Space station beckons ice cloud project

Sometime in the year 2003, if all goes well, a UW–Madison experiment, designed to probe the nearly invisible ice clouds of Earth, will be hitched by astronauts to the International Space Station.

The project, known as CIRRUS, is one of five projects selected by NASA in a preliminary competition to develop some of the first scientific payloads for the orbiting space station. It is the only project in the competition that will be student-driven from beginning to end, says Steven Ackerman, the UW–Madison atmospheric scientist.

“Our proposal is unique because we’ll have students build the instrument,” Ackerman says. “They’ll be involved from end to end. It’s an opportunity for students to really get a taste of what it’s like to work for NASA or an organization like that.”

Of the five projects, two will be chosen for deployment in space, either aboard the space station or other craft such as a space shuttle or satellites. By making the cut, Ackerman’s team of Wisconsin students, scientists and engineers will receive $300,000 to complete a proposal to design, build, deploy and operate a $15 million device capable of looking through the atmosphere to detect and characterize the ubiquitous particles of ice that play a key role in weather and climate.

CIRRUS, or Cloud Infrared Radiometer for University Earth System Science, will be designed to sample the far-infrared light reflected by the ice particles that exist, for example, in wispy high-altitude cirrus clouds and in the tops of massive thunderheads.

But the broad goal, he says, is to get some idea of how much ice truly exists in the atmosphere, how it is concentrated and the range of ice particle sizes. By reflecting light and interacting with other forms of water in the atmosphere, these atmospheric ice particles help regulate climate and influence patterns of local and regional weather.

“We want to see how much ice exists in the atmosphere, which is something we don’t know. It’s a very hard measurement to make and right now there are no Earth-viewing instruments that even make measurements in these wavelengths.”

Ackerman says the information that would be collected by CIRRUS is the last frontier, the last data needed to fine-tune the supercomputer-driven climate models that scientists use to predict future climate. “It’s the last big knob in the climate models that has no parameters. With CIRRUS, we would be able to collect data that no one else has seen before, and we could refine estimates that now differ by an order of magnitude.”

The multibillion-dollar space station is now under construction by NASA and its international partners about 500 kilometers (310 miles) above the Earth. The advantage of the space station is that it will permit measurements to be made day and night. If deployed, CIRRUS would be perched on the outside of the space station for two years, allowing measurements to be made over the seasons.

“It would look down from the space station and look at ice in four different far-infrared wavelengths,” he says.

The advantage of the far-infrared, a region of the electromagnetic spectrum invisible to the human eye, is that it provides a capability to look through clouds and sample ice wherever it exists in the atmosphere. Most other satellite-borne instruments can’t look past the tops of clouds, Ackerman says.

“Thunderclouds, for example, are hard for satellites to measure because they only see the top. We would be able to see all the way through the cloud.”

The full-blown CIRRUS proposal will be developed over the next year and also will involve students and faculty from the colleges of Letters and Science and Engineering. If selected, the CIRRUS instrument would be built at UW–Madison’s Space Science and Engineering Center, one of a few university-based centers capable of building spaceflight hardware.

“It’s exciting because it brings teaching right into the research,” Ackerman says. “And of all the proposals submitted, ours is the only one where students would actually build the instrument.”