There were many problems that needed to be prepared for the expedition to Planet X. Although they could reach a planet, which was highly suspected to be Eris Star, at the discrete disc through the cosmic tunnel, they still needed to fly from Eris to Planet X.
The flight time was not short. It would take at least half a month or a month or two. Before an effective transportation system was established, flying tools were a big problem. Although Planetary realm powerhouses could fly in space for a long time, this consumed a lot of energy. Their strength might be damaged if they encountered an unexpected situation.
Moreover, dozens of Planetary realm experts were flying in space. They were relatively scattered and were not conducive to overall movement and communication. It would be best to use the Aerospace Combat Jet to fly in space to solve this problem.
However, the Aerospace Combat Jet could not fly through the cosmic tunnel.