February 2004
HAO Sunrise
NCAR is involved in numerous international collaborations.
Staff Notes Monthly will be highlighting several in the next few issues.
NCAR scientists and engineers, working with colleagues in Germany and Spain, are moving ahead with plans to build a powerful solar telescope that will be carried high up in the atmosphere by a balloon.
Bruce Lites and Kim Streander
At the heart of what's known as the Sunrise project is a lightweight, one-meter telescope that will circle Antarctica for about two weeks at an altitude of approximately 130,000 feet (39,600 meters). Its advanced instrumentation will provide high-resolution images of the Sun's outer surface, or photosphere, enabling scientists to get unprecedented views of small-scale magnetic fields that drive solar variability and profoundly affect Earth's atmosphere.
The international team expects to launch the telescope in late 2007. If the instrument can be recovered intact and funding is available, it will be launched again the following year to obtain additional images.
A computer-generated image of the Sunrise telescope and gondola, with its large solar panels. The gondola will be carried by a 30-million-cubic-foot balloon.
"This project will allow us to view features of the Sun that we've never seen before," says Bruce Lites (HAO), a principal investigator on the Sunrise project. "We hope to see magnetic fields continually interacting with convective motions and affecting the outer solar atmosphere."
The telescope is being developed at a time when an array of sophisticated new solar instruments are coming on line. They include the one-meter Swedish Solar Telescope that is capturing unprecedented images from a site on the Canary Islands; the Solar B project, which will place a suite of instruments in a Sun-synchronous orbit around Earth next year, and a coronal multichannel polarimeter being developed by HAO to examine magnetic fields in the corona.
Images from the ground-based Swedish telescope have been dazzling the scientific community for more than a year. They show, for the first time, the three-dimensional structure of the Sun's photosphere, as well as small sunspots that traverse what appear to be raised ridges.
As detailed as these images are, Sunrise will provide far more information, in part because it will reach an altitude at which it will not have to contend with distortions caused by Earth's atmosphere. The balloon-mounted telescope is expected to capture images as small as 40 kilometers across, compared to 90 kilometers for the Swedish telescope. In addition, Sunrise will train its instruments on the same small area of the Sun for two weeks, thereby allowing researchers to witness dynamic changes in magnetic fields. Ground-based telescopes, in contrast, cannot continually capture images from the Sun because of Earth's rotation.
"Throughout this decade, we'll be seeing much more detailed images of the Sun from a number of experiments," Bruce says "Sunrise should be a big part of this research picture."
New insights into magnetic fields
Learning more about the Sun has long been a high scientific priority. The Sun is the main source of light and energy for life on Earth and the principal driver of atmospheric motion. Solar disruptions, such as coronal mass ejections, have profound impacts on our upper atmosphere, touching off geomagnetic storms that affect sensitive communications and other systems on Earth. But scientists need specialized instruments to examine the Sun in detail, and they remain uncertain about the causes of solar variability and disruptions.
The primary goal of the Sunrise project is to investigate the structure and dynamics of the Sun's magnetic field. The magnetic field fuels solar activity and causes variations in radiation, which may be a significant factor in long-term changes in our climate.
The project also may help scientists glean insights into magnetic fields in general. The universe contains numerous objects, such as stars, that are dominated by magneto-hydrodynamical and plasma processes, but only the Sun is close enough to examine in any detail.
"Sunrise will broaden our understanding of the really fundamental physical processes of the outer atmosphere of stars and the forces that drive stellar winds," Bruce explains.
NCAR staffers, using NSF funding and a grant from NASA, will design the gondola and telescope pointing system. They are also working on the data system and cameras for one of the key instruments, a polarimetric spectrograph for high-precision spectral line measurements.
German researchers at several institutes, including the Max Planck Institute for Aeronomy, are building the telescope, creating a tracking and alignment system for the telescope, providing optics and mechanisms for the polarimetric spectrograph, and designing a filtergraph for high-resolution images in the visible and UV spectral ranges. Spanish researchers at the Astrophysics Institute of the Canary Islands are designing the Imaging Magnetograph Experiment, which will provide two-dimensional magnetic field maps.
Working with international collaborators is vital on such a major project, Bruce explains. "The solar community is not large, so solar physicists around the world need to work with each other," he says. "In times of limited funding, it's especially important to pool our resources and move forward on really big projects."
At HAO, Kim Streander is the instrument project manager. A number of other HAO staffers are involved in the project, including HAO director Michael Knölker, David Elmore, Terry Leach, Alice Lecinski, and Ron Lull. In ATD, Clarke Chambellan and Jack Fox are working on the gondola and telescope pointing system. The balloon, supplied by the National Science Balloon Facility, will be designed to hold 30 million cubic feet of air so that it can carry the 4,000-pound payload.
The design challenges include creating a set of instruments to keep the telescope aimed at a specific area of the Sun. The telescope's angle must remain within 15 arc seconds, or 1/240th of a degree—no small feat on a soaring balloon that will be twisting in flight. The instruments, including an anti-spin device that will act as a big flywheel to keep the gondola pointed at the Sun, will be tested next year on a trial flight in Texas.
"This is an exciting project, and it definitely confronts us with some interesting challenges," says Jack Fox, director of ATD's Design and Fabrication Services.
•David Hosansky
Also in this issue...
Tom Windham soars to Washington
CG auditorium draws large crowds
Staffers organize women's self-protection class
