Orbiter going round Mars, perhaps carrying oxygen tank (4,2,2,4)

'tank' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'orbiter going round mars perhaps carrying oxygen' is the wordplay.
I cannot really see how this works, but
'orbiter' could be 'comet' (I have seen 'Celestial orbiter ' mean 'comet' so perhaps 'orbiter' could also mean 'comet') and 'comet' is located in the answer.
'going' could be 'on' (both can mean functioning or activated) and 'on' is found in the answer.
'round' could be 'o' (round can mean a round object) and 'o' is found within the answer.
'oxygen' could be 'o' (O is the chemical symbol for oxygen) and 'o' is found within the answer.
'mars perhaps' could be 'god' (mars is a kind of god) and 'god' is found in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?