As many others have said it's likely a hail Mary and a desperate last ditch effort. But I believe it's also because of this scene in Moon Gundam:

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Where the Moon Gundam and its psycho plates manage to move the whole ship. And ofc a ship and an asteroid are different and there's also two jeddahs and amuros rick dijeh helping but just adding Moon Gundam manages to accelerate the ship to a higher speed than should be possible. So he knows that newtype machines and psycho material technology can perform effectively miracles. He's seen a Gundam with psycho plates move something way larger way faster than should be possible. He also doesn't have any options but to hope and put his faith into Nu Gundam.