PAX meaning in Space Science ?

A passenger (also abbreviated as pax) is a person who travels in a vehicle but bears little or no responsibility for the tasks required for that vehicle to arrive at its destination or otherwise operate the vehicle. The vehicles may be bicycles, buses, passenger trains, airliners, ships, ferryboats, and other methods of transportation.

Crew members (if any), as well as the driver or pilot of the vehicle, are usually not considered to be passengers. For example, a flight attendant on an airline would not be considered a passenger while on duty and the same with those working in the kitchen or restaurant on board a ship as well as cleaning staff, but an employee riding in a company car being driven by another person would be considered a passenger, even if the car was being driven on company business.