OBSGEODX

[m/s] geocentric JWST X velocity at MJD-AVG

X component of the JWST velocity vector, relative to the geocentric terrestrial reference frame, in meters/second, at the mid-point of the exposure in the J2000 (ECI) coordinate system, which is an Earth-centered inertial frame defined by the Earth's mean equator and equinox on 2000-Jan-01. Science Data Processing code (SDP) obtains this from the observatory ephemeris data according to the following precedence: When the definitive ephemeris contains data bracketing and within 60 seconds of the exposure's MJD-AVG time, the JWST_DX geocentric value is linearly interpolated from that data. If there is only definitive ephemeris data prior to but still within 60 seconds of the exposure's MJD-AVG time, that JWST_DX geocentric value is used. Otherwise, if the predicted ephemeris contains data bracketing and within 60 seconds of the exposure's MJD-AVG time, the JWST_DX geocentric value is linearly interpolated from that data. If there is only predicted ephemeris data prior to but still within 60 seconds of the exposure's MJD-AVG time, that JWST_DX geocentric value is used. In the unlikely case that neither ephemeris type has bracketing data, the JWST_DX geocentric value used is the definitive or predicted (in that order of precedence) ephemeris value at the latest ephem_time that is prior to the exposure's MJD-AVG time.

Attribute Value
data type float
enumerated Values not defined
units m/sec
example
default value
special processing VALUE_REQUIRED
source Science Data Processing (SDP)
software source
calculation The JWST_X geocentric coordinate value obtained from the observatory ephemeris data is converted from km/s to m/s and assigned to OBSGEODX.
DB destination ['ScienceCommonExt.obsgeodx', 'GuideStarExt.obsgeodx']
data type in DB float
instrument ALL
mode All
product level 1b
FITS hdu SCI
FITS header section Ephemeris