Astronauts experience detrimental loss to bone and muscle during long-term space flight. MRI is desired to monitor bone and muscle loss, but current portable systems remain unsuitable for the International Space Station (ISS). We built a 25 kg dipolar Halbach magnet dedicated to the transmit array spatial encoding (TRASE) method over a cylindrical region of interest (ROI), which satisfies the requirements for MRI on the ISS. Still, the natural axial gradient is not well suited to slice selection because it has a quadratic-type profile producing unwanted aliasing. We propose a technique to implement a linear axial B0 gradient for encoding.