Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for channel bonding in an adaptive coding and modulation mode. In some implementations, a system receives packets of a data stream for transmission in a satellite communications system. The system determines a modulation and coding arrangement for the received packets. The system generates code blocks that include data from the packets of the data stream. The system assigns the generated code blocks for transmission on different carriers. One or more of the different carriers is operated in an adaptive coding and modulation mode to support multiple modulation and coding arrangements within a single carrier. The system transmits the code blocks on the different carriers using the determined one or more modulation and coding arrangements.