Satellite communications are perceived as an essential supplement to terrestrial networks due to their benefits of providing seamless coverage and global connectivity. On the basis of existing multiple-input multiple-output (MIMO) satellite communication, the large-scale MIMO technology, which is capable of fully exploring spatial degrees of freedom and diversity gain, is expected to be applied in satellite communications to meet the ultra-high data rate requirements of 6G. However, a number of practical factors such as limited payloads, lineof- sight channels, and channel aging pose great challenges to the implementation of large-scale MIMO in satellite systems. To this end, this article provides an overview of core technologies that are promising to handle these issues. Specifically, we first outline the concept and evolution of satellite MIMO. Then, the advantages and challenges of practical satellite large-scale MIMO communications are highlighted. Next, the technical issues and potential solutions of core technologies are discussed. Finally, we provide novel design guidelines for potential technologies in future satellite communications.