Get spacecraft position¶
Getting MSO/VSO position of spacecraft¶
MSO/VSO is commonly used for data analysis.
Definition of the frames is
- x-axis
A vector from Mars/Venus to Sun
- z-axis
Outer product of the Mars/Venus velocity vector with respective to the Sun and x-axis. In other word, perpendicular to the orbital plane of Mars and Venus, pointing to north.
- y-axis
Outer product of z- and x-axes. (Close to anti-parallel to the velocity vector of Mars/Venus with respective to the Sun.)
Question 1¶
The following provides the spacecraft position in MSO at 2007-10-23T20:00:00 for MEX.
>>> import datetime
>>> from irfpy.mexpvat import mexspice
>>> mexspice.init()
>>> print(mexspice.get_position(datetime.datetime(2007, 10, 23, 20, 0, 0)))
[ 657.85025367 -2177.86777831 12580.52647702]
The key here is to call mexspice.init() function. It furnsh all the needed SPICE kernels.
Question 2¶
In the same manner as MEX, can you get the spacecraft position in VSO at 2007-10-23T20:00:00 for VEX?
>>> import datetime
>>> from irfpy.vexpvat import vexspice
>>> vexspice.init()
>>> print(vexspice.get_position(datetime.datetime(2007, 10, 23, 20, 0, 0)))
[-18480.45501421 -12553.85741085 -53308.79391638]
Getting positions in general¶
Question 3¶
The function irfpy.mexpvat.mexspice.get_position() and irfpy.vexpvat.vexspice.get_position()
can get the keywords of target, origin, and frame.
- target
SPICE name of the body to get its position
- origin
SPICE name of the body that is centered at
- frame
SPICE name of the frame
For example, if one wants to know the Sun (“SUN”) direction in the Martian geological coordinate (“IAU_MARS”), you may call it as
>>> import datetime
>>> from irfpy.mexpvat import mexspice
>>> mexspice.init() # Once per session is ok.
>>> print(mexspice.get_position(datetime.datetime(2007, 10, 23, 20, 0, 0),
... target='SUN', origin='MARS', frame='IAU_MARS'))
[ 1.76581081e+08 -1.32088158e+08 -3.92706156e+07]
Exercise¶
Plot the X-R position of VEX in the VSO frame between 2007-10-01T00:00:00 and 2007-10-02T00:00:00.
Obtain the closest approach time and distance of MEX on 2007-10-15.