MAXI Attitude Files (gdt.missions.maxi.attitude)

The MAXI mission provides attitude files that specify the orientation of MAXI relative to the J2000 frame that is sampled at an approximate 1-s cadence over a day. We can open these files using the MaxiAttitude class and extract the frame information from them.

For example we can read the example attitude file that is in the testing/example data:

>>> from gdt.core import data_path
>>> from gdt.missions.maxi.attitude import MaxiAttitude
>>> att_file = data_path / 'maxi-gsc/mx_mjd58849.att.gz'
>>> att = MaxiAttitude.open(att_file)
>>> att
<MaxiAttitude(filename="mx_mjd58849.att.gz") at 0x103afafa0>

To extract the MAXI frame, we do the following:

>>> frame = att.get_spacecraft_frame()
>>> frame
<MaxiFrame: 86401 frames;
 obstime=[631152082.011275, ...]
 quaternion=[(x, y, z, w) [ 0.76156184, -0.55583739,  0.14661502, -0.29928647], ...]>

Notice that this MaxiFrame object contains 86401 different frames, each defined at a particular obstime and with a quaternion defining the rotation between the MAXI frame and the J2000 frame. We can use this frame to do all of the things described in MAXI Reference Frame. For example, if we create an Astropy SkyCoord of an object on the sky, we can rotate it into each of the MAXI frames.

>>> from astropy.coordinates import SkyCoord
>>> coord = SkyCoord(100.0, -30.0, unit='deg')
>>> maxi_coords = coord.transform_to(frame)
>>> (maxi_coords.az, maxi_coords.el)
<Longitude [162.47630661, 162.46212383, 162.44592815, ...,  28.67196423,
              28.68926214,  28.70586066] deg>,
 <Latitude [ 33.71676537,  33.77730426,  33.83788703, ..., -32.13139582,
            -32.18918228, -32.2475741 ] deg>)

Or we can go in the other direction, and convert a MAXI coordinate into the celestial frame:

>>> maxi_coord = SkyCoord(50.0, 25.0, frame=frame, unit='deg')
>>> # convert to the Galactic frame
>>> maxi_coord.galactic
<SkyCoord (Galactic): (l, b) in deg
    [(335.29677607, -10.47592442), (335.26120761, -10.50898651),
     (335.22413471, -10.54205297), ..., (240.98969174,  45.17289394),
     (240.99658923,  45.22071526), (241.00427102,  45.26932204)]>

We can also extract a single frame or slice multiple frames:

>>> frame[100]
<MaxiFrame: 1 frames;
 obstime=[631152182.0114429]
 obsgeoloc=[(0., 0., 0.) m]
 obsgeovel=[(0., 0., 0.) m / s]
 quaternion=[(x, y, z, w) [ 0.7679603 , -0.53712165,  0.10544197, -0.33259481]]>

>>> frame[100:110]
<MaxiFrame: 10 frames;
 obstime=[631152182.0114429, ...]
 quaternion=[(x, y, z, w) [ 0.7679603 , -0.53712165,  0.10544197, -0.33259481], ...]>

Note that the attitude file contains only the attitude information, and there is no positional information, which is contained within the orbit file and is discussed further in MAXI Orbit Files. See MAXI Reference Frame for information about how to combine the attitude and orbit information into a single MaxiFrame object.

For more details about working with spacecraft frames, see Spacecraft Attitude, Position, and Coordinates.

Reference/API

gdt.missions.maxi.attitude Module

Classes

MaxiAttitude()

Class for reading a MAXI attitude file.

Class Inheritance Diagram