MRI is desired for monitoring bone and muscle deterioration in astronauts during long-term spaceflights and on the International Space Station (ISS). However, the magnet is generally too heavy to be transported to the ISS. Therefore, we designed a light (~10kg) magnet that allows transmit array spatial encoding (TRASE) MRI of the ankle on the ISS. The magnet is based on a sparse Halbach geometry with magnetic block-pairs. The positions of the block-pairs were optimized using a genetic algorithm. We intend to manufacture the magnet and test the entire MRI system on a Falcon 20 jet.