Using a combination of ground based and space instruments, TERRIERS surveyed the upper atmosphere using a technique called tomography, measuring ultraviolet light emissions, to construct an image of Earth's ionosphere.

While the ionosphere had been studied in detail in the past, at the time of TERRIERS' launch there were no means to obtain global three dimensional maps of electron density. Such measurements were of crucial importance in understanding many upper atmosphere phenomena. As secondary goals, TERRIERS examines related upper atmospheric phenomena, and tested the utility of long term solar irradiance measurements.

The spacecraft spun at 3 rpm in "Thompson Spinner" configuration. Attitude and spin rate control was via 3 magnetic torque coils. Attitude determination was by sun sensors, magnetometers and horizon crossing indicators. The atellite used 16W of orbit-averaged power and could downlink telemetry at 250 kbit/s in S-band. The spacecraft bus was based on, though not an exact copy of AeroAstro's HETE design.

Primary payload was 5 imaging spectrometers, 4 of which operated in the night portion of the orbit. TERRIERS also carried 2 photometers, and a Gas Ionization Solar Spectral MOnitor (GISSMO) which was an optics-free solar EUV spectrometer. Riding piggyback at the base of the spacecraft bus was a small payload built by Cleveland Heights High School.

Design Life: 1 year. Typical orbit: 550 km circular, sun synchronous (9am/9pm).

• 1999 May 18 - TERRIERS - Launch Site: Point Arguello WADZ. Launch Complex: -. Launch Vehicle: Pegasus. Perigee: 537 km (333 mi). Apogee: 552 km (342 mi). Inclination: 97.80 deg.
  TERRIERS was part of NASA's Student Explorer Demonstration Initiative (STEDI), which was a precursor program to the UNEX (University Explorer) series. STEDI was managed by USRA (the Universities Space Research Association) for NASA, while UNEX was to be more directly managed by NASA-GSFC. TERRIERS was to be operated by the space physics group at Boston University for ionosphere studies, and carried TESS, a set of extreme ultraviolet (EUV) spectrographs to get electron density and thermosphere emission profiles. The GISSMO instrument measured the solar EUV flux. The spacecraft was built by AeroAstro and based on HETE. TERRIERS was placed in the correct orbit, but it failed to orient its solar panel to the Sun and ran out of battery power by May 20. Controllers were optimistic that when its orbit processes to a better sun angle the satellite could be revived. Additional Details: TERRIERS.