The Shuttle Amateur Radio Experiment is designed to demonstrate the feasibility of contact between the shuttle and ground-based amateur radio operators, often called "hams." SAREX also serves as an educational tool, allowing school children around the world to learn about space firsthand by speaking directly to astronauts aboard the shuttle. Ham radio operators communicate with the shuttle via VHF-FM voice transmission, a mode that makes contact widely available without the purchase of expensive equipment.

The SAREX-II payload comes in three configurations: Configuration A for communicating with amateur radio stations within the orbiter line of sight (LOS) in one of three modes--voice, SSTV, or data; Configuration B for voice communication only; and Configuration C for communicating in either voice or data mode with amateur stations within orbiter LOS. The C-configuration can also operate in the attended mode for voice communication and either attended or automatic mode for data communication.

For STS-93, SAREX-II will use Configuration C-Q, which is the same as Configuration C with the addition of a new digital signal processor (DSP) unit installed between the headset and the SAREX interface module. The DSP unit is an electronic box that performs digital signal processing of the downlink and uplink audio transmissions to enhance the voice clarity and quality.

SAREX II C-Q includes all the Configuration C components: hand-held FM transceiver, interface module, payload and general support computer (PGSC), spare battery set, window antenna, packet module, headset assembly, personal recorder, and the required cable assemblies. The packet module contains a power supply and packet terminal node controller (TNC). The power supply provides power for the TNC and the hand-held transceiver. The TNC interconnects with a radio transceiver that enables data to and from the computer to be transmitted to and received from other amateur radio stations.

Five schools will be participating in SAREX-II communications during STS-93:

Memorial Middle School in Pharr, Tex.
Ponaganset Middle School in North Scituate, R.I.
Awty International School in Houston, Tex.
Buzz Aldrin Elementary School in Reston, Va.
Osceola Elementary School in Ormond Beach, Fla.