STEREO Spacecraft

The two STEREO observatories are nearly identical with selective redundancy. The building of the spacecraft bus and the integration of the instruments were done by the Johns Hopkins University Applied Physics Laboratory (APL).

The two solar-powered observatories with 3-axis-stabilization, each had a mass at launch of approximately 1,364 pounds (620 kilograms, including propellant). The spacecraft communicate with the APL-based Mission Operations Center via NASA’s Deep Space Network.

The significant challenge in spacecraft design is the large number and extent of the instrument fields-of-view, coupled with the various instruments’ competing design requirements to ensure successful science observations.

The major design drivers to support the science instrument performance are a conductive outer surface for the energetic particle experiments, stringent electromagnetic compatibility and interference requirements for the radio burst tracker, and contamination control of both volatiles and particulates for the imager experiment.

The spacecraft bus consists of six operational subsystems supporting two instruments and two instrument suites. This combination provides a total of 16 instruments per observatory. The subsystems include: command and data handling; radio frequency communications; guidance and control; propulsion; power; and thermal.

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Key Characteristics of Twin Observatories

• Mass: 1,364 pounds (620 kilograms)
• Dimensions:
• 3.75 feet (1.14 meters)
• 4.00 feet (1.22 meters) wide (launch configuration)
• 21.24 feet (6.47 meters) wide (solar arrays deployed)
• 6.67 feet (2.03 meters) deep
• Power consumption: 475 watts
• Data downlink: 720 kilobits per second
• Memory: 1 gigabyte
• Attitude:
• Control – within 7 arcseconds (0.0019 degrees)
• Knowledge – within 0.1 arcsecond (0.000028 degrees)

*1 arcsecond = 1/3,600 of a degree