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.