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Stratospheric Sun-watching

Test flight paves way for Sunrise mission


by David Hosansky and Nicole Gordon

Sunrise 1

Slender hoses, blown into arcs by the wind, partially fill the Sunrise balloon with helium before launch. A large portion of the balloon is left unfilled so it can expand as it ascends into the stratosphere, where air pressure is considerably lower. (Photos by Carlye Calvin.)

In a landmark test flight on 3 October, NCAR and a team of partners successfully launched a solar telescope—borne by a balloon larger than a Boeing 747 jumbo jet—to an altitude of 36,600 meters (120,000 feet). The test clears the way for long-duration polar balloon flights beginning in 2009 that will capture unprecedented details of the Sun's surface.

"This unique research project will enable us to view features of the Sun that we've never seen before," says Michael Knölker, director of NCAR's High Altitude Observatory and a principal investigator on the project. "We hope to unlock important mysteries about the Sun's magnetic field structures, which at times can cause electromagnetic storms in our upper atmosphere and may have an impact on Earth's climate."

The project, known as Sunrise, is an international collaboration involving NCAR, NASA, Germany's Max Planck Institute for Solar System Research and Kiepenheuer Institute for Solar Physics, Spain's Astrophysics Institute of the Canary Islands, and the Swedish Space Corporation. Additional U.S. partners include the Lockheed Martin Corporation and the University of Chicago. Funding for NCAR's work on the project comes from NASA and NSF.

The project may usher in a new generation of balloon-borne scientific missions that cost less than sending instruments into space. Scientists also can test an instrument on a balloon before making a commitment to launch it on a rocket.

The balloon, with its gondola of scientific instruments, departed from the Columbia Scientific Balloon Facility in Fort Sumner, New Mexico. It flew for about 10 hours, capturing stable images of the solar surface and additional data from the various instruments of the sophisticated payload. The gondola then separated from the balloon and descended with a parachute, landing safely in a wheat field in the Texas Panhandle.

"We were able to verify the workings of the entire system end to end," says David Elmore, an NCAR engineer who oversaw the test flight. "We can now move on to planning the first full-scale mission with confidence."

Sunrise 2

The Sun rises behind the silhouetted Sunrise telescope just prior to launch on 3 October.

Observing the midnight Sun

The ultimate goal of the Sunrise project is to investigate the structure and dynamics of the Sun's magnetic fields. The fields fuel solar activity, including plasma storms that buffet Earth's outer atmosphere and affect sensitive telecommunications and power systems. The fields also cause variations in solar radiation, which may be significant factors in long-term changes in Earth's climate.

The Sunrise project is scheduled next for a multiday flight over the Arctic in the summer of 2009, launching from Kiruna, Sweden. By taking advantage of the midnight Sun, the telescope will be able to capture continuous images for a period of several days to as long as two weeks, possibly orbiting the Arctic. It may be launched later on another long-distance flight over the Arctic or the Antarctic.

From its stratospheric perch, the telescope will sit above most of the turbulence of the atmosphere and ultraviolet-absorbing water vapor and ozone. It will be able to view stable images in the ultraviolet range, which allow for higher resolution than can be obtained from Earth's surface.

The telescope will capture features on the solar surface as small as 30 kilometers across (about 19 miles), more than double the resolution achieved by any other instrument to date. This will enable scientists to examine structures on the Sun that are believed to be key to understanding the mechanisms driving solar activity. In addition, by observing the same area during an entire flight over high latitudes in summer, the telescope will enable scientists to continually witness changes in the magnetic fields without the interruption of night.

Sunrise 3

Secure within its gondola, the Sunrise telescope hangs suspended from its crane-like launch vehicle at dawn.

A sharp focus from a twisting balloon

The Sunrise project has presented engineers with a number of extraordinary challenges. The balloon is designed to carry 6,000 pounds of equipment, including a 1-meter (39-inch) solar telescope, additional observing instruments, communications equipment, computers and disk drives, solar panels, and roll cages and crush pads to protect the payload on landing. The equipment must be able to withstand dramatic changes in temperature, and the steel and aluminum gondola cannot vibrate in ways that could interfere with the operation of the telescope.

One of the most difficult aspects of the engineering work was to design the gondola in such a way that the telescope in flight would remain focused on a specific and relatively tiny area of the Sun, even while twisting on a soaring balloon for a week or longer during the full-scale research missions. To accomplish this, the gondola includes both a torque motor drive to keep the gondola and telescope in the correct orientation and a precision guiding and compensation system to constantly correct the telescope's aim.

In addition to the telescope, the gondola on its full-scale research missions will carry a polarimetric spectrograph that will measure wavelengths in the Sun's electromagnetic spectrum and enable scientists to make inferences about its magnetic fields. Another instrument, known as an imaging magnetograph, will provide two-dimensional magnetic field maps.

Because the gondola is designed to withstand considerable force when it lands, the instruments can be launched on repeated missions. "This is a very economical way of rising above the atmosphere and capturing images that cannot be captured from Earth," Knölker says. "What we are doing is laying the groundwork for the next generation of space flights."

An unexpected arrival

During the test flight, the gondola landed on a family farm outside Dalhart, Texas. It was quite a surprise for the Nefsteads, who found it in their wheat fields. When the Sunrise crew arrived early the next morning to recover the payload, two TV stations from Amarillo were already on the scene. As it happens, Scott Nefstead is a math teacher at the local high school and involved in the school's science club.

Knölker later tracked the family down via the high school and invited them on an expenses-paid trip to NCAR. "The family was very supportive and friendly, so I thought we should give something back to them," he says. In December, the family will take a grand tour of NCAR and get an especially close look at HAO, meeting the scientists and engineers who designed the gondola that crashed onto their land. Knölker is also working with UCAR Education and Outreach to prepare materials for Nefstead to use in his classroom.

On the Web
 

Sunrise images and visuals

 
 

 

 


 

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