There was no petroleum and natural gas in the outside world anymore. If we only used solar energy, it would require a few days to travel through a radiation zone. Also, it depended on whether their spaceship was a cargo spaceship. If it couldn’t fit any cargo, it would be useless.

Additionally, the larger the spaceship, the bigger the expense. It also relied on luck if it ran on solar energy.

If you were lucky, it would be sunny all the time so the sun’s rays could charge the spaceship.

If you were unlucky, you ran out of energy after a few days and you had to wait for the sun to show again. Stopping in the wilderness of the radiation zone was a dangerous thing to do.  

I recalled that Noah City only had one small...