This guy was amazing - beyond some key quantum physics , the dyson sphere (surround your home star with reflective material to power a star engine) , etc. he came up with this nugget (from the bio here) :
He then proposed that comets – lumps of ice and organic chemicals that periodically orbit the sun – could serve as nurseries for genetically altered trees that could grow, in the absence of gravity, to heights of hundreds of miles, and release oxygen from their roots to sustain human life. “Seen from far away, the comet will look like a small potato sprouting an immense growth of stems and foliage. When man comes to live on the comets, he will find himself returning to the arboreal existence of his ancestors,” he told a delighted audience.