.tm')

utc_start = "2019 1 Jan 06:40:00"

utc_end = "2019 1 Jan 07:20:00"

et_start = sp.utc2et(utc_start)

et_end = sp.utc2et(utc_end)

et_mid = (et_start + et_end)/2

num_dt = 500

et = hbt.frange(et_start, et_end, num_dt)

name_target = 'MU69'

name_observer = 'New Horizons'

dist = np.zeros(num_dt)

phase = np.zeros(num_dt)

for i,et_i in enumerate(et):

(state,_) = sp.spkezr(name_target, et_i, 'J2000', 'LT+S', name_observer)

dist[i] = np.sqrt(np.sum(state[0:3]**2))

plt.plot(et - et_mid, dist)

plt.xlabel('Dist [km]')

plt.ylabel('Seconds from c/a')

plt.show()

print("dist[0] = {}".format(dist))