Spitzer goes "Beyond" for final mission
Beyond is the name given to the final 30-month mission extension of NASA's Spitzer Space Telescope. Starting in October, the veteran instrument will carry out new observations in astronomy, cosmology, and the search for planets beyond the Solar System.
Launched on August 25, 2003 atop a Delta II rocket from Space Launch Complex 17B at Cape Canaveral Air Force Station, Florida, the infrared observatory went into a heliocentric orbit trailing the Earth. Due to its slower orbital speed, it drifts away from the Earth's orbit at about 0.1 astronomical units (9.3 million mi, 15 million km) per year.
Designed for deep space infrared studies, Spitzer was equipped with an Infrared Array Camera (IRAC), Infrared Spectrograph, and a Multiband Imaging Photometer. However, the latter two required constant cooling with liquid helium to work, which ran out in 2009. NASA switched from a "cold" to "warm" mission, relying on the two still functioning cameras of the four on the IRAC that continued to operate at the "high" temperature of minus 405º F (minus 207º C, 30 Kelvin).
"With the IRAC team and the Spitzer Science Center team working together, we've really learned how to operate the IRAC instrument better than we thought we could," says Giovanni Fazio, principal investigator of IRAC. "The telescope is also very stable and in an excellent orbit for observing a large part of the sky."
NASA says that when the Beyond mission, also known as Cycle 13, starts on October 1, Spitzer will enter a new field as it observes objects that it wasn't originally designed to handle. These include distant galaxies dating back to the early Universe, the black hole resting at the core of our galaxy, and the ongoing search for exoplanets.
According to the space agency, though Spitzer wasn't built for planet hunting, it can handle the standard tests for looking for exoplanets, such as changes in the host star's light profile during planetary transits. It also has an extremely accurate star-targeting system and can control unwanted temperature changes to minimize errors.
"We never even considered using Spitzer for studying exoplanets when it launched," says Sean Carey of NASA's Spitzer Science Center at Caltech in Pasadena, California. "It would have seemed ludicrous back then, but now it's an important part of what Spitzer does."
However, NASA says that Spitzer's life extension is not without challenges. Because the telescope is drifting away from Earth, the increasing distance means that the spacecraft's antenna needs to be pointed at a higher angle. This not only exposes the telescope to more sunlight and more heat, but means that the solar panels don't get as much light, which puts stress on the batteries. It also means that NASA has to override Spitzer's safety cutouts to prevent it from going into safe mode.
"Balancing these concerns on a heat-sensitive spacecraft will be a delicate dance, but engineers are hard at work preparing for the new challenges in the Beyond phase," says Mark Effertz, the Spitzer spacecraft chief engineer at Lockheed Martin.
NASA says that Spitzer will continue its Beyond mission until the James Webb Space Telescope completes it commissioning phase after its scheduled 2018 launch.
"Spitzer is operating well beyond the limits that were set for it at the beginning of the mission," said Michael Werner, the project scientist for Spitzer at NASA's Jet Propulsion Laboratory in Pasadena, California. "We never envisioned operating 13 years after launch, and scientists are making discoveries in areas of science we never imagined exploring with the spacecraft."
The video below discusses Spitzer's continuing mission.