USERS (Unmanned Space Experiment Recovery System) is a Japanese microgravity experiment satellite.

The 1.7 tonne (with fuel), 700 W satellite consists of a Re-Entry Module (REM) and a Service Module (SEM) that provides power and a communications link to the REM. In turn, REM consists of a Re-Entry Vehicle (REV) and a Propulsion Module (PM). After 8.5 months in orbit, REM was separated to deorbit and the REV was recovered with its contents in may 2003. The SEM remained in orbit until 15. June 2007.

The main objective of DRTS (Data Relay & Tracking Satellite) is inter-satellite communications experiments to relay data between the target spacecraft (low earth orbit satellites, space stations, etc.) and ground stations.

- High-Speed Data Relay Experiment
- High speed data transmission is a key technology to support various space activities such as global data reception from Earth observation satellites. DRTS will transmit high rate data over 240 megabits per second.
- High-Accuracy Acquisition and Tracking Technology Experiment
DRTS has an advanced system which can acquire and track the target spacecraft accurately.
- Communications Network Experiment

NASDA is also planning to evaluate the data relay time allocation method on several test spacecraft during the test.