Integral Position/Attitude History Data (gdt.missions.integral.orbit)

The ORBIT contains the spacecraft location, velocity in orbit and pointing information of an entire observation duration.

To read an ORBIT file, we open it with the IntegralOrbit class:

>>> from gdt.core import data_path
>>> from gdt.missions.integral.orbit import IntegralOrbit
>>> filepath = data_path.joinpath('integral/sc_orbit_param.fits.gz')
>>> orbithist = IntegralOrbit.open(filepath)
>>> orbithist
<SPIOrbit(filename="sc_orbit_param.fits.gz") at 0x11fde4b60>
No. Name    Ver     Type    Cards   Dimensions
    0       PRIMARY 1       PrimaryHDU      20      ()
    1       INTL-ORBI-SCP   1       BinTableHDU     90      244R x 16C

The data and the header information of orbitfile can also be accessed:

>>> orbithist.ertfirst
    '2009-04-01T02:11:24'

>>> orbithist.date
'2010-02-12T13:32:05'

>>> orbithist.obtstart
'00000213629501702144'

>>> orbithist.obtend
'00000213631552716800'

>>> orbithist.swid
'078900560010'

>>> orbithist.revol_header
'789'

>>> orbithist.bcppid
'07890056'

The spacecraft frame can be created from the IntegralOrbit object. The spacecraft position and orientation as a function of time, and other spacecraft informations can be asseced in the following way:

>>> orbithist.obtime # The Central on-board time
array([[    0, 49739, 32496,     0],
       [    0, 49739, 32624,     0],
       [    0, 49739, 32752,     0],
       ... ... ...
       [    0, 49739, 63472,     0],
       [    0, 49739, 63600,     0]], dtype=uint16)

>>> orbithist.revol_frac
array([789.63171907, 789.63175003, 789.63178098, 789.63181194,
       789.6318429 , 789.63187386, 789.63190481, 789.63193577,
       789.63196673, 789.63199769, 789.63202864, 789.6320596 ,
       ... ... ...
       789.63890121, 789.63893216, 789.63896312, 789.63899408,
       789.63902504, 789.63905599, 789.63908695, 789.63911791,
       789.63914887, 789.63917982, 789.63921078, 789.63924174],
      dtype='>f8')

>>> orbithist.distance # distance of spacecraft from the center of the Earth
    array([152873.50458927, 152869.90392388, 152866.30236285, 152862.69990592,
           152859.09655321, 152855.49230478, 152851.88716029, 152848.28111949,
           152844.67418299, 152841.0663504 , 152837.45762176, 152833.84799724,
           ... ... ...
           152014.06864013, 152010.25912516, 152006.44870551, 152002.63738093,
           151998.82515173, 151995.01201739, 151991.19797804, 151987.38303371,
           151983.56718419, 151979.75042971, 151975.93277014, 151972.11420526],
          dtype='>f8')

>>> orbithist.xpos # The X component of the s/c position vector
    array([ -9869.01716747,  -9874.22968703,  -9879.4421359 ,  -9884.65451437,
            -9889.86682214,  -9895.07905905,  -9900.29122547,  -9905.50332169,
            -9910.71534674,  -9915.92730106,  -9921.1391845 ,  -9926.35099672,
            ... ... ....
           -11076.34480159, -11081.53981805, -11086.73475384, -11091.92960924,
           -11097.12438369, -11102.31907782, -11107.51369135, -11112.70822413,
           -11117.90267637, -11123.09704764, -11128.29133803, -11133.48554772],
          dtype='>f8')

>>> orbithist.yvel #The Y component of the s/c velocity vector
    array([-0.07534239, -0.07534906, -0.07535574, -0.07536242, -0.07536909,
           -0.07537577, -0.07538245, -0.07538912, -0.0753958 , -0.07540248,
           -0.07540915, -0.07541583, -0.0754225 , -0.07542918, -0.07543586,
           ... ... ...
           -0.07687639, -0.07688305, -0.07688971, -0.07689638, -0.07690304,
           -0.0769097 , -0.07691636, -0.07692303, -0.07692969, -0.07693635,
           -0.07694301, -0.07694968, -0.07695634, -0.076963  ], dtype='>f8')

>>> orbithist.ra_scx # Right ascension of s/c viewing direction
    array([300.6038247 , 300.68771488, 300.77160933, 300.85550816,
           300.93941146, 300.97924805, 300.97924805, 300.97924805,
           300.97924805, 300.97937012, 300.97937012, 300.97937012,
           ... ... ...
           300.97943115, 300.97943115, 300.97943115, 300.97943115,
           300.97943115, 300.97943115, 300.97943115, 300.97943115,
           300.97943115, 300.97943115, 300.97949219, 300.97949219],
          dtype='>f8')

>>> orbithist.dec_scz # Declination of the s/c Z-axis
    array([6.66949393, 6.66861575, 6.6677966 , 6.66703648, 6.66633538,
           6.6748333 , 6.6748333 , 6.6748333 , 6.6748333 , 6.67769432,
           6.67769432, 6.67769432, 6.67769432, 6.67777777, 6.67777777,
           ... ... ...
           6.67777777, 6.67777777, 6.67777777, 6.67777777, 6.67777777,
           6.67777777, 6.67777777, 6.67777777, 6.67769432, 6.67769432,
           6.67769432, 6.67769432, 6.67808342, 6.67808342], dtype='>f8')

>>> orbithist.posangle #Position angle in degree
    array([-83.31257692, -83.31308774, -83.31353566, -83.31392067,
           -83.31424276, -83.30554264, -83.30554264, -83.30554264,
           -83.30554264, -83.3026745 , -83.3026745 , -83.3026745 ,
           ... ... ...
           -83.3025897 , -83.3025897 , -83.3025897 , -83.3025897 ,
           -83.3025897 , -83.3025897 , -83.3026761 , -83.3026761 ,
           -83.3026761 , -83.3026761 , -83.30228349, -83.30228349],
          dtype='>f8')

Regarding the spacecraft frame, we can retrieve it as a SpacecraftFrame object:

>>> integral_frame = orbithist.get_spacecraft_frame()
>>> integral_frame[0]
<IntegralFrame: 1 frames;
obstime=[J2000.000]
obsgeoloc=[(-9869017.16747001, 7480682.06699442, 1.52371094e+08) m]
obsgeovel=[(-651.56893536, -75.34238658, -490.01369203) m / s]
quaternion=[(x, y, z, w) [-0.56344884,  0.35278101, -0.34882014,  0.66060236]]>

This frame has a location in Earth Inertial Coordinates (obsgeoloc), the velocity of the spacecraft with reference to the Earth Inertial Coordinate frame (obsgeovel), and the spacecraft orientation quaternion, each for a given time stamp (obstime).

Now if we define a SkyCoord of some object of interest in RA and Dec:

>>> from astropy.coordinates import SkyCoord
>>> coord = SkyCoord(100.0, -30.0, unit='deg')

And we can rotate this into the INTEGRAL frame with the following:

>>> integral_coord = coord.transform_to(integral_frame[0])
>>> (integral_coord.az,integral_coord.el)
(<Longitude [142.63112391] deg>, <Latitude [13.75208102] deg>)

Now we can tranform to ICRS coordinates:

>>> integral_coord.icrs
<SkyCoord (ICRS): (ra, dec) in deg
    [(100., -30.)]>

or Galactic coordinates:

>>> integral_coord.galactic
<SkyCoord (Galactic): (l, b) in deg
    [(239.1152521, -15.45266077)]>

or any other coordinate frames provided by Astropy.

Reference/API

gdt.missions.integral.orbit Module

Classes

IntegralOrbit()

Class for reading a INTEGRAL ORBIT file.

Class Inheritance Diagram

Inheritance diagram of gdt.missions.integral.orbit.IntegralOrbit