Scientists Designing a 'Space Railroad'


Oct. 21, 2004 — -- A next-generation space telescope is being designed with a set of eyes that can roll around the cosmos on their own private railroad.

Engineers at NASA's Goddard Space Flight Center in Greenbelt, Md., are working on a proposed orbiting observatory made up of two powerful telescopes that will analyze space in ultraviolet light. Two eyes are better than one, the lead scientists explain, especially if they're linked by a railroad-like beam.

The twin telescopes will use the 120-foot track to zoom back and forth, absorb images and cover the depth and scope of a giant telescope more than twice their individual size.

"By moving your telescopes to many different separations and angles, you can build an image that has much greater detail and overall view," explained David Leisawitz, principle investigator for the Space Infrared Interferometric Telescope at Goddard. "But, unlike launching a single large telescope, you don't need a giant rocket to get it to space."

SPIRIT is one of nine proposals under consideration for NASA's Origins program, which seeks to find fundamental answers about the universe and its formation. The project also represents one of two recent efforts to take a technology that's usually limited to Earth-bound applications and use it in space.

Interferometry was invented in the late 1800s by Albert Michelson, who discovered that by measuring the difference in readings from two or more separate telescopes, he could calculate data that reflected the space between the instruments. A number of ground-based telescopes use the principle today, including the Keck Observatory in Hawaii, which detects visible and the longer infrared light from space, and the Very Long Baseline Array, whose 10 radio antennas are sprawled across the United States and its territories from St. Croix to the Virgin Islands to Hawaii.

SPIRIT won't have nearly the range of its ground-based counterparts, but it would have a key advantage of being in space and being mobile. The twin telescopes will move along the beams like railroad cars and combine their images to achieve the resolving power of a telescope 120 feet across.

"You need the mobility to fill in the space that would be occupied by a larger telescope," explained Leisawitz. "We can't necessarily make images quickly because two smaller telescopes don't absorb as much light, but we can cover a lot of sky."

It may take more effort to hoist multiple telescopes into space, but the payoff is huge. Space telescopes don't need to peer through the haze of Earth's atmosphere. They can also stay very cold while in the shade -- in the range of about 350 degrees Fahrenheit below zero. This is especially important for the SPIRIT telescope since it will be detecting infrared light, which is a light form of heat. The SPIRIT team is designing multiple sun shades and a cryo-cooler to make sure the unit stays frigid.

"Having heat around the telescopes would be like waking up on a very foggy morning," said Leisawitz. "By staying cold, we will be able to see huge distances."

From its perch some 93 million miles behind Earth, SPIRIT will use its lenses to penetrate faraway dust clouds. Newborn stars are often surrounded by disks of dust and gas. The same environment can give rise to new planets. All this is visible in infrared light since the central star warms the debris around it, generating heat in the form of infrared light.

Peering deep into space is like seeing back in time since light has a limited speed. This means the light that is detectable can be millions, even billions of years old. In this way, a telescope like SPIRIT will be able to watch how stars and planets formed millions of years ago.

The Spitzer Space Telescope, now in orbit, has begun making similar observations with its infrared telescope. But, as planned, SPIRIT's dual-telescope gazing power should be about 100 times stronger than Spitzer.

Besides SPIRIT, one other NASA mission is now in the making to use the dual visibility of two joined telescopes. The Space Interferometry Mission is scheduled for launch in about five years and will fly up to four interferometers with two telescopes each, mounted on a single 33-foot bar. The telescopes won't be able to glide around as in the SPIRIT telescope design, but the entire unit will be able to rotate. SIM's main mission is to identify and study distant habitable planets as well as analyze the motion of galaxies.

"SIM is a very precise instrument," said Andrew Gould, an Ohio State University astronomer who is part of the SIM team. "If you placed a dime on its side on the moon, SIM could see it from as far away as Earth."

From 1990, the Hubble Space Telescope has wowed scientists and the public alike with its spectacular pictures of the deep universe. But the future of the famous space telescope is now uncertain since NASA chief Sean O'Keefe scrapped a manned mission to service the telescope in January. NASA may send a robot to do the repair work, but, in the meantime, projects like SPIRIT and SIM show that scientists are eager to take the next generation of space telescopes to a new level.

If approved, SPIRIT could be ready for launch by 2016 while SIM is slated to blast to orbit by the end of 2009. While scientists have an inkling of what these kinds of telescopes could reveal, the most exciting data could be the unexpected.

"Every time we send out a new instrument, we find new things," says Leisawitz. "I'm sure we will discover things we haven't really dreamed of yet."

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