def test_orbits_are_same():
epoch = Time("2018-07-23")
# Orbit Parameters of Ceres
# Taken from https://ssd.jpl.nasa.gov/horizons.cgi
ss = Orbit.from_classical(
Sun,
2.767107584017257 * u.au,
0.07554802949294502 * u.one,
27.18502520750381 * u.deg,
23.36913256044832 * u.deg,
132.2919806192451 * u.deg,
21.28958091587153 * u.deg,
epoch,
)
ss1 = Orbit.from_horizons(name="Ceres", epoch=epoch)
assert ss.pqw()[0].value.all() == ss1.pqw()[0].value.all()
assert ss.r_a == ss1.r_a
assert ss.a == ss1.a
def test_plane_is_set_in_horizons():
plane = Planes.EARTH_ECLIPTIC
ss = Orbit.from_horizons(name="Ceres", plane=plane)
assert ss.plane == plane
def test_from_horizons_raise_valueerror():
with pytest.raises(ValueError) as exep:
Orbit.from_horizons(name="Dummy")
assert ("ValueError: Unknown target (Dummy). Maybe try different id_type?"
in exep.exconly())
def transfer_vel(body1, body2, attractor):
"""Returns transfer parameters for body1 (e.g. Earth) to body2 (e.g. Mars).
Optionally, the main attractor can be specified. If omitted, Sun is assumed.
Returns:
helio1 - heliocentric velocity at departure (before Hohmann) (body1)
helio2 - heliocentric velocity at arrival (body2)
v1 - heliocentric velocity at departure (after Hohmann burn)
v2 - heliocentric velocity at arrival (before Hohmann burn)
tof - time of flight (in days) """
# How to obtain the orbit. The from_horisons method seems to be no longer supported
# as of perylune 0.16.3.
method = "ephem" # allowed values are ephem, horizons_orbit
if attractor is None:
attractor = Sun
# Let's assume the calculations are done for 2020.
date_start = time.Time("2020-01-01 00:00", scale="utc").tdb
date_end = time.Time("2021-12-31 23:59", scale="utc").tdb
name1, id_type1 = name_to_horizons_id(body1)
name2, id_type2 = name_to_horizons_id(body2)
if method == "ephem":
# Get the ephemerides first and then contruct orbit based on them. This is the recommended
# way. See warning in Orbit.from_horizons about deprecation.
ephem1 = Ephem.from_horizons(name=name1,
epochs=time_range(date_start,
end=date_end),
plane=Planes.EARTH_ECLIPTIC,
id_type=id_type1)
ephem2 = Ephem.from_horizons(name=name2,
epochs=time_range(date_start,
end=date_end),
plane=Planes.EARTH_ECLIPTIC,
id_type=id_type2)
# Solve for departure and target orbits
orb1 = Orbit.from_ephem(Sun, ephem1, date_start + 180 * u.day)
orb2 = Orbit.from_ephem(Sun, ephem2, date_end)
elif method == "horizons_orbit":
# This is the old way. Sadly, it produces way better values.
orb1 = Orbit.from_horizons(name=name1,
attractor=attractor,
plane=Planes.EARTH_ECLIPTIC,
id_type=id_type1)
orb2 = Orbit.from_horizons(name=name2,
attractor=attractor,
plane=Planes.EARTH_ECLIPTIC,
id_type=id_type2)
else:
raise "Invalid method set."
# The escape_delta_v returns a tuple of escape velocity at current, periapsis, apoapsis.
helio1 = heliocentric_velocity(orb1)
helio2 = heliocentric_velocity(orb2)
#vesc1 = escape_vel(orb1, False)[1]
#vesc2 = escape_vel(orb2, False)[1]
hoh1, hoh2, tof = hohmann_velocity(orb1, orb2)
return helio1, helio2, hoh1, hoh2, tof
