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Tomographic Experiment using Radiative Recombinative Ionospheric EUV and Radio Sources, also called STEDI 2 and UNEX 02


Designation 25735 / 99026A
Launch date 18 May 1999
nCountry of origin United States
Mission Scientific: ionosphere study
Perigee/Apogee 550 km sunsynchronous (9:00)
Inclination 97.7°
Launch vehicle Pegasus #27

After launch the satellite experienced attitude control problems causing the battery to discharge.

End of life

Decay 21 Oct 2023

Technical data


Prime contractor Boston University
Platform Aeroastro
Mass at launch 125 kg
Mass in orbit  
Solar array  
Stabilization spin stabilized
DC power 31 W
Design lifetime 1 year

The satellite bus is being built by AeroAstro while the instrument package is produced by the Center for Space Physics at Boston University and the University of Illinois at Urbana-Champain (UIUC). Cleveland Heights High School is also constructing a small experiment to go on the satellite.

Terriers primary goal is to, for the first time, demonstrate meridional 2D (latitude-altitude) and global 3D imaging of the ionospheric electron density and thermospheric photo-emission profiles using EUV emissions and tomographic techniques. Secondary goals of Terriers focus on the study of several ionospheric and thermospheric phenomena through the use of this novel combination of techniques and observations. As a tertiary goal, Terriers will test the utility of long term solar EUV irradiance measurements using a new technique that we have recently proven on a sounding rocket. GISSMO measures the solar EUV, one of the primary sources for the upper atmosphere.

Telemetry: 2.2729 GHz
Might also use 150/400 MHz

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