one of them main problems is muscle reduction caused by lack of excersise in zero gravity
You have been travelling is correct. You would never say you have been on travelling, although for poetic emphasis you could say you have been travelling on.
That would depend on where in the world you are measuring or travelling from, and if you are travelling, it would depend on what way you were travelling.
No, a photon is not time travelling
BUS-ING
Travelling with Pets was created in 2007.
The Travelling Players was created in 1975.
Travelling long distances and travelling the pacific ocean, travelling up river etc.
You would be travelling south.
The duration of Travelling with Pets is 1.62 hours.
long travelling and cross travelling meter
The duration of The Travelling Players is 3.83 hours.