The IRIS satellite design is derived from several previous NASA/LMSAL spacecraft. By re-using prior designs Lockheed Martin was able to reduce technical, scheduling and cost risks. Solar arrays omitted for clarity. Credit: LMSAL
IRIS is NASA's Interface Region Imaging Spectrograph. Its primary goal is to understand how heat and energy move through the lower levels of the solar atmosphere.
IRIS is a class of spacecraft called a Small Explorer, which NASA defines as costing less than $120 million. Lockheed Martin (LM) Solar and Astrophysics Laboratory in LM’s Advanced Technology Center is the principal investigator institution and has overall responsibility for the mission, with major contributions from Lockheed Martin Civil Space, NASA Ames, Smithsonian Astrophysical Laboratory, Montana State University, Stanford University and the University of Oslo.
IRIS weighs 440 pounds. It is approximately 7 feet (2.1 meters) long and, with its solar panels extended, is a little over 12 feet (3.7 meters) across.
Instrument - Telescope
The IRIS telescope structure is nearly identical to the Solar Dynamic Observatory's (SDO) Atmospheric Imaging Assembly (AIA) telescope structure except, instead of four telescopes, IRIS has only one. Credit: NASA/LMSAL
IRIS carries a single instrument: an ultraviolet telescope combined with an imaging spectrograph. The telescope’s primary mirror has a diameter of about eight inches (20 cm). While it will only be able to see about one percent of the sun at a time, it will be able to resolve that image to show features that are as small as 150 miles (240 km) on the sun. Such high resolution will serve as a microscope for larger instruments that capture images of the whole sun simultaneously. IRIS will collaborate with NASA’s Solar Dynamics Observatory (SDO), for example, to target active regions on the sun.
The images from IRIS's telescope will record observations of material at specific temperatures, ranging from 5000 K and 65,000 K (and up to 10 million K during solar flares). This range is tailored to observe material traveling on the surface of the sun, called the photosphere, and in the lowermost layers of the atmosphere, called the chromosphere and transition region.
The instrument will capture a new image every five to ten seconds, and spectra about every one to two seconds. These unique capabilities will be coupled with state of the art 3-D numerical modeling on supercomputers. Using both together, scientists will be able to trace how solar material at different temperatures courses through the chromosphere and transition region.
Spectrograph - Imager
Diagram of spectrograph and slit-jaw imager with part of the internal structure and baffling. Credit: NASA/LMSAL