Utilizing new developments in solar arrays, electric propulsion and lower-cost expendable launch vehicles, NASA’s proof-of-concept mission is the Extra-Zodiacal Explorer (EZE), a 1,500-pound EX-class observatory. Its engine, NASA’s Evolutionary Xenon Thruster (NEXT), is an improved type of ion drive. Using electric power supplied by solar panels, the NEXT engines operate by removing electrons from atoms of xenon gas, then accelerating the charged ions through an electric field to create thrust. While these types of engine provide much less thrust at any given time than traditional chemical rockets, they are much more fuel efficient and can operate for years.
A fogbank is the least useful location for a telescope, yet today’s space observatories effectively operate inside one. That’s because Venus, Earth and Mars orbit within a vast dust cloud produced by comets and occasional collisions among asteroids. After the sun, this so-called zodiacal cloud is the solar system’s most luminous feature, and its light has interfered with infrared, optical and ultraviolet observations made by every astronomical space mission to date.
“To put it simply, it has never been night for space astronomers,” said Matthew Greenhouse, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Md. Light from zodiacal dust can be a thousand times brighter than the sources astronomers actually target, limiting sensitivity in much the same way that bright moonlight hampers ground-based observatories. The dust and its unwanted illumination are greatest in the plane of Earth’s orbit, the same plane in which every space telescope operates.
Placing future astronomy missions on more tilted orbits would let spacecraft spend significant amounts of time above and below the thickest dust and thereby reduce its impact on observations. So Greenhouse teamed with Scott Benson at NASA’s Glenn Research Center in Cleveland, Ohio, to investigate how these “dark sky” or extra-zodiacal orbits might improve mission science and to develop a means of cost-effectively reaching them.
“Just by placing a space telescope on these inclined orbits, we can improve its sensitivity by a factor of two in the near-ultraviolet and by 13 times in the infrared,” Greenhouse explained. “That’s a breakthrough in science capability with absolutely no increase in the size of the telescope’s mirror.”