Star status for a satellite designed at Berkeley
After two months in space, solar flare mission gets rave reviews, new name

By Robert Sanders, Public Affairs

10 April 2002 | Nearly two months after the Feb. 5 launch of NASA’s solar flare satellite, known as HESSI, campus scientists who designed and built it couldn’t be happier. The satellite is working flawlessly and has already captured numerous explosive flares as well as X-ray and gamma ray flashes from elsewhere in the cosmos.

“It’s absolutely beautiful,” said Robert Lin, principal investigator for the HESSI mission and professor of physics. “We have seen some really neat stuff.”

Lin also is pleased that the satellite has been rechristened RHESSI — the Reuven Ramaty High-Energy Solar Spectroscopic Imager — in honor of the late NASA scientist who pioneered the fields of solar-flare physics, gamma-ray astronomy and cosmic ray research. Ramaty died last year of Lou Gehrig’s disease after a long and distinguished career with NASA.

“He was one of the people who pushed real hard to get HESSI funded,” said Lin, who proposed to NASA that it change the satellite’s name to honor Ramaty. “He was really looking forward to HESSI’s launch, but he passed away before the spacecraft went up. It’s appropriate that we name it after him.”

RHESSI to date has imaged more than 50 small and medium X-ray flares, though so far it has imaged no large solar flares emitting gamma rays. Flares are among the most powerful events on the Sun, and can occasionally disrupt satellites, communication systems and power grids on Earth. Scientists believe solar flares are powered by the violent release of magnetic energy, but how this happens is a mystery.

“Their behavior is really amazing, much more complicated than people guessed beforehand,” Lin said. “They will take a while to analyze.”

NASA created a movie of one of the flares, an explosion that occurred Feb. 20. The blast was equal to one million megatons of TNT and gave off powerful bursts of X-rays.

“We are thrilled to be making the first high-resolution movies of flares using their high-energy radiation,” said Brian Dennis, the RHESSI mission scientist at Goddard. “We want to understand how solar flares can explosively release so much energy.”

During its planned two-year mission, RHESSI will study the secrets of how solar flares are produced in the Sun’s atmosphere. RHESSI is the first NASA Small Explorer mission managed in the “principal investigator” mode, where Lin and his team are responsible for most aspects of the mission, including the science instrument, spacecraft integration and environmental testing, and spacecraft operations and data analysis.

The RHESSI scientific payload is a collaborative effort among Berkeley, Goddard, the Paul Scherrer Institut in Switzerland and Lawrence Berkeley National Lab. The mission also involves scientific participation from France, Japan, The Netherlands, Scotland and Switzerland.