def extrapolate_orbit_kepler(P, V, t, t0, mu=3.9860044188e14):
orbit = TwoBodyOrbit("", mu=mu) # create an instance
orbit.setOrbCart(t0, P, V) # define the orbit
Pout, Vout = orbit.posvelatt(t) # get position and velocity at t1
kepl = orbit.elmKepl() # get classical orbital elements
return Pout, Vout, kepl
class TwoBodyPred:
"""class for two body prediction
"""
def __init__(self, pname):
self.orbit = TwoBodyOrbit(pname, 'Sun', common.solarmu)
return
def fix_state(self, jd, ppos, pvel):
self.jd = jd
self.sunpos, self.sunvel = common.SPKposvel(10, self.jd)
jdsec = self.jd * common.secofday
self.ppos = ppos
self.pvel = pvel
pos = self.ppos - self.sunpos
vel = self.pvel - self.sunvel
self.orbit.setOrbCart(jdsec, pos, vel)
return
def set_pred_dv(self, dv, phi, elv):
relv = math.radians(elv)
rphi = math.radians(phi)
ldv = np.array([
dv * np.cos(relv) * np.cos(rphi),
dv * np.cos(relv) * np.sin(rphi),
dv * np.sin(relv)
])
self.pred_vel = self.pvel + \
common.ldv2ecldv(ldv, self.ppos, self.pvel, \
self.sunpos, self.sunvel)
jdsec = self.jd * common.secofday
pos = self.ppos - self.sunpos
vel = self.pred_vel - self.sunvel
self.orbit.setOrbCart(jdsec, pos, vel)
return
def points(self, ndata):
xs, ys, zs, times = self.orbit.points(ndata)
return xs + self.sunpos[0], ys + self.sunpos[1], zs + self.sunpos[2], \
times / common.secofday
def posvelatt(self, jd):
jdsec = jd * common.secofday
pos, vel =self.orbit.posvelatt(jdsec)
# sunpos, sunvel at jd
spos, svel = common.SPKposvel(10, jd)
return pos + spos, vel + svel
def fta(self, jd, tepos):
# compute fixed time arrival guidance
# jd : date of arrival
# tepos position of target at jd (barycenter origin)
dsec = (jd - self.jd) * common.secofday
ipos = self.ppos - self.sunpos
# sun position at end
esunpos, esunvel = common.SPKposvel(10, jd)
tpos = tepos - esunpos
ivel, tvel = lambert(ipos, tpos, dsec, common.solarmu, ccw=True)
iprobe_vel = self.pvel - self.sunvel
delta_v = ivel - iprobe_vel
localdv = common.eclv2lv(delta_v, self.ppos, self.pvel, self.sunpos,
self.sunvel)
return common.rect2polar(localdv)
def ftavel(self, jd, tepos):
# compute fixed time arrival guidance
# jd : date of arrival
# tepos position of target at jd (barycenter origin)
dsec = (jd - self.jd) * common.secofday
ipos = self.ppos - self.sunpos
# sun position and velocity at end
esunpos, esunvel = common.SPKposvel(10, jd)
tpos = tepos - esunpos
ivel, tvel = lambert(ipos, tpos, dsec, common.solarmu, ccw=True)
iprobe_vel = self.pvel - self.sunvel
delta_v = ivel - iprobe_vel
localdv = common.eclv2lv(delta_v, self.ppos, self.pvel, self.sunpos,
self.sunvel)
dv, phi, elv = common.rect2polar(localdv)
bc_ivel = ivel + self.sunvel
bc_tvel = tvel + esunvel
# returns intial velocity and terminal velocity (SSB origin)
return dv, phi, elv, bc_ivel, bc_tvel
def vta(self, jd, tpos, tvel):
print('vta function is under construction')
return
def elmKepl(self):
kepl = self.orbit.elmKepl()
kepl['epoch'] /= common.secofday # convert to 'JD(day)'
kepl['T'] /= common.secofday # convert to 'JD(day)'
if kepl['e'] < 1.0:
kepl['n'] *= common.secofday # convert to 'deg/day'
kepl['P'] /= common.secofday # convert to 'days'
return kepl