cheta.utils.ss_vector#

cheta.utils.ss_vector(start, stop=None, obj='Earth')#

Calculate vector to Earth, Sun, or Moon in Chandra body coordinates between start and stop dates at 5 minute (328 sec) intervals.

The return value in a NumPy structured array table (see below) which contains the distance in km from Chandra to the the solar system object along with the corresponding direction vectors in Chandra body coordinates and in the ECI frame. For convenience the attitude quaternion components are also provided.

Output table columns:

  • times: time in CXC seconds

  • distance: Distance to object (km)

  • body_x: X component of object in Chandra body coordinates

  • body_y: Y component of object in Chandra body coordinates

  • body_z: Z component of object in Chandra body coordinates

  • eci_x: X component of object relative to Chandra in ECI coordinates

  • eci_y: Y component of object relative to Chandra in ECI coordinates

  • eci_z: Z component of object relative to Chandra in ECI coordinates

  • q1: component 1 of the attitude quaternion

  • q2: component 2 of the attitude quaternion

  • q3: component 3 of the attitude quaternion

  • q4: component 4 of the attitude quaternion

Example:

from cheta.utils import ss_vector
from Ska.Matplotlib import plot_cxctime
vec = ss_vector('2010:001', '2010:030', obj='Sun')
figure(1)
clf()
subplot(2, 1, 1)
plot_cxctime(vec['times'], vec['body_x'], '-b')
plot_cxctime(vec['times'], vec['body_y'], '-r')
plot_cxctime(vec['times'], vec['body_z'], '-g')
subplot(2, 1, 2)
plot_cxctime(vec['times'], vec['distance'])
Parameters:

  • start – start time (DateTime format)

  • stop – stop time (DateTime format)

  • obj – solar system object (‘Earth’, ‘Moon’, ‘Sun’)

Returns:

table of vector values