toJson method 
    
    
    
  Implementation
  Map<String, dynamic> toJson() {
  return {
    'flickr_images': flickrImages,
    'name': name,
    'launch_date_utc': launchDateUtc,
    'launch_date_unix': launchDateUnix,
    'launch_mass_kg': launchMassKg,
    'launch_mass_lbs': launchMassLbs,
    'norad_id': noradId,
    'epoch_jd': epochJd,
    'orbit_type': orbitType,
    'apoapsis_au': apoapsisAu,
    'periapsis_au': periapsisAu,
    'semi_major_axis_au': semiMajorAxisAu,
    'eccentricity': eccentricity,
    'inclination': inclination,
    'longitude': longitude,
    'periapsis_arg': periapsisArg,
    'period_days': periodDays,
    'speed_kph': speedKph,
    'speed_mph': speedMph,
    'earth_distance_km': earthDistanceKm,
    'earth_distance_mi': earthDistanceMi,
    'mars_distance_km': marsDistanceKm,
    'mars_distance_mi': marsDistanceMi,
    'wikipedia': wikipedia,
    'video': video,
    'details': details,
    'id': id,
  };
}