Researchers hope NASA's latest solar observatory will answer a fundamental question of how the sun creates such intense energy.
Scheduled to launch June 26, the IRIS spacecraft will point a telescope at the region of the sun called the chromosphere to look for signs of how energy moves from the sun's surface to the glowing corona, heating up from 6,000 degrees to millions of degrees in the process.
The IRIS mission, short for Interface Region Imaging Spectrograph, calls for the 7-foot-long spacecraft to point its ultraviolet telescope at the sun to discern features as small as 150 miles across. It will look at about 1 percent of the sun's surface.
"IRIS will show the solar chromosphere in more detail than has ever been observed before," said Adrian Daw, deputy project scientist. "My opinion is that we are bound to see something we didn't expect to see."
Scientists plan to combine the results of IRIS' surveys with the raft of information from NASA's Solar Dynamics Observatory, which observes the whole sun at once.
"IRIS almost acts as a microscope to SDO's telescope," said Jim Hall, NASA’s Launch Services Program’s mission manager for IRIS. "It's going to look in closely and it's going to look at that specific region to see how the changes in matter and energy occur in this region. It's going to collectively bring us a more complete view of the sun."
The answers are relevant to many aspects of life including the ways the sun's behavior helps dictate many elements of Earth's climate and weather patterns. Aberrations such as coronal mass ejections, commonly known as solar flares, also are of great interest to spacecraft designers who have to figure out ways to protect instruments and electronics from them.
"We're always looking for the answers to why and everything starts at the root with the sun," Hall said.
IRIS will ride into low Earth orbit on an Orbital Sciences Corp. Pegasus XL rocket. The Pegasus is famous as the only air-launch winged launcher in NASA's inventory. Though small compared to the gigantic boosters that send heavy satellites into orbit and probes to distant worlds, the Pegasus' size and flexibility has allowed numerous missions to be launched that would have been too small for larger rockets. The IRIS launch is the 42nd launch of the Pegasus. The last 27 missions, dating back to 1996, have been successful.
"Pegasus has been a tremendously successful launch vehicle for NASA," said Tim Dunn, NASA launch director for the IRIS mission. "We have launched 18 successful missions on Pegasus. The team is very dynamic, very flexible. They're able to accomplish a tremendous amount in a very short time."
The Pegasus and its IRIS payload will be carried to about 39,000 feet under Orbital’s “Stargazer” L-1011 carrier aircraft after taking off from Vandenberg Air Force Base in California. Flying over the Pacific Ocean off the California coast, the plane will release the Pegasus rocket to begin its flight into orbit.
The Pegasus will ignite its solid-fueled first stage five seconds into its fall and arch skyward with the main wing giving it lift and the three fins in the back steering it through the thick layers of Earth's lower atmosphere.
The rocket’s first stage will burn its load of fuel in 73 seconds and fall away. The second stage, which has no wings, will ignite 94 seconds into flight and push IRIS higher and faster into space. The third stage will take over after that, delivering IRIS into its orbit and separating from the rocket about 13 minutes after launch.
The launch is taking place from the West Coast because IRIS will go into a roughly polar orbit, meaning it will cross over the north and south pole regions of Earth on each pass around the planet.
"Eight months out of the year, we are freely viewing the sun in that orbit," Hall said.
Once IRIS is in space with its solar panels unfolded to provide electricity and the telescope flipped open, scientists expect to see intriguing data pretty quickly.
"I think the biggest surprise will come once the mission is launched and it starts to observe the sun," Daw said. "We know to some extent what we hope to learn, what specific science questions we are going to answer, but there's always that element of surprise."
NASA's Kennedy Space Center