"This observatory is like the infrared cousin of the Hubble Space Telescope. It sees things the Hubble can't see, which is part of the reason why we have the Great Observatories Program," said Dr. Michael Bicay, assistant director of the Space Infrared Telescope Facility Science Center.
With the Space Infrared Telescope Facility, scientists will seek out infrared light shrouded by cosmic dust. Infrared light, which is not visible to the human eye, is typically absorbed by Earth's atmosphere. Using infrared, scientists expect the observatory will help them probe the early life of the cosmos and detect discs around other stars, where planets may be forming.
The Space Infrared Telescope Facility is the final mission under NASA's Great Observatories Program, which includes Hubble, the Chandra X-ray Observatory and the Compton Gamma-Ray Observatory. The mission is also an important part of NASA's Origins Program, which seeks to answer the questions: Where did we come from? Are we alone?
The mission brings with it several technological advancements, the most significant of which is that of infrared detector technology. "The interesting science has always been out there, but until recently we didn't have the technology to discover and characterize it," Bicay said.
When infrared detector technology was first discovered, the U.S. Department of Defense used it to look down on Earth, a bright object, and view missile trails from space. Doing the reverse - viewing space, a dark environment containing faint astronomical objects, from Earth - wasn't possible without further refining the detectors to measure weak signals such as those in the infrared. This required the combined efforts of researchers and observers from NASA, several educational institutions and the aerospace industry.
Built to Last for Less
The observatory has an innovative architectural design. Like cellular phones, the package just keeps getting smaller.
Previous infrared telescopes in space have used "cold-launch" cryogenic architecture, in which all the spacecraft's components (the telescope, science instruments and a tank containing liquid helium coolant) were dropped into a big container that functioned like a thermos. In this new "warm-launch" cryogenic architecture, a much smaller container surrounds only the instrument chamber and a much smaller liquid helium tank, but not the telescope. The result is a lighter, smaller spacecraft that is less costly and easier to launch.
Contributing to the observatory's lightness is a sturdy, heat-resistant telescope, with a total mass of less than 110 pounds (50 kilograms). (The Hubble Space Telescope weighs 24,500 pounds or 11,475 kilograms). The innovative launch architecture, combined with 95 gallons (360 liters) of liquid helium, yields an estimated mission lifetime of at least two and a half years. NASA plans to adopt this approach, with variations, in the design of future space-based observatories and infrared telescopes such as the James Webb Space Telescope, scheduled to launch in 2010.
Letting Mother Nature Call the Shots
Also contributing to the observatory's originality is its resourceful choice of orbit. Scientists abandoned the idea of placing the observatory into an Earth orbit; instead they will put it into an Earth-trailing heliocentric orbit. In other words, the observatory will be launched into an orbit where it will simply drift behind Earth as it circles the Sun. The observatory will then drift away from Earth at the rate of about 15 million kilometers, or 9.3 million miles, each year.
The Earth-trailing orbit takes full advantage of Mother Nature to enable its "warm-launch" architecture. As the observatory drifts from Earth into deep space, it will use the temperature of its surroundings to cool itself. Within a few weeks after launch, it will have cooled down to deep space temperatures of about 35 degrees Kelvin (-238 degrees Celsius or -397 degrees Fahrenheit). This natural cooling process allows the observatory to carry much less liquid helium cryogen than it would need in an Earth orbit, where temperatures can reach 250 degrees Kelvin (-23 degrees Celsius or -10 degrees Fahrenheit).
"We let Mother Nature do most of the cooling for us," Bicay said. "It's as if I were having a picnic and wanted cold soda. If the soda was already kept cold in a refrigerator, I wouldn't need as much ice."
Another benefit of the orbit is that the observatory will have a large, instantaneous view of the celestial sky. The view will be limited only by two pointing constraints, as sensitive observatories such as this one and the Hubble Space Telescope must avoid looking at or anywhere near extremely bright objects like the Sun, Earth and Moon. The observatory cannot point closer than 80 degrees in the direction of the Sun, in order to minimize the heating of the telescope by solar radiation. Also, the observatory cannot point more than 120 degrees away from the Sun because it needs to illuminate the solar panels and produce electricity to power itself. Even with these constraints, a third of the sky will be instantaneously visible to the observatory at any given time, allowing scientists optimum viewing efficiency and streamlining mission operations.
JPL is responsible for the observatory's mission operations, while all scientific data is processed at the Space Infrared Telescope Facility Science Center at Caltech.
March 17, 2003
Contacts: JPL/Charli Schuler (818) 354-3965