Mission Timeline Animation

This animation 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 a still image of this timeline.

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Placing STEREO into Orbit

STEREO mission designers determined that the most efficient and cost-effective way to get the twin observatories into space was to launch them aboard a single rocket and use lunar swingbys to place them into their respective orbits. This is the first time lunar swingbys have been used to manipulate orbits of more than one spacecraft. Mission designers will use the moon's gravity to redirect the observatories to their appropriate orbits – something the launch vehicle alone can't do.

After launch, the observatories will fly in an orbit from a point close to Earth to one that extends just beyond the moon. Approximately two months later, mission operations personnel at the Johns Hopkins University Applied Physics Laboratory (APL), in Laurel, Md., will synchronize spacecraft orbits, directing one observatory to its position trailing Earth in its orbit. Approximately one month later, the second observatory will be redirected to its position ahead of Earth.

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Observatories Separate after Launch
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Solar Panels Deploy
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Gravitational Pull
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Flying Close to Earth
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Lunar Swingby
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