A satellite provides communication between user terminals (UTs) and ground stations that connect to other networks, such as the Internet. Because the satellite is within range of many UTs at any given time, many UTs are in contention to use an uplink to send upstream data to the satellite. This saturates a random-access channel (RACH) on the uplink. When a UT has data to uplink, it sends a short buffer data status (SBDS) message using the RACH. The minimal size of the SBDS facilitates use of a non-orthogonal multiple access uplink. Based on the SBDS, the satellite allocates a grant to the UT to use the uplink. Additional messages from the UT involving buffer status may be sent using the granted uplink. Unsolicited grants may be issued to the UT based on analysis of uplink and downlink traffic. If needed, the RACH may still be used to request additional grants.