Satellite State

satstate

A convenience class representing a satellite position and velocity, and optionally 6x6 position/velocity covariance at a particular instant in time

This class can be used to propagate the position, velocity, and optional covariance to different points in time.

pos property

state position in meters in GCRF frame

Returns:

Type	Description
NDArray[float64]	npt.ArrayLike[np.float64]: 3-element numpy array representing position in meters in GCRF frame

vel property

Return this state velocity in meters / second in GCRF

Returns:

Type	Description
NDArray[float64]	npt.ArrayLike[np.float64]: 3-element numpy array representing velocity in meters / second in GCRF frame

qgcrf2lvlh property

Quaternion that rotates from the GCRF to the LVLH frame for the current state

Returns:

Type	Description
quaternion	satkit.quaternion: Quaternion that rotates from the GCRF to the LVLH frame for the current state

cov property

6x6 state covariance matrix in GCRF frame

Returns:

Type	Description
NDArray[float64] | None	npt.ArrayLike[np.float64] | None: 6x6 numpy array representing state covariance in GCRF frame or None if not set

time property

Return time of this satellite state

Returns:

Type	Description
time	satkit.time: Time instant of this state

__init__(time, pos, vel, cov=None)

Create a new satellite state

Parameters:

Name	Type	Description	Default
time	time	Time instant of this state	required
pos	NDArray[float64]	Position in meters in GCRF frame	required
vel	NDArray[float64]	Velocity in meters / second in GCRF frame	required
cov	NDArray[float64] | None	Covariance in GCRF frame. Defaults to None. If input, should be a 6x6 numpy array	None

Example

import numpy as np

t = satkit.time(2024, 1, 1)
pos = np.array([6.781e6, 0, 0])       # meters, GCRF
vel = np.array([0, 7.5e3, 0])          # m/s, GCRF
state = satkit.satstate(t, pos, vel)

propagate(time, propsettings=None)

Propagate this state to a new time, specified by the "time" input, updating the position, the velocity, and the covariance if set

Parameters:

Name	Type	Description	Default
time	time | duration	Time or duration from current time to which to propagate the state	required
propsettings	propsettings	object describing settings to use in the propagation. If omitted, default is used	None

Returns:

Name	Type	Description
satstate	satstate	New satellite state object representing the state at the new time

Example

# Propagate forward by 90 minutes
new_state = state.propagate(satkit.duration(minutes=90))
print(new_state.pos)