On the Sunny Side of the Universe

Solar observatories in space have an Icarus problem: the object of their desire is the agent of their demise.

Melting wax collapsed the wings of the mythological Greek. For observatories in orbit, a bad case of cataracts from solar radiation degrades precision optics.

One solution is to build an observatory without optics: no mirrors, no prisms, no lenses of any kind. And that’s what two College physicists have done.

Darrell Judge and Leonid Didkovsky of the USC Space Sciences Center, part of USC College’s physics and astronomy department, have developed an optics-free instrument to measure the extreme ultraviolet range of solar radiation.

“It can look at the sun day after day, year after year, without harm,” Judge said of the instrument, formally known as an optics-free spectrometer.

Didkovsky, a College research scientist, added that on long missions, in particular, “It could be very, very useful and important to use something like optics-free spectrometry, because you have no degradation.”

NASA recognized the invention with one of four major grants this year for suborbital scientific research.

The grant will allow Judge and Didkovsky to build a prototype and test it in an unmanned space flight.

The extreme ultraviolet and X-ray parts of the spectrum figure heavily in solar research, since the massive explosions known as solar flares produce energy mainly in that range.

While the intensity of visible solar light is nearly constant, the amount of ultraviolet and X-ray radiation from the sun can increase several times over during a solar flare.

The resulting storms can disrupt the electricity grid, knock out spacecraft and even alter Earth’s climate, said Judge, a professor of physics and astronomy who also holds appointments in the USC Viterbi School of Engineering.

“These are real effects,” he said, adding that a better understanding of solar flares could lead to the development of an early-warning system.

More generally, Judge said, the sun can cause long-term changes in Earth’s atmosphere. Extreme ultraviolet light drives reactions in the upper atmosphere that influence Earth’s climate, weather and radio communication.

“What produces the mix of particles that’s in our atmosphere is solar input,” he said.

The optics-free spectrometer, an improvement on an earlier design by Judge, looks like a squat cylinder about three and a half inches across and three inches high. Typically it contains neon gas, which interacts with solar photons to produce electrons.

A specially designed electric field then guides and focuses a narrow stream of electrons to a detector at the back of the cylinder.

By varying the strength of the electric field, researchers can collect and count electrons in a range of energies and then work backwards to map the peaks and valleys of the ultraviolet spectrum.

Scientists already are measuring extreme ultraviolet radiation with an optical spectrometer, also designed by Judge, aboard the sun-orbiting spacecraft known as the Solar and Heliospheric Observatory.

But the instrument needs frequent calibration to detect losses in sensitivity. Gaseous impurities wafting out of even the cleanest spacecraft get baked onto optical surfaces by the sun’s rays.

If it works as intended, the new optics-free spectrometer also should be maintenance-free. Judge and Didkovsky are hoping to test the instrument on an unmanned rocket flight in 2008.

Separate projects at Dartmouth College, the University of Wisconsin-Madison and the University of Colorado at Boulder also received part of a total $4.2 million grant from NASA’s sounding rocket science program.

NASA sounding rockets make brief flights into space with payloads that include atmospheric probes, telescopes, spectrometers and other research tools. Many high-profile NASA missions have used technology developed and tested on sounding rockets.