NASA scientists begin testing of EXES Spectrograph
By Anthony Wood
June 5, 2014
NASA scientists are eager to get to grips with a new toy for observing the heavens, the Echelon-Cross-Echelle Spectrograph (EXES). Mounted on a heavily-customized Boeing 747, the spectrograph has undergone two successful test flights and when declared operational, will comb the sky for infrared frequency light aboard the largest flying telescope ever constructed.
The spectrograph is essentially a piece of observational equipment designed to separate wavelengths of light using a series of mirrors. EXES represents the cutting edge of this form of observational technology, boasting a 3 ft (1 m) bar of aluminum, painstakingly crafted to act as 130 distinct mirrors with the ability to separate light at a precision of one part in 100,000.
EXES is mounted aboard NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA). The hulking modified 747 was announced to be operational on June 2 and plays host to a number of sophisticated scientific experiments of which EXES is the seventh. The spectrograph is attached to what is undoubtedly the most visually-impressive apparatus carried aboard SOFIA, an 8 ft (2.5 m) telescope which, when SOFIA is in flight, observes the heavens through a vast cavity door embedded in the side of the impressive aircraft.
You might wonder why as advanced a piece of celestial observational equipment as EXES was not simply designed as a satellite and sent up into orbit with other infrared detecting missions. The simple answer is that EXES, weighing in at nearly 1,000 lb (454 kg), would be a significant and costly challenge to mount atop a rocket and blast into space. It is much cheaper and almost as effective to make the necessary observations from within Earth's atmosphere.
With SOFIA flying at heights of up to 45,000 ft (13,716 m) above Earth's surface, 99 percent of our planet's water vapor lies below the vast airborne telescope. This is of particular importance when considering that a significant part of EXES's job will be to study the formation process of stars and planets by observing water vapor as it orbits a protostar. Such observations would be impossible to capture if EXES, like all ground-based infrared spectrographs, had to peer through a thick layer of water vapor whilst penetrating Earth's atmosphere.
"The combination of EXES's high spectral resolution and SOFIA's access to infrared radiation from space provides an unprecedented ability to study celestial objects at wavelengths unavailable from ground-based telescopes," states Pamela Marcum, program scientist at the SOFIA Science Center. Marcum continues, "EXES on SOFIA will provide data that cannot be obtained by any other astronomical facility on the ground or in space, including all past, present or those observatories now under development."
EXES had already begun to make important observations over the course of its two commissioning flights. During the first flight the spectrograph studied Jupiter’s atmosphere, aiding in the understanding of how gas rises from the giant's gloomy interior to mix with its tumultuous surface. On its second foray into the skies, EXES took readings regarding the chemical composition of gas surrounding the imaginatively-named star AFGL 2591.
The first two proving flights have been considered to be a complete success, with the spectrograph well on the way to becoming fully operational. However, further flights will be required before EXES is performing at optimal levels in all of its modes.