MIssion Timeline

This graphic depicts the highly elliptical phasing orbits used to position the twin STEREO observatories into their final heliocentric orbits where they’ll capture the first-ever 3-D images of the sun. Both spacecraft completed four orbits – labeled A1 to A4 – while awaiting the proper position of the moon needed to complete their lunar swingby maneuvers.

On Dec. 15, 2006, the twin spacecraft encountered the moon (S1) and completed the mission’s first lunar swingby. The “A” spacecraft passed only 7,340 km (approx. 4,550 miles) from the moon’s surface; then lunar gravity was used to hurl the spacecraft away from Earth, placing the observatory slightly “ahead” of Earth.

During the initial lunar gravitational assist, the “B” spacecraft flew higher above the moon at a distance of 11,776 km (approx. 7,300 miles) above the moon’s surface where the lunar gravity was slightly weaker. Although the moon’s gravity slightly boosted the “B” observatory’s orbit, the spacecraft re-encountered the moon on Jan. 21, 2007, at S2. The “B” spacecraft came within 8,818 km (approx. 5,468 miles) from the moon’s surface, swinging past the lunar body in the opposite direction of the “A” spacecraft and into an orbit “behind” Earth.

Click here for an animation of this timeline.

Credit: Johns Hopkins University Applied Physics Laboratory

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