# Which coordinates does "Satellite is in correct position" imply? time and direction or only x,y,z?

command: "get satellite in correct position". Intension: satellite adjusts to a certain angle and move through space. Is the command sufficient?

Position := which{t,s,d,x,y,z}?

• Can you please provide some context and explain which state type are you using and fixed to what? May 6, 2014 at 19:31

A satellite's position in its target (or current) orbit is characterized by seven variables:

• Time (specifying one of the reference frames to account for relativistic effects).
• Position vector (cartesian or polar coordinates) in a known reference frame (Earth-centric fixed, or Earth-centric rotating, for instance).
• For the same reference frame, instantaneous velocity vector.

If you are responsible for launching it, you have to make sure the satellite can be controlled. To achieve this, the satellite's attitude and rotation rates should be within pre-determined limits. This gives you 6 more numbers to watch at separation and orbit insertion.

I can't tell what context you're referring to, but IMHO the word "position" refers only to the satellite's current location in space, specified for example by (x, y, z) coordinates.

Given that interpretation, being in the correct "position" is useless if the satellite is moving in the wrong direction and/or at the wrong speed. If a communications satellite is directly above the desired spot on the equator, at exactly the right altitude for a geosynchronous orbit, but it happens to be plummeting toward the Earth at 1000 kilometers per second, then it's in the right "position" but it's going to have a very bad day.

The word "position", at least as it's usually used in English, does not include information about the velocity.

If there's a context in which the word "position" does include both location and velocity (which both need to be correct), then please update your question to clarify just what that context is. It's common, in technical fields, for English words to be used in a way that differs from their common English meanings.

Theoretically, a satellite could be in the correct position but travelling in the opposite direction (or at some other angle). In practice though, that's not how satellite launches work. Satellites are launched on rockets that fly into a particular orbit. Orbits are characterised by various parameters but the most important are the apogee (the highest point in the orbit above Earth), perigee (the lowest point) and inclination (the angle of the orbital path, with respect to the equator). The inclination is determined by the direction the rocket flies so this is already well monitored during the flight. By the time the payload satellite is released from the rocket, the main concern for the ground controllers is to check that the satellite reaches the right apogee and perigee, which is determined by the duration and timing of the rocket motor burns. The direction is no longer in doubt. Mission controllers informally refer to the satllite having reached the correct 'position' but what they really mean is that the entire orbital track has the right shape.