WHILE new American space probes still can't get off the pad, some of those launched many years ago continue to pay scientific dividends. You could say that United States space science is running on the momentum gained from some superb spacecraft engineering. One such dividend announced recently was paid by the Voyager 1 and 2 planet-observing spacecraft. They have provided the most precise measurements yet made of certain types of cosmic ray particles - atoms of star dust - that drift into the solar system from outer space.
NASA launched the Voyagers a decade ago to study Jupiter and Saturn. When Voyager 1 swung by Saturn in November 1980, it headed upward out of the plane of the ecliptic - the plane in which Earth orbits. Voyager 2, which reached Saturn in August 1981, went on to survey Uranus in January 1986. It is now headed for Neptune in August 1989. These additional planetary surveys are also extra dividends from an investment in a spacecraft whose nominal mission ended nearly six years ago.
The cosmic particles that the twin spacecraft are detecting include atoms of helium, hydrogen, nitrogen, oxygen, and neon. From an interstellar perspective, the Sun that dominates our sky is just another average star. Its influence fades out somewhere beyond the farthest planet. Scientists call this interstellar frontier the heliopause. Interstellar particles that drift across it into the solar system proper interact with the ``wind'' of particles and magnetic fields flowing outward from the Sun. They can become electrically charged and can be accelerated to high energies. Sometimes they are pushed to such high speeds that they shoot along at a tenth the speed of light.
According to Voyager project scientist Edward Stone, the twin spacecraft have returned the most precise measurements ever made of the characteristics of these cosmic bullets. Also, for the first time, they have detected the presence of carbon and argon atoms among the cosmic debris. These data help scientists understand better where cosmic rays come from and what happens to such particles once they come inside the solar system. As Stone explained, scientists now can relate the cosmic ray observations to the abundance of elements in the interstellar gas. The new data tend to confirm scientists' suspicions that such material probably came originally from stars that exploded as supernovae.
The data for this kind of research can't be gathered from Earth. Scientists need to send instruments throughout the solar system. This is what the outstanding engineering that produced spacecraft such as the Voyagers is enabling them to do, even though the spacecrafts' original missions ended years ago. The hardware is rugged enough to keep on working. No wonder the National Space Club gave the Voyager Project a second Nelson P. Jackson Aerospace Award for engineering excellence last March!
This project - which is managed by the NASA Jet Propulsion Laboratory - typifies the quality of design and workmanship that have kept a number of craft working well beyond reasonable expectations.
Pioneer 10, a Jupiter probe launched in March 1972, and Pioneer 11, a Jupiter and Saturn probe launched in April 1973, continue to send back data as they, too, head for interstellar space. Together with the Voyagers, they make up what Voyager project manager Richard P. Laeser calls ``an armada of spacecraft'' that should eventually explore the heliopause interstellar frontier itself. The craft have been working so well that Laeser has said he expects them to continue to serve scientists until well into the 21st century.
Other long-working members of the Pioneer family have been probing space near Earth's orbit. NASA finally abandoned Pioneer 9, launched in November 1968, last March. Controllers had been unable to contact the craft since 1983. But Pioneers 6, 7, and 8 remain on the active duty roster.
Inspired by the past, one JPL design team hopes to do even better. It's studying how to build a craft that would travel a thousand times farther than the distance Earth is from the Sun - a thousand astronomical units - and would continue working for 50 years. The craft would measure the interplanetary and interstellar media and send back precision pictures of star fields to compare with pictures taken from Earth.
Called Project TAU (for thousand astronomical units), this is a very ambitious engineering challenge. But it's the kind of challenge that spacecraft designers may well be able to meet if their past achievements are any guide.
A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.