PASADENA — For more than 25 years, the SR-71 Blackbird carried the eyes in the sky that allowed U.S. military and intelligence agencies to obtain detailed photographs of hot spots around the globe.
Now the famed spy plane is carrying cameras focused on the universe above instead of the world below.
Applying Cold War technology to post-Cold War goals, Jet Propulsion Laboratory scientists are beginning to use the SR-71, the world's fastest and highest-flying production aircraft, for peacetime experiments.
In March, the Blackbird carried an ultraviolet camera that photographed stars and planets. And there are proposals to use the plane to get a clearer look at asteroids, Venus and aurora borealis.
Although the accuracy of the data gathered by instruments carried aloft by the plane must be tested further, JPL scientists agree its has great potential as a flying observatory.
The plane could be used for experiments to measure the volume of Earth's ozone layer or the formation of holes in the layer.
The plane could also make it easier for scientists to examine global weather patterns.
"SR-71s can help us solve some of the problems facing us in the 21st Century," said Jacklyn R. Green, a project scientist for a JPL program that uses the Blackbird.
The Air Force retired the Blackbird in early 1990 and sent most of its 20 remaining planes to museums.
Three of the SR-71s were loaned to the National Aeronautics and Space Administration's Dryden Flight Research Facility at Edwards Air Force Base for high-speed aeronautical research.
But the planes' capabilities make them particularly useful for scientists in the fields of planetary science, geology, physical geography, astronomy and the like.
The triple-sonic SR-71 cruises at an altitude above 85,000 feet and a speed of more than 2,200 m.p.h.
In 1990, a Blackbird set a record flying from Los Angeles to Washington in 68 minutes, 17 seconds.
The top altitude of other planes used for astronomical and scientific research is about 65,000 feet, limiting their usefulness because that elevation still is below much of Earth's ozone layer, said Arthur Lane, a JPL research scientist.
The SR-71 flies high enough to get a clearer view of the heavens, Lane said.
Although balloons can reach an altitude of 100,000 feet or more, their path is determined by winds, and a launch costs about $300,000, Green said.
Rockets offer more control but are far more costly, about $10 million per launch. Satellites are also expensive.
The Cadillac of high-altitude research is the space shuttle, but JPL program manager Jim Kelley said it can take years to get an experiment on one of those flights.
"With the SR-71, we're able to fly a mission . . . cost-effectively and with low risk," Green said.
A Blackbird flight costs about $100,000 per hour, including fuel, she said.
Besides its relatively low cost, the SR-71 makes it possible to put instruments aloft quickly when needed.
When a volcano erupts, for example, the plane could take to the sky, equipped with a camera to record volcanic plumes and ash clouds, Lane said.
Ever since word started circulating that the former spy planes could be used for science, interest in the flights has been growing.
Now researchers in other countries want to get their experiments on board.
"Something developed during the Cold War, a strictly military use, is now being used for a non-military civilian thing, and that's great," said JPL's Kelley. "It could be an inexpensive, fast way to test ideas" rather than launching them into space on a rocket.
Lane said the plane's worthiness to science must still be proved.
But the potential, he said, is great. "In certain areas it will allow some major advances to happen," Lane said. "We think it's got capabilities that are very important. We believe . . . we will be able to make much more accurate measurements."
One issue to be studied is how the plane's tremendous speed affects the data it collects.
Scientists would like to know, for example, how the high air temperature generated by the plane's passage affects the delicate sensing instruments and the data they collect.
An SR-71 flew twice in March with an upward-looking ultraviolet camera system installed in its nose bay.
The first flight, on March 9, was intended to ensure that the camera, called SWUIS for Southwest Ultraviolet Imaging System, would operate at Mach 3.
During the 90-minute flight, which began and ended at Edwards AFB in the Antelope Valley, the plane cruised at an altitude of 83,000 feet over Nevada, Arizona, New Mexico and Utah.
Vibrations were not detected in the camera, according to Green.
Alan Stern, of the Southwest Research Institute in San Antonio, said the ultraviolet camera was built as a shuttle payload for photographing planets and may be flown aboard one of the orbiters in late 1994 or early 1995.
The scientific results produced by an SR-71 flight do not compare to those of a shuttle flight, he said, but the SR-71 flights are far more readily available.