Open-source flight/space simuators for Linux

Hello folks,

I am looking for open-source combo flight/space simulators for Linux. I
found FlightGear simulator but it only provides flights but not space and
Celestia simulator but it only supports space area. I know two
closed-source flight simulators (X-plane and Orbiter) supports both flights
and space. Does anyone know about any open-source flight simulator supports
both for space plane, rockets, etc?

Thanks,
Tim