Occasionally you will come across objects floating in space which can be brought aboard your ship via the tractor beam. They will vary in nature, but sooner or later you will find one which catches fire every few minutes. Continue with your mission as normal, but keep purging area 1 (where the object will be stored) each time it catches fire.
If you have not done this 50 times by the time you return to Athena Station - DON'T select Athena Station. Do nothing except keep purging area 1 when the object catches fire. Your crew will orbit Athena Station automatically in the meantime.
Remember you can speed up time to make this go faster! When you select 'purge' there will be a five-second countdown which cannot be speeded up - but then just speed up time straight after this until you need to purge again.