Cape Canaveral, Fla. ? A long-delayed NASA probe designed to study the solar system’s most powerful explosions is scheduled for launch this afternoon.

The High Energy Spectroscopic Imager, dubbed HESSI for short, will spend two years analyzing the massive flares periodically belched outward by the sun. The largest of those flares occasionally damage communication satellites and disrupt power grids.

“They release about a billion megatons equivalent of TNT in a time scale of a few seconds to a few minutes,” said Robert Lin, the project’s principal scientist at University of California, Berkeley. “What we’ve found out in the past about these explosions is that a large fraction of the total energy of these flares comes out first as very high-energy particles.”

The $85-million mission is scheduled to get under way at 2:26 p.m. CST. HESSI will head toward an orbit 370 miles above Earth atop an air-launched Pegasus rocket dropped from the bottom of a modified Lockheed L-1011 jet.

After taking off from Cape Canaveral Air Force Station, the jet will deploy the rocket while flying 39,000 feet above the Atlantic Ocean some 130 miles southeast of the Cape. Forecasters are predicting an 80-percent chance of favorable weather.