def create_node_from_list(self, t_list, ind_list):
"""Returns a node, using the t_list and ind_list to specify the path.
Args:
t_list (list): Epochs (MJD) of depart/approach.
ind_list (list): Indices of the asteroids to approach or depart from
Returns:
Node: Node that contains the full history of the path.
"""
# create the initial orbit:
initial = Orbit(name='Initial', index=ind_list[0])
rv = select_asteroid(ind_list[0]).rv(t_list[0])
initial.from_rv(t_list[0], *rv)
# create the initial node:
node = Node(t_list[0],
index=ind_list[0],
approach_orbit=initial,
parent=None)
# create all the legs:
for t, ind in zip(t_list[1:], ind_list[1:]):
node = node.create_next_node(target_ind=ind, target_epoch=t)
return node
def create_next_node(self, target_ind, target_epoch):
"""Function creates next node to be visited by solving Lambert, updating current sc mass
Args:
target_ind (int): next asteroid to be visited
target_epoch (float): epoch at which next asteroid is to be visited [MJD]
Returns:
(node): node object of input asteroid to be visited at input epoch
"""
t0 = self.epoch
r0, v0 = self.approach_orbit.rv()
# find next ast and get its position (vel not needed)
ast = select_asteroid(target_ind)
r_target, v_target = ast.rv(target_epoch)
# solve lamberts problem
v1, v2 = lb.lambert(mu, r0, r_target, (target_epoch - t0) * day2s)
# note that a maneouver is needed at the initial epoch to set us on a rendevousz path with target ast
dv = v1 - v0 # only the initial change in velocity needed
#incrememental cost (delta V, mass)
if self.parent_node is None:
# starting at earth
inc_cost = max(0, norm(dv) - 4.0)
# call mass_at_node to compute remaining mass after maneuver
#m_node = mass_at_node(1500, inc_cost) # FIXME - SAYS THAT mass_at_node() is not defined...
else:
inc_cost = norm(dv)
# call mass_at_node?
# create new orbit, index=-2 since it is a transfer
o_new = Orbit(name=f'Trx{self.len_of_chain()+1:2.0f}')
o_new.from_rv(target_epoch, r_target, v2)
# create new node
new_Node = Node(epoch=target_epoch,
index=target_ind,
approach_orbit=o_new,
parent=self)
# update cost and manouever history
new_Node.maneuvers = self.maneuvers + [(t0, dv)]
new_Node.cost = self.cost + inc_cost
return new_Node
