REX
Radiation Experiment

The REX satellites are designed to study scintillation effects of the Earth's atmosphere on RF transmissions. Rex 2 was also the first spacecraft to successfully employ GPS navigation for full closed loop attitude control. The basic design features of both spacecraft are similar, though there are some obvious differences, i.e. no GPS equipment on the first REX. Specifications presented here are for Rex 2.

Spacecraft
Three axis stabilized, nadir pointing to within 5 degrees. Passive attitude control provided by 21 foot gravity gradient boom with two 20 inch long nickel/iron magnetic hysteresis rods mounted at the tip for damping purposes (4 lbs. total). Active control acieved through pitch bias momentum system, including one wheel and three torque coils. Attitude determination is provided by GPS equipment, coarse sun sensors, and a magnetometer.

Payload
The primary communications experiment built by the US Air Force Rome Laboratories advances research on electron density irregularities that cause diruptive scintillation effects on radio signals transmitted through the Earth's ionosphere. Rex II GPS receivers, supplied by Trimble Navigation, are able to resolve spacecraft position to 100m, velocity to 0.2 m/sec, and attitude to within 0.3 deg.

Country of Origin	United States
Customer/User	US Air Force Space Test Program (STP)
Manufacturer(s)	CTA Space Systems
Size	8 sided, 30 inch diameter, 22 inches tall
Orbit	REX I: 770 x 870 km, 89.6 deg. inclination REX II: 450 nm cicular, 90 deg. inclination
Design Life	1 year, goal of three years

Launch Facts

Name	Int'l Desig.	Date	Site	Vehicle	Orbit	Mass(kg)
Notes
REX	1991-045A	6/29/91	WSMC	Scout G1	LEO	85
Radiation Experiment; tested communications components in high radiation environment
REX 2	1996-014A	3/9/96	WSMC	Pegasus	LEO	110
Radiation Experiment; communications tests