NASA has selected a team of astrophysicists at Stanford University to design and oversee the primary experiment aboard the Solar Dynamics Observatory (SDO) – a new research satellite scheduled for launch in August 2007. According to NASA officials, part of SDO's mission is to learn how to predict destructive flares and solar storms generated by the Sun's mysterious magnetic fields. The satellite will be designed to remain in geosynchronous orbit 22,000 miles above Earth for at least five years, providing a constant stream of data about the complex magnetic fields generated deep in the solar interior.
"SDO's inclined orbit will form a figure-8 over the Earth during the day, giving us continuous, 24-hour-a-day sunlight for most of the year," said Stanford physics Professor Philip H. Scherrer, principal investigator of SDO's lead experiment called the Helioseismic Magnetic Imager (HMI).
Scherrer and his Stanford colleagues will oversee construction of the HMI instrument in collaboration with engineers at the Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif. The instrument will be designed to generate three-dimensional pictures of the solar interior using a technique known as "helioseismology," which maps the inside of the Sun by measuring the velocity of low-frequency sound waves that ricochet below the surface.
Scherrer is currently principal investigator of a similar Stanford-based experiment called the Michelson Doppler Imager (MDI) now on board the Solar and Heliospheric Observatory (SOHO) – a satellite jointly operated by NASA and the European Space Agency. Launched aboard SOHO in 1995, MDI has given scientists their first glimpse of the powerful subsurface flows that produce sunspots and solar flares. According to Scherrer, the HMI instrument aboard SDO will allow researchers to create 3-D images of solar magnetic regions and surface magnetic fields in much greater detail.
MDI and the other experiments aboard SOHO are expected to continue until the new SDO spacecraft comes online in 2007. SDO is the first mission in NASA's Living With a Star (LWS) program – a long-range project designed to study the dynamics that drive the intricate Earth-Sun system.
"The Sun is a magnetic star, and we live in its extended atmosphere" Scherrer noted. "High-speed solar winds, mass ejections and flares are all linked to the variability of magnetic fields that originate in the solar interior. Many of these phenomena can have profound impacts on our technological society – disrupting radio communications and causing power outages. A driving purpose of LWS is to understand enough about the Sun's magnetic variability so that we can predict when these events will affect Earth."
In addition to HMI, the SDO spacecraft will carry two related experiments to be led by scientists at the University of Colorado-Boulder and the Naval Research Laboratory in Washington, D.C. According to NASA officials, the total cost of SDO's payload from development through five years of operation will be about $123 million -- of which $65 million is budgeted for HMI.
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