Johns Hopkins Gazette | April 20, 2009
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The newspaper of The Johns Hopkins University April 20, 2009 | Vol. 38 No. 31
APL Spacecraft Capture a Solar Storm in 3-D

By Kristi Marren
Applied Physics Laboratory

The APL-built and -operated twin STEREO observatories have made the first 3-D measurements of solar explosions, known as coronal mass ejections, enabling scientists to see their size and shape, and to image them as they travel approximately 93 million miles from the sun to Earth. Scientists will be able to use this information to help determine how these strong solar storms will impact Earth's atmosphere.

The Solar TErrestrial RElations Observatory's science data is enhanced, in part, due to the STEREO guidance and control team at the Johns Hopkins University Applied Physics Laboratory. The team is helping mission scientists more easily reconstruct 3-D imagery by very accurately pointing the spacecraft and reducing its jitter or movement.

"By tuning each spacecraft's control software — much like a race car's control system is tuned for optimal performance on the track — spacecraft system performance is now approximately five times better than at launch and seven times better than specifications require," said Andy Driesman, STEREO's system engineer at APL.

Since STEREO's launch in 2006, the APL team has been proactively tuning spacecraft and ground systems, maximizing data return and optimizing contact with satellites used to downlink data. The APL-based mission operations center downloads six to nine gigabytes of data each day — approximately 20 percent to 80 percent more data than the science team expected.

Coronal mass ejections, or CMEs, are powerful solar explosions that can have damaging effects when hitting Earth's upper atmosphere at speeds of nearly 1 million miles per hour. These giant clouds of electrically charged gas called plasma can disrupt satellite communications, including GPS and/or cell phone signals, or induce large currents in power grids, which can cause power disruptions or blackouts.

"Using STEREO observations, we can extract a CME's properties and are able to determine when it will reach Earth, at what speed and with how much energy it will impact Earth's magnetosphere," said Angelos Vourlidas, of the Naval Research Laboratory and project scientist for STEREO's SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) imaging suite. Disruptions to the magnetic envelope surrounding Earth can often trigger auroras. These bright bands of light, often visible at night in northern and southern regions, can interfere with communications between air-traffic controllers and pilots flying near Earth's polar regions.

STEREO is sponsored by NASA Headquarters' Science Mission Directorate. NASA Goddard Space Flight Center's Solar Terrestrial Probes Program Office manages the mission, instruments and science center. APL designed and built the spacecraft and is operating the twin observatories for NASA during the mission.

For more on the mission, go to: and


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