They chose to leave the ship way too fast...
The math dude said that all 5 people would survive for about a year and 2 months (I think 2 months, don't quite remember). They had to survive for 2.5 years. He then said that only 2 could survive for 2.5 years.
From the energy consumption standpoint if 5 people could survive for a year and 2 months, then 2.5 people could survive for a year and 4 months (close to 6 months).
This means that the 5 people could have at least survived for at *least* a week or something before having to head out there to die. Stupid decision to leave so quickly.