posvel stsdas.hst_calib.hsp

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SEE_ALSO

NAME

posvel -- Calculate state vector and velocity of the spacecraft.

USAGE

posvel mjd intable

DESCRIPTION

This task calculates the state vector and velocity of the spacecraft based on a fitted ephemeris model described below:

```	X = F(2) * [cos(F(3)) * cos(F(1))
- sin(F(3)) * cos(F(4)) * sin(F(1))]

Y = F(2) * [cos(F3)) * cos(F(1))
+ cos(F(3)) * cos(F(4)) * sin(F(1))]

Z = F(2) * sin(F(4)) * sin(F(1))

F(i) = f(i,1) + f(i,2) * t + f(i,3) * t**2
+ f(i,4) * cos(g) + f(i,5) * sin(g)
+ f(i,6) * cos(2g) + f(i,7) * sin(2g)

g = g1 + g2 * t + g3 * t**2

```
where t is the epoch since FIT_START. Velocities are obtained by taking time derivatives of X,Y,Z.

The state vector and velocity are in the coordinate system of J2000 (= JD 2451545.0) equinox.

PARAMETERS

mjd [real]
Input modified Julian day number.
intable [file name]
Name of the input table which contains fitted ephemeris coefficients. The table contains the following columns:

```'FIT_START'     Starting epoch of the fitted ephemeris in seconds since
1980.0 (int).
'FIT_END'       Ending epoch of the fitted ephemeris in seconds since
1980.0 (int).
'G1', 'G2', 'G3',
'F1_1', 'F1_2', 'F1_3', 'F1_4', 'F1_5', 'F1_6', 'F1_7',
'F2_1', 'F2_2', 'F2_3', 'F2_4', 'F2_5', 'F2_6', 'F2_7',
'F3_1', 'F3_2', 'F3_3', 'F3_4', 'F3_5', 'F3_6', 'F3_7',
'F4_1', 'F4_2', 'F4_3', 'F4_4', 'F4_5', 'F4_6', 'F4_7'
Fitted ephemeris coefficients (double).

```
(x) [real, 1-D array of elements]
Output state vector components (in kilometers) relative to the equinox of J2000 (JD 2451545).
(v) [real, 1-D array of elements]
Output velocity components (in kilometers per second) relative to the equinox of J2000 (JD 2451545)

EXAMPLES

1. Find the position and velocity vectors of MJD 48000.3 by using the ephemeris fitting coefficients table yposvel\$intable.tab.

```hs> posvel 48000.3 "yposvel\$intable"
hs> print (posvel.x[1:3])  #print the position result on the screen
hs> print (posvel.v[1:3])  #print the velocity result on the screen
```