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Most of us have experienced the frustration of pollution, fog, or clouds turning a night of stargazing into an exercise in frustration. Turns out, NASA has been dealing with the same problems since it started launching large telescopes. Even in orbit, telescopes can’t see too well through the dust that litters the inner Solar System. But a team of NASA scientists have come up with a way to lift astronomy out of this cosmic fog.
Venus, Earth, and Mars all orbit within a dust cloud made by comets and occasional collisions between asteroids. This so-called zodiacal cloud is the Solar System’s most luminous feature after the Sun and can be up to a thousand times brighter than the objects astronomers are actually targeting. The light affects orbital observations the same way light from a full Moon affects ground based observations. The zodiacal cloud is so bright that it has interfered with every infrared, optical, and ultraviolet astronomical observation mission NASA has ever launched.
“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 the cloud is greatest in the plane of Earth’s orbit, the same plane in which every space telescope operates.
So how is NASA planning to get away from the cloud? By tilting future telescopes’ orbits. This type of adjustment would let spacecraft spend a significant portion of each orbit above and below the thickest dust, giving it a clearer view of objects in space.
“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.”
Greenhouse has teamed up with Scott Benson and the COllaborative Modeling and Parametric Assessment of Space Systems (COMPASS) study team, both at NASA’s Glenn Research Center in Cleveland, OH. They’re investigating missions to put a telescope in this type of angle plane — an extra-zodiacal orbit — using new developments in solar arrays, electric propulsion and lower-cost expendable launch vehicles.
They’ve developed a proof-of-concept mission called the Extra-Zodiacal Explorer (EZE), a 1,500-pound EX-class observatory. EZE would launch on a SpaceX Falcon 9 rocket. A powerful new solar-electric drive as its upper stage would direct the spacecraft on a gravity-assist manoeuver past Earth or Mars, a flyby that would redirect the mission into an orbit inclined by as much as 30 degrees to Earth’s.
NASA’s Evolutionary Xenon Thruster (NEXT) engine is an improved type of ion drive. It operates by removing electrons from atoms of xenon gas and 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.
Two of these advanced engines, which get their power from onboard solar arrays, would be housed in the EZE upper stage. They would fire to send the spacecraft on the planetary flyby that would put it into an extra-zodiacal orbit. “We’ve run one NEXT thruster for over 40,000 hours in ground testing, more than twice the thruster operating lifetime needed to deliver the EZE spacecraft to its extra-zodiacal orbit,” Benson explained. “This is mature technology that will enable much more cost-effective space missions across both the astrophysics and planetary science disciplines.”
If this concept mission works, the team says, it will be the best performance from an observatory in the history of NASA’s Explorer program. It will also be a game changer. As Greenhouse explained, “it will make extra-zodiacal orbits available to any astronomer proposing to NASA’s Explorer program. This will enable unprecedented science capability for astrophysics Explorers.”