IRIS mission gains extension and Chilean cooperation

by Chris Bergin and William Graham

NASA’s Interface Region Imaging Spectrograph (IRIS) satellite has been provided with a mission extension via a $19 million award from the Agency. The extension will also provide additional involvement for IRIS, with Chilean cooperation and more collaborative observations with observatories in California and Europe.


The Interface Region Imaging Spectrograph, or IRIS, is a small satellite observing the sun at ultraviolet wavelengths, in order to study the transfer of energy in the chromosphere and transition region.

IRISInitially designed for a two-year mission, IRIS carries an ultraviolet spectrometer attached to a telescope with a diameter of 20 centimeters (8 inches).

The satellite returns images and spectra produced every few seconds, allowing material to be tracked as it passes through the chromosphere.

The Sun’s surface, or photosphere, has a temperature of around 6,000 Kelvin (5,726 degrees Celsius); however the outer layer of its atmosphere, the corona, has a temperature far exceeding this.

With no fusion occurring in the outer layers of the Sun, scientists would expect the corona to be cooler than other layers, however in the thin transition region, the Sun’s temperature rises dramatically.

It is hoped that by providing high-resolution observations of the photosphere, chromosphere and transition region, IRIS can help physicists to understand the processes involved.

The results – which included IRIS being able to catch nine of the largest flares (X-class) and almost 100 of the second largest class of flares (M-class) and numerous weaker C-class flares – have been promising, paving the way for the mission extension.

The $19.4 million contract extends Lockheed Martin’s support for the orbiting observatory through September 2018, with a further extension possible through September 2019.

“IRIS has taken more than 24 million images or spectral measurements of the sun since its launch three years ago, and it has led to more than 115 scientific papers,” said Dr. Bart De Pontieu, IRIS science lead at Lockheed Martin’s Advanced Technology Center.

“In this new extension, IRIS will be able to study a wide range of phenomena, including the source regions of fast solar wind, a stream of charged particles that continuously emanates from the sun at speeds of 1,000 km/s and fills the space around the Earth.”

IRISThe IRIS satellite was also constructed by Lockheed Martin. The spacecraft has a mass of 183 kilograms (403 lb); 87 kilograms of which is the scientific payload.

The spacecraft can downlink data at a rate of 15 megabits per second by means of a directional x-band transponder.

It makes fifteen passes per day over its four ground stations in Alaska, Svalbard, Antarctica and Virginia.

The satellite’s peak power consumption is 340 watts, with electrical power being provided by two solar panels measuring 135 by 64 centimeters (53 by 25 inches).

IRIS was the eleventh mission to launch as part of NASA’s Small Explorer (SMEX) program, which is part of the wider Explorer program.

2016-09-19-231002The spacecraft was launched by Orbital ATK’s Pegasus rocket in 2013, deployed from the belly of Stargazer carrier plane.

Stargazer departed runway 12/30 at Vandenberg, before Pegasus was dropped over the Pacific Ocean at coordinates 36.0 north, 123.0 west. At deployment, Stargazer was at an altitude of 11.89 kilometers (39,000 ft) and flying at a velocity of 243 meters per second (797 ft/sec).

Once Stargazer entered its designated drop zone, and the countdown reached zero, the rocket was released. Five seconds later, the first stage motor ignited to begin the rocket’s ascent to orbit.

The ascent to spacecraft separation was without issue, allowing for IRIS to begin its mission.

2016-09-19-230716With the extension, IRIS will continue observations for more specific computer models that reveal what heats the Sun’s chromosphere, a layer of the Sun’s atmosphere that is responsible for most of the ultraviolet light that we receive on Earth.

IRIS will also work with a slew of ground-based telescopes that are coming online with powerful new instrumentation such as the German GREGOR telescope, the Swedish Solar Telescope in the Canary Islands and Big Bear Solar Observatory, California.

The spacecraft will also be involved with the first solar observing campaigns newly approved for the large, international radio-telescope in Chile called ALMA. Coordinated observations of ALMA and IRIS will provide a new window into what drives the dynamics and heating of the low solar atmosphere.

(Images via NASA and Lockheed Martin).

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